What really happened at the Big Bang?

Modern science is full of all kinds of mind-blowing theories that describe and explain the behavior of the cosmos under conditions that no one has directly observed. Perhaps the most important example is the study of the Big Bang, which is the beginning of the universe itself. I've talked about the Big Bang in other videos, and some of the comments are

what

you might call skeptical, including people who dismiss the idea by saying that since no one was there at the time, we can't possibly know anything. And, of course, we know a lot. But I find that many people have serious misconceptions about

what

the Big Bang was.

So I thought I'd dispel some of them and then tell you what we know. Perhaps the most common misconception is that what I call the universe began as a giant firecracker. In this model, all the matter in the universe was concentrated in a single place and then exploded, spreading the matter throughout space and the cosmos. The location could have been anywhere, maybe over there somewhere. This is not at all what

happened

. The reality is much, much stranger than that. Another misconception is that the Big Bang explains the exact and precise moment of creation. It is not like this.

It explains things after the moment of creation, not the beginning, and certainly not before. We don't understand any of those things in detail. And that's fine. Scientists admit when they don't know something. A third misconception is that, before the beginning, the universe was located in one place, with zero size and infinite density, what physicists call a singularity. Yes, that's not true either. No scientist

really

believes in a literal singularity, despite what you may have read in some books. The singularity arises by pushing Einstein's theory of relativity to the point where it breaks. It is simply a wrong idea.

So what does the Big Bang theory say? And I want to be clear: this video does not talk about the data that supports the idea. Just the theory itself. The Big Bang theory says that the universe was smaller and hotter and has been expanding for billions of years. To better understand the theory, perhaps it is best to start with what we see today and turn the clock back to the beginning. Let's start with what we see around us: a universe that is flat, or almost so, meaning we can use the simplest mathematics. The part of the universe that we can see is 92 billion light years in diameter and the universe is at least 500 times larger than what we see.

In a previous video, I said the distance was at least 250 times greater, but better measurements have now expanded that number. The current universe may actually be infinite and let's start with that as a good working hypothesis. If that is true, our visible universe is just a bubble in a sea of ​​eternity, stretching forever in all directions. That's a little difficult to draw, so let's focus on one of the three dimensions, say left to right. If we do that, we can present that direction simply as a number line like the one you learned about in grade school, with a zero point and then two arrows pointing left and right.

We can make a decision and define the Earth as the center. We can then separate the universe into parts that are close enough to see and parts that are so far away that we cannot see them. Choosing the Earth as the center does not mean that the Earth is the center of the entire universe, but rather that it is simply the center of the part of the universe that we can see. The universe is expanding now, but if we turn back the clock, we can see that in the past the universe was getting smaller. If we run it until time equals zero, we will see that the entire visible universe has collapsed to what appears to be zero size.

But we also see that even though we reduced the visible universe to a tiny size, the number line is still infinite. That means that even when the universe began, it may already have been infinite in size. So that's kind of mind-blowing. Furthermore, we see that all points in the visible universe collapsed at the same point. If all points in the universe were once equal, that is another reason why we can say that every point in the universe can be considered the center. So, this dispels the Big Bang idea of ​​the firecracker. The Big Bang is just the expansion of space, not the movement of matter through space.

Now let's address the idea that space is flat. Certainly, the data is consistent with that conjecture, but it is not proven. Maybe space is curved, but just super big, just like parts of the Earth can appear flat, when (clears throat) it's very obviously a giant sphere. How does that work in this expanding spatial image? Well, maybe it's true. Perhaps space did not start out as flat, but rather has a twisted and complicated shape. If so, we must reconcile the flat space we see with the possible curved truth. And scientists do so by invoking an addition to the traditional Big Bang theory.

This addition is called inflation. In inflation theory, just a tiny fraction of a second after the Big Bang, the universe expanded incredibly fast. From about ten to minus 36 seconds to perhaps ten to minus 32 or 33 seconds, the universe expanded at speeds faster than light. By some estimates, during this time, the universe expanded between ten and twenty-six times, and our visible universe went from a size smaller than a proton to about the size of a grapefruit. Other calculations give different answers. Precise numbers are not crucial. But the big idea is that this superluminal expansion can take on any shape foreign to the infant universe and make it appear flat, which is what we see today.

And, after inflation stopped, the universe continued to expand as we see it today. This expansion after inflation is what most scientists would call the big

bang

. Well, what about the singularity, the idea that all matter in the visible universe collapsed into a single point with infinite density? Well, it's true that the visible universe collapsed into a tiny volume, but the volume was probably not zero size. Remember that the size zero thing came from Einstein's theory of general relativity and we know that his theory doesn't work on small size scales. To do this, we need a new and improved theory, which we call quantum gravity.

Since we don't have a theory of quantum gravity, we don't know the details, but what we believe is that, due to quantum mechanics, the size of the visible universe was simply ridiculously small, but not mathematically zero. Finally, what

happened

before the Big Bang, when the universe was perhaps still infinite in size, but with the matter of the visible universe crushed into a tiny volume? The simple fact is that we don't know. There are many ideas, including our universe spilling out of another universe like a drop in a lava lamp, or multiple universes floating in a big space called the multiverse, crashing into each other, or - and this is the least speculative - that there is only one universe, the one we live in, and it essentially existed forever in a flattened state, waiting to expand, like a bowstring just before it comes loose.

And, in this scenario, it is familiar quantum mechanics that freed the string. These are the key points of the Big Bang. So let's put it all together starting from the beginning and moving the clock forward. We will start at time equal to zero and ignore what came before it started. Maybe I'll make a video about the various ideas people have about it. But not today. To simplify the explanation, we will show only one dimension. The matter and energy of the visible universe was crushed into an unimaginably small volume, represented by this point here on the number line.

The volume was incredibly small, but it was not size zero. In fact, to tell the truth, we don't know much about the conditions then. While the conditions of the creation instance are unknown, it could well have been some kind of quantum foam, with particles flickering in and out of existence. Something caused the universe to begin to expand. We don't know what. And the first thing that happened was inflation, which was an extremely rapid expansion of space, where the visible universe grew from much smaller than a proton to maybe the size of a grapefruit. Remember that for our purposes, the exact numbers don't matter.

Then, in a time of about ten to minus 32 seconds or so, the energy that drove the inflation dissipated and went out. The expansion of the universe was then at a standstill, and this is the period that scientists call the classical Big Bang and which still continues today. From that moment on we know a lot about what happened. The universe was hot. Particle physics and then nuclear physics dominated the landscape. The universe expanded and cooled, giving rise to atoms, stars, galaxies and, finally, us. The key message about the Big Bang is that it was not an explosion.

It is simply the expansion and stretching of space. And another important point is that no place in our universe is the place where the universe began or, equivalently, every place in our universe could be considered the center. No place is special. It is also true that no reputable scientist will claim that we understand in detail what happened at the exact moment the universe began. We just don't do it. But we are analyzing it and we know much more than a century ago. Imagine what we will know in a century. Hopefully, my medical colleagues will make a breakthrough that will allow me to still be around to see it.

Because, man, I sure want to know. It is not like this? Even though we don't know everything about how the universe began, I am constantly amazed by the fact that we know so much. We hope this video has given you a better idea of ​​what we know and some of the most common misconceptions. If you liked the video, be sure to like and share it on social media. And be sure to subscribe to the channel, including hitting the little bell icon to get notified the next time I make a video about the Big Bang, which I certainly will.

After all, the Big Bang is physics, and of course physics is everything.