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Novikov explains it approximately this way. Suppose you have a wormhole between points A and B. So from A to B - and from B to A - you can go by two different
by avmich 6y ago
Novikov explains it approximately this way.
Suppose you have a wormhole between points A and B. So from A to B - and from B to A - you can go by two different roads, one is pretty long (say, 1 light month), and another is very short (negligible distance).
Next, suppose B end swiftly rotates around point A, so fast that time in B goes slower than time in A. This means clock in B is going slower than in A, and over 20 years in A only 10 years will pass by clock in B. That can be confirmed by observation - telescopes in A will see slower clock in B, telescopes in B will see faster clock in A (it's B going around A, not vice versa).
That is, if we're talking about telescopes, looking through "regular" space. Since A and B are also connected by the wormhole, looking through wormhole will show us that clocks are synchronized. Over the wormhole, A and B are not moving, so clocks don't deviate from one another.
We can stop B flying around A now. Now suppose B clock has accumulated 10 years of difference from A clock - again, looking via "regular" space. We're leaving point A, flying to point B over the "regular" space and spending 5 years - way slower than speed of light, so our clock is practically synchronous to A clock. At the start of flight, A clock show 20 years, and B clock is 10 years, and by the end of flight A clock is 25 years and B clock is 15 years. After arriving at B, we jump into wormhole and get back to A, when A clock shows the same as B clock - that is, 15 years. According to A clock, we left at 20 years and came back at 15 years. Time travel.
- AaronFriel 6y agoThis is the scenario the author Stephen Baxter used in the book Timelike Infinity. Wormhole technology on a ship sent in a relativistic journey circling the solar system, used to bootstrap humanity and influence it in the past. There is a catch, this sort of time travel like many others only allows one to go back as far as the creation of the wormhole. Sort of like in Primer, it isn't a general form of time travel. You can take the wormhole forward, or from the other end backwards, but not prior to the time it was created.
- Acinyx 6y agoNice explanation, this made more sense to me than most of the explanations I have heard about this before. But, wouldn't this just constrain the possible features of a wormhole? The issue is fixed if traveling/observing through the wormhole has the same time dilation: Both through telescope as through the wormhole, the clocks can be observed to go slower. After 20 years at A, both the telescope as observation through the wormhole show 10 years have passed at B. If we don't stop B from spinning: The regular space traveler takes 5 years, as observed from A, to reach B, so reaches B at A:25 years, B:12,5 years. If they leave immediately after arrival, they'll end up again at A at A:30y, B:15y. Otoh, the wormhole travel leaves at A:20y ends up at B at 10y and gets back to A immediately: A still at 20y and B at 10y. Mixed travel:regular travel starts at A:20, B:10y, reaches B at A:25y, B:12,5 and jumps back through the wormhole at the same time as seen from A and B.
- Ixio 6y agoExactly ! Why don't we suppose traveling/observing through the wormhole has the same time dilation ? I've heard of FTL=time-travel a couple of years ago for the first time and I would love to be able to argue with someone knowledgeable about it to understand. I hoped this HN thread would have answers. However all the answers here seem to have holes in same. I'm starting to wonder if FTL=time-travel isn't like Schrödinger's cat: a hypothetical thought experiment terribly misunderstood by the masses.
- ikeboy 6y agoIf travel through the wormhole takes exactly as long as travel via space, what kind of wormhole is it?
- pb82 6y ago> Since A and B are also connected by the wormhole, looking through wormhole will show us that clocks are synchronized. Can you please elaborate on that a bit more? That's the part I don't understand. Why would you observe synchronized clocks when looking through the wormhole?
- avmich 6y agoSpace in the wormhole is regular space. So we have regular properties of space and time - and if A and B are separated by a short distance, and they don't have accelerated motion against each other, the clocks have no reason to deviate. > Why would you observe synchronized clocks when looking through the wormhole? I think it's the same question as why we observe diverging clocks when looking via the "regular" space. Einstein provided answers to that - in "regular" space (that is, outside the wormhole - the space in wormhole is also space, with properties of space, including relativistic ones) we have accelerated motion, which is absolute and slows down clock in B, but not in A. In "wormhole space" we don't have that, so there is no reason to have, or observe, that difference. I think, other than entrance to the wormhole, you can't really say which of paths is "regular space" - the long one or through the wormhole, as you may argue that in fact A and B are close by, but they also have a wormhole with really long path - and the rest of the Universe - inside.