# Time Travel Question \[changed title\] **URL:** \ **Category:** Factual Questions\ **Created:** [April 22, 2004, 3:11am UTC](https://boards.straightdope.com/t/time-travel-question-changed-title/241347 "2004-04-22T03:11:18Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![START](https://avatars.discourse-cdn.com/v4/letter/s/2bfe46/32.png) [@START](https://boards.straightdope.com/u/START)\ **Post date:** [April 22, 2004, 3:11am UTC](https://boards.straightdope.com/t/time-travel-question-changed-title/241347/1 "2004-04-22T03:11:18Z")
I have this theory that I came up with a few weeks ago after science class and studying about how long it takes the light from the stars to reach our eyes. It is like looking many years into the past. Alot of this is sort of hypothetical but let’s get over that part…lets assume that we could send some humans far enough out in space that the light and images from earth would take one year to reach their eyes. Now here comes the hard part, explaining this; so when they get there they have a device with them that is able to see the earth…would they be looking into a past earth? If so if they could see people on the earth would it be the people doing things that happened a year ago? Could this be a step toward time travel? although we wouldn’t be there we could observe from a great distance the events that went on a year or two ago. Now I know how fast light travels and to get far enough away that it would take a year to reach you is now impossible but does my theory have any slight chance of being workable? Assuming we found a way to get that far out into space. If nobody understands what I’m trying to say I will come back and word it differently. ---
**Author:** ![Duckster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/duckster/32/1244_2.png) [@Duckster](https://boards.straightdope.com/u/Duckster)\ **Post date:** [April 22, 2004, 3:17am UTC](https://boards.straightdope.com/t/time-travel-question-changed-title/241347/2 "2004-04-22T03:17:47Z")
You have your own answer. Assuming you have humans one light year away from Earth with the ability to see Earthlings. They will be viewing them as they were a year earlier. Got it? 😃 ---
**Author:** ![Joe\_Random](https://avatars.discourse-cdn.com/v4/letter/j/e8c25b/32.png) [@Joe\_Random](https://boards.straightdope.com/u/Joe_Random)\ **Post date:** [April 22, 2004, 3:31am UTC](https://boards.straightdope.com/t/time-travel-question-changed-title/241347/3 "2004-04-22T03:31:44Z")
> [@START](#): > > If so if they could see people on the earth would it be the people doing things that happened a year ago? Yes. But remember that, since it is impossible to travel faster than light, they had to have departed from the earth _more_ than a year ago, so they’d be seeing things that happened _after_ they left. > [@](#): > > Could this be a step toward time travel? Nope. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [April 22, 2004, 3:34am UTC](https://boards.straightdope.com/t/time-travel-question-changed-title/241347/4 "2004-04-22T03:34:38Z")
You can’t travel faster than the speed of light. So no matter how far or how fast you went you would only see images from after you left. These images will be of times earlier than your present, just as every image of a star in the sky tells us the way that star looked several years earlier. (The nearest stars are 4 light-years away, so we see what they looked like 4 years ago, etc.) But this can in no way be termed time travel. There is no way, even in theory, to do the kind of time travel viewing you speak of. Time travel itself is not forbidden by general relativity and several physicists - starting with Kip Thorne - have looked at the physics of it all. Doing time travel involves building wormholes and using exotic materials with properties that are not even imaginably realizable so creating one is out of the question for any foreseeable future. And you can’t go back in time before the time machine was built, which may explain why we never see time travelers. But you simply can’t outspeed light. ---
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [April 22, 2004, 3:41am UTC](https://boards.straightdope.com/t/time-travel-question-changed-title/241347/5 "2004-04-22T03:41:25Z")
EVERYTHING you see is in the past. The very words you see on the monitor are about a picosecond old. ---
**Author:** ![ITR\_champion](https://avatars.discourse-cdn.com/v4/letter/i/c67d28/32.png) [@ITR\_champion](https://boards.straightdope.com/u/ITR_champion)\ **Post date:** [April 22, 2004, 3:48am UTC](https://boards.straightdope.com/t/time-travel-question-changed-title/241347/6 "2004-04-22T03:48:56Z")
There are some theoretical physicists who aren’t totally convinced that you can’t beat the speed of light barrier. Theories involving wormholes and other abnormalities abound, some have even suggested that humans will be able to create rips in spacetime via various means using advanced technology. None of it has ever been observed however. If it were true, then it would be possible for a specific person to travel out into space, look back, and “see themself”. This actually creates a number of paradoxes, which is one reason why many believe that faster-than-light travel will always be impossible. ---
**Author:** ![John\_Kentzel-Griffin](https://avatars.discourse-cdn.com/v4/letter/j/ccd318/32.png) [@John\_Kentzel-Griffin](https://boards.straightdope.com/u/John_Kentzel-Griffin)\ **Post date:** [April 22, 2004, 3:55am UTC](https://boards.straightdope.com/t/time-travel-question-changed-title/241347/7 "2004-04-22T03:55:11Z")
There is no problem with viewing the past. If you could interact with the past, that might pose a problem, but we view the past all the time. [moderator hat on] It helps to have descriptive titles. I’ve changed the title for you. [moderator hat off] ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [April 22, 2004, 4:57am UTC](https://boards.straightdope.com/t/time-travel-question-changed-title/241347/8 "2004-04-22T04:57:00Z")
> [@ITR champion](#): > > There are some theoretical physicists who aren’t totally convinced that you can’t beat the speed of light barrier. Theories involving wormholes and other abnormalities abound, some have even suggested that humans will be able to create rips in spacetime via various means using advanced technology. None of it has ever been observed however. If it were true, then it would be possible for a specific person to travel out into space, look back, and “see themself”. This actually creates a number of paradoxes, which is one reason why many believe that faster-than-light travel will always be impossible. None of what you have suggested “beats” the speed of light. Wormholes and other “rips” in spacetime change the topology of the background manifold. Locally, nothing is travelling faster than light, although globally they are reaching points in spacetime that would be outside the forward light cone were it not for the “rip”. ---
**Author:** ![devilsknew](https://avatars.discourse-cdn.com/v4/letter/d/4da419/32.png) [@devilsknew](https://boards.straightdope.com/u/devilsknew)\ **Post date:** [April 22, 2004, 6:00am UTC](https://boards.straightdope.com/t/time-travel-question-changed-title/241347/9 "2004-04-22T06:00:34Z")
Is there a quantum version of faster than light? Aren’t there phenomenon at a quantum level that happen instantaneously over distance between related particles. Excuse me for being so general, I’m not sure what it involves…antielectrons maybe? ---
**Author:** ![Freejooky](https://avatars.discourse-cdn.com/v4/letter/f/ba8739/32.png) [@Freejooky](https://boards.straightdope.com/u/Freejooky)\ **Post date:** [April 22, 2004, 6:58am UTC](https://boards.straightdope.com/t/time-travel-question-changed-title/241347/10 "2004-04-22T06:58:42Z")
> [@Exapno Mapcase](#): > > And you can’t go back in time before the time machine was built, which may explain why we never see time travelers. I’ve always heard this anecdote, and wondered - _why not?_ ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [April 22, 2004, 7:39am UTC](https://boards.straightdope.com/t/time-travel-question-changed-title/241347/11 "2004-04-22T07:39:47Z")
> [@devilsknew](#): > > Is there a quantum version of faster than light? Aren’t there phenomenon at a quantum level that happen instantaneously over distance between related particles. Excuse me for being so general, I’m not sure what it involves…antielectrons maybe? The closest thing, as being discussed in the thread on Hidden Variables theories, is the resolution of an EPR state. No information is really being sent, though, so no signal is passing the speed of light. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [April 22, 2004, 3:45pm UTC](https://boards.straightdope.com/t/time-travel-question-changed-title/241347/12 "2004-04-22T15:45:10Z")
> [@Freejooky](#): > > I’ve always heard this anecdote, and wondered - _why not?_ Short answer from [Wikipedia’s Time Travel page](http://en.wikipedia.org/wiki/Time_travel): > [@](#): > > A proposed time-travel machine using a wormhole would (hypothetically) work something like this: A wormhole is created somehow. One end of the wormhole is accelerated to nearly the speed of light, perhaps with an advanced spaceship, and then brought back to the point of origin. Due to time dilation, the accelerated end of the wormhole has now experienced less subjective passage of time than the stationary end. An object that goes into the stationary end would come out of the other end in the past relative to the time when it enters. One significant limitation of such a time machine is that it is only possible to go as far back in time as the initial creation of the machine; in essence, it is more of a path through time than it is a device that itself moves through time, and it would not allow the technology itself to be moved backwards in time. This could provide an alternative explanation for Hawking’s observation: a time machine will be built someday, but hasn’t been built yet, so the tourists from the future can’t reach this far back in time. > > Creating a wormhole of a size useful for macroscopic spacecraft, keeping it stable, and moving one end if it around would require significant energy, many orders of magnitude more than the Sun can produce in its lifetime. Construction of a wormhole would also require the existence of a substance known as ‘exotic matter’, or ‘negative matter’, which, while not known to be impossible, is also not known to exist in forms useful for wormhole construction (but see for example the Casimir effect). Therefore it is unlikely such a device will be ever constructed, even with highly advanced technology. Long answer: [Black Holes and Time Warps: Einstein’s Outrageous Legacy](http://www.amazon.com/exec/obidos/ASIN/0393312763/qid=1082648377/sr=2-1/ref=sr_2_1/104-3046370-9992731), Kip Thorne’s original book on the subject. ---
**Author:** ![AmbushBug](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ambushbug/32/4600_2.png) [@AmbushBug](https://boards.straightdope.com/u/AmbushBug)\ **Post date:** [April 23, 2004, 4:35am UTC](https://boards.straightdope.com/t/time-travel-question-changed-title/241347/13 "2004-04-23T04:35:26Z")
> [@Enola Straight](#): > > EVERYTHING you see is in the past. > > The very words you see on the monitor are about a picosecond old. Probably closer to a nanosecond, if I remember the details of Admiral Grace Hopper’s [appearance on David Letterman](http://www.tvtome.com/tvtome/servlet/PersonDetail/personid-158925/Grace_Hopper/) correctly, she produced a handful of lengths of wire, about 15cm long or so (hard to judge on TV) and she called them her “handful of nanoseconds”, as she explained that’s about how long it took a near-speed-of-light signal to travel that length. After Dave and the audience were comfortable with the concept, she produced a small paper packet of pepper - with perfect timing she revealed it to be he “packet of picoseconds”. Dave had little he could say to this amazing woman 😃 ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [April 23, 2004, 4:39am UTC](https://boards.straightdope.com/t/time-travel-question-changed-title/241347/14 "2004-04-23T04:39:37Z")
> [@AmbushBug](#): > > Probably closer to a nanosecond, if I remember the details of Admiral Grace Hopper’s [appearance on David Letterman](http://www.tvtome.com/tvtome/servlet/PersonDetail/personid-158925/Grace_Hopper/) correctly, she produced a handful of lengths of wire, about 15cm long or so (hard to judge on TV) and she called them her “handful of nanoseconds”, as she explained that’s about how long it took a near-speed-of-light signal to travel that length. After Dave and the audience were comfortable with the concept, she produced a small paper packet of pepper - with perfect timing she revealed it to be he “packet of picoseconds”. But did she go over to the band to let Pete (the piper) pick the paper pepper packet?