8 ms·
I thought this was simple. You can't go faster than light. If you go through a wormhole (Or just send information) you go faster than light (Ignoring Hollywood
by aaron695 6y ago
I thought this was simple. You can't go faster than light.
If you go through a wormhole (Or just send information) you go faster than light (Ignoring Hollywood's incorrect movie Event Horizon where you just bend paper), so you go back in time.
So it's not possible.
Because you can kill you father (or something mathematical with information) which is a paradox.
End of story.
- mpalmer 6y agoI think that might be stretching what it means to be fast. Wormholes seem to be about warping space. Rate of motion doesn't enter into it.
- briga 6y agoWhat's to say we live in a world without paradoxes?
- rd07 6y agoWell, wormhole is not about how to travel faster than light, but about creating a shortcut between 2 points in a certain dimensional space by using a higher dimensional space. The most used explanation is using a piece of paper, the shortest route to travel between 2 points in a piece of paper is a straight line. But, we can shorten it by folding that paper and create a hole that connect the 2 points through the 3th dimension.
- yellowapple 6y agoI don't understand why "faster than light" automatically implies "go back in time". If it takes me 10 seconds to travel 10 lightyears, then that means I should still be traveling forward in time (specifically by 10 seconds), no? Like, it might apply on a "moving through local space faster than light" sense because physics is weird like that, but the whole idea behind wormholes is to shrink the actual distance traveled (from the traveler's point of view).
- ikeboy 6y agoBecause of relativity, you can have locations A and B in spacetime and a frame of reference such that A happens before B and a different frame such that B happens before A. So, if you're at A, you can travel faster than the speed of light and arrive before B happens. Then, after B happens, you can travel back to before A happens.
- komali2 6y agoWait whaaaat? This is the first I've heard of this. I've a vague understanding of causality. I thought the arrow of Time moved in one direction only? How can A come before B come before A from, from one observer?
- ikeboy 6y agoIt can't, if that observer always moves slower than the speed of light in all reference frames.
- 6gvONxR4sf7o 6y agoIf events A and B are close to each other in space time (light from one can have arrived at the other by then), then the ordering is fixed. If they are far from each other (light won't get from one to another by then), then time gets weirder. The notion of what is simultaneous to what gets weird. If you and I are moving relative to each other, we're going to disagree on which distant events happen at the same time. If that happens, then whether something's happening now might change depending on reference frame. The ordering can be t(A) = t(B) or t(A) != t(B). Since no frame is privileged, we can also change the other way around, so t(A) != t(B) can be t(A) < t(B) or t(A) > t(B) depending on reference frame. It's only flexible like that for things that could be simultaneous in some frame, which at least in special relativity means light from one can't have gotten to another yet. I never took general relativity, so who knows how it works in that setting. https://en.wikipedia.org/wiki/Relativity_of_simultaneity#Thought_experiments https://en.wikipedia.org/wiki/Relativity_of_simultaneity#Tho...
- Causality1 6y ago
- weswpg 6y agoYou're right and the person you're replying to is wrong. PBS spacetime videos on Youtube explain it well
- maxcan 6y agoBest show on YouTube. Such a PBSST addict
- moron4hire 6y agoI suppose it requires a stretch of the understanding of what it would mean to go "back in time". If you were to literally travel backwards in time, but not retain knowledge of the future, that would be useless. What is desired is to be in a state where you are at time T with knowledge from time T+1. So, by traveling through the wormhole, you would arrive there with knowledge that could not have reached it from the direct path until some time later. You might even travel through the wormhole, observe your own past, and return back again. But yes, generally speaking, there is no known means to travel back in time before the moment of creation of the time machine itself.
- aaron695 6y ago> 10 seconds to travel 10 lightyears You can look at the equations, but you will literally go back in time if you do this. This is simple I believe. Go there, go back, you've gone back in time, up to the SoL time slows then after it reverses. But you can't go 10 seconds to travel 10 light years, speed of light is absolute so no time travel for you. People believe wormholes are a loop hole because they puncture space or something something Event Horizon. This I also believe is untrue. Go through a wormhole, either it takes the equivalent of the speed of light to get there for the true distance, or it's not possible to send information through.
- yellowapple 6y ago> This is simple I believe If it was simple then I wouldn't be asking. > Go there, go back, you've gone back in time How? If it takes me 10 seconds to travel 10 lightyears, then I should've gone forward in time by 10 seocnds, no matter if I'm measuring by my own frame of reference or an observer's (i.e. if it's my stopwatch v. an observer's stopwatch that's counting the seconds). > But you can't go 10 seconds to travel 10 light years, speed of light is absolute And it's never been adequately explained to me why that is.
- pankajdoharey 6y agoYes you will still be travelling forward in time just that your relative time will be slower at speeds approaching the speed of light. So fundamentally you won't be going back in time but much forward in time than you observe. Checkout minute physics YouTube channel course of relativity https://youtu.be/1rLWVZVWfdY https://youtu.be/1rLWVZVWfdY
- 6gvONxR4sf7o 6y agoA path is a collection of points in space and time. Certain collections of points in space and time can be said to be all simultaneous to each other. If your path exceeds the speed of light, then to somebody, your path is a collection of simultaneous positions (at least in special relativity. I don't know GR) My notion of simultaneity can be different from that somebody's. If they think event A and B are at the same time, I might think they're different. Waving hands, no frame is privileged, so I could think they're different as (A < B) if I'm moving this way, or (A > B) if I'm moving that way (relative to this person). That means that the events this person thinks are simultaneous (you leaving and you arriving) can appear in either order to others depending on reference frame. It can look like you arrived when you left (same time), you arrived after you left, or you arrived before you left.
- Ono-Sendai 6y agoYou might be interested in my blog post about it: http://forwardscattering.org/post/36 http://forwardscattering.org/post/36 (Special relativity, faster-than-light communication, and absolute time and space)
- Ixio 6y agoYour blogpost might benefit from explaining further the following line: "Special relativity says that the rocket has a different coordinate frame than the space stations. In particular the x axis, which corresponds to all the points in space at the same rocket-time, is not the same as the x-axis for the space stations." I'm on the lookout for an explanation of why FTL=time-travel that I'll finally understand. However in your blogpost my limited knowledge of Special relativity fails to make sense of the whole argument.
- cygx 6y agoI don't understand why "faster than light" automatically implies "go back in time". If it takes me 10 seconds to travel 10 lightyears, then that means I should still be traveling forward in time (specifically by 10 seconds), no? Say you had a faster than light transmitter that can send signals with (from your perspective) twice the speed of light (2c). If the receiver has no relative motion, everything seems to work fine. But if the receiver moves away from you fast enough (I think 0.5c should do it, but don't quote me on that one), then, from the receiver's perspective, the transmission will happen instantaneously. If the receiver moved even faster than that, the signal would seem to arrive before it had been sent(!), and if they had their own faster-than-light transmitter, they could relay the message back into the emitter's past.
- AnIdiotOnTheNet 6y agoFor more information, see: https://en.wikipedia.org/wiki/Tachyonic_antitelephone https://en.wikipedia.org/wiki/Tachyonic_antitelephone
- yellowapple 6y ago> But if the receiver moves away from you fast enough (I think 0.5c should do it, but don't quote me on that one), then, from the receiver's perspective, the transmission will happen instantaneously. Why? I mean, I get that time is progressing more slowly for the receiver because it's traveling at relativistic speeds, but instantaneous arrival of anything doesn't seem to follow from that, and therefore... > If the receiver moved even faster than that, the signal would seem to arrive before it had been sent(!) ...neither does this. Further, the whole point of wormholes (in the context of superluminal travel/communication) is that neither the signal nor the receiver is actually moving at relativistic speeds, but rather that the signal is instead taking a shorter path between two points in spacetime specifically to avoid having to move at such speeds from a local perspective.
- qubex 6y agoYou start from Earth and go two light years in one year using an FTL drive of some kind. A day before departing you look and you see your spacecraft in spacedock and, peering through a telescope, your two-year-old spacecraft in orbit around your destination. You’ve been watching it for a year already. From your viewpoint prior to launch, there’s two of you, and the distant one is old. EDIT: I’m wrong, and stand corrected. Relativity is so very slippery!
- brianberns 6y agoI don't think this is right. You leave at t=0 and arrive at your destination at t=1 year. It then takes two years for the image of your arrival to travel back to Earth, where it can be perceived at t=3 years. However, when you arrive at your destination, you can look back at Earth and see an image of yourself 1 year prior to your departure.
- qubex 6y agoYup, I think you’re right, and that I’m wrong.
- brianberns 6y agoBTW, the other weird thing about this scenario is that if you look backwards along your trajectory, you will see a movie of your journey playing in reverse! Also, in regard to your edit: this doesn’t really have anything to do with relativity. Newton would’ve come to the same conclusion.
- qubex 6y agoMy reference to relativity was to indicate that I thought it would lead to different conclusions than the Newtonian case. As for the two images, it’s well covered on PBS Spacetime’s overview of the Alcubierre Drive from several years back that if a bystander were to observe a FTL craft traverse their field of view laterally, they’d indeed see two images, each heading in opposite directions, as you indeed allude to.
- avmich 6y ago> I thought this was simple. You can't go faster than light. People also thought that time is universal and common for all places. According to history of physics, theories usually have limits to their applicability. For relativity theory, currently known limits are in the presence of large gravity centers; but it doesn't mean that those are the only limits. Even putting aside elegant, in my view, proposals to circumvent speed limit, like Alcubierre drive, we don't know if this speed limit is "absolute". It's part of very well working theory, yes, but we don't know what we can learn yet.
- ivalm 6y agoDistances between objects can increase faster than speed of light (due to expansion of space, for example) the problem here is that with wormholes you might have causality violation (also not sure if the universe’s topology supports holes).
- 6gvONxR4sf7o 6y agoImagine this as a counterexample. A wormhole could connect two distant points as being the same time in some specific frame. Go through either end at t=0, come out the other at t=0. Go through at t=1, come out at t=1. If that's the only FTL travel there is, then there are only two options to get back to your original position. The short way through the wormhole, but we've established that causality is maintained in that direction. Or the long way, but it'll take long enough that in any frame you get back after you leave. Either way, you can't get back before you left and can't affect things before you left. You get into trouble if there are two wormholes like this that connect points in different reference frames. You could go through the first wormhole at (t=0, x=A) to (t=0, x=B), then the next wormhole at (t'=1, x=B) to (t'=1, x=A), where I'm using t' as the time in this second wormhole's frame. Even if (t=0, x=B) is before (t'=1, x=B) in all frames, there could be some t' frames where (t'=1, x=A) is before (t=0, x=A), letting you return before you left. But at least there's some scenario (only one wormhole exists) that doesn't have tricky causal implications. And there are other setups where even going back in time isn't paradoxical. Take this viewpoint: You just can't kill your father when you go back. "It didn't happen" is the same as "It won't happen," so it's a non issue. If you go back and try to kill him, then instead of you succeeding, whatever happened will happen (which we already know wasn't your father dying). Mathematically, it's a loop. You can't continue forwards around a loop to get somewhere that isn't behind you. As a tautology, the only loop-containing solutions to the physical equations would be the ones containing self-consistent loops.