Physics Still Can't Explain Why the Universe Is So Vast?

[00:00:00]93 billion lightyears wide. That's how big the observable universe is. Not the whole universe, just the part light has had time to reach you from. And here's the part physics genuinely cannot answer. Nobody knows why it needs to be that big. Not big like impressive. Big like absurd.

[00:00:22]Big like you could fit a million earths inside the sun. And the sun is a rounding error next to the distance between galaxies. And the distance between galaxies is a rounding error next to the size of the observable universe itself.

[00:00:37]By the end of this video, you'll understand why some physicists think the universe's size isn't an accident, a waste, or a coincidence. It might be a requirement. And you'll never look at the night sky the same way again.

[00:00:51]One planet needs to exist. Physics builds 93 billion lightyear to make it possible. Why? Put it in numbers you can actually hold. If you shrank the sun down to the size of a period on this screen, the nearest star would still be roughly 4 miles away.

[00:01:09]Now, stop thinking in stars and start thinking in galaxies. The distance between your galaxy and its nearest large neighbor is over 2 million lighty years. meaning the light you'd see from it tonight left before a single member of your species had learned to walk upright.

[00:01:28]And that neighbor is close. Most galaxies in the observable universe are so distant their light has been traveling since before Earth itself finished forming.

[00:01:40]Look up on a clear night away from city lights, and you'll see maybe 2,000 stars with your bare eyes. 2,000 out of an estimated 200 billion in your galaxy alone. And your galaxy is one of roughly two trillion. Not two trillion stars, two trillion galaxies. Each one holding hundreds of billions of stars of its own. Here's a strange fact most people never think to question. The night sky is dark.

[00:02:10]It sounds too obvious to be interesting.

[00:02:13]Of course, it's dark. It's night. But an 18th century astronomer named Hinrich Olers points out something unsettling.

[00:02:21]If the universe were infinite, unchanging, and packed full of stars in every direction, then every single line of sight from your eyes into the sky should eventually hit a star. The whole sky should blaze day and night, edge to edge, like the surface of the sun. It doesn't. The sky is dark with pinpoints of light scattered through it.

[00:02:46]Which means the universe you're looking at isn't infinite and unchanging. It has a size. It has an age. And the size and the age are somehow tied together in a way that makes the darkness above you possible. It took nearly 200 years after first raised the question for physics to actually resolve it. And the resolution turned out to be the expansion of the universe itself.

[00:03:12]Distant starlight isn't just faint because it's far away. It's also stretched, redshifted by the expansion of the space it travels through. Shifted out of visible light entirely for the oldest and most distant sources.

[00:03:27]A finite expanding aging universe doesn't just explain why the night sky is dark. It's the only kind of universe that could produce a sky like the one above you at all. Here's the question nobody actually asks because it sounds backwards.

[00:03:44]Why isn't the universe smaller?

[00:03:47]A smaller universe would have been easier. Less matter to spread out. Less time needed for gravity to pull stars together. Less waiting around for life to show up. Instead, physics builds something almost incomprehensibly large.

[00:04:01]Waits 13.8 billion years. And only then on one planet out of an estimated 10 seextillion possible planets does anything start asking why am I here? If big wasn't necessary, the universe wasted an unthinkable amount of space and time getting here. So the real question isn't why the universe is vast.

[00:04:23]It's whether it had a choice and whether waste is even the right word for something that so far has only ever produced one known example of a mind capable of measuring it. The standard answer you'll get from most science channels is simple. The universe is big because it's old and it's been expanding since the Big Bang. Space itself has been stretching for 13.8 billion years.

[00:04:46]So, of course, it's enormous by now.

[00:04:48]Give anything enough time to expand and it gets big. End of story. This picture comes from real hard one observations.

[00:04:56]In the 1910s, an astronomer named Vesto Slifer notices that light from distant galaxies is stretched toward the red end of the spectrum, a sign they're moving away. In 1929, Edwin Hubble takes that observation further and shows something enormous. The farther away a galaxy is, the faster it's receding. Not a few galaxies drifting apart at random. all of them in every direction, rushing away from every other one, exactly as you'd expect if space itself were a thing doing the stretching.

[00:05:30]This is the textbook version, and it's not wrong. Exactly. The universe has been expanding the entire time, and Hubble's observation is one of the best confirmed results in the history of astronomy. But this explanation quietly skips the actual question. It tells you how the universe got big. It says nothing about why the initial expansion had to happen at the rate it did for as long as it did to leave room for something like you to eventually exist and ask about it. It's old isn't the same as it had to be this size. And that gap is where this gets interesting. In the 1920s, a physicist named Alexander Freriedman does the math on Einstein's own equations and finds something unsettling. The rate the universe expanded in its first fraction of a second isn't a small detail. It's everything. Cosmologists calculate that if the expansion rate in the first fraction of a second after the Big Bang had been off by even one part in a 100,000 trillion trillion trillion trillion trillion, a number so small it doesn't fit on a calculator screen. The universe would have either collapsed back on itself within moments or blown apart so fast that matter could never have clumped into a single star. Then in 1998, two independent teams of astronomers, one led by Saul Pearlmutter, the other by Brian Schmidt and Adam Ree, find something nobody expected and nobody had asked for. The universe's expansion isn't just continuing, it's accelerating. Something is actively pushing space apart faster over time, pushing against every model that assumed gravity would eventually slow things down. They call it dark energy. Nobody to this day knows what it actually is. It's simply the name given to whatever is doing this. The discovery wins the 2011 Nobel Prize in Physics for confirming something physicists were fairly sure wasn't supposed to be happening. There are broadly two competing guesses about what dark energy actually is and physics hasn't settled between them. The simpler guess treats it as a cosmological constant, a fixed, unchanging property built into the fabric of space itself, the same everywhere and at every moment, quietly pushing outward no matter what else is happening. The stranger guess is called quintessence. A dynamic field, something more like an invisible energy that can change in strength over time and even across different regions of space. Which would mean the push you're measuring today isn't necessarily the push the universe felt a billion years ago or the push it will feel a billion years from now. Telling these two apart requires measuring the universe's expansion with a precision current instruments are only just beginning to reach. Until that measurement lands, the force responsible for roughly twothirds of everything in the universe remains functionally a placeholder name for an unsolved equation.

[00:08:25]And this is where it stops being a story about size and starts being a story about precision. Because a universe this vast isn't the result of things spreading out carelessly. It's the result of one number tuned to a level of exactness nothing about physics requires it to have and a mysterious force nobody can name that keeps making it bigger.

[00:08:46]The vastness isn't a side effect of time passing. It's the signature of an expansion rate calibrated with a precision that if you saw it in a lab experiment, you'd assume someone designed it on purpose. And it's still happening right now, accelerating for reasons nobody can fully explain. Try shrinking it. Take the universe and in your head compress it down to a tenth of its actual size. Same amount of matter, same laws, just packed tighter. Run the physics forward. Gravity with everything packed that much closer together pulls harder, faster. Stars form early, burn hot, and die in a fraction of the time.

[00:09:26]Galaxies collide instead of drifting past each other. The whole show, birth to heat death, might finish before a single planet ever gets three billion stable years to grow something as slow cooking as a nervous system.

[00:09:40]If the idea that space itself might be sized on purpose is the kind of thing that rewires how you see a starry sky, this channel exists for exactly that feeling. Stick around. A smaller universe might not have had time to make you. Now run the experiment the other way. Imagine it 10 times bigger. Matter spread 10 times thinner.

[00:10:02]Gravity struggles to pull anything together at all. Galaxies barely form.

[00:10:07]Stars stay sparse, scattered, alone, separated by distances so vast that even light-based communication between any two lifebearing worlds, if they existed at all, would take longer than most civilizations are likely to survive.

[00:10:23]The vastness you're living inside right now might not be excess, and it might not be deficient either. It might be the narrow window in between, the one setting on an almost infinite dial of possibilities that produces enough density to build stars and enough space between them to let a stable planet actually form and cool without being sterilized by a neighbor going supernova next door. So why is the universe this particular size, this particular age, expanding at this particular rate?

[00:10:55]Physics has three serious answers, and like always on this channel, none of them has been proven over the others.

[00:11:03]The first is pure chance. Under this view, the initial conditions of the Big Bang were random, and you simply happen to be living in the outcome that occurred. No design, no selection, just the role of a cosmic die that landed on vast instead of small or non-existent.

[00:11:21]Statistically, this is a deeply uncomfortable answer because the odds involved are almost incomprehensibly narrow. But deeply uncomfortable isn't the same as false. The second is cosmic inflation, specifically eternal inflation, a theory developed by physicists including Alan Guth and Andre Linde. Under this model, the Big Bang isn't a single event. It's a runaway expansion that once triggered never fully stops, spinning off countless separate bubble universes, each with potentially different physical constants, different expansion rates, different sizes. Under eternal inflation, a universe like yours, vast enough, stable enough, patient enough to grow something that could ask this question, isn't unlikely. It's inevitable somewhere among an effectively infinite number of other bubble universes that never got the chance. The third is the anthropic principle applied specifically to scale rather than to physical constants. You shouldn't be surprised the universe is exactly big enough and exactly old enough to produce you. Because if it weren't, you wouldn't be here to notice the alternative.

[00:12:32]Under this view, a universe too small or too young simply never gets a species capable of measuring it. Every observer who has ever asked, "Why is the universe so vast?" is by definition standing inside one of the universes vast enough to make that question possible.

[00:12:52]Smaller universes don't have anyone in them to complain about being smaller.

[00:12:56]There's a fourth complication layered under all three of these, and it's currently one of the biggest unsolved problems in cosmology.

[00:13:03]Different methods of measuring the universe's expansion rate. One using the cosmic microwave background, the oldest light in existence, and another using nearby exploding stars called supernovi, give two different answers. Not close, but different, measurably, persistently different in a disagreement astronomers now call the Hubble tension.

[00:13:28]Either one of the measurement methods has a hidden flaw nobody's found yet, or there's new physics at work that current models don't account for. Either way, the exact rate at which the universe became this vast is right now still an open, unresolved argument inside physics itself. Notice something about all three main answers. None of them requires an external creator and none of them rules one out either. Chance, inflation, and anthropic selection all describe mechanisms.

[00:14:02]What sits behind the mechanism, whether it's truly random or truly designed or something physics doesn't yet have language for, is the part no equation currently answers. There's a stranger possibility hiden underneath all three.

[00:14:16]one that questions whether vast even means what you assume it means. Some theoretical physicists working from an idea called the holographic principle have proposed that all the information describing the three-dimensional volume of the universe could in principle be encoded on a much smaller two-dimensional surface at its boundary.

[00:14:38]The way a hologram stores a 3D image on a flat piece of film.

[00:14:43]If that's true, even in a limited sense, then the vastness you experience isn't necessarily a measure of how much actually exists. It might be closer to a projection, a readout of information stored far more compactly than the volume of space suggests.

[00:15:01]Nobody is claiming this is settled physics, but it's a serious enough idea that it shows up in peer-reviewed work on black hole thermodynamics, not just speculative philosophy. A reminder that even the concept of size gets slippery once you push it far enough. Let's actually sit inside the number for a second because 93 billion lightyear is one of those phrases that's easy to say and almost impossible to feel. Light travels at roughly 186,000 m/s.

[00:15:32]Fast enough to circle the entire Earth 7 and a half times in a single second. And yet, light from the most distant galaxies you can detect has been traveling toward you for over 13 billion years. And because space itself has kept expanding the entire time that light was in transit, those galaxies are now even farther away than the distance their old light suggests. Which is how you get an observable universe 93 billion lighty years across. Even though it's only 13.8 8 billion years old. The universe has been outrunning its own light. The oldest light you can see, the cosmic microwave background, comes from just 380,000 years after the Big Bang, when the universe first becomes transparent enough for light to travel freely. That faint glow detectable in every direction you point a sensitive enough antenna is still arriving, still stretched, still cooling, still carrying the fingerprint of the exact expansion rate that determined how big everything downstream of it would eventually become. Zoom into the structure itself and the vastness gets stranger. Still, galaxies aren't spread evenly through that 93 billion lightyear sphere. They cluster into filaments and walls separated by enormous empty voids, some spanning hundreds of millions of light years of almost nothing at all. One such region discovered by astronomers and still debated in terms of its exact scale appears to stretch for over a billion light years with the density of galaxies far below the cosmic average. A gap in the structure of the universe larger than a thousand Milky Ways laid end to end.

[00:17:20]Roughly speaking, the visible matter in the universe accounts for a small fraction of everything estimated to exist with dark matter and dark energy making up the overwhelming majority of the total.

[00:17:34]You're not just living in something vast. You're living in something where most of what makes up vast is still to physics functionally invisible. Even the act of measuring this scale required building instruments that are themselves almost absurd feats of engineering.

[00:17:51]The James Webb Space Telescope, orbiting nearly a million miles from Earth, is sensitive enough to detect the faint infrared glow of galaxies whose light has been traveling since within a few hundred million years of the Big Bang itself, capturing photons that have been in transit uninterrupted for over 13 billion years, arriving at a mirror built by a species that didn't exist for the first 13.7999 billion of those years. And this is where the scale stops being trivia and starts being the whole point. Because every single galaxy in that 93 billion lightyear sphere has to exist, form stars, cook heavier elements in those stars cores, and scatter them across space before a single planet like Earth could even be built out of the leftovers. Every atom of calcium in your bones, every atom of iron in your blood is forged inside a star that had to live, die, and explode before you could exist.

[00:18:51]That takes generations of stars.

[00:18:54]Generations of stars take unfathomable stretches of time and space to produce.

[00:19:00]Even your own galactic neighborhood is still midstory. The Milky Way and the Andromeda galaxy are drifting toward each other right now on a collision course roughly 4 billion years out. One more slow motion event inside a universe that measures its major plot points in hundreds of millions of years at a minimum. The vastness isn't decoration around the edges of your existence. It's the manufacturing process that built the raw material of your body running at a scale you're now using to ask why it had to be so large in the first place.

[00:19:36]Here's the insight that flips the whole question on its head. You've been treating the universe's size as the mystery. But maybe the actual mystery is smaller and stranger than that. Not why is the universe so big, but why did a universe this big produce something small enough and slow enough and improbable enough to stand still and wonder about it?

[00:19:59]A universe capable of building a star forging assembly line spanning 93 billion lightyear is also somehow precise enough to build a three-pound brain capable of doing the math on all of it. The vastness and the smallalness aren't opposites here. One had to exist to build the other. And the same expansion rate that seems wasteful at a glance is the exact rate that gave gravity enough time and matter enough room to build something capable of noticing the waste.

[00:20:30]So where does that leave you? Standing under a sky you now know is 93 billion lightyear wide. Path one. It's pure chance. You happen to exist in the specific role of the cosmic dice that produced a universe vast enough for you to exist. No reason, no design, just outcome. Path two, it's one bubble among an effectively endless number of universes, most of which never got big enough, stable enough, or patient enough to build anyone capable of noticing.

[00:20:56]You're not special for being here.

[00:20:58]You're just in the branch where here was possible. Path three, the vastness itself is the mechanism, a law or a constant or a fine-tuned condition physics hasn't fully named yet, still tangled up in unresolved arguments like the Hubble tension that makes a universe like this the necessary not accidental precursor to something like you. There's a version of path 3 that goes further still one worth sitting with before you pick a door. If the holographic principle turns out to describe something real, then even the size of the universe might not be the most fundamental fact about it. It might be a downstream consequence of something more basic, some deeper structure of information that current physics can only glimpse at the edges of black holes and cosmic horizons.

[00:21:43]Under that reading, asking why is the universe so vast might be a bit like asking why a shadow is a particular shape without yet understanding the object casting it. Physics can hand you all three doors. It cannot walk you through one and tell you which was correct. That part is still yours to decide, and it will likely still be yours to decide long after the Hubble tension itself gets resolved. Because a solved equation has never once on its own settled a question this size. So the next time you look up and the sky feels too big to take in, that feeling isn't a flaw in your perception. It's accurate.

[00:22:22]It is too big to take in. It was always going to be.

[00:22:28]93 billion lightyears of galaxies, star forges, and empty dark had to run their course before there was a mind small enough and curious enough to look up and ask why.

[00:22:42]Every one of those galaxies formed without knowing it was building toward anything. Every star that died to seed the next generation with heavier elements did so with no awareness that billions of years later some of that scattered material would organize itself into something capable of turning a telescope back toward the dark and asking what it was all for.

[00:23:07]Maybe that's the answer physics keeps circling without quite landing on. The universe isn't vast in spite of you. It might be vast because of you.