# Speed of Light - Time Travel **URL:** \ **Category:** Factual Questions\ **Created:** [August 24, 2001, 2:33pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908 "2001-08-24T14:33:42Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Jdeforrest](https://avatars.discourse-cdn.com/v4/letter/j/49beb7/32.png) [@Jdeforrest](https://boards.straightdope.com/u/Jdeforrest)\ **Post date:** [August 24, 2001, 2:33pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/1 "2001-08-24T14:33:42Z")
I was thinking, according to Neuton everything has a equal and opposite reaction. Well if you achieve the speed of light, time stops. If you exceed the speed of light, time moves backwards. So in order to go into the future, you would have to travel at negative c? ---
**Author:** ![Popup](https://avatars.discourse-cdn.com/v4/letter/p/94ad74/32.png) [@Popup](https://boards.straightdope.com/u/Popup)\ **Post date:** [August 24, 2001, 3:06pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/2 "2001-08-24T15:06:28Z")
Our new friend **Jdeforrest** claims to have been thinking… He does however seem to suffer from some misconceptions: [list=1] [li] It’s **Newton**.[/li][li] It is not possible to achieve the speed of light.[/li][li] Even if you did, in your frame of reference time doesn’t stop.[/li][li] It is not possible to exceed the speed of light.[/li][li] Time does not move backwards.[/li][li] The easiest way to travel forwards in time is to sit still, that way you travel into the future at the blinding speed of 1s/s.[/li][/list=1] (Apologies if this seems rude **Jdeforrest** , it’s just that lots of people here don’t like that kind of pseudoscience. And we don’t like people just poping in asking silly questions before aclimatizing to the board. Please hang around for a while and you’ll get the hang of it.) ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [August 24, 2001, 3:13pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/3 "2001-08-24T15:13:21Z")
> [@](#): > > I was thinking, according to Neuton everything has a equal and opposite reaction. Well if you achieve the speed of light, time stops. It’s Newton and it has nothing to do _“with equal and opposite reaction.”_ > [@](#): > > If you exceed the speed of light, time moves backwards. Time doesn’t move backward, but causality could be violated. But it can’t be done so don’t worry about it. > [@](#): > > So in order to go into the future, you would have to travel at negative c? How exactly would you generate a negative velocity? Just keep sitting in your chair. Every second you travel one second into the future. If you want to travel into the future faster than other Earthlings then acquire some velocity. ---
**Author:** ![Triskadecamus](https://avatars.discourse-cdn.com/v4/letter/t/b19c9b/32.png) [@Triskadecamus](https://boards.straightdope.com/u/Triskadecamus)\ **Post date:** [August 24, 2001, 3:23pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/4 "2001-08-24T15:23:37Z")
You have got a lot of reading to do, if you really want to understand the relationship between time and the speed of light as described by Einstein. The brief answer to your question is no, you cannot go back in time, that is not what Einstein said. The real result of the dilation of time described by Einstein is that each increase in speed requires a greater application of energy to accomplish. That means you can’t accelerate a physical object even to the speed of light, much less beyond it. You seem to think, given your reference to Newton, that one is hurled back into time as an opposite force effect to the foreword motion of going faster than light. The two phenomena are not so simply related. I searched for a primer on relativity and the time dilation effect, but didn’t find anything that seemed to be basic enough to be comprehensible to an elementary study, and still had all the information needed to answer your question. So my best answer is that the mathematics of faster than light time travel are complex, but do show that the possibility exists that in some portions of space time, under some very exotic conditions massive particles might move to non sequential times. Evidence that any particle has ever done so was not available to me. But the answer to your question still remains, no, you can’t travel backwards in time by going faster than light, because you can’t travel faster than light in the first place. (The ordinary world answer.) ## Tris “It should be possible to explain the laws of physics to a barmaid.” ~ Albert Einstein ~ “Man, you should see the bar where Einstein used to drink.” ~ Triskadecamus ~ ---
**Author:** ![mhendo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mhendo/32/3159_2.png) [@mhendo](https://boards.straightdope.com/u/mhendo)\ **Post date:** [August 24, 2001, 3:29pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/5 "2001-08-24T15:29:14Z")
I thought we got time travel with the last Presidential election. Or does does it only _feel_ like we’ve been going backwards ever since? 🙂 ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [August 24, 2001, 4:14pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/6 "2001-08-24T16:14:43Z")
> [@](#): > > tc wrote: > > 1. Even if you did, in your frame of reference time doesn’t stop. I feel I must nitpick here simply because this is such a widespread misconception. If something is traveling at the speed of light (a photon) it _can’t have_ a frame of reference. Light must travel at c with respect to all frames of reference and light can’t travel at c with respect to light. If light _could_ have a frame of reference then time would come to a stop and distance in its direction of travel would contract to zero. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [August 24, 2001, 4:27pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/7 "2001-08-24T16:27:47Z")
There once was a young maid named Bright Who could travel faster than light. She took off one day In a relative way And returned on the previous night! ---
**Author:** ![mhendo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mhendo/32/3159_2.png) [@mhendo](https://boards.straightdope.com/u/mhendo)\ **Post date:** [August 24, 2001, 4:38pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/8 "2001-08-24T16:38:41Z")
I’ve just been on the [tiger thread](http://boards.straightdope.com/sdmb/showthread.php?threadid=83485). You’re in quite a rhyming mood today. ---
**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:** [August 24, 2001, 5:01pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/9 "2001-08-24T17:01:51Z")
> [@](#): > > \*Originally posted by Triskadecamus \* > **But the answer to your question still remains, no, you can’t travel backwards in time by going faster than light, because you can’t travel faster than light in the first place. (The ordinary world answer.)** This isn’t quite correct. _Theoretically_ you can travel backwards in time. The real question is, how do you manage to travel faster than light? If you mean to strap a rocket to your ass and speed up to past light speed then everyone is correct…you can forget it. Among other problems your mass (and I know that the term ‘mass’ is misleading here but I don’t know what is commonly used in its place today) would approach inifinty as you approached light speed. If you somehow actually reached light speed then your mass would be infinite and you’d need an infinite amount of power to move your now stupendously sized ass. However, there a ways around this…theoretically. One method I’ve heard involves two metal plates that are charged with electricity to a high degree and form a ‘connection’ between themselves. Now, take one plate on a spaceship ride fro awhile at some significant percentage of light speed to experience noticeable time dilation. The plate on the spaceship will now be in the ‘past’ while the plate left on earth would be in the future. Step through and you can travel backwards and forwards in time at your leisure but only to the points the two plates are at. Unfortunately the energy required to make this happen is monstrous and probably completely lethal to anything passing through the plates. I also read some speculation that merely introducing an object to pass between the plates would destabilize the connection and cause it to collapse. Still…I don’t believe there is anything in the math that prohibits time travel…it’s just the practical applications that become impossible (or very nearly so). Try [this](http://www.biols.susx.ac.uk/home/John_Gribbin/Time_Travel.html) link for some more info. ---
**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:** [August 24, 2001, 6:07pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/10 "2001-08-24T18:07:49Z")
If you could get the effect of faster than light travel somehow (using a wormhole, or some other such method to avoid the problems involved), you could travel back in time, and vice versa. Nobody knows yet for certain whether FTL is possible, though. If you want, I can go dig up an explanation for this, but be warned: It gets pretty involved. On another note, could we refrain from piling on **Jdeforrest** here? Yes, he had some misconceptions in his OP. That’s why he asked the question in the first place, because he’s not a physicist, and he knew that he didn’t know the answer already. The proper thing to do is to answer his questions and educate him, not to insult him. ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [August 24, 2001, 7:19pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/11 "2001-08-24T19:19:28Z")
> [@](#): > > There once was a young maid named Bright > Who could travel faster than light. > She took off one day > In a relative way > And returned on the previous night! > [@](#): > > This isn’t quite correct. Theoretically you can travel backwards in time. The real question is, how do you manage to travel faster than light? Nope. Time cannot be reversed. It’s true that a faster than c traveler could arrive at B before they left A, but for the round trip **everyone** must agree that he arrived back after he set out. In other words causality can be violated but time cannot be reversed. (I thought I had already posted this, but, if I did, it must have been in some other thread.) ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [August 24, 2001, 7:22pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/12 "2001-08-24T19:22:02Z")
My last post only applies to SR, and does not include GR. ---
**Author:** ![Jdeforrest](https://avatars.discourse-cdn.com/v4/letter/j/49beb7/32.png) [@Jdeforrest](https://boards.straightdope.com/u/Jdeforrest)\ **Post date:** [August 24, 2001, 7:35pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/13 "2001-08-24T19:35:32Z")
Okay, that makes some more sense. Its the frame of reference thing that keeps messing me up. I thought I remembered reading in another post that as you surpass the speed of light, time starts flowing in reverse. So I started thinking, “Well, if thats how you travel to the past, how do you travel to the future?” Well with frame of reference in mind, all you would have to do is slow time down significantly enough for youself so that time for everybody else is just zipping by. Kinda like cryogenic stasis. ---
**Author:** ![bugg](https://avatars.discourse-cdn.com/v4/letter/b/ecae2f/32.png) [@bugg](https://boards.straightdope.com/u/bugg)\ **Post date:** [August 24, 2001, 7:48pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/14 "2001-08-24T19:48:23Z")
> [@](#): > > \*Originally posted by Ring \* > \*\*How exactly would you generate a negative velocity? > \*\* By moving backwards 🙂 As for discussing anything that occurs fast than light, you’re into the ultratheoretical and science as we know it can’t help you much; “all bets are off” ---
**Author:** ![geepee](https://avatars.discourse-cdn.com/v4/letter/g/ebca7d/32.png) [@geepee](https://boards.straightdope.com/u/geepee)\ **Post date:** [August 24, 2001, 8:05pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/15 "2001-08-24T20:05:58Z")
hey didn’t they fly 2 747s with atomic clocks and compared them to an atomic clock on the ground , when they got back the atomic clocks on the 747s had not advanced as much as the one on the ground , which was some form of time dialation oh and the more energy to travel faster to travel x2 the speed you move at you need to increase energy input by a factor of 4 ---
**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:** [August 24, 2001, 8:18pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/16 "2001-08-24T20:18:53Z")
> [@](#): > > \*Originally posted by Ring \* > **In other words causality can be violated but time cannot be reversed.** Just out of curiosity is another way of stating this through one of the laws of thermodynamics? That is, does the law of entropy always increasing form a basis for an arrow of time? If you reversed time would you perforce be decreasing entropy and that is impossible? As to your example of everyone agreeing that I left _before_ I returned on a hyperspeed journey couldn’t you drawup a situation where I left point A at an apparent speed greater than C (say via wormhole) and I jumped into another wormhole that popped me back to where I started couldn’t I arrive before I left? (Yes, I know this throws all sorts of weird impossibilities such as what if I prevented myself from starting my journey in the first place…I’m just curious why everyone _has_ to agree I returned _after_ I left. NOTE: If the answer to that is too involved just say so and suggest I sing-up for 10 years of graduate physics). ---
**Author:** ![23skidoo](https://avatars.discourse-cdn.com/v4/letter/2/f04885/32.png) [@23skidoo](https://boards.straightdope.com/u/23skidoo)\ **Post date:** [August 24, 2001, 8:21pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/17 "2001-08-24T20:21:20Z")
> [@](#): > > \*Originally posted by sailor \* > \*\*There once was a young maid named Bright > Who could travel faster than light. > She took off one day > In a relative way > And returned on the previous night! \*\* There once was a couple named Bright Who could make love much faster than light They started one day In a relative way And came on a previous night ---
**Author:** ![geepee](https://avatars.discourse-cdn.com/v4/letter/g/ebca7d/32.png) [@geepee](https://boards.straightdope.com/u/geepee)\ **Post date:** [August 24, 2001, 8:22pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/18 "2001-08-24T20:22:38Z")
QUOTE :However, there a ways around this…theoretically. One method I’ve heard involves two metal plates that are charged with electricity to a high degree and form a ‘connection’ between themselves. Now, take one plate on a spaceship ride fro awhile at some significant percentage of light speed to experience noticeable time dilation. The plate on the spaceship will now be in the ‘past’ while the plate left on earth would be in the future. Step through and you can travel backwards and forwards in time at your leisure but only to the points the two plates are at yeah i heard of that too but to pass an object or respectable size like 60kilos (you maybe) it takes more energy than is visible in the universe , apparently somebody is trying it with photons somewhere ---
**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:** [August 24, 2001, 8:24pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/19 "2001-08-24T20:24:25Z")
> [@](#): > > \*Originally posted by Whack-a-Mole \* > NOTE: If the answer to that is too involved just say so and suggest I **sing-up** for 10 years of graduate physics. As long as you’re suggesting graduate level physics classes perhaps some third grade english would be in order as well. Please revise the bold portion in the quote above to: **signup**. ---
**Author:** ![Jdeforrest](https://avatars.discourse-cdn.com/v4/letter/j/49beb7/32.png) [@Jdeforrest](https://boards.straightdope.com/u/Jdeforrest)\ **Post date:** [August 24, 2001, 8:34pm UTC](https://boards.straightdope.com/t/speed-of-light-time-travel/77908/20 "2001-08-24T20:34:20Z")
> [@](#): > > \*Originally posted by geepee \* > **hey didn’t they fly 2 747s with atomic clocks and compared them to an atomic clock on the ground , when they got back the atomic clocks on the 747s had not advanced as much as the one on the ground , which was some form of time dialation** Yes, the speed of light changes as it gets out of earths gravity well. Its explained in a little more detail in this thread [http://boards.straightdope.com/sdmb/showthread.php?threadid=81580](http://boards.straightdope.com/sdmb/showthread.php?threadid=81580). [Next page](https://boards.straightdope.com/t/speed-of-light-time-travel/77908.md?page=2)