Tag Archives: relativity

Wormholes and Donut Holes

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I’ve heard people claim that in order to understand wormholes, you need to understand five-dimensional space.

Well that’s just silly.

A wormhole is often described as a hole in space-time. It can be imagined as a black hole where instead of getting crushed when you fall in to the center, you emerge somewhere else (or even some-when else: wormholes are possibly the only way to get time travel). They’re a staple of science fiction, even if they aren’t always portrayed accurately.

Probably not what a wormhole looks like

How does this work? Well like many things in physics, it’s helpful to imagine it with fewer dimensions first:

Suppose that you live on the surface of a donut. You can’t get up off the surface; you’re stuck to its gooey sugary coating. All you can do is slide around it.

It’s a simple life

Let’s say that one day you’re sitting on the pink side of the donut, near the center. Your friend lives on the non-frosted side, and you want to go see her. You could go all the way back to the outside edge of the donut, around the side, and down to the bottom, but you’re tired and the frosting is sticky. Luckily, you can use your futuristic pastry technology, the donut hole! Instead of going around the outside, you dive in through the inside hole, getting to your friend’s house much faster.

That’s really all a wormhole is. Instead of living on a two-dimensional donut surface, you live in a world with three space dimensions and one time dimension. A wormhole is still just like a donut hole: a shortcut, made possible by space being a non-obvious shape.

Now earlier I said that you don’t need to understand five-dimensional space to understand wormholes, and that’s true. Yes, real donuts exist in three dimensions…but if you live on the surface only, you only see two: inward versus outward, and around the center. It’s like a 2D video game with a limited map: the world looks flat, but if you go up past the top edge you find yourself on the bottom. Going from the top edge directly to the bottom is easier than going all the way down the screen: it’s just the same as a wormhole. You don’t need extra dimensions to have wormholes, just rules: when you go up far enough, you come back down. Go to the center of the wormhole, and come out the other side. And as one finds in physics, it’s the rules, not naïve intuitions, that determine how the world works. Just like a video game.

Some thoughts about the current Flame Challenge

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Ever tried to explain something to an eleven year old?

It’s not the same as talking to a six year old. There’s no need to talk down, or to oversimplify: eleven is smart enough to understand most of what you have to say. On the other hand, most eleven year olds haven’t had chemistry or physics, or algebra. They’re about as intelligent as they’re going to get, but with almost no knowledge base, which makes them a uniquely relevant challenge for communicating science.

That’s the concept behind Alan Alda’s Flame Challenge: eleven year olds around the country pick a question and scientists (via video, images, or text) attempt to answer it. Last year, the challenge question was “What is a flame?” a question from Alan Alda’s own youth. This year, the eleven year olds had their first opportunity to choose, and they chose a doozy: “What is time?”

This is…well, a difficult question. Not just hard to explain, it’s a question that could mean one of several different things. Alan Alda has embraced the ambiguity and assures contestants that they can pursue whichever interpretation they think best, but in the end the judges are eleven year olds around the country, and it will be their call whether an answer is sufficient.

(As an aside, I think this sort of ambiguous question isn’t a fluke: barring a new vetting procedure, we’re going to keep getting questions like this. If an eleven year old wants to understand something with a definite answer, he or she will just Google it. It’s only the ambiguous, tricky, arguably poorly-formed questions that can’t be answered by a quick search.)

I’ve been brainstorming a bit, and I’ve come up with a few meanings for the question “What is time?”

  • How should time travel work? In my own limited experience with kids asking about time, this is usually what they’re going for. Screw the big philosophical questions: can I go kill a dinosaur, and if I do, should I be worried that everyone will be speaking Chinese when I get back? In some ways this is the easiest question to answer because, barring Everett-style interpretations of quantum mechanics, there really is only one way for time travel to work consistent with current science, and that’s through wormholes. Wormholes aren’t an especially difficult concept: all they really require is some understanding of the idea that space can be curved. Flatland in particular proves ideal for teaching students to think of space as more than just three static directions, which is why I’m considering the (potentially wildly overambitious) idea of submitting an animated Flatland story dealing with wormholes and time travel for the Flame Challenge. By the way, any budding scientist-animators who are interested in collaborating on such a project are more than welcome! I’m not sure I can do this without help. By the way, one downside of this approach is that it is very well covered by movies and other media, so it is entirely possible that most eleven year olds know this already.
  • What makes time different from other dimensions? There is a flippant physicist answer to this question, and that is that time has a different sign in the Minkowski metric. What that means, in very vague terms, is that while rotations in space will always come back to where they started, if you rotate something in both space and time (it turns out all this means is gaining speed) you can keep going indefinitely, getting closer and closer to the speed of light without ever getting back to your previous speed. If you want to know why time is special like that, that’s harder to say, but occasionally papers bubble up on arXiv claiming that they understand why this should be the case. I’d love it if an author of one of those papers made a submission to the Flame Challenge.
  • Why does time have an arrow? Why does it only go forwards? This is not the same question as the previous one! This is much harder, and depending on who you talk to it relates somehow to entropy and thermodynamics or to quantum mechanics, or even to biology and psychology. It’s tricky to explain, but there have been many attempts, and I don’t doubt that a substantial number of the submissions will be in this vein.
  • How does Special Relativity (or General Relativity) work? How can time go faster or slower? This is a more specialized version of the question about why time is unique, and one that Alan Alda has made mention of in his interviews. Teaching Special Relativity or General Relativity to eleven year olds is a challenge, which is not to say it is impossible but rather the reverse: unlike the other questions, this is unambiguous enough that with enough work someone could do it, and possibly advance the field of science communication in doing so.
  • Is time real? Could time be an illusion? There are a number of variations of this, ranging from purely philosophical to directly scientific. Is it better to think of everything as happening at once, and our minds simply organizing it? Is time merely change, or could time exist in a changeless universe? There is a lot of ambiguity in answering this form of the question, and while we’ll see a few people trying to go in this vein I doubt there’s an answer that will satisfy the world’s eleven year olds.
  • Side topics. Someone could, of course, go on a completely different route. They could explain clocks, and timekeeping throughout the ages. They could talk about the definition of a second. They could talk about the beginning of time, and what that means, or discuss whether or not time had a beginning at all. They could talk about the relationship between energy and time, how one, via Noether’s Theorem, implies the other. There are many choices here, and the trick is to avoid straying too far from the main point. Eleven year olds are not forgiving folks, after all.

I am very much looking forward to seeing what people submit, and if all goes extraordinarily well, I may even have a submission too. It’s a very difficult topic this year, but we’re scientists! If anyone can do it, we can.