Brian Cox
speaker
1,719 appearances
13 recordings
8 series
first heard Oct 2024
last heard 16 Jun
Brian Cox’s voice in public audio — every appearance, attributed to the second.
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recordings per month · last 12 monthsRecordings per month over the last 12 months — 9 in all, peaking in Jun 2026 with 3.
Appearances
So in this young universe, 380,000 years after the Big Bang, that's only hydrogen and helium gas, basically, and a bit of lithium, some of the lighter elements, but basically hydrogen and helium. So you've got an almost smooth, almost featureless universe then. But these little density fluctuations are very important because as the universe expanded and cooled, they collapsed to form the galaxies.
So without those ripples, without that pattern, we would not exist. Nothing of interest would exist. And so the question is, where did that come from, that pattern? It's fundamentally important.
and the theory of inflation that i mentioned earlier that there's this time before the universe got hot and dense that theory predicted that pattern before it was observed so this idea that you've got this very stretch very quickly stretching space by the way so it's so the stretch if i can remember the number is if you consider two points in space during inflation the distance between them was doubling
every 10 to the minus 37 seconds, which is 0.0000000000. So it's incredible rate of expansion that draws to a close. And those theories... So there's inflation there. So those theories... predicted slight variations in the rate at which inflation stops.
I mean, it is. He doesn't like inflation as a theory. He doesn't? Oh, no. So our universe is accelerating in its expansion at the moment, which is one of the great mysteries that was discovered in the 1990s by a friend of mine, actually. Brian Schmidt got the Nobel Prize for this discovery.
He told me once, I don't know if I told you the story before, but he told me that he'd made this measurement and it wasn't really, he was looking at supernova explosions. And he'd seen that the suggestion in the data was that the universe is accelerating in its expansion, not slowing down, but speeding up. in its rate of expansion. And no one was expecting it, so he thought it was just wrong.
But he couldn't find anything wrong with his data. So he published it and thought, well, that's the end of my career. Oh, boy. He was quite young. I think he might have even been a postdoc, and he just published it. That's a good scientist, right? I don't think this is right, but I can't see anything wrong with it. I'll publish it. Someone else will tell me where my mistake was.
And there was no mistake, and he won the Nobel Prize for that discovery. That's the 1990s. So this idea of the universe is accelerating in its expansion. The way that it does that is really important. Is it going to carry on doing that? Is whatever's driving that expansion going to change in some way, which could actually re-collapse the universe again?
We give it a name, by the way, dark energy, this thing. But we don't know what it is. I think it's very fair to say. But it looks a bit like inflation, but it's way slower. So maybe they're linked. Maybe it's the same kind of thing. We don't really know. And so it's one of the great mysteries.
But the universe, it looks like the universe is going to continue to expand forever and to continue to accelerate.
Yeah, dark matter's in some sense marginally less confusing in the sense that at least we have an idea of what it might be. Whereas dark energy, there are people listening to it, there are people working on it, so there are theories about what it might be. But I think it feels less explicable, given what we know, than dark matter.
But we haven't discovered what... We think dark matter might be some kind of particle. that has got certain properties and doesn't interact very strongly. It interacts like neutrinos, basically, that you mentioned earlier. So it really doesn't interact very strongly. But we thought we might have seen those particles. We're looking for them.
They would be passing through this room now, and so we could build a detector in here, and we do that, and we look for these particles. We haven't seen them. We thought we might make them at the Large Hadron Collider at CERN. I think many people thought that we'd see the signature of these things, and we haven't done. So it could be that we're not right with that picture.
So, yes, it's about 5% matter, about 70% dark energy, and the rest, so 25% dark matter. So we're just less than 5% this. That's crazy. And stuff we can see. So everything we can see in the sky, all the gas and the dust and the galaxies and the stars and the black holes, all those things, less than 5%. According to the standard model of cosmology.
Yeah. Wow. But those are models. I mean, it's important to say that it's interesting because until... So we have a hypothesis, which is strongly supported by lots of bits of evidence, that dark matter is some kind of particle. So that's the broadly, that's what you find in the textbooks. But it's true that until you find it, until you see it, then you haven't shown it to be correct.
Are there alternative theories? There are. Are they compelling? No, they all have problems. And most of them have problems with that pattern, the CMB, the cosmic microwave background that we just saw. Because that pattern, what you're looking at actually in that pattern is acoustic, it's waves, sound waves essentially in the early universe that go through the plasma of the early universe.
And they go out and we know what speed they go through that plasma. So it's almost like you're looking at a pond and you're throwing stones into the pond. And they all land in the pond at the same time and send ripples out, little circular ripples in the pond. And they all overlap. And that's what that pattern is. So we're looking at sound waves going through this plasma. And those theories...
uh require the dark matter the dark matter fits well if it's in there in in this plasma in this kind of soup that this subatomic particle soup that's the early universe and the way the sound waves go through it fit that idea so that's one thing but the the the idea also came from looking at galaxies and how they rotate and galaxies and how they bend light and and
And deform space and time and how they interact together. So there's loads of different bits of information, observations of the universe from the cosmic microwave background all the way through to galaxies and the formation of galaxies and the theories that we have there that suggest there are these particles around that interact very weakly with light.
So they don't really interact with light at all, which is why we don't see them, which is why they're dark. That's just like a neutrino, right? So like heavy neutrinos. And actually there was a theory once that maybe they were heavy neutrinos, but that's kind of disfavored now. And so we have loads of kind of different bits that fit. This is how you do science.
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