# Fermi's Paradox and Time Travel. **URL:** \ **Category:** Great Debates\ **Created:** [February 10, 2011, 6:01am UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867 "2011-02-10T06:01:44Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Jim\_B](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jim_b/32/4338_2.png) [@Jim\_B](https://boards.straightdope.com/u/Jim_B)\ **Post date:** [February 10, 2011, 6:01am UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/1 "2011-02-10T06:01:44Z")
I don’t know if Fermi’s Paradox is the right term, but seems to apply here: If time travel is possible (a _big_ “if” I realize), then where are all the tourists from the future? You notice I put this in GD, since I assume it is a matter of great debate. BTW, I personally believe time travel is possible. Actually, I am of the notion that almost _everything_ in science fiction (and other places) is possible, we just haven’t figured it out yet. Then, where are all the time travelers? I don’t know, maybe they in fact **are** here, they’re just hidden somehow. What do the rest of you think? 🙂 ---
**Author:** ![Onomatopoeia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/onomatopoeia/32/4145_2.png) [@Onomatopoeia](https://boards.straightdope.com/u/Onomatopoeia)\ **Post date:** [February 10, 2011, 6:09am UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/2 "2011-02-10T06:09:38Z")
Time travel doesn’t exist…until it is developed, then it will have always existed, but since it doesn’t, it will have never been developed. My head hurts. ---
**Author:** ![NCDane](https://avatars.discourse-cdn.com/v4/letter/n/ecccb3/32.png) [@NCDane](https://boards.straightdope.com/u/NCDane)\ **Post date:** [February 10, 2011, 6:48am UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/3 "2011-02-10T06:48:54Z")
> [@Jim\_B](#): > > I don’t know if Fermi’s Paradox is the right term, but seems to apply here: If time travel is possible (a _big_ “if” I realize), then where are all the tourists from the future? I don’t think Fermi’s paradox has anything to do with time travel. It has to do with extra terrestrial intelligence (ETI), asking why, if ETI exists (or is abundant), haven’t we detected any sign of it yet? > [@Jim\_B](#): > > You notice I put this in GD, since I assume it is a matter of great debate. > > BTW, I personally believe time travel is possible. Actually, I am of the notion that almost _everything_ in science fiction (and other places) is possible, we just haven’t figured it out yet. Then, where are all the time travelers? I don’t know, maybe they in fact **are** here, they’re just hidden somehow. > > What do the rest of you think? 🙂 Your turn on the paradox is interesting, though. The so-called “sum over histories” approach to Quantum Mechanics treats all particles _as if_ they were taking all possible routes from point A to point B, including routes backward in time, which is definitely permitted by theory. IMO the notion of time travel is unsettling, and I hope it never takes place. I think there may be some tension of thermodynamics with the concept of backward time travel, since that might imply a disallowed amount of increase in order. That would suit be fine; there are a gracious plenty really and truly weird possibilities out there without having to worry about some now unknown process hurtling us back to times we would be best off not having to relive. Then again, I guess i wouldn’y mind being 20 years younger. 30 years. 40. ---
**Author:** ![Alessan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alessan/32/465_2.png) [@Alessan](https://boards.straightdope.com/u/Alessan)\ **Post date:** [February 10, 2011, 6:54am UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/4 "2011-02-10T06:54:47Z")
Maybe time travel creates an entirely new universe (the whole “trousers of time” effect). In that case, maybe we’re the original reality - the one that invents time travel - and the ones we travel too will be alternate earths. ---
**Author:** ![Kozmik](https://avatars.discourse-cdn.com/v4/letter/k/8dc957/32.png) [@Kozmik](https://boards.straightdope.com/u/Kozmik)\ **Post date:** [February 10, 2011, 7:07am UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/5 "2011-02-10T07:07:32Z")
> [@Onomatopoeia](#): > > Time travel doesn’t exist…until it is developed, then it will have always existed, but since it doesn’t, it will have never been developed. > > My head hurts. It won’t need to be developed.. My head really hurts. ---
**Author:** ![E-Sabbath](https://avatars.discourse-cdn.com/v4/letter/e/e19adc/32.png) [@E-Sabbath](https://boards.straightdope.com/u/E-Sabbath)\ **Post date:** [February 10, 2011, 11:21am UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/6 "2011-02-10T11:21:40Z")
The one model I know of for functional time travel involves a singularity being moved at nigh-C, to create relativistic separation between the entrance and exit. (This is the Hawking-approved method.) It will only work to travel back in time until the moment it was created. So even if time travel works, it isn’t going to automatically visit all times. ---
**Author:** ![DrFidelius](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drfidelius/32/3447_2.png) [@DrFidelius](https://boards.straightdope.com/u/DrFidelius)\ **Post date:** [February 10, 2011, 12:41pm UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/7 "2011-02-10T12:41:43Z")
Why do you think there is anything tourist-worthy about this time period? Just because you live here? Come on now. The fifth through the 23rd centuries CE are like the fly-over part of the US. Some people do stop there, usually just to visit relatives, but not enough to notice. Researchers don’t bother since almost important is recorded, and simply viewing archives heisenbergs the continuum much less than direc tobservation. ---
**Author:** ![Candyman74](https://avatars.discourse-cdn.com/v4/letter/c/ad7895/32.png) [@Candyman74](https://boards.straightdope.com/u/Candyman74)\ **Post date:** [February 10, 2011, 1:14pm UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/8 "2011-02-10T13:14:59Z")
> [@DrFidelius](#): > > Why do you think there is anything tourist-worthy about this time period? Just because you live here? Come on now. The fifth through the 23rd centuries CE are like the fly-over part of the US. Some people do stop there, usually just to visit relatives, but not enough to notice. Researchers don’t bother since almost important is recorded, and simply viewing archives heisenbergs the continuum much less than direc tobservation. But people do go to the fly-over part of the US. ---
**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:** [February 10, 2011, 1:27pm UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/9 "2011-02-10T13:27:03Z")
> [@E-Sabbath](#): > > The one model I know of for functional time travel involves a singularity being moved at nigh-C, to create relativistic separation between the entrance and exit. (This is the Hawking-approved method.) > > It will only work to travel back in time until the moment it was created. So even if time travel works, it isn’t going to automatically visit all times. The Beckett Limitation? ---
**Author:** ![Steve\_MB](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/steve_mb/32/5339_2.png) [@Steve\_MB](https://boards.straightdope.com/u/Steve_MB)\ **Post date:** [February 10, 2011, 3:06pm UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/10 "2011-02-10T15:06:06Z")
If time travel into the past prior to the creation of the time machine is possible and the outcome of events is not fixed, there is a risk of altering history in a way that erases the machine from existence. As the number of trips increases, the probability of this approaches one: [QUOTE=Larry Niven] If the universe of discourse permits the possibility of time travel and of changing the past, then no time machine will be invented in that universe. [/QUOTE] ---
**Author:** ![The\_Amazing\_Hanna](https://avatars.discourse-cdn.com/v4/letter/t/977dab/32.png) [@The\_Amazing\_Hanna](https://boards.straightdope.com/u/The_Amazing_Hanna)\ **Post date:** [February 10, 2011, 3:20pm UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/11 "2011-02-10T15:20:11Z")
Maybe real time travel is more like Stargate than Doctor Who? So you have to set up a portal on the receiving end as well, and hope that nobody for the rest of eternity decides to toss a nuclear bomb through for laughs. ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [February 10, 2011, 3:26pm UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/12 "2011-02-10T15:26:34Z")
One of the biggest problems facing time travllers is the power needed to facilitate their temporal sojourns. You need something of the order of 1.21 gigawatts, which is only obtainable by stealing plutonium from Libyans or from a lighting bolt striking a clock tower. ---
**Author:** ![Tom\_Tildrum](https://avatars.discourse-cdn.com/v4/letter/t/e95f7d/32.png) [@Tom\_Tildrum](https://boards.straightdope.com/u/Tom_Tildrum)\ **Post date:** [February 10, 2011, 4:41pm UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/13 "2011-02-10T16:41:06Z")
> [@These are my own pants](#): > > One of the biggest problems facing time travllers is the power needed to facilitate their temporal sojourns. You need something of the order of 1.21 gigawatts, which is only obtainable by stealing plutonium from Libyans or from a lighting bolt striking a clock tower. You only have to thread a conduit forward in time to Earth’s sun going nova, and from there you can download all the power you’d ever need. ---
**Author:** ![Onomatopoeia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/onomatopoeia/32/4145_2.png) [@Onomatopoeia](https://boards.straightdope.com/u/Onomatopoeia)\ **Post date:** [February 10, 2011, 5:45pm UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/14 "2011-02-10T17:45:11Z")
> [@Tom\_Tildrum](#): > > You only have to thread a conduit forward in time to Earth’s sun going nova, and from there you can download all the power you’d ever need. No, no. You simply bleed limitless power from another universe and hope a Hard One doesn’t notice you slowly destroying them. ---
**Author:** ![John\_DiFool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_difool/32/19543_2.png) [@John\_DiFool](https://boards.straightdope.com/u/John_DiFool)\ **Post date:** [February 10, 2011, 5:48pm UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/15 "2011-02-10T17:48:43Z")
[Cue the old lady who was apparently on her cell phone in a 1920’s movie](http://cubiclebot.com/videos/time-traveler-spotted-in-charlie-chaplins-1928-film-the-circus/)… ---
**Author:** ![Tom\_Tildrum](https://avatars.discourse-cdn.com/v4/letter/t/e95f7d/32.png) [@Tom\_Tildrum](https://boards.straightdope.com/u/Tom_Tildrum)\ **Post date:** [February 10, 2011, 7:02pm UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/16 "2011-02-10T19:02:54Z")
> [@Onomatopoeia](#): > > No, no. You simply bleed limitless power from another universe and hope a Hard One doesn’t notice you slowly destroying them. 😃 ---
**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:** [February 10, 2011, 7:20pm UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/17 "2011-02-10T19:20:01Z")
> [@Tom\_Tildrum](#): > > You only have to thread a conduit forward in time to Earth’s sun going nova, and from there you can download all the power you’d ever need. Time travel into the future is very complicated-wouldn’t it be easier to shoot that conduit backwards and let the Big Bang provide the juice? ---
**Author:** ![bouv](https://avatars.discourse-cdn.com/v4/letter/b/bc8723/32.png) [@bouv](https://boards.straightdope.com/u/bouv)\ **Post date:** [February 10, 2011, 10:41pm UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/18 "2011-02-10T22:41:02Z")
> [@Czarcasm](#): > > Time travel into the future is very complicated-wouldn’t it be easier to shoot that conduit backwards and let the Big Bang provide the juice? See, I’m of the opposite opinion. I think if time-travel is ever developed, it will only be one way…to the future. First off, I think this is pretty consistent with current theories about faster-than-light travel (ie, you will age at the rate you experience time, so if you travel for one hour, you are an hour older,) but the rest of the universe will age exponentially faster, (perhaps years in that hour.) Secondly, it avoids all the “go to the past, do something to screw up the future” paradoxes. ---
**Author:** ![Nzinga\_Seated](https://avatars.discourse-cdn.com/v4/letter/n/b5ac83/32.png) [@Nzinga\_Seated](https://boards.straightdope.com/u/Nzinga_Seated)\ **Post date:** [February 10, 2011, 11:12pm UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/19 "2011-02-10T23:12:33Z")
> [@bouv](#): > > See, I’m of the opposite opinion. I think if time-travel is ever developed, it will only be one way…to the future. First off, I think this is pretty consistent with current theories about \*\*faster-than-light travel \*\*(ie, you will age at the rate you experience time, so if you travel for one hour, you are an hour older,) but the rest of the universe will age exponentially faster, (perhaps years in that hour.) > > Secondly, it avoids all the “go to the past, do something to screw up the future” paradoxes. Bolding mine. Nit pick. \*Almost \*as fast as light. **struts all around the thread** Look at Nzinga, gettin’ it in with the science! ---
**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\ **Post date:** [February 10, 2011, 11:52pm UTC](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867/20 "2011-02-10T23:52:34Z")
The fly in the ointment is this: the future DOES NOT EXIST! What we refer to as “the future” will eveolve from the actions of people alive now-there are an infinite number of possible futures, based upon actions being made today. For example-my failure to sell some stock tomorrow might trigger a market crash. Plus, and future humans would have bodies made from atoms that are now part of living humans-hpow an two things exist together , if their constituent parts share the same atoms? [Next page](https://boards.straightdope.com/t/fermis-paradox-and-time-travel/570867.md?page=2)