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Speaker 1: Hey, Daniel, So, who do you think is going to

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Speaker 1: figure out the secrets of the universe? Is there, like

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Speaker 1: somebody that you you know or have been keeping your

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Speaker 1: eye on?

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Speaker 2: Oh? Man, I wish I knew the answer to that question.

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Speaker 1: Well, but like, do you think it's someone we already

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Speaker 1: know about, like a smart person like Lisa Randall or

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Speaker 1: Ed Witten.

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Speaker 2: It could be, but my money is on somebody smart,

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Speaker 2: somebody young, maybe somebody who's listening to this podcast right now.

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Speaker 1: Whoa so like, how would you feel if it turned

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Speaker 1: out that, like the big questions weren't answered by you,

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Speaker 1: but you were upstaged by some like ten year old

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Speaker 1: after you failed for decades.

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Speaker 2: After failing for decades, I would be relieved if somebody

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Speaker 2: else came along to figure this stuff out for us.

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Speaker 1: I feel like that's that's the right answer. The answer

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Speaker 1: matters more than the person. Love it.

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Speaker 2: Hi. I'm Daniel. I'm a particle physicist and a professor

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Speaker 2: at UC Irvine, and I just desperately want the answers.

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Speaker 1: I'm Kelly Wienersmith. I'm a parasitologist at Race University, and

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Speaker 1: I also desperately want the answers. But the questions need

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Speaker 1: to be about parasites, and.

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Speaker 2: You're also the Hugo Award winning author of a nonfiction book. Congratulations.

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Speaker 1: Thanks. I'll try to not scream too loud that the

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Speaker 1: trophy arrived, and I am still losing my mind every

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Speaker 1: time I look at it. I cannot believe that that happened.

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Speaker 1: But I also can believe that Zach didn't prepare an

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Speaker 1: acceptance speech, even though the flight to Glasgow takes like

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Speaker 1: eight hours. He just assumed we weren't going to win,

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Speaker 1: so he prepared nothing and I almost killed him.

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Speaker 2: Oh well, well, I'm sure his spontaneous speech was even

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Speaker 2: better than anything he could have written. It was fine,

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Speaker 2: but I wanted all of you out there to appreciate it.

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Speaker 2: Kelly is not just one of the hosts on this podcast,

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Speaker 2: but she's actually an award winning best selling science writer,

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Speaker 2: so we're grateful to have her here. Thanks very much

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Speaker 2: for joining us.

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Speaker 1: Oh you're the best. Thanks Daniel, I love being.

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Speaker 2: Here, and welcome to the podcast. Daniel and Jorge Explain

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

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Speaker 2: everything about the universe. It's ups and its downs, it's

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Speaker 2: lefts and its rights, the things that wins the awards

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Speaker 2: for and the things that drive physicists crazy. Hopeful that

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Speaker 2: somebody young out there will figure it all out for.

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Speaker 1: Us as soon as possible. Guys get on.

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Speaker 2: It, and as part of that process, we want you

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Speaker 2: to be thinking about the nature of the universe. Yes,

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Speaker 2: you are relaxing as you fall asleep, or you are

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Speaker 2: commuting to work and hoping to be educated and entertained,

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Speaker 2: but this podcast also requires you to do some work

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Speaker 2: to fit all these ideas into your head and to

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Speaker 2: write to us when they don't quite click together. If

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Speaker 2: you have a question about the nature of the universe,

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Speaker 2: we want to hear it. That's part of the progress

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Speaker 2: of science. Everybody out there wondering and thinking and trying

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Speaker 2: to figure this stuff out. So please send me your

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Speaker 2: questions to questions at Daniel and Jorge dot com. You

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Speaker 2: will definitely hear back from us, and sometimes we choose

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Speaker 2: those questions to answer or write here on the podcast.

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Speaker 1: And sometimes the questions that you get from people new

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Speaker 1: to the field are way better than any question you

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Speaker 1: get at a department seminar with a bunch of pros

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Speaker 1: in the field, because, like you're not constrained by all

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Speaker 1: the assumptions that people who have been in the field

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Speaker 1: for a while have. So we get some pretty great

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Speaker 1: questions from the listeners.

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Speaker 2: Yes, absolutely we do, and we get questions that I

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Speaker 2: don't anticipate, and so I hope that these questions line

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Speaker 2: up with your questions. That these ones we've chosen are

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Speaker 2: also questions that other folks out there have and want

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Speaker 2: to hear the answer to. So please don't be shy.

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Speaker 2: If you're thinking of a question, somebody else also wants

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Speaker 2: to hear the answer, and I need somebody to write

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Speaker 2: in and send it to me. So please don't be shy.

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Speaker 2: I love hearing from all of you.

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Speaker 1: Please keep Daniel company, guys.

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Speaker 2: And so today on the podcast, we'll be answering listener

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Speaker 2: questions number sixty eight who and we are featuring a

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Speaker 2: question from a young future physicist, Clara from Germany. So,

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Speaker 2: without further ado, here's Clara's question.

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Speaker 3: Hello and Clara from Germany, twelve years old and you

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Speaker 3: listen of your podcast. My question is could it be

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Speaker 3: possible that the universe is finite in one direction and

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Speaker 3: incident and all the others? Your podcast is just writing

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Speaker 3: you two guys can explain so well.

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Speaker 1: Thanks Clara, So, Daniel, when I was twelve years old,

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Speaker 1: I was sequestered in my bedroom listening to Silverchair and

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Speaker 1: playing the first three chords to smells like teen Spirit

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Speaker 1: by Nirvana, but not bothering to learn any the rest

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Speaker 1: of the song. I was not pondering the nature of

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Speaker 1: the universe. So good on you, Clara. What were you

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Speaker 1: doing when you were twelve, Daniel.

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Speaker 2: I was reading a lot of science fiction and a

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Speaker 2: lot of fantasy, and I definitely was pondering the nature

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Speaker 2: of the universe. I remember trying to think about whether

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Speaker 2: space was in three dimensions everywhere, or maybe parts of

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Speaker 2: the universe might have additional dimensions, and really struggling to

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Speaker 2: get my mind around what that meant and what would

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Speaker 2: be like to exist in those dimensions. So, yeah, Clara

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Speaker 2: and I have a lot in common. Good job, Clara.

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Speaker 1: Well some of us are late blossoming nerds, I guess.

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Speaker 1: But what we get there eventually, So give us some

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Speaker 1: background on what we knew about this question so far, Daniel.

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Speaker 2: Yeah, Clara's question touches on two really important ideas, and

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Speaker 2: she's doing something I love, which is trying to bring

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Speaker 2: two ideas together. You know, physics is about unification of

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Speaker 2: your understanding. It's not like chemistry where you use this

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Speaker 2: equation over here and that equation over there, and it's

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Speaker 2: just like these patches of understanding and physics. We hope

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Speaker 2: to have a complete cloth, you know, to stitch everything

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Speaker 2: together into one idea. So it's really important that when

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Speaker 2: you hear or related ideas, you try to understand how

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Speaker 2: they fit together. And that's what she's doing here and here.

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Speaker 2: The related ideas are about the size and the scope

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Speaker 2: of the universe, like is the universe infinite or is

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Speaker 2: the universe finite? And when you just imagine space and

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Speaker 2: the whole universe, you probably just fill your mind with blackness,

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Speaker 2: and you imagine that it goes on forever. That you

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Speaker 2: could shoot a laser beam and it would just fly

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Speaker 2: on forever and ever until it hits something. But if

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Speaker 2: the universe was empty, it would just go on forever.

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Speaker 2: You can imagine these like dotted lines of x, y,

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Speaker 2: and z dimensions just stretching out to infinity, limited only

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Speaker 2: by your imagination. That's an infinite universe. And we don't

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Speaker 2: know if the universe is infinite, but such an infinite universe,

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Speaker 2: though it's a little bit weird to hold in your mind.

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Speaker 2: Is actually one of the most natural ideas for how

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Speaker 2: the universe might be shaped.

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Speaker 1: Is this a question that you think will have an

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Speaker 1: answer to in your lifetime or what will we be

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Speaker 1: wondering if the universe is finite or infinite three hundred

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Speaker 1: years from now?

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Speaker 2: Wow? Awesome. It's hard to prove that the universe is

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Speaker 2: infinite because if it goes on forever, then you need

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Speaker 2: infinite data to prove that. But we might be able

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Speaker 2: to prove the opposite. We might be able to prove

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Speaker 2: that it's not infinite because you could discover that the

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Speaker 2: universe is finite because the extent of the universe is

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Speaker 2: connected to another question about the shape of the universe,

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Speaker 2: Like if the universe is flat, and by flat, we

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Speaker 2: don't mean like a two D sheet of paper, We

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Speaker 2: mean the two parallel lines will not cross. It's a

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Speaker 2: three dimensional version of flatness. But if the universe is curved,

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Speaker 2: so the two parallel lines either diverge or do cross

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Speaker 2: over each other, and again curved in three dimensions in

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Speaker 2: a sort of general relative VisiC sort of way. That

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Speaker 2: means that the universe could be finite, that it could

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Speaker 2: loop around on itself again in a weird three dimensional way,

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Speaker 2: not exactly the same, like the surface of a sphere

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Speaker 2: loops around on itself, but in analogy to that. So,

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Speaker 2: if we discover that space is curved, that suggests the

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Speaker 2: space might be finite, and so we can't prove that

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Speaker 2: it's infinite, but we might discover that it is finite.

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Speaker 1: WHOA, I feel like I'm lost in thought here. So

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Speaker 1: if it's curved, then what's on the other side of

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Speaker 1: the curve.

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Speaker 2: No, this is a big mental pothole that we should

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Speaker 2: totally address, because if you imagine the universe as finite

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Speaker 2: and curved, you probably have in your mind something like

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Speaker 2: a sphere, a ball.

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Speaker 1: Right, I'm thinking of a doughnut because I'm hungry, all right.

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Speaker 2: It could also be a donut, right, But the problem is,

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Speaker 2: as soon as you name some object like that, you

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Speaker 2: imagine it with its boundaries inside some other vast mental space.

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Speaker 2: Like if I close my eyes and I think of

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Speaker 2: a donut, it's hovering in some blackness, and that's a mistake.

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Speaker 2: I've like sketched around it some empty space. But when

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Speaker 2: we talk about the universe as finite, we don't mean

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Speaker 2: like there's a bunch of stuff, and around it is

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Speaker 2: empty space. We mean finite including I mean, that's all

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Speaker 2: there is. Don't sketch anything around it. Don't fill in

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Speaker 2: that mental space with something. The finite universe is limited

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Speaker 2: in size, but it doesn't have an edge of boundary.

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Speaker 2: Every point on it is exactly the same. It's very,

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Speaker 2: very difficult to think about. It's very counterintuitive.

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Speaker 1: Yeah, I feel like the world is split into people

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Speaker 1: who think that that's fun and people who just are

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Speaker 1: really frustrated. There might be a different camps there.

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Speaker 2: So we should get to Claria's question, but first we

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Speaker 2: have to take a quick break.

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Speaker 1: What do we think let's follow up on Clara's idea.

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Speaker 2: Yeah, so Claren's question is porque Nola's does, right. She's like,

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Speaker 2: why can't it be infinite and finite? And she's saying,

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Speaker 2: what if you have a few dimensions in which it's infinite,

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Speaker 2: but other dimensions in which it's finite. So imagine, for example,

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Speaker 2: like an infinite cylinder. In one dimension it goes on forever,

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Speaker 2: but in the other dimensions it's limited. You know, it's

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Speaker 2: like a centimeter wide or a meter wide or something.

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Speaker 2: So you can picture geometric shapes which are like this,

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Speaker 2: that are infinite in one dimension and finite in others.

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Speaker 2: And she's basically asking, could our universe be like that?

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Speaker 2: Could it have two different kinds of dimensions, some that

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Speaker 2: are infinite and some that are finite.

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Speaker 1: Are there any current theories that encapsulate that, Like, has

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Speaker 1: she identified a theory that physicists are working with right

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Speaker 1: now as far as you know, or is this a

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Speaker 1: totally new way of thinking about it?

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Speaker 2: Claire's actually thought her way into a very popular area

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Speaker 2: of research right now, because it's totally possible to have

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Speaker 2: a geometry of the universe where you have some infinite

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Speaker 2: dimensions and some finite there's no theoretical reason saying you

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Speaker 2: can't do that. And first let's talk about like how

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Speaker 2: to try, frustratingly to visualize that your mind, and then

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Speaker 2: let's talk about why theorists are excited about this kind

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Speaker 2: of idea. So we know that there are three dimensions

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Speaker 2: in our universe X, y, and z. These are the

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Speaker 2: normal spatial dimensions, and let's just say those are infinite,

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Speaker 2: that they go on forever. If you shine a laser

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Speaker 2: beam out into space, if you don't hit some other

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Speaker 2: galaxy or some alien eyeball, it's just going to go

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Speaker 2: on forever, and if you shine two, they're going to

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Speaker 2: be in parallel forever. Right, So that's infinite flat space. Okay,

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Speaker 2: so hold that in your mind. Now we want to

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Speaker 2: add a fourth dimension, and we don't want to add

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Speaker 2: a fourth infinite dimension some new direction you could shoot

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Speaker 2: your laser beam, which is already very difficult to put

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Speaker 2: into your three D mental space. Let's add a fourth

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Speaker 2: finite dimension. And so the sort of two mental ways

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Speaker 2: to visualize this one is take your three D infinite

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Speaker 2: space and at every point, replace that point with a loop,

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Speaker 2: like a little circle, you know, like a bracelet.

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Speaker 1: Essentially, I'm getting angry, you're getting angry. I'm kidding. Let's

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Speaker 1: go forward, all right, lots of loops in infinite space, yes, exactly.

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Speaker 2: So instead of space being filled with points, now it's

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Speaker 2: filled with loops. And where you are along that loop

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Speaker 2: is essentially the fourth dimension. So now you have like

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Speaker 2: four numbers in your address, three numbers to tell you

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Speaker 2: where you are in the usual three D space, and

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Speaker 2: one to tell you how far you are along this loop.

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Speaker 2: So now space is like more complex.

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Speaker 1: Is there a way to help me picture that? Like

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Speaker 1: like I move in a direction and I get stuck

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Speaker 1: in a loop, and it's like being in a whirlpool.

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Speaker 1: Or is that extra dimension time and it determines how

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Speaker 1: long I'm there?

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Speaker 2: The extra dimension is not time, it's space, right, okay,

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Speaker 2: And you could still move through three D space jumping

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Speaker 2: from loop to loop the same way you can, like

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Speaker 2: move only in X without changing your y value. An

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Speaker 2: alternative way to think about it, instead of an infinite

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Speaker 2: space filled with loops is to take a single loop

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Speaker 2: and at every point put infinite space in it. So

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Speaker 2: imagine like a big loop of infinite spaces instead of

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Speaker 2: an infinite space of loops. It doesn't really matter which

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Speaker 2: order you think about it. Geometrically, it's the same, and

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Speaker 2: both of them will give you a migraine because it's

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Speaker 2: about four dimensions at all, But that's my best thing.

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Speaker 2: Especially in an audio format. This is challenging to describe,

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Speaker 2: but the bottom line is, yes, Claire, it's possible to

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Speaker 2: build a geometry where space is finite in some dimensions

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Speaker 2: and infinite in others. And this is actually very exciting

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Speaker 2: theoretically because it might explain one of the open puzzles

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Speaker 2: in physics, which is why gravity is so much weaker

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Speaker 2: than the other forces. Like, if you think of gravity

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Speaker 2: as a force, we know that it's much much weaker

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Speaker 2: than all the other forces out there. And like the

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Speaker 2: canonical example is that you can hold up a paper

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Speaker 2: clip using a kitchen magnet, which is counteracting the entire

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Speaker 2: gravitational force of the Earth, right, a huge mass or

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Speaker 2: you know, like a toddler's legs are strong enough to

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Speaker 2: overcome the groundravity of the Earth and learn to jump.

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Speaker 2: That's electromechanical.

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Speaker 1: And they're so cute and squishy, I know, and.

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Speaker 2: They're defeating an entire planet's gravity. Right. So gravity is

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Speaker 2: a crazy weak force, and that's a puzzle for physicists

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Speaker 2: because we like things to be in balance. We like

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Speaker 2: to understand why things are out of balance if they are.

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Speaker 2: So the explanation is, maybe the reason gravity is weak

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Speaker 2: is because it's special. Maybe the universe has a bunch

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Speaker 2: of other dimensions. But like Claria suggests, their loops and

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Speaker 2: their small little dimensions, their loops are like a centimeter

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Speaker 2: or even a millimeter or even smaller. And so what

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Speaker 2: happens is that gravity actually isn't weaker than the other forces.

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Speaker 2: It's just the same strength, but it feels weaker to

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Speaker 2: us because at distances bigger than a centimeter or bigger

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Speaker 2: than these dimensions, it's already sort of bled out into

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Speaker 2: these other dimensions. It spreads out in these other dimensions,

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Speaker 2: and so it seems weak to us. So that's like

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Speaker 2: a cool explanation for another puzzle in particle physics, if

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Speaker 2: we could prove that the universe did have additional dimensions

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Speaker 2: that were finite.

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Speaker 1: So one of my favorite parts of doing science is

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Speaker 1: designing experiments. Is there an experiment you could design to test, like,

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Speaker 1: for example, to look for those loops? Or this is

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Speaker 1: just too hard because it's all too big and it

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Speaker 1: goes on too long.

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Speaker 2: No, there absolutely is an experiment, but you're not gonna

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Speaker 2: like it.

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Speaker 1: You don't know me, but you probably know me well enough.

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Speaker 1: I'm probably not gonna like it, but go for it.

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Speaker 1: Tell me.

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Speaker 2: I mean it might destroy the planet. So if you're

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Speaker 2: cool with that, then yeah.

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Speaker 1: No, No, my kids are on this planet. You know

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Speaker 1: how I feel about when you endanger my kids.

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Speaker 2: So the idea is to do an experiment that tests

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Speaker 2: whether gravity gets really strong when things get close together.

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Speaker 2: And one way you can do that is try to

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Speaker 2: just measure the gravity of things that are really close together,

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Speaker 2: Like take two balls and put them a millimeter apart

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Speaker 2: and measure their gravity. This turns out to be really,

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Speaker 2: really hard because gravity is so weak and anything you

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Speaker 2: build is going to have really weak rindsvity. And there's

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Speaker 2: some real experimental virtuoso's at University of Washington who've been

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Speaker 2: doing these kinds of experiments and it's really amazing. They

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Speaker 2: have to isolate it from like anytime somebody coughs three

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Speaker 2: blocks away, or like a dog wags its tail and

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Speaker 2: changes the airflow or whatever. It's ridiculous what they have

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Speaker 2: to buffer themselves against because they're looking for such a

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Speaker 2: tiny effect. On the other hand, we can also do

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Speaker 2: it at the Large Hadron Collider because if gravity gets

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Speaker 2: really powerful when things get close together, Hey, that's what

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Speaker 2: we do all day. We take protons, we put them

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Speaker 2: really close together. And so the idea is maybe sometimes

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Speaker 2: when protons get really close together, their gravity gets really

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Speaker 2: strong and they make a tiny black hole. And so

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Speaker 2: these extra dimensions could enhance the power of gravity at

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Speaker 2: short distances and give us a chance to make more

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Speaker 2: black holes than we otherwise could, maybe even seeing one

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Speaker 2: evaporate in our detector and of course not destroying the

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Speaker 2: earth and keeping Kelly's children alive and healthy.

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Speaker 1: Thank you my children in particular. And so if we're

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Speaker 1: worried about dimensions, does creating a black hole is that,

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Speaker 1: you know, sort of analogous to the loops in the

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Speaker 1: dimensions that you were talking about, the.

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Speaker 2: Black hole, if it exists, would also exist in those

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Speaker 2: other dimensions. But ideas that those dimensions also weaken the

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Speaker 2: gravity for things that are further apart than the size

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Speaker 2: of those dimensions, and so you can create a black

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Speaker 2: hole by getting things really really close. That's sort of

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Speaker 2: the idea. We've never seen a black hole the large

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Speaker 2: Adron collider, so we have no experimental proof of any

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Speaker 2: of these additional spatial dimensions. There's another way you could

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Speaker 2: look for them, which is to look for weird echos

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Speaker 2: of the particles that we have seen. Like if the

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Speaker 2: electron exists in our universe, there might be an echo

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Speaker 2: of the electron in which it's like vibrating in this

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Speaker 2: additional dimension, and so it would look like an electron

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Speaker 2: but with more mass, like a heavier version of the electron,

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Speaker 2: and because of resonance effects, you would get a bunch

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Speaker 2: of these, you would get like one that's heavier, and

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Speaker 2: when that's twice is heavy and three times is heavy,

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Speaker 2: you get this whole tower of weird heavy electrons. So

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Speaker 2: we've looked for those and haven't seen them. So yes,

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Speaker 2: we can look for these things. No, we have no

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Speaker 2: evidence that the universe does have additional finite dimensions on

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Speaker 2: top of the three probably infinite dimensions that we know about.

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Speaker 1: And finding another dimension doesn't immediately answer the question. Is

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Speaker 1: the universe finite in one direction and infinite in the other, Right,

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Speaker 1: you'd still need additional information, that's just part of it.

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Speaker 2: Yeah, that's right. First step is discover the other dimension.

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Speaker 2: Second is to measure the curvature of that dimension. If

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Speaker 2: it's highly curved, then it probably is a loop. Then

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Speaker 2: it probably is finite. Clara wins the Nobel Prize. If

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Speaker 2: it turns out to be infinite, then like that blows

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Speaker 2: our minds in a whole other way. Like another infinite

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Speaker 2: dimension in our universe.

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Speaker 1: That would be crazy or infuriating.

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Speaker 2: Or headache inducing.

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Speaker 1: Now it would be cool.

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Speaker 2: All right, So that's the answer for Clara. Yes, the

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Speaker 2: universe could have finite and infinite dimensions. At the same time,

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Speaker 2: as much as that's difficult to think about, and while

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Speaker 2: we are doing experiments to search for these additional dimensions,

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Speaker 2: we do not yet have any evidence that they exist.

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Speaker 2: But we're going to keep looking to hope to provide

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Speaker 2: Clara with the Nobel Prize in the future.

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Speaker 1: Yeah, thank you for this amazing question.

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Speaker 2: And thanks to everybody out there who thinks about the universe,

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Speaker 2: wonders about it, wants to understand it, and writes to us.

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Speaker 2: Send us your questions to questions at dangelan Jorge dot com.

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Speaker 2: Everybody gets an answer and some people get highlighted on

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Speaker 2: the podcast.

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Speaker 1: Woo, it's like getting a hugo.

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Speaker 2: Yes, you can put it on your CP for sure.

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Speaker 2: All right, Thanks very much Kelly for helping me answer

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Speaker 2: these questions.

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Speaker 1: Thanks so much for having me on the show. It

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Speaker 1: was a lot of fun, all right.

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Speaker 2: Everyone, tune in next time for more science and curiosity.

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Speaker 2: Come find us on social media where we answer questions

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Speaker 2: and post video. We're on Twitter, Discorg, Insta, and now TikTok.

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Speaker 2: Thanks for listening, and remember that Daniel and Jorge Explain

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Speaker 2: the Universe is a production of iHeartRadio. For more podcasts

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Speaker 2: from iHeartRadio, visit the iHeartRadio app, Apple podcasts, or wherever

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Speaker 2: you listen to your favorite shows.