https://youtubetranscript.com/?v=n42ufWYRjDk
30 years ago we wouldn’t even have been able to ask the question, much less answer it, is that it’s quite likely that our universe could and did spontaneously arise out of nothing, no space, no time, and maybe no laws. And if you ask what would be the properties of a universe today, 14 billion years later, that arose from nothing spontaneously without any supernatural shenanigans, the properties of that universe would be precisely the properties of the universe we observe. Now that doesn’t prove that’s the case, that just makes it plausible, but to me that’s a fascinating thing. And again, we never, 30 years ago we didn’t have the tools to even in some sense ask that question. But very early… We’re still estimating the birth of about 14 billion years ago? 13.8, yeah. Now if you actually look at the numbers which we can measure, we now know that number, 13.8 to an accuracy of, you know, plus or minus of maybe a few, a hundred million years or two, 13.75 I think is the most recent number. And it’s amazing, the fact that you can get beyond one decimal place in cosmology is just remarkable. And I really, it really is a testament to the developments. When I was even a young assistant professor at Yale, I remember talking to an older colleague who said that nature would always conspire so that we could never measure the fundamental quantities of the universe better than within a factor of two. Because that’s, it had always been the case up to that point. Every time someone claimed to have a better measurement, you’d go out and look at astrophysical uncertainties and realize it was wrong. And now we’re talking about measuring things to four or five or six decimal places. It’s really, it’s really a transformation and one we’re celebrating, which is what I tried to do in that book. But the early picture, the fact that we evolved from a Big Bang is not in dispute. Let me make that clear. The Big Bang happened just like evolution happened and the Earth is round and all the other things we know. There’s no doubt that the early history of the universe was a hot Big Bang. Now, so, and in fact, everything we now see, all the galaxies we now see and all the particles in those galaxies, the hundred billion stars in each galaxy, the hundred billion galaxies, all of that material was contained in a region smaller than the size of a single atom. And that’s just- So, okay, let me ask you a question about that. Sure. I mean, is it reasonable to conceptualize something like that as having a size? Because we’re considering size within the universe and it’s almost when you say that the universe at the beginning had a size, it’s like it was an object in a universe that had a size. But- It’s a really good question and I should be clear in my language. The universe could be infinite. I want to ask as a physicist and Wheeler would have liked this Einstein certainly that operational questions. I don’t know how big the universe is, whether it’s in or not, but what I do know is how big is the visible universe. So, if I ask you how big was the region which now comprises the visible universe today at an earlier time, that has a good- that’s well defined. That region, the size of an atom could have existed in a universe which was infinite even then. There could have been, it could have been an infinitely dense universe that was infinitely big. Okay? So, all we can ask, and this is really a big change also from when I was a student, because we used to, when I was a kid or when I was even a student, we’d talk about universe and universe would mean everything, a kind of ill-defined quantity, everything. What the heck is everything? Now we’re much more well-defined. We say our universe, a good definition of our universe, is that region with which we could have interacted in the past and with which we will be able to interact into the future, even if the future is infinitely long. And that may not be everything, right? That could be just a small region of a much bigger thing which we now call a multiverse. So, it’s reasonable to describe our universe as that region into which we could have had causal contact, namely which cause could have produced effect, right? And if there’s any region outside of it which we can never affect or be affected by, that might as well not be considered part of our universe. And that distance, that causally interactable distance, that’s defined or limited by the speed of light? The speed of light and the age of the universe. So, for example, in the early history of the universe, that’s called the horizon. In analogy with the earth, when you look out at the earth, you can, you know, when it curves, you can only see out to a certain distance. And we call the causal horizon that region with which light could have traveled to interact with us since the beginning of time. Right. And that’s the universe as far as we’re concerned, because nothing outside of that can affect us in any way. Exactly. So, operationally, it’s a much better definition of the universe to be that which we can be causally affected by. And so, and because that changes with time, that’s what is our observable universe changes with time, and we’ll get to it because things have changed a lot in the last few years. So, does that mean that the universe that causally affects us is, we’re at the center of it? No. Well, actually, yes and no. We’re always at the center of our own universe, right? I mean, psychologically and physically. Well, but because of the causality argument that you just laid out, it seems to imply that directly because- Well, it certainly does in the sense that if you want to think of it, and that this is one of the confusions that many confusions which I may add to during this podcast, but we’ll try not to, is that, you know, when we look out at this thing called the cosmic microwave background radiation, it’s a residual radiation left over from the hot Big Bang, and it comes from a sphere, if you wish, that’s located with us at the center. Because early on in the history of the universe, when it was hot and dense, light interacted with matter, and basically it followed a random walk. It wasn’t free to travel because all the universe was charged and light would interact and bounce off things. But at a certain point, when the universe was about 300,000 years old, matter became neutral. Protons captured electrons to form hydrogen for the most part, and neutral matter doesn’t interact with light as strongly as charged particles. And that meant that that radiation, which was kind of trapped early on when the universe was 300,000 years old, could suddenly travel freely through the universe without really interacting. And when we look out, basically we see space and the light could travel and travel and travel, but we’re looking back further in time when we look out. And if we look out in that direction, back to a time when the universe was 300,000 years old, we’re kind of sort of going to see a wall, if you wish, because we can’t see before that time because the light couldn’t have propagated out, just like it can’t propagate out through a wall. Only from the surface of the wall can we see it. So when I look at the microwave background from Earth, I’m looking, if you wish, at the sphere located almost 13, well actually it’s because the expansion of the universe is more than, it’s about 26 billion light years in each direction because the universe expanded during the time that the light has been traveling. But don’t worry about that complexity. We’re looking at a sphere located a certain, let’s say, 10 to 20 billion light years away from us in all directions and we literally can’t see beyond that. But the sphere we’re looking at depends upon where we are so that if we were doing the same experiment on an intelligent species in another galaxy located 100 million light years away, literally the cosmic microwave background that they would see would be slightly different because it’d be a sphere centered on a different place. And that’s why actually the predictions we can make in some sense as cosmologists are somewhat statistical because we’re talking about a thermal distribution and galaxies and lots of disorder. And so the picture, and we’ve taken pictures of the microwave background, it’s won at least two Nobel prizes for those pictures, the picture that we see has statistical properties which would be identical to those observed by another observer 100 million light years away. But the specifics, the hot spots and the cold spots would be different because they’d be looking at a different slice of a statistical distribution. So that does, correct me if I’m wrong, that does seem to imply that the universe is a globe around us, let’s say. Our visible universe. Our visible universe, sorry, I want to be precise with my words too. And so I move halfway across the universe and the globe is still there but now it’s shifted that far and so then I could move another halfway and it would shift again. So this globe moves with the observer so to speak. And that certainly seems to imply that it extends beyond the globe that we see because if you move it moves. So and exactly well and it wouldn’t if there was some edge but there’s no evidence of any edge. Okay, I think that the point is that even before the weirdness of empty space and inflation, we was recognized that the part of the universe we see is unlikely to be the everything there is. We’re limited in what we can see because of what’s seeable, just like being on earth. And it’s limited because of the speed of light and the age of the universe but also because of the way the universe was constituted in certain stages. And the way it’s expanded ever since.