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Speaker 1: Welcome to stuff from the Science Lab from how stuff

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Speaker 1: works dot com. Hey guys, and welcome to the podcast.

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Speaker 1: This is Alisoon dotom elk the science Center how stuff

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Speaker 1: works dot com. And this is Robert Lamb, science for

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Speaker 1: Rider at how stuffworks dot com. Hey Allison, Hey Robert.

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Speaker 1: Have you ever traveled back in time? M hmm, no,

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Speaker 1: have you? No? I haven't, so I guess we're woefully

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Speaker 1: unprepared for this podcast. We were talking about traveling back

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Speaker 1: in time. It's part two or part one of our series.

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Speaker 1: What order you're taking? Yeah, we already covered traveling into

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Speaker 1: the future in our first installment. And you know what,

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Speaker 1: traveling back in time is not as easy as traveling forward. No.

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Speaker 1: I mean, as we pointed out in the last one.

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Speaker 1: I mean we're all traveling into the future at a

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Speaker 1: very slow right every day. But traveling into the past,

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Speaker 1: it's not happened naturally. Yeah, you get a lot more

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Speaker 1: stumbling blocks. So like, for example, the name of our podcast,

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Speaker 1: Hey grandpa, you have the very famous grandfather paradox. Yeah,

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Speaker 1: you want to hit this one. This is a this

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Speaker 1: is a pretty uh pretty It's one of one of

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Speaker 1: the great things about time travels, just thinking about the

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Speaker 1: problems of time travel into the past, and the grandfather

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Speaker 1: paradox is one of the big ones. And you guys

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Speaker 1: have probably heard of this, but for the sake of

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Speaker 1: there's people who haven't. Okay, so the grandfather paradox is

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Speaker 1: pretty cool. Basically, the idea is, if you were to

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Speaker 1: go back in time and kill your own grandfather, what

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Speaker 1: would happen. It's like, I'm going to go back in

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Speaker 1: time and and kill my grandfather. Bam, my grandfather is

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Speaker 1: dead in the past. That means he never meets my grandmother.

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Speaker 1: They never have a kid, and they never have a kid.

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Speaker 1: I'm never born, so I never go back in time

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Speaker 1: to kill my grandfather. Right, how do you reconcile these things?

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Speaker 1: They're in laws? The paradox. Yeah, anything you would go

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Speaker 1: back in time to fix by fixing it, you would

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Speaker 1: you would destroy the need that arose to go back

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Speaker 1: and fix it. You would destroy the problem and then

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Speaker 1: with me a problem to fix. It's like this loop. Yeah,

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Speaker 1: and this also gets that another big problem with backward

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Speaker 1: time travel in that it violates the rule of causality,

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Speaker 1: cause and effect. Um. This is a big one for Hawking.

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Speaker 1: He's always talking about this when he talks about time travel. Yeah,

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Speaker 1: I mean, it's like a fundamental aspect of the universe,

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Speaker 1: and that cause comes before effect, and if effect came

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Speaker 1: before cause, that would be that would be crazy. That's

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Speaker 1: like having dessert before your meal, you know. Plus it

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Speaker 1: just doesn't sound as good affect and cause that doesn't

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Speaker 1: rull off the tongue. Yeah, not at all. And just

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Speaker 1: because the French do eat salad at the end of

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Speaker 1: their meals doesn't make it right. No, that's it's clearly

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Speaker 1: they're toying with forces beyond our comprehension. So while I

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Speaker 1: was researching this program, I came across Carl Sagan's interview

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Speaker 1: with a PBS their Nova program, and and Nova asked

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Speaker 1: him whether you thought backwards time travel would ever be possible,

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Speaker 1: And Sagan had this to say, such questions are purely

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Speaker 1: a matter of evidence, and if the evidence is inconsistent

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Speaker 1: or insufficient, then we withhold judgment until there's better evidence.

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Speaker 1: Right now, we're in one of those classic, wonderfully evocative

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Speaker 1: moments in science when we don't know, when there are

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Speaker 1: those on both sides of the debate, and when what

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Speaker 1: is at stake is very mystifying and very profound. Indeed,

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Speaker 1: as long as we're talking about Sagan, we should talk

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Speaker 1: about wormholes. Yeah. Yeah, he's one of the big the

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Speaker 1: big names behind wormholes, right, or the big inspiration for

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Speaker 1: research into wormholes, right, yeah, the because of his book Contact.

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Speaker 1: Did you ever Recontact that way? Now? I saw the movie,

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Speaker 1: Jodie Foster didn't, really don't. I just recently read that

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Speaker 1: the character of Ellie Earraway was based on the real

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Speaker 1: life study explorer UM and scientist Jill Tarter. Sorry Jill

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Speaker 1: if I just muled your last name. All right, So

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Speaker 1: what is a wormhole? Right? Do you guys remember these

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Speaker 1: from Rinkle in Time? Did you read Wrinkle on Time? No,

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Speaker 1: that's one of those series I should have read, but

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Speaker 1: you should. You should. In fact, I'm going to go

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Speaker 1: back and read it. It's amazing. So a wormhole is

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Speaker 1: a hypothetical structure, right, A long, thin tunnel connecting two

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Speaker 1: points in space time, um, the way I like to

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Speaker 1: imagine it. And I know there's some sort of a um,

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Speaker 1: there's some sort of cool analogy involving an aunt. Right,

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Speaker 1: But I think back to the movie Event Horizon, which

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Speaker 1: is kind of a kind of a crappy, kind of

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Speaker 1: a fun sci fi horror film where like they fly

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Speaker 1: a spaceship into a black hole and travel to Hell

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Speaker 1: or something. But there's a scene where Sam Neil of

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Speaker 1: Jurassic Park fame is explaining something and he takes like

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Speaker 1: a poster off the wall and he folds it right

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Speaker 1: so that point A that's on the far side of

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Speaker 1: the one fast end of the sheet, and point B

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Speaker 1: on the other far into the sheet. He be binds

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Speaker 1: the paper until those two are touching back to back,

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Speaker 1: and then he shoves a pencil through the through both

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Speaker 1: holes and bang, there's our warm hole. Right, thank you,

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Speaker 1: Sam Neil. Yeah, that's the one good thing you can

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Speaker 1: get out of that movie. Yeah. The other one I've

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Speaker 1: heard is really similar. You squish a piece of paper together,

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Speaker 1: you get ant, say, the ant pokes a hole through it,

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Speaker 1: and the aunt doesn't want to travel that far. That's

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Speaker 1: like a universe to go from one then of the

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Speaker 1: piece of paper to another, so it just travels through

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Speaker 1: the little wormhole and the couple of piast paper to

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Speaker 1: get where it's going. So there you have it. Aunts,

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Speaker 1: Masters of space and Time, not really. Yeah. Wormholes are

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Speaker 1: also called Einstein Rosen bridges and which sounds like something

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Speaker 1: you would get done at a dental office, so no

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Speaker 1: wonder that one didn't stick. Yeah, and John Wheeler was

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Speaker 1: thought to have come up with the original term of wormhole,

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Speaker 1: and they're considered possible because they very nice leaping into

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Speaker 1: Einstein's theory of relativity, which, as you guys probably remember,

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Speaker 1: states that any mass curve spacetime. And the nice thing

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Speaker 1: about wormholes is that when you're talking about traversing a wormhole,

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Speaker 1: you're still talking about going at speed slower than the

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Speaker 1: speed of light. A lot of the study into wormholes

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Speaker 1: comes back to contact again, right, Yeah. Most recently thorn

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Speaker 1: Um Kip Thorne in particular got into it when Carl

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Speaker 1: Sagan as Thorne, who has done a physicist at cal

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Speaker 1: Tech with help for getting the protagonist in Contact, which

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Speaker 1: we just we're talking about Ellie air Away. He wanted

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Speaker 1: to get Eli to travel faster to a distant star

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Speaker 1: and he needed a means together there, so he asked

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Speaker 1: Thorn for some help, and Thorne of course suggested a wormhole.

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Speaker 1: He plugged a hole in a plot by creating a

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Speaker 1: hole in space time. Well Well done, Robert, well done.

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Speaker 1: And hockeying is also pretty big in this area. Um.

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Speaker 1: But let's get back to Thorne for a second. Thorne

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Speaker 1: slots even led to an idea for a time travel

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Speaker 1: machine based on these things called thorn plates. And we're

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Speaker 1: actually not going to get into them today because I

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Speaker 1: think that would be really hard to explain over a podcast,

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Speaker 1: but there is a there is an idea for a

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Speaker 1: time travel machine based on thorn Thorne's other big contribution

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Speaker 1: was he put the kibosh on care holes. So, according

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Speaker 1: to good old Kevin Bonser, who wrote the article on

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Speaker 1: time travel on her site, care holes are these rotating

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Speaker 1: black holes that could be used as portals for time

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Speaker 1: travel or traveled to parallel universes. So in there is

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Speaker 1: this New Zealand mathematician by the by the name of

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Speaker 1: Roy care and he proposed the first realistic theory for

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Speaker 1: a black hole. So there are a few problems with wormholes,

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Speaker 1: aside from the fact that they're purely hypothetical and might

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Speaker 1: not even be real at all. And there's that, and that,

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Speaker 1: and that is that, um, if we were able to

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Speaker 1: create one or find one, because their theories that they

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Speaker 1: like occur naturally at the quantum level, like just momentarily,

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Speaker 1: like in the quantum foam, which always makes me think

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Speaker 1: of pie for some reason. Really, it makes me think

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Speaker 1: of a temper pedic mattress. Yeah, I think it's like

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Speaker 1: a green like c foam pie. Is that a thing?

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Speaker 1: A c foam pie? No green pie? Maybe I think

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Speaker 1: that it was like a dessert my mom made or

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Speaker 1: something foam pie. That sounds revolting, Robert, Sorry, Robert's mom. Well,

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Speaker 1: the dessert was good, but my recollection of it maybe

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Speaker 1: a little afraid. But um, no way, I would like

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Speaker 1: to sleep on quantum foam. Didn't you think that would

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Speaker 1: be nice? Yeah? But if it has wormholes in it,

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Speaker 1: it's it might be problematic because these things, these things

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Speaker 1: would be like popping in and out of existence. In

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Speaker 1: each one would be a little tunnel to some other

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Speaker 1: corner of time and space, you know. Might be it

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Speaker 1: might lead to the center of a black hole. Might

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Speaker 1: we do a planet where like you know, kangaroos, rule

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Speaker 1: might go into the future, might go into the past.

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Speaker 1: You don't know, And they're just popping in and out

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Speaker 1: of existence. But if you could grab one, you could

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Speaker 1: you could theoretically use some sort of unrealized technology to

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Speaker 1: like pull it open. Expanded enough to like fly spaceship

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Speaker 1: through or something. Right, Well, they speculate that keeping one

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Speaker 1: open would require exotic matter or a matter that has

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Speaker 1: a net negative mass energy density, which is handy for

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Speaker 1: pushing things apart, right, and that stuff hard to find. Yeah,

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Speaker 1: I think it is. I don't think about any but so, yeah,

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Speaker 1: there's there's that UM. And then also there's some theories

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Speaker 1: that if you could get one and you could actually

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Speaker 1: hold it open, there would be like so much radiation

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Speaker 1: heading into the wormhole that it would fry you, or

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Speaker 1: it would create a radiant there would be like a

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Speaker 1: radiation feedback loop, kind of like what happens with with

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Speaker 1: audio equipment. Yeah, this is Hawking's big thing. Yeah, that

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Speaker 1: it would be like in the same way that that

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Speaker 1: audio feedback could destroy a speaker. Um, it would destroy

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Speaker 1: the warmhole and whatever you were trying to throw back

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Speaker 1: through it, you know, your your terminators or time machines

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Speaker 1: or whatever. But luckily there are other equally high pothetical

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Speaker 1: theories out there. There are. Indeed, one of them is

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Speaker 1: the cosmic string slash got loop soon as User's guide

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Speaker 1: to time Travel on wired uh. The n YU theoretical

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Speaker 1: physicist Michio Kaku mentions one method thought up by ninety

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Speaker 1: one Princeton physicist J. Richard Gott. And this involves searching

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Speaker 1: for an infinitely long cosmic string leftover from the Big Bang.

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Speaker 1: Have you seen it? It It is lying around the universe lately,

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Speaker 1: not recently. I think what you need is a some

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Speaker 1: sort of a cosmic kitten. Right, that's a horrible joke.

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Speaker 1: I can't believe we just made that. So once you

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Speaker 1: find such a string, you arrange it in a rectangle

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Speaker 1: shape that's roughly fifty four thousand light years long and

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Speaker 1: point zero one light years wide. He's in gravity, so

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Speaker 1: that's fine. You just bang that out in an afternoon.

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Speaker 1: This is just this is another one of those. It's

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Speaker 1: like a thought experiment, and it's um you know, it's

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Speaker 1: it's purely hypothetical. Um. Right. So God's idea is that

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Speaker 1: the strings could warp space time in such a way

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Speaker 1: as to allow backwards time travel. It wouldn't be good

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Speaker 1: for four time travel, though, So let's move on to

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Speaker 1: the next one. Yeah, this and this is the giant cylinder. Yeah,

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Speaker 1: it's the Van stoke Um cylinder, which which sounds like

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Speaker 1: a pretty good uh like country band name, I think UM.

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Speaker 1: And this idea is that you get a huge cylinder,

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Speaker 1: in fact, a cylinder so big that it's it's infinite,

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Speaker 1: so even you know, just more astronomical to even try

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Speaker 1: and uh, you know, envision all right, you get this.

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Speaker 1: So you get this enormous cylinder, get it spinning at

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Speaker 1: near light speed. We don't want to we don't want

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Speaker 1: to go faster than light speed because we don't want

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Speaker 1: to get silly here with this stuff, this scheme UM,

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Speaker 1: and it would anyway, it gets going real fast and

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Speaker 1: it ends up dragging space time and into its rotation.

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Speaker 1: So in nineteen four, Frank J. Tippler, a cosmologist and physicist,

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Speaker 1: pointed out that the field surrounding the cylinder would violate

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Speaker 1: causality quote unquote in the sense that it allows it

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Speaker 1: closed a timelike line to connect any two events and

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Speaker 1: space stop. This suggests that a finite rotating cylinder would

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Speaker 1: also act as a handy time machine. Okay, he didn't

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Speaker 1: say handy, he just said as a time machine. Yeah,

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Speaker 1: there's there's nothing handy about this cylinder idea. But again,

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Speaker 1: it's it's all about it's not about saying, hey, here's

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Speaker 1: a realistic time travel device. It's kind of like, all right,

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Speaker 1: these are the this is what we're up against in

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Speaker 1: the universe. What would it take to break the laws

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Speaker 1: of the universe and make it possible? Yeah? Right, And

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Speaker 1: let's not forget that science builds on other science, so

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Speaker 1: you have to get some wacky ideas out there to

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Speaker 1: get some realistic ones. But let's stick with unrealistic for

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Speaker 1: another For yet another segment, let's stock takeions. Yeah, so,

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Speaker 1: like we've mentioned, according to the Einstein's theory of relativity,

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Speaker 1: nothing can go faster than light. Light is the universal

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Speaker 1: speed limit. But take eons are the universal speed limit breakers, right. Indeed,

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Speaker 1: they are going to get pulled over by the universal cops.

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Speaker 1: But they're too speedy. So ordinary matter is prevented from

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Speaker 1: ever reaching the speed of light because of the fact

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Speaker 1: that it would require infinite energy. Takeons, of course, are

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Speaker 1: no ordinary matter, and of course they're hypothetical, although they

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Speaker 1: do make an appearance on Star Trek and in the

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Speaker 1: Skeptics Dictionary. Check it out. In the Skeptics Dictionary, it

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Speaker 1: says that there's a whole line of New Age products

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Speaker 1: that range from beads, belts, and shoe inserts to sweat bands,

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Speaker 1: power pillars, massage oils, and volley files of take on water.

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Speaker 1: If that's true, those guys can make a mint showing

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Speaker 1: physicists where to get some take so the new Agers

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Speaker 1: can figure out where to get them about the physicists can't.

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Speaker 1: Nazis take is that if takeons exist, the universe could

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Speaker 1: be filled with them, but they interact so weekly with

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Speaker 1: ordinary matter that we couldn't detect them. So far, none

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Speaker 1: of the big accelerator labs have detected an interaction which

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Speaker 1: can only be explained by tachons. So let's say I

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Speaker 1: were to order a bunch of take eons from my

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Speaker 1: New Age supplier and they were actually real takeions, not

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Speaker 1: not fake tachons. Um is that, how do I go

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Speaker 1: back in time with these guys? So we just wrote

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Speaker 1: an article on this for Through the Wormhole for Discovery,

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Speaker 1: and it was on quantum nonlocality entangled physics and in

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Speaker 1: fact take on. So here's the experiment that one of

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Speaker 1: the writers, Susan Nassar, came up with. Pretend all the

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Speaker 1: clocks in the world are broken. Okay, done, Just forget

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Speaker 1: about having any means to tell time. Instead, just imagine

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Speaker 1: point A and point B. Okay, so we're gonna say

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Speaker 1: that time has moved forward when light leaving A reaches by.

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Speaker 1: When light leaves A, it's now, but when it reaches

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Speaker 1: B it's later. Okay, Now add a take in into

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Speaker 1: the mix, and which you'll remember it travels faster than light,

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Speaker 1: so no surprise here. You're going to release the photon

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Speaker 1: and the tacon at the same time, and the sub

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Speaker 1: atomic particle is going to reach B first, not the photon.

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Speaker 1: So when it reaches B, what time is it? It's before? Now? Okay,

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Speaker 1: what happened? Did it move backward in time? It's kind

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Speaker 1: of an interesting thought experiment. Okay, so think of think

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Speaker 1: of the photon as the turtle and the take eon

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Speaker 1: as the hair exactly. And so when the turtle, the

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Speaker 1: turtle leaves point A now and when he arrives at

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Speaker 1: point point B it's later. But the problem here is

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Speaker 1: the hair beats him to point B, so he gets

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Speaker 1: there before now. But the handy thing about takons is

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Speaker 1: there hypothetical So they so the tortoise, as usual, wins

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Speaker 1: the race because that hair, it just it can never

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Speaker 1: pull it off. That sounds a little crazy. They are

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Speaker 1: in fact a little crazy, and that is in fact

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Speaker 1: where we're going to wrap up today's podcast on backwards

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Speaker 1: time travel. I'm gonna get myself some tachions though. If

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Speaker 1: any anybody wants to supply me with take eons uh

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Speaker 1: dis contact me hook me up. So as always, you

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Speaker 1: can type time travel into a search bar on her

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Speaker 1: homepage and see what good stuff that brings up. Stuff

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Speaker 1: on warp drives, which we didn't cover today, or time

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Speaker 1: travel or weather space is a shape, all that good stuff.

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Speaker 1: And we are all over social networking, aren't we, robbert

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Speaker 1: Um And hey, why do we have all these pictures

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Speaker 1: of lizards? We do have some pictures of lizards. Listener mail, Yeah,

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Speaker 1: we got listening mouth from bath and Beth writes, Hi,

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Speaker 1: I really enjoy your podcast. Thanks for investigating such cool

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Speaker 1: topics and for putting it up for free. I'm a

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Speaker 1: graduate student in ecology and evolutionary biology staying lizards, so

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Speaker 1: I was especially interested in your podcast on regeneration. That

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Speaker 1: was a fun one, Yeah, Beth writes I was thus

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Speaker 1: a little sad when you didn't talk about tail loss

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Speaker 1: and regrowth and lizards, although I agree that salamanders are

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Speaker 1: definitely more impressive, and then she goes on to write,

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Speaker 1: lizard tails don't regenerate in the same way that salamander

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Speaker 1: lives limbs do reground tails have a tube of cartilage

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Speaker 1: in the center rather than bothe. Nonetheless, I thought you

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Speaker 1: might enjoy seeing a photo of a lizard with a

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Speaker 1: funny looking fork tail that I caught during recent field work,

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Speaker 1: and that she sent three photo us and the lizard. Indeed,

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Speaker 1: how's this fork tail? Which is really unusual? And I'm

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Speaker 1: just going to assume that she did not pull the

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Speaker 1: tail off that lizard just to impress us. No, I

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Speaker 1: do not think that's it. That she writes that I

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Speaker 1: think would probably happened was that she suffered a tailbreak

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Speaker 1: the lizard she started to regenerate her tail and then

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Speaker 1: had to partial break higher up than stimulated new tail

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Speaker 1: growth from the broken part, even though the rest of

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Speaker 1: the tail is still attached. It sounds complicated, but the

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Speaker 1: pictures are well worth it. So yeah, send us send

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Speaker 1: us pictures of your lizard tales and various other things.

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Speaker 1: We we would love to get them. Uh. And you

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Speaker 1: have another another letter doing it? I do, I do?

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Speaker 1: I have one from an Aussie uh And Karen writes,

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Speaker 1: Hey guys, First, I'd like to say I love the

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Speaker 1: various topics you choose. I'm quite handy at quiz Nights

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Speaker 1: thanks to you. My only grip is how you pronounced

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Speaker 1: in Australian cities in terms. For instance, Geelong isn't with

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Speaker 1: a hard G like engulf, it's a soft G like

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Speaker 1: G that's long. Perhaps project casting you could check an

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Speaker 1: AUSEE site as to how we pronounce things. Very sorry, Karen,

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Speaker 1: we apologize and we will indeed follow up on that

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Speaker 1: aggestion in the future. Yeah, all Australian websites are blocked

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Speaker 1: on our server. I don't know what's up with that,

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Speaker 1: So if you guys want to send us an email,

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Speaker 1: you know where to find us. Science stuff at has

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Speaker 1: Differs dot com for more on this and thousands of

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Speaker 1: other topics. Does it how stuff works dot Com. Want

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Speaker 1: more how stuff works, check out our blogs on the

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Speaker 1: house stuff works dot com home page