Latest / Daniel and Kelly’s Extraordinary Universe / Listener Questions Volume #1

Transcript

Listener Questions Volume #1 · Daniel and Kelly’s Extraordinary Universe

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Speaker 1: Every discovery, every moment of insight, every aha or eureka
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Speaker 1: with the ideas click together in someone's mind to reveal
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Speaker 1: a deep truth about the universe. All of those begin
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Speaker 1: the same way with a question. In fact, all of
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Speaker 1: science starts with questions. The reason we know things about
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Speaker 1: clouds and beetles and black holes is because someone out
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Speaker 1: there had a question that kept them up at night,
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Speaker 1: so they were willing to stay up late looking at
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Speaker 1: the stars or counting beetles until they figured it out.
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Speaker 1: Science is just people asking questions they couldn't let go.
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Speaker 1: But it's not just professional scientists who ask questions and
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Speaker 1: move us forward. It's everyone. It's you, and we think
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Speaker 1: your questions also deserve answers, or at least replies that
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Speaker 1: make sense and help you grapple with what we do
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Speaker 1: and don't know about the topic. So if you have
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Speaker 1: a question about science or whatever, please write to us
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Speaker 1: to questions at Daniel and Kelly dot org. We'd love
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Speaker 1: to hear from you, and sometimes we'll answer those questions
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Speaker 1: right here on the pod. And so on today's episode,
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Speaker 1: we're going to be answering questions submitted by listeners and
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Speaker 1: more than that, and I'll admit to being a little
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Speaker 1: bit nervous about this part. We're going to go back
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Speaker 1: to those listeners with our answers and follow up to
1:21
Speaker 1: see if our explanations scratch their itch or not. Today
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Speaker 1: Daniel and Kelly are getting graded by the listeners. So
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Speaker 1: today on Daniel and Kelly's Extraordinary Universe, we'll be answering
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Speaker 1: questions from listeners, Volume one.
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Speaker 2: Hello, I'm Kelly Wienersmith, and I am so excited that
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Speaker 2: we're having our first listener Questions episode today.
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Speaker 1: Hi, I'm Daniel. I'm a particle physicist, and I love
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Speaker 1: answering questions from the internet about physics, about philosophy, even
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Speaker 1: about dating.
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Speaker 2: Really, you've answered questions on the show about dating.
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Speaker 1: People send me all sorts of questions, you know. They
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Speaker 1: send me their treatise on the nature of the Universe,
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Speaker 1: They send me questions about career advice, how to get
2:18
Speaker 1: into physics, and yes, sometimes people ask me questions about
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Speaker 1: their dating life, and hey, I don't claim any particular
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Speaker 1: expertise there, but I'll share my thoughts.
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Speaker 2: Sure. Yeah, no, I'll share my thoughts on anything. So
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Speaker 2: I was actually going to ask you, what is the
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Speaker 2: weirdest or most surprising, like no negative connotation needed, but
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Speaker 2: weirdest or most surprising question you've ever been asked related
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Speaker 2: to your career as a physicist.
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Speaker 1: Oh wow, that is such a good question. Now mentally,
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Speaker 1: cycling through the thousands of questions I've gotten over the years,
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Speaker 1: I think one of the most challenging questions to answer
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Speaker 1: are ones about people's personal experiences. People writing sometimes about
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Speaker 1: like their UFO experiences or their paranormal experiences, and they
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Speaker 1: want my physics knowledge and like, what else could have
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Speaker 1: explained it? And that's a delicate line to walk, because
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Speaker 1: you don't want to suggest that what they experienced is
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Speaker 1: not what they think they experienced, but you also want
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Speaker 1: to help them disentangle it and think about what else
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Speaker 1: might have explained it. That's maybe like the most oddball
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Speaker 1: and challenging kind of question to answer. I also sometimes
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Speaker 1: get really touching stories, like a woman who went through
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Speaker 1: her father's old belongings. He was, of course, a retired engineer,
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Speaker 1: and she found in there a treatise on the nature
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Speaker 1: of the universe, and she sent it to me and
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Speaker 1: she's like, look, I don't know if this is anything,
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Speaker 1: but if it is something, I feel terrible not sharing
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Speaker 1: it with the world. Can you tell me if this
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Speaker 1: is worthwhile or not?
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Speaker 2: Aw, that's so cute. I know, was it worthwhile or
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Speaker 2: was it fun to read? But maybe not earth changing?
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Speaker 1: There was nothing really earth chattering in there, but I
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Speaker 1: think she was happy to know that at least somebody
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Speaker 1: had looked at it.
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Speaker 2: What's so cool that you were able to provide that?
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Speaker 1: And how about you? Do you get weird questions from
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Speaker 1: the internet about parasites? People send you pictures of bits
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Speaker 1: of their body and be like, Kelly, what is this?
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Speaker 1: Do I need to go to the er?
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Speaker 2: I do get photos of feces from time to time,
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Speaker 2: and it's worth noting that I cannot identify parasitic infections
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Speaker 2: from a picture of a bell movement their microscopic and
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Speaker 2: I can't. Also, I'm not a medical professional.
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Speaker 1: So everybody out there who was about to email Kelly
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Speaker 1: a picture of their poop not worth your time.
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Speaker 2: Please don't. I think the hardest question for me to answer, though,
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Speaker 2: was I was doing an interview for our book soon ish,
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Speaker 2: and I think the person doing the interview hadn't really
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Speaker 2: read the book, and so his question was, so, tell
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Speaker 2: me about the robots? The robots, and there was like
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Speaker 2: a different robot in every single chapter, and so I
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Speaker 2: didn't have any idea what he was talking about. This
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Speaker 2: is when I learned the trick that when you do
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Speaker 2: an interview, if someone asks you a question that you
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Speaker 2: don't really know what they're trying to get at, you
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Speaker 2: just decide what is the most interesting thing I feel
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Speaker 2: like talking about right now? And so I just picked
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Speaker 2: like my favorite robot and went off on that tangent.
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Speaker 2: It was, that's a learning experience.
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Speaker 1: Sounds like you're ready to run for higher office.
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Speaker 3: Now.
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Speaker 1: I'm going to dodge your question to talk about the
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Speaker 1: thing I want to talk about instead.
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Speaker 2: I don't think i'd make a good politician, all right.
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Speaker 1: Well, you know I would vote for you to represent Virginia,
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Speaker 1: but not California. I don't think you can really appreciate
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Speaker 1: everything that California has to offer.
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Speaker 2: I lived in California for a while. Is it that
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Speaker 2: you don't like Virginia and that's why you would vote
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Speaker 2: for me for Virginia. You want to harm Virginia in somewhere?
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Speaker 1: Well, no, no, no, Virginia is for lovers. It's fantastic.
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Speaker 1: I just don't feel like you appreciate California. I mean,
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Speaker 1: you did leave, right, and so clearly you don't understand
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Speaker 1: that it's objectively the best place in the world to live.
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Speaker 2: You know, I have not regretted leaving, sorry to say so.
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Speaker 2: I guess you're right. I shouldn't be representing California. And
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Speaker 2: maybe I'm going to regret that a decade from now
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Speaker 2: when I run for governor of California, if I've moved back.
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Speaker 2: But for now, I think we're just going to go
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Speaker 2: with no politics for Kelly.
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Speaker 1: That sounds good because I'm gonna have to hold off
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Speaker 1: on endorsing you until I hear you change your opinion California.
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Speaker 1: All right, But let's not talk about Kelly's your future
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Speaker 1: plans to take over the world slash Solar system slash universe.
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Speaker 1: Let's get to questions from listeners, because today on Daniel
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Speaker 1: and Kelly's Extraordinary Universe, we are answering questions from you.
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Speaker 1: We think your questions are important. We want you to
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Speaker 1: understand the universe. We want you to get that satisfying
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Speaker 1: moment where everything clicks in your mind, and so we
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Speaker 1: encourage you to write to us with your questions to
6:21
Speaker 1: questions at Danielankelly dot org. We will write back to you.
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Speaker 1: You'll hear what we do and don't know about whatever
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Speaker 1: it is you're interested in.
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Speaker 2: We can't we do hear from you.
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Speaker 1: Our first question today is from a really fun guy
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Speaker 1: named Barima who lives in Germany. He has a question
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Speaker 1: about gravity. Here is Barima's question.
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Speaker 3: Hello, my name is Brima, living in Germany from England.
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Speaker 3: I'm a big fan of the podcast and I love
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Speaker 3: what you guys are about, Sir. Gravity becomes so strong
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Speaker 3: that it tarts space time, and I was thinking dark
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Speaker 3: energy basically does the same, but in reverse because it's
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Speaker 3: expanding the universe. Both of these phenomena bend or expand
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Speaker 3: fabric of space time. So my question is could dark
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Speaker 3: energy be anti gravity? Thank you for your time and
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Speaker 3: I hope you guys have a great day.
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Speaker 2: Thank you so much for the question, Barima. Well, you know, Daniel,
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Speaker 2: that sounds like a question.
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Speaker 4: For you.
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Speaker 1: Gravity, space time and dark energy. Ooh, this is my
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Speaker 1: jam for sure.
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Speaker 2: We've recently recorded episodes on what is time and what
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Speaker 2: is space which might provide some important context. But how
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Speaker 2: do we answer this question more directly?
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Speaker 1: This is a great question because it gives us an
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Speaker 1: opportunity to connect a lot of ideas. You hear a
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Speaker 1: lot about space time as a fabric, black holes, having
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Speaker 1: extreme gravity, dark energy pulling space apart. How does it
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Speaker 1: all work? How do you think about that altogether? My
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Speaker 1: interpretation of Brima's question is that he's thinking about black
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Speaker 1: holes and he's heard that black holes tear space time,
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Speaker 1: so he's thinking about that as like pulling space itself apart.
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Speaker 1: And he's also heard that the universe is expanding in
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Speaker 1: an accelerating way, which feels like it's ripping space apart,
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Speaker 1: and so he's wondering, like, are those the same thing
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Speaker 1: or are they the opposite? Because black holes attract and
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Speaker 1: dark energy is pulling space apart, how does it all work?
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Speaker 1: And is dark energy actually the opposite form of gravity?
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Speaker 1: So we're going to give Burrimo a way to think
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Speaker 1: about dark energy in terms of gravity in general relativity
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Speaker 1: and link all these ideas together. But we should probably
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Speaker 1: start with black holes and space time and think about
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Speaker 1: what it means to tear space time.
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Speaker 2: Apart, and does this have anything to do We had
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Speaker 2: a conversation about a map and how you can like
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Speaker 2: make the cities closer or farther apart. Is that the
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Speaker 2: right way to start thinking about this problem, or now
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Speaker 2: that we're talking about black holes, we're in a totally
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Speaker 2: different universe.
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Speaker 1: No, that's exactly the right way to start thinking about this.
8:43
Speaker 1: Let's get a mental picture of what space is or
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Speaker 1: space time is, and what it means to tear space
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Speaker 1: time or what happens when gravity gets really really strong.
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Speaker 1: So let's start with a model of space. What is
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Speaker 1: space space? We don't know what it is fundamentally, but
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Speaker 1: we know that we can measure the distance between two points.
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Speaker 1: You have like a ruler. You can measure how many
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Speaker 1: ticks are between two points, and you can do that
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Speaker 1: between La and Virginia, or you can do that between
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Speaker 1: Canada and Mexico, or between Seattle and Miami or whatever.
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Speaker 1: You can measure distances between points. So we know that
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Speaker 1: we can measure these distances. We don't understand what is
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Speaker 1: the underlying fabric and what is it doing and how
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Speaker 1: does it work, But we can measure these distances, and
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Speaker 1: we notice that if you put a mass in space,
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Speaker 1: like a star or a planet or whatever, those distances
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Speaker 1: get kind of wonky like things get closer together, things
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Speaker 1: get further apart. This is what we mean when we
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Speaker 1: say space is curved. It's not like it's curving in
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Speaker 1: some external dimension with a whole crazy rubber sheet analogy.
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Speaker 1: It just means that it's changing the intrinsic distances between stuff.
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Speaker 1: The curvature of space is not external and some other dimension.
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Speaker 1: It's internal. It's intrinsic. It's just a relative change of distances.
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Speaker 1: And so when we say space is curve, we just
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Speaker 1: mean you're tweaking all of those distances.
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Speaker 2: I think if I were listening to the podcast, this
9:57
Speaker 2: is where I would pause it and just stare at
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Speaker 2: the wall for five minutes and be like, how do
10:02
Speaker 2: I make sense of this? It's all kind of complicated,
10:05
Speaker 2: but yeah, I'm following.
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Speaker 1: Yeah, And you call up this mental picture of a map.
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Speaker 1: So imagine you had a map the United States and
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Speaker 1: you laid it flat on a table and you measure
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Speaker 1: the distances between these cities. Those distances have to follow
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Speaker 1: some rules because the map is flat. If you measure
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Speaker 1: all those distances like from LA to Seattle, and Seattle
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Speaker 1: to New York and New York to Miami and Miami
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Speaker 1: back to LA, that's kind of a square, right, you
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Speaker 1: measure all those distances, and those distances have to follow
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Speaker 1: some rules because the map is flat on the table. Like,
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Speaker 1: from those distances, I can tell you how far it
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Speaker 1: is from LA to New York. It's constrained by those
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Speaker 1: other measurements. But what if I told you I'm just
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Speaker 1: going to go in and make LA and New York
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Speaker 1: closer together, I'm just squeezing them together. Well, then the
10:47
Speaker 1: map can no longer be flat because I have to
10:49
Speaker 1: like bunch up the material between LA and New York.
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Speaker 1: And that's what curving space does. It changes the relative
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Speaker 1: distances between these points, so they no longer add up
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Speaker 1: in the same way they would if they were on
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Speaker 1: flat space. That's what curved space is, just changes those
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Speaker 1: relative distances. And the crazy thing is that you can
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Speaker 1: do that. You can develop a model of space that
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Speaker 1: incorporates all these weird changes of distances. And that's what
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Speaker 1: we call curved space, all right.
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Speaker 2: So it's never tearing. There's never a spot where it
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Speaker 2: like breaks and then there's nothing in between. It just
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Speaker 2: kind of gets like curvy, like a roller coaster.
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Speaker 1: At some point exactly, you can't really tear space time.
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Speaker 1: That's like a dramatic visual people use, but it's not
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Speaker 1: a helpful way to think about it. And remember, we
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Speaker 1: don't know what space is. We have this beautiful mathematical
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Speaker 1: description from Einstein that lets us think about this concept
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Speaker 1: of curvature in terms of these changing relative distances, but
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Speaker 1: that's just our model. It's useful for describing space. Doesn't
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Speaker 1: always tell us what space actually is, but it does
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Speaker 1: predict crazy stuff like if you have a huge amount
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Speaker 1: of mass, the curvature gets really really strong, and you
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Speaker 1: get things like black holes, places where space is so
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Speaker 1: curved that light can no longer escape because not only
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Speaker 1: does it change the relation so distances, it changes like
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Speaker 1: the directions, and inside a black hole, space is now
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Speaker 1: one directional. Every direction inside a black hole is just
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Speaker 1: towards the center. It's not that light can't escape because
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Speaker 1: the force of gravity is so strong. It's because every
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Speaker 1: direction is towards the center. Now there are no other
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Speaker 1: directions inside a black hole. So a black hole is
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Speaker 1: so massive it like rearranges the relationships between points in space.
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Speaker 2: Okay, so the order of the direction there is that
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Speaker 2: the black hole starts pulling on space. It's not that
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Speaker 2: like space gets bent for some other reason, and that
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Speaker 2: causes a black hole.
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Speaker 1: Yeah, that's right. The presence of mass causes the bending
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Speaker 1: of space, and that's what the black hole is. Yeah, exactly. Okay,
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Speaker 1: So that's the way to think about like gravity and
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Speaker 1: black holes and bending of space time. But Burma is
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Speaker 1: asking us to connect that to the expansion of the
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Speaker 1: universe and how the universe we've noticed in the last
12:51
Speaker 1: twenty years or so is not just getting bigger, it's
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Speaker 1: getting bigger faster and faster as time goes on. And
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Speaker 1: this is the mystery we call dark energy. We don't
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Speaker 1: understand the source of that expansion or why it's accelerating.
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Speaker 2: Okay, so we know that it's accelerating, and we're using
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Speaker 2: dark energy as the explanation, and is that the extent
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Speaker 2: of what we know about dark energy is that it
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Speaker 2: is the magical way that this all works out.
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Speaker 1: Essentially, dark energy is shorthand for saying, we see the
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Speaker 1: universe is accelerating its expansion, we don't understand why. Please
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Speaker 1: somebody figure it out, and we don't have a working explanation.
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Speaker 1: We have sort of like a sketch on the back
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Speaker 1: of a napkin idea that might work out, But currently
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Speaker 1: the calculations are not connecting, and they're off by like
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Speaker 1: ten with one hundred zeros. But the sketch of the
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Speaker 1: explanation actually comes from general relativity. General relativity, of course,
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Speaker 1: is Einstein's generalization of Newton's gravity. Newton says, masses attract
13:47
Speaker 1: each other because there's a force. Einstein says, no, Actually
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Speaker 1: it's more complicated. Space time curves and it gives mostly
13:53
Speaker 1: the same behavior. But there's a little bit more to
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Speaker 1: Einstein's general relativity than just mass bend space time. Einstein's
14:00
Speaker 1: relativity also lets other things happen. So, for example, Einstein says, yes,
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Speaker 1: if you have mass in space time, then space curves
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Speaker 1: and things get closer together. But also if you fill
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Speaker 1: the universe with potential energy, not mass energy, but some
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Speaker 1: weird kind of potential energy, then it causes the opposite effect.
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Speaker 1: It causes things to move apart. It's like a negative pressure.
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Speaker 1: This is the fascinating thing is that Newton's gravity is
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Speaker 1: just attractive. You can only pull stuff together. Einstein's gravity
14:29
Speaker 1: is a generalization of that and allows in some weird
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Speaker 1: situations for things to get pushed apart by general relativity.
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Speaker 2: Okay, so we've got gravity and dark energy. Gravity pulls in,
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Speaker 2: dark energy pushes out. How do we determine who wins where?
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Speaker 1: Yes, all right, great question. But first I want to
14:46
Speaker 1: be technical about what we mean by gravity, because when
14:49
Speaker 1: some people hear gravity, they think the pulling together part.
14:53
Speaker 1: Other people hear gravity they think general relativity, which can
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Speaker 1: include dark energy. So in some sense, gravity could be
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Speaker 1: the attractive part and the dark energy part, or some
15:02
Speaker 1: people could just think about gravity as the attractive part.
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Speaker 1: So let's just call gravity the attractive part, and when
15:08
Speaker 1: we're talking about the whole shebang, we'll call it that
15:10
Speaker 1: general relativity. So you're asking about, like when is the
15:13
Speaker 1: attractive part of gravity, things tugging on each other when?
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Speaker 1: And when does dark energy the universe pulling itself apart? When?
15:19
Speaker 1: And that depends on distance. So the attractive part of
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Speaker 1: the parts is like Newton, that gets strong when things
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Speaker 1: are closer together, Like the closer you are to a star,
15:28
Speaker 1: the more it's gravity is going to pull on you,
15:30
Speaker 1: the more space time is bent in a way that's
15:32
Speaker 1: going to move you closer, and as you get further away,
15:35
Speaker 1: that fades. So like we don't feel much gravity from
15:38
Speaker 1: Jupiter because it's kind of far away. We don't feel
15:40
Speaker 1: much gravity from other stars because they're even further away,
15:43
Speaker 1: et cetera, et cetera. So gravity gets weaker with distance.
15:47
Speaker 1: Dark energy has the opposite relationship. Dark energy is like
15:50
Speaker 1: every chunk of space is getting bigger. So if you
15:54
Speaker 1: just have one little chunk of space, it's getting bigger
15:56
Speaker 1: by a tiny amount. But if you have lots of
15:58
Speaker 1: chunks of space huge day distances, then that adds up,
16:02
Speaker 1: and so over big distances, dark energy becomes very very powerful.
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Speaker 1: So like between our galaxy and other galaxies, there's a
16:10
Speaker 1: lot of space. If all that space is expanding by
16:13
Speaker 1: a little bit, all those little bits add up to
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Speaker 1: a huge expansion. So dark energy gets more powerful at
16:19
Speaker 1: greater distances. So, for example, between our cluster of galaxies
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Speaker 1: and the neighboring cluster of galaxies, dark energy is winning.
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Speaker 1: There's not enough gravity to hold those together, and they're
16:29
Speaker 1: getting pulled apart by dark energy. All that space is
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Speaker 1: expanding faster, and gravity can hold stuff together. But in
16:36
Speaker 1: our Solar system, though, there is dark energy here and
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Speaker 1: it is expanding the space between our planet and the Sun.
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Speaker 1: Gravity is more powerful because it's a fairly small distance
16:45
Speaker 1: so gravity wins, so shorter distances, like smaller than a
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Speaker 1: galactic supercluster, gravity wins big distances, bigger than a galactic supercluster,
16:55
Speaker 1: dark energy wins.
16:57
Speaker 2: Okay, so that makes sense to me. And so you
16:59
Speaker 2: said that that dark energy is a form of kinetic.
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Speaker 1: Energy potential energy.
17:05
Speaker 2: Actually, wow, they're the same thing.
17:07
Speaker 1: They're so one hundred percent not the same time.
17:10
Speaker 2: Smart. Okay, it's a form of potential energy. And so
17:13
Speaker 2: does that make dark energy like negative potential energy? Our
17:18
Speaker 2: gravity and dark energy just opposites of one another.
17:22
Speaker 1: Yeah, great question. So number one, we don't know where
17:24
Speaker 1: the potential energy comes from. That's the big mystery. Like
17:27
Speaker 1: to have enough potential energy to explain the accelerating expansion
17:31
Speaker 1: we see, you'd need a lot more energy than we
17:33
Speaker 1: can account for. If you add of all the potential
17:35
Speaker 1: energy we know about in the universe from the Higgs
17:37
Speaker 1: field and all the other fields and all that stuff,
17:39
Speaker 1: you get a number. That number we calculate doesn't match
17:43
Speaker 1: the accelerating expansion we see in the universe, and it's
17:46
Speaker 1: not even close. The two numbers are off by ten
17:49
Speaker 1: to the one hundred and twenty. So general relativity has
17:53
Speaker 1: a mechanism to create this negative pressure requires positive potential energy.
17:59
Speaker 1: We can't explain source of that potential energy we don't know,
18:02
Speaker 1: So that's the remaining mystery, Like there is no potential
18:05
Speaker 1: energy we know about that is capable of doing this,
18:07
Speaker 1: which might mean there's some other field out there we
18:09
Speaker 1: don't understand. But it requires positive potential energy to create
18:13
Speaker 1: this negative pressure, this pulling things apart. So to bring
18:17
Speaker 1: this sort of back to Bhima's question, he's asking, like,
18:20
Speaker 1: could dark energy be anti gravity? And the answer is
18:24
Speaker 1: kind of yes, Like dark energy is a component of
18:27
Speaker 1: general relativity that allows for pulling things apart, sort of
18:30
Speaker 1: opposite to the attractive part of gravity. So if you
18:34
Speaker 1: consider gravity to just be the attractive part of general relativity,
18:37
Speaker 1: and then yeah, dark energy is sort of the opposite
18:39
Speaker 1: of that. It's still a component of general relativity, but
18:43
Speaker 1: it has the opposite effect that creates negative pressure.
18:46
Speaker 2: Okay, well, thank you for that great question, Burima.
18:49
Speaker 1: And so now I'm curious whether we answered Bhurima's question,
18:52
Speaker 1: whether we scratched his itch, or whether we totally misunderstood,
18:55
Speaker 1: or whether we just confused him further with our crazy
18:58
Speaker 1: description of LA and my so I reached out to
19:02
Speaker 1: Burima and I sent him our conversation to hear what
19:04
Speaker 1: he had to say. Here's Burma's reaction. Okay, thank you
19:08
Speaker 1: very much Burima for joining us here on the podcast
19:11
Speaker 1: and for sending in such a wonderful and fun question.
19:14
Speaker 1: So tell me what did you think of our answer
19:16
Speaker 1: and did we answer your question? Did we create more
19:18
Speaker 1: questions in your mind? I'm dying to hear your thoughts.
19:22
Speaker 5: Yeah, So thank you for answering the question. It's great
19:24
Speaker 5: to be here. I think you guys pretty much answered
19:28
Speaker 5: the question bang on. It did blow my mind, if
19:31
Speaker 5: I'm being one hundred percent honest, because at first I
19:34
Speaker 5: was like, Okay, where is this going, and then at
19:36
Speaker 5: the end sort of just landed it very nicely. It
19:39
Speaker 5: did raise another question that I have. You mentioned the
19:43
Speaker 5: dark energy sort of being caused by potential energy, and
19:48
Speaker 5: my follow up question was does that have anything to
19:51
Speaker 5: do with then zero point energy?
19:54
Speaker 1: Yeah, so the two things are definitely connected. Zero point
19:57
Speaker 1: energy is a description of basically minimum energy that a
20:01
Speaker 1: quantum field can have. Quantum fields are like oscillating in space.
20:04
Speaker 1: There's zigging and zagging, they're whizzing back and forth. There's
20:07
Speaker 1: energy there of their motion, the changing of their values.
20:10
Speaker 1: That's kinetic energy, and they can also have potential energy
20:12
Speaker 1: if they're in some weird configuration. Zero point energy just
20:16
Speaker 1: says that the total energy, the combination of kinetic and
20:19
Speaker 1: potential and any other kind of energy, can never go
20:21
Speaker 1: to zero because quantum fields can never be totally flat
20:25
Speaker 1: like a classical field. An electrical field can be just zero.
20:28
Speaker 1: You can have like no electric field because you have
20:30
Speaker 1: no electric charges. It can be totally zero. But if
20:33
Speaker 1: it's a quantum field, it's always buzzing and frothing a
20:35
Speaker 1: tiny little bit. There's a minimum energy there. But the
20:39
Speaker 1: potential energy we think is causing dark energy comes from
20:42
Speaker 1: a field we don't know. We don't know what field
20:44
Speaker 1: is out there doing it. There's only one field we
20:47
Speaker 1: know about that has a lot of potential energy. That's
20:49
Speaker 1: the Higgs field. We know that it fills space with
20:52
Speaker 1: this weird potential energy that gives all particles mass. But
20:55
Speaker 1: when we sit down and try to calculate is the
20:57
Speaker 1: potential energy from the Higgs field enough to explain dark
21:00
Speaker 1: energy and the acceleration, we find that it's not like
21:03
Speaker 1: they're different by ten with one hundred zeros. So, yeah,
21:08
Speaker 1: we're not even close to understanding the source of dark energy. Yeah,
21:12
Speaker 1: we're not even close to being close.
21:15
Speaker 5: Yeah, okay, yeah, well thank you, yeah.
21:19
Speaker 1: Yeah, well, thanks very much for sending your question and
21:22
Speaker 1: for doing this follow up. Lots of fun to chat
21:24
Speaker 1: with you.
21:24
Speaker 5: Yeah, thank you very much. It's been a pleasure and
21:27
Speaker 5: I learned something.
21:29
Speaker 1: And that's our entire goal. All Right, Thanks everyone, And
21:32
Speaker 1: if you have a question about the nature of the universe,
21:35
Speaker 1: or if you'd heard something you haven't quite understood, please
21:37
Speaker 1: send it to us. We'd love to answer your question.
21:40
Speaker 2: All right, Well that was our first question. Now we're
21:43
Speaker 2: going to move on to a question in Kelly's wheelhouse,
21:45
Speaker 2: which we'll get to after the break. All right, we're
22:05
Speaker 2: back from the break and we're going to tackle our
22:06
Speaker 2: first biology oriented listener question. So Charlie Davidson had this
22:12
Speaker 2: question for us.
22:14
Speaker 6: Hi, Daniel and Kelly, I've got a question for your
22:16
Speaker 6: new podcast about slime mold computation. How is it possible
22:21
Speaker 6: for a bunch of single celled organisms to perform programmable
22:25
Speaker 6: computational tasks for people? It just seems wild to me,
22:30
Speaker 6: so I'd love to hear more about it and find
22:32
Speaker 6: out how on Earth that works. Thanks very much, by.
22:35
Speaker 2: Bye, oh Man, Charlie. In my family, we call this
22:39
Speaker 2: the ten thousand dollars question because that's how much money
22:44
Speaker 2: we lost thinking about this problem. So here is the story,
22:48
Speaker 2: all right. So slime molds are single celled organisms that
22:53
Speaker 2: are thought to be really great at solving mases. This
22:56
Speaker 2: has become like a fact that's entered the you know,
22:58
Speaker 2: general consciousness. You say something about slime molds and they'll
23:01
Speaker 2: be like, oh, they're really great at solving mazes, and
23:04
Speaker 2: they've become famous for like solving straight up mazes. They've
23:07
Speaker 2: also become famous for being able to recreate transportation systems.
23:11
Speaker 2: So if you put a bunch of different cities on
23:14
Speaker 2: a map, and you put a piece of oat on
23:17
Speaker 2: the different cities, the slime mold will start growing on
23:20
Speaker 2: that oat. I believe it's actually eating the bacteria and
23:22
Speaker 2: the fungus on that oat, and then it will spread
23:25
Speaker 2: out and it will find the other oats, and if
23:28
Speaker 2: it's working the way we want it to work, it
23:31
Speaker 2: will then contract and only have the shortest paths between
23:35
Speaker 2: those things. And so perhaps you've seen videos that like
23:40
Speaker 2: where the slime molds have created this map that is
23:42
Speaker 2: almost exactly the same as like the map of the
23:44
Speaker 2: transportation system matches up almost perfectly with what the slime
23:47
Speaker 2: mold did. It's really impressive.
23:49
Speaker 1: This is really appealing. I understand why people are into
23:51
Speaker 1: this because it suggests like there's another way to do calculations,
23:54
Speaker 1: or this is like a biological computer, or maybe even
23:57
Speaker 1: some like awareness. Right. I feel like we were so
24:00
Speaker 1: hungry to discover we're not alone in the universe that
24:03
Speaker 1: we're looking for like aliens here on Earth, even in
24:05
Speaker 1: slime molds.
24:06
Speaker 2: Yeah right, well, I mean if slime olds can be
24:08
Speaker 2: that smart, what else have we missed? Right? That's incredible. Yeah,
24:11
Speaker 2: and did you see the dark matter example?
24:13
Speaker 1: Mm hmmm I did. Yet they used slime molds to
24:16
Speaker 1: understand the filaments of dark matter between galaxies, which was
24:20
Speaker 1: pretty cool.
24:21
Speaker 2: I think that they used a computational model based on
24:24
Speaker 2: the behavior of slime molds. Yeah, since it's like a
24:27
Speaker 2: three D things that would be a little bit harder
24:28
Speaker 2: to do.
24:29
Speaker 1: No, I don't think they had like cosmic slime molds
24:31
Speaker 1: between actual galaxies. That would be awesome.
24:33
Speaker 2: Wow, that would be made me scary but interesting. So
24:37
Speaker 2: my husband and I got really excited about these slime molds.
24:39
Speaker 2: We're like, you know, this seems like such an easy
24:43
Speaker 2: thing that you should be able to recreate at home.
24:45
Speaker 2: And so many science experiments are you know that we
24:48
Speaker 2: remembered that we did at school when we were kids.
24:50
Speaker 2: We're like, not super exciting. They didn't necessarily stay with you.
24:53
Speaker 2: So we got really excited about making slime mold mazes
24:57
Speaker 2: that you could sell pretty cheaply to class so that
25:00
Speaker 2: they could recreate these experiments.
25:02
Speaker 1: I'm getting an ironic foreshadowing vibe here that you're setting
25:06
Speaker 1: us up for a big disappointment. Is this going to
25:07
Speaker 1: be another Kelly throws cold water on things?
25:09
Speaker 2: I mean, that's what I do, right, How else could
25:11
Speaker 2: this have.
25:12
Speaker 1: Gone into your skills? Kelly?
25:15
Speaker 2: You know, yeah, I didn't think this was going to
25:16
Speaker 2: be my niche, but it is, so here we go,
25:18
Speaker 2: all right. So Zach was excited about this first. I
25:21
Speaker 2: was busy with something else at the time. So we
25:23
Speaker 2: were living in Alabama and he was like in our
25:25
Speaker 2: humid garage trying to use legos to build mazes, and
25:29
Speaker 2: then he was pouring auger in there, and augur, is
25:32
Speaker 2: this thing that like when it's hot it's sort of
25:33
Speaker 2: like viscous and fluidy, but when it cools, it cools
25:36
Speaker 2: to like kind of smooshy surface that something can grow on.
25:39
Speaker 2: So he was trying to like make mazes in our
25:42
Speaker 2: garage out of this stuff. And then he went to
25:44
Speaker 2: Carolina Biological website and he bought slime mold. Specifically, he
25:48
Speaker 2: bought fisarm polycephalus, which is the main like yellow species
25:51
Speaker 2: that people usually see when they're thinking of these mazes.
25:54
Speaker 1: But tell us briefly, what is a slime mold exactly?
25:57
Speaker 1: Is it a mold? Is it slime? Is it totally
25:59
Speaker 1: badly named?
26:00
Speaker 2: It's not really a slime. It's not really a mold.
26:02
Speaker 2: It's its own thing. It has a complicated life cycle.
26:05
Speaker 2: But when it's at the part of its life cycle
26:07
Speaker 2: where it is solving these mazes, it's a single cell
26:12
Speaker 2: with a bunch of nuclei in it. Wow, which is
26:15
Speaker 2: kind of amazing. I think we should actually have a
26:17
Speaker 2: whole episode on why organisms would ever have multiple nuclei
26:21
Speaker 2: in the same cell, Like what problems does that solve?
26:23
Speaker 2: Because my brain like more than one nucleus. That just
26:26
Speaker 2: doesn't make sense. So he was trying to do it
26:28
Speaker 2: that wasn't working, and so then we moved to Virginia
26:31
Speaker 2: and he was like, okay, you know what, I'm going
26:33
Speaker 2: to like outsource to experts. So he hired an engineer
26:36
Speaker 2: and he was like, all right, engineer, I want you
26:37
Speaker 2: to make me a really nice maze because the augur
26:40
Speaker 2: kept like seeping through my legos. It just wasn't working
26:43
Speaker 2: the way I wanted it. To make me a really
26:45
Speaker 2: nice maze with a really nice cover. And the engineer
26:47
Speaker 2: is like, okay, great, I'll do that, but it's going
26:50
Speaker 2: to cost ten thousand dollars to make an injection molded maze.
26:54
Speaker 2: And Zach was like, oh, that's a little steep, but
26:56
Speaker 2: I really think kids would enjoy this, and we're going
26:59
Speaker 2: to do it. So he pays and he does it. Yeah,
27:02
Speaker 2: I know, And so he ran it by me and
27:04
Speaker 2: I was like, I don't know that that's a great decision,
27:06
Speaker 2: but okay, let's try it.
27:08
Speaker 1: This is what happens when you have one family with
27:10
Speaker 1: two nuclei right yere, different nuclei i making different decisions,
27:13
Speaker 1: like you know, this slime mold is spending ten k
27:15
Speaker 1: over here, and that nuclei is objecting to it. You know,
27:18
Speaker 1: it's like a model of a family.
27:19
Speaker 2: That's totally true. I should have known this problem was coming.
27:22
Speaker 2: So he gets this maze, and you know, we've had
27:24
Speaker 2: a lot of conversations about like, oh, it's so funny
27:26
Speaker 2: that Carolina Biological sells slime mold, but they don't sell
27:29
Speaker 2: these mazes. I wonder why they don't sell these mazes.
27:32
Speaker 2: And so we get the mazes and then Zach's like, okay,
27:34
Speaker 2: so now I'm taking this project to the biologist. So
27:36
Speaker 2: I got a bunch of augur, I got a bunch
27:38
Speaker 2: of slime molds. I'm like using my sterile technique, and
27:41
Speaker 2: I'm trying to run these mazes. And it's my job
27:44
Speaker 2: to write the protocol and the direction so the classrooms
27:46
Speaker 2: can do this. And so I start doing it and
27:49
Speaker 2: it's not working. The slimepuwter is not solving the maze
27:54
Speaker 2: the way it's supposed to.
27:55
Speaker 1: So what is it supposed to do? Exactly, Like you
27:57
Speaker 1: put it in the beginning and you put an ode
27:59
Speaker 1: at the end. It's supposed to find the shortest path
28:01
Speaker 1: through the maze exactly, and how could it possibly do that?
28:05
Speaker 1: Like it's supposed to explore every direction and then eventually
28:08
Speaker 1: figure out which of the paths is found is the shortest,
28:11
Speaker 1: and then slowly coalesce onto that. Is that the best
28:13
Speaker 1: case scenario.
28:14
Speaker 2: So that's what we thought was supposed to be happening.
28:16
Speaker 2: And so I contacted an expert who works in this field,
28:20
Speaker 2: and I was like, it's not working for me? Why
28:22
Speaker 2: is it not working for me?
28:23
Speaker 1: Meaning what were you seeing? Like it just didn't find
28:25
Speaker 1: the end or found the wrong path, or it just didn't.
28:27
Speaker 2: Go anywhere, or it was not finding the shortest path.
28:30
Speaker 2: I see something like twenty to thirty percent of the
28:33
Speaker 2: time it would end up at the right path, which
28:36
Speaker 2: was essentially like random chance. And I contacted a person
28:39
Speaker 2: who was doing even simpler experiments in their class. But
28:42
Speaker 2: it was like a peatrit dish and then an oat
28:44
Speaker 2: in the middle is a starting point and an oat
28:46
Speaker 2: on one side, and so it should have been very
28:49
Speaker 2: simple to just like it expands and then it was
28:51
Speaker 2: supposed to just sort of contract to just be this
28:53
Speaker 2: short straight line distance. And they were like, oh, yeah,
28:56
Speaker 2: that experiment never worked, but apparently at always, well maybe
28:59
Speaker 2: your students are doing something wrong. So I reached out
29:01
Speaker 2: to this expert and he's like, well, first of all,
29:04
Speaker 2: the way that it solves it is it's following a
29:06
Speaker 2: chemical trail, and so the chemical trail needs to be
29:11
Speaker 2: incredibly easy to detect. So instead of oatmeal, you could
29:14
Speaker 2: try something that's like creates more chemicals and makes a
29:17
Speaker 2: more clear path. And I was like, well that's not
29:21
Speaker 2: how I had been taught that this works. And I
29:23
Speaker 2: was like, okay, well, what percent of the time, if
29:26
Speaker 2: I'm doing it right, should I expect it to solve
29:29
Speaker 2: the maze? Because, like I'm thinking, the answer should be
29:31
Speaker 2: close to one hundred percent. Based on what people are
29:32
Speaker 2: saying on Twitter.
29:34
Speaker 1: Always are reliable resource. Twitter is basically one big documentary, Right,
29:38
Speaker 1: you can rely on it?
29:39
Speaker 6: Yeah?
29:39
Speaker 2: Right. We spent ten k based on Twitter advice. It
29:41
Speaker 2: was a great choice.
29:42
Speaker 1: I cig Twitter in my science papers all the time.
29:44
Speaker 2: Oh wow, No, of course it's a good thing. You've
29:48
Speaker 2: got tenure.
29:50
Speaker 1: Anyway, So you're told that these things don't actually solve
29:53
Speaker 1: the problem. They just follow a trail, which is very
29:55
Speaker 1: different from like considering all the past to figure out
29:58
Speaker 1: which is shortest and then coalescing on that one. That's
30:00
Speaker 1: like they just walked through to the solution.
30:02
Speaker 2: Sometimes I'll smell a hot dog, and I'll just walk
30:04
Speaker 2: towards the source of the hot dog, and it's like,
30:06
Speaker 2: not that different. That's not impressive that I can do that.
30:09
Speaker 1: Can you actually resist hot dogs? Like if you walk
30:11
Speaker 1: after hot dog, everybody knows you're kryptonite. Now wow, it's
30:17
Speaker 1: just like.
30:18
Speaker 2: I actually can't. I worked at the zoo once and
30:20
Speaker 2: we switched from all beef hot dogs to all meat
30:23
Speaker 2: hot dogs. Ooh, and wondering what that downgrade meant put
30:28
Speaker 2: me off hot dogs because I started thinking about it
30:30
Speaker 2: too hard. But anyway, well, let's not droll on hot dogs.
30:32
Speaker 2: So I ask, Okay, if I find the perfect, very
30:36
Speaker 2: smelly thing that the slime mold can like queue in on,
30:39
Speaker 2: that's gonna work better than my oats, what percent of
30:42
Speaker 2: the time should I expect this to work? And they
30:44
Speaker 2: said thirty or forty percent. That's not great, no, And
30:48
Speaker 2: that's when I realized. I went back through all the
30:50
Speaker 2: papers and I was like, oh my gosh, it says
30:53
Speaker 2: for the slime molds that solved the maize, but they
30:56
Speaker 2: don't include the number of times the maze wasn't solved,
31:00
Speaker 2: And so I think a lot of times what's happening
31:02
Speaker 2: is like these scenarios are set up, and the one
31:05
Speaker 2: time out of one hundred that the slime mold gets
31:07
Speaker 2: it close, they're like, WHOA, that's incredible and that's what
31:10
Speaker 2: makes the news. And maybe I'm missing something, but it
31:13
Speaker 2: seems to me that, like, maybe under absolutely perfect conditions,
31:16
Speaker 2: when you replicate things a bunch of times, slime molds
31:18
Speaker 2: come up with the right answer. But as far as
31:20
Speaker 2: I can tell, mostly they're following a chemical gradient. Probably
31:24
Speaker 2: chemical gradients aren't that strong in nature, like as strong
31:27
Speaker 2: as you're able to make it in these enclosed mazes.
31:29
Speaker 2: So I am personally not super impressed with slime old
31:32
Speaker 2: computational abilities. And maybe that's just me being bitter that
31:36
Speaker 2: we weren't able to make these kits to give to
31:39
Speaker 2: classrooms and we like tanked all this time and money
31:41
Speaker 2: on the project. But that is my take on slime
31:44
Speaker 2: mold computational ability.
31:46
Speaker 1: It sounds to me like somebody's got a room full
31:47
Speaker 1: of monkeys and one of them types of Shakespeare, and
31:50
Speaker 1: they're like, look, monkeys can tap Shakespeare. Let's make a
31:52
Speaker 1: meme about it. I mean, is it better than that,
31:54
Speaker 1: is actually a little bit better than random? Or is
31:56
Speaker 1: it completely exaggerated.
31:58
Speaker 2: I think it is probably a little better than random.
32:01
Speaker 2: Some of the problems that they're being asked to solve
32:03
Speaker 2: are really complicated. But I do think it's mostly following
32:06
Speaker 2: a chemical gradient, which is less interesting than doing computations
32:10
Speaker 2: about the shortest way to get to a thing or whatever.
32:12
Speaker 2: But I just feel like the whole answer has been
32:14
Speaker 2: kind of over sold. And if somebody thinks that I'm
32:17
Speaker 2: wrong and I've missed something, I would love to hear that,
32:19
Speaker 2: because actually, we just found out that we have to
32:21
Speaker 2: make a decision about whether or not we're going to
32:23
Speaker 2: throw out that injection mold thing.
32:25
Speaker 1: You still have it.
32:26
Speaker 2: It's in a warehouse somewhere, and they're like, you can
32:28
Speaker 2: either pay two hundred dollars to get rid of it,
32:30
Speaker 2: or we can ship it to you on a palette.
32:32
Speaker 2: And I'm like, I'm a palette. Where am I going
32:34
Speaker 2: to keep this thing? Let us know if you know
32:36
Speaker 2: the answer. But like, slime molds are still awesome, those
32:40
Speaker 2: paths that they're creating that is a single cell with
32:43
Speaker 2: multiple nuclei. There's also slime molds called dog vomit slime mold,
32:48
Speaker 2: which you often find in your mulch on moist, warm
32:52
Speaker 2: summer days and it does kind of look like dog
32:54
Speaker 2: vomit and it's one of my favorite full of go septica.
32:57
Speaker 2: And so slime molds are fascinating and we had the
33:00
Speaker 2: miscategorized for a while. We kind of couldn't figure out
33:02
Speaker 2: what they were. But I'm not totally convinced that they
33:06
Speaker 2: are amazing problem solvers.
33:09
Speaker 1: Sorry, And are they always single cells? I mean we're
33:13
Speaker 1: talking about an extended thing, right, It's like this single
33:15
Speaker 1: cell can be like a meter across. That kind of
33:17
Speaker 1: blows my mind.
33:18
Speaker 2: They have different stages in their life cycle. I think
33:22
Speaker 2: at other stages they might not be single celled. Not
33:25
Speaker 2: an expert on these, but at the stage that everybody's
33:28
Speaker 2: seeing for the maze solving stage, they are a single
33:32
Speaker 2: solve with a bunch of nuclei.
33:34
Speaker 1: And are there other examples of things out there in
33:36
Speaker 1: nature that can do something similar and that are also
33:39
Speaker 1: over sold or is there anything out there that actually
33:41
Speaker 1: can solve this kind of problem in an impressive way
33:44
Speaker 1: or is biology all just a dank meme.
33:49
Speaker 2: I'm reaching real far back here. I watched this really
33:52
Speaker 2: interesting lecture from a woman who studied crows. So this
33:56
Speaker 2: isn't like maze solving, but they're super clever. Like if
33:59
Speaker 2: there was another crow in the room, they would bury
34:02
Speaker 2: their treat and then when the crow turned around, they
34:04
Speaker 2: would take the treat out and they'd bury it somewhere else.
34:07
Speaker 2: So they knew like that bird was watching me and
34:10
Speaker 2: I want to trick it, and that's not watching now,
34:11
Speaker 2: So now it's time for me to move where I
34:13
Speaker 2: hid my cash. Clever, there are very smart organisms. I
34:17
Speaker 2: think this is just an exciting thing that escaped that
34:19
Speaker 2: has maybe since been oversold.
34:22
Speaker 1: It sounds like the puzzle you really sold was why
34:25
Speaker 1: Carolina Biological doesn't carry meses in their catalog.
34:29
Speaker 2: Exactly that is the puzzle we solved. And so now
34:33
Speaker 2: we need to find out does Charlie Davidson like answers
34:37
Speaker 2: that are kind of a bummer? And did I mistakenly
34:40
Speaker 2: assume that he wanted to talk about slime wolds but
34:42
Speaker 2: he had another single celled organism in mind. Let's hear
34:46
Speaker 2: from Charlie and find out.
34:48
Speaker 6: Thank you for answering the question, guys, that's exactly what
34:51
Speaker 6: I wanted to have answered. The computational bitites of slime
34:55
Speaker 6: molds are no longer impressive to me either, but never mind,
34:58
Speaker 6: can't win them all. I was hoping it would be
35:01
Speaker 6: something far more amazing, but it's the way it is,
35:04
Speaker 6: I guess. Thank you so much, sake. I do believe
35:07
Speaker 6: we have dog vomit slime mold. In the UK, we
35:09
Speaker 6: call it, which is brew If it's the same thing.
35:12
Speaker 6: I'm not sure which name I prefer, but either or
35:15
Speaker 6: ice codes. Thanks very much, look forward to future podcasts.
35:19
Speaker 1: All right, enough about single cell organisms, hot dogs and
35:22
Speaker 1: slime molds. When we come back, we're going to tackle
35:24
Speaker 1: another question about space and time and black holes. All right,
35:45
Speaker 1: we're back, and we are answering questions from the audience.
35:47
Speaker 1: Questions from people like you. If there's something about the
35:50
Speaker 1: universe it's never clicked in your mind, or if you've
35:53
Speaker 1: heard us talk about something that didn't quite make sense
35:55
Speaker 1: to you, please write to us. We want to follow up.
35:58
Speaker 1: We want those ideas to connect in your head so
36:01
Speaker 1: that you feel like you understand as well. We will
36:03
Speaker 1: answer any questions you send to us to questions at
36:06
Speaker 1: danieland Kelly dot org, even dating questions. Though we don't
36:11
Speaker 1: claim any expertise.
36:12
Speaker 2: Oh I'm an expert. I did a lot of dating.
36:14
Speaker 2: But I don't know if anyone wants my advice.
36:18
Speaker 1: Well, if they know Zach, that they can evaluate whether
36:20
Speaker 1: they think that went well for you or not.
36:23
Speaker 2: Yeah, it's up in the air.
36:26
Speaker 1: TBD. All right. In the meantime, here's a question we
36:30
Speaker 1: got from Derek in New Hampshire, who's thinking about black
36:33
Speaker 1: holes and Hawking radiation.
36:36
Speaker 4: I was wondering, can a black hole be so massive
36:40
Speaker 4: that not even Hawkins radiation can escape from its gravitational pull?
36:45
Speaker 4: Look forward to you and your answer.
36:47
Speaker 1: Thanks.
36:47
Speaker 2: All right, So this is a great question. We did
36:50
Speaker 2: a little bit of an intro into black holes as
36:52
Speaker 2: part of the very first question. Maybe the right place
36:55
Speaker 2: to start is what is Hawking radiation?
36:59
Speaker 1: Yeah? Great, So Derek's basically asking about the glow that
37:03
Speaker 1: we think black holes might make. We talked in the
37:06
Speaker 1: earlier question about what black holes are. They are regions
37:10
Speaker 1: of space time that are so bent, so deformed, that
37:13
Speaker 1: space is now only pointing inwards. So you shine a
37:16
Speaker 1: flashlight inside a black hole, it's only going to go
37:19
Speaker 1: towards the center. There's no path out from behind the
37:21
Speaker 1: event horizon. And that's a description of a black hole
37:24
Speaker 1: that comes from general relativity it's Einstein's theory that says
37:27
Speaker 1: space gets bent and the space tells matter how to
37:29
Speaker 1: move and all this kind of stuff. But we know
37:32
Speaker 1: that general relativity can't be the final story of the
37:34
Speaker 1: universe because it's not compatible with the other story we
37:37
Speaker 1: have about the universe, which is quantum mechanics. And in particular,
37:41
Speaker 1: Einstein's theory of black holes predicts that they're totally black,
37:45
Speaker 1: that if you look at a black hole, there's no glow.
37:48
Speaker 1: It's not emitting anything, No light comes off of the
37:51
Speaker 1: black hole. But if you do try to account a
37:54
Speaker 1: little bit for quantum mechanical effects, and this is what
37:56
Speaker 1: Hawking did, it predicts something different. It predicts that black
37:59
Speaker 1: holes aren't not actually totally black, that they glow very
38:02
Speaker 1: faintly with this radiation he called, of course, Hawking radiation.
38:07
Speaker 2: He named it after himself. Isn't someone supposed to do
38:11
Speaker 2: that for you?
38:12
Speaker 1: He actually worked it out with a student of his.
38:14
Speaker 1: But yeah, it's called Hawking radiation and not Hawking Beckenstein radiation.
38:18
Speaker 2: The next wasp by discover is gonna be Wienersmith's wasp
38:21
Speaker 2: do it of course.
38:23
Speaker 1: Okay, this is really a very impressive bit of physics.
38:26
Speaker 1: It's like an end run around a bigger problem. The
38:29
Speaker 1: biggest problem in modern physics right now is like, how
38:31
Speaker 1: do we reconcile quantum mechanics, which tells us that like
38:35
Speaker 1: stuff doesn't have a specific location, it can be here
38:38
Speaker 1: or it can be there. And general relativity, which tells
38:41
Speaker 1: us like space gets bent based on where stuff is,
38:44
Speaker 1: and general relativity can't handle if stuff doesn't have a
38:47
Speaker 1: specific location, Like if the particles may be here and
38:50
Speaker 1: maybe there is, space may be bent here and maybe
38:53
Speaker 1: bent there or partially bent here, partially bent there. Nobody
38:56
Speaker 1: knows how to bring these two things together, which is
38:58
Speaker 1: what you have to do if you want, I want
39:00
Speaker 1: a theory of general relativity that's consistent with quantum mechanics.
39:04
Speaker 1: Nobody knows how to do that. Big question, lots of
39:06
Speaker 1: Nobel prize is waiting. But what Hacking did was like
39:09
Speaker 1: an end run around that. He's like, can't figure out
39:11
Speaker 1: the big problem, but maybe I can sort of chip
39:13
Speaker 1: away at it a little bit. So he found a
39:16
Speaker 1: little trick that let him think about what happened to
39:19
Speaker 1: quantum fields near an event horizon, and his trick let
39:23
Speaker 1: him make this prediction that black hole should glow a
39:26
Speaker 1: little bit.
39:26
Speaker 2: Can you remind me what an event horizon is?
39:29
Speaker 1: Right? Thank you? An event horizon is what we think
39:30
Speaker 1: of is like the edge of the black hole. Inside
39:32
Speaker 1: the event horizon, everything is trapped forever. Outside the event horizon,
39:36
Speaker 1: you're still free. So you can approach a black hole,
39:39
Speaker 1: be near the event horizon, and then escape and go
39:41
Speaker 1: back to your planet and live a happy life. If
39:43
Speaker 1: you cross the event horizon, you're in the black hole forever.
39:47
Speaker 1: I think there's also a lot of confusion out there
39:49
Speaker 1: about hawking radiation and what it means and how to
39:52
Speaker 1: think about it, because I've said that we don't understand
39:56
Speaker 1: how particles are affected by really strong gravity, And the
39:59
Speaker 1: typical story you hear is that hawking radiation comes from
40:03
Speaker 1: particles being created near the event horizon, like particle antiparticle
40:08
Speaker 1: pairs popping out of the vacuum and one falls into
40:11
Speaker 1: the event horizon and the other doesn't. And so to
40:14
Speaker 1: do that calculation, it feels like you'd need to understand
40:16
Speaker 1: how gravity works for particles. Well, the thing is, that's
40:20
Speaker 1: not how hawking radiation works. That's the well worn pop
40:24
Speaker 1: side cartoon version of it, but it doesn't actually make
40:27
Speaker 1: any sense. I mean, virtual particles can't be treated like
40:31
Speaker 1: real particles. They're not real particles. You shouldn't think of
40:34
Speaker 1: the vacuum as like filled with actual particles that can
40:37
Speaker 1: fall into black holes. And we don't know how to
40:39
Speaker 1: do those calculations for gravity of particles. Instead, what Hawking
40:43
Speaker 1: did was take a very different approach. He just said,
40:46
Speaker 1: what happens to quantum fields if there's a discontinuity in space,
40:51
Speaker 1: if there's an event horizon, how do I solve the
40:54
Speaker 1: mathematics of a quantum field near an event horizon? And
40:58
Speaker 1: what he found was the only way to make the
40:59
Speaker 1: math work for quantum field near an event horizon was
41:03
Speaker 1: to have an outgoing wave of radiation, and that's what
41:06
Speaker 1: he interpreted as Hawking radiation. He doesn't have a microscopic
41:10
Speaker 1: particle picture of Hawking radiation. What's happening to individual particles?
41:14
Speaker 1: We don't know how to do that, but we do
41:16
Speaker 1: know that quantum mechanics says, if there's an event horizon
41:19
Speaker 1: in space, then your quantum fields have to radiate. And
41:23
Speaker 1: the really cool thing about this is that you don't
41:25
Speaker 1: need a complete solution to quantum gravity to attack it.
41:28
Speaker 1: In this way. This is really Hawking's brilliance of finding
41:31
Speaker 1: a sort of an end run around having to have
41:33
Speaker 1: the whole picture and still getting this one result from
41:36
Speaker 1: this mathematical trick. And there's another beautiful angle to this
41:40
Speaker 1: to make it a little bit more satisfying. Even though
41:42
Speaker 1: you can't think about the individual particles and how they're
41:45
Speaker 1: affected by gravity, you can think about hawking radiation like thermodynamically.
41:50
Speaker 1: The way Hawking thought about it and his student Bekenstein
41:53
Speaker 1: was that black holes eat information, black holes eat entropy. Right,
41:58
Speaker 1: all the disorder in the universe into a black hole.
42:01
Speaker 1: Is it decreasing? Is it violating the second law of thermodynamics.
42:04
Speaker 1: They showed that on one hand, you can think about
42:06
Speaker 1: it mathematically quantum fields radiating energy near an event horizon,
42:10
Speaker 1: But you can also think about it thermodynamically, meaning that
42:13
Speaker 1: black holes, if they have information, if they have entropy,
42:17
Speaker 1: they should have temperature. And if they have temperature, then
42:20
Speaker 1: they glow like everything else in the universe that has temperature.
42:24
Speaker 1: I glow, you glow, the sun glows. Things glow based
42:27
Speaker 1: on their temperatures. Hotter things glow with higher frequency, colder
42:32
Speaker 1: things glow with lower frequency. More infrared hot things glow
42:36
Speaker 1: in like the X ray and the ultraviolet. So it
42:38
Speaker 1: turns out you can model black holes as if they
42:41
Speaker 1: are black body radiators, things that glow just based on
42:45
Speaker 1: their temperature. Of course, they're extraordinarily cold, tiny, tiny temperatures.
42:50
Speaker 1: And the weird thing is that as a black hole
42:52
Speaker 1: gets bigger, it gets more massive, it actually gets colder
42:56
Speaker 1: and it glows more dimly. So smaller black holes glow
43:00
Speaker 1: more brightly and evaporate more quickly, and larger black holes
43:04
Speaker 1: glow more dimly because they're colder. So that's another fun
43:07
Speaker 1: way that you can think about hawking radiation that helps
43:10
Speaker 1: you sort of get a mental picture of it.
43:12
Speaker 2: Okay, and then one more follow up question. So when
43:14
Speaker 2: we've talked in the past, we've said that quantum mechanics
43:18
Speaker 2: and general relativity they don't make the same predictions, But
43:22
Speaker 2: usually that doesn't matter because any question that you have
43:26
Speaker 2: usually just requires you to think in one of those terms.
43:29
Speaker 2: That's right, Why with black holes, is it important to
43:32
Speaker 2: understand both of them?
43:34
Speaker 1: Yeah, great question. Usually you can ignore general relativity when
43:38
Speaker 1: you're doing quantum mechanics because particles have almost no mass
43:41
Speaker 1: and so they hardly bend space, their gravity is basically irrelevant.
43:45
Speaker 1: Usually you could ignore quantum mechanics when you're doing general
43:48
Speaker 1: relativity because you're dealing with big masses like planets, and
43:50
Speaker 1: for planets, the quantum mechanical effects a'll average out to zero,
43:53
Speaker 1: so usually you could ignore one or the other. When
43:56
Speaker 1: you're dealing with black holes, you're dealing with very short
43:58
Speaker 1: distances or very very strong gravity. So now you want
44:01
Speaker 1: to know the answer to like what happens to a
44:03
Speaker 1: particle near the edge of an event horizon. You have
44:07
Speaker 1: like very very strong gravity enough to pull on a particle,
44:10
Speaker 1: and you want to know what's going to happen to
44:12
Speaker 1: my electron? Is going to go this way? Or is
44:13
Speaker 1: it going to go that way? Or if it splits
44:15
Speaker 1: into other particles, what happens to it. Now you want
44:17
Speaker 1: to answer questions about the gravity of particles, you need
44:20
Speaker 1: to be able to include the effects of gravity and
44:23
Speaker 1: to be able to describe that particle as a quantum
44:25
Speaker 1: mechanical object, So you need both. Usually you don't care
44:29
Speaker 1: about the gravity on individual electron, but if you want
44:31
Speaker 1: to understand things like Hawking radiation, what happens to a
44:34
Speaker 1: particle near the event horizon? You need the answers to those.
44:37
Speaker 2: Okay, so let's suggest black holes. If we could understand them,
44:39
Speaker 2: that might be the way that we merge our understanding
44:42
Speaker 2: of those two things.
44:43
Speaker 1: Oh. Absolutely, if we could see inside an event horizon,
44:46
Speaker 1: we would know the answer to how to unify quantum
44:49
Speaker 1: mechanics and gravity, because we would see is there a
44:51
Speaker 1: singularity like general relativity predicts and quant mechanics says it's impossible,
44:55
Speaker 1: or is there something else weird and fuzzy? But of
44:58
Speaker 1: course we can't so we know the answer. It's there,
45:00
Speaker 1: but it's frustratingly hiding behind the veil of the black hole.
45:04
Speaker 1: The Derek's question was basically, could you make a black
45:06
Speaker 1: hole so massive that even its hawking radiation can't escape?
45:12
Speaker 1: So here you have a black hole and its emitting radiation.
45:15
Speaker 1: Could it suck at that back in? Could the hawking
45:17
Speaker 1: radiation get trapped by the black hole? The answer is,
45:20
Speaker 1: we don't really know, because what you're asking requires us
45:23
Speaker 1: to be able to think about the gravity on particles
45:26
Speaker 1: near a black hole, and we just don't know how
45:28
Speaker 1: to do that right because we don't know how to
45:30
Speaker 1: think about gravity for things where we don't have a
45:32
Speaker 1: way to describe their location exactly where they are through
45:35
Speaker 1: space and time. General relativity is basically a classical theory.
45:38
Speaker 1: It assumes that everything has a location and momentum, and
45:41
Speaker 1: that can be well defined and you can do those calculations.
45:44
Speaker 1: So short answer is, Derek, we don't know. The best
45:47
Speaker 1: answer though is probably not. Hawking's calculations suggest that black
45:50
Speaker 1: holes glow outside of the event horizon. Basically, what he
45:54
Speaker 1: did in his calculation is figure out what happens to
45:57
Speaker 1: a quantum field near an event horizon, and his solution
46:00
Speaker 1: suggests there has to be outgoing radiation, and that radiation
46:03
Speaker 1: is past the event horizon. So even if the gravity
46:06
Speaker 1: is very very strong, it's past the event horizon, which
46:09
Speaker 1: means technically it can still escape. That's the definition of
46:12
Speaker 1: the event horizon. So if it couldn't escape, it would
46:16
Speaker 1: be within the event horizon. But hawking radiation is always
46:18
Speaker 1: emitted past the event horizon, so probably it's.
46:22
Speaker 2: Free, all right. So Derek, we want to know if
46:25
Speaker 2: that explanation was satisfying. So we've reached out to Derek,
46:29
Speaker 2: and here's what he said.
46:31
Speaker 1: You did.
46:31
Speaker 7: You an excellent job at it, answering the question as
46:33
Speaker 7: best as you could I ever want to have a
46:35
Speaker 7: big fear of missing out? And I can only hope
46:38
Speaker 7: that technology will allow us to have the answers for
46:42
Speaker 7: these types of questions.
46:44
Speaker 1: Thank you.
46:44
Speaker 2: Okay, so that's it for today. Thank you so much
46:48
Speaker 2: to Barima and Charlie and Derek for sending in their questions.
46:52
Speaker 2: We hope to get more questions. Actually, we already have
46:54
Speaker 2: a stack ready for our listener questions number two, So
46:57
Speaker 2: if you send your questions, be patient. We are going
47:00
Speaker 2: to get to all of them, and we really appreciate
47:02
Speaker 2: your questions. Can't wait to hear from you. Send us
47:05
Speaker 2: emails at questions at Danielankelly dot org.
47:09
Speaker 1: Because it's not just our curiosity that drives sigence forward,
47:12
Speaker 1: it's yours. It's the reason we're doing it. It's collective
47:15
Speaker 1: curiosity of humanity is why we have science. So thanks
47:18
Speaker 1: everyone for pushing knowledge forward.
47:28
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47:32
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47:34
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