Why Does the Universe Exist at All?

Why does the universe exist at all? That may be the deepest question in science. Not just how the universe changes or what it's made of, but why there's anything here in the first place. Physics has taken this question surprisingly far. It has shown that empty space may not be truly empty, that the universe may have zero total energy, and that cosmic inflation may have turned a microscopic fluctuation into everything we see.

But every explanation opens an even deeper mystery. Why do the laws of physics exist? Why are they so precise? And why does the universe seem structured in a way that allows matter, stars, planets, and life? To answer that, we need to examine the physics behind existence itself. That's coming up right now.

Look around and you'll notice everything in the universe follows consistent rules. From apples falling off trees to planets orbiting the sun. These rules are what we call the laws of physics, and they can often be written as concise mathematical equations.

These laws don't change from one corner of the cosmos to another, nor from one time to another. They've been the same, as far as we know, over billions of years.

Why these specific laws? Why are they what they are? Why should the universe obey neat mathematical laws at all? There's no obvious reason that reality couldn't have been a chaotic mess of unrelated rules.

In a hypothetical reality, like a video game world, a character analyzing their universe might find a jumble of arbitrary, quirky rules put in by a programmer. But by contrast, our universe's laws have an almost magical regularity. They display symmetries, patterns that remain unchanged under various transformations.

As I showed in a prior video, this is why certain quantities like energy and momentum are always conserved.

Could they have been different? Certain symmetries demand certain laws. Emmy Noether showed that if you want the laws of the universe to remain the same over time, then the law of energy conservation has to be true, meaning that energy cannot be created or destroyed, at least not locally. And if you want the laws to be the same here as on the moon or as on a different galaxy, then the law of momentum conservation has to be true. I have a video on why these laws must be true under those symmetries here if you want to know the details.

Closely related to symmetry is the potential for unification in physics: the idea that all the different forces and particles we see might be aspects of one single fundamental principle.

Unification has been the holy grail of physics. History has seen some great successes here. Isaac Newton realized that the gravity holding us here on Earth and the gravity guiding planets are one in the same law.

In the 19th century, James Clerk Maxwell discovered that electricity, magnetism, and light are all unified in a single theory of electromagnetism. In the 1960s, physicists showed that electromagnetism and the weak nuclear force, which is responsible for certain kinds of radioactive decay, are actually two facets of one electroweak force.

These triumphs encouraged the idea that the four fundamental forces we know of—that is, electromagnetism, the strong force, the weak force, and gravity—might all merge into one force at high energies or early moments of the Big Bang. In other words, the many laws we have now could be branches of a single trunk. The laws of the universe could exist as they do because at the deepest level, there's only one law, which may even be an elegant and simple one.

This is one of the reasons why so many physicists are working on the elusive theory of everything.

So, the mystery is not only why matter exists, it's also why the universe obeys coherent laws at all. And that leads to a second puzzle: Even if there are deep mathematical laws underneath reality, why do those laws allow a universe like ours?

Another answer regarding why our laws exist could be found if we look at the universe from an anthropic point of view. The laws seem almost custom-made for the existence of complexity and life. Scientists refer to this as fine-tuning.

There are fundamental constants in physics, fixed numbers like the strength of gravity, the charge of an electron, and the mass of a proton, et cetera, which could, in theory, have been different.

Tweaking these values even a little in some cases would result in a universe where life, or even chemistry and stars, could never arise. There's nothing mathematically wrong with those other hypothetical universes. They just wouldn't be so interesting because there would be no galaxies, no planets, no DNA, maybe not even any atoms at all.

For example, a slight increase in the strength of the electromagnetic force might cause atoms to stick together so tightly that chemistry as we know it couldn't happen. A tiny decrease in the strong nuclear force could make atomic nuclei unstable, meaning no complex elements beyond hydrogen. Change the balance of these forces or the masses of particles just a little bit, and the universe might have consisted of nothing but diffuse gas, or collapsed into a black hole, or never form stars to begin with.

The bottom line is, out of an unimaginably large space of possible physical laws and constants, the set that yields a complex, life-friendly universe like ours is extremely tiny, like hitting the bull's eye of a dartboard exactly in the center.

The fact that everything is so precisely set, or fine-tuned, is puzzling. It's as if the universe rolled the dice and somehow landed exactly in the very special values that allow life like ours to exist. Why?

The anthropic principle could be a possible explanation. In simple terms, it says the universe's laws have to allow life, at least somewhere, because otherwise, we wouldn't be here to notice the laws in the first place.

In other words, out of all the possible universes with all sorts of laws, it should be no surprise that we find ourselves in one of the rare cases where the laws are compatible with observers existing.

Invoking this anthropic principle is not satisfying because it doesn't pinpoint a cause so much as to say we got lucky and only the lucky cases get observers. So, if you buy this idea, then you should marvel at how special our universe's laws are because the many bad rolls of the dice could just produce no one to marvel at anything.

That's one way to answer the question. Maybe we should not be surprised that we live in a universe compatible with observers. But that becomes much more powerful if there are many universes to choose from.

This is where the next idea may make the anthropic principle more powerful: the idea that perhaps there are many, many universes out there, each with different laws. If that's the case, then it's no wonder that one of them turned out to be like ours.

So, what if our universe with the specific set of laws is just one of many? This is the premise of the multiverse hypothesis. The multiverse is a speculative theory that there could be other universes besides our own, possibly an infinite number of them, forming a vast cosmic ensemble.

These other universes might have completely different fundamental constants and even entirely different laws of physics. Some might be dead and boring with no structure. Others might have laws so wildly different that we can't even imagine what they'd be like.

Keep in mind, however, that life could not be ruled out in all the other universes. They could certainly have a different form of life, just not the kind we're familiar with. We happen to live in one universe that's just right for our kind of life. And that's not a coincidence. It's why we're in this one and not some other one.

This approach takes the sting out of fine-tuning. If there are countless universes with varying properties, it's not so impossible that one of them hit the jackpot. It's like saying it's incredibly unlikely to win the lottery, but if enough people buy tickets, someone is bound to win. We could be the winning ticket.

The anthropic principle would say that conscious observers will only find themselves in those universes that happen to permit conscious beings to exist. You might say, "Wait a minute. This is just a cop-out way to explain a crazy idea. Prove it."

Well, while we can't prove it because there's no direct evidence, there are scientific reasons to take the multiverse idea seriously. There are multiple theories in physics that suggest a multiverse.

For example, eternal inflation theory, which is an extension of the Big Bang theory. It predicts that our universe might be just one bubble in an eternally expanding foam of bubble universes.

String theory, when combined with inflation, hints at a landscape of possible universes with different properties. I have a video on this up here if you want to know more about this.

There's also the many worlds interpretation of quantum physics, which posits that every quantum event branches into parallel realities, a form of multiverse where essentially every possible outcome for the universe exists in some branch.

This idea is interesting because it provides a mechanism for multiple universes. But it's important to stress that so far these other universes remain hypothetical.

Some scientists criticize multiverse concepts for being untestable and therefore not scientific. After all, how do you confirm the existence of worlds you can never observe?

That said, the multiverse is a serious idea being discussed in the scientific community precisely because it would naturally answer a lot of the "why these laws" types of questions. And it's implied in several scientific theories. And if true, it could turn what looks like an astonishing one in a trillion coincidence into something inevitable.

It would be humbling, implying that our universe might not be unique or special or designed, just one lucky bubble in a vast multitude of universes. But even if the multiverse does not fully answer the deepest version of the question, it still assumes some machinery that generates universes in the first place.

So now we shift from explanations of why our universe has these laws to a more direct question: How could any universe begin at all?

Why is there something rather than nothing? If nothing existed before the universe, how could a whole universe just appear? Did something or someone external create it?

Why do we even think the universe came from nothing? To answer that, we need to first understand what nothing means in physics.

When you hear that word, you might imagine a complete void: no matter, no energy, not even space or time, absolute nothingness.

But in modern physics, even what we call empty space isn't truly empty. Why not? Because of quantum mechanics.

In quantum physics, even the vacuum of space with no particles or radiation is still teeming with activity. These are quantum fluctuations where particles and their antiparticles spontaneously appear and annihilate each other constantly. This isn't just theory, it's been observed in experiments. Empty space is more like a bubbling soup of virtual particles popping in and out of existence.

Now, you might say, "Wait a minute. If these fluctuations existed before the universe came to be, before there was time, how could it happen? Because don't these fluctuations require time to exist?" The answer is no. The quantum fluctuations are due to the intrinsic uncertainty of quantum states. We use time language to describe it, but the math says that no external time is necessary.

This is one of the most important distinctions in the whole discussion. The nothing of physics is not always the same as the nothing of philosophy.

And once you allow quantum structure, the next question becomes whether a universe could emerge without violating conservation laws. Many physicists suspect that the total energy of our universe is exactly zero.

How could it be zero when there is so much matter, light, and energy around? Because gravity's energy is negative. How can gravity have negative energy?

Well, think of it this way: It takes positive energy to pull two masses apart against the pull of gravity. So, conversely, we can think of objects bound by gravity as having negative energy. In a uniform expanding universe, the negative gravitational energy could cancel out the positive energy of the matter and radiation.

Stephen Hawking explained it like this: The universe's matter is positive energy, gravity is negative, and they sum up to zero. If true, it means creating a universe from nothing doesn't actually require any net energy. It's like borrowing $10 from the bank with your left hand while at the same time handing the bank $10 with your right hand. You incur no net debt.

This idea is very important because if the universe can exist with zero total energy, quantum physics might allow it to arise spontaneously.

Physicists Alexey Filippenko and Jay Pasachoff put it this way: "Quantum theory provides a natural explanation of how energy could come out of nothing."

In quantum mechanics, having exactly zero of something with absolute certainty is forbidden. There are always uncertainties and fluctuations. That means what we think of as nothing might not stay nothing and can unpredictably fluctuate into something.

You can think of this in terms of entropy and statistics as well. A universe with absolutely nothing would be a very low entropy state, perhaps the lowest entropy imaginable. There's only one such state, but there are innumerable billions, trillions, almost an infinite number of states of a universe with at least something. A universe with something would have higher entropy than with nothing. The universe always tends towards higher entropy states. The reason is that there are astronomically more higher entropy disorganized states than lower entropy organized states.

So, the state of the universe being something is much more likely than nothing, and that could be the reason we have something rather than nothing.

This leads to an incredible idea: The universe could be a giant quantum fluctuation. Nobel Prize-winning physicist Edward Tryon said, "The universe is simply one of those things that happens from time to time." It's an interesting way to say that our whole cosmos might have popped into existence from nothing due to a random quantum event.

If that sounds radical, the next step is even more extraordinary, because a tiny quantum-born universe would still have to grow into the immense cosmos we see today. That's where inflation enters the story.

Let's dig deeper on that, though. Why would a quantum fluctuation produce an entire universe? We usually see these fluctuations only making tiny particle pairs. But imagine a fluctuation that created a small, dense nugget of energy, a minuscule universe.

If our universe started that way, it had to expand enormously to become what we see today. This is where the theory of cosmic inflation comes in.

Inflation says that in a fraction of a second after the start, the universe expanded exponentially, faster than even the speed of light, effectively. And this is not forbidden; space can travel faster than the speed of light. However, nothing in space can travel faster than light.

Why is cosmic inflation not a crazy idea? Because it explains observations: the size, the uniformity, and flatness of the universe we observe. In fact, inflation is the leading theory of our cosmic origin, strongly supported by evidence like the cosmic microwave background radiation, which is the leftover radiation from the Big Bang, and the observed distribution of galaxies we see today, which matches the predictions of inflation models.

Here's how these ideas tie together: A tiny universe born from nothing could inflate into a vast cosmos. Think of it like blowing a tiny soap bubble into a giant balloon in an instant.

Renowned cosmologist Alan Guth, one of the fathers of inflation theory, famously described the universe as the ultimate free lunch.

Why a free lunch? Because you get everything from nothing without paying any energy cost. The positive and negative energies cancel out and the universe grows. It borrows energy from the gravitational field and balances the books.

So, inflation gives a mechanism for a quantum-size "nothing" fluctuation to become an entire universe filled with matter and energy.

So far, physics gives us a remarkable picture: a quantum vacuum, zero net energy, and inflation. But, one major problem still remains.

If the early universe produced matter from energy, where did the antimatter go?

You see, from what we understand about physics and what we observe, every time that matter is created from energy, an equal amount of antimatter is also created at the same time. And when matter and antimatter combine, they annihilate each other back into energy. In fact, this is how quantum fluctuations work. So, how could we get a universe with only matter? What happened to all the antimatter? Shouldn't it have an equal amount of antimatter so that we end up back to a universe with only fluctuating fields and no matter at all?

Well, this is an unresolved issue, but the leading hypothesis from physicists to explain this discrepancy is the following: Most of the antimatter annihilated with matter into radiation, but a tiny matter-only excess survived.

They estimate that this tiny proportion was about one particle out of a billion that survived. How do we know that it's one in a billion? Because we observe about a billion photons for every matter particle, because two photons are created for every matter and antimatter particle that are annihilated. That one in a billion leftover is what built all the stars, planets, and matter that we observe in the universe.

Now, you should ask, how the heck did that tiny imbalance occur? To end up with some matter left over, the early universe must have briefly violated some matter-antimatter symmetry somewhere.

In 1967, Andrei Sakharov outlined a kind of recipe of how this could happen. This is now called the Sakharov conditions.

To summarize, three things happened due to the conditions of the early universe, which left a tiny extra bit of matter behind.

First, some rare reactions could actually change how many matter particles existed. Second, the laws of physics are very slightly biased, so that matter and antimatter don't behave exactly the same. It's like a biased coin that lands heads a tiny fraction of a percentage more than tails.

And third, the universe was expanding and cooling so fast that this tiny bias froze in before it could be evened out. And as the cosmos cooled, nearly all the pairs annihilated, but that tiny surplus remained.

And that tells us something crucial: Even if physics can explain how a universe emerges, it still has to explain why this universe did not self-cancel back into radiation, which means the question of existence is tied not only to cosmic origin, but also to the specific asymmetries built into nature.

Now, so far we've been talking as if the laws of physics are at the deepest level of reality. But another line of thought is that maybe the laws are not fundamental at all, but instead emergent, meaning they arise out of something more basic.

In everyday physics, we already see emergence, for example, temperature and pressure in a gas. These aren't fundamental properties of molecules; they emerge from the collective behavior of trillions of molecules moving and colliding.

The idea here is perhaps at the most microscopic fundamental scale the universe follows some ultra-simple rule, and everything we call the laws of physics at higher levels—from chemistry to biology to astrophysics—are just effective laws that come out of the underlying system when it gets large and complex.

This is taken seriously in physics research. For example, some approaches to quantum gravity suggest space-time itself might not be fundamental. It could emerge from something like entangled quantum information.

So, the concept of gravity might emerge from more basic quantum interactions. There are theories of emerging gravity trying to show this.

If true, then asking why do the laws exist as they do might translate to why does the underlying system produce these emergent rules? This may be easy to answer if the base rules are simple.

The emerging idea would also add an interesting twist to the idea of a designed universe. If a very simple underlying rule set naturally yields complexity, you don't need someone to fine-tune each law. It self-organizes.

A great example of this is the behavior of a flock of birds. It's based on three simple rules based on the behavior of a bird's neighbor, not a single leader.

One, don't get too close to each other. Two, don't get too far away from another bird. And three, fly in a parallel direction.

If you watch, it looks almost designed, but it's emergent. Just three simple principles.

In fact, the video you're seeing here is a computer simulation based on just these three rules. It looks like an actual flock of birds. Likewise, maybe our universe's laws are the end result of some basic simple principles organizing itself.

Another philosophical angle is to consider why is mathematics so accurately able to model the way our universe works. Why should the abstract world of numbers align so well with reality?

Physicist Max Tegmark turns this argument on its head. He argues that the universe is mathematics and the physical world is its abstraction, that we simply perceive the mathematical universe as physical because we are inside it.

At this point the question has expanded. Maybe the universe exists because deeper quantum laws allow it. Maybe because our universe is one of many. Or maybe because what we call physical law is itself an emergent pattern arising from something even more primitive.

And yet, even after all that, the biggest cosmic mysteries remain unresolved.

We've sent people to the moon, split the atom, even photographed a black hole. We think we know a lot. But here's the cosmic joke: 95% of the universe is invisible and unexplained.

Our two greatest theories, relativity and quantum mechanics, literally break down when we try to use them together. And some of the most basic questions, like why time moves forward or why there's something instead of nothing, still have no satisfying answer.

I made a couple of videos on what the answers could be. The links are in the description. But these ideas are largely speculative. And these aren't just trivial questions, either. They're the keys to reality.

Solving even one of them could rewrite our future: new technologies, new ways to think about existence, maybe even a new understanding of what "universe" means.

What better place to start than arguably the biggest mystery? Our two greatest theories, general relativity and quantum mechanics, describe different worlds.

Relativity describes behavior of large-scale objects like planets, stars, and space-time. Quantum mechanics accurately describes phenomena at the smallest scales.

Each works extremely well in its own domain, but if you try to use both at once, say to describe something that's very tiny but with immense gravity, such as the singularity inside a black hole or the very first moments of the Big Bang, the equations break down into nonsense.

We get infinities.

We lack a quantum theory of gravity that can unite the certainty of relativity with the probabilistic nature of quantum mechanics. Developing this is often called finding a theory of everything.

Until we have it, we don't truly know what happens in the most extreme situations. That's a huge problem, but also an open frontier. And it's arguably the biggest puzzle in fundamental physics.

And that is the deeper reason this mystery remains open. The very moment we most want to understand the beginning of the universe may be the very place where our current theories stop being reliable.

Here's another long-standing mystery. All the stuff I talk about—atoms, forces, light, planets, people—accounts for only about 5% of the universe's content. The rest is mysterious.

About 27% of the universe is dark matter and 68% is dark energy. These "dark" components carry misleading names. They're not just dark as in unlit. They're essentially invisible and detected only through their effects.

We call it matter because it doesn't emit, reflect, or absorb light. Yet it has mass and gravity. We infer it's out there because galaxies rotate faster than they should if only visible matter existed. And galaxy clusters have extra gravity bending light around them.

The numbers say dark matter is about five times more abundant than regular matter. But what is it? We don't know.

It could be some new type of subatomic particle that hardly interacts with normal matter, sometimes fancifully called WIMPs, or weakly interacting massive particles. It's a big mystery. Basically, an entire invisible world of matter right under our noses, or rather surrounding our galaxies, that we have yet to identify.

Scientists have built deep underground detectors filled with liquid xenon and are waiting for faint bumps from dark matter particles. But so far, nothing significant has been found. Sky surveys like Euclid and the Vera Rubin Observatory are mapping how galaxies clump to trace where dark matter hides.

But dark matter is only part of the invisible puzzle. The bigger mystery is what's pushing the universe apart.

This is even stranger.

In the late 1990s, astronomers discovered the expansion of the universe is speeding up over time. Galaxies are flying away from each other faster and faster. This was the opposite of what everyone expected. Gravity from matter should slow expansion.

To explain this acceleration, we introduced dark energy, a kind of unseen influence that pushes space apart.

Current data suggests dark energy makes up about two-thirds of the cosmos, 68%. We know it's there because we see its effects on cosmic expansion. But we have almost no clue what it actually is.

It might be a property of space itself, Einstein's cosmological constant, essentially energy woven into the fabric of space that has a repulsive gravity effect. Or it could be something dynamic, like a new field, sometimes called quintessence.

Either way, why the expansion is accelerating is unknown. This is a huge puzzle because it ties into the fate of the universe.

Dark energy is a term that basically means we have no idea. But something's making space expand faster.

It's humbling because most of the energy in the universe is in this dark form, 95% including dark matter and dark energy. And we can't explain it.

But scientists are trying to figure it out. Projects like DESI and Euclid measure how galaxies spread across cosmic history to learn whether dark energy is constant, like Einstein's cosmological constant, or something dynamic, like a new energy field.

So where does that leave us?

Physics has not solved the mystery of existence completely, but it has transformed it.

The universe may have emerged from a quantum process. Its total energy may be zero. Inflation may have blown a microscopic beginning into a cosmic one. The laws of physics may be fine-tuned, selected through a multiverse, or even emergent from something deeper.

And still the biggest questions remain open. We don't know what dark matter is. We don't know what dark energy is. We don't yet have a working quantum theory of gravity. And we still don't know why the laws of nature are what they are.

So the next question, why does the universe exist at all, is not just one mystery. It's a doorway into nearly all the deepest mysteries in modern physics.

And maybe someone watching this video will figure it out or at least point us in the right direction.

Thanks for watching.

I'll see you in the next video, my friend.