# 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:** 3
**Author:** ![Tibby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tibby/32/17030_2.png) [@Tibby](https://boards.straightdope.com/u/Tibby)\ **Post date:** [July 17, 2022, 4:10am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/41 "2022-07-17T04:10:48Z")
> [@Kedikat](#): > > Maybe the point of the big bang could be set as zero? > If there is nothing pre big bang that is in effect in our universe? That might have been moving at the time? Kanye West believes he’s the center of the Universe. We can use him as reference point 0/0/0/0. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [July 17, 2022, 4:12am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/42 "2022-07-17T04:12:28Z")
That supposes that the past the time travellers travel to is the same universe as ours. Maybe it’s like a multiverse thing where travelling back in time creates a new universe where that has happened, leaving the other universe alone. It’s not that far removed from the many worlds view on quantum theory. Or maybe a time machine can only send you back to the time it was created. Make it tomorrow then in a year you can travel back to tomorrow but you can never travel back to today. ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [July 17, 2022, 4:14am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/43 "2022-07-17T04:14:45Z")
Space/Time is a fundamental property of the universe. They are not two separate things, it is one thing that we humans cannot understand. We keep thinking of these as two separate things. If we ever come to a better understanding of space/time perhaps we can understand a bit more. Time seems to be progressing from an earlier starting point but that view may be wrong. It remains possible that everything that has ever happened, and everything that ever will happen, has already occured. Like a very detailed picture or painting where you see more details each time you look. Space/time is one thing, and one thing that we do not understand, and seeing them as two separate things keeps us from understanding. The worm dreams of understanding the nature of dirt, why so much has been provided for him, why it is so good, why the dirt seems to be designed for the worm. The worm cannot understand me pissing on my lawn on a Saturday afternoon. There are bigger things going on in the universe that the worm has no ability to understand, even if communication were possible. ---
**Author:** ![Kedikat](https://avatars.discourse-cdn.com/v4/letter/k/ed655f/32.png) [@Kedikat](https://boards.straightdope.com/u/Kedikat)\ **Post date:** [July 17, 2022, 4:18am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/44 "2022-07-17T04:18:36Z")
Well, he is close enough in the universal timeline that it won’t disturb calculations too much, that it is actually me. So okay. Go with that. ---
**Author:** ![Tibby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tibby/32/17030_2.png) [@Tibby](https://boards.straightdope.com/u/Tibby)\ **Post date:** [July 17, 2022, 4:22am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/45 "2022-07-17T04:22:51Z")
Come to think of it, Kanye may not want to be absolute-0 because he wouldn’t like the entire universe expanding _away_ from him. So, you it is. ---
**Author:** ![Kedikat](https://avatars.discourse-cdn.com/v4/letter/k/ed655f/32.png) [@Kedikat](https://boards.straightdope.com/u/Kedikat)\ **Post date:** [July 17, 2022, 4:24am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/46 "2022-07-17T04:24:03Z")
I have issues with multiverse theories, due to the infinite creation of mass and energy. Especially that they do not effect the other universes. How far apart are they? But then where the hell did all of the known universe mass and energy come from? I do have a very shallow idea of that too. But it is worthless. ---
**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:** [July 17, 2022, 4:25am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/47 "2022-07-17T04:25:20Z")
> [@lissener](#): > > We will never develop time travel. Because if we were to do so any time in the future, we would have heard about it by now. > > QED Unless it was invented and, eventually and inevitably, someone time travels and inadvertently kills the inventor before it gets invented. Given time, anything can and will be Fucked Up Beyond All Repair. ---
**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 17, 2022, 4:29am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/48 "2022-07-17T04:29:20Z")
> [@Richard\_Pearse](#): > > Or maybe a time machine can only send you back to the time it was created. Make it tomorrow then in a year you can travel back to tomorrow but you can never travel back to today. I have seen this suggested as a real possibility (as far as any of this is a possibility). The idea was you get two portals (whatever that is) entangled. You then put one on a really fast spaceship and fly it around at relativistic speeds so its clock runs differently. When it returns to earth the two portals will be “entangled” but in different times. Stepping from one to the other is moving forward and back in time. But you can only go back to when the portals were created. I know that is all hocus-pocus sci-fi but the notion makes some sense about not being able to travel to before the portal was created (so, Hawking was just too early for his time traveler party). ---
**Author:** ![Kedikat](https://avatars.discourse-cdn.com/v4/letter/k/ed655f/32.png) [@Kedikat](https://boards.straightdope.com/u/Kedikat)\ **Post date:** [July 17, 2022, 4:30am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/49 "2022-07-17T04:30:48Z")
In general I consider the universe in mass, energy, distance. Time is not an actual physical thing. When you try as a sentient being to figure out what is happening from your point of view, then you have to create time as a part of the equation. It helps to relate it to you, not the universe. Time does not exert any force, has no mass, has no energy. It is only a concept to relate the universe to you. ---
**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 17, 2022, 4:33am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/50 "2022-07-17T04:33:29Z")
I always thought that if time travel was invented a few billion people would instantly pop up around 1930 and assassinate Hitler (remember that ALL future people would be pointing back to a narrow band in time so all future billions would seem to materialize in 1910-1935 (give or take)). Someone should make that movie. Hitler giving a speech and a million people materialize and shoot him. ---
**Author:** ![Kedikat](https://avatars.discourse-cdn.com/v4/letter/k/ed655f/32.png) [@Kedikat](https://boards.straightdope.com/u/Kedikat)\ **Post date:** [July 17, 2022, 4:34am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/51 "2022-07-17T04:34:58Z")
Yeah. Or they had all the time to figure out how to hide time travel. Which I previously said is crap but fun to converse about. ---
**Author:** ![Ponderoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ponderoid/32/19221_2.png) [@Ponderoid](https://boards.straightdope.com/u/Ponderoid)\ **Post date:** [July 17, 2022, 4:43am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/52 "2022-07-17T04:43:36Z")
> [@Folly](#): > > Time and Relative Distance in Space. > TARDIS seems like a catchy name. > > ETA: Dangit, I just looked it up and the D is Dimension Your expansion works just fine too. A while back there was a paper on [Traversable Acausal Retrograde Domains in Spacetime](https://iopscience.iop.org/article/10.1088/1361-6382/aa6549). ---
**Author:** ![Kedikat](https://avatars.discourse-cdn.com/v4/letter/k/ed655f/32.png) [@Kedikat](https://boards.straightdope.com/u/Kedikat)\ **Post date:** [July 17, 2022, 4:45am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/53 "2022-07-17T04:45:10Z")
I would not volunteer to to go back in time to kill Hitler, unless there was a foolproof way to prove to me that it would for sure be a better world. But. That better world may also include having many millions not being born or extra millions being born, etc, etc… But they did not die, for they never lived at all. Oh my god the conceptual mass murder. How accurate are the timeline projections? Will I come back into existence at all to even see what a shit show I initiated? As mentioned previously, what if I grandfather paradox time travel out of existence? Fun stuff. ---
**Author:** ![Kedikat](https://avatars.discourse-cdn.com/v4/letter/k/ed655f/32.png) [@Kedikat](https://boards.straightdope.com/u/Kedikat)\ **Post date:** [July 17, 2022, 4:47am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/54 "2022-07-17T04:47:07Z")
Never mind. ---
**Author:** ![Kedikat](https://avatars.discourse-cdn.com/v4/letter/k/ed655f/32.png) [@Kedikat](https://boards.straightdope.com/u/Kedikat)\ **Post date:** [July 17, 2022, 5:03am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/55 "2022-07-17T05:03:03Z")
Here is a time travel thing I considered. I buy an ounce of gold. Put it on my coffee table and leave it there for ten years. After ten years I time travel back one day at a time or even one second or less at a time to retrieve that ounce of gold and bring it back to my future. If my time machine is finely tuned enough. To micro seconds? How many tons of gold could I take from the past to the present. Seems to be a lot of mass energy violations. I am subtracting mass from the past universe and creating it in the present universe. ---
**Author:** ![Folly](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/folly/32/3219_2.png) [@Folly](https://boards.straightdope.com/u/Folly)\ **Post date:** [July 17, 2022, 5:15am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/56 "2022-07-17T05:15:00Z")
> [@lissener](#): > > We will never develop time travel. Because if we were to do so any time in the future, we would have heard about it by now. > > QED Some theoretical time travel devices (e.g., a wormhole where the two ends are at different points in time) don’t allow you to travel back to a time before the time travel device existed. ---
**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 17, 2022, 7:13am UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/57 "2022-07-17T07:13:50Z")
> [@Richard\_Pearse](#): > > Four dimensions, x, y, z, and t relative to a known reference point, such as the time machine itself. I don’t think coming up with a coordinate system is a problem, it’s how to travel in the negative direction on the t coordinate that is the problem. It may be quite feasible to travel arbitrarily along the _t_ dimension inside a black hole, not that it would do you much good. The equations describing the spacetime geometry around a black hole suggest that, if they can be extrapolated beyond the event horizon, time becomes a spacelike coordinate there, while the radial dimension pointing to the singularity becomes timelike. It’s an intriguing way of explaining why you can never escape from a black hole – “outside” is no longer in a spatial direction, but is in the past. ---
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [July 17, 2022, 3:32pm UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/58 "2022-07-17T15:32:18Z")
> [@Kedikat](#): > > I am subtracting mass from the past universe and creating it in the present universe. Any time travel violates conservation of matter - for a while. You take your 1000 lb time machine and jump ahead 40 years. For those 40 years, the universe is missing 1000lb of matter. Or you travel 40 years into the past, and for as long as you are there, the universe has an extra 1000lbs.\* But the universe isn’t run like a mathematical equation. More like an engineering approximation. As long as the universe _at the end_ has the same amount of matter as it started with, if the books balance at the end, all is fine. And since the universe never ends, no violation of conservation of matter happened. We’re safe, the universe doesn’t go POOF. \*and the numbers never match. While in the past, you breathed, Did you take in the EXACT same amount of air you exhaled? How about that deli sandwich you ate. That massive deuce you left after. No, the numbers never balance. ---
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [July 17, 2022, 3:39pm UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/59 "2022-07-17T15:39:15Z")
I don’t believe time travel is possible. It causes too many issues. But I love time travel stories. And so it is a story telling tool. Any time machine useful for a story _has_ to be a space machine as well. You just have to decide if the time machine remains in the same “space” as it travels through time (Doc’s Delorean) or goes anywhere in the universe (The Guardian of Forever). The thing everyone avoids is that the second time machine is the most efficient space drive ever! I want to go to the Andromeda galaxy .000001 seconds in the future. Done! Throw your warp drive, your transwarp conduits, your 12 parsec hyperdrives, in the trash. ---
**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 17, 2022, 5:35pm UTC](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066/60 "2022-07-17T17:35:14Z")
Sure. Relativity is predicated on a few principles that changed all previous thinking. - Space and time are not separate things, but one thing, space-time, that is indivisible. - There is no absolute space, i.e. no fixed point, no center, only reference frames. - Spacetime is relative to reference frames. Although inside your reference frame time always passes at 1 sec/sec for you and your ruler always measures 1 meter as 1 meter, an observer in another reference frame moving at a different constant velocity (special relativity) or accelerating (general relativity) will measure your space and time differently. This was radical stuff and contrary to intuition, so people didn’t believe until they started testing. There must have been 10,000 increasingly sophisticated tests of relativity in the 117 years since, and every one has confirmed its predictions, to the tune of several decimal places. You can have absolute space or relativity, but never both. Physicists took relativity. It’s just equations and that’s what physics is. Relativity gave us GPS: who’d want to give that up? But that produced a nightmare for non-physicists. In return for GPS, they had to give up their intuitive way of thinking about the way the universe worked. What, the universe doesn’t have a center? What about the Big Bang, isn’t that the center? Worse, they live 99% of their lives in a world where Newton’s physics applies almost perfectly, and that is absolute space, the “clockwork universe” in which every action is mathematically predicable. Relativity boils down to Newton at low speeds, so the equations still work, but where does the shift occur? That’s not intuitively obvious. More worser, the equations are so hard that many interesting questions still haven’t been answered except for some simplified universe like anti-De Sitter Space which is “a maximally symmetric Lorentzian manifold with constant negative scalar curvature.” Whatever that is. The issue is frustrating for both sides. A whole popular science book is necessary to gradually bring amateurs up to the point where they can understand the background for the concepts, so they have a hint of what the physicists mean. A paragraph online lacks all that required context. Even a too long post like this one is needed simply to explain why a short paragraph doesn’t satisfy. Luckily, the Dope has a squad of patient physicists willing to put in time and effort, to whom I give thanks. [Previous page](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066.md?page=2) [Next page](https://boards.straightdope.com/t/time-travel-space-and-relativity/968066.md?page=4)