Black holes represent the one place in the universe where our two best theories of reality—Einstein's theory of relativity and quantum mechanics—break down, creating fundamental paradoxes like the singularity and the information paradox. Scientists are exploring radical solutions such as fuzz balls, gravastars, and wormholes, while also investigating whether gravity itself might be an emergent phenomenon rather than a fundamental force. This represents the frontier where physics must be remade to understand the nature of reality.
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We Might Be Completely Wrong About Black HolesAdded:
Black holes are the one place in the universe where our best two theories of reality, Einstein's theory of relativity and quantum mechanics starts to break down. That's why understanding black holes, what they are and how they work is key to understanding well everything.
Over the next 2 hours, we're going to do just that. These videos will talk about what we think is happening at the edge of reality and how scientists are trying to remake the laws of nature to explain black holes. We'll start with the paradox at the center of every black hole, the one that physicists have been arguing about for about 50 years. Then we'll widen into gravity itself, the force that creates them, and ask if we really even understand it. We'll travel inside CERN, where scientists are looking at other places other than gravity to see where the standard model, physics's crown jewel, begins to lose a bit of its shine. And we'll end on the most audacious solutions modern physics has to offer. So, let's dive in at the deep end. What happens at the center of a black hole?
Behold Sagittarius Aar 15 million miles wide with a mass of 4 million suns. It's located smack dab at the center of our galaxy. But don't let this picture fool you. The black hole itself is invisible.
You'd be drifting towards this object that's millions of miles wide and you can never see it. You could only ever see the light swirling around its edge and the space twisting and tearing as it pulls everything in. Sagittarius Aar is what's known as a super massive black hole. And super massives are sort of a fan favorite, but they're really just one of many different types of black hole that exist. Now, we've been covering black holes for decades at New Scientist. We publish so much about black holes. So, today we pulled together everything our experts know about these mysterious and terrifying astrophysical objects. Part of the reason why we love black holes and why physicists are so fascinated with them is because they're kind of where all our best theories of physics break. Grasping them, really understanding them will require us to paper over the cracks of physics that exist today will require us to reconcile quantum mechanics and gravity. And it will require us to understand spacetime like we've never understood it before. There's also something really mysterious about black holes. How do you detect something you can't really see? Maybe we can hear these invisible objects collide over a billion lightyears away. And how could an object known for trapping everything slowly evaporate into nothing? So, I hope you join us as we go a bit deeper because the closer you look, the more unsettling things become. Some black holes were already super massive when the universe was still in its infancy.
Others might be baby black holes left over from the big bang, now hiding anywhere, maybe even in our own solar system, and possibly holding the key to dark matter. And once you get to the center of it all, you'll hit two problems that still haunt modern physics. The singularity and the question of what happens to information when it falls into that singularity.
Those are the mysteries that we're going to unpack in this video. We'll cover different kinds of black hole from the ones we've already observed, super massives, missing links, and more. All the way through to a wacky assortment of things we think could solve our problems with black holes like wormholes, graars, and these things called fuzz balls. So, let's get started.
First things first, the basics. Black holes are simple and serious. Now, each of them can be described with only three numbers. The mass, the rotation, and electric charge. And yet, they challenge our understanding of the rules of which our cosmos is arranged. There are three kinds of black holes for which we have strong observable evidence. The most common variety, your garden variety of black hole is known as the stellar mass black hole. Stella mass black holes are everywhere. There's millions scattered across the galaxy alone. They form when a star no longer possesses enough fuel to generate this outward pressure and instead succumbs to gravity. First in a dramatic supernova explosion, then collapsing in on itself. Okay, so hold that thought. This is a good time to ask a few basic questions. For starters, what is a black hole? Well, you might have seen a diagram like this before or have heard Einstein describe spacetime like a fabric that stretches and distorts and mass is placed in it. That warping describes how objects with mass all have a gravitational field. Things that travel close to an object fall towards it rolling across the natural curve of this fabric. Now, only a few months after Einstein published his equations describing this effect, a guy called Carl Schwarz found a pretty alarming result. He said that if you had a mass that was big enough, compacted in a small enough volume, it would cause spaceime to diverge and just curve into infinity. We call that a singularity.
Now the curvature and gravitational pull of these regions be so strong that light that gets too close to the surface known as the event horizon. It would just get trapped and as a result black holes would appear to us as pits of darkness, you know, like that's why they're called black holes. But they would have these bright wobbly rings of light around them as light skates across its surface. Now Einstein was skeptical. To him, this seemed like a mistake. like maybe it existed in the mass of general relativity but we never really see them but we have actually observed them. Now if you imagine an invisible household vacuum cleaner even though you could not see the appliance itself you'd know it was there because bits of dust would react as the vacuum cleaner approached.
In this way, beginning the 1960s, telescopes began spotting black holes by how stars and gases behaved in the immediate vicinity, seemingly orbiting empty space. Since then, our sleuththing abilities and tools have improved. The mid 1990s, astronomers began tracking the orbits of several stars circling a source of radio waves, and it turned out it was emitted by our good friend, Sagittarius, a star. The next big leap in black hole detection came in 2016 when the laser interpherometer gravitational wave observatory. Try saying that three times fast. Aka LIGO witnessed a collision between two black holes. This clash created ripples in spaceime. It's precisely the ones predicted by Einstein's theory of general relativity. Fast forward 3 years and scientists have published a holy grail of sorts. the first ever image of a black hole. In this case, a super massive. Now, as the name implies, super massives are like the much larger sibling of stellar masses. And they're not only a little bit larger, they're much, much larger. This brings us on to the monsters living in the middle of our galaxy.
Now, a typical stellar mass black hole stretches 30 kilometers wide across its event horizon. That's 15 miles for Americans. As for the Milky Way's resident super massive Sagittarius A star, try multiplying those numbers by roughly a million. The matter contained in black holes is measured in what is known as a solar mass. That's the amount of mass contained in our planet sun.
Now, as the name implies, super masses aren't just insanely huge. While the mass of a stellar mass black hole ranges from a few suns worth to up to a few dozen, the largest known example of a super massive black hole contains the mass of our sun 66 billion times over.
But it's highly compacted. In relative terms, imagine the entire Earth squeezed down to the size of an object 2 1/2 cm across. That's 1 in. Like stellar mass black holes, we surmised the existence of super masses long before we ever even saw one. Over a half a century ago, scientists identified these things called quazars. That the brightest known object in the universe. They speculated that the quazars blinding light was caused by an amount of heat that could only be generated as matter approached the event horizons of these colossal black holes. As matter enters these super masses, something known as an accretion disc is formed. This concentrated plasma is propelled by the black holes rotation. Now, the first ever snapshots removed most of our lingering doubt regarding the existence of black holes. And even more spectacularly, earlier this year, the James Webb telescope even managed to capture the super massive within our own galaxy, Sagittarius AAR. Now, despite their huge size, these giants are surprisingly common, sitting at the center of nearly every Milky Way sized galaxy. Astrophysicists speculate that the ubiquity of super masses could be meaningful. And here's why. We have observed a super massive black hole formed over 13.3 billion years ago, a mere 500 million years after the Big Bang. That presents an appropriately enormous mystery. Based on what we know about how black holes form, how could one get that big that quickly? Perhaps rather than forming from collapsed stars, these early black holes contained the mass of many accumulated smaller objects, clouds of gas. In that case, perhaps there's a connection between super masses and the formation of galaxies themselves. In the search for answers to that and other questions, scientists have turned their celestial gaze to the next black hole on our tour.
The so-called missing link.
Intermediate black holes most certainly exist. The problem, we haven't been able to find many of them. Many speculate that the formation of these intermediatesized black holes is tied to dense collections of stars known as globular clusters. The hypothesis goes something like this. A single star expires and forms a stellar mass black hole. This then nudges nearby neighbors to collapse and join the party and a nent intermediate black hole is formed.
Intermediate black holes contain a solar mass of approximately 1 to 300 suns.
Very big compared to the stellar mass black holes, but a drop in the bucket compared to super masses. And perhaps drops in the bucket are exactly what they are. Functioning as a sort of galactic food chain, maybe stellar mass black holes combined to form intermediates. Thousands, if not millions of intermediates that are gobbled up to beget super massives. So back to that mystery, the primordials.
All right, small, medium, and large black holes definitely exist. We've seen them. But we think that may also be an extra small type of black hole, one that might even be key to resolving the mystery of the elusive dark energy and dark matter. So so-called primordial black holes could be hiding just about anywhere, maybe even in our own solar system. These baby black holes would have begun forming immediately after the Big Bang. In the universe's earliest days, fluctuations in spaceime would have created an uneven distribution in the density of matter throughout the universe. Some lumpy bits in the primitive cosmic soup. In areas of relatively high density, micro black holes whose mass would have been able to be measured in singledigit kilog may have formed. But as if locating primordial black holes wasn't hard enough, like finding needles in an intergalactic hay stack, the advanced age further complicates the challenge.
Steven Hawking predicted that black holes emit a type of radiation, what we call Hawking radiation, and as they do so, they steadily shrink. Like melting ice, the smaller they get, the faster they decrease in size. Given the rate of this evaporation, primordial black holes formed shortly after the Big Bang would have already disappeared. The search is now underway for the telltale gamma rays that would represent these ancient black holes last breath. But quite a lot is writing on it. Many believe that primordial black holes may prove to be the secret hiding place for dark matter, the elusive invisible glue that binds our universe. But here we come to a bump in the road. What if our concept of a black hole is flawed? As our investigation deepens, additional doors open to an astonishing array of possibilities. Black holes within black holes, secret passageways to travel throughout time and space, and more. All possible solutions to a pair of very big problems.
The problem be they ultra small, small, medium or large, all black holes are major pains for physicists. So what was Einstein's problem with them? And why was he so opposed to the idea that they could exist when it was first pointed out by Schwarz?
Because black holes, as we've described them thus far, break theory and they present two super massive problems. Each relates to the idea of a singularity.
the points of infinite density believed by many to exist in the center of black holes. In theories like general relativity, infinities are a sign that something is badly broken. Einstein, when he first formulated his theory, relied on spaceime being made of a geometry that just smoothly extends.
That's how we make the mass of general relativity and energy conservation work.
But if it suddenly just veers off into infinity, it's unclear what happens to those other laws. And because of this problem, Einstein attempted but failed to prove that black holes were impossible.
And then there is the information paradox originally detailed by Steven Hawking. This paradox pits our understanding of the physical world in the largest sense against our understanding of the world in the smallest. This is where we get the clash of our two best theories of reality.
General relativity and quantum mechanics. General relativity holds that information about matter compressed inside a singularity should just be lost. The problem, the laws of quantum mechanics state that information cannot be destroyed. In tackling these twin challenges, scientists have attempted to tweak the equations and put forth a radical proposal that what we're actually looking at aren't singularities, but are a type of cosmic impostor. They've conjured up blueprints for alternate concepts of black holes in which the maths adds up. This process is known as regularization and the resulting models are therefore known as regular black holes. But as you are about to see, they are anything but.
Here are a trio of cosmic curve balls with quirky names and even quirkier properties.
Meet string theory's contribution to the conversation. Fuzz balls. One of the main strengths of the fuzzball model is that on paper it solves both the singularity problem and the information paradox in one fell swoop. How? Well, string theorists think that reality, every particle in the universe, is actually made up of even tinier vibrating strings and membrane-like structures called brains. They think that a black hole could be a dense tangle of these strings and brains knitted together in a compact object. To a distant observer, a fuzzball might look like a conventional black hole, but up close, the surface of a fuzzball would be like a weird quantum thicket, a strange vibrating structure constantly absorbing and remitting radiation instead of just gobbling it up. The fuzzball sidesteps the information paradox by getting rid of the idea of an event horizon and singularity.
Information never really disappears. It just gets entangled and stored in this mess of quantum strings in the black holes intricate internal structure. The catch, we all quite fortunately live outside of black holes. And from an outsider's perspective, there is nothing which allows us to visually distinguish black holes as understood within general relativity from black holes as re-imagined by string theory. The same can be said of the two additional and just as exotic possibilities.
Grava stars.
Another way to tackle the information paradox. What if instead of a point of singularity at the center, you have a shell created by a type of repulsive energy? Stay with me here. We know that the universe is expanding, but we don't quite exactly know how. Some speculate that the force driving the expansion of the universe originates from something called vacuum energy. Think of it as the energy intrinsic to the fabric of spacetime even after you strip away all matter, radiation, and particles that could be in it. Well, what if black holes have a bubble of repulsive vacuum energy at that core? And this region pushes outward, preventing them from collapsing into a singularity. The walls of the bubble would be like an ultra thin shell of incredibly dense matter, a kind of gravitational membrane. And this is the concept behind gravitational vacuum stars aka grav stars. An even more elaborate variation of grav stars has also been suggested. These are known as knee stars. One graar wholly contained within another are universe's version of Russian nesting dolls. Or how about something even more outside the box? What if black holes, at least some of them, aren't really black holes at all? This leads us to a name you've likely heard before, but contrary to what you might guess, they're not solely stuck in the realm of science fiction.
Wormholes.
As seen starring in Hollywood hits like Interstellar, you've probably know about the basic concept of wormholes. What you may not know is that these hypothetical tunnels burring through spaceime could in some ways mimic black holes. Oh, and also they could be very real. The idea of secret cosmic doorways bridging the universe past and present may sound fanciful, but that theoretical existence is supported by general relativity. Like fuzzballs and gravis stars, wormholes offer an alternative to the problematic concept of singularity. An extremely exciting one. What if something that looks like a black hole from the outside is actually one of these intergalactic portals? In this scenario, some black holes might not be cosmic dead ends, which escape is impossible, but a doorway to something called a white hole, the theoretical yin to the black holes yang into which nothing can enter and from which matter spews forth. Even on a theoretical level, a functional wormhole seems fairly far-fetched. One challenge would be maintaining that fragile stability. Ordinary matter has positive pressure and energy, both of which contribute to things like being gravitationally attracted to mass. But to keep a wormhole propped open, you would need something that produces repulsive gravitational effect, matter with a negative energy density. Think of this exotic matter like placing a jack under a car. Gravity pushes the car down. The jack pushes back and keeps the car propped up. For the record, NASA maintains that black holes are not wormholes, meaning the tantalizing, if somewhat terrifying, opportunity to go skipping through time and space will probably not present itself anytime soon.
Everything you have learned about black holes may sound totally absurd, and yet both our theories and observations tell us that they truly do exist. We've come to the end of our story, at least for now. The next great frontier, well, that's a proposal to extend our best black hole telescope, the Event Horizon Telescope, into space. The distance between this new explorer and our Earthbased observatories would allow us to capture the most elusive photon rings around black holes in a much more detail, providing a clearer outline of spaceime at the boundaries where we expect them to break down. The Black Hole Explorer, if funded next year, would launch in 2031.
Black holes provide an excellent playground for testing the limits of scientific possibility. They reveal profound truths about our universe and raise even more profound questions. To name but one, can a black hole be destroyed? And if so, do we possess the tools to do it?
The information paradox we just walked through is one of the most important unsolved problems in modern physics debated for over 50 years. Why? Because when we apply our best theories of the universe, general relativity, and quantum mechanics to black holes, neither fully stand up. And the thing pulling them apart is the missing quantum description of gravity. In the next episode, we join the quest to understand this fundamental force, where scientists are testing gravity at scales we have never reached before using cold metal bars near absolute zero or microscopic gold beads held in quantum states. Some are even searching for particles that carry gravity, while others are testing something even stranger that gravity might not be a fundamental force at all.
Physics is filled with mysteries and believe it or not, gravity remains one of them. We rely on gravity to explain things large and small and yet at a fundamental level, we still don't fully understand it. At the heart of the challenge, a rift between general relativity and quantum mechanics, two spectacularly successful theories that won't play nicely together. Gravity has so far refused to fit into the quantum framework that so elegantly describes all of the other forces. Finding a theory of quantum gravity has long been the holy grail of modern physics. But what if this is the wrong question to be asking? New ideas are gaining traction that suggest gravity may not be fundamental after all. What if it emerges from some other underlying structure? So is our theory of gravity missing something or is it fundamentally wrong? In this video, we are going to explore the experiments where scientists are investigating gravity thanks to innovative and ingenious techniques.
Cooling metal bars to near absolute zero, suspending microscopic gold beads, and searching for signs that gravity might be quantum. But we'll also put some of the most abstract theories about spaceime to the test as well.
This is potentially going to be one of the first experiments that can actually shine a light on that sort of issue.
>> As those experiments push forward, some physicists are asking even deeper questions. What if gravity isn't fundamental at all? What if it's an emergent effect, a kind of geometrical mirage arising from deeper rules? Others go even further still, pondering whether gravity may not only depend on the universe, but also on us as observers within it. The quest to decode gravity is about more than whether it is a particle, a wave, or something else entirely. Reality and life itself is unimaginable without gravity. It has shaped our world. It holds the universe together. And let's not forget, it's the only thing keeping us from floating into space.
>> The way gravity acts on you is the same for everything in you, for every single cell of your body, for every single atom in your body, for every single fundamental particle in your body. Gravity acts on you and on me and on everybody in exactly the same way. Is the most inclusive thing you can imagine. What makes this ongoing quest so fascinating and so maddening is not simply that we can't find answers. It's that gravity forces us to question our questions. If something as fundamental as gravity will not fit into any of our existing frameworks, then what does that tell us about the frameworks themselves?
Join New Scientist as we tackle a mystery at the very heart of physics and explore how the search for quantum gravity may upend our understanding of reality itself.
Do we know anything about gravity?
Gravity seems simple. Anything that contains mass also has gravity. What goes up must come down. For as long as we've been aware of gravity, we've treated it like a thing, a specific ingredient in the universe's cupboard alongside other fairly well-defined things like electrons or quarks. In the textbook view, gravity is part of the bedrock of reality, one of four fundamental pillars of nature alongside electromagnetism and both the strong and weak nuclear force, which makes up the foundations of the standard model of particle physics. This view assumes the universe is built on laws that are objective and unchanging. And we have good reason to make this assumption. For over a hundred years, this framework has passed every test we've thrown at it with flying colors. The one outlier, how to get gravity to fit into the quantum nature of our world. Einstein's general relativity tells us that mass and energy curve spacetime. And it's these curved paths that lead to gravity. For nearly 100 years, physics has attempted to find a way to quantize this space-time curvature, answering the question of whether spacetime is continuous or discrete. But is this even the right question? What if gravity isn't even fundamental in nature after all?
In the summer of 2009, while on vacation, physicist Eric Verland had his passport stolen, marooned on an endless holiday. How bad for him, he read a paper by fellow physicist Ted Jacobson obsessively. Over and over, certain its implications were profound, even more so than the author himself might have realized. Jacobson had demonstrated that mathematically the gravity of spacetime might behave like a thermodynamic system which is made up of many small parts.
For Verland this provided a bit of a Eureka moment. If gravity obeys the laws of thermodynamics, he reasoned then maybe it has been miscast as a fundamental force all along. What if, Ferland wondered, gravity is instead what's known as an emergent phenomenon, not a thing in and of itself, but an accidental product or a byproduct of another phenomenon, even multiple interrelated phenomena. Now, a helpful comparison might be like the air pressure in your tires. It may seem like air is physically pushing against the inside of your Michelins. Other tire brands are available, but pressure isn't something that just exists. Millions of air molecules in that confined space create pressure. But you can't actually isolate a single molecule or particle driving pressure in and of itself.
Pressure is a collective effort. It's emergent. Ver became convinced that gravity works along similar lines.
specifically that it is an accidental artifact of the second law of thermodynamics which holds that entropy, the universe's natural tendency toward disorder, must always increase.
This is where things get delightfully strange. Allow me to introduce the holographic principle.
Despite what the name might suggest, the holographic principle, it's not about physical matter, but it's about information. It suggests that all the information needed to describe a region of space may be encoded on a surface with fewer dimensions. Similar to how holograms store three-dimensional images on a two-dimensional film. In other words, the physics of a three-dimensional world can in some cases be fully described by equations defined in two dimensions. Now, it's not because the extra dimension isn't real, but because it may not be fundamental to how information is organized. Now, that might sound like a mathematical curiosity, but remarkably, the rules governing our apparently three-dimensional universe still work when translated into this lower dimensional description. What if that isn't just a coincidence?
In this view, the universe is not a container full of objects, but a projection of information. Verind took this notion a step further by introducing the idea of a holographic screen.
But what does this all mean for gravity?
In the Newtonian view, if you drop an apple, it falls because the Earth's mass pulls it. In Einstein's view, the apple falls because the Earth warps spaceime, creating a curve that the apple follows.
In Eric Verlin's view, there may be no fundamental pull or curve at all.
Instead, what we call gravity could arise from a deeper statistical tendency, one rooted in entropy.
We may consider entropy to be synonymous with disorder. But it's more accurate to think of it as the number of different ways a system can be arranged while still looking the same overall. Picture a pair of dice. Many combinations give you a total of six, but there's only one way to roll a two. So, we can say that six has higher entropy than two, not because it's messier, but because there are more combinations that add up to six. The same logic explains why gas spreads out to fill a room. It's not being pulled outward. There are simply vastly more ways for the molecules to be spread out than to remain bunched together. Verlin's idea is that gravity could work in a similar way at a deeper informationbased level of reality.
Configurations where masses are closer together may simply correspond to higher entropy. What we perceive as gravitational attraction could then be spacetime reflecting that underlying statistical drive. not a fundamental force but the result of deeper phenomena we don't directly see this idea is known as entropic gravity and it's a bit out there with a dramatic flare famously declared that for me gravity doesn't exist now it's a very very new approach it's probably a bit controversial and it might ruffle some feathers but whether this is a new view of gravity that's on the horizon horizon. It doesn't stop the work that's already in motion. Maybe gravity will turn out to be entropic, but for now, the hunt is still on for a theory of quantum gravity.
Chapter 2, quantum gravity.
And since gravity interacts with everything, if it interacts with quantum things like light, like electrons, it has to be quantum itself. You can't have a quantum system interacting with something which is fundamentally just classical. Science has always thrived on outside of the box thinking. But when it comes to gravity, physicists may be particularly open to radical ideas. Why?
Because nothing else has worked. Gravity has been stumping science for over a century now. Despite its lofty status as one of the fundamental pillars of nature, gravity has always been a bit of an odd one out alongside the others. If gravity is a fundamental interaction force, it follows that there ought to be a particle that does gravity's bidding.
That is to say, actually causes the space-time curvature. Photons, for example, are the particles that carry the electromagnetic force. The physical agents of gravity have been named gravitons. The trouble is, no one's ever seen one. And what's more, compared to the other pillars, the force of gravity is very faint. And not just slightly so.
The weak nuclear force is still 10 trillion trillion times stronger than that of gravity. We may think the force of gravity is strong, but that's only because we associate it with extremely large objects. Like, it's one thing for Earth's gravity to cause an apple to fall from a tree, but what about the gravity generated by a single apple? As you can probably imagine, the challenge of isolating a single graviton in action is extremely difficult. What's more, gravity is the battleground where the two dominant worlds of physics come into conflict. General relativity and quantum mechanics. General relativity accurately describes very large things and portrays reality as continuous and predictable, the smooth and free flowing fabric of spaceime. Meanwhile, quantum mechanics, the best framework we have to understand very small things, insists that everything is made of discrete and individual quanta and that reality is far more random. Very often we are able to paper over modern physics's split personality. We apply a double standard and let relativity explain the big stuff and quantum cover the small stuff. The big missing question at the moment in physics in general is the relationship between quantum mechanics and gravity.
So what we are trying to do in this experiment is create something that mimics spacetime which is the domain of relativity and gravity theory with a material that has very quantum properties. It gives us a way to start approaching the question from an experimental perspective as to whether or not gravity is a quantum field like all the others or if it genuinely stands apart the way that mathematics as we currently understand it makes it seem.
For decades, physicists have attempted to bridge this gap and to quantize gravity, to break Einstein's smooth continuous fabric into the divisible random chunks of the quantum world. This has so far failed and it's created an irreconcilable breaking point. Whatever the nature of reality might be, it cannot be fundamentally described as one single big thing and a bunch of small and distinct things simultaneously without there being a deeper underlying framework. Take quantum theory's famous double slit experiment. In the experiment, physicists fire individual electrons at a wall with two narrow openings and then record where each electron lands on a screen behind it.
According to quantum mechanics, an electron doesn't pass through one slit or the other until it's detected. It behaves as if it goes through both at the same time. A prediction that has been confirmed repeatedly in experiments. But here's the catch.
Electrons have mass, and mass, according to general relativity, produces gravity.
So if an electron really does take both paths at once, does it create a tiny gravitational pull at both slits too?
General relativity says it can't.
Gravity in Einstein's theory has a single well-defined location. If quantum theory and general relativity are both complete, that leaves us with a problem.
So where do we go from here? Well, option one, we can assume gravity is quantum and keep looking for gravitons.
Now, that's great in principle, but in practice, it's very daunting. For example, pursuing the Higs Bzon took over 50 years and the world's largest science experiment to detect and turn theory into experimental reality. And compared to the task of observing quantum gravity in action, that was a walk in the park. Our most powerful machine, the Large Hadron Collider, is roughly a quintilion times too weak to probe gravity's quantum nature.
Theoretical physicist Freeman Dyson famously suggested that any detector sensitive enough to do so would have to be so massive it would collapse into a black hole. Physicist Claudia Duram sketches the uphill climb we face. And yet the gravitational waves you observe the estimate is that it was it would roughly contain 10^ the 40 gravitons. So now you're going to say well let's now prove that there is a graviton. So you just want to see the effect of one of them.
>> Can you imagine?
>> Difficult.
>> Luckily there are other options. Now as we speak scientists are building the experiments that might finally unlock the universe's most closely guarded secret.
Chapter three, the experiments.
Not one, but three different kinds of experiments are currently in the works.
Each seeks to isolate gravity in action and to thereby test a different theory regarding its nature. First and foremost, an experimental blueprint submitted in late 2024 by a group led by Igor Picovsky at Stockholm University.
If we can't isolate gravitons anytime soon, at least perhaps we can see evidence of their work, assuming they exist, that is. As our ability to take more sensitive lab measurements increases, so too does our ability to detect their subtle and so far theoretical movements. Here's how this experiment, still in the developmental phase, would work. A microscopic metal bar, similar to a tiny tuning fork, would be cooled to nearly absolute zero.
Lasers could then put the bar into a fuzzy quantum state, where it both vibrates and remains still at the same time, a state the physicists call a superposition.
If gravity itself has quantum properties, Picovsky argues it could subtly affect the superposition of the fork. Detecting those effects wouldn't reveal individual gravitons, but it could provide indirect evidence that gravity behaves like a quantum field.
Now, skeptics note that it may be impossible to distinguish the effects of gravitons from those of classical gravitational disturbances. But even if this experiment can't detect the elusive individual graviton in action, it could still reveal whether gravity itself leaves a telltale quantum imprint. And that's really exciting. But it's not the only experiment out there. The next one we'll talk about is a quantum sync test.
This idea, which two different teams of scientists simultaneously arrived at in 2017, represents an attempt to discover if gravity is not a quantum particle, but instead a quantum connection.
Researchers hope to place two microscopic beads in a quantum state where their positions are uncertain.
They would then isolate these masses from all other possible forces except gravity. And then they wait. What they hope will happen is entanglement, that famous hallmark of the quantum world.
Quantum physics posits that when two quantum objects interact, their properties can become entangled. Now, entanglement just means that two quantum properties can be correlated across a distance. Meaning, if you change one, the other will change in response. Kiara Marletto alongside her colleague Blatco Vedral from the University of Oxford in the UK proposed this experiment.
>> So in the experiment you're trying to create a quantum correlation between these two masses which is called entanglement by using gravity as a channel. A channel that allows these two masses to interact with each other and to create these correlations. Now the test says that if you can detect this entanglement, of course this is a big if in the sense it's a challenging experiment, but if you can detect the entanglement and guarantee that nothing else did it, so it's really happened through gravity only, then gravity as a mediator of entanglement must be quantum itself.
However, conducting this experiment, it's far easier said than done. Go too small and the gravity is too weak. Go too big and you can't maintain the quantum state. The masses we need to pull it off are at least a million times larger than what we can currently put in a quantum state. Although that may sound insurmountable, Marcus Aspel Meyer, who leads one of the groups racing to make this experiment a reality, predicts someone may be able to perform this experiment within the next 15 years.
But what if we don't see entanglement?
The next logical move on the chessboard is to test whether the classical understanding of gravity as a fundamental force is correct or whether, as Eric Verlin has posited, it is instead emergent. And the best part is that this work is already underway.
Experiments devised by physicists Dan Carney and Marcus Aspelmeer use ultra sensitive devices such as weights on twisting pendulums or gold beads suspended on springs to measure the gravitational pull between vanishingly small objects. What are they looking for? As their measurements become increasingly precise, scientists can test whether gravity behaves exactly as our best theories predict or whether tiny deviations begin to appear. Now, if gravity is not a fundamental force, but instead arises from some deeper microscopic processes, those underlying rules could leave faint fingerprints that hint at how gravity scales or changes under different physical conditions. Now, the goal isn't to catch gravity in the act, but to probe for areas where our current picture might subtly begin to break down. For now, gravity still looks smooth and classical. But with each increase in sensitivity, experiments like these focus the space of possibilities, ruling out some ideas, altering others, and bringing once purely theoretical questions into the realm of experimental science. But there's more. As radical a notion as it might seem, what if the true nature of reality is far stranger even than most of us have ever previously pondered?
Chapter 4, who made who?
So, back to that radical idea. Now, you might be wondering, well, what happens if those quantum gravity experiments fail? What if gravity is not actually quantized? Earlier we discussed ideas by Eric Verland centered around entropic gravity that gravity might actually be emergent. But what about another idea that may challenge how we actually determine what is real? If two observers disagree about the contents of the universe, then you've got to start asking yourself which one is real?
What does real even mean? Are the things that we take for granted that we observe in nature objective or is you know reality something that's just locally defined by the observer that's looking which brings us to a new way of thinking proposed by physicist Daniel Oriti.
Ariti argues that the original sin of all physics may be what he calls naive realism. This is the assumption that the world including gravity must be made of fixed objective and eternal laws. He calls this core belief the scientific equivalent of God. Something we cling to blindly only because we fear trying to make sense of our world without it. From this radical point of view, we don't just observe reality. We participate in creating it through the very language and models we use to describe it. Now, you've likely heard of the observer effect in quantum physics. It refers to the way measuring a system can sometimes change the system itself. For example, how measuring a particle's wave function can cause it to collapse. Daniel Orishi suggests that the observer effect is far more widespread than we suspect that it's part of the bedrock of reality. In his view, the deepest layer of reality isn't spacetime itself. Instead, he suggests that spacetime may arise from tinier quantum building blocks, objects that can interact and become entangled.
When huge numbers of these building blocks interact, familiar things begin to emerge. Space appears, time appears, and gravity appears. Not as a fundamental force, but as a largecale effect of all those interactions. Much like temperature emerges from molecules, gravity may emerge from entanglement.
In this picture, observers are themselves part of this great mesh of entanglement. They constantly measure and shape how these strange atoms of reality create the geometry of spacetime.
Ori says we have to embrace the fact that we make reality. Could it really be that in reading the rule book of nature, we are also helping to write it? Now, that's a pretty speculative idea. It might seem like it's a little bit out there. There's no real experiments we could ever devise to test this, but it is a really interesting thought experiment. Surely, there must be some way to explain the phenomenon we call gravity. And yet, time and again, gravity has broken all of the rules that have allowed us to explain everything else. So maybe it's not that surprising that we're starting to look in more radical directions as a way to find answers. So I guess what really at the basis fascinates me about gravity is that this there's always going to be a next thing. We know gravity as described by general relativity. The fact that we know it fails down is something very powerful in itself because it gives us an indication that we should be looking for something else. This is how science works. You you you you embrace this failure and that's how you can go to the next level.
What next?
After a century of searching, it is rightly frustrating that answers to so many questions about gravity still elude us. But in science, ignorance is not failure. The next best thing to having answers is having questions. And there are still plenty left to explore. The experiments being built today, like the twisting pendulums, the gold beads, and the quantum bars, they may finally tell us how gravity arises. But they may also tell us something far more challenging.
They may reveal that the frameworks we use to describe reality are incomplete.
that the universe is not just waiting to be discovered, but that it is shaped by the questions we are capable of asking.
If gravity is a question that pushes physics to the breaking point, what happens when we turn that same scrutiny inward?
As we reflect on two key areas of physics, black holes and gravity, it's clear that neither is as settled as the textbook suggests. But there's an even more fundamental question underpinning it all. Why does anything exist at all?
And how do we probe the building blocks of reality? CERN is most famously the home of the Large Hadron Collider, a 27 km underground ring where we smash particles into each other near the speed of light and try to break physics and better understand the known laws of reality. It's been responsible for groundbreaking new physics, most notably the discovery of the Higs Bzon in 2012.
and is a world leader in antimatter research. However, in order to probe even deeper and hopefully discover the things that help us actually understand black holes, it must run at higher energy levels. In the next video, we catch up with the new director general of CERN, Mark Thompson, an important juncture as the LHC is due to shut down for 2 years for upgrades, paving the way for even more exciting physics. But is there anything left to discover? And are large particle accelerators really the future of particle physics?
>> The technologies we develop here at CERN, they do change the world. We understand a lot, but there are really big questions that we don't know the answer to. Big questions like dark matter. Is the Higs Bzon a fundamental particle? Does the Higs Bzon interact with the dark matter? At some point, we are going to find answers to some of these really, really big questions. And the only way you can do that is with high energy colliders. We are going to break the standard model that we have.
We are going to find a in its armor.
>> Mark Thompson, you are the new director general at CERN. Thank you so much for joining New Scientist today. And there's a bit of background noise today because we are in SM18 with this amazing machine behind us. Can you explain a bit about the room we're in right now? Yeah. So, it's great it's great great to have a chance to speak to you. So, what you see next to me is a test string of the high luminosity LHC magnets. So, come this summer, we're switching off the LHC for a period of 4 years to install this remarkable technology in place just around where the experiments are. This will give us a machine that's 10 times brighter than the Large Hadron Collider, 10 times more data. So, it really is an opportunity to explore the universe in a way we haven't done before. This this technology here didn't exist when we built the LHC. And actually, what we're doing is we're we're testing it on the surface because when you go underground, the tunnel is actually quite narrow. So, it's much easier to do tests up on the surface. So, very very advanced technology, very exciting. Um, big step forward. And just to give some context about where we are outside this room, we're surrounded by the Swiss and French Alps. Underneath us, there's a enormous 27 km ring that makes up the main collider at CERN, the LHC. There's a lot of misconception maybe from the public.
It seems quite secretive what's going on here. We we had to get through a lot of security to kind to get in here. Can you just explain what is the point of the LHC? What is the point of CERN and kind of what actually happens here? The world scientific community particularly in Europe have come together at CERN basically to explore the universe to understand the fundamental nature of the universe. That's CERN's mission. It's as simple as that. We want to understand how the universe works.
CERN is the world's biggest particle phys physics laboratory. The Large Hadron Collider is the world's biggest collider 27 km in circumference. It's about 80 m below where we are now. And what we do is we accelerate protons in two different directions around the ring. So we start with a tiny bottle of hydrogen and we put those individual basically protons. Well, actually then we we attach a charge to them and that's not quite the same. We put them in a a small linear accelerator to accelerate them up to a not very high energy. Then we put them into a small circular accelerator called the PS. Then we put them into a bigger circular accelerator to get them up to higher higher energy.
And all the time we're increasing the energy of these protons. And then we put them in the large hadron collider. And we have these big blue magnets that steer them around the ring. So they keep them going in the circle. And they have to be big and powerful because we're accelerating these particles to 99.999991% of the speed of light. So you have to have strong magnets to keep them on that circle. And every time they go around, we give them a little kick with kind of what we call radio frequency accelerations. And that's how we accelerate them up to these very very high energies. So you've got one ring of protons going this way around, one going this way around. And then as they come towards the experiment, they they're circulating in the ring about that far apart. We then push them together, bring them to a tiny point, and that's when you get this massive collisions, and that's what we photograph those collisions. And we can figure out from those images what happened quantum mechanically when these protons collided. And that's how we try and understand how the universe really works at a fundamental level. Certainly in our underground facilities, we can't just let people wander down there is well you can you can even see here there's a lot of liquid helium. There's a lot of high power. But in terms of our site, we're actually quite open. We have the science gateway which I would recommend to everyone to visit if you get the chance.
It's the number one tourist attraction in Geneva. a science gateway, a science exhibition, being the number one tourist attraction is an amazing thing, but it's all about the science. That's what we're here to do.
>> And now you're the director general of the entire organization. I was reading that you were the first in your family to go to university and and as a teenager, you actually read about CERN.
Can you tell me that story a little bit about when you first heard about this and the kind of the journey you took to to get here?
>> I I'm not quite sure when it was. It was either when I was 13 or 14. I read a popular textbook and I'm still searching for it. and it must be somewhere at home in Cambridge or my my my former home but I hadn't found it and I read the book and I I I was kind of fascinated by the subject how does the universe work but I actually found it quite frustrating because the book didn't give enough information at that point I just wanted to know more and that really I think set me in that direction I wanted to be a particle physicist from a very young age my family was very non-academic south coast of England but I you know I was lucky enough to be good at mathematics quite good at physics as well which helped um and then obviously really interested in science really inspired and passionate about science then I went to Oxford to study physics and well here I am now CERN has been here for a really long time been here for decades um since you were an undergraduate when you think about what has changed since you were first learning about particle physics to where we are now what are the biggest things about the universe that we've actually found out since CERN has been operating >> when When I first read about CERN, we hadn't yet discovered the W bzons. We have three main forces and plus gravity, which is a bit special. We know about electromagnetism and we know the particle that makes that work. But back in the the early 80s, we've never seen the particles associated with the weak force. Those were seen discovered at CERN. That was a major step forward.
It's not so long ago. We didn't know that these particles called neutrinos had mass. I've also done neutrino physics as well as kaleidop physics.
That's not so long ago. Just over 25 years ago, we thought these particles or some people thought these particles were massless. We now know they're not. Very strange.
And the real massive discovery obviously was the discovery of the the Higs Bzon in 2012.
And the Higs Bzon is something completely different. It's nothing like anything else we've ever seen.
Completely new type of matter. And what makes the Higs Bzon so special is in some sense it's everywhere. So if you go to the deepest depths of the universe where there's nothing, you still feel the presence of the we call it the Higs field. If you imagine all of the other particles whizzing through the universe, in some sense they have no mass but in some sense they feel the presence of the Higs field which is kind of everywhere ever present in the universe and that gives all of the particles we see something that looks like mass. So the Higs and the Higs field determine the properties of all of the other particles in a a very real sense. So it's quite unique, really really strange. Um massive massive discovery. So that was a huge break breakthrough in 20 2012.
>> When you list out those discoveries kind of W bzons, nutrinos, the Higs Bzon, you could argue looking from where we are now that it was almost like a golden age of discovery for particle physics. We were really filling out all the gaps that we didn't know about. Do you think you could argue that that golden age is now behind us and we kind of we've we found everything or or do you think there are still a lot? I mean uh we've definitely not found everything and and if you if you take a big you look back at re really big gamechanging discoveries you can think of things like neutrino mass the Higs bzon discovery of gravitational waves discovery of dark energy these things come along not every few years they're every 5 to 10 years so you don't get these really gamechanging discoveries all the time and and you shouldn't expect to and we're we're now at a point of time where we understand the universe really well, but we also understand there are so many questions we don't we can we measure but we don't understand. So we know there's dark matter out there at some point. We will discover what it is. We don't know when but we will discover what it is. We know that the particles that make up the universe have a very strange pattern of masses that doesn't really look like a pattern actually. It just looks like they're semi- random. That's all to do with the Higs boson. But we don't understand that pattern. So there are all these huge gaps in our knowledge that we understand a lot. But there are big qu really big questions that we don't know the answer to. We don't know why there's any matter left in the universe after the big bang. In principle big bang you produce matter, antimatter some point it comes together you get nothing. We get energy. That's not what happened. We know that's not what happened but we don't know why or how that happened. So there there are all these really big questions out there and um that's what we're doing. We're exploring we are exploring the universe and at some point we are going to find answers to some of these really really big questions but you don't expect them to come along every two or three years.
You expect the really big breakthroughs every you know maybe every 10 years.
You know, I'm optimistic in 10 years time we will we will see something hopefully something completely unexpected that might answer one of these really really big questions are out there.
>> Do you have a personal favorite question that kind of >> keeps you up at night or that you would just love to answer if you could pay a million dollars or or billions?
>> I I actually have two.
>> Okay.
>> I want to know what dark matter is.
Definitely want to know what dark matter is. We have many possible ideas for what it could be and we're looking in many different places for it but we haven't seen it yet. We know it's there. So that's really interesting. And the other question I touched on before it's understanding the pattern of masses of the particles. Something is making all of the 12 building blocks of the universe that we see have that pattern of masses. We really don't understand that. there's something really fundamental hidden in there that I would love to know really why why the particles have that pattern or that semi-random pattern actually >> and in terms of finding dark matter or or a candidate dark matter particle do you think kind of the LHC and CERN has a good chance of finding that >> depends what it is there's a very popular theory out there called super super symmetry um if the origin of dark matter is a super symmetric weakly interacting massive particle, a wimp.
Um, there's a good chance that we will still have have the chance to find it at the Large Hadron Collider. Now, there are other models because we haven't yet seen it. So, we've started to look in other places where dark matter could be a very very light type of particle and we're now doing experiments to try and look at different different possibilities for dark matter. And you have to do that in different places. But you know it's quite possible that you know 10 years time we'll be sitting there saying yeah we we found dark matter at the LHC. Who knows?
>> You mentioned earlier that we are currently or we're about to upgrade the the current LHC operators. What will actually be happening in these next 5 years? I you mentioned at the beginning you have quite an active job but >> will it be less involved than than previous directors who have kind of while the machine's been running?
>> Uh I I actually think it's much more than that. Um the the LHC is one the LHC is a wonderful machine. It's a technology technological marvel. It it runs absolutely beautifully. We've just started this year's operations very recently and it's again it's running beautifully. I mean it's really amazing.
So now it runs very very very smoothly.
Takes a lot of effort to make it do that. But what we're doing in the summer, so at June the 29th, 6:00 a.m., we switch off the LHC and we switch off for 4 years. And what we're doing is we're replacing about 1.2 km of the 27 km ring with this very very advanced technology. And what that does is when the particles come around, they they come around and then we bend them towards each other. If you make the bunches of protons smaller and smaller, you get many, many more collisions. You concentrate everything in the same place. That's what these super high field magnets are doing. So, it's a really challenging project. This is technology that is so really absolutely cutting edge. You won't be able to see it from there. We we have this incredible superconducting cable that powers these magnets. Installing this is a massive task. It's by far the biggest thing that CERN has done for the last 20 years. And at the same time, the big experimental collaborations, Atlas and CMS, which we sometimes call the general purpose detectors, these are the ones that where you do the hig boss on physics, you explore super symmetry, they're upgrading their giant detectors.
You know, this is like replacing the silicon technology that you know in an iPhone 10 with the silicon technology in an iPhone 17. These are again the biggest projects that the experiments have done for the last well since building the detectors themselves. So it's a very different phase but actually it's a very very exciting phase and very very challenging. It's you know this these these are really really big projects. So so in some sense it's just different um for me actually it's kind of really I really you know I like I like technology as well as the science.
It's really really exciting and you know we're we're really laser laser focused on actually succeeding on this massive these massive projects.
>> You mentioned that it's one of the largest things that Cern has done in the past 20 years. Why is it so technologically difficult?
>> This is superconducting technology based on nobium free tin. So it's really a technology I say we didn't have before.
You have to power these magnets. You have to provide them with liquid helium.
And you can see from this room actually this arm is like one of the arms that will sit on one side of the detector.
Firstly, you have to build the place where these magnets are going to sit.
Above them, we have the powering galleries, the things that provide the power, provide the liquid helium. It's just big engineering as well as very very advanced technology. You've got to get it right. I mean, this is such a big big project. And what we're doing here in this this building um SM18 right right now um is this is a test a test spring. We're testing the technology and it's much easier to test it here rather than in the confined spaces of the LHC tunnel. And we've already learned some really critical information about some of the design of this. We've updated the design based on our tests. And it's amazing to be here today that this is now operating. is at its operating temperature of 1.9 Kelvin. So this is a superconducting liquid helium system operating at 1.9 Kelvin. That was a massive milestone for us in this project. So we're now confident that when we go underground and start installing the high luminosity large hatron collider, we will be successful.
We know what we're doing. We we've tested the installation procedures here.
So yes, it's it's it's complex technologically but also logistically. M you mentioned that a lot of this work is now future facing kind of we're we're looking forward to 5 10 years away but as you mentioned there are still collisions happening underground we're still taking data can people just forget about the stuff that's happening now and we're only excited about the future like should should we also be expecting to find new discoveries from this run as well who know I mean who knows right so we've probably analyzed the about half of the large hadron collider data to date maybe a little bit more than that So there's still a very active program of research just looking at the data we've got sitting on our our very large discs already. Who knows who knows what we're going to find. We're going to me measure things more precisely and we're going to search for new physics in that data. So it's quite possible we will see something and that that program of exploring the vast amount of data that we've uh taken already that's going to carry on while we're building the high luminosity large colliders. In addition to that, we're switching our accelerator infrastructure off during this long shutdown. But about halfway through that four-year period, we start up some of the smaller accelerators, the ones that kind of feed in in big loops to feed into the LHC.
And they provide um scientific opportunities. We call it we call it our non- collider program. So science will keep going on at CERN or will come back at CERN very quickly. Different kind of science. We don't just do collider science here. Here we have this very rich program of uh non-colid physics. I mean including you know we may may come on to it later. The antimatter factory as part of that non- collider program.
>> This may be a good a good time to ask about the antimatter factory. There's loads of really exciting science coming out. I think there's an upcoming experiment uh transporting it which I'll let you talk about. But could you give an idea of kind of what that antimatter factory is and and why you have it here?
So for every particle we have, so like the electron, we have an anti- particle.
It's like it's opposite in charge. It's the same mass. We also have protons, the things that sit inside us, but there are antimatter equivalents of those protons.
Now around us today, pretty much everything is just matter kind of kind of obviously. There are occasionally you get cosmic rays from outer space of that which are antimatter as well, but not very many of them.
Now, there are some very deep theories that say predict that antimatter really does look like matter but looked at in a a very strange mirror. So, it has different charge have the same mass but it has other properties that are related.
So the the antimatter factory called AD anti-roton decelerator Elena is actually one of our smaller accelerator systems and we are producing anti-roton and then we're making anti-attos as well. And what we're trying to do is we're trying to see if the antimatter equivalent of protons or the antimatter equivalent of hydrogen atoms, antihydrogen, does that have the same properties as normal matter? And that's what our theory predicts. But of course, you want to test that theory very precisely. So that's what we're doing is we're looking at the difference between matter, both protons and anti-rotons, and anti-atoms, particularly hydrogen, and making very, very precise measurements to see if antimatter really does look like just matter looked at in a very strange mirror.
>> And you're producing incredibly small amounts of it because it's so hard to kind of contain. I've read somewhere that it's by Graham one of the most expensive materials in the world, but soon it won't just be here as well. I've I've heard there are reports that you you'll be moving it out of so it's it's it's a remarkable development actually.
So the base the base experiments at the anti-atter factory >> is very clever. It it traps single anti-rotons or you know particles about you know these antimatter protons in a very in a very very clever magnetic very very clever magnetic trap. The way it does it is is amazing.
Now the place where we we we we trap the anti-rotons at the moment is quite near the accelerator.
And if you want to make really precise measurements on antimatter, you you need to be away from magnetic fields, away from natural electrical disturbances. And of course, where we create it, there's an accelerator nearby. So So it's not the ideal environment to make those measurements.
So what we're doing is what's called base step. It's to take some antimatter, antirotons, store them, and then transport them around the site. And the ultimate aim of that is we will then be able to do these antimatter experiments elsewhere on the site where where there's no kind of no magnetic fields, no mag big magnets to make more precise measurements. And in principle once we've mastered this tech this this technique of moving the antimatter around you can then transport the antimatter to laboratories elsewhere in Europe. We really want to see if we can move it around and perform experiments in quieter quieter environments. Quieter than in here.
>> We expect there's not going to be a problem of course but uh you people have watched films antimatter matter very dangerous. It's not of course it's tiny tiny amounts but we'll move it around the site and that's the demonstration that we really can move we can move antimatter and that will uh define what we can do in the future.
>> Antimatter and matter as you mentioned are uh they annihilate when they meet.
Why is it so difficult to transport actual antimatter to another laboratory for instance?
>> Yeah. So I mean that's absolutely right.
So you can't you can't just get a blob of antimatter and put it down on the table. It would as you say annihilate.
So what you have to do if with the antimatter is you have to keep it away from matter. So you you have to contain it in a way that you're not containing it physically. So you have to contain it in magnetic traps or laser traps. the clever technology is in the way you shape the magnetic fields um that mean that the kind of the anti-roton gets stuck basically in this in this in this in this trap and it's amazing the these antimatter traps you can trap antimatter in there for months I mean it's not it's just it is quite incredible actually it's really incredible technology >> and so in 10 years time when when this uh technology of transporting antimatter around is more advanced and mature you could be driving down the motorway way in Germany or France or Switzerland and possibly be next to a truck with antimatter inside it. Is that the kind of the the vision here? Eventually, >> we're not going to have freight freight trains uh truckloads of antimatter going around the world. I mean, and and again, we're talking about a very very few in this case anti-roton.
But but the key is to take them to places where um you have specialized laboratories where there are there there's no magnetic field that no vibrations and you can make very very precise measurements because we've already made measurements looking at matter and antimatter and you know to date they seem to have the properties you would expect them to. We want to increase the precision. We want to make as precise measurements as possible.
There's a theory called CPT which basically says if you take matter, swap its charge, look in the mirror, and run time backwards, you get the same answer.
It's a very very fundamental part of our our theory. And that says the antimatter should look just like the matter. And that's what we want to test with really ultra high precision. And there are just a few laboratories around Europe where you can really make that those increased precision measurements. So it's not going to be trains of antimatter traveling around the uh traveling around Europe. It's yeah very rare. It'll be very very rare and very specialized. I'd like to ask a bit about the future of particle physics and the future of colliders. From some quarters there is a fair amount of cynicism now around particle physics saying we've we've discovered most of the kind of the zoo of uh of particles that were predicted by quantum thermodynamics and quantum mechanics um and that now you're just kind of filling in the gaps. Is there still a need for large colliders and and big collider projects?
>> There are these really really big questions out there and we know we know what we don't know or we know what we don't understand. Big questions like dark matter. Is the Higs Bzon a fundamental particle? We actually don't know that. Does the Higs Bzon interacts with the dark matter? We know it's there. We don't know the answer to that question. Why does the Higs Bzon have the properties that it does? Is the Higs Bzon on its own or are there multiple Higs Bzons? But we know there are all these questions out there we don't know the answers to. And anytime I write I mean I do this occasionally. I write down my 10 big questions in particle physics. Half of them have something to do with the Higs boson. And the only way you can really start to address those questions is to make what we're calling a Higs factory produce many Higs bosons in very very clean environments. So we can then look at the properties of the Higs boson, is it like we expect it to be and if we see deviations from the properties we expect, we might then learn we will then learn something about the unknown the unknown universe. So we're kind of trying to use the Higs as a tool to look into the unknown universe and the only way you can do that is with high energy colliders. There's no other there's no other way you can actually look at that. The Higs Bzon is completely unique. So, we've discovered this completely unique type of matter and it is a type of matter, something like we've never seen anything like it before. Its properties are really strange. Really strange properties.
We've discovered something and now we really want to understand what it is.
And by understanding what what what it is, we you know, we think we've got a very good chance of learning about some of the really big questions that we don't know the answers to. And the only way you can do that is with colliders.
>> One of the potential plans for a future collider is is this um future circular collider which would be more than three times the size of of the current ring and hugely expensive as well. Is there a need for that in particular? I can understand you can make the argument feeding a future collider. But in terms of that collider specifically, do we need that? the last year across Europe um in the UK and all of our European member states each individual scientific community came together and asked themselves the question what should we do next at CERN what is the next collider for CERN there's a massive consensus that the FCC is by far the best machine to do the science I mean there so it came out clear number one and even number two actually but really a clear consensus that scientifically this machine is the right thing to do.
And that's really because the capability of this particular machine compared to the other things you can do, it's just huge gap in the scientific sensitivity.
And it's very unusual even in a specific scientific community, you get such strong agreement. And it's so we're convinced it's the right machine, the best machine to do the science that we we feel we need to do to, you know, continue it continue our exploration of the universe. And it's it's a very expensive or it would be a very expensive project. People from the other sciences or even the public might argue why aren't we spending that money on curing cancer or or solving climate change. Um why should we kind of devote that many resources to to something like that?
>> Yeah, I always think I'm not sure that's quite the right way to look at it. The starting starting off with the cost the cost we believe is 15 billion Swiss Franks. So it is a large number that is spread across 15 years. The construction period the cost will be shared by 25 member states. It will be we'll have contributions we hope to have contributions from outside Europe potentially contributions from the European Union. So when you kind of put all the pieces together you can see how you can put that jigsaw puzzle of money together. And I think in any scientific ecosystem, whatever that means, you're going to have a range of experiments.
You're going to do some small things over this side and at one end you, you know, you have to have these really big bets do the really really ambitious science and the FCC is the one that's, you know, right out at the end. I don't believe it's stopping other science happening. I mean the you know the medical research will continue regardless of the FCC but it's that it's long-term sharing the costs over many years in many countries we you know we believe it is achievable we still have to get approval from multiple governments but that's certainly the way I would look at you have to have these big bets the other aspect to this um sitting where we are today just outside Geneva at the heart of Europe there is one area of science where Europe has global leadership absolutely clear global leadership and that's particle physics and that's because Europe came together here and by doing that science we're developing technology pushing the technological forefronts in ways that you would not be able to do if you didn't build these you know vast collider infrastructures and that really really helps Europe as a whole develop that technological base and that has huge economic benefits and there have been a number of studies on this so we do science and we're here for the science but by doing the science we're pushing technology beyond what we have today and that benefits the whole the whole of you know all of our member states.
>> We've seen um in other countries uh for instance the UK that the funding issue come up and right now the UK research um council has said that they are thinking of not funding uh UK scientists to work on the LHCB because it doesn't kind of align with their goals of of being economically valuable. I just wonder what what what you thought of that issue kind of that the idea that science has to be economically valuable and also that the UK kind of cutting funding to to LHCB scientists.
>> I mean around Europe I mean the economic situation at the moment is quite challenging. There's no there's no question about it. So it's not it's not I would say it's not a don't I don't want to pick on a particular country but we are seeing you know there's economic challenges across Europe. From the perspective of the FCC we're not asking for money now that we we're actually going to be investing the money in the early 2030s. So we don't know what the economy will be like at the moment but I do think it's our duty as as sir not just to make the scientific case but to actually make that wider economic case and that case is there and the challenge of making that case is sometimes the technologies we develop here at CERN or in big science they they do change the world but they change the world 20 years down the line. If you didn't do the investment early on, you there are things you just would not end up with.
So I know it's a very a rather rather dated dated example now, but the worldwide web was developed 500 meters away from where we are now in a in a small office inside CERN as a way of sharing data between physicists.
That really has changed the way the world works. The accelerator technologies we develop are not only useful for things like cancer therapy, very advanced cancer therapy which use proton accelerators for example, but they're also used in other fields of science. So if you look at things like in the UK, the diamond light source, that's a storage ring. It's a ring that sends electrons around. It's an it's an accelerator. That technology was developed to do this fundamental science. But that technology is now used to understand biology at really deep deep deep at its deepest level. So if we hadn't developed the accelerator technology, we would we would know so less about structural biology drug discovery. So the the economic benefits are are huge, but sometimes they're very long-term. That's the difficulty in making the case. And you know, you just have to keep pushing pushing technology and on not to develop technology per se, but to meet your scientific goal and then that technology will find its way somewhere. And these are big technological breakthroughs. These are these are not incremental breakthroughs.
But we have to make that case. We have to make the the case for the value of our science beyond its intellectual cultural values. So it's an important point. Will there ever be kind of a final accelerator? Will scientists ever be happy kind of saying, "Right, we've we've made the biggest accelerator we can. We've answered the questions." Or if we do build that 97 km ring, will people start saying, "We need to build an even larger ring."
>> It's a very interesting question. From what we know today, there's a there's a there's a grouping of interesting physics at what we call the electroeak scale. So the W bzons, the Z Bzon, the Higs Bzon, and the top quark, the very heavy quark. That's very strange. They're all similar masses. And we call this the electroeak scale. So there's something special going on at this scale of a few hundred gig electron volts. So what we're doing with the FCC, the electron posetron collider, is we're exploring that electroeak scale with very, very high precision. So there's a real key target there. One of the advantages of something like the FCC is it starts off being an electron posetron collider but potentially in 30 40 years time our successors could say well actually what we need now is a hadron collider again like the large hadron collider but a bigger one we would then have the tunnel so it paves the way to doing the next phase of our exploration. Now we're very focused on FCC the electron positron collider now that's what we're selling you know that's what we're going out to our member states to sell but it does set the path potentially very very long term and that would that would enable you to explore the scale up you know it's it's like a 100 times the scale of what we're looking at now now so we're kind of really exploring this whole space you know the electroeak scale higs wzeds and it gives us a pathway to discover you know to to search what's going on, you know, 100 times that scale. If you don't see anything there, then I think you start asking that question. But we're we're we're exploring this the place where we think it feels like it's the right place to see something, something completely new.
>> And when you say exploring that question, you mean is our understanding broken or do we need to build another collider?
>> Yes. As I say, I I think there are there are good arguments. I mean, they're very they're quite complicated theoretical arguments. There are real questions around something called the hierarchy problem which is why the Higs is as light as it is. Why is the Higs at the electroeak scale? And there are answers to that question. One of them being super potentially super symmetry. Now if it's super symmetry that is the answer to that question. It can't lie too far away from this scale we're looking at now. And that's really why you know by exploring first with a very precision electron posetron collider and then poss possibly with the successor to the very large you know the large collider the future circular collider a hadron mode you're looking in the right place you're kind of guided by some of the things we don't understand now if at that point you don't see anything then there then you're not then necessarily being guided by the science and the science guides where we're looking at if that if that makes sense then but we you know I'm actually quite optimistic that at some stage in the next 10 10 plus years we are going to break the standard model that we have we are going to find a in its armor um and it might not be where we expect it to be but but what we're doing with all of our big scientific problem uh projects is we're we're looking in the right place or looking in the right places we're asking the universe the right questions >> one of the reasons that CERN started um in the kind of postwar period was to bring scientists from different European countries together. We're seeing without getting too much into any into the political environment, we're seeing increasing kind of uh isolationism and and and the the fractioning of countries. Um is there something important about the way that Sun operates kind of having I don't know how many scientists from different countries work here, but that the kind of that spirit of cross collaboration here in the current political climate.
>> I absolutely absolutely agree with that.
I I think the science we do, we're just asking a very simple question. Let's understand how the universe works. It's a very, if I call it a safe question and the only way you can answer that question is by people collaborating and CERN's success, I mean CERN is remarkable. It really is by far the biggest best particle physics laboratory anywhere in the globe. And that's built on that cross European primarily European collaboration. Long-term, it's a treaty organization. So you sign up and you collaborate and it's a very safe place for people of many different nationalities to come together and work to a common goal. So if you go to our cafeteria at lunchtime, there's about a thousand people will be there any one time. We think there are typically, well, we don't know the exact numbers, but 110 different nationalities, mostly young people, young scientists. And you know what they're going to be talking about? They're going to be talking about physics and science and occasionally football and occasionally rugby. But it's very, very dynamic. So the young people, the young scientists really collaborate very strongly. And what I think you also see in the wider international community even though the world is becoming quite fragmented at the moment that's that's you don't see that here you see the opposite.
One of the reasons why it's so difficult to reconcile gravity with quantum mechanics is because quantum theory is just strange. It has properties that are unimaginable in the everyday world that we interact with. For example, it's possible for quantum particles to exist in a state of superp position where it's in a combination of two mutually incompatible outcomes. That forces us to ask the question of whether gravity can exist in a superp position as well. So, let's take a beat to explore one of the hardest quantum theories to wrap our heads around, the multiverse. You've probably heard it described as parallel versions of yourself, alternate lives, the roads not taken. That's not what physicists mean. The real multiverse is stranger. It comes from two completely different places. Quantum theory's hardest unsolved problem and the cosmology of the first split second after the Big Bang. Both taken seriously lead to the same conclusion. Our universe might not be the only one. The final episode walks through both ideas and the experiments now starting to look for evidence.
Most people think that the multiverse means infinite versions of you. Other lives, other choices, other worlds where everything played out differently. But that's not what physicists mean at all.
Because the real multiverse isn't about alternate versions of your life. It's about something far stranger. And it comes from our best theories of the universe and reality itself. In some cases, scientists now think that it might even be testable. Here at New Scientist, we've been following the science of the multiverse for decades.
And what's emerging is not just one idea, but several very different versions of reality that all point to the same unsettling possibility that our universe may not be the only one. In this video, we're going to explore the real multiverse. From quantum many worlds to the vast cosmos really special are just one of countless random outcomes. Chapter 1. The multiverse is not what you think. In films like Sliding Doors and Everything Everywhere All at Once, depictions of parallel universes draw on our innate curiosity about the paths our lives might have taken. Protagonists meet variations of themselves who made different decisions, who possess distinct abilities. The idea that all of our unfulfilled aspirations, all the lives not lived are realized somewhere out there in the multiverse.
Like, what if I chose to study chemistry instead of physics at university? Uh, the horror. But this is not how physicists think about the multiverse.
Unlike the movies, the scientific notion of the quantum multiverse has little to do with our personal decisions, never mind our wildest fantasies. Sadly, when physics talk, physicists talk about the multiverse, they mean different things, and none of them are the things that people have in mind from watching the Marvel movies, etc. >> No, it's even weirder than that.
Instead, it stems from physicists attempts to make sense of the reality we do experience. The quantum multiverse is actually taken quite seriously in some physics circles as a way to resolve one of the biggest conundrums in physics.
Now I need to take you back to the 1920s when physicists were struggling to parse a new theory of reality called quantum mechanics. This new theory describes the vanishingly tiny and staggeringly strange the realm of atoms and subatomic particles. The weirdest thing is that these particles appear to exist in a superp position of many possible states all at once. Let's say we were trying to pin down where a particle was. Now, we can't pin them down exactly like we can ordinary objects. Instead, we see that particles act like they're in multiple places all at once. That is until you measure them at which they suddenly take on definite properties like they suddenly end up here and only here. The Schrodinger equation captures this vagueness. Incorporating a mathematical concept called the wave function to encode all possible outcomes. It allows us to calculate the probability that our particle will manifest in a particular place when we measure it. But it can't tell us for certain the outcome of a single measurement. In other words, all we have until we look are probabilities.
So how does the concrete classical reality that we see which itself is ultimately made up of atoms and particles emerge from this fuzzy quantum netherworld? Physicists call this the measurement problem, and it is the central mystery of quantum theory. You might think that this isn't a big deal.
After all, I could open up the weather app on my phone, and you could say that's going to have a 75% chance of sunshine in London tomorrow. Yeah, good luck with that. But the weather just does take on one definite outcome. So, isn't that the same thing? Not at all.
Remember, quantum objects behave like they're in a superp position of possible states until they're observed, a mixture or combination of possibilities. That's distinct from something like the weather, where the reality reflects only one of many scenarios that are possible.
And the probabilities that I see on my weather app, they arise mostly from ignorance. In quantum mechanics, the probabilities are baked in, encoded in the wave function. In fact, it should be mathematically impossible for the wave function to just go from a mixture of these different possibilities to just one.
>> The measurement problem is just the question of what do you mean by the phrase measurement in quantum mechanics.
You know, when you say when I measure a system, its wave function collapses and I get a definite outcome like the cat's alive or the cat's dead or whatever.
What counts as a measurement? Does it need to be a human being? Can it be a video recorder or what? We have no firm answers to those questions.
>> Now, one way to deal with this problem is just to say that there isn't a problem that we need to solve. The wave function, these probabilities that it represents, it's all just a kind of mathematical shortorthhand that it's not actually representative of reality.
That's what many people call the Copenhagen interpretation.
>> The phrase the Copenhagen interpretation is sometimes used to talk about a certain approach to the quantum measurement problem. It's a little bit problematic because no one agrees on what the Copenhagen interpretation actually is. People like Neils Boore and Verer Heisenberg pioneered it, but they didn't agree with each other or even with their own selves from paper to paper sometimes. But it's the basic idea that there is something fundamental about measurement, right? That we describe systems mathematically in a certain way in quantum mechanics. But if you're a hardcore Copenhagen person, that description of the system when it's not being measured doesn't really describe the real world. The real world is just the measurement outcome.
>> In the 1950s, Hugh Everett was grappling with this problem. Everett suggested that when the wave function snaps into a single definite outcome, something that we call the wave function collapse, those other possibility scenarios don't just vanish. Instead, he arrived at an astonishing conclusion that every time a measurement is made, all possible outcomes contained in the wave function are realized in many separate worlds that branch off from our own. So rather than a collapse, there's a split avoiding the mathematical impossibilities from before.
Essentially, Effort's bold move was to say that all different parts of a quantum superp position really do exist.
It's just that they exist in separate non-interacting worlds. This is known as the many worlds interpretation of quantum mechanics. But you can call it the quantum multiverse.
>> Because when I measure a quantum system here in my lab and I get two possible different results, I will get two different universes. The one universe that I was in splits into two. And in each one of the two different ones, I now have a definite measurement outcome.
To be clear, it is an interpretation that a good number of bonafide physicists take seriously. But since these branching universes never really interact with ours, the idea can't be tested with observations. And that leads to a couple of tricky questions. First, if all of these other worlds really exist, where are they? And more importantly, why don't we ever see any sign of them? The answer is not what you might expect. In fact, these other worlds aren't out there at all. Chapter 2. Where are these other worlds hiding?
The short answer is that they're not located in physical space. You wouldn't find them lurking just beyond the observable universe. Even if we could somehow see beyond the cosmic horizon.
Rather, they exist within a larger mathematical structure. Because what we call worlds here are actually just different components of a single wave function that of the entire universe encoding all possible outcomes of all quantum measurements or observations.
The branching involved is not a spatial separation but division within the structure of this wave function. This is why some of today's leading many worlds proponents, including Shan Carroll at John Hopkins University in Baltimore, have argued that talk of parallel worlds is actually misleading because it suggests physically separate locations.
>> There is no physical location of them because location in space is something that exists in each world. The cosmo, the many worlds of quantum mechanics simply exist simultaneously. So these worlds have absolutely no physical connection with our own which means you really don't need to worry about the fate of your doppelgangers. But this also helps to explain why if every quantum possibility is realized the singular reality we experience is not completely incoherent or chaotic. Why we could exist in a quantum multiverse without ever noticing its infinite weirdness. The explanation involves a phenomenon called decoherence. the process through which quantum objects or systems lose their quantumness including superp positions as they interact with their surroundings. Basically, the larger quantum object or system is, the more it interacts with other objects and the faster its quantumness vanishes. In the context of many worlds, branches are decohered relative to each other, effectively isolating them from one another, but then never completely destroyed.
>> That's decoherence. Decoherence is when a quantum system that was in a superp position of two different possibilities becomes entangled with the environment around it. And the relevance of of that to many worlds is that that's the moment when the world split when decoherence happens when your system becomes entangled with the environment. Now that decoherence that entanglement is irreversible. So basically classicality the the fact that the classical Newtonian universe is such a good approximate description of reality is because it's those quantum mechanical states that remain robust and unaffected by becoming entangled with their environments.
>> Today most physicists agree that this is why the everyday world looks classical rather than quantum. But it might also apply to the many world scenario. The thing is, you could argue that the insistence on separate non-interacting branches of reality means many worlds is deliberately constructed to explain why we don't see contradictory outcomes. The maths of quantum theory only gives you the wave function governed by the Schrodinger equation. But it doesn't explicitly say the universe splits up into independent worlds. And many worlds says nothing about why branching works that way. For instance, at what level does branching occur? When are branches sufficiently decohered from one another that they stop interacting with each other? It's very difficult to answer these questions because from the outset, we can't ever measure or ever interact with other universes. In this picture, reality in each and every branch appears consistently classical rather than chaotic. But each observer, each of us can only ever experience one branch.
This is why even if we live in a quantum multiverse, our reality wouldn't look weird or confusing at all. The other quantum worlds will always be beyond our perception. But that's not the case for another form of parallel universe. Now, let's look at a version of the multiverse that might leave traces in our own universe. Chapter 3, the universe that keeps making new universes. To get to grips with this other multiverse, we need a drastic shift in scale from the tiny realm of the quantum theory to the biggest of all pictures, cosmology. Now, this isn't related to the many worlds interpretation of quantum mechanics. The cosmological multiverse refers to quite literally bubbles out of cosmic inflation. The idea is that in the split second after the big bang, spacetime itself expanded exponentially, a stupendous stretching that explains why the universe is unfathomably uniform and smooth at the larger scale when there's nothing in the big bang picture alone to suggest why that should be the case.
Inflation is an incredibly successful theory and widely accepted. The problems and the fun began when cosmologists realized that inflation could be an ongoing process. In this picture, quantum effects can randomly cause some patches of spaceime to continue expanding very quickly, creating bubble universes that expand faster than our own. Importantly, because the background universe continues to balloon, new bubble universes are constantly being formed in different regions with each effectively isolated from the others because the space between them expands faster than light can cross. Eternal inflation therefore creates an endless froth of bubbles, an increasing number of separate universes. Cosmologists call this the inflationary multiverse.
As if that's not mind-boggling enough, you also have to get your head around the idea that these other universes could look nothing like our own. That's because some physicists have also decided to throw string theory into a multiverse mix. String theory operates in 10 or even more dimensions. In addition to the three of space that we're familiar with plus time, there are six more dimensions that would be scrunched up into unimaginably small spaces. In our universe, they form a particular configuration which determines the properties of our particles and our laws of physics. But they can form at least 10 to the power of 500 different configurations. Meaning that universes can fall into that many categories, each with different particles and laws of physics. You could, for example, have a different speed of light. Now, some of these bubbles just pop or stop existing because not all configurations of physical laws are conducive to stable pockets of spaceime. In fact, most configurations aren't. Our universe, in particular, has constants that seem finely tuned to us existing in it. If you were to visit another universe, even for a moment, you decay in an instant.
But you can't, of course, even if there is another universe conducive to our sort of life, you could never get there even if you traveled at the speed of light forever because you would have to travel through a piece of space that inflating cinder. But unlike quantum many worlds, the inflationary multiverse would at least exist in physical space.
And because of that, some physicists reckon it might even be possible to find observational evidence of its existence.
That's right, evidence of a multiverse.
Something that could turn physics on its head. Chapter 4. Can we actually find new evidence? Okay, so the logic behind the inflationary multiverse seems sound enough, but there also happens to be zero empirical evidence for its existence, which is why some physicists have made it their mission to find some.
The most obvious option is to search for a fingerprint from other universes in our own. Now, back to the quest for evidence of a multiverse. We know that the invading space between bubble universes would quickly hurl them apart.
If two were formed sufficiently close together, however, it's possible they could have collided before being separated, and we might find evidence of that in marks or scars left behind in our own universe. Most cosmologists agree that the best place to start looking is a cosmic microwave background or CMBB, the faint afterglow of the big bang. In fact, a team led by Herana Paris at the University of Cambridge in the UK has proposed that the colliding bubble universes should have left circles-shaped scars in the CMB. They even created an algorithm to comb through images of the CMBB for such imprints. What they found was promising.
four patches of the sky were compatible with the shape of collision imprints, but it wasn't evidence. There's just too much uncertainty in our understanding of the rate at which these new bubble universes should form and the probability that they would collide to make precise predictions. This is why another group of physicists have recently begun trying to make replicas of this process in the lab. To understand how this experiment might work, we need to return to the quantum weirdness for a moment. I want you to picture a landscape of hills and valleys with a ball representing our universe rolling around. When our universe ball is at the top of a hill, inflation is on and it's very rapid. When it's at the bottom of a hill, inflation slows or stops completely. These hills and valleys are like an an on and off switch for inflation. If you want to know the technical term for this, physicists call this landscape an inflaton field, but I prefer the term inflation roly pololy.
And it's not actually a physical landscape, but hang with me. The lowest valley in this inflation roly pololy is known as the true vacuum. We have reason to believe that more than one vacuum state exists, but also that most are false, meaning that they're not the lowest possible energy. These would look like roly pololy valleys that are locally deep but not the deepest that exist. These valleys are known as metastable. Imagine our universe ball is in one of these false vacuums. Quantum mechanics makes it possible for us to tunnel through the walls of the valley to the other side where we could suddenly start rolling to a lower energy state. Cosmologists call this a false vacuum decay and they care about it because it would explain how our universe and maybe others first began.
For instance, what if our universe started out in a false vacuum before tunneling and reaching a true vacuum, which is what we observe today? The trouble is that we can't know for sure.
And unless we know the details of this process, we can't trust our theories.
Luckily, almost a decade ago, physicists in New Zealand discovered that under the right conditions, the equations describing false vacuum decay in the early universe can be simulated in a kind of exotic matter called a Bozy Einstein condensate in which bubbles akin to a true vacuum are created. By studying the formation and behaviors of such bubbles in the lab, we can learn about how multiple universe might have formed, including the chances they would collide. This insight forms the basis of an exciting new experimental project led by Zoron Hadzubich at the University of Cambridge designed to be a direct analog of cosmological vacuum decay. The first stage produces the Boosezi Einstein condensate by making potassium atoms colder than anything in the universe.
The next involves preparing the condensate in a metastable vacuum state and waiting and finally watching as expanding bubbles of true vacuum form.
Hudi Babage and his colleagues reckon that this gives us a proxy for the otherwise unobservable processes thought to have first created new universes and a chance to re-evaluate whether or not those unexplained patches in the cosmic microwave background really could be imprints from the multiverse. All of which goes to show that one of the major criticisms of inflationary multiverse, namely that it is too untestable, may no longer be true because our own universe may already be the evidence. Chap why our universe works at all. It might inflate really exists without having to directly observe it.
Remember when I said the most configurations of physical laws are super unstable? Well, it turns out that our universe is actually one of the few with the perfect combination of physical laws and constants to sustain the existence of matter and by extension life itself. If things were even slightly different, life as we know it wouldn't exist. It seems odd that we should be so lucky. Or as physicists put it, our universe seems mysteriously fine-tuned. The multiverse offers an explanation. There are an infinite number of bubble universes. A few of them should, statistically speaking, have the conditions necessary to support life, however unusual those conditions may be. And humans will naturally find themselves in one of those. This is what we call the anthropic principle. Humans can only exist and observe in a universe compatible with our existence. So, of course, we think it looks fine-tuned.
And it opens the door to a falsifiable statistical prediction. If there really are many universes, each with different physical constants and laws, and if observers can only arise in some of them, then we should expect to live in a universe that's not merely just compatible, but unusually conducive to life. In other words, our universe should be near optimal when it comes to habitability. McCullen Sindora at the Blue Marble Institute for Space Science in Seattle has found a way to test that by modeling how habitability depends on the values of physical constants.
Looking at each scenario to figure out how many stars form, how long they live for instance, and how often planets form, and how easily life could emerge on them. Sindora can then ask, "If these constants varied across universes, where would life and conscious observers be most likely to appear?" If our universe is not right at the top of that list, that could count as evidence against the multiverse hypothesis. The big problem, of course, is that testing these predictions relies on us finding life elsewhere in the universe to give us a sense of how common life is here. And we haven't, at least not yet. Chapter six, the real implication of the multiverse.
Ultimately, we don't know if the inflationary multiverse exists. And the truth is that we'll probably be waiting for a good while until we find any evidence at all, never mind something everyone can agree on. From the multiverse that physicists describe using quantum theory where reality we see is just emergent from a vague fog of probabilities to the multiverse that seeks to explain how our universe began and evolved into what we see today.
These ideas that we've explored in this video are some of the most interesting and polarizing in modern physics.
>> All of these are very controversial theories. So the many worlds interpretation of quantum mechanics is certainly not a majority view. It's a very very common view within certain closely selected subsets of physicists who think about quantum cosmology and things like that. But most physicists don't subscribe to it. But on the other hand, most physicists don't think deeply about the measurement problem and the foundations of quantum mechanics at all.
So they don't have a favorite way of thinking about it.
>> This is the boundary where physics and metaphysics begin to blur. Some people would rather steer clear of these gray areas, but we at New Scientists love asking what science can tell us about the nature of reality. Here, science is way more interesting than science fiction. And while the gap between the two might be part of the reason some people dismiss the multiverse out of hand, what we've learned along the way here suggests that we should keep an open mind.
Black holes are everywhere. at the center of nearly every major galaxy in the universe. There's one at the center of ours, four million times the mass of the sun. What makes them remarkable is not that they exist, but that we still know so little about them. We started this marathon with one claim that somewhere in the universe where the rules break. We've seen that the breakdown isn't local. It runs through gravity itself, through the matter that makes up our bodies, which should have annihilated at the Big Bang, and through the question of whether our universe is the only one. We're not at the end of physics. We're somewhere in the middle of it. The most honest answer to almost every question raised tonight is that nobody knows yet. If this changes how you think about the universe, please subscribe. Let us know in the comments which of these unsolved problems unsettles you the most. And if you want to keep going, we have another marathon on whether reality itself works the way we think. See you next time.
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