What happened before the Big Bang?

One of the oldest mysteries, pondered by generations of profound thinkers, is the question of how the universe began. And we know a lot about

what

happened

. Science provides a strong and compelling narrative for much of the story, but it is not complete. Let me summarize

what

we know for sure. We know that the visible universe was once smaller and hotter and is expanding. We know that there was a moment when the expansion began. We know that that moment was about 13.8 billion years ago. For more than fifty years we have known about cosmic microwave background radiation, also called CMB.

The CMB is the oldest thing we can see in the history of the universe. In fact, it is the remnant glow from when the universe began. The CMB presents a picture of when the universe was about four hundred thousand years old, which is when the universe was about 0.003 percent of its current age. If we equate my current age with the age of the universe, looking at the CMB is like looking at a baby photo of me when she was 14 hours old. Man, I was a cute baby. However, while the oldest thing we can see existed literally 400,000 years after the universe began, we actually know the conditions of the universe long, long before that time.

For example, at the time we can see the CMB, the universe had a temperature of about 2,700 degrees Celsius. But the universe is expanding and cooling. Even in earlier times, the universe was hotter than that. While we can't see the universe when it was much hotter, we routinely recreated the conditions of the early universe in huge particle accelerators like the Large Hadron Collider on Europa. When we crush lead nuclei, temperatures reach 7 trillion degrees Celsius. You have to be a little more careful with the definition of temperature when talking about the most energetic collisions ever made, but when the LHC collides beams of protons, researchers believe that the last common temperature in the universe was when it was a tenth of a billionth of an old second.

That's ten seconds minus thirteen for the amateur scientific public. So these are all facts. If we define the moment at which the expansion of the universe began to be time equal to zero, we have concrete data for times after ten to minus thirteen seconds. That should impress you greatly. It still surprises me and it's what I do every day. But for all we know, there are still things we don't know. For example, there is that period of time between time equal to zero and ten to the power of negative thirteen seconds. Science does not know exactly what

happened

during that time.

And we don't know if time is equal to zero and even less what happened before that. On the other hand, not knowing everything is very different from knowing nothing. We have some very informed ideas. The most popular idea that explains both the expansion of the universe and the uniformity of matter and energy is an idea that says that at a time from about ten to minus thirty-six seconds the universe began to expand at speeds faster than light. . Now you might think that this is impossible, because you have learned that nothing can move faster than light, but that is not entirely true.

It's true that nothing can move through space faster than light, but there are no restrictions on the speed at which space can expand. Therefore, this period, which by the way is called the inflation period, does not violate any laws of physics. What would cause space to start expanding so rapidly? Well, we only have an educated guess about this. In our current universe, we have four known forces, called electromagnetism, gravity, and the strong and weak nuclear forces. Judging by what we know about the behavior of those forces, it seems as if, at high enough energies, they coalesce to form a single force.

This is how Isaac Newton realized that there is only one explanation for why things fall and the planets march across the sky, and that one thing is now what we call gravity. If all forces were once equal and now act differently, then there must have been a time when they became different. And one idea is that what gave the energy to make the universe expand is when the strong nuclear force became different from the others. That's called a phase transition and it's a perfectly reasonable idea. In case the idea is confusing, here's an analogy. Suppose you have a container containing air and water.

If the temperature of the container is above the boiling point of water, the container will contain both air and water vapor. However, when the temperature drops below one hundred degrees Celsius, water becomes liquid, while air remains gaseous. At that temperature, two things that seemed the same suddenly look different. Now, you should not believe in any inflation, nor in the idea that a single force starting to look like four forces is what caused inflation to exist. But both are quite reasonable guesses and require no physics beyond what we know to be true from observation. In fact, both ideas are exactly consistent with the known data.

Okay, we're not there yet when the universe began, but we're almost there. Let's recap what we do know. Assuming that no new physical principles arise at higher energies, we have time equal to zero, followed by approximately ten minus forty-three seconds. Before forty-three seconds to ten, the energies and temperatures are so high that all known physics fails. None of our intuitions of what we know can apply during that time. From ten to minus forty-three seconds to about ten to minus thirty-six seconds, the universe expanded and cooled relatively slowly. About ten minus thirty-six seconds, the strong force became different from the others, causing the visible universe to swell from much smaller than an atom to something the size of a grapefruit.

The inflation period only lasted about ten to minus thirty-two seconds. From that moment until ten minutes to thirteen seconds, the universe continued to expand, but now it was sliding by inertia. After ten seconds thirteen less, the expansion continued to move forward, and that is the moment when we finally have concrete data. Everything that happens after ten seconds or thirteen less is solidly known. All of the above are speculations, even if they are sensible speculations. Okay, so how was time equal to zero? Well, since before forty-three seconds to ten all of our known physical laws fail, we don't know.

In fact, without a breakthrough in physics, we cannot know. So, there is an admission for you. Science can't tell you anything certain about this time. But that's okay. It is not a sin not to know something. It is only a sin to think so, when clearly it is not. However, what are some ideas? Turns out there are some. Certainly, the entire visible universe was much smaller than it is now. But the entire universe (including parts so distant we will never see them) had to have been much larger than the visible universe (at least 500 times larger). Drawing a three-dimensional universe is difficult, so I will try to present the key ideas using a one-dimensional support.

Suppose that when the universe began, we represented the visible universe as this one-dimensional line, with us as the center. If that is the visible universe, the smallest the rest of the universe can be is represented as the circumference of this circle. This is the smallest the universe can compare to the visible universe. Now the universe could be much bigger than that. In fact, the circle could be infinitely large, meaning that the universe effectively has no curvature and is infinite. On the other hand, the universe could have had a wavy shape. Science does not know and may never know the answer to that.

So let's focus on the visible universe. Was very small. All matter and energy in the universe was reduced to super, incredibly microscopic size. It wasn't size zero (this is a common misconception), but it was very, very, small. What was the universe like when it was so small? Remember that we know that the known laws of physics didn't work back then, so no one knows. We imagined that perhaps it looked like today's space-time, with matter and energy constantly appearing and disappearing. And that word space-time is important. It is also often misused when people talk about the Big Bang.

This is because people hear that time slows down when gravity becomes strong, which certainly happens when matter is compressed to such a small volume. But what really happens is that when a person who is not in a strong gravity region looks at a person who is in a strong gravity region, time appears to slow down for the strong gravity person, at least from the point of view. from the person's view of weak gravity. But for someone with strong gravity, time seems to continue as usual. Additionally, it is often said that the Big Bang created space and time and there is some truth to that.

Without a doubt, the Big Bang expanded space and time. But remember that the theory of general relativity, along with all other known physics, does not apply before time equals ten to the power of minus forty-three seconds. That means that statements about time that does not exist at time equal to zero or earlier should be considered suspicious. So what are considered reasonable ideas? There are some, but always remember that they are really speculations. There are three. The first is that the universe always existed in a supercompact state, like a taut bowstring. Then, using the same ideas that govern quantum mechanics, the universe moved into a state of expansion, much like shooting an arrow.

Basically, this is very similar to how nuclear decay works. That idea is static and requires that the universe existed forever, however long those conditions mean. The other ideas require a less static environment, but are much more speculative. Suppose there are additional dimensions besides the usual three of space and one of time. If that is the case, it is possible that there are different universes in those higher dimensions that we cannot interact with. That's not so different from birds that fly in three dimensions, when we must walk in two. If that's the case, then perhaps the universe we exist in now has always existed, floating in higher dimensions.

Perhaps our universe collided with another universe and the energy from the impact was what caused our universe to heat up and expand. It's hard to imagine we'll find an experimental signature that confirms this conjecture, although scientists have had some testable ideas. Then there is a third idea, which is called eternal inflation. Perhaps the universes move like drops in a lava lamp, and the drops separate and combine. In this idea, a universe existed and we sprung from it. Similarly, universes have emerged from our universe. In this idea, there is a constant creation of universe after universe, each from a parent universe.

Again, it is difficult to see how we would confirm this idea. Of course, you have to remember that the bottom line is that we don't really know what happened at time zero, and certainly not before. Furthermore, since we have no data on the nature of the universe before ten to thirteen seconds and we believe there is a time when known physics absolutely must fail, it is premature to even give the impression that we have an educated guess. After all, as my colleagues and I explore higher and higher energies, we may discover something that radically changes our current ideas.

In that case, the data can guide our thinking in a very different direction. In fact, I would be surprised if the final answer was what one might have read in popular science literature. I wish I could have told you that science knew what the answer will be, but that would be a lie and I will never lie to you. We know a lot, I mean, we know a ton about how the universe went from a hot, dense state to where we are now, but we don't know everything. And it will take a lot of time and the effort of thousands of scientists to get closer to understanding how the universe came to be.

I mean, exploring the unknown and pushing back the boundaries of our current ignorance is what my colleagues and I do. In fact, if you'll excuse me, I think I hear the call from the lab. Talk to you later. Well, that was a heady video. There's a lot to it, both what we know and what we don't. I hope you learned something, including the fact that there is still a lot to learn. If you liked the video, be sure to like and subscribe to the channel, including clicking the little bell icon. And, of course, share it on social networks, so that all your friends can learn a little more about physics.

After all, and after this video, I'm sure you'll agree: physics is everything.