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Speaker 1: Hey, or Hey, I've got a physics dad joke for you.

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Speaker 2: Well, is that a joke that's only funny to physicist dads.

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Speaker 1: Let's find out why do physicists complain about the price

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Speaker 1: of protons.

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Speaker 2: I don't know what.

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Speaker 1: They think they've been overcharged.

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Speaker 2: I think I paid too much for that joke.

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Speaker 1: What do you mean it was free?

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Speaker 2: Exactly? I am positive I was overcharged.

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Speaker 1: Oh, that's such a negative reaction.

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Speaker 2: I am hory Ham, a cartoonist and the creator of

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Speaker 2: PhD Commics. Hi.

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Speaker 1: I'm Daniel. I'm a particle physicist and a professor at

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Speaker 1: UC Irvine, and I'm always trying to find the in

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Speaker 1: this crazy cosmos.

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Speaker 2: What does that mean is? Do you think the universe

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Speaker 2: is funny?

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Speaker 1: The universe is kind of hilarious, and you can respond

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Speaker 1: to it either by being freaked out, like wow, this

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Speaker 1: place is insane, or you can laugh at it and

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Speaker 1: say like wow, somebody out there has a sense of

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Speaker 1: humor when they put this thing together.

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Speaker 2: Oh, do you think the universe appreciates being left at

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Speaker 2: what if it's not doing it on purpose?

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Speaker 1: I like to think we're laughing along with the universe.

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Speaker 1: You know, we're not mocking it. We're appreciating the cleverness

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Speaker 1: of its structure, which sometimes you know elicits a chuckle.

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Speaker 2: Yeah, But is it funny like funny haha, or is

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Speaker 2: it funny like.

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Speaker 1: I think it's a big mixture of the two. It's

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Speaker 1: sometimes pretty weird and that makes me laugh.

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Speaker 2: But anyways, welcome to our podcast, Daniel and Jorge Explain

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Speaker 2: the Universe, a production of iHeartRadio, in which we.

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Speaker 1: Try our best to find the sense in the universe.

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Speaker 1: We look out there at all the particles buzzing and

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Speaker 1: frothing and doing all sorts of bizarre things and try

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Speaker 1: to weave it together into a story. Something in our

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Speaker 1: minds explains why electrons zig this way and why protons

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Speaker 1: zig that way, and how they all come together to

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Speaker 1: make this incredible, delicious, hilarious universe that we appreciate.

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Speaker 2: That's right, because it is a pretty curiously funny universe,

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Speaker 2: full of amazing mysteries and contradictions sometimes and paradoxes, and

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Speaker 2: here in the podcast we try to find the punchline

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Speaker 2: to it all, just to deliver some lass and maybe

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Speaker 2: also some mind blowing moments.

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Speaker 1: Sometimes what you need is humor to crack open a

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Speaker 1: deep mystery of the universe. We'd love to joke our

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Speaker 1: way into the hearts of black holes and understand what

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Speaker 1: is the singularly most funny joke in the universe.

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Speaker 2: Well, my job is definitely to find jokes and write jokes.

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Speaker 2: But are you saying that your job is also a joke?

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Speaker 1: No, you got to have a straight man on the podcast.

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Speaker 2: Right, Which in a physics podcast, which one is the

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Speaker 2: straight man?

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Speaker 1: We're both straight men in one way and jokesters in

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Speaker 1: another way.

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Speaker 2: We're both crooked. Is that what you're saying.

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Speaker 1: Look, I'm just trying to keep everybody out there awake.

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Speaker 1: I've been getting all these emails from people saying they

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Speaker 1: love to fall asleep to the podcast. And as much

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Speaker 1: as I'm glad that people are finding some way to

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Speaker 1: appreciate it, I hope they're at least staying awake to

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Speaker 1: the end.

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Speaker 2: We're more of a meditation podcast. Is that where we are?

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Speaker 1: I'm trying to transition us from meditation to humor.

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Speaker 2: I think that's a big business. Actually, like podcasts that

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Speaker 2: helps you fall asleep. I heard like a really good

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Speaker 2: book to fall asleep. This is some kind of math

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Speaker 2: book by Stanley Tushi or Tony Shlou one of those actors.

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Speaker 2: They just read this math book really slowly and people

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Speaker 2: found it and they found it a great way to

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Speaker 2: fall asleep.

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Speaker 1: Great physics ASMR. Well, maybe when they sleep, one of

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Speaker 1: our listeners will get a bolt of inspiration, an idea

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Speaker 1: helps us crack open some of the mysteries of the universe.

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Speaker 1: Or maybe that's too charged an idea.

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Speaker 2: I wonder if people are listening to us just as

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Speaker 2: they are falling asleep, if we have a chance now

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Speaker 2: to like implant ideas into their subconscious.

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Speaker 1: Welcome to podcast inception right.

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Speaker 2: Send money to Jorge tomorrow. You will wake up refreshed

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Speaker 2: and feeling alive and feeling like you and to Venmo

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Speaker 2: me a few thousand dollars.

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Speaker 1: Maybe you're in a dream right now and this podcast

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Speaker 1: isn't really happening.

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Speaker 2: Hopefully won't turn into a nightmare.

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Speaker 1: Hopefully you'll get a torrent to cash from the listeners.

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Speaker 2: But speaking of dark topics and scary nightmares, let's talk

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Speaker 2: about black holes. Black Holes are notoriously I guess humorous

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Speaker 2: in the sense that they are big mysteries and they

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Speaker 2: seem to be full of contradictions inside them.

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Speaker 1: That's right, like dad jokes, black holes are some of

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Speaker 1: the most extreme things in the universe. Instead of being

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Speaker 1: the funniest things in the universe, they are the most massive,

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Speaker 1: the most dense, the most gravitationally powerful things in the universe.

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Speaker 2: Would you say they're the holy grail of dad jokes?

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Speaker 2: Or does that make too light over the gravity of

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Speaker 2: the situation.

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Speaker 1: I think that was a massively successful joke.

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Speaker 2: Well, at least it doesn't suck us. I guess that's

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Speaker 2: all black holes do.

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Speaker 1: Jokes aside, black holes are the most massively interesting things

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Speaker 1: in the ar because we think they have within them

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Speaker 1: some of the answers to the deepest questions in modern physics.

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Speaker 1: What is a theory of quantum gravity? What happens when

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Speaker 1: you take tiny particles and squeeze them all together so

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Speaker 1: that they are gravitationally powerful? And so people are always

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Speaker 1: trying to figure out a way to crack open a

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Speaker 1: black hole to somehow peek inside and get a snapshot

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Speaker 1: of those secrets of the universe.

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Speaker 2: Yeah, because it seems like black holes can eat pretty

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Speaker 2: much anything, right, any kind of matter, any kind of light,

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Speaker 2: any kind of energy. It can absorb even dark matter.

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Speaker 1: Right, black holes can certainly eat dark matter, that's right.

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Speaker 1: And because everything out there in the universe has energy

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Speaker 1: and energy means gravity, everything in the universe is attracted

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Speaker 1: to a black hole. But there are of course always

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Speaker 1: some caveats to that. If black holes have electric charges,

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Speaker 1: you might be able to turn them from attractive into repulsive,

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Speaker 1: and you might also weirdly be able to crack them open.

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Speaker 2: Yeah, that's another interesting thing that black holes can eat

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Speaker 2: is they can eat electric charge. Right, Like, if you

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Speaker 2: throw an electron into a black hole or a bunch

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Speaker 2: of electrons, the black hole is going to gain a

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Speaker 2: negative charge.

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Speaker 1: That's right, because charge is conserved in the universe. It

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Speaker 1: doesn't just go away. So in the same way that

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Speaker 1: when you add energy to a black hole, it gains

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Speaker 1: in mass proportional to that energy, when you add a

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Speaker 1: charged particle to a black hole, it gains its charge.

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Speaker 2: Do we actually know that, Daniel, Or is that just

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Speaker 2: from the theory that the theory says that if you

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Speaker 2: throw an electron in the black hole, now is a

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Speaker 2: little bit more negatively charged or does charge maybe I

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Speaker 2: don't know, decompose inside of a black hole and turn

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Speaker 2: into energy.

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Speaker 1: That's definitely just from the theory. We're not even one

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Speaker 1: hundred percent sure that black holes exist in the universe.

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Speaker 1: We have a bunch of candidates that seem like black holes,

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Speaker 1: but of course there's a whole bevy now of proposals

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Speaker 1: for what they might be instead of black holes. But

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Speaker 1: we think that charge is conserved in our universe, and

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Speaker 1: so even if those particles transform into some other state,

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Speaker 1: the electric charge is made. But again that's just theoretical.

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Speaker 1: But that electric charge does create some very strange conditions

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Speaker 1: inside and outside the black hole.

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Speaker 2: And I guess the question you can ask is how

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Speaker 2: many electrons can you throw into a black hole? And

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Speaker 2: is there possibly a maximum number of them that you

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Speaker 2: can throw in?

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Speaker 1: That's right, because as black holes get more and more charged,

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Speaker 1: they get weirder and weirder, and so if you can

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Speaker 1: add an infinite amount of charge to a black hole,

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Speaker 1: you might even be able to crack it open.

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Speaker 2: So to be on the podcast, we'll be asking the

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Speaker 2: question do black holes have a maximum electric charge? Now,

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Speaker 2: this is like how much they charge for people to

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Speaker 2: go inside or what?

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Speaker 1: Yeah, I think we get a podcast discount though.

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Speaker 2: Oh yeah, two for one, two podcast hosts for.

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Speaker 1: One because we've been featuring black holes on the podcast

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Speaker 1: so many times. We're basically like friends of the black Hole.

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Speaker 1: By now we're on the sort of special VIP list.

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Speaker 2: We're like the mater shells for a black hole, the

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Speaker 2: black hole industry.

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Speaker 1: That's right, we're paid under the table by big black hole.

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Speaker 2: The problem is they can never pay us because nothing

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Speaker 2: can escape a black hole. You have to go in

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Speaker 2: there to get your money.

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Speaker 1: They tell us it's in there, but we haven't actually

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Speaker 1: verified that.

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Speaker 2: Well, this is kind of a weird question. Can a

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Speaker 2: black hole have a maximum electric charge? Which is weird

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Speaker 2: to think about because it doesn't seem like a hole

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Speaker 2: can have a maximum. A black hole can have a

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Speaker 2: maximum of anything, right, Like, black holes can gobble mass

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Speaker 2: and energy almost as much as it wants, as far

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Speaker 2: as we know, right.

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Speaker 1: Yeah, there's no theoretical limit to the mass that black

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Speaker 1: hole can have. There's some practical limits there because they

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Speaker 1: have to actually absorb the stuff and has to fall

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Speaker 1: in at the right angle, and sometimes black holes can

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Speaker 1: create conditions that repel the stuff around them. So practically speaking,

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Speaker 1: there does seem to be a limit to how big

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Speaker 1: black holes have gotten in our universe. But Theoretically, there's

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Speaker 1: no limit to how big a black hole can get.

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Speaker 1: It can be billions of solar masses. It could be

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Speaker 1: trillions of solar masses. It could be quadrillions of solar masses.

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Speaker 1: It can keep inventing metric pre fixes, and black holes

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Speaker 1: could theoretically grow to be that large. But that's not

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Speaker 1: the same for a black holes spin or for a

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Speaker 1: black hole's charge. As these black holes get more and

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Speaker 1: more charged, that they get weird and they start to

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Speaker 1: border on breaking the rules.

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Speaker 2: Of general relativity, and then they get charged with the

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Speaker 2: crime of breaking the rules. That's right, and they go

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Speaker 2: to physics jail, But they're tracked with physicist dads for

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Speaker 2: the rest of their existence, telling them bad dad jokes.

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Speaker 1: That's a terrible punishment. Absolutely, yeah, No, The punishment for

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Speaker 1: going to physics jail is that you puff out of existence. Right.

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Speaker 1: Going to physics jails means you've broken a law of

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Speaker 1: the universe and therefore you no longer exist.

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Speaker 2: It seems kind of harsh.

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Speaker 1: Hey, everybody knows the rules. These are just the consequences

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Speaker 1: of your actions, man, But.

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Speaker 2: Don't you need to know the law before? I guess

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Speaker 2: you can break the law? Without knowing it and still

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Speaker 2: be guilty. It seems a little unfair.

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Speaker 1: Well, maybe people should listen to this podcast. We'll educate

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Speaker 1: them about what the laws of physics are so they

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Speaker 1: can avoid breaking the rules and go into physics jail.

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Speaker 2: No, no, then we're we're live, Daniel. They might sue

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Speaker 2: us for, you know, not telling them the full story.

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Speaker 1: Well, anybody who's broken the laws no longer exists, so

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Speaker 1: they can't sue us.

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Speaker 2: Oh yeah, that's true too.

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Speaker 1: Well.

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Speaker 2: As usually, we were wondering how many people out there

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Speaker 2: had thought about this question of whether black holes can

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Speaker 2: have a maximum electric charge.

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Speaker 1: So thanks very much to all of you who volunteer

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Speaker 1: to answer these questions. We really appreciate it. And if

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Speaker 1: you would like to hear your voice on the podcast

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Speaker 1: in the future, please don't be shy. Write to me

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Speaker 1: two questions at Danielandjorge dot com and I will set

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Speaker 1: you up.

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Speaker 2: So think about it for a second. Do you think

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Speaker 2: black holes can have a maximum electric charge? Here's what

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Speaker 2: people have to say.

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Speaker 3: I do not think that a black hole would have

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Speaker 3: a maximum electrical charge. I think it would all be

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Speaker 3: dependent on how big it is, so I would think

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Speaker 3: that the bigger the black hole is, the more the higher,

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Speaker 3: like the maximum electrical charge would be.

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Speaker 4: I would have thought that a black hole would remain

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Speaker 4: roughly neutral or probably no theoretical limit to the charge

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Speaker 4: it could have. I do wonder if a high charge

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Speaker 4: black hole could discharge with some sort of lightning. Perhaps.

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Speaker 2: If black holes can grow indefinitely, then maybe they can

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Speaker 2: grow their electric charge indefinitely as well. All Right, a

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Speaker 2: pretty interesting range of answers. Some people said maybe, some

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Speaker 2: people said probably not, and some people said it depends.

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Speaker 1: I feel like these are all leaning towards the direction

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Speaker 1: that black holes could have an arbitrary charge.

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Speaker 2: M Yeah, because I guess that makes sense, right, Like,

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Speaker 2: if it can eat an infinite amount of mass, why

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Speaker 2: can it have an infinite amount of charge.

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Speaker 1: Well, as we'll see, mass in charge are different, right,

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Speaker 1: Mass tends to accumulate more mass and create more attractive gravity.

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Speaker 1: It's not the same thing with electric charge, right. Electric

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Speaker 1: charge can do things that mass can't do, like it

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Speaker 1: can repel other charges. So it gets to be quite complicated.

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Speaker 2: Well, they gat to it, Daniel. Let's recap what a

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Speaker 2: black hole is again.

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Speaker 1: The basic idea of a black hole and what we

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Speaker 1: need to understand for today's episode is that it's a

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Speaker 1: region of space where particles can never escape. So we

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Speaker 1: talk about this thing called the event horizon, behind which

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Speaker 1: things are hidden forever. What the event horizon really means

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Speaker 1: is that there's a region of space that if a

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Speaker 1: particle enters it, it will never leave. Like if you

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Speaker 1: fast forward to the infinite future of the universe, that

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Speaker 1: particle never escapes the event horizon. It's not like literally

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Speaker 1: a physical barrier in that sense. It's just a region

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Speaker 1: you draw in space and say, by the way we've

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Speaker 1: done the calculation, anything that enters here never leaves. And

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Speaker 1: the reason is that space time is curved so much

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Speaker 1: by the mass of the center that the particles never escape.

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Speaker 1: And it's important to understand that the event horizon is

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Speaker 1: not something you can ever exactly say where it is

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Speaker 1: right now. In order to really know where the event

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Speaker 1: horizon is, you have to kind of do that calculation

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Speaker 1: out to the future infinity and say, oh, these particles

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Speaker 1: never escape, but those particles do escape.

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Speaker 2: But you can take a picture of a black hole,

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Speaker 2: wouldn't that kind of tell you the size of it

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Speaker 2: and to what extent the black part of the black

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Speaker 2: hole is.

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Speaker 1: Yeah, you can take a picture of a black hole,

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Speaker 1: and we've done it. We have a couple of really

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Speaker 1: cool images, and you can see a ring of gas

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Speaker 1: around it, and then at the center you see an

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Speaker 1: area that isn't emitting any light. What I'm saying is that,

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Speaker 1: mathematically speaking, or most technically in general relativity, the region

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Speaker 1: around the black hole that we call the event horizon

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Speaker 1: is something you can only ever determine, sort of like

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Speaker 1: in the infinite future of the universe. Like, even if

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Speaker 1: you're looking at the black hole and you see no

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Speaker 1: light emitted from it, that doesn't mean that there isn't

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Speaker 1: like some path for a photon to like graze just

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Speaker 1: within it and eventually make it out. You sort of

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Speaker 1: like can't call it the event horizon until all those

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Speaker 1: particles have had their chance to escape and you can

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Speaker 1: say which ones made it and which ones can't.

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Speaker 2: All right, So then it's a region of space where

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Speaker 2: nothing can get out, not even light. But there's some

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Speaker 2: debate about what's exactly at the center of a black

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Speaker 2: hole and whether or not it's possible for something to

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Speaker 2: be at the middle, or maybe it's fuzzier than people think.

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Speaker 1: Exactly in general relativity, we have this picture of the

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Speaker 1: interior of a black hole is being very very curved

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Speaker 1: in space time, which means everything falls towards the center.

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Speaker 1: In fact, space time is so distorted that, like the

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Speaker 1: timelike coordinate for these things, the future path of everything

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Speaker 1: is just to head towards the center of the black hole,

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Speaker 1: and that creates sort of a runaway condition where it

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Speaker 1: gets more curved, and then things fall further in, which

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Speaker 1: makes it more curved, and so things fall in no

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Speaker 1: stopping it, and so eventually it just all coalesces into

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Speaker 1: the densest possible point. In general relativity, we call this

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Speaker 1: a singularity, and nobody knows if a singularity is real

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Speaker 1: or if there are really singularities inside black holes. I

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Speaker 1: think if you pulled a bunch of physicists, something like

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Speaker 1: ninety nine percent of them would say singularities are not real,

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Speaker 1: that this picture from general relativity is sort of like

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Speaker 1: an indication that the theory has broken down, not like

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Speaker 1: an actual physical prediction the singularities.

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Speaker 2: Are there, right, But I guess it maybe depends on

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Speaker 2: how you define a black hole, like is the black

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Speaker 2: hole the region of space within the event horizon, or

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Speaker 2: do you only call a black hole the singularity in

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Speaker 2: the middle.

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Speaker 1: Well, we can never observe anything within it. So I

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Speaker 1: think the operational definition of the black hole is something

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Speaker 1: that creates an event horizon, and then there's a question

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Speaker 1: of what's inside it, what has created that event horizon,

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Speaker 1: and general relativity says, actually, any equal distribution of mass

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Speaker 1: within the event horizon would cause a black hole. It's

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Speaker 1: just that general relativity predicts that distribution of mass will

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Speaker 1: collapse into a singularity. Other theories predict that it won't

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Speaker 1: predict that. You have other sorts of weird states, like

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Speaker 1: quantum mechanics says you can't have a singularity. It's too

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Speaker 1: much information concentrated at one point. You know the location,

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Speaker 1: you know the energy. It's just it violates the basic

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Speaker 1: laws of quantum mechanics, and so various theories of quantum

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Speaker 1: gravity predict like weird fuzzy blobs at the hearts of

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Speaker 1: black holes. But the truth is we don't know, and

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Speaker 1: we'd love to know, because that would help us build

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Speaker 1: a deeper theory of the unit. It would help us

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Speaker 1: understand how to unify quantum mechanics and general relativity. But frustratingly,

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Speaker 1: those answers are all hidden within the black hole.

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Speaker 2: Right, Like inside of the black hole, everything could be

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Speaker 2: bunched up in the middle of the black hole, or

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Speaker 2: maybe things are more evenly spread out, or maybe it's

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Speaker 2: in some kind of fun, interesting flowery pattern of stuff

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Speaker 2: inside of the black hole.

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Speaker 1: Right. Yeah, we have theories of like fuzzballs from string theory.

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Speaker 1: We have theories of gravitationally slowed down collapsing stars. We

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Speaker 1: have theories where a black hole will eventually turn into

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Speaker 1: a white hole. There's many, many theories for what might

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Speaker 1: be happening inside them. The reality of what's happening inside

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Speaker 1: there is probably something even weird or something that no

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Speaker 1: existing human physicist has imagined. If we could crack these

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Speaker 1: things open and see what was inside, probably we would

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Speaker 1: all be shocked. It'd be one of those delicious moments

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Speaker 1: of science when we're like, what is going on? That's impossible,

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Speaker 1: And then of course we'd be scrambling to come up

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Speaker 1: with explanations. But those explanations would give us the clue

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Speaker 1: is to like, what's really happening. What space really is

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Speaker 1: deep down is space a bunch of quantum things that

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Speaker 1: have woven themselves together to make the universe or is

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Speaker 1: something else going on?

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Speaker 2: Yeah, and I guess the problem is that, you know,

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Speaker 2: you can't study what's inside of a black hole because

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Speaker 2: if you ever get inside of a black hole, you're

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Speaker 2: never getting out. Or even if you can send a

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Speaker 2: robot or something, the robot can send a signal because nothing,

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Speaker 2: not even radio ways or light can escape the black hole. Right,

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Speaker 2: that's the main problem.

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Speaker 1: That is the main problem. But fortunately black holes are

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Speaker 1: more complex than this picture. What we've talked about so

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Speaker 1: far is basically just a dot of mass. It's not spinning,

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Speaker 1: it doesn't have electric charge, it's just mass. And so

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Speaker 1: in general relativity you call this a short style black hole.

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Speaker 1: It's like the simplest possible model of a black hole.

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Speaker 1: But we don't think that any of the black holes

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Speaker 1: actually out there in the universe are like this. We

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Speaker 1: think it's more likely that black holes have a little

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Speaker 1: bit of charge and maybe even have a lot of

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Speaker 1: spin that can really change what happens to a part

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Speaker 1: of that comes near the black hole in sort of

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Speaker 1: surprising ways, especially if the black hole ends up with

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Speaker 1: a lot of charge.

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Speaker 2: Interesting. So, usually people think of black holes as just

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Speaker 2: absorbing mass, but maybe when it absorbs other things like

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Speaker 2: charge or the spin of things. Maybe the picture changes,

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Speaker 2: and so let's get into what those changes could be

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Speaker 2: and whether or not divide. Let us open a black hole,

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Speaker 2: but first, let's take a quick break. Or are we're

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Speaker 2: talking about black holes and whether or not they have

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Speaker 2: a maximum electric charge. I wonder if black holes have

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Speaker 2: like a little battery meter to tell you when they're

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Speaker 2: fully charged, or maybe they do, but you just can't

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Speaker 2: see it because it's a black hole.

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Speaker 1: I think if you overcharge a black hole, either you

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Speaker 1: or the black hole or both might have to go

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Speaker 1: to physics jail.

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Speaker 2: Wait, why would the why would the black hole have

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Speaker 2: to go to jail too? I mean, wouldn't it be

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Speaker 2: the victim in this case because it was overcharged?

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Speaker 1: You're right, it's totally not fair, but it would be

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Speaker 1: the one breaking the rules. General relativity tells us that

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Speaker 1: if you put too much charge in a black hole, weird, surprising,

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Speaker 1: nonsense things might happen.

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Speaker 2: Mm. But I guess the question is who's going to

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Speaker 2: put the black hole in handcuffs? Is there physics police

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Speaker 2: that is gravity proof?

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Speaker 1: If there's physics police out there, I hope they're not

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Speaker 1: policing my physics. Dad jokes, because then I am.

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Speaker 2: In trouble, you'll get multiple life sentences. I'll do more physics.

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Speaker 1: I hope to get off relatively lightly.

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Speaker 2: Well, we know that if a black hole is a

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Speaker 2: regional's face or nothing can escape, not even light, and

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Speaker 2: so it's really hard to look inside of them. But

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Speaker 2: only if you consider mask going into a black hole.

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Speaker 2: If you consider other things going into a black hole,

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Speaker 2: the picture changes, maybe to the point where you can

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Speaker 2: open a black hole. So let's talk about some of

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Speaker 2: these other things that can go in. One of them

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Speaker 2: was a spin that's right. When we calculate the radius

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Speaker 2: of the event horizon, our prediction for the region of

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Speaker 2: space where if you enter it you're trapped forever. That

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Speaker 2: calculation is pretty simple if the black hole.

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Speaker 1: Only has mass, right, if it's just a dot of

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Speaker 1: stuff and it's not spinning, so that's the short styled

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Speaker 1: black hole. But if the stuff is spinning, and the

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Speaker 1: calculation is a little bit more complicated, we call this

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Speaker 1: a curb black hole KERR, and it has a different

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Speaker 1: event horizon, like the radius of the event horizon of

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Speaker 1: a spinning black hole is different from the radius of

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Speaker 1: the event horizon of a black hole with the same mass,

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Speaker 1: but that's not spinning. And you might ask like, well,

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Speaker 1: how can black hole spin? What can you do to

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Speaker 1: spin a black hole? Well, you know, angular momentum in

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Speaker 1: the universe is conserved, and so if something hits the

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Speaker 1: black hole with angular momentum, the black hole is going

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Speaker 1: to have angular momentum. The same way if your friend

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Speaker 1: pushes you, but they don't push you straight on, they

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Speaker 1: push you like on your shoulder, it could spin you around.

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Speaker 1: If an electron falls into the black hole but doesn't

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Speaker 1: fall straight in, if it falls like a little bit

442
00:20:57,760 --> 00:20:59,800
Speaker 1: to the side, then it's going to push the black

443
00:20:59,800 --> 00:21:01,600
Speaker 1: hole a little bit and get it spinning.

444
00:21:01,760 --> 00:21:04,080
Speaker 2: Interesting, that's a weird picture to think of a black

445
00:21:04,119 --> 00:21:06,600
Speaker 2: hole spinning, Like can a hole spin? What would it

446
00:21:06,640 --> 00:21:08,399
Speaker 2: mean for a hole to spin? Does that mean that

447
00:21:08,440 --> 00:21:11,520
Speaker 2: the event horizon is spinning or just that the things

448
00:21:11,640 --> 00:21:14,400
Speaker 2: inside of the black hole have kind of a general

449
00:21:14,560 --> 00:21:15,119
Speaker 2: spin to it.

450
00:21:15,200 --> 00:21:18,240
Speaker 1: Yeah, the event horizon is not itself a physical thing, right,

451
00:21:18,280 --> 00:21:20,600
Speaker 1: it's a distance from the center, So in that sense,

452
00:21:20,680 --> 00:21:23,840
Speaker 1: that part doesn't spin, but the mass inside the black

453
00:21:23,880 --> 00:21:27,680
Speaker 1: hole is spinning. Now, a singularity a dot in space

454
00:21:27,720 --> 00:21:30,960
Speaker 1: that has no extent that can't spin. Right, A true

455
00:21:31,240 --> 00:21:34,840
Speaker 1: singularity with no volume can't have any spin because spin

456
00:21:34,960 --> 00:21:39,760
Speaker 1: requires some length. So inside a black hole that is spinning,

457
00:21:39,760 --> 00:21:42,840
Speaker 1: we don't think there is a singularity. General relativity predicts

458
00:21:42,880 --> 00:21:46,879
Speaker 1: something else. It predicts a ringularity, a little ring of

459
00:21:47,000 --> 00:21:50,520
Speaker 1: singularities that's spinning. So that's what's sort of like keeping

460
00:21:50,560 --> 00:21:52,960
Speaker 1: the spin alive. That the event horizon you can still

461
00:21:53,000 --> 00:21:56,359
Speaker 1: calculate at some radius, and the space around the black

462
00:21:56,359 --> 00:21:59,639
Speaker 1: hole now gets weird. You get frame dragging effects. So

463
00:21:59,640 --> 00:22:01,840
Speaker 1: we've talked about a few times on the podcast. So

464
00:22:01,880 --> 00:22:05,040
Speaker 1: in Einsteiny and gravity, it matters whether something is spinning

465
00:22:05,200 --> 00:22:07,480
Speaker 1: or not. You have a different gravitational effect.

466
00:22:08,200 --> 00:22:10,800
Speaker 2: So if your black hole is spinning, it doesn't have

467
00:22:10,840 --> 00:22:14,680
Speaker 2: a singularity in the middle like a point you're saying,

468
00:22:14,680 --> 00:22:16,200
Speaker 2: it has like a weird.

469
00:22:16,000 --> 00:22:17,920
Speaker 1: Ring, Yeah, a ringularity.

470
00:22:18,160 --> 00:22:20,679
Speaker 2: So then does the event horizon also change shape or

471
00:22:20,800 --> 00:22:21,840
Speaker 2: is it still a sphere.

472
00:22:22,000 --> 00:22:24,440
Speaker 1: The event horizon itself is still a sphere, but now

473
00:22:24,440 --> 00:22:26,879
Speaker 1: you have a region around the event horizon called the

474
00:22:27,119 --> 00:22:30,280
Speaker 1: ergosphere where things get weird. We talked to once in

475
00:22:30,320 --> 00:22:33,320
Speaker 1: a podcast about whether you can extract energy from black holes,

476
00:22:33,480 --> 00:22:35,880
Speaker 1: and in this ergosphere, which is sort of a doughnut

477
00:22:35,880 --> 00:22:38,320
Speaker 1: shaped region around the black hole. The black hole will

478
00:22:38,320 --> 00:22:41,200
Speaker 1: make things spin in a weird way, and you can

479
00:22:41,280 --> 00:22:44,040
Speaker 1: use that to extract energy from the black hole. So

480
00:22:44,119 --> 00:22:46,640
Speaker 1: a spinning black hole has sort of two different regions.

481
00:22:46,720 --> 00:22:49,400
Speaker 1: Is this spherical event horizon and then there's this doughnut

482
00:22:49,520 --> 00:22:51,720
Speaker 1: shaped ergosphere around it.

483
00:22:51,640 --> 00:22:54,280
Speaker 2: Where space time is curved differently or is it all

484
00:22:54,320 --> 00:22:57,320
Speaker 2: still curved like a sphere? Like what does this ergo

485
00:22:57,520 --> 00:22:58,000
Speaker 2: sphere do?

486
00:22:58,280 --> 00:23:01,600
Speaker 1: So space time is different inside the ergosphere and not

487
00:23:01,760 --> 00:23:04,399
Speaker 1: inside the ergosphere, and it's different in this sort of

488
00:23:04,400 --> 00:23:07,159
Speaker 1: a complicated way. It's always, of course pointing towards the

489
00:23:07,200 --> 00:23:09,119
Speaker 1: black hole. If you're in the ergosphere, you're going to

490
00:23:09,160 --> 00:23:11,560
Speaker 1: feel a gravitational pull towards the black hole. But if

491
00:23:11,600 --> 00:23:14,600
Speaker 1: you're in the ergosphere, you also feel other effects because

492
00:23:14,600 --> 00:23:17,280
Speaker 1: space time has this frame dragging thing happening to it,

493
00:23:17,320 --> 00:23:19,920
Speaker 1: which is sort of counterintuitive because we think of gravity

494
00:23:19,960 --> 00:23:22,919
Speaker 1: as like just attractive it just pulls you towards stuff.

495
00:23:22,960 --> 00:23:25,919
Speaker 1: But this frame dragging effect can actually also create a spin.

496
00:23:26,520 --> 00:23:29,720
Speaker 1: Remember that we've measured this frame dragging effect using gravity

497
00:23:29,800 --> 00:23:33,440
Speaker 1: Probe B. This satellite that orbits the Earth with super

498
00:23:33,560 --> 00:23:37,119
Speaker 1: hyper precise gyroscopes that measure these kinds of spins. So

499
00:23:37,160 --> 00:23:40,960
Speaker 1: if you're within the ergosphere or near any spinning object,

500
00:23:41,280 --> 00:23:43,199
Speaker 1: Einstein says, you're going to get a little bit of

501
00:23:43,200 --> 00:23:44,720
Speaker 1: a twist as well as a pole.

502
00:23:45,400 --> 00:23:48,040
Speaker 2: Interesting. Now, let's talk about charge, because you said you

503
00:23:48,080 --> 00:23:50,399
Speaker 2: can also change the properties of a black hole by

504
00:23:50,560 --> 00:23:53,520
Speaker 2: throwing in charge. And this happens when you throw in

505
00:23:53,640 --> 00:23:56,159
Speaker 2: charge objects into the black hole, like electrons. If you

506
00:23:56,200 --> 00:23:58,679
Speaker 2: throw an electron in the black hole is going to

507
00:23:58,760 --> 00:23:59,960
Speaker 2: gain a negative charge.

508
00:24:00,160 --> 00:24:02,359
Speaker 1: Yeah, so you take a black hole and you toss

509
00:24:02,400 --> 00:24:05,439
Speaker 1: in an electron, it'll happily gobble it up. But that

510
00:24:05,560 --> 00:24:08,680
Speaker 1: charge doesn't just go away. Right, the electron had an

511
00:24:08,680 --> 00:24:11,639
Speaker 1: electric field, and just before it fell into the black hole,

512
00:24:11,800 --> 00:24:14,080
Speaker 1: there was an electric field there. Now that electron has

513
00:24:14,119 --> 00:24:18,040
Speaker 1: gone inside the black hole, there's still an electric field there. Right,

514
00:24:18,040 --> 00:24:21,200
Speaker 1: it's sort of frozen in time from the last moment

515
00:24:21,400 --> 00:24:24,680
Speaker 1: just before the electron crossed the event horizon. No more

516
00:24:24,720 --> 00:24:27,680
Speaker 1: information can update it. Like what the electron does within

517
00:24:27,760 --> 00:24:30,840
Speaker 1: the event horizon can't change the electric field. And so

518
00:24:30,840 --> 00:24:32,840
Speaker 1: there's an electric field there, and you can ask like, well,

519
00:24:32,840 --> 00:24:35,359
Speaker 1: where does that come from? Well, the whole black hole

520
00:24:35,560 --> 00:24:37,480
Speaker 1: now has an electric charge.

521
00:24:37,680 --> 00:24:40,080
Speaker 2: Like from a distance, if you were to see a

522
00:24:40,160 --> 00:24:42,880
Speaker 2: black hole up ahead of you, you would suddenly deteg

523
00:24:43,480 --> 00:24:45,600
Speaker 2: that it's a little bit more negatively charged, right Like

524
00:24:45,640 --> 00:24:47,359
Speaker 2: if you had a magnet, it would be a little

525
00:24:47,359 --> 00:24:49,320
Speaker 2: bit more attracted to it. Perhaps if you had a

526
00:24:49,320 --> 00:24:52,800
Speaker 2: positive charge, you'd feel more of a pull towards the

527
00:24:52,840 --> 00:24:53,960
Speaker 2: black hole exactly.

528
00:24:54,000 --> 00:24:56,960
Speaker 1: And the super weird thing is, think about what happens

529
00:24:57,000 --> 00:24:59,400
Speaker 1: to the next electron. So you have like a bag

530
00:24:59,440 --> 00:25:01,560
Speaker 1: full of electric as you throw one in, Now your

531
00:25:01,560 --> 00:25:04,320
Speaker 1: black hole has a negative charge. Now electron number two,

532
00:25:04,359 --> 00:25:07,280
Speaker 1: what happens to it, Well, it feels a gravitational attraction

533
00:25:07,680 --> 00:25:09,520
Speaker 1: from the mass of the black hole, but now it

534
00:25:09,520 --> 00:25:13,720
Speaker 1: feels an electrostatic repulsion from the charge of the black hole.

535
00:25:14,160 --> 00:25:16,440
Speaker 1: The black hole is negatively charged, so just like the

536
00:25:16,480 --> 00:25:19,840
Speaker 1: electron that fell in, it's going to repel electron number two.

537
00:25:19,920 --> 00:25:22,520
Speaker 1: So electron number two feels an attraction towards a black

538
00:25:22,520 --> 00:25:25,160
Speaker 1: hole and a repulsion as well.

539
00:25:25,240 --> 00:25:28,240
Speaker 2: Right. Interesting, It's sort of like if you are collecting

540
00:25:28,280 --> 00:25:31,240
Speaker 2: electrons in your pocket. At some point it'd be harder

541
00:25:31,280 --> 00:25:33,920
Speaker 2: to throw another electron in because you have so much

542
00:25:33,920 --> 00:25:36,720
Speaker 2: a negative charge in your pocket. That adding another electrical

543
00:25:37,040 --> 00:25:39,160
Speaker 2: negative charge would be hard to.

544
00:25:39,080 --> 00:25:41,159
Speaker 1: Do exactly, And this is why I mentioned earlier like

545
00:25:41,560 --> 00:25:45,080
Speaker 1: mass and charge are different. Mass just attracts itself. The

546
00:25:45,080 --> 00:25:47,040
Speaker 1: more mass you have, the more mass you're attracted to,

547
00:25:47,359 --> 00:25:50,800
Speaker 1: the more it pulls on other masses. But charge is different. Right,

548
00:25:50,840 --> 00:25:53,800
Speaker 1: if something accumulates a lot of negative electric charge, it

549
00:25:53,840 --> 00:25:56,919
Speaker 1: will then repel other things with negative electric charge, and

550
00:25:56,960 --> 00:26:00,240
Speaker 1: that has a really important consequence for where the event

551
00:26:00,280 --> 00:26:03,080
Speaker 1: horizon is. If you try to solve all equations and calculate, like, well,

552
00:26:03,119 --> 00:26:05,919
Speaker 1: where is the event horizon for a black hole with

553
00:26:06,080 --> 00:26:08,720
Speaker 1: or without an electric charge? You discover that a black

554
00:26:08,720 --> 00:26:12,200
Speaker 1: hole with an electric charge has a smaller event horizon.

555
00:26:12,400 --> 00:26:15,600
Speaker 2: Well, it's only pushing away other negative electric charges. But

556
00:26:15,760 --> 00:26:19,760
Speaker 2: like for if you're a positron or a positively charged particle,

557
00:26:19,960 --> 00:26:24,119
Speaker 2: now your really negative black hole is more attractive. So

558
00:26:24,119 --> 00:26:27,960
Speaker 2: it wouldn't the event horizon grow for a positively charged particle.

559
00:26:28,080 --> 00:26:30,880
Speaker 1: Well not exactly. There are two things going on here

560
00:26:30,920 --> 00:26:35,359
Speaker 1: at once. First, the event horizon radius does depend on

561
00:26:35,520 --> 00:26:38,879
Speaker 1: the charge of the black hole. Right, as the charge

562
00:26:38,920 --> 00:26:42,640
Speaker 1: of the black hole increases, the radius shrinks, and we're

563
00:26:42,680 --> 00:26:45,960
Speaker 1: tempted to say that that's because of the electromagnetic force

564
00:26:46,320 --> 00:26:49,920
Speaker 1: from the charge now working against gravity, right, gravity pulling

565
00:26:49,960 --> 00:26:53,359
Speaker 1: things in and the electromagnetic force pushing things away. But

566
00:26:53,400 --> 00:26:55,679
Speaker 1: that's not actually what's happening when it comes to the

567
00:26:55,680 --> 00:26:58,639
Speaker 1: event horizon. If it were, it would mean that the

568
00:26:58,680 --> 00:27:02,959
Speaker 1: event horizon would be different for different charges of particles. Positive,

569
00:27:03,040 --> 00:27:06,439
Speaker 1: neutral or negative particles would see different event horizons. But

570
00:27:06,560 --> 00:27:09,760
Speaker 1: it isn't. It shrinks the event horizon for all particles,

571
00:27:09,880 --> 00:27:14,040
Speaker 1: regardless of charge. And unfortunately there's not a very simple

572
00:27:14,119 --> 00:27:17,080
Speaker 1: intuitive way to understand that. I actually talk to a

573
00:27:17,160 --> 00:27:19,800
Speaker 1: bunch of GR experts, and the best I can do

574
00:27:19,960 --> 00:27:21,800
Speaker 1: is to tell you that the size of the black

575
00:27:21,840 --> 00:27:26,639
Speaker 1: hole is affected by the electromagnetic energy that's inside the

576
00:27:26,680 --> 00:27:29,520
Speaker 1: event horizon. But it's not in a simple way. Remember

577
00:27:29,520 --> 00:27:32,560
Speaker 1: that GR is based on the stress energy tensor, and

578
00:27:32,600 --> 00:27:35,280
Speaker 1: it's not just that more energy means more curvature. It's

579
00:27:35,359 --> 00:27:38,040
Speaker 1: quite complicated, and in the end, the greater the charge,

580
00:27:38,080 --> 00:27:41,320
Speaker 1: the smaller the event horizon. But the second thing is

581
00:27:41,320 --> 00:27:44,520
Speaker 1: that the black hole charge does push or pull on

582
00:27:44,680 --> 00:27:48,480
Speaker 1: particles outside the event horizon, and that does depend on

583
00:27:48,600 --> 00:27:51,639
Speaker 1: the charge of the particle. So a negatively charged black

584
00:27:51,640 --> 00:27:55,879
Speaker 1: hole can resist negative particles from ever crossing over the

585
00:27:55,920 --> 00:27:59,959
Speaker 1: event horizon, and it can accelerate positively charged particles towards it.

586
00:28:00,040 --> 00:28:02,280
Speaker 1: The event horizon is the same for all of them,

587
00:28:02,640 --> 00:28:05,240
Speaker 1: but the black hole charge can prevent some particles from

588
00:28:05,240 --> 00:28:08,080
Speaker 1: crossing it, or it can assist them. What I think

589
00:28:08,160 --> 00:28:11,440
Speaker 1: is super fascinating is that the event horizon is shrinking

590
00:28:11,520 --> 00:28:14,800
Speaker 1: as the charge grows. So you toss in an electron

591
00:28:14,840 --> 00:28:17,760
Speaker 1: and the event horizon shrinks, and then if you cram

592
00:28:17,880 --> 00:28:21,639
Speaker 1: another electron in there, the event horizon shrinks further, and

593
00:28:21,720 --> 00:28:23,680
Speaker 1: so you can keep going. You keep going, and there's

594
00:28:23,680 --> 00:28:27,480
Speaker 1: a point where you have so much charge that essentially

595
00:28:27,520 --> 00:28:29,000
Speaker 1: you erase the event horizon.

596
00:28:29,119 --> 00:28:32,440
Speaker 2: WHOA, Okay, Now I think you're imagining a scenario where

597
00:28:32,480 --> 00:28:35,600
Speaker 2: you only put electrons, Like you make a black hole

598
00:28:35,640 --> 00:28:38,920
Speaker 2: out of electrons, and you only put more electrons in it,

599
00:28:39,000 --> 00:28:41,040
Speaker 2: and then you ask, what does that black hole look

600
00:28:41,120 --> 00:28:44,520
Speaker 2: like to another electron? So, now, like, if you do

601
00:28:44,560 --> 00:28:47,160
Speaker 2: the math, does it work out that it does erase

602
00:28:47,200 --> 00:28:49,640
Speaker 2: the black hole to an electron? Because I imagine if

603
00:28:49,640 --> 00:28:52,320
Speaker 2: there's a singularity in the middle of the black hole,

604
00:28:52,680 --> 00:28:55,000
Speaker 2: then you sort of can't beat a singularity, can you.

605
00:28:55,960 --> 00:28:58,200
Speaker 1: That's exactly the question, right, And so people have been

606
00:28:58,200 --> 00:29:01,840
Speaker 1: doing these kinds of calculations, and according to general relativity,

607
00:29:02,040 --> 00:29:05,560
Speaker 1: there's a maximum charge that a black hole can have,

608
00:29:06,160 --> 00:29:09,240
Speaker 1: and if you manage somehow to give it more charge

609
00:29:09,320 --> 00:29:12,880
Speaker 1: than that, then effectively there will be no event horizon.

610
00:29:13,040 --> 00:29:18,080
Speaker 1: You've removed the event horizon. You revealed the singularity. Like

611
00:29:18,120 --> 00:29:21,000
Speaker 1: you sit down and do the calculations. The radius of

612
00:29:21,040 --> 00:29:23,880
Speaker 1: the event horizon depends on the mass enclosed in the

613
00:29:23,920 --> 00:29:26,720
Speaker 1: black hole and on the charge of it. And if

614
00:29:26,720 --> 00:29:29,800
Speaker 1: the charge gets above a certain number relative to the mass,

615
00:29:29,960 --> 00:29:33,120
Speaker 1: then there's no solution. Right. As the charge grows, the

616
00:29:33,200 --> 00:29:35,680
Speaker 1: radis event horizon shrinks and shrinks and shrinks and shrinks,

617
00:29:35,760 --> 00:29:38,400
Speaker 1: until eventually it's at zero. And that's what we call

618
00:29:38,440 --> 00:29:41,840
Speaker 1: the maximum charge the extremal black hole. And if you

619
00:29:41,920 --> 00:29:46,440
Speaker 1: somehow added another electron to that, nobody knows what would happen, Right,

620
00:29:46,480 --> 00:29:49,000
Speaker 1: would you get a naked singularity? Would we all go

621
00:29:49,080 --> 00:29:52,080
Speaker 1: to physics jail? Nobody knows. Let's find out.

622
00:29:52,320 --> 00:29:55,400
Speaker 2: Well, I guess I imagine the math is complicated because

623
00:29:55,440 --> 00:29:58,520
Speaker 2: an electron also has mass. Right, So if you throw

624
00:29:58,560 --> 00:30:01,080
Speaker 2: an electron into a black hole. Well, you are increasing

625
00:30:01,120 --> 00:30:03,560
Speaker 2: the mass of the black hole, making it more of

626
00:30:03,560 --> 00:30:06,520
Speaker 2: a whole, but you're also making it more repellent to

627
00:30:06,600 --> 00:30:09,080
Speaker 2: other electrons. And you're saying that the way it works

628
00:30:09,120 --> 00:30:12,120
Speaker 2: out is that electrons maybe have more charge than they

629
00:30:12,160 --> 00:30:14,600
Speaker 2: have mass, and so therefore if you make a black

630
00:30:14,600 --> 00:30:16,880
Speaker 2: hole out of just electrons, it is going to repel

631
00:30:16,960 --> 00:30:17,720
Speaker 2: other electrons.

632
00:30:17,800 --> 00:30:19,480
Speaker 1: Yeah, there's sort of two parts of the question. One

633
00:30:19,560 --> 00:30:22,720
Speaker 1: is like, assume that somehow you can get enough electrons

634
00:30:22,760 --> 00:30:25,200
Speaker 1: in there, what would happen? And the answer to that

635
00:30:25,280 --> 00:30:28,640
Speaker 1: question is nobody knows. Right, nobody knows what would happen.

636
00:30:28,760 --> 00:30:31,840
Speaker 1: It predicts basically a naked singularity. And there's been a

637
00:30:31,840 --> 00:30:34,720
Speaker 1: lot of discussion in theoretical physics for a long time

638
00:30:34,800 --> 00:30:38,320
Speaker 1: about like, hmm, this seems weird. Would the universe actually

639
00:30:38,320 --> 00:30:42,240
Speaker 1: allow this or would something stop it? And Roger Penrose

640
00:30:42,240 --> 00:30:45,800
Speaker 1: has this idea called the cosmic censorship hypothesis that says

641
00:30:46,080 --> 00:30:48,160
Speaker 1: something is going to intervene. There must be a reason

642
00:30:48,200 --> 00:30:51,320
Speaker 1: why this is impossible, because you can't have a singularity

643
00:30:51,400 --> 00:30:55,320
Speaker 1: just out in space. Naked singularity is like an anathema

644
00:30:55,440 --> 00:30:58,600
Speaker 1: to particle physicists or to theoretical physicists, so they imagine

645
00:30:58,680 --> 00:31:01,680
Speaker 1: something must prevent from happening. And then the other question,

646
00:31:01,800 --> 00:31:04,200
Speaker 1: the second question, or the other part of it, is

647
00:31:04,560 --> 00:31:08,080
Speaker 1: could you actually ever create this situation? Is there something

648
00:31:08,120 --> 00:31:11,680
Speaker 1: preventing us? What could be preventing us from getting enough

649
00:31:11,680 --> 00:31:13,720
Speaker 1: electric charges altogether, all at once?

650
00:31:14,120 --> 00:31:17,280
Speaker 2: But again, I feel like this is only if you're

651
00:31:17,320 --> 00:31:20,720
Speaker 2: an electron. The black hole disappears only if you're an electron.

652
00:31:20,960 --> 00:31:24,640
Speaker 2: But like, light still can't escape this all electron black hole,

653
00:31:24,720 --> 00:31:28,960
Speaker 2: right because light is neutral, Right, Like light doesn't carry

654
00:31:28,960 --> 00:31:30,480
Speaker 2: you have a lot of negative charge in it.

655
00:31:30,520 --> 00:31:33,840
Speaker 1: The black hole charge only affects charged particles on the

656
00:31:33,920 --> 00:31:37,840
Speaker 1: outside of the event horizon, so it prevents more electrons

657
00:31:37,880 --> 00:31:41,320
Speaker 1: from falling in, but it doesn't prevent photons or protons

658
00:31:41,560 --> 00:31:44,560
Speaker 1: or other positively charged particles from falling in. But remember

659
00:31:44,600 --> 00:31:47,080
Speaker 1: that the event horizon is the event horizon, and the

660
00:31:47,200 --> 00:31:49,960
Speaker 1: radius of the event horizon is the same for all

661
00:31:50,000 --> 00:31:53,200
Speaker 1: particles charged or neutral. Having a charge on the black

662
00:31:53,200 --> 00:31:56,560
Speaker 1: hole shrinks the event horizon for all particles.

663
00:31:56,920 --> 00:31:59,280
Speaker 2: But if you were I think maybe the point is

664
00:31:59,280 --> 00:32:01,600
Speaker 2: that if something has a negative electric charge, it could

665
00:32:01,640 --> 00:32:04,880
Speaker 2: maybe escape what we see as the black hole.

666
00:32:04,960 --> 00:32:06,720
Speaker 1: I think the more accurate way to say it is

667
00:32:06,760 --> 00:32:10,120
Speaker 1: that outside the event horizon, electrons would be repelled by

668
00:32:10,120 --> 00:32:13,760
Speaker 1: the charge, but photons could still fall in once they

669
00:32:13,800 --> 00:32:16,600
Speaker 1: pass the event horizon. It doesn't matter what the charge was,

670
00:32:16,680 --> 00:32:20,520
Speaker 1: and all particles of any charge see the same event horizon.

671
00:32:20,760 --> 00:32:24,520
Speaker 2: And protons would see us super duper extra huge event horizon.

672
00:32:24,640 --> 00:32:28,080
Speaker 1: Right, Not exactly. It's true that outside of the event

673
00:32:28,120 --> 00:32:32,400
Speaker 1: horizon of a negatively charged black hole, protons would feel

674
00:32:32,400 --> 00:32:36,320
Speaker 1: a strong attraction from the electromagnetic force and get pulled

675
00:32:36,400 --> 00:32:40,000
Speaker 1: in towards the event horizon. So at some distance outside

676
00:32:40,040 --> 00:32:44,120
Speaker 1: the event horizon, electrons are repelled and protons are attracted

677
00:32:44,160 --> 00:32:46,720
Speaker 1: towards it. So it sort of effectively sweeps up more

678
00:32:46,760 --> 00:32:50,640
Speaker 1: protons at larger radii than electrons. But the event horizon

679
00:32:50,760 --> 00:32:53,640
Speaker 1: isn't actually different. The point of no return is the

680
00:32:53,680 --> 00:32:56,560
Speaker 1: same for the two particles outside the event horizon. It's

681
00:32:56,600 --> 00:32:59,959
Speaker 1: still possible for those protons to avoid falling in if

682
00:33:00,000 --> 00:33:02,680
Speaker 1: if someone comes along and zaps them with energy to

683
00:33:02,720 --> 00:33:05,200
Speaker 1: push them back away from the event horizon. But there's

684
00:33:05,240 --> 00:33:08,360
Speaker 1: another outcome which is super weird, which is that black

685
00:33:08,400 --> 00:33:11,560
Speaker 1: holes which are charged can repel each other, like in

686
00:33:11,600 --> 00:33:14,120
Speaker 1: our universe. We see black holes eat each other, they

687
00:33:14,120 --> 00:33:16,320
Speaker 1: attract each other, they gobble each other up, they form

688
00:33:16,400 --> 00:33:19,240
Speaker 1: a super black hole. But if you had two negatively

689
00:33:19,360 --> 00:33:22,920
Speaker 1: charged black holes, they would actually repel each other right

690
00:33:22,960 --> 00:33:25,520
Speaker 1: the same way two electrons do, and if it had

691
00:33:25,640 --> 00:33:29,360
Speaker 1: enough charge, they would avoid falling in together. You might

692
00:33:29,400 --> 00:33:32,200
Speaker 1: even get them into like a stable configuration where these

693
00:33:32,200 --> 00:33:34,760
Speaker 1: two forces are in balance and they could orbit each other.

694
00:33:35,680 --> 00:33:37,920
Speaker 2: Now what I said earlier, is that true. Like if

695
00:33:37,920 --> 00:33:40,000
Speaker 2: we see a black hole, it looks like it has

696
00:33:40,040 --> 00:33:42,360
Speaker 2: an event horizon. It has a certain radius to the

697
00:33:42,360 --> 00:33:44,320
Speaker 2: black sphere, but if it happens to have a lot

698
00:33:44,320 --> 00:33:47,560
Speaker 2: of negative charge, that means that something could escape what

699
00:33:47,720 --> 00:33:50,240
Speaker 2: we see as the neutral event horizon.

700
00:33:50,360 --> 00:33:53,320
Speaker 1: Yeah, exactly. Remember the event horizon not a physical barrier.

701
00:33:53,360 --> 00:33:55,760
Speaker 1: It's just like the limit where we say nothing that

702
00:33:55,800 --> 00:33:58,600
Speaker 1: passes this will ever escape. But it's just determined by

703
00:33:58,640 --> 00:34:02,040
Speaker 1: whether particles do or do not escape. So it's interesting

704
00:34:02,160 --> 00:34:04,680
Speaker 1: because the event horizon is at the same place for

705
00:34:04,880 --> 00:34:08,680
Speaker 1: all of the particles, electrons, photons, protons. If they pass it,

706
00:34:08,719 --> 00:34:12,359
Speaker 1: there's no coming out. But electrons, photons, and protons are

707
00:34:12,400 --> 00:34:15,720
Speaker 1: more or less likely to fall into that event horizon

708
00:34:15,840 --> 00:34:19,040
Speaker 1: because of their charge. Technically, that doesn't change the location

709
00:34:19,160 --> 00:34:22,000
Speaker 1: of the event horizon, but it does mean the fate

710
00:34:22,080 --> 00:34:25,800
Speaker 1: of particles depends on their charge. There are some places

711
00:34:25,960 --> 00:34:30,000
Speaker 1: near a negatively charged black hole where electrons cannot go

712
00:34:30,120 --> 00:34:33,600
Speaker 1: because of their negative charge. They'll get repelled, but protons can.

713
00:34:33,840 --> 00:34:37,480
Speaker 1: They are attracted, so protons will fall in and eventually

714
00:34:37,560 --> 00:34:40,680
Speaker 1: get past the event horizon, but electrons will never reach

715
00:34:40,719 --> 00:34:41,600
Speaker 1: the event horizon.

716
00:34:41,920 --> 00:34:44,520
Speaker 2: I feel like we've just kind of destroyed the definition

717
00:34:44,640 --> 00:34:47,359
Speaker 2: of the holes a little bit because we've usually talked

718
00:34:47,400 --> 00:34:49,640
Speaker 2: about black holes as saying, you know, region of space

719
00:34:49,640 --> 00:34:51,880
Speaker 2: where nothing, not even light can escape. But it sounds

720
00:34:51,920 --> 00:34:53,319
Speaker 2: like it sort of depends on the charge of the

721
00:34:53,320 --> 00:34:53,799
Speaker 2: black hole.

722
00:34:53,960 --> 00:34:55,839
Speaker 1: Yeah, it does depend on the charge of the black hole.

723
00:34:56,239 --> 00:34:58,960
Speaker 1: And in practice this isn't that big a deal because

724
00:34:58,960 --> 00:35:01,879
Speaker 1: we think that most black holes don't have a lot

725
00:35:01,880 --> 00:35:04,520
Speaker 1: of charge. I mean, things out there in the universe

726
00:35:04,680 --> 00:35:08,440
Speaker 1: tend to be mostly neutral, like stars are mostly neutral,

727
00:35:08,680 --> 00:35:11,480
Speaker 1: the Earth is mostly neutral, and that's because the electromagnetic

728
00:35:11,520 --> 00:35:14,600
Speaker 1: force is pretty strong. So if a black hole somehow

729
00:35:14,719 --> 00:35:17,160
Speaker 1: ends up with a significant charge, it's going to end

730
00:35:17,239 --> 00:35:20,960
Speaker 1: up very powerfully attracting the opposite charge, like it will

731
00:35:20,960 --> 00:35:24,359
Speaker 1: pull very hard on protons flying nearby and suck them

732
00:35:24,440 --> 00:35:28,040
Speaker 1: up and end up being neutralized. So the electromagnetic force,

733
00:35:28,080 --> 00:35:31,080
Speaker 1: because it has two charges and is very powerful, tends

734
00:35:31,080 --> 00:35:33,400
Speaker 1: to mostly neutralize stuff. So we don't think this is

735
00:35:33,400 --> 00:35:35,759
Speaker 1: something that happens very often in the universe, very very

736
00:35:35,840 --> 00:35:36,840
Speaker 1: charged black holes.

737
00:35:37,160 --> 00:35:39,479
Speaker 2: Yeah, I guess that was kind of the earlier point

738
00:35:39,520 --> 00:35:41,399
Speaker 2: that you were trying to make, which is that maybe

739
00:35:41,400 --> 00:35:44,320
Speaker 2: it's impossible to make these super duper charged black holes.

740
00:35:44,400 --> 00:35:47,160
Speaker 2: And so let's get into the scenarios that you would

741
00:35:47,160 --> 00:35:51,880
Speaker 2: need to make a repellent black hole, a super negative

742
00:35:51,880 --> 00:35:54,280
Speaker 2: black hole, and what would it mean about the laws

743
00:35:54,360 --> 00:35:56,560
Speaker 2: of the universe. So let's dig into that. But first

744
00:35:56,640 --> 00:36:11,880
Speaker 2: let's take another quick break. All right, we're talking about

745
00:36:11,880 --> 00:36:15,120
Speaker 2: black holes and whether or not you can make one

746
00:36:15,280 --> 00:36:19,880
Speaker 2: disappear in a way by overcharging it, by putting so

747
00:36:19,960 --> 00:36:23,760
Speaker 2: much electric negative charge into it that it actually starts

748
00:36:23,800 --> 00:36:26,800
Speaker 2: to repel other negative charges, and so to an electron,

749
00:36:27,080 --> 00:36:30,120
Speaker 2: the black hole just kind of disappears. Now, theoretically, you're

750
00:36:30,120 --> 00:36:32,040
Speaker 2: saying that this is sort of possible, Like if I

751
00:36:32,080 --> 00:36:35,200
Speaker 2: can construct a black hole with enough negative charge, it

752
00:36:35,239 --> 00:36:37,560
Speaker 2: would sort of disappear. There wouldn't be a black hole.

753
00:36:37,600 --> 00:36:41,719
Speaker 1: Theoretically, yeah, theoretically according to general relativity, which again we

754
00:36:41,800 --> 00:36:44,680
Speaker 1: know is probably wrong about what's going on inside a

755
00:36:44,680 --> 00:36:48,040
Speaker 1: black hole. But if you follow this theory, it says

756
00:36:48,160 --> 00:36:51,240
Speaker 1: that if you did somehow manage to add enough charge

757
00:36:51,280 --> 00:36:54,799
Speaker 1: to a singularity, then the event horizon would shrink down

758
00:36:54,840 --> 00:36:58,600
Speaker 1: to zero. You essentially would reveal the singularity to the universe.

759
00:36:58,640 --> 00:37:01,400
Speaker 1: You have a naked singularity.

760
00:37:00,800 --> 00:37:04,200
Speaker 2: Well, meaning like I'm neutrally charged overall, all of my

761
00:37:04,560 --> 00:37:07,839
Speaker 2: particles are canceling each other out, So like this black

762
00:37:07,840 --> 00:37:10,040
Speaker 2: hole would still be deadly to me. I would still

763
00:37:10,080 --> 00:37:12,759
Speaker 2: die going into it. But maybe if I was made

764
00:37:12,840 --> 00:37:14,520
Speaker 2: up of only electrons, I could get out.

765
00:37:14,680 --> 00:37:17,080
Speaker 1: If you were made of electrons, you would be repelled

766
00:37:17,080 --> 00:37:20,160
Speaker 1: by it, so you'd have less chance to fall in again.

767
00:37:20,200 --> 00:37:22,960
Speaker 1: Depending on the charge of the black hole, and if

768
00:37:23,000 --> 00:37:25,680
Speaker 1: the black hole is charged, it would have a smaller

769
00:37:25,719 --> 00:37:28,800
Speaker 1: event horizon, so you could get closer and still escape,

770
00:37:29,120 --> 00:37:31,759
Speaker 1: but once you cross the event horizon, you aren't coming out.

771
00:37:31,880 --> 00:37:34,200
Speaker 1: I still would not recommend a trip to a highly

772
00:37:34,280 --> 00:37:36,799
Speaker 1: charged black hole, even if you could shoot electrons at

773
00:37:36,800 --> 00:37:38,400
Speaker 1: it and have them survive. But this is a real

774
00:37:38,440 --> 00:37:41,240
Speaker 1: opportunity for physics to try to figure out, like what happens.

775
00:37:41,600 --> 00:37:44,640
Speaker 1: Does this mean that something weird would actually happen in

776
00:37:44,680 --> 00:37:47,279
Speaker 1: the universe, or is there some reason why this is

777
00:37:47,320 --> 00:37:51,440
Speaker 1: not possible, something like preventing this from occurring. I remember

778
00:37:51,440 --> 00:37:54,160
Speaker 1: there's been lots of times in theoretical physics when they

779
00:37:54,239 --> 00:37:57,479
Speaker 1: predicted something really weird they thought, well, that certainly can't happen.

780
00:37:57,560 --> 00:38:00,600
Speaker 1: There must be something preventing it. Like black holes, which

781
00:38:00,600 --> 00:38:03,440
Speaker 1: for a long time people imagine or a ridiculous prediction

782
00:38:03,520 --> 00:38:07,120
Speaker 1: of general relativity in the universe must somehow arrange for

783
00:38:07,160 --> 00:38:10,279
Speaker 1: them to never exist, but then we think we see them.

784
00:38:10,719 --> 00:38:13,719
Speaker 1: So the question for super charged black holes and like

785
00:38:13,840 --> 00:38:17,200
Speaker 1: naked singularities is like, is this something which could actually happen,

786
00:38:17,239 --> 00:38:19,239
Speaker 1: you could really do this and see it, or is

787
00:38:19,280 --> 00:38:22,359
Speaker 1: there some reason why it's impossible to set this thing

788
00:38:22,440 --> 00:38:22,959
Speaker 1: up this way?

789
00:38:23,239 --> 00:38:25,520
Speaker 2: Yeah, I think what you're saying is that we probably

790
00:38:25,600 --> 00:38:27,960
Speaker 2: don't see a lot of super negatively charged black holes

791
00:38:27,960 --> 00:38:30,719
Speaker 2: out in the universe. And so there's two possibilities. One

792
00:38:30,800 --> 00:38:34,000
Speaker 2: is that there's something theoretical, some kind of fundamental law

793
00:38:34,000 --> 00:38:36,879
Speaker 2: in the universe that prevents that from happening. And there's

794
00:38:36,920 --> 00:38:42,160
Speaker 2: also maybe more practical limitations or barriers making this, Like

795
00:38:42,239 --> 00:38:44,520
Speaker 2: you just can't practically make a black hole like this

796
00:38:44,600 --> 00:38:50,240
Speaker 2: because you can't aggregate enough negatively charged stuff together practically speaking,

797
00:38:50,560 --> 00:38:52,360
Speaker 2: from what we have in the universe exactly.

798
00:38:52,440 --> 00:38:55,440
Speaker 1: And it's fascinating if the practical limitation is sort of

799
00:38:55,440 --> 00:38:58,879
Speaker 1: what saves us from the principled problem, I would say, like, wow,

800
00:38:58,880 --> 00:39:01,160
Speaker 1: this would be a crazy we'd all go to physics

801
00:39:01,200 --> 00:39:03,520
Speaker 1: jail if this happened. And then it turns out, well,

802
00:39:03,719 --> 00:39:06,120
Speaker 1: you can't actually build that kind of thing, Like there's

803
00:39:06,120 --> 00:39:09,080
Speaker 1: no theoretical reason why it can't exist, but you couldn't

804
00:39:09,160 --> 00:39:12,799
Speaker 1: ever assemble it. That's really fascinating the insight into like

805
00:39:12,920 --> 00:39:15,799
Speaker 1: how the universe protects itself from going to physics jail.

806
00:39:15,920 --> 00:39:17,440
Speaker 1: And so there's been a bunch of papers over the

807
00:39:17,520 --> 00:39:20,520
Speaker 1: last twenty years trying to do this calculation. Like heuristically,

808
00:39:20,520 --> 00:39:23,480
Speaker 1: you can imagine, all right, as I tossed electrons in,

809
00:39:23,840 --> 00:39:26,239
Speaker 1: the thing gets more negatively charged and that makes it

810
00:39:26,320 --> 00:39:29,800
Speaker 1: harder to toss in the next electron. Right, But people

811
00:39:29,800 --> 00:39:32,479
Speaker 1: have sat down and actually done this calculation, which turns

812
00:39:32,480 --> 00:39:34,919
Speaker 1: out to be quite complex, and papers over the last

813
00:39:34,920 --> 00:39:38,319
Speaker 1: few years have concluded that the self force from the

814
00:39:38,400 --> 00:39:40,879
Speaker 1: black hole. As the black hole gets more and more

815
00:39:40,920 --> 00:39:44,640
Speaker 1: negatively charged, it will repel those electrons and it will

816
00:39:44,680 --> 00:39:48,080
Speaker 1: prevent more charge from falling in before it hits this

817
00:39:48,200 --> 00:39:52,080
Speaker 1: sort of maximum before the event horizon decreases to zero.

818
00:39:52,560 --> 00:39:55,360
Speaker 2: Right, that's the practical. Although, what happens if you shoot

819
00:39:55,360 --> 00:39:59,400
Speaker 2: an electron with like super fast, Like if I shoot

820
00:39:59,400 --> 00:40:01,960
Speaker 2: an electron in towards the center of the black hole

821
00:40:02,000 --> 00:40:05,839
Speaker 2: with enough energy, want it overcome the electric repulsion and

822
00:40:05,920 --> 00:40:07,960
Speaker 2: get close enough to the black hole where it gets

823
00:40:08,000 --> 00:40:09,000
Speaker 2: sucked in by gravity.

824
00:40:09,160 --> 00:40:11,359
Speaker 1: Yeah, I love that your temptation is to like try

825
00:40:11,360 --> 00:40:13,359
Speaker 1: to break the rules and like build an electron gun

826
00:40:13,400 --> 00:40:15,040
Speaker 1: and shoot it at a black hole just to see

827
00:40:15,040 --> 00:40:19,640
Speaker 1: what happens. That's exactly what leads us down the road

828
00:40:19,680 --> 00:40:22,120
Speaker 1: do great discoveries. And so you know, the way to

829
00:40:22,120 --> 00:40:24,879
Speaker 1: think about it is that anything that manages to fall

830
00:40:24,880 --> 00:40:27,760
Speaker 1: into the black hole is basically going to have more

831
00:40:27,920 --> 00:40:30,440
Speaker 1: mass than charge. Like, anything that falls in, it's going

832
00:40:30,480 --> 00:40:31,880
Speaker 1: to have some mass, and so it's going to make

833
00:40:31,880 --> 00:40:34,239
Speaker 1: the black hole bigger, which is going to allow it

834
00:40:34,320 --> 00:40:36,799
Speaker 1: to have more charge without sort of like going over

835
00:40:36,840 --> 00:40:39,439
Speaker 1: this threshold. And so basically anything that manages to fall

836
00:40:39,480 --> 00:40:42,040
Speaker 1: in has to have a certain mass to charge ratio.

837
00:40:42,400 --> 00:40:44,240
Speaker 1: And as soon as you get above the place where

838
00:40:44,280 --> 00:40:46,920
Speaker 1: electrons can no longer fall in, then you're asking like, well,

839
00:40:46,920 --> 00:40:49,520
Speaker 1: couldn't you force them in? Couldn't you like build an

840
00:40:49,520 --> 00:40:51,680
Speaker 1: electron gun that makes them go super duper fast and

841
00:40:51,719 --> 00:40:53,960
Speaker 1: forces them in? And effectively, what you're doing there is

842
00:40:54,000 --> 00:40:56,799
Speaker 1: you're adding more energy to the electrons, and when the

843
00:40:56,840 --> 00:40:59,640
Speaker 1: black hole eats that electron, now it gets even more

844
00:40:59,760 --> 00:41:02,640
Speaker 1: energy and that adds to its mass, and so that

845
00:41:02,760 --> 00:41:05,400
Speaker 1: keeps it from going over the limit. So if you

846
00:41:05,440 --> 00:41:09,240
Speaker 1: shoot super high energy electrons at it, that energy keeps

847
00:41:09,239 --> 00:41:11,200
Speaker 1: it from going over the threshold.

848
00:41:10,800 --> 00:41:14,160
Speaker 2: Keeps it from going over the threshold for its size.

849
00:41:14,360 --> 00:41:16,680
Speaker 2: But if I grow the black hole, then it can

850
00:41:16,760 --> 00:41:18,560
Speaker 2: have more negative charge, right.

851
00:41:18,480 --> 00:41:21,600
Speaker 1: Yeah, exactly, So anything you can squeeze into a charge

852
00:41:21,600 --> 00:41:25,239
Speaker 1: black hole has to grow its mass more than its

853
00:41:25,360 --> 00:41:28,440
Speaker 1: charge effectively in order to keep it from violating this limit.

854
00:41:28,800 --> 00:41:31,640
Speaker 1: And practically it turns out you can't actually shoot anything

855
00:41:31,719 --> 00:41:34,000
Speaker 1: to a black hole to break that limit. Anything you

856
00:41:34,040 --> 00:41:36,480
Speaker 1: can actually get into the black hole would have to

857
00:41:36,560 --> 00:41:40,440
Speaker 1: have more mass than charge or more energy than charge.

858
00:41:40,200 --> 00:41:42,880
Speaker 2: Equivalently, So it sort of sounds like you're saying that

859
00:41:42,960 --> 00:41:46,120
Speaker 2: I can shoot more electrons into a super negatively charge

860
00:41:46,200 --> 00:41:48,040
Speaker 2: black hole. I just have to give it enough energy

861
00:41:48,080 --> 00:41:49,800
Speaker 2: and then it'll get sucked in exactly.

862
00:41:49,840 --> 00:41:53,319
Speaker 1: So technically there's no maximum charge to a black hole.

863
00:41:53,520 --> 00:41:57,080
Speaker 1: There's a maximum ratio. Like for a given mass, there's

864
00:41:57,080 --> 00:41:59,839
Speaker 1: a maximum charge. If you make it more massive, then yeah,

865
00:42:00,120 --> 00:42:02,640
Speaker 1: can have more charge, but you can't have more energy

866
00:42:02,640 --> 00:42:05,560
Speaker 1: in the charge effectively than in the mass. So there's

867
00:42:05,600 --> 00:42:08,719
Speaker 1: no like absolute number that says black holes can't be

868
00:42:08,760 --> 00:42:11,640
Speaker 1: more charged than this, But there is a ratio of

869
00:42:11,680 --> 00:42:13,600
Speaker 1: the charge to mass for a black hole.

870
00:42:13,719 --> 00:42:17,480
Speaker 2: So it's kind of a complicated maximum charge than an

871
00:42:17,560 --> 00:42:20,360
Speaker 2: electron a black hole can have, Like I think you're saying, like,

872
00:42:20,400 --> 00:42:22,920
Speaker 2: for a certain size of black hole, you can't just

873
00:42:23,000 --> 00:42:25,279
Speaker 2: throw any electron in. It has to be an electron

874
00:42:25,440 --> 00:42:28,440
Speaker 2: that has more mass or more velocity or energy than

875
00:42:28,480 --> 00:42:32,560
Speaker 2: it has charge. So really there's no limit to the

876
00:42:32,680 --> 00:42:35,319
Speaker 2: maximum charge of a black hole. It just starts to

877
00:42:35,400 --> 00:42:38,200
Speaker 2: limit the kinds of electrons you can throw in.

878
00:42:38,400 --> 00:42:41,680
Speaker 1: Yeah, things which would violate this ratio, Things that have

879
00:42:41,840 --> 00:42:44,800
Speaker 1: like a lot of charge but almost no mass, would

880
00:42:44,800 --> 00:42:47,160
Speaker 1: not end up in the black hole because they would

881
00:42:47,200 --> 00:42:50,239
Speaker 1: be repelled by the black hole's charge. So things that

882
00:42:50,239 --> 00:42:53,280
Speaker 1: would put this black hole in physics jail can't actually

883
00:42:53,320 --> 00:42:54,960
Speaker 1: fall into the black hole.

884
00:42:54,880 --> 00:42:58,760
Speaker 2: But to some kinds of electrons, to like slow moving electrons.

885
00:42:59,000 --> 00:43:01,279
Speaker 2: I think you're saying that the black hole does kind

886
00:43:01,280 --> 00:43:04,800
Speaker 2: of disappear and for them, the singularity is sort of exposed.

887
00:43:04,880 --> 00:43:07,279
Speaker 1: No, slow moving electrons would be repelled by this thing, right,

888
00:43:07,320 --> 00:43:10,439
Speaker 1: They wouldn't have enough energy essentially to get in there.

889
00:43:10,600 --> 00:43:13,240
Speaker 2: Well, that's what I mean, Like the event horizon disappears

890
00:43:13,280 --> 00:43:13,839
Speaker 2: for them, right.

891
00:43:13,760 --> 00:43:15,800
Speaker 1: They would never even be able to enter that region

892
00:43:15,840 --> 00:43:16,320
Speaker 1: of space.

893
00:43:16,760 --> 00:43:19,399
Speaker 2: Yeah, But I think what you're saying is that there's

894
00:43:19,440 --> 00:43:21,960
Speaker 2: maybe like an electron out there for a certain black

895
00:43:21,960 --> 00:43:24,440
Speaker 2: hole with a lot of negative charge that could get

896
00:43:24,440 --> 00:43:27,239
Speaker 2: into the regular event horizon, go right up to the

897
00:43:27,320 --> 00:43:30,239
Speaker 2: singularity and then come back out because it has just

898
00:43:30,719 --> 00:43:34,600
Speaker 2: enough more electric charge and mass for it to be

899
00:43:34,640 --> 00:43:35,600
Speaker 2: able to get out again.

900
00:43:35,719 --> 00:43:37,960
Speaker 1: Yes, for an extremal black hole, but then that electron

901
00:43:38,160 --> 00:43:40,400
Speaker 1: would be forced out. It wouldn't be able to join

902
00:43:40,440 --> 00:43:44,160
Speaker 1: the singularity and reveal the Singularity to the next electron.

903
00:43:44,320 --> 00:43:46,600
Speaker 1: Like that event horizon still has to be non zero.

904
00:43:46,920 --> 00:43:49,759
Speaker 1: There's no way to get that last electron into the

905
00:43:49,800 --> 00:43:53,280
Speaker 1: singularity to make the event horizon actually have zero redius

906
00:43:53,320 --> 00:43:54,440
Speaker 1: for the next one m.

907
00:43:55,360 --> 00:43:58,240
Speaker 2: So let's maybe dig into what you mean by physics

908
00:43:58,239 --> 00:44:02,040
Speaker 2: to jail and breaking the law. Why exposing a black

909
00:44:02,080 --> 00:44:04,280
Speaker 2: hole's singularity break the laws of physics?

910
00:44:04,400 --> 00:44:06,000
Speaker 1: Yeah, it's a great question. We don't really know what

911
00:44:06,040 --> 00:44:08,400
Speaker 1: that means. General relativity has no solution there. It's like

912
00:44:08,440 --> 00:44:10,120
Speaker 1: you try to solve the equations and you get the

913
00:44:10,160 --> 00:44:12,759
Speaker 1: square root of a negative number. So now what's the

914
00:44:12,840 --> 00:44:15,680
Speaker 1: radius of the event horizon. Well, we don't really know, right.

915
00:44:16,000 --> 00:44:18,680
Speaker 1: General relativity basically breaks down there. It doesn't know what

916
00:44:18,760 --> 00:44:21,520
Speaker 1: to predict. It can't even predict things as nonsensical as

917
00:44:21,560 --> 00:44:25,160
Speaker 1: a singularity. There's just really no prediction there. And so

918
00:44:25,239 --> 00:44:28,480
Speaker 1: we don't really know what would happen according to general

919
00:44:28,480 --> 00:44:31,280
Speaker 1: relativity in that regime. And that's sort of the bigger

920
00:44:31,360 --> 00:44:36,640
Speaker 1: story that general relativity isn't predicting singularities orringularities or post

921
00:44:36,680 --> 00:44:40,120
Speaker 1: extremal black holes. It's really breaking down here. It's saying

922
00:44:40,440 --> 00:44:43,600
Speaker 1: it can't make any predictions. The sign of an infinity

923
00:44:43,880 --> 00:44:46,000
Speaker 1: or you know, like square roots of negative numbers in

924
00:44:46,040 --> 00:44:48,799
Speaker 1: the theory is telling you that you've gone beyond the

925
00:44:48,880 --> 00:44:51,759
Speaker 1: limits of that theory, that it's an approximate theory, and

926
00:44:51,800 --> 00:44:54,640
Speaker 1: you've pushed it into a territory where it does not belong,

927
00:44:54,719 --> 00:44:56,920
Speaker 1: where it cannot make any reasonable predictions.

928
00:44:57,120 --> 00:45:00,600
Speaker 2: Hmmm, well it would break I guess our theory of it.

929
00:45:00,680 --> 00:45:03,440
Speaker 2: But that's also assuming the universe follows our theories, Like

930
00:45:03,640 --> 00:45:05,359
Speaker 2: maybe it could do. It would just break our math.

931
00:45:05,440 --> 00:45:08,319
Speaker 1: Yeah, it would break our math. Certainly, something would happen, right,

932
00:45:08,480 --> 00:45:11,680
Speaker 1: the universe probably wouldn't disappear in a puff of logic.

933
00:45:12,080 --> 00:45:15,640
Speaker 1: If you did somehow force an electron inside an already

934
00:45:15,680 --> 00:45:18,840
Speaker 1: extremo black hole, something would happen, and whatever that would

935
00:45:18,840 --> 00:45:21,360
Speaker 1: be would be a great clue to tell us, like

936
00:45:21,480 --> 00:45:24,200
Speaker 1: what's really going on. It would force the universe in

937
00:45:24,200 --> 00:45:27,719
Speaker 1: some sense to reveal what its true laws are, you know,

938
00:45:27,760 --> 00:45:30,160
Speaker 1: And that's what experimental physics is all about. It's like

939
00:45:30,480 --> 00:45:32,680
Speaker 1: forcing the universe in a corner where it has to

940
00:45:33,080 --> 00:45:36,440
Speaker 1: give up some secrets, or it has to tell us

941
00:45:36,440 --> 00:45:39,560
Speaker 1: what happens in this situation, which gives us some answer.

942
00:45:39,800 --> 00:45:42,200
Speaker 1: Maybe it would reveal some weird naked singularity and we'd

943
00:45:42,239 --> 00:45:45,640
Speaker 1: learn how to modify general relativity, or maybe you would explode,

944
00:45:45,760 --> 00:45:47,680
Speaker 1: or maybe you would turn into a wormhole, or we

945
00:45:47,760 --> 00:45:50,320
Speaker 1: just don't really know. But whatever happened in that situation

946
00:45:50,360 --> 00:45:54,000
Speaker 1: would be a huge clue towards solving quantum gravity, to

947
00:45:54,120 --> 00:45:58,000
Speaker 1: understanding what happens when things get very very small and

948
00:45:58,480 --> 00:45:59,759
Speaker 1: very very gravitational.

949
00:46:00,160 --> 00:46:01,879
Speaker 2: All right, well, it sounds like the answer to our

950
00:46:01,920 --> 00:46:04,640
Speaker 2: main question then is do black holes have a maximum

951
00:46:04,640 --> 00:46:08,640
Speaker 2: electric charge? And it sounds like the answer is sort

952
00:46:08,640 --> 00:46:12,440
Speaker 2: of like it has a maximum electric charge for certain

953
00:46:12,880 --> 00:46:15,920
Speaker 2: other electric charges, but not others. It doesn't have a

954
00:46:15,920 --> 00:46:19,120
Speaker 2: maximum electric charge in terms of how much charge any

955
00:46:19,160 --> 00:46:21,640
Speaker 2: black hole can be because you can have maybe infinite

956
00:46:21,960 --> 00:46:24,799
Speaker 2: electrical charge if you have an infinitely large black hole.

957
00:46:24,880 --> 00:46:26,879
Speaker 1: That's right. If you want to charge up your black hole,

958
00:46:27,040 --> 00:46:29,640
Speaker 1: you also got to make it massive at the same time.

959
00:46:30,080 --> 00:46:32,560
Speaker 1: That's the recipe for charging up your black hole. You

960
00:46:32,600 --> 00:46:34,759
Speaker 1: can't just take your black hole and add charge without

961
00:46:34,800 --> 00:46:37,400
Speaker 1: adding mass. That would break the rules of the universe.

962
00:46:37,640 --> 00:46:40,120
Speaker 2: Well, it would break the rules of the practical universe.

963
00:46:40,160 --> 00:46:42,839
Speaker 2: But theoretically, you know, if if I was you know,

964
00:46:43,160 --> 00:46:46,120
Speaker 2: if I had a cart blong on doing anything I

965
00:46:46,120 --> 00:46:48,480
Speaker 2: wanted in the universe, could I create a universe with

966
00:46:48,600 --> 00:46:52,399
Speaker 2: suddenly a super duper extra charge black hole for its

967
00:46:52,440 --> 00:46:53,720
Speaker 2: mass to appear.

968
00:46:53,800 --> 00:46:56,680
Speaker 1: Yeah, I think there's no theoretical reason why that arrangement

969
00:46:56,800 --> 00:47:00,800
Speaker 1: cannot exist. There's just no theoretical way to build it.

970
00:47:00,880 --> 00:47:04,680
Speaker 1: Starting from a universe and creating that configuration seems to

971
00:47:04,719 --> 00:47:09,920
Speaker 1: be impossible. Though the actual configuration itself isn't technically impossible,

972
00:47:10,160 --> 00:47:12,799
Speaker 1: right to put enough electrons in the same place where

973
00:47:12,840 --> 00:47:16,160
Speaker 1: you lelate that condition. But practically speaking, we don't know

974
00:47:16,200 --> 00:47:17,839
Speaker 1: of any way to build it. But if you were

975
00:47:17,880 --> 00:47:19,800
Speaker 1: somehow able to do it, we would break the laws

976
00:47:19,840 --> 00:47:22,480
Speaker 1: of our universe as we understand it, but we'd learn

977
00:47:22,520 --> 00:47:24,960
Speaker 1: more about the true laws of the actual universe.

978
00:47:25,239 --> 00:47:27,120
Speaker 2: Well, you wouldn't break the laws of the universe. You

979
00:47:27,160 --> 00:47:30,000
Speaker 2: would just kind of break the practical laws of the universe.

980
00:47:30,000 --> 00:47:32,840
Speaker 2: It'd be unexplained, Yes, it'd be unexplained. Like if you

981
00:47:33,000 --> 00:47:35,560
Speaker 2: came across one of these things in space, you'd have

982
00:47:35,640 --> 00:47:37,680
Speaker 2: no way of explaining how it got there.

983
00:47:38,120 --> 00:47:40,000
Speaker 1: And that's important, right. We look out in the universe,

984
00:47:40,040 --> 00:47:42,680
Speaker 1: we see stuff, We see atoms out there and all

985
00:47:42,680 --> 00:47:44,680
Speaker 1: sorts of different elements, and we want to explain, like

986
00:47:44,680 --> 00:47:46,120
Speaker 1: how do we get to this state? You start from

987
00:47:46,120 --> 00:47:48,680
Speaker 1: the Big Bang, How is it possible to build all

988
00:47:48,680 --> 00:47:51,160
Speaker 1: these heavy metals, and we have theories for how that happens.

989
00:47:51,400 --> 00:47:53,400
Speaker 1: Everything that's out there in the universe, we look for

990
00:47:53,440 --> 00:47:56,279
Speaker 1: an explanation for how it was made, how it was assembled,

991
00:47:56,320 --> 00:47:57,640
Speaker 1: and so this would be a big.

992
00:47:57,520 --> 00:47:59,640
Speaker 2: Mystery, unless, of course, it was just a bunch of

993
00:48:00,120 --> 00:48:04,120
Speaker 2: this is Dad's telling negative jokes that I'm imploded into

994
00:48:04,200 --> 00:48:06,799
Speaker 2: a super overcharged black hole.

995
00:48:06,960 --> 00:48:08,399
Speaker 1: I hope they all collapse in shame.

996
00:48:08,760 --> 00:48:11,799
Speaker 2: All right, Well, we hope you enjoyed that. Thanks for

997
00:48:11,880 --> 00:48:13,520
Speaker 2: joining us, See you next time.

998
00:48:21,400 --> 00:48:24,200
Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain

999
00:48:24,280 --> 00:48:28,279
Speaker 1: the Universe is a production of iHeartRadio. For more podcasts

1000
00:48:28,280 --> 00:48:32,920
Speaker 1: from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever

1001
00:48:33,000 --> 00:48:34,720
Speaker 1: you listen to your favorite shows.