Why Our Brains Can’t Grasp the True Scale of the Universe

Añadido: 2026-05-14

[00:00:23]Since the very beginning of time, man has looked to the night sky and asked the same questions.

[00:00:32]Where are we? How far do the stars go?

[00:00:37]And are we alone?

[00:00:40]Today, these same questions linger in the minds of every human with an inquisitive nature.

[00:00:49]Is our world just a speck in an infinite universe surrounded [music] by many other worlds and species?

[00:00:56]Or is it possible that we are the only intelligent life in the universe?

[00:01:04]If our universe is truly infinite, then it is thought that anything that could happen has happened an infinite number of times.

[00:01:14]There will be infinite worlds and infinite intelligent [music] life forms, even infinite copies of ourselves.

[00:01:23]But we may also exist in an infinite universe which is one of infinitely many universes each existing in possibly infinite dimensions.

[00:01:36]This series explores the many theories and ideas as to where we [music] all are in this immense system which seemed to come from nothing in the big bang 13.8 billion years ago.

[00:01:49]New understanding says this may not be the full story.

[00:01:54]We look at the ideas and theories from a human perspective and hear from our best scientific minds who spend their lives trying to understand these monumental concepts.

[00:02:07]How do we try and understand what may be simply beyond human comprehension?

[00:03:03]How do we define the concept of infinity?

[00:03:07]As we are finite beings, this seems to defy our human limitations.

[00:03:14]>> That is such a hard question.

[00:03:17]That is the Well, that's a very difficult I [laughter] was hoping you would weren't going to start with that one cuz it's uh you need I I've got no answer to that really.

[00:03:44]So when when you say the word infinity, let me think.

[00:03:53]I don't even know how to answer that question.

[00:03:59]Infinity is is a horrible concept. It is it is mindblowing in in the literal sense of the word. it to try to comprehend it, you really just crumble.

[00:04:11]And certainly I crumble.

[00:04:16]>> Infinity is everything and beyond. Think of the largest or furthest thing you can think of and then go beyond that and [music] beyond that and beyond that or in the other direction.

[00:04:33]Um, cut it in half, cut it in half, cut it in half.

[00:04:38]Infestimally, you can never never get to the end of it.

[00:04:47]In the Buddhist world, we talk very much about infinite space or uh infinite consciousness.

[00:04:54]And you know, I still don't understand what that means, but that for me has a real sense of uh possibility, of opening, of spaciousness.

[00:05:09]In a way, defining something goes against the very principles of infinity, putting it in a box. But at the same time, you need to be able to label this concept of infinity.

[00:05:21]>> When I think of the word infinity, I think of infinite combinations and possibilities for existence and creation.

[00:05:30]The word infinity, it has a magical quality actually. I think um people are always interested in infinity. It brings up ideas of the meaning of life. What is there after death?

[00:05:45]Are things [music] pre-ordained? I suppose in a way >> infinity is a quandry, a puzzle, an enigma.

[00:05:56]I was told about infinity when I was a child. And to be honest with you, to this day I've struggled with the notion of infinity, it's very very hard to grapple.

[00:06:07]>> When we say that the universe is infinite, what we actually saying is our measurement of the size of the universe cannot actually be determined because we cannot reach the point or the time or the volume or the energy where there is a definite value.

[00:06:24]>> Well, infinity clearly exists [music] as a concept. We can think about it. We can talk about it. Whether the universe is infinite or whether there's [music] actually anything infinite in nature, that's an open question.

[00:06:37]>> When I hear the [music] word infinity, I think of space stretching on forever. As best of our knowledge, it does. You know, as far as we know, the universe isn't there's no brick wall. We don't see any evidence of brick wall. And it ties [music] in with the theory. As far as we know, the universe just goes on forever in all directions.

[00:07:08]This is a TV show like no other.

[00:07:12]It is the very origins of our universe.

[00:07:16]It is the proof of an event that happened a very long time ago.

[00:07:23]You are seeing images created by the cosmic microwave background.

[00:07:30]This is the energy left over from the big bang which happened billions of years ago and we can still see it today.

[00:07:41]But what was the big bang?

[00:07:46]The Big Bang Theory is a theory based on calculations that the universe is currently expanding. And using these calculations in reverse to determine the past, it shows that our universe is about 13.7 billion years old.

[00:08:06]At this time, all the matter of the universe was concentrated into a tiny space the size of a grape with near infinite density and incredible temperatures.

[00:08:19]This grapesized object contained all the matter of the universe.

[00:08:25]This then began to expand rapidly to later form the stars and galaxies and is still expanding today.

[00:08:37]From the big bang, it is thought that our four dimensions were formed. Three spatial dimensions and one of time.

[00:08:46]But how can we be sure that the big bang really happened?

[00:08:52]>> We see the afterglow of the big bang, the cosmic microwave background. We can see so many signatures [music] that give us confidence that this idea that the universe started off in a far hotter, denser [music] state than it is today. And that ever since that moment has been expanding and has [music] becoming ever more diluted and cooler.

[00:09:12]That is a measured statement of fact.

[00:09:14]That is a very much a history book of our universe. And we have the images and understanding to show that >> the big bang theory was something that postulated a beginning and then an expansion then a what? Um is it a a contraction back to a big crunch or is it um an expanding universe forever?

[00:09:40]One of the hardest things for humans to conceive is the concept that the Big Bang was the creation of everything that we know. That from seemingly nothing, everything that we know was created.

[00:09:56]How can we understand something from nothing? Or must there always have had to be something?

[00:10:05]There's so many things now in the [music] world. So many people, so many different countries. It's hard to believe that there was nothing because there's no so many in the world. How it's possible that it just pops up from nothing to this? I Yeah, it's hard to believe.

[00:10:31]I can't believe that the world was created from nothing. And if you think of it in terms of infinity, [music] infinity means there is no beginning or no end. So there was no beginning. You see what I mean?

[00:10:46]>> How did the world just arise out of virtually nothing? Just out of a pin prick, you know, such a huge world, such complexity out of, you know, nothing.

[00:10:59]Wouldn't that violate the usual laws of conservation?

[00:11:05]>> The law of the conservation of mass is a fundamental principle of physics.

[00:11:12]According to this law, matter cannot be created or destroyed but only rearranged.

[00:11:21]Fire is an example of this. When wood is burnt, it turns mass into energy in the form of heat.

[00:11:31]So how did the big bang violate this fundamental principle and create huge energies and matter from absolutely nothing?

[00:11:42]How did something come into existence from nothing? And what was there before the big bang? You think of [music] the big bang as sort of generating the first moment and then there being moments after that. And the it seems like a very natural question to ask. Well, how much time was there before the Big Bang happened? Was there anything there? Was there nothing there?

[00:12:03]>> Some people have a problem with the idea [music] that you can get something from nothing. And this idea that a big bang just spontaneously [music] springs into existence and there was nothing before that. They have a problem with that as well. They should. We've got no way of imagining that process.

[00:12:20]The human mind isn't capable of doing that. And actually in this case even matters a hard job with this as well.

[00:12:26]And we really have the problem that when you're talking about the big bang you really are up against the limits of our science.

[00:12:37]We now think in terms of spaceime and our best science tells us that there was a starting point to the spacetime.

[00:12:48]If that's true, then we know that their past is not eternal. One thing we do know is that the dimensions that we're talking about, both temporary and spatially, are so enormous that we can hardly conceive of the dimensions of the the universe.

[00:13:09]>> The universe is expanding. It came [music] from this enormous explosion about 13.8 billion years ago. But as soon as you get very close to the big bang, everything starts falling apart.

[00:13:18]Our physics breaks down there. We [music] know it does. And then if you ask the question, what happens at the big bang or before the big bang, you have to throw up your hands. Our physics [music] just doesn't go there. We really don't have any idea. But there's various ideas. So one is that the big bang actually started from nothing. There's no space [music] and time before that.

[00:13:35]There isn't even a concept before.

[00:13:37]There's no time. And you get some quantum fluctuation which sees this universe. I should stress that's one theory. And so when people say what's before the big bang, people ascribe to that [music] say well that's a meaningless question. That's like saying what's north of the north pole or something because that's where the time started. But not everybody subscribes to that and um there's other models in which [music] indeed there was a pre-existing space and time and then you can quite reasonably say what triggered the big bang. We still don't know. By the way, [laughter] brings us no close to an answer. But at least you [music] can then ask a sensible question.

[00:14:13]>> Quantum theory is the theoretical basis that explains the nature and behavior of energy and matter at subatomic levels.

[00:14:22]It may be the answer to the very strange conditions that created our universe and how this immense universe was created seemingly from nothing.

[00:14:35]To understand how the universe came into existence at all is the first fundamental problem. And [music] it all starts with understanding something about what we call space. Space and time for that matter. I suppose we thought up until the 1930s that space was empty. It was nothingness. But Einstein slowly taught us that space is not nothingness.

[00:14:57]There's something to it which can [music] stretch and bend. And so the big bang created space and time and that began to stretch and unfold. And the way it came into existence is all to do with the quantum world, the quantum universe.

[00:15:14]>> The quantum world is a world where things can jump in and out of existence.

[00:15:19]So, could our universe be one of these quantum fluctuations?

[00:15:24]Did our universe literally jump into existence from absolutely nothing?

[00:15:31]>> That's the con popular conception of the big bang, that things started from literally nothing and [music] created the universe as we know it. But we know that that's at best a caricature. Now, why do we know that? We know that because really that requires us to extrapolate our laws of physics back to a time essentially time zero. And that's the time when our understanding of quantum mechanics and gravity need to be combined for the theory to make sense because that's the time on which quantum mechanical effects would matter for gravity. And it turns out that that is a a problem that's perplexed physicists for about a hundred years now. really since Einstein came up with his general theory of relativity and the combination of that and quantum mechanics has proved to be a very difficult nut to crack.

[00:16:25]There's a concept called the Heisenberg uncertainty principle and quite literally out of nothing you can get something. You wait long enough and because you can never say with certainty where an object is in space or time. You can say one or other [music] but not both. What it allows to happen is something to appear what they call a quantum fluctuation. So you can have this nothingness and out of this nothingness you can get something something for nothing for a certain amount of time as long as that amount of time obeys the Heisenberg's uncertainty principle.

[00:17:01]So in terms of Einstein there was nothing before the big bang. But when we bring quantum mechanics into play, there's a real probability that [music] our universe wasn't born in the big bang, but it actually grew out of something else. We don't yet have the mathematics though to understand gravity and [music] the other forces in these huge densities to say what that was.

[00:17:28]The idea that all time and matter was at the time of the Big Bang the size of a pee or grape is a common perception.

[00:17:38]But is this really the case? Or is there more to this idea?

[00:17:43]>> Well, I can't believe that the universe used to be the size of a pee because [music] the universe right now goes forever and ever. It's just hard to compare it to a tiny little vegetable.

[00:17:55]>> If you take all of the stuff that we can see today and you ask how big was it at 10us 34 seconds after the big bang the answer to that question is yeah about a grape. But that's not everything that there is. That's just everything that we can see.

[00:18:13]So if we take our universe as we know it now and if it is infinite in extent, if it goes to infinity, you could travel forever and never get to the edge, then it's always been infinite from the start. You cannot go from a finite universe to an infinite universe. You were infinite from the start. What people talk about when they talk about the universe being the size of a P, what they mean is the observable universe was the size of a P. All of the universe we can see around us today, all the galaxies we can see, they were in a volume the size of a P. And that P was in a volume that would potentially stretch to infinity.

[00:19:00]Our best theory to date is the Big Bang theory. But this is a theory and only describes one event in possibly billions of previous events.

[00:19:12]We just don't know.

[00:19:15]It is also a very unsatisfactory concept to many, leaving only more questions than answers.

[00:19:23]So if the Big Bang was not the beginning of time and space, what existed before?

[00:19:31]Perhaps another universe gave seed to our universe.

[00:19:36]Perhaps the universe has always existed and the big bang was just an event within our infinite universe.

[00:19:45]Or perhaps another dimension or dimensions were created such as our three of space and one of time and that dimension contained our universe.

[00:19:59]These theories are a lot more palatable than the something from nothing concept.

[00:20:07]>> I'm not sure if I believe the big bang because uh maybe there was also before the big bang something and they also cannot prove that there was something.

[00:20:17]How can something come from nothing?

[00:20:19]Like to me, I find that much more perplexing than the idea that things have always been there and infinitely changing and infinitely expanding and infinitely multiplying and infinitely diversifying.

[00:20:33]I don't know. Maybe this world expands and expands and expands to the point that it then starts to contract to the extent that it can come through this tiny hole and and explode out the other side.

[00:20:55]I think the big bang was a sequence in an infinitely changing universe, multiverse, galaxy, world, earth, just one big constant flow.

[00:21:11]I have real trouble understanding how you could have nothing and then suddenly have something. So to my mind a logical conclusion but not scientific is that something has always existed. So that sort of argues that there has always been something and I don't even know what something is but something that allows the laws of physics to merge and that must have always existed in the past and presumably will always exist into the future.

[00:21:43]There are lots of models according to which the big bang was in some sense the first moment of this universe but that doesn't mean that there wasn't something before that. So, so maybe there was the end of some other universe which at its end then generated this next universe.

[00:22:01]>> It's very difficult to describe or work with a universe which starts out of nothing whatsoever. We don't have the mathematical or physical tools to describe that. And so many of us prefer models where a big bang starts in a pre-existing universe or there's something before it. There's a pre-existing time. Uh it's much easier to comprehend. It's much easier to work with to postulate about what came before.

[00:22:35]I don't even have the tools to ask the question.

[00:22:39]the physics breaks down the guiding principles and those theories they can't help anymore at that point now maybe some absolute gun will in the future understand this and come up with a theory of everything that reconciles these seeming impossibilities the emergence of everything we see from nothing or even the creation of time itself but right now our theories just don't give us a tool to ask the question what came at time zero and simply can't conceive of nothing. It is physically impossible to imagine as it is to conceive of an infinite of something.

[00:23:23]There is now an alternative theory that the big bang was in fact many big bangs.

[00:23:30]That the big bang was simply everywhere at once and there was no one location.

[00:23:36]This is of course as hard a concept to understand as the original big bang theory.

[00:23:42]How do we begin to understand such concepts?

[00:23:48]>> So one possible way that we can have the big bang that we know and love and actually can measure is that really what happens is there are a lot of little bangs. Little bangs are still vast and create entire universes like our own.

[00:24:00]But they're little in the sense that really what there is is there's a much larger universe out of which little bangs happen for quantum mechanical random reasons every so often. And it doesn't have to be very often indeed. It can be pretty random and pretty rare, but just often enough that it happens.

[00:24:17]And once it happens, you [music] could have a universe that is mostly very boring. But every so often in perhaps even more dimensions than just our three spatial dimensions, you have a bang happening. And maybe that bang is always very similar. Or maybe sometimes it even creates a universe with different laws of physics. So bangs happen. Sometimes they may create a universe that looks like our own with protons and neutrons and three dimensions. Sometimes it [music] may create universes with only Higs Bzons and six dimensions and maybe things in between that we can't even describe. So every time this happens, we could get a new universe inflating out of this background and then making something that could last forever or maybe only last for a finite amount of time and then collapse in on itself. But this way you can have things which locally look finite. So they had a beginning, but in fact overall things could be infinitely large and infinitely long lasting. So that's one way that you can have both big bang or big bangs and infinity. And you can still have things coming into existence not really out of nothing but just out of something else than what we see here.

[00:25:35]The Big Bang Theory is a solid scientific theory of what it describes, but it is now understood to be very lacking in detail and maybe only part of a multifaceted event.

[00:25:50]This theory is perhaps only the beginning of our understanding.

[00:25:55]Mathematically and physically, we cannot actually determine what the Big Bang was. can physically calculate our universe right after the big bang. But that last fraction of a fraction of a second, we can never do because we don't actually have a tool that can do it yet.

[00:26:12]So when we try and go to measure or calculate or explain what the big bang was, we need space and time, but the big bang was the beginning of space and time. So we're trying to explain something that created something that the tools that we're using are reliant on to explain the thing that we're trying to measure. So you get chasing your tail. So the the philosophical view here is that we're not able to ever calculate or measure or determine what the big bang was because we don't have a way to describe the universe without using the stuff in the universe.

[00:26:52]Trying to discover what the Big Bang actually was seems as elusive as ever.

[00:26:58]How do we move forward to try and find the answers?

[00:27:04]>> So if we take the equations of the universe, we can run the universe back to this time uh 10 the minus 40 seconds after the big bang when everything we know in the universe was [music] down in something for example the size of a golf ball. We believe at that point that physics is essentially just in a form where the laws of quantum mechanics as we know today are still working. We know that quantum fluctuations where things come in and out of existence will create gravitational waves and that we have a chance if those fluctuations are big enough of detecting them in the cosmic microwave background. Now, there's a lot of physics that we're extrapolating through. And so, the hope is that when we see those fluctuations, we'll be able to understand everything that's happening at those energies above where the Large Hadron Collider can essentially probe here on Earth and where we get to right after the time of the Big Bang.

[00:28:07]We have some theories now that can potentially explain what could have seeded the big bang. Quantum physics for example says that the if you take everything out of space, you take turn it just into a complete vacuum. So you take all the particles out, you take the light out so that there's nothing left. Nevertheless, you're left with this like quantum foam, this seedthing froth of virtual particles that are popping in and out of existence all the time. And this is just sort of the nature of the vacuum itself.

[00:28:40]And it could be that our universe was born from that kind of quantum foam. So that's what was likely to be before the big bang.

[00:28:58]One of the dimensions that was created in the big bang was time.

[00:29:04]Time is one of our four dimensions.

[00:29:07]Three in space and one of time.

[00:29:14]Time is the least understood dimension.

[00:29:17]Seemingly born in the big bang. What is this strange dimension?

[00:29:23]It has no mass or physicality and is as intangible as we can imagine.

[00:29:32]Time is particularly important to humans as everything we do is ruled by time.

[00:29:39]Our lives are measured in a finite number of years, a day in a finite number of hours.

[00:29:46]Our lives last a fraction of time compared to the age of the universe?

[00:30:02]Could time be something exclusive to our universe? Or is it part of the fabric of everything that is?

[00:30:13]I actually think that time is a man-made concept. So in essence, it doesn't go on forever and ever. And it does. It simply is.

[00:30:28]I read this theory that at the moment of the Big Bang, there were four dimensions, but there were four spatial dimensions. And as the Big Bang progressed, one of those spatial dimensions [music] turned into a time dimension. So as you get closer and closer to the Big Bang, the the idea of time makes less and less sense.

[00:30:48]As you get closer and closer to that moment of the Big Bang, that moments cease to exist.

[00:31:00]If the big bang really was the thing that generated ultimately spacetime, then there's no sense in which there was nothing prior to it. There's no sense in which there were moments prior to it.

[00:31:10]There was [music] no place for nothing to be and there was no time for nothing to be in.

[00:31:19]The Big Bang defines the beginning of time. So, you can't ask what was before it because there's no time. Now that's not to say that we can't come up with some sort of structure according to which the big bang is [music] nested in some larger structure in which there are multiple big bangs. But the interesting thing about them is that it's not that there's anything before the big bang.

[00:31:42]Before makes no sense. There is something else and that something else may be connected to the big bang some way but the connection is not through time because time as we know it is something about this universe.

[00:32:00]Although this is our current understanding, is it possible that time has existed in some form or another before the big bang?

[00:32:10]>> There seems to be a a natural tendency for symmetry. So if we think about time, we can think that there's an infinite past and an infinite future.

[00:32:24]Does this tendency towards symmetry suggest that time has always existed and will always exist into the future?

[00:32:37]We think of time as a onedirectional one-dimensional one-way street. And we think of space as oh you can move in every direction. You can go up and you can go down. You can do whatever you want. You have complete freedom. And this is inherently entied in this issue where time seems to be the seconds go by, hours, days, years, that we're always seemingly going forward in time because that's how we measure time. But really, time is no different than the spatial dimensions.

[00:33:14]So time is a particularly complicated construct. That is one where physics does indicate it is possible to have space without time. It's possible for time to maybe not have existed in the past. There still would have been something. It just may not have involved time as we know it right now.

[00:33:34]>> If our universe does have an end, that will end time in our universe. So therefore, it'll end space and it'll end everything. Um what that means, we don't know yet.

[00:33:45]If time ends, does that mean infinity cannot exist?

[00:33:51]And could our universe's past be the same as our future?

[00:33:57]Tomorrow doesn't look like today, and it definitely doesn't look like it did yesterday, or at least 13.6 [music] billion years ago. The universe had a very different beginning, and it will have a very different end.

[00:34:13]So time in the past is bounded by a big bang where we have space-time foam and there's no time earlier than that. At least that's the standard model. What about the future? Well, the universe is expanding. Will it ever stop expanding?

[00:34:25]What [music] will happen in the far future? Well, the stars will all burn out. Everything will fall into black holes. The black holes will evaporate.

[00:34:31]You'll get all kinds of radiation. And this radiation will get longer and longer and longer. And then you will be in what's called a state of maximum entropy. Now maximum entropy, nothing happens. And if there are no gradients, no structure, no tables, no suns, no watches, no anything. And that means you won't be able to measure time. So in one case, time goes on forever without an end, infinite in the far future. And the other is, well, wait a minute, once I run out of the ability to measure it, what am I talking about? And so there it kind of peters out as we lose the ability to measure it.

[00:35:11]Einstein came up with an even more mindblowing theory born out of his theory of relativity.

[00:35:18]It is the block universe theory.

[00:35:22]In the block universe theory, time and space are embedded in a block type structure where there is no difference between the past and the future and we are all spread out in time. The passing of time is purely a mental construct.

[00:35:42]>> A view of time that began with Einstein is that our whole world is one giant block. So people often call this the block universe view. And it's the view according to which the past, the present, and the future are all [music] there. It's one big block of spaceime.

[00:35:56]And there are relations between time. So there's earlier times and later times.

[00:36:00][music] But there's no sense in which the past times are there, but the future times aren't. Everything is just out there and uh you and I happen to be located at a particular point in the block. The dinosaurs are located at a particular point in the block. There are also um all of the future moments located. So if it turns out that there are going to be really um super intelligent robots at some point, they're also out there already in spaceime doing super intelligent roboty kinds of things.

[00:36:32]The block universe theory has recently come up against much skepticism.

[00:36:38]But what structure, if any, does time take?

[00:36:42]>> Whether time is infinite or finite, [music] we can still ask interesting questions about what sort of structure it has. So most of us probably assume that time is linear. At least that's how we probably imagine it. We think of the past as being sort of uh back along a line and we think of the future as being forward along a line. And we conceptualize time as being uh a little bit like a a ruler and we find ourselves somewhere along that ruler. But of course there's lots of different ways that time could be um time could be branching. Could be that time is actually this massive kind of tree with many branches. Or it could be that time is a loop. So it could be for instance that [music] in some sense what you think of as the very first moment is also at the very same time the very last moment.

[00:37:24]So if you think about time as being a loop, if the very first moment is at the same time the very last moment, then since the very first moment has in some [music] sense happened, then the very last moment has also happened. And so you might think this seems like a very uh dismal view of the world because it seems as though everything that's future is both future and past. So if the past is fixed, then the future must also be fixed. And so, [music] um, there's no sense in which we can make things other than they're going to be because the future just is the past from a different direction.

[00:38:02]Time remains to be a very hard to grasp dimension, and being finite makes this an even harder concept to fathom.

[00:38:13]But is it possible to move around within this loop or block of time?

[00:38:18]One way we know of actually happens every time we look into the night sky.

[00:38:25]>> When you're looking up into the stars, you're looking into the distant past.

[00:38:28]And of course, you know, the nearby stars, you're seeing them as they were 3, four years ago. The far away stars in this galaxy, you're seeing them as they were, you know, many thousands of years ago. Other galaxies, you're seeing them as they were a long, long, long time ago. And if I get out a telescope and um [music] I used to play with telescopes a little bit when I was a kid and you look at the really really faint stuff, you're seeing stuff that goes back almost the beginning of time. So when I look up into the stars, I think people talk about time machines. We've got one. Just look up into the stars and you're seeing [music] the past, the distant past. And I'm wondering, are there people there?

[00:39:07]Am I seeing stars or [music] that have planets on which there are people up there? And if they're not there as I see them, are they there now?

[00:39:18]>> So perhaps our perceived linear progression of time is in fact malleable.

[00:39:24]And one day we might discover a way to navigate through this elusive dimension as we do freely in the other three dimensions of space.

[00:39:38]>> We just don't know how to treat time properly. it it it's been the it's been the unwanted stepchild of physics I think in terms of our everyday thinking and uh if we actually properly think about it and appreciate it then uh then I think we'll grow to accept all the consequences it [music] means including infinity