# Time Travel, Space and Relativity **URL:** \ **Category:** In My Humble Opinion\ **Created:** [July 17, 2022, 12:29am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066 "2022-07-17T00:29:26Z")\ **Posts on this page:** 20\ **Page:** 5
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [July 18, 2022, 12:25am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/81 "2022-07-18T00:25:59Z")
This does indeed have something to do with quantum electrodynamical Feynman diagrams, where electrons are represented by lines with an arrow pointing one way, and positrons with the arrow pointing the other way: [![](https://web.archive.org/web/20160322051818im_/http://www.quantumdiaries.org/wp-content/uploads/2010/03/QEDrules.png) ](https://web.archive.org/web/20160322051818im_/http://www.quantumdiaries.org/wp-content/uploads/2010/03/QEDrules.png) But I am not sure what it buys you to imagine the positrons (or the electrons) as going “backwards in time”. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [July 18, 2022, 12:33am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/82 "2022-07-18T00:33:04Z")
> [@Moriarty](#): > > Now if I could just figure out how to speed this process up… The wooden box at the end of the journey awaits you patiently. I’m not convinced speeding this process up is really what you want. But you do you; far be it from me to intervene. 😉 ---
**Author:** ![DorkVader](https://avatars.discourse-cdn.com/v4/letter/d/73ab20/32.png) [@DorkVader](https://boards.straightdope.com/u/DorkVader)\ **Post date:** [July 18, 2022, 12:33am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/83 "2022-07-18T00:33:22Z")
Dr. Don Lincoln, Fermilab, Youtube science explainer for Fermilab explained it that way, that’s what helps me make sense of it. You’re moving through time at light speed unless you are also moving along the spatial axiseseseses (axes?). Then your speed of causality is divided amongst the 4 axes of travel (3 spatial one time) My take away from it all is that time coordinates are plottable similar to spatial coordinate, but to move about the time axis like you would spatial axes require a massive investment of energy to affect your inertia. Like you’re actually trying to affect the inertia of the entire universe sooooo, good luck, maybe it will eventually end up just being a technical problem, but I ain’t gonna see the day. My take away is not clear on being able to actually leave your original light cone or if it shifts around with you as you traverse the time axis in a non-linear way or not. I don’t think this is accurate in any way, just my crude understanding. ---
**Author:** ![dougrb](https://avatars.discourse-cdn.com/v4/letter/d/76d3ee/32.png) [@dougrb](https://boards.straightdope.com/u/dougrb)\ **Post date:** [July 18, 2022, 1:27am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/84 "2022-07-18T01:27:58Z")
> [@DorkVader](#): > > Then your speed of causality is divided amongst the 4 axes of travel (3 spatial one time) That’s why it makes my head hurt. ---
**Author:** ![msmith537](https://avatars.discourse-cdn.com/v4/letter/m/d9b06d/32.png) [@msmith537](https://boards.straightdope.com/u/msmith537)\ **Post date:** [July 18, 2022, 12:35pm UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/85 "2022-07-18T12:35:18Z")
> [@Kedikat](#): > > 10 minutes ago is just that. A situation of all things in the universe that is no longer in existence, except if a being with memory observed and remembered it. It exists only in a memory. Exactly. Presumably all the information about the state of the universe ten minutes ago exists in some form (like a photograph or viewing an object ten light-minutes away). But short of rearranging the entire universe with your Omega 13 device, it’s not really clear to me how one could “travel” to ten minutes ago. ---
**Author:** ![Moriarty](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/moriarty/32/49_2.png) [@Moriarty](https://boards.straightdope.com/u/Moriarty)\ **Post date:** [July 18, 2022, 12:52pm UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/86 "2022-07-18T12:52:54Z")
> [@LSLGuy](#): > > The wooden box at the end of the journey awaits you patiently. I’m not convinced speeding this process up is really what you want. But you do you; far be it from me to intervene. Touché. Of course, it depends on the moments, right? Sometimes an hour can drag on for eternity and sometimes it’s a fleeting instant. It’s all relative. [![Imgur](https://i.imgur.com/c3YiPrW.png) ](https://imgur.com/c3YiPrW) ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [July 18, 2022, 1:01pm UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/87 "2022-07-18T13:01:12Z")
> [@Moriarty](#): > > Of course, it depends on the moments, right? Sometimes an hour can drag on for eternity and sometimes it’s a fleeting instant. It’s all relative. [![](https://imgc.artprintimages.com/img/print/to-you-it-was-fast-new-yorker-cartoon_u-l-q1l04zs0.jpg?artPerspective=n) ](https://imgc.artprintimages.com/img/print/to-you-it-was-fast-new-yorker-cartoon_u-l-q1l04zs0.jpg?artPerspective=n) ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [July 18, 2022, 1:01pm UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/88 "2022-07-18T13:01:16Z")
I am not sure that it is completely well understood whether past information can be erased, for example by throwing it into a black hole. ---
**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:** [July 18, 2022, 1:06pm UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/89 "2022-07-18T13:06:13Z")
> [@DorkVader](#): > > Dr. Don Lincoln, Fermilab, Youtube science explainer for Fermilab explained it that way, that’s what helps me make sense of it. I love his videos. Here is the one I think you are referring to. Well worth the few minutes to view. [![](https://img.youtube.com/vi/A2JCoIGyGxc/maxresdefault.jpg "Why can't you go faster than light?") ](https://www.youtube.com/watch?v=A2JCoIGyGxc&t=175) ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [July 18, 2022, 2:07pm UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/90 "2022-07-18T14:07:05Z")
> [@wolfpup](#): > > > [@Moriarty](#): > > > > Of course, it depends on the moments, right? Sometimes an hour can drag on for eternity and sometimes it’s a fleeting instant. It’s all relative. > > [comic removed from quote for space] Reminds me of a bit by comedian Ron White during the Blue Collar Comedy Tour days. He’s describing sex with his wife in terms of a rodeo. He then comments something like “There’s some doubt about me staying on for the FULL eight seconds…” I’m now in day 9 of 10 of COVID isolation. Having lived alone in one guest bedroom, one bathroom, and one patio with only you folks for company for 9 days I can say time has sure dragged. Despite how much fun I could have had with the same 9 consecutive days off around town with my wife. There is such a thing as too much couch potato. ---
**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:** [July 18, 2022, 5:06pm UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/91 "2022-07-18T17:06:42Z")
Brian Greene was the first person I know of to use this analogy, though it wouldn’t surprise me if someone else used it before. If you poke in to the detail though, at best it is a trivial and slightly misleading statement, but at the same time it is a good analogy The analogy comes the 4-velocity of a particle, observer, etcwhich is always c, when defined. 4-velocity is analogous to 3-velocity as it is the differential of 4-position wrt to proper time. However the 4-velocity turns out just to be the unit vector (using normalized units such as c=1) tangent to the object’s wordline. So you can reduce the analogy to the statement that a unit vector always has a lenght of ‘1’, which is trivial as it is just the defintion of a unit vector. The 4-velocity is also undefined for a lightspeed particle like a photon. The reason it is a good analogy though is it makes you think about how unit timelike vectors project on to each other, without even explaining what a timelike vector is. Since Minkowski, realivity has mostly been thougt of geometrically and the geometrical thinking motivated general relativity and this analogy introcues geometrical thinking by stealth. ---
**Author:** ![msmith537](https://avatars.discourse-cdn.com/v4/letter/m/d9b06d/32.png) [@msmith537](https://boards.straightdope.com/u/msmith537)\ **Post date:** [July 18, 2022, 9:53pm UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/92 "2022-07-18T21:53:10Z")
> [@Exapno\_Mapcase](#): > > Wasn’t it Richard Feynman who first introduced the notion that antimatter is ordinary matter traveling backwards in time? > > This made a number of people unhappy then, and my understanding is that even fewer are happier about it now. > > But two physicists, three opinions also applies. Same question. What does it even mean “traveling backwards through time”? Like the antimatter jumps back into the particle accelerator before I turn it on, like those inverted bullets in Tenet? ---
**Author:** ![msmith537](https://avatars.discourse-cdn.com/v4/letter/m/d9b06d/32.png) [@msmith537](https://boards.straightdope.com/u/msmith537)\ **Post date:** [July 18, 2022, 9:56pm UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/93 "2022-07-18T21:56:26Z")
> [@Moriarty](#): > > > [@LSLGuy](#): > > > > The wooden box at the end of the journey awaits you patiently. I’m not convinced speeding this process up is really what you want. But you do you; far be it from me to intervene. > > Touché. > > Of course, it depends on the moments, right? Sometimes an hour can drag on for eternity and sometimes it’s a fleeting instant. It’s all relative. > > [''When you are courting a nice girl .......... '' - Albert Einstein [917 × 390] - Imgur](https://imgur.com/c3YiPrW) I thought that quote was attributed to the physicist L.L. Cool J in the aquatic documentary Deep Blue Sea. ---
**Author:** ![Buck\_Godot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/buck_godot/32/6573_2.png) [@Buck\_Godot](https://boards.straightdope.com/u/Buck_Godot)\ **Post date:** [July 18, 2022, 10:50pm UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/94 "2022-07-18T22:50:22Z")
This reminds me of a story arc in a recent season of Legends of Tomorrow (Spoliered below: note it isn’t actually about Hitler) They want to stop WW1 by preventing arch duke Ferdinand from being assassinated. When they get there they find that there is a bar filled with time travelers many of whom are waiting their turn to try. But it turns out that the death of Ferdiand is an unalterable fixed point in time and anyone who tries to stop it fails and usually ends up dead. The rest of the patrons are there for the entertainment of watching the first group fail. ---
**Author:** ![dougrb](https://avatars.discourse-cdn.com/v4/letter/d/76d3ee/32.png) [@dougrb](https://boards.straightdope.com/u/dougrb)\ **Post date:** [July 18, 2022, 11:02pm UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/95 "2022-07-18T23:02:17Z")
> [@Asympotically\_fat](#): > > at best it is a trivial and slightly misleading statement, but at the same time it is a good analogy The analogy implies that you can only slow down the passage of time by moving thru space. Does the math say otherwise? (for the purpose of moving backward/fwd in time). ---
**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:** [July 18, 2022, 11:24pm UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/96 "2022-07-18T23:24:23Z")
> [@msmith537](#): > > What does it even mean “traveling backwards through time”? Physicists don’t look at things traveling through time. They have equations. Equations can have pluses or minuses. Feynman saw that the equations put a minus sign in whenever antimatter was considered. Otherwise they were equivalent to matter’s equations. So what did that mean? Feynman noted that it was equivalent to saying that matter travels forward in time and antimatter travels backwards in time. In fact, a position might be an electron that had traveled into the future and returned as a positron. (Sorry for an oversimplified take.) What is time? Relativity and quantum theory each treat time differently so they’re no help. Right now it’s all let’s you and them argue. ---
**Author:** ![dougrb](https://avatars.discourse-cdn.com/v4/letter/d/76d3ee/32.png) [@dougrb](https://boards.straightdope.com/u/dougrb)\ **Post date:** [July 19, 2022, 12:38am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/97 "2022-07-19T00:38:46Z")
> [@Exapno\_Mapcase](#): > > put a minus sign That has screwed me before. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [July 19, 2022, 12:41am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/98 "2022-07-19T00:41:51Z")
> [@LSLGuy](#): > > I’m now in day 9 of 10 of COVID isolation. Having lived alone in one guest bedroom, one bathroom, and one patio with only you folks for company for 9 days I can say time has sure dragged. Despite how much fun I could have had with the same 9 consecutive days off around town with my wife. > > There is such a thing as too much couch potato. Very sorry to hear that you tested positive. Quarantines are no fun, but at least it’s almost over now. Take care of yourself! ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [July 19, 2022, 12:52am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/99 "2022-07-19T00:52:13Z")
Thank you. It’s been the most logistical hassle for the least symptoms and apparent health impact of my entire life. Considering how many people my age have died of COVID, to be bitching about how mild it’s been seems … ungrateful. As General Kuhster said of all matters military in that epic work of cinematic literature, _The Great Race_ > [@](#): > > To win is imperative. To win easily, a blessing. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [July 19, 2022, 2:52am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/100 "2022-07-19T02:52:37Z")
> [@Buck\_Godot](#): > > This reminds me of a story arc in a recent season of Legends of Tomorrow (Spoliered below: note it isn’t actually about Hitler) > > They want to stop WW1 by preventing arch duke Ferdinand from being assassinated. When they get there they find that there is a bar filled with time travelers many of whom are waiting their turn to try. But it turns out that the death of Ferdiand is an unalterable fixed point in time and anyone who tries to stop it fails and usually ends up dead. The rest of the patrons are there for the entertainment of watching the first group fail. > **[Wikihistory](https://www.tor.com/2011/08/31/wikihistory/)** > > Wikihistory by Desmond Warzel [Previous page](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066.md?page=4) [Next page](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066.md?page=6)