# If Time Travel is possible **URL:** \ **Category:** In My Humble Opinion\ **Created:** [January 21, 2014, 2:20pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365 "2014-01-21T14:20:05Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![weemart](https://avatars.discourse-cdn.com/v4/letter/w/f14d63/32.png) [@weemart](https://boards.straightdope.com/u/weemart)\ **Post date:** [January 21, 2014, 2:20pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/1 "2014-01-21T14:20:05Z")
If a person who can time travel where to read this story today and email these guys before August 2013 as requested would the story automatically change to say they got 1 reply? Would I remember that I had read the story with no reply received or would I now remember that they got 1 reply? Or would I need to re-read the story to see that they got a reply? Does the fact that they’ve had no reply mean they’ll never get a reply or is it possible that a person who can time travel will reply once they read the story? My head hurts. weemart ---
**Author:** ![weemart](https://avatars.discourse-cdn.com/v4/letter/w/f14d63/32.png) [@weemart](https://boards.straightdope.com/u/weemart)\ **Post date:** [January 21, 2014, 2:21pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/2 "2014-01-21T14:21:08Z")
Helps if I post the link lol > **[Top ways to search the Internet for time travelers on EarthSky | Human World...](https://earthsky.org/human-world/top-ways-to-search-online-for-time-travelers/)** > > Key strategy involves Internet searches for a mention of something before it actually happened. Learn more on EarthSky. ---
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [January 21, 2014, 2:32pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/3 "2014-01-21T14:32:31Z")
Simple answer: We’re not sure which of your possibilities is the right one, because we don’t know how time travel works. For more information, please read the Wikipedia article, [Rules of Time Travel](https://en.wikipedia.org/wiki/Time_travel#Rules_of_time_travel). ---
**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:** [January 21, 2014, 3:20pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/4 "2014-01-21T15:20:51Z")
Reported for move to IMHO, then a move back to General Questions on May 23rd, 2043. ---
**Author:** ![weemart](https://avatars.discourse-cdn.com/v4/letter/w/f14d63/32.png) [@weemart](https://boards.straightdope.com/u/weemart)\ **Post date:** [January 21, 2014, 3:33pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/5 "2014-01-21T15:33:36Z")
Would be more impressive if it got moved yesterday. ---
**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:** [January 21, 2014, 3:43pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/6 "2014-01-21T15:43:47Z")
> [@weemart](#): > > Would be more impressive if it got moved yesterday. You said that tomorrow, so it did. ---
**Author:** ![Laggard](https://avatars.discourse-cdn.com/v4/letter/l/9de053/32.png) [@Laggard](https://boards.straightdope.com/u/Laggard)\ **Post date:** [January 21, 2014, 3:46pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/7 "2014-01-21T15:46:42Z")
Isn’t it true that you cannot change something that happened in the past? For example, if you went back to when your dad was a child there is no way you could kill him because that would mean you never existed? So you could try to kill him but you would never succeed? Is that right? ---
**Author:** ![weemart](https://avatars.discourse-cdn.com/v4/letter/w/f14d63/32.png) [@weemart](https://boards.straightdope.com/u/weemart)\ **Post date:** [January 21, 2014, 3:48pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/8 "2014-01-21T15:48:08Z")
But it didn’t exist yesterday so it can’t be moved then. What we’d actually need is for someone to tell me yesterday were to post the original post so that I’d know where to put it and there would be no need for it to be moved. ---
**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:** [January 21, 2014, 3:50pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/9 "2014-01-21T15:50:03Z")
> [@weemart](#): > > But it didn’t exist yesterday so it can’t be moved then. What we’d actually need is for someone to tell me yesterday were to post the original post so that I’d know where to put it and there would be no need for it to be moved. Sounds loopy to me. ---
**Author:** ![weemart](https://avatars.discourse-cdn.com/v4/letter/w/f14d63/32.png) [@weemart](https://boards.straightdope.com/u/weemart)\ **Post date:** [January 21, 2014, 3:50pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/10 "2014-01-21T15:50:05Z")
If u were to kill your dad b4 u were born you’d never have existed therefore u couldn’t come back to kill him. It would appear that it’s most likely u can change the future but not something that directly affects u. ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [January 21, 2014, 3:54pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/11 "2014-01-21T15:54:48Z")
You don’t need time travel to change the future, you just need to, like, do stuff. ---
**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:** [January 21, 2014, 3:55pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/12 "2014-01-21T15:55:01Z")
> [@weemart](#): > > If u were to kill your dad b4 u were born you’d never have existed therefore u couldn’t come back to kill him. > > It would appear that it’s most likely u can change the future but not something that directly affects u. Damn it-it took me 2 days to reestablish the word “you” into the English language. I _really_ hate the Moth Effect. ---
**Author:** ![weemart](https://avatars.discourse-cdn.com/v4/letter/w/f14d63/32.png) [@weemart](https://boards.straightdope.com/u/weemart)\ **Post date:** [January 21, 2014, 3:59pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/13 "2014-01-21T15:59:32Z")
> [@njtt](#): > > You don’t need time travel to change the future, you just need to, like, do stuff. That’s not changing the future, just affecting it. ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [January 21, 2014, 4:04pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/14 "2014-01-21T16:04:03Z")
I once read an article that argued that time travel was inherently self-negating. The argument went that you start by supposing that time travel is easy. Say that discovering how to travel in time is no more difficult than invented the steam engine. And once time travel is invented, people use it. They travel into the past and change events. So pretty much every time it’s used, history is being changed. And with time travel being so easy, history is changed millions of times. And eventually with all of those millions of different pasts, the world stumbles into a history where time travel isn’t discovered. It doesn’t matter how easy time travel is, there must be some chain of historical events where it isn’t discovered. And if the world lands in that pattern one time, it stops - because in that history there is no time travel and that means there are no further changes in the past. ---
**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:** [January 21, 2014, 4:05pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/15 "2014-01-21T16:05:05Z")
> [@weemart](#): > > That’s not changing the future, just affecting it. You cannot rewrite an unwritten story-you can only affect how it is written in the first place. ---
**Author:** ![weemart](https://avatars.discourse-cdn.com/v4/letter/w/f14d63/32.png) [@weemart](https://boards.straightdope.com/u/weemart)\ **Post date:** [January 21, 2014, 4:08pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/16 "2014-01-21T16:08:57Z")
> [@Little\_Nemo](#): > > I once read an article that argued that time travel was inherently self-negating. The argument went that you start by supposing that time travel is easy. Say that discovering how to travel in time is no more difficult than invented the steam engine. And once time travel is invented, people use it. They travel into the past and change events. So pretty much every time it’s used, history is being changed. And with time travel being so easy, history is changed millions of times. And eventually with all of those millions of different pasts, the world stumbles into a history where time travel isn’t discovered. It doesn’t matter how easy time travel is, there must be some chain of historical events where it isn’t discovered. And if the world lands in that pattern one time, it stops - because in that history there is no time travel and that means there are no further changes in the past. So effectively we’ve already time travelled time travel out of existence? ---
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [January 21, 2014, 4:14pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/17 "2014-01-21T16:14:41Z")
> [@Little\_Nemo](#): > > I once read an article that argued that time travel was inherently self-negating. The argument went that you start by supposing that time travel is easy. Say that discovering how to travel in time is no more difficult than invented the steam engine. And once time travel is invented, people use it. They travel into the past and change events. So pretty much every time it’s used, history is being changed. And with time travel being so easy, history is changed millions of times. And eventually with all of those millions of different pasts, the world stumbles into a history where time travel isn’t discovered. It doesn’t matter how easy time travel is, there must be some chain of historical events where it isn’t discovered. And if the world lands in that pattern one time, it stops - because in that history there is no time travel and that means there are no further changes in the past. Cute idea, but I think you’re wrong. You are confusing time travel being _impossible_ with time travel being _discovered_. In other words: As you describe, it is quite likely that with all of those millions of different pasts, the world would stumble into a history where time travel hasn’t been discovered yet. But tomorrow it might get discovered. Or next year. Or eventually. But it will happen - unless it is impossible. And for it to be possible in one sequence of events, but impossible in another, doesn’t make sense to me; you’d need not merely a change to events, but some sort of change to natural law. ---
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [January 21, 2014, 4:18pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/18 "2014-01-21T16:18:16Z")
By the way, it seems to me that in **Little Nemo** ’s scenario, it doesn’t really matter whether time travel is difficult or easy, as long as it is _possible_. The only difference between difficult and easy, is how long it takes from the first invention until it is ubiquitous, which does not affect the main logic of the argument. ---
**Author:** ![weemart](https://avatars.discourse-cdn.com/v4/letter/w/f14d63/32.png) [@weemart](https://boards.straightdope.com/u/weemart)\ **Post date:** [January 21, 2014, 4:20pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/19 "2014-01-21T16:20:56Z")
I suppose if we needed a certain rare element in order to time travel and ppl from the future used the whole supply of that element to travel back in time then needed to use the whole supply of the element in the past to travel forward again then time travel would never be discovered since the complete supply of the element would have been used in the past b4 time travel was possible. ---
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [January 21, 2014, 4:36pm UTC](https://boards.straightdope.com/t/if-time-travel-is-possible/679365/20 "2014-01-21T16:36:06Z")
> [@weemart](#): > > I suppose if we needed a certain rare element in order to time travel and ppl from the future used the whole supply of that element to travel back in time … That was a major plot point in several episodes of [Seven Days](https://en.wikipedia.org/wiki/Seven_Days_(TV_series)). Headquarters used Element 115 to send the time traveler a week back in time, and that used up the entire supply of Element 115. But the time traveler ends up in a new timeline where – from the perspective of the people at Headquarters – the time-travel device has never been used yet, and so they have what they need. [Next page](https://boards.straightdope.com/t/if-time-travel-is-possible/679365.md?page=2)