# Time Travel: Possible or Impossible? **URL:** \ **Category:** Great Debates\ **Created:** [January 7, 2009, 1:55am UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178 "2009-01-07T01:55:46Z")\ **Posts on this page:** 17\ **Page:** 7
**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:** [January 15, 2009, 3:33pm UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/121 "2009-01-15T15:33:59Z")
> [@Paleface](#): > > Would that be Eastern Standard Time or Mountain Time? You are confusing arbitrary, man-made divisions to prove time does not exist. Man does the same thing with length. You can measure an inch or a mile or a parsec. They are arbitrary divisions humans have made to give name to a certain distance. So too with time. You can have a second or a minute or a light-year. You can divide time into any slices you want and call it what you want. Time still exists as its own thing. ---
**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:** [January 15, 2009, 3:48pm UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/122 "2009-01-15T15:48:49Z")
> [@Paleface](#): > > No, nature cares about motion. Speed is what man has created as a way to measure an aspect of motion. Motion, by definition, has speed as an integral component of it (all things in motion have a speed). Speed, by definition, has a time component. To remove the time component would make the whole concept meaningless. So would removing the length component. They go hand-in-hand. > [@](#): > > Or the more compressed things appear due to a doppler effect of light. An object moving toward an observer appears to compress, due to the compression of the light rays. As the object passes and moves away from the observer, the object appears to enlongate due to the stretching of the light rays. Nope, this contraction is not due to the Doppler effect. The thing actually contracts. It is called a [Lorentz Contraction](http://en.wikipedia.org/wiki/Length_contraction). Follow the link and read about it. The Doppler effect would just make the thing traveling toward us more blue. > [@](#): > > Now, let’s take two astronauts on a space-station. One takes their vehicle on a little spin, say some orbits of 93 million miles, traveling as 1/2 lightspeed, which would take the vehicle @ 1 sec to orbit the space-station. > > The astronaut that remained on the station observes his partners joyride on radar and observes 1 sec for each orbit. After 3,600 orbits, his buddy re-docks at the space station. The astronaut that remained on the station commented, “Well, you did 3,600 orbits, and it took you an hour.” > > The astronaut who took the joyride said, “No, I was only gone 45min.” > > Time did not slow down, the physical effects of the motion caused the astronaut’s perspective of time to slow down. If his 3,600 orbits only took 45min. , then he was traveling faster than 1/2 lightspeed, but this was not observed by his partner monitoring the orbits on radar. No again. You have essentially re-stated the [Twin Paradox](http://en.wikipedia.org/wiki/Twin_paradox). Except that the paradox is not paradox. The reason being the person orbiting underwent an acceleration which changes his reference frame and then back again to on the station. This breaks symmetry between the two so the orbiting astronaut will age less. The station and the astronaut will disagree about how long the orbits took is all. If you traveled at 0.9999999999999999999999951c you could go from here to the center of our galaxy in 3.2 seconds as you perceive it. To us on earth your trip took 32,000 years. We can tell the difference because you accelerated to very near light speed and we did not. ---
**Author:** ![Paleface](https://avatars.discourse-cdn.com/v4/letter/p/f19dbf/32.png) [@Paleface](https://boards.straightdope.com/u/Paleface)\ **Post date:** [January 16, 2009, 1:41pm UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/123 "2009-01-16T13:41:37Z")
From the “twin paradox” link: > [@](#): > > Specific example > Consider a space ship traveling from Earth to the nearest star system outside of our solar system: a distance d = 4.45 light years away, at a speed v = 0.866c (i.e., 86.6 percent of the speed of light). The Earth-based mission control reasons about the journey this way (for convenience in this thought experiment the ship is assumed to immediately attain its full speed upon departure): the round trip will take t = 2d / v = 10.28 years in Earth time (i.e. everybody on earth will be 10.28 years older when the ship returns). The amount of time as measured on the ship’s clocks and the aging of the travelers during their trip will be reduced by the factor , the reciprocal of Here, we enter the realm of religion. > [@](#): > > the Lorentz factor. In this case and the travelers will have aged only 0.500×10.28 = 5.14 years when they return. OK… the original journey consisted of traveling to a star located 4.45 light years away, traveling at .866 lightspeed. At that particular rate of speed, a round trip takes 10.28 years. If, after the Lorentz factor, the trip only took 5.14 years, then the travelers exceeded lightspeed, which, supposedly, is not possible. ---
**Author:** ![Paleface](https://avatars.discourse-cdn.com/v4/letter/p/f19dbf/32.png) [@Paleface](https://boards.straightdope.com/u/Paleface)\ **Post date:** [January 16, 2009, 2:02pm UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/124 "2009-01-16T14:02:49Z")
Anyways, not saying you are wrong or I am correct… it’s just a debate. Thanks ---
**Author:** ![Ice\_Cream\_Conquest](https://avatars.discourse-cdn.com/v4/letter/i/e480ec/32.png) [@Ice\_Cream\_Conquest](https://boards.straightdope.com/u/Ice_Cream_Conquest)\ **Post date:** [January 16, 2009, 3:58pm UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/125 "2009-01-16T15:58:57Z")
People interested in this should check out Timemaster by Robert Forward. He’s a hard sf writer, and he explores the details of time travel and how paradoxes are avoided. He bases that part on hard science as much as possible. A couple of points: 1. To get things started, he posits negative matter to get around the difficulties of creating time travel, and the book deals with the science from there. 2. It’s an interesting exploration of the subject, but it’s not avery good novel. ---
**Author:** ![ivan\_astikov](https://avatars.discourse-cdn.com/v4/letter/i/58f4c7/32.png) [@ivan\_astikov](https://boards.straightdope.com/u/ivan_astikov)\ **Post date:** [January 16, 2009, 4:01pm UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/126 "2009-01-16T16:01:21Z")
> [@Whack-a-Mole](#): > > You are confusing arbitrary, man-made divisions to prove time does not exist. Man does the same thing with length. You can measure an inch or a mile or a parsec. They are arbitrary divisions humans have made to give name to a certain distance. So too with time. You can have a second or a minute or a light-year. You can divide time into any slices you want and call it what you want. Time still exists as its own thing. Time needs a reference point, and that is provided by human beings. Without them it would mean nothing. ---
**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:** [January 16, 2009, 4:04pm UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/127 "2009-01-16T16:04:43Z")
> [@Paleface](#): > > From the “twin paradox” link: Here, we enter the realm of religion. OK… the original journey consisted of traveling to a star located 4.45 light years away, traveling at .866 lightspeed. At that particular rate of speed, a round trip takes 10.28 years. If, after the Lorentz factor, the trip only took 5.14 years, then the travelers exceeded lightspeed, which, supposedly, is not possible. No religion to be found anywhere here. These are well understood and mostly well tested phenomenon (Lorentz Contraction has not been because we cannot go that fast…some think the LHC will test this aspect). Remember the Lorentz “Contraction” is not time dilation (which also occurs but is a different effect) but actual stuff getting shorter parallel to the direction of travel. So, our astronauts would record it as less distance to the star than we do on earth. If you went light speed (you can’t of course but if you could) the universe would be infinitely thin to you. ---
**Author:** ![pancakes3](https://avatars.discourse-cdn.com/v4/letter/p/ba9def/32.png) [@pancakes3](https://boards.straightdope.com/u/pancakes3)\ **Post date:** [January 16, 2009, 4:22pm UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/128 "2009-01-16T16:22:32Z")
> [@ivan\_astikov](#): > > Time needs a reference point, and that is provided by human beings. Without them it would mean nothing. highfalutin gobbedygook. would you consider length to not exist if people weren’t ready with meter sticks and tape measures to record it? i would hope not. the same applies to time. time exists whether you’re measuring it or not as does length. both will exist even if there were no humans. yes? ---
**Author:** ![begbert2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/begbert2/32/3357_2.png) [@begbert2](https://boards.straightdope.com/u/begbert2)\ **Post date:** [January 16, 2009, 10:10pm UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/129 "2009-01-16T22:10:21Z")
> [@ivan\_astikov](#): > > Time needs a reference point, and that is provided by human beings. Without them it would mean nothing. So you’re saying that, prior to humans, that time didn’t pass? The dinosaurs would like a word with you. ---
**Author:** ![ivan\_astikov](https://avatars.discourse-cdn.com/v4/letter/i/58f4c7/32.png) [@ivan\_astikov](https://boards.straightdope.com/u/ivan_astikov)\ **Post date:** [January 16, 2009, 11:27pm UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/130 "2009-01-16T23:27:15Z")
> [@pancakes3](#): > > highfalutin gobbedygook. > > would you consider length to not exist if people weren’t ready with meter sticks and tape measures to record it? i would hope not. the same applies to time. time exists whether you’re measuring it or not as does length. both will exist even if there were no humans. yes? No. No humans = no time, no inches, no lightyears, nothing. Wasn’t there until we thought about it. > [@begbert2](#): > > So you’re saying that, prior to humans, that time didn’t pass? The dinosaurs would like a word with you. And what would that be - “ **KRAAAAARKKKK!** Is it tea-time yet?”? ---
**Author:** ![ivan\_astikov](https://avatars.discourse-cdn.com/v4/letter/i/58f4c7/32.png) [@ivan\_astikov](https://boards.straightdope.com/u/ivan_astikov)\ **Post date:** [January 16, 2009, 11:34pm UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/131 "2009-01-16T23:34:42Z")
Missed the window but thought this was worth adding. Horses were measured by hands because we didn’t have rulers. ---
**Author:** ![Frylock](https://avatars.discourse-cdn.com/v4/letter/f/ce7236/32.png) [@Frylock](https://boards.straightdope.com/u/Frylock)\ **Post date:** [January 17, 2009, 12:35am UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/132 "2009-01-17T00:35:53Z")
If things did not have dimension prior to the advent of human beings, then there can be no explanation as to why things happened the way they did prior to the advent of human beings. There can be no reason given why planets went around in their orbits. Indeed, there can be no way to _say_ that they went around in their orbits at all. -FrL- ---
**Author:** ![begbert2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/begbert2/32/3357_2.png) [@begbert2](https://boards.straightdope.com/u/begbert2)\ **Post date:** [January 17, 2009, 12:37am UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/133 "2009-01-17T00:37:42Z")
> [@ivan\_astikov](#): > > And what would that be - “ **KRAAAAARKKKK!** Is it tea-time yet?”? No, it would be, “I say, good chap, you’re saying that time didn’t pass during the several million years we were around, which on the face of it is an obviously false statement - my brain may be the size of a walnut, but even I know that millions of years can’t pass if time isn’t passing. Oh, and by the way, could you pass me your arm? I’m feeling a bit peckish.” ---
**Author:** ![ivan\_astikov](https://avatars.discourse-cdn.com/v4/letter/i/58f4c7/32.png) [@ivan\_astikov](https://boards.straightdope.com/u/ivan_astikov)\ **Post date:** [January 17, 2009, 3:09am UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/134 "2009-01-17T03:09:47Z")
> [@begbert2](#): > > No, it would be, “I say, good chap, you’re saying that time didn’t pass during the several million years we were around, which on the face of it is an obviously false statement - my brain may be the size of a walnut, but even I know that millions of years can’t pass if time isn’t passing. Oh, and by the way, could you pass me your arm? I’m feeling a bit peckish.” Is this a Strawosaurus or something? I’m going to have to ask for a cite that dinosaurs spoke anything like that. You’ll be telling me the more educated ones actually knew there was a meteor due, and whiled away their final seconds( out term - not theirs) discussing existential angst, next. ---
**Author:** ![BrainGlutton](https://avatars.discourse-cdn.com/v4/letter/b/82dd89/32.png) [@BrainGlutton](https://boards.straightdope.com/u/BrainGlutton)\ **Post date:** [January 17, 2009, 5:21am UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/135 "2009-01-17T05:21:44Z")
Yes, time travel is possible. I’d tell you how I know that, but it would violate the laws of caus- . . . um . . . I’ll shut up now. ---
**Author:** ![dotchan](https://avatars.discourse-cdn.com/v4/letter/d/9d8465/32.png) [@dotchan](https://boards.straightdope.com/u/dotchan)\ **Post date:** [January 18, 2009, 2:12am UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/136 "2009-01-18T02:12:19Z")
Technically, we are all time traveling right now - into the future. (Except, like some kind of paradox, we never quite make it into the future and are always trapped in some intangible “now”.) Traveling back in time probably involves some violation of the second law of thermodynamics and maybe the conservation of mass and energy as well. And the past might be intangible to us, or we’d screw things over royally even if we just stood there (because we’d be displacing molecules that were undisturbed before), though that would also depend on how resistant the universe is to changes in the past. …the implications of the past being unchangable, however, is that the future is similarly fated to happen exactly the way it’s going to, since the future is nothing more than the past to someone further into the future. Time travel totally makes my head hurt. ---
**Author:** ![wsbenge](https://avatars.discourse-cdn.com/v4/letter/w/b38774/32.png) [@wsbenge](https://boards.straightdope.com/u/wsbenge)\ **Post date:** [January 18, 2009, 3:52pm UTC](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178/137 "2009-01-18T15:52:03Z")
I don’t think time travel is functionally possible, but I have seen pieces of the future. That, of itself, stuns me. Those glimpses of the future were never important, and had no impact upon my life, except to show me that it is possible. I think such things are pretty heavily controlled. [Previous page](https://boards.straightdope.com/t/time-travel-possible-or-impossible/480178.md?page=6)