# What's the name of this paradox? **URL:** \ **Category:** Factual Questions\ **Created:** [April 8, 2004, 3:47am UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891 "2004-04-08T03:47:09Z")\ **Posts on this page:** 16\ **Page:** 2
**Author:** ![coop](https://avatars.discourse-cdn.com/v4/letter/c/87869e/32.png) [@coop](https://boards.straightdope.com/u/coop)\ **Post date:** [April 8, 2004, 12:20pm UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891/21 "2004-04-08T12:20:47Z")
Short story by Ray Bradbury: [http://www.sba.muohio.edu/snavely/415/thunder.htm](http://www.sba.muohio.edu/snavely/415/thunder.htm) ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [April 8, 2004, 1:54pm UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891/22 "2004-04-08T13:54:47Z")
> [@Dan Norder](#): > > Uh, where did you get that idea? That sounds more like the sort of thing a fictional TV show would come up with to explain away weaknesses of its premise (Quantum Leap, for one, which never made sense). > > I’ve heard of plenty of scenarios that would get people to travel back in time well beyond the time this planet was even formed, which is more than enough the purposes of this discussion. Can you cite these? All the “serious” time travel proposals I’ve heard (i.e., those from physicists working in general relativity, which deals with the structure of time among other things) work exactly the way **ricksummon** described. (Wormholes, cosmic strings, etc.) ---
**Author:** ![clairobscur](https://avatars.discourse-cdn.com/v4/letter/c/839c29/32.png) [@clairobscur](https://boards.straightdope.com/u/clairobscur)\ **Post date:** [April 8, 2004, 3:00pm UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891/23 "2004-04-08T15:00:49Z")
> [@ricksummon](#): > > . Also, if you accept a “many-worlds” cosmology, time travellers cannot visit their own pasts, only alternate pasts. I don’t think so. In a “many world” universe, an individual has only one past. But if he travels back to this past, he’s creating a new “branch” becoming at this point and he creates a different _future_ . So he won’t be able to travel back to his original universe (where he had not travelled back in the past until the moment he did) but only to an alternative future, an universe where his time travel has taken place and was always accounted for. I’m probably very unclear, here. Hope some will understand what I meant. By the way, assuming that time travel would be possible, I would assume that the time traveller would be transported back to the same place in space where the “time machine” is situated. Sine earth, the solar system, the galaxy, etc…move quite quickly, you would have to send back a spaceship for our time-traveller is going to find himself in a lonely place, long away from any planet. Or course, I suppose that if the technology allowed to travel back in time, they could as well be able to teleport people to a given place, too, and make sure there’s nothing already present at this spot (like an atom of something, a butterfly, a concrete wall, etc…). ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [April 8, 2004, 3:14pm UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891/24 "2004-04-08T15:14:57Z")
> [@Dan Norder](#): > > Uh, where did you get that idea? That sounds more like the sort of thing a fictional TV show would come up with to explain away weaknesses of its premise (Quantum Leap, for one, which never made sense). I don’t know about **ricksummon** , but I got that idea from the writings of Dr. Kip Thorne, a well-respected physicist. ---
**Author:** ![Flash-57](https://avatars.discourse-cdn.com/v4/letter/f/839c29/32.png) [@Flash-57](https://boards.straightdope.com/u/Flash-57)\ **Post date:** [April 8, 2004, 5:19pm UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891/25 "2004-04-08T17:19:20Z")
> [@Jarrod87](#): > > Thats why i dont believe time travel will ever exist in the way people imagine it, because if it did we would already have it now Actually, it’s kind of the opposite. If someone in the future invents backwards time travel, sooner or later, someone will use it to go back and will do something, accidently or on purpose, that prevents that case of time travel from being invented. In other words, backwards time travel never gets invented for good. Given an unlimited amount of time, it always gets uninvented. ---
**Author:** ![ianzin](https://avatars.discourse-cdn.com/v4/letter/i/ed655f/32.png) [@ianzin](https://boards.straightdope.com/u/ianzin)\ **Post date:** [April 8, 2004, 5:31pm UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891/26 "2004-04-08T17:31:43Z")
> [@NoCoolUserName](#): > > For the best “causality loop” story ever written, read _By His Bootstraps_ by **RAH**. Meanwhile can someone invent a machne that enables all Dopers to read the mind of ‘NoCoolUser Name’, so that everyone knows who ‘RAH’ is meant to be. Obviously, it would have been waaay too much trouble to actually write the author’s name out in full. ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [April 8, 2004, 5:38pm UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891/27 "2004-04-08T17:38:23Z")
It’s not a true paradox because it’s self-consistant, it does violate casuality tho’. ---
**Author:** ![aldiboronti](https://avatars.discourse-cdn.com/v4/letter/a/9fc348/32.png) [@aldiboronti](https://boards.straightdope.com/u/aldiboronti)\ **Post date:** [April 8, 2004, 5:41pm UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891/28 "2004-04-08T17:41:46Z")
> [@ianzin](#): > > Meanwhile can someone invent a machne that enables all Dopers to read the mind of ‘NoCoolUser Name’, so that everyone knows who ‘RAH’ is meant to be. Obviously, it would have been waaay too much trouble to actually write the author’s name out in full. Robert Heinlein is the author. Another classic time travel paradox story of his is [All You Zombies](http://www.heinleinsociety.org/rah/works/shortstories/allyouzombies.html) ---
**Author:** ![BrotherCadfael](https://avatars.discourse-cdn.com/v4/letter/b/977dab/32.png) [@BrotherCadfael](https://boards.straightdope.com/u/BrotherCadfael)\ **Post date:** [April 8, 2004, 5:48pm UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891/29 "2004-04-08T17:48:31Z")
> [@NoCoolUserName](#): > > For the best “causality loop” story ever written, read _By His Bootstraps_ by **RAH**. > > For the definitive discussion of time travel, see _The Theory and Practice of Time Travel_ by **Larry Niven**. > Collected in “All the Myriad Ways.” I was going to suggest calling it the “By His Bootstraps” paradox… ---
**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:** [April 8, 2004, 5:56pm UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891/30 "2004-04-08T17:56:57Z")
Everyone conversant with science fiction should know that both the best and the worst of time travel stories were written by Robert A. Heinlein. And if you didn’t know, then it’s a good thing I told you, because you should know. As for a time machine which allows for access to the indefinite past, the Alcubierre warp drive is no more impossible than a Thorne wormhole, and like all FTL methods, it can also be used for time travel. ---
**Author:** ![daffyduck](https://avatars.discourse-cdn.com/v4/letter/d/ec9cab/32.png) [@daffyduck](https://boards.straightdope.com/u/daffyduck)\ **Post date:** [April 8, 2004, 6:29pm UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891/31 "2004-04-08T18:29:04Z")
Of course when people talk about going back in time, what they really mean is they want to go forward in time to the past. If you truly went back in time, how would you know? Five days from now, you stumble on a machine that transports you back to today. But today, you have no idea what will be happening in five days, so you could be back in time right now and not even know it! ---
**Author:** ![Lobelia\_Overhill](https://avatars.discourse-cdn.com/v4/letter/l/54ee81/32.png) [@Lobelia\_Overhill](https://boards.straightdope.com/u/Lobelia_Overhill)\ **Post date:** [April 8, 2004, 9:18pm UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891/32 "2004-04-08T21:18:44Z")
It’s _the_ Paradox. Other forms of paradox have prefixes, such as the grandfather paradox. And there are Time Travel Tourists, they look like all other tourists, except they never give tips … ---
**Author:** ![Rico](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rico/32/3582_2.png) [@Rico](https://boards.straightdope.com/u/Rico)\ **Post date:** [April 8, 2004, 9:59pm UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891/33 "2004-04-08T21:59:56Z")
> [@Lobelia Overhill](#): > > And there are Time Travel Tourists, they look like all other tourists, except they never give tips … So **that’s** who’s been attending my band’s recent gigs… ---
**Author:** ![NoCoolUserName](https://avatars.discourse-cdn.com/v4/letter/n/5fc32e/32.png) [@NoCoolUserName](https://boards.straightdope.com/u/NoCoolUserName)\ **Post date:** [April 8, 2004, 10:03pm UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891/34 "2004-04-08T22:03:52Z")
> [@ianzin](#): > > Meanwhile can someone invent a machne that enables all Dopers to read the mind of ‘NoCoolUser Name’, so that everyone knows who ‘RAH’ is meant to be. Obviously, it would have been waaay too much trouble to actually write the author’s name out in full. Sorry. I mistakenly thought I was in Cafe Society, where RAH can only mean Robert A Heinlein. _Mea culpa_. ---
**Author:** ![HPL](https://avatars.discourse-cdn.com/v4/letter/h/3da27b/32.png) [@HPL](https://boards.straightdope.com/u/HPL)\ **Post date:** [April 8, 2004, 11:41pm UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891/35 "2004-04-08T23:41:19Z")
> [@aldiboronti](#): > > Robert Heinlein is the author. Another classic time travel paradox story of his is [All You Zombies](http://www.heinleinsociety.org/rah/works/shortstories/allyouzombies.html) That is a facinating Premise. It’s also rather creepy and disturbing. Does have a few obvious problems, but still facinating. ---
**Author:** ![YellowTail](https://avatars.discourse-cdn.com/v4/letter/y/b5ac83/32.png) [@YellowTail](https://boards.straightdope.com/u/YellowTail)\ **Post date:** [April 8, 2004, 11:45pm UTC](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891/36 "2004-04-08T23:45:04Z")
> [@daffyduck](#): > > Of course when people talk about going back in time, what they really mean is they want to go forward in time to the past. If you truly went back in time, how would you know? Five days from now, you stumble on a machine that transports you back to today. But today, you have no idea what will be happening in five days, so you could be back in time right now and not even know it! Firesign Theatre, anyone? [Previous page](https://boards.straightdope.com/t/whats-the-name-of-this-paradox/238891.md?page=1)