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
If you go to Westminster Abbey in London, look on the floor of the abbey on his memorial stone, and he's in there next to Newton and Shakespeare and all these people, and he's there. And chiseled in stone on the floor of Westminster Abbey is his equation for the temperature of a black hole. So it was this tremendously important discovery.
So he discovers these things glow, and he calculates how they glow. They're very low temperature, but they emit things, which means that they shrink because they're emitting stuff, and so they're shrinking. So that means they have a lifetime. So first of all, one day they'll be gone. So that means that you have to address this question of what happened to all the stuff that fell in.
And his calculation said that there's no record at all of anything that fell in, in all this radiation that's come off the black hole. So it's purely information-less radiation. So what that means is that black holes destroy information, according to that calculation. And that's a big deal because nowhere else in all of physics does anything erase information from the universe.
So it's really true that if I got this notepad and pen, right, and I wrote some things on it, and then I set fire to this, even just incinerated it, put it in a nuclear explosion, whatever. In principle, according to all the laws of nature that we know, if you collected everything that came off, all the radiation, all the bits of ashes and things,
and you could just measure it all, then just in principle, the idea is you could reconstruct the information. So it all gets scrambled up and thrown out. And so in practice, you can't do it. But just in principle, the laws of nature say that information is not destroyed. It's just scrambled up in a way that you can't reconstruct.
But this calculation that Stephen did said there is no information in that radiation at all. Zero, just nothing. So it seemed that uniquely in the universe, black holes erase information.
So really in bits, I mean, the idea is, and I should say it's very much in principle this, so no one thinks in practice you could reconstruct what I wrote down on this if you set fire to it. But in principle... Well, maybe sometime in the future. Yeah, in principle, you could just collect everything.
Then somewhere in all that radiation and ashes and light that's come off the thing is the information. It's there. So you could reconstruct the book or what I wrote on this page in principle. But the thing about Stephen's calculation was that even in principle, it said there is no information.
And by the way, it's kind of easy to see why, actually, because this radiation, this Hawking radiation that comes off the black hole, it's coming from the horizon of the black hole. So I should say what the horizon is maybe.
Remember I said that the sun, if you squashed it down within three kilometres of radius, you'd get this kind of distortion in space and time from which if you went in across this region, three kilometres, you went inside it, you couldn't get out. So that's called the event horizon.
So you wouldn't notice if you fell through the horizon of the black hole in the Milky Way galaxy if you went into that one. We could be falling through that horizon now in this room, and we wouldn't notice anything except that we couldn't get out again. And ultimately, in a few hours, in that case, time would end for us. So you go to the end of time. We could talk about that.
There's a picture of that. Maybe I should talk about it. This is getting quite complicated already, isn't it? We didn't start in a relaxing way, did we?
No need to. Let's get right into it. So we wouldn't notice anything. Not for the big black holes. So, yes, these supermassive black holes, we could fall across this horizon. It's just like being in empty space for us. So we'd just be talking now when we could have been talking on the outside of the horizon.
And by the time I finished the sentence, we could be on the inside of the horizon, inside the black hole. And... according to Einstein's theory at least, which is the theory that predicted them initially, we could just do that, we could just go in And we wouldn't notice for a bit. The thing we would notice ultimately is you go inexorably. Nothing you can do.
You go to this thing called the singularity once you've crossed the horizon. And you are going to that thing. And then the question arises, what is that thing? And one answer is we don't know. But in Einstein's theory, it's the end of time.
So one way of picturing what's happened here is so distorted is space and time by the collapse of a star or the collapse of loads of stuff to make these big supermassive black holes. We don't quite know how they form, actually, but it's collapsing stuff. So it distorts space and time so much. that in a real sense, they kind of flip over. They get mixed up.
And so this singularity, which you might have thought of as the point to which this thing collapsed, this infinitely dense point, you might think. But actually, more correctly to be seen as the end of time. Because everything's got mixed up. So you go to the end of time. And it's just like saying, why can't I escape that thing? It's like, why can't we escape tomorrow? So we are going to tomorrow.
And if I said to you, let's run away from tomorrow, you'd go, I can't run away from tomorrow.
Is that the idea? If you draw the thing, you can draw a map of it, and it just literally time ends, just purely in Einstein's theory. This is 1915, his theory of general relativity. You just get a line there, a line that says there's no future beyond this line. It just stops. Okay. So, I mean, admittedly, that's not... We think there's a lot more to it than that.
Well, that's the thing. So we're starting to get hints about what might happen, which is leading us. So to backtrack a bit, why does this calculation Stephen did, why does it say there's no information in this radiation? The thing is, it's coming from the horizon. So there's loads of ways to think about it.
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