# Can one theoretically travel faster than light relativistically? **URL:** \ **Category:** Factual Questions\ **Created:** [September 3, 2021, 5:41pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057 "2021-09-03T17:41:45Z")\ **Posts on this page:** 20\ **Page:** 13
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [November 1, 2021, 3:03am UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/243 "2021-11-01T03:03:26Z")
The video linked above discusses and accounts for that (I think…it may be you mean something different). ---
**Author:** ![tomh4040](https://avatars.discourse-cdn.com/v4/letter/t/ee7513/32.png) [@tomh4040](https://boards.straightdope.com/u/tomh4040)\ **Post date:** [November 2, 2021, 9:48am UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/245 "2021-11-02T09:48:06Z")
RitterSport, yes, after you answer my question. Tom. ---
**Author:** ![RitterSport](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rittersport/32/6326_2.png) [@RitterSport](https://boards.straightdope.com/u/RitterSport)\ **Post date:** [November 2, 2021, 10:59am UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/246 "2021-11-02T10:59:55Z")
Sure. Which question, the one about the two clocks, that has been answered many times already? If it’s that one, the clock in ship B moves slower from the reference frame of A and the clock in ship A moves slower from the reference frame in ship B. Now, to put them next to each other and compare them, you have to accelerate one or the other, and that makes things more complicated and involves general relativity. Let’s say you slow down B and reverse it to bring it next to A – then (I think), you’ll find that B is behind than A when all was said and done – but, of course, once you do the required accelerations to bring them together, they are no longer in inertial reference frames. What’s nice about the particle example is that you don’t need to get anything into another frame, you can just measure how long they last. This avoids the GR complications of the clock example. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [November 2, 2021, 11:33am UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/247 "2021-11-02T11:33:24Z")
> [@RitterSport](#): > > you have to accelerate one or the other, and that makes things more complicated and involves general relativity. This is mostly a red herring, and was clearly a problem in the previous thread on the subject. It isn’t the time dilation in the accelerating frame that changes the time, that exists, but is a minor correction. What acceleration does is swap reference frames, so that the travelling clock has a history in two _different_ reference frames. @Andy_L above pointed out the simplifying experiment. Fly two clocks, Ba and Br, one outgoing and one incoming, and when they intersect in space, at that moment, have the incoming clock synchronise with the outgoing. This provides the effect of an instantaneous change of reference frames of the clock’s time, and avoids the additional calculation required during the acceleration period (both SR and GR). That calculation can be done, but it just tedious and doesn’t really help matters. ---
**Author:** ![tomh4040](https://avatars.discourse-cdn.com/v4/letter/t/ee7513/32.png) [@tomh4040](https://boards.straightdope.com/u/tomh4040)\ **Post date:** [November 2, 2021, 3:15pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/248 "2021-11-02T15:15:11Z")
It has not been answered, it has been evaded, and the answerer’s own question posed instead. I keep being accused of not using reference frames, but as I have repeatedly said, the number of reference frames is implicit in the question. “There are two clocks in relative motion…” That sentence tells you all you need to know about how many IFRs there are. But I will spell it out for you - there are two. Two clocks in motion - do you understand now? ---
**Author:** ![RitterSport](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rittersport/32/6326_2.png) [@RitterSport](https://boards.straightdope.com/u/RitterSport)\ **Post date:** [November 2, 2021, 3:23pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/249 "2021-11-02T15:23:24Z")
I do! There are two clocks in motion, A and B, and they are travelling away from each other at high speed. A person travelling with clock A will observe that clock B is moving more slowly. A person travelling with clock B will observe that clock A is moving slowly. The B clock really is moving more slowly from the reference frame of the person in A (and vice versa). This is demonstrated by particles moving at high speed. A person sitting outside of a particle accelerator will observe that particles moving at high speed relative to the person will have a longer half-life, and that additional time is exactly as predicted by relativity. That’s because, from the person sitting outside of the accelerator’s reference frame, the particle’s “clock” is moving more slowly. Your turn! ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 2, 2021, 3:25pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/250 "2021-11-02T15:25:19Z")
If anything’s being evaded here, it’s the answer, not the question. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [November 2, 2021, 3:28pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/251 "2021-11-02T15:28:11Z")
You seem to know what answer you want to hear, so why not give it? Which clock is ticking more slowly, and why? If you can’t answer your own question, then you can either accept the answers from those who _can_, or accept that you are unable to understand what it is that you are asking. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [November 2, 2021, 3:38pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/252 "2021-11-02T15:38:24Z")
Indeed. It’s the guy hiding from the answer that has declared that he’s not listening to answers. Everyone else keeps answering the question, as annoying as that may be for the guy who doesn’t want to hear it. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [November 2, 2021, 10:21pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/253 "2021-11-02T22:21:39Z")
> [@tomh4040](#): > > But I will spell it out for you - there are two. Two clocks in motion - do you understand now? Excellent. So there are only two reference frames involved in the question. Now which one is the question posed in? You have not fully described the question since by your own admission there are two reference frames. Otherwise we simply answer the question for both of them, and leave it to you do pick which of the two answers you need. So here you are again, In the reference frame of Clock A, Clock B is slower. In the reference frame of Clock B, Clock A is slower. Perfect, the question is answered according to your demands. It is answered in both the reference frames you have given. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [November 2, 2021, 11:29pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/254 "2021-11-02T23:29:20Z")
> [@k9bfriender](#): > > You seem to know what answer you want to hear, so why not give it? He has. The answer he wants to hear, which he has already given, is that his question exposes a logical contradiction, and he will entertain no objection to this claim; all objections are either not comprehended and derisively dismissed, or, I suspect, not read at all. The conclusions we are then supposed to draw are the following: 1. Einstein was fundamentally wrong when he propounded his special theory of relativity, and despite the man’s legendary intellect and profound insights, the wrongness of his theory can be “proved” with a childishly simplistic rhetorical question based on a very obvious false premise. 2. The entire scientific community has been duped by Einstein’s theory, and stubbornly refuses to listen to either Herbert Dingle or to our own **TomH**. A Nobel prize winning physicist has even brazenly suggested that Herbert Dingle doesn’t know what he’s talking about! 3. Nearly a century of accumulated empirical evidence fully supporting relativity theory exactly according to its predictions must be disregarded because … well, I have no idea why. Apparently we must abandon the scientific method because of unspecified mysterious reasons, and rely instead on internet memes from personal blogs. ---
**Author:** ![RitterSport](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rittersport/32/6326_2.png) [@RitterSport](https://boards.straightdope.com/u/RitterSport)\ **Post date:** [November 3, 2021, 1:31pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/255 "2021-11-03T13:31:45Z")
@tomh4040, I gave a good faith answer to your question. I’m hoping you’ll do the same for me. As a reminder, I’m asking how you explain the longer half-life for particles in motion relative to the observer, vs. particles at rest relative to the observer. Also explain why the longer half-life matches exactly what the theory of relativity would expect in terms of time dilation effects. ---
**Author:** ![Cheesesteak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cheesesteak/32/3694_2.png) [@Cheesesteak](https://boards.straightdope.com/u/Cheesesteak)\ **Post date:** [November 3, 2021, 5:59pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/256 "2021-11-03T17:59:02Z")
> [@tomh4040](#): > > Einstein said that these effects were and are real, so which clock is running slow, and why that one? You can invoke reference frames in your answer if you want to, the question does not need to explicitly mention them. > [@tomh4040](#): > > how many IFRs there are. But I will spell it out for you - there are two. You are not appreciating the idea that two separate IFRs means that your first question has two separate answers. There isn’t one ‘real’ answer because there isn’t one ‘real’ frame of reference. You can pick which one you want to answer from, or answer from both, but you can’t leave the frame of reference undefined. Leaving it undefined implies that there is a default frame of reference to answer from, and there isn’t. ---
**Author:** ![tomh4040](https://avatars.discourse-cdn.com/v4/letter/t/ee7513/32.png) [@tomh4040](https://boards.straightdope.com/u/tomh4040)\ **Post date:** [November 3, 2021, 10:36pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/257 "2021-11-03T22:36:17Z")
Rittersport, no you did not give me a good faith (or any other sort of) answer to my question. Nobody has because it cannot be answered truthfully by a relativist. Einstein said that these effects were and are real, so in reality one clock runs slower than the other. He also said that the effects are symmetrical, so if clock A runs slower than clock B, then clock B runs slower than clock A. This is impossible. According to relativity, which clock runs slower, and why that one? You will get the answer to your question tomorrow. Tom. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [November 3, 2021, 10:40pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/258 "2021-11-03T22:40:59Z")
> [@tomh4040](#): > > He also said that the effects are symmetrical, so if clock A runs slower than clock B, then clock B runs slower than clock A. This is impossible. The point you seem to be missing is that, according to the theory of relativity, this is _not_ impossible. ---
**Author:** ![tomh4040](https://avatars.discourse-cdn.com/v4/letter/t/ee7513/32.png) [@tomh4040](https://boards.straightdope.com/u/tomh4040)\ **Post date:** [November 3, 2021, 10:46pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/259 "2021-11-03T22:46:25Z")
Cheesecake, no there are not two separate answers (there might be if the effects were imaginary).The theory says that these effects are real, and that clock A runs slower than clock B, and clock B runs slower than clock A. A clear contradiction as the theory requires each of two identical clocks to be slower than the other. Tom. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [November 3, 2021, 10:53pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/260 "2021-11-03T22:53:01Z")
It is not a contradiction in the theory of relativity. A theory pretty much has to do two things. It has to be internally consistent and it has to make accurate real-life predictions. Relativity does both of those things. All you are doing is demonstrating that it is not consistent with _another_ theory of how things work, but so what? It doesn’t have to be, it only needs to be consistent within itself, and it is. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 3, 2021, 11:01pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/261 "2021-11-03T23:01:34Z")
Ah, I see. You think that “from one specific reference frame” implies “not real”. But things can be real, and still be different in different reference frames. In A’s reference frame, clock B really is slower. In B’s reference frame, clock A really is slower. Both are really true, because A and B are measuring different times. ---
**Author:** ![RitterSport](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rittersport/32/6326_2.png) [@RitterSport](https://boards.straightdope.com/u/RitterSport)\ **Post date:** [November 3, 2021, 11:32pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/262 "2021-11-03T23:32:01Z")
> [@tomh4040](#): > > Rittersport, no you did not give me a good faith (or any other sort of) answer to my question. Hmm, I don’t really appreciate this answer. Even if you think I’m wrong, I really did try and answer in good faith to the best of my ability. I did the best I could to answer your question. Please do the same for mine. ---
**Author:** ![Czarcasm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/czarcasm/32/4050_2.png) [@Czarcasm](https://boards.straightdope.com/u/Czarcasm)\ **Post date:** [November 3, 2021, 11:56pm UTC](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057/263 "2021-11-03T23:56:10Z")
> [@tomh4040](#): > > Nobody has because it cannot be answered truthfully by a relativist. So called “relativists” are lying? [Previous page](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057.md?page=12) [Next page](https://boards.straightdope.com/t/can-one-theoretically-travel-faster-than-light-relativistically/950057.md?page=14)