# time travel **URL:** \ **Category:** Great Debates\ **Created:** [February 12, 2003, 4:24pm UTC](https://boards.straightdope.com/t/time-travel/154590 "2003-02-12T16:24:52Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [February 13, 2003, 5:04pm UTC](https://boards.straightdope.com/t/time-travel/154590/21 "2003-02-13T17:04:44Z")
> [@](#): > > I wonder why ‘light-speed’ is the limit then? Not light-speed +/- 1 mps. e = mc[sup]2[/sup] ± 3db 😃 [sub]I picked up a button with that on it at a convention once.[/sub] ---
**Author:** ![Earthworm\_Jim](https://avatars.discourse-cdn.com/v4/letter/e/f07891/32.png) [@Earthworm\_Jim](https://boards.straightdope.com/u/Earthworm_Jim)\ **Post date:** [February 13, 2003, 6:05pm UTC](https://boards.straightdope.com/t/time-travel/154590/22 "2003-02-13T18:05:58Z")
> [@](#): > > \*Originally posted by Whack-a-Mole \* > \*\*A whole bunch of reasons. Here are some of them: > > [ul] > > [li] Your mass increases as you approach the speed of light. Once you reach light speed you would have infinite mass which has a few implications…one of which is you’d need infinite energy to move you (more energy than the entire Universe has available).[/li]\ > [li] An implication of the above two reasons would be also having you occupy every point in space simultaneously.[/li][/ul] > \*\* Why aren’t these true for light itself? ---
**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:** [February 13, 2003, 6:15pm UTC](https://boards.straightdope.com/t/time-travel/154590/23 "2003-02-13T18:15:29Z")
> [@](#): > > \*Originally posted by Beelzebubba \* > \*\*Why aren’t these true for light itself? \*\* Light has no rest mass. You do. ---
**Author:** ![FriendRob](https://avatars.discourse-cdn.com/v4/letter/f/ecc23a/32.png) [@FriendRob](https://boards.straightdope.com/u/FriendRob)\ **Post date:** [February 13, 2003, 6:22pm UTC](https://boards.straightdope.com/t/time-travel/154590/24 "2003-02-13T18:22:44Z")
> [@](#): > > \*Originally posted by Max Carnage \* > \*\*I wonder why ‘light-speed’ is the limit then? Not light-speed +/- 1 mps. \*\* This is equivalent to asking “Why is the photon massless?” Assume there is a speed limit, call it _c_. According to the rules of special relativity, anything that moves at _c_ must be massless. So, if the speed of light equals _c_, then photons have no mass. ( **beelzebubba** , that’s why the argument doesn’t apply to light.) Now, if photons had a _really tiny_ mass they would travel at less than _c_. In that case it would be possible to travel faster than light, but you wouldn’t go backward in time. ---
**Author:** ![X\_Slayer\_ALE](https://avatars.discourse-cdn.com/v4/letter/x/bbe5ce/32.png) [@X\_Slayer\_ALE](https://boards.straightdope.com/u/X_Slayer_ALE)\ **Post date:** [February 13, 2003, 8:13pm UTC](https://boards.straightdope.com/t/time-travel/154590/25 "2003-02-13T20:13:20Z")
> [@](#): > > \*Originally posted by Whack-a-Mole \* > \*\*I didn’t contradict myself…I was just speculating hypothetically what would happen if you moved at the speed of light or faster although I realize it is not possible for us to actually do so.] You did when you posted that what I initially proposed was impossible when in fact it is possible and has already been proven. > [@](#): > > \*Originally posted by Whack-a-Mole \* > \*\* > To further bend your brain…if you travel faster than the speed of light you can NEVER slow down to below light speed. This is true for anything moving faster than light…even tachyons. Once you’re on one side of the light speed fence you stay there and cannot cross the light speed barrier going in either direction. \*\* alright, what about the theory that you can tunnel outside of the normal space-time continuum and emerge in a distant location. Relative to you, you did not travel faster than light nor travel a great distance, however, relative to everyone in the normal continuum, you transversed a distance with a length of time that would be equivalent to going faster than the speed of light. You merely took a universal shortcut. ---
**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:** [February 13, 2003, 8:54pm UTC](https://boards.straightdope.com/t/time-travel/154590/26 "2003-02-13T20:54:07Z")
> [@](#): > > \*Originally posted by X~Slayer(ALE) \* > You did when you posted that what I initially proposed was impossible when in fact it is possible and has already been proven. I merely misread your post. When you said “comeback to your origin and one year hs passed” I figured you meant your origin in time which you cannot do by your proposal. Maybe for you, by travelling very fast, only feels a few seconds or minutes pass while those on earth see a year pass but you cannot return to exactly when you started this way…you always move forward in time even if only very slowly compared to others. > [@](#): > > alright, what about the theory that you can tunnel outside of the normal space-time continuum and emerge in a distant location. Relative to you, you did not travel faster than light nor travel a great distance, however, relative to everyone in the normal continuum, you transversed a distance with a length of time that would be equivalent to going faster than the speed of light. You merely took a universal shortcut. I’ve argued this point before on these boards before with people like **Chronos** and he maintains that if you move from point X to point Y faster than light could get there then you perforce have travelled through time. Like you I argued that if you had a hypothetical gateway through hyperspace such that your distance travelled was vastly shortened you could seemingly travel faster than light speed without violating causality. Unfortunately **Chronos** didn’t buy my arguements and to be honest he is much more of an authority in these matters than I am (IIRC he’s a Physics student himself unless he’s graduated by now). ---
**Author:** ![I\_Brian](https://avatars.discourse-cdn.com/v4/letter/i/c89c15/32.png) [@I\_Brian](https://boards.straightdope.com/u/I_Brian)\ **Post date:** [February 13, 2003, 9:56pm UTC](https://boards.straightdope.com/t/time-travel/154590/27 "2003-02-13T21:56:04Z")
The big problem here is the assumption that Special Relativity is somehow infallible. It has a lot of rising contenders who wise to see SR amended in some minor - yet far-reaching - form or another. Note that any opinion on the matter is therefore culterally determined in the subjective, rather than able to grasp any form of objective reality on the subject. ---
**Author:** ![I\_Brian](https://avatars.discourse-cdn.com/v4/letter/i/c89c15/32.png) [@I\_Brian](https://boards.straightdope.com/u/I_Brian)\ **Post date:** [February 13, 2003, 9:59pm UTC](https://boards.straightdope.com/t/time-travel/154590/28 "2003-02-13T21:59:01Z")
Hmm…won;t let me edit my own post… Of course, note the following typo correction: It has a lot of rising contenders who _wish_ to see SR amended in some minor - yet far-reaching - form or another. ---
**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:** [February 13, 2003, 10:47pm UTC](https://boards.straightdope.com/t/time-travel/154590/29 "2003-02-13T22:47:07Z")
> [@](#): > > \*Originally posted by I, Brian \* > \*\*It has a lot of rising contenders who _wish_ to see SR amended in some minor - yet far-reaching - form or another. \*\* Like what? I’m not tryingot be a pain…I’m genuinely curious. I think General and Special Relativity are some of the most secure theories science has ever put forward. They been tested and re-tested over and over and so far they hold up great. Of course, GR and SR don’t answer everything so you get things like Quantum Mechanics holding down the other end of the spectrum. Unfortunately integrating GR and QM has been problematical to say the least. Given the success of GR/SR however I wonder if you more mean something that expands upon it in the way that Relativity expands upon Newtonian physics. Newtoninan physics works just great for 99.999% of your day-to-day problems (building things, trajectories, etc.). It only falls apart at the extremes where Relativity steps in and does a more refined and accurate job. In short, are these things that will put Relativity on the trash heap of scientific theories or stand on the shoulders of what Relativity has already laid down? ---
**Author:** ![X\_Slayer\_ALE](https://avatars.discourse-cdn.com/v4/letter/x/bbe5ce/32.png) [@X\_Slayer\_ALE](https://boards.straightdope.com/u/X_Slayer_ALE)\ **Post date:** [February 14, 2003, 12:49am UTC](https://boards.straightdope.com/t/time-travel/154590/30 "2003-02-14T00:49:27Z")
AHA! Houston, **Whack-a-Mole** and I have agreement. You can travel forwards in time but never backwards. I think the key to all of this is that neither special relativity nor general relativity allows time travel into the past. If you have that limitation then hyperspace travel will not violate causality because at best it is instantaneous travel of great distances. One never goes back in time always forward. As in the case of star travel, if a hyperspace ship took off for the nearest star and you have a telescope trained at that star, even if the ship only takes one second to travel that great distance you will never see any evidence of that ship because what you see in the telescope is the past. ---
**Author:** ![The\_Ryan](https://avatars.discourse-cdn.com/v4/letter/t/7feea3/32.png) [@The\_Ryan](https://boards.straightdope.com/u/The_Ryan)\ **Post date:** [February 14, 2003, 7:00am UTC](https://boards.straightdope.com/t/time-travel/154590/31 "2003-02-14T07:00:14Z")
What exactly is time travel? Normally when we say “travel” we mean that at one time we’re at one place, and at another time we’re at another. But what would it mean to say at one time we’re at one time, and at another we’re at another? I don’t see that the OP has been rigorously stated. > [@](#): > > \*Originally posted by Whack-a-Mole \* > I’ve argued this point before on these boards before with people like **Chronos** and he maintains that if you move from point X to point Y faster than light could get there then you perforce have travelled through time. I’m not sure what arguments he presented, so I might just be repeating what he said, but for every pair of events A and B separated by more space than time, there is some reference frame in which A occurs before B, and there is another in which B occurs after A. In Newtonian physics, such a statement would be paradoxical, but in relativity there is no problem as long as no one can travel faster than light, because anyone travelling slower than light will travel through more time than space. In relativity, there is no absolute “now”, so your statement that you emerged on the other side of the wormhole at the “same” time that you entered it is based on your personal, subjective view of what is the “same” time. From another’s point of view, you may have entered several years before or _after_ you emerged on the other side. While you claim that your time coordinate hasn’t changed, others would disagree. This probably wouldn’t be so hard to convince you if we switch space and time. I’m going to reprise my previous paragraph, but replace every word “time” with “space” and vice versa. All the alterations will be in bold [In this case, consider a situation where instead of going through a wormhole and going a large spatial distance but no temporal distance, imagine going through a wormhole and going a large temporal distance but no spatial distance]. For every pair of events A and B separated by more **time** than **space** , there is some reference frame in which A occurs before B, and there is another in which B occurs after A [before, “before” and “after” referred positions in time, so in accordance with the switch now they mean positions in space]. In Newtonian physics, such a statement would be paradoxical, but in relativity there is no problem **because there is no absolute rest.** In relativity, there is no absolute **“here”** , so your statement that you emerged on the other side of the wormhole at the “same” **place** that you entered it is based on your personal, subjective view of what is the “same” **place**. From another’s point of view, you may have entered several **lights** years before or _after_ you emerged on the other side. While you claim that your **space** coordinate hasn’t changed, others would disagree. I think it’s not too hard to see how relativity leads to the conclusion that every displacement consisting of more space than time can be viewed as no spatial movement (“I was standing still”) positive movement (“I was drifting forward relative to some reference frame”) or negative (“I was drifting backwards”). It shouldn’t be too much of a leap to see that any displacement of more space than time can be seen as no temporal movement, forward temporal morvement, or negative temporal movement. ---
**Author:** ![don\_t\_ask](https://avatars.discourse-cdn.com/v4/letter/d/e68b1a/32.png) [@don\_t\_ask](https://boards.straightdope.com/u/don_t_ask)\ **Post date:** [February 14, 2003, 7:12am UTC](https://boards.straightdope.com/t/time-travel/154590/32 "2003-02-14T07:12:00Z")
Aussie scientist Paul Davies has put out a book _How to Build a Time Machine_ which I have just acquired. When I’ve built one I’ll get back to you. Here is his piece in [Scientific American](http://www.sciam.com/article.cfm?articleID=0004226A-F77D-1D4A-90FB809EC5880000&pageNumber=1&catID=2) about how it’s done. ---
**Author:** ![I\_Brian](https://avatars.discourse-cdn.com/v4/letter/i/c89c15/32.png) [@I\_Brian](https://boards.straightdope.com/u/I_Brian)\ **Post date:** [February 14, 2003, 8:30am UTC](https://boards.straightdope.com/t/time-travel/154590/33 "2003-02-14T08:30:39Z")
**Whack-a-mole** There have been a number of reports recently in New Scientist magazine showcasing alternatives - last week was about something called Doubly Special Relativity. Most of the theories simply amend a very small part of SR itself. I’m afraid I don;t have a specific link, but there may be something on the [New Scientist website](http://www.newscientist.com). > [@](#): > > if you more mean something that expands upon it in the way that Relativity expands upon Newtonian physics. That’s precisely right - but once you start tinkering with the basics - even to a small degree - the absolutes of SR being discussed above become quite uncertain. ---
**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:** [February 14, 2003, 2:58pm UTC](https://boards.straightdope.com/t/time-travel/154590/34 "2003-02-14T14:58:48Z")
> [@](#): > > \*Originally posted by X~Slayer(ALE) \* > \*\*AHA! Houston, **Whack-a-Mole** and I have agreement. You can travel forwards in time but never backwards. I think the key to all of this is that neither special relativity nor general relativity allows time travel into the past. \*\* Uhmm…I don’t think we agree on this actually. I’m pretty sure that Relativity _does_ allow for time travel to the past. I’m pretty sure Relativity is a mathematically symmetric system. That is, it works backwards or forwards so reverseing time doesn’t pose a mathematical problem for the theory even though it poses a helluva lot of problems to our notions of causality. As I said before Kip Thorne (a noted physicist) actually set out to prove time travel was impossible because he tired of the incessant questions about it and figured to settle it once and for all. Try as he might however he could find nothing in our current theories that prohibited time travel in either direction. That said most figure there must be something to prevent it because the causality problems boggle the mind (unless you use things like parallel universes which boggle the mind just as much themselves). Clearly there is still a lot to learn about our universe yet. ---
**Author:** ![DaddyMack](https://avatars.discourse-cdn.com/v4/letter/d/dc4da7/32.png) [@DaddyMack](https://boards.straightdope.com/u/DaddyMack)\ **Post date:** [February 14, 2003, 3:08pm UTC](https://boards.straightdope.com/t/time-travel/154590/35 "2003-02-14T15:08:08Z")
SR, GR, and quantum mechanics etal are all mathematical constructs used to explain, or make sense out of, what we observe in nature. The second thing you learn when using the quadric equation to solve some problem is to ignore the imaginary part. There is no imaginary current or imaginary magnetic forces. Discussing how it is possible to travel forward in time because of this or that mathematical construct sounds to me like using math to justify some N dimensional worlds where aliens exist ala Art Bell. Using any form of math can result in interesting paradoxes for example [http://www.tetrakatus.com/logic/jacob/math.html](http://www.tetrakatus.com/logic/jacob/math.html) This does not mean that there is something strange about reality but that the method for explaining reality needs modification. SR and GR are used to explain reality, it would be a mistake to use them to create an imaginary reality and then to believe that that reality exist or is even possible. There **was** a past, there **is** a present and there **will be** a future. Observation confirms this. ---
**Author:** ![Kix](https://avatars.discourse-cdn.com/v4/letter/k/e19adc/32.png) [@Kix](https://boards.straightdope.com/u/Kix)\ **Post date:** [February 14, 2003, 6:37pm UTC](https://boards.straightdope.com/t/time-travel/154590/36 "2003-02-14T18:37:31Z")
Lets think I have a Time machine and I am going to test it for the first time so I enter it and punch exactly one minute into the future (or the past make any choice). I enter it press the button and poof I am one minute in the futere/past. !!! COOL ISNT IT? Yeah think again because When I reapear in this dimension and timeline Ill be floating in space and Earth will be axactly 180 000 kms away from me (the earth and the solar system is moving as pactically everything else in the universe. So appart of controlling time we have to control space so we can pinpoint the location of the point in time and SPACE of our destination …so its not as easy as it looks… ---
**Author:** ![Exoskeleton](https://avatars.discourse-cdn.com/v4/letter/e/d2c977/32.png) [@Exoskeleton](https://boards.straightdope.com/u/Exoskeleton)\ **Post date:** [February 14, 2003, 11:52pm UTC](https://boards.straightdope.com/t/time-travel/154590/37 "2003-02-14T23:52:03Z")
I don’t think anyone has yet mentioned the _Kepler Cylinder_, a possible time travel device first conceived in the 70s by a physicist (can’t remember first name) named Kepler. I have read the theory behind it and I have a soggy grasp on the idea. It has to do with ‘light cones’, a concept I cannot faithfully retell here; but to understand the workings of the cylinder you have to come to terms with that first. The machine is a gigantic, supermassive cylinder which spins at an incredible speed, resulting the tipping of ‘light cones’ in its immediate vicinity, which allows for time travel into the future or the past. I have read where the cylinder needs to be the size of a planet or greater, but then I’ve read other places that it can be relatively small, but needs to rotate that much faster to make up for the smaller size. ---
**Author:** ![msmith537](https://avatars.discourse-cdn.com/v4/letter/m/d9b06d/32.png) [@msmith537](https://boards.straightdope.com/u/msmith537)\ **Post date:** [February 15, 2003, 2:09am UTC](https://boards.straightdope.com/t/time-travel/154590/38 "2003-02-15T02:09:35Z")
Time travel is possible. ---
**Author:** ![msmith537](https://avatars.discourse-cdn.com/v4/letter/m/d9b06d/32.png) [@msmith537](https://boards.straightdope.com/u/msmith537)\ **Post date:** [February 15, 2003, 2:10am UTC](https://boards.straightdope.com/t/time-travel/154590/39 "2003-02-15T02:10:51Z")
I will now attempt to travel backwards in time by a minute or so and post a message. ---
**Author:** ![leechow09](https://avatars.discourse-cdn.com/v4/letter/l/858c86/32.png) [@leechow09](https://boards.straightdope.com/u/leechow09)\ **Post date:** [February 15, 2003, 3:11am UTC](https://boards.straightdope.com/t/time-travel/154590/40 "2003-02-15T03:11:27Z")
I think–now, this is only what I think–that time is just some invention created only for convenience. So time travel and the likes would be ruled out indefinitely. And of course, there would be the infinite paradoxes that would result from time travel: if you traveled back in time and killed your grandfather before your father was conceived, then you wouldn’t have been born, then you wouldn’t have gone back in time, but then who shot your grandfather, etc. [Previous page](https://boards.straightdope.com/t/time-travel/154590.md?page=1) [Next page](https://boards.straightdope.com/t/time-travel/154590.md?page=3)