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View Full Version : Time Travel is possible, sort of (new news)



Roger E. Moore
2018-Aug-27, 02:39 PM
https://www.sciencealert.com/physicists-just-came-up-with-a-mathematical-model-for-a-viable-time-machine

It seems to look good on paper, they say, but I haven't a clue how it works. Also, no materials to build it yet.

Roger E. Moore
2018-Aug-27, 02:40 PM
http://iopscience.iop.org/article/10.1088/1361-6382/aa6549/meta;jsessionid=F0836BB9CB9CAE5578D9E6B7E07F4CF5.c 1.iopscience.cld.iop.org

And there is the link to the original paper, with abstract.

Ken G
2018-Aug-28, 12:29 AM
I think these researchers need to think a little more about the contradictions inherent in their phrase "mathematically possible." It's certainly mathematically possible that I'm going to win the Olympic gold medal in luge, marry Jennifer Aniston, and discover the theory of everything, all next year. But I'm not writing any papers to show that it would be mathematically possible, because nobody should care if it's possible, when I haven't the vaguest idea how I would actually do it.

Similarly, if they proved it was "mathematically impossible," that wouldn't mean squat either. The chances of it actually being possible would not be changed one iota, because we pretty much already know that if it does turn out to be possible in practice, it will be because of physics we have not yet dreamed of.

Jens
2018-Aug-28, 01:04 AM
"The time direction of the space-time surface also shows curvature. There is evidence showing the closer to a black hole we get, time moves slower," said Tippett.

Am I missing something, or is this just weird? Everybody knows that time moves slower (from an outside observer's perspective) as the gravitational field gets stronger! I know a guy who has built a clock (http://www.riken.jp/en/pr/press/2015/20150210_1/) that can be used to tell an altitude difference of 6 cm, because of the gravitational time dilation...

Jens
2018-Aug-28, 01:06 AM
I don't have a subscription to the journal, and can't see it, but I guess what they mean by "exotic matter" is the same as what is required for the Alcubierre drive, i.e. matter with negative mass. Since such particles likely do not exist, then it is an interesting math argument but so what, as Ken G said.

grant hutchison
2018-Aug-28, 01:19 AM
There's what seems to be an earlier iteration of this paper on arxiv, dated 2013: Traversable Achronal Retrograde Domains In Spacetime, (https://arxiv.org/abs/1310.7985) which has the advantage that the full text is available. (It was a good idea to change "achronal" to "acausal".)

Grant Hutchison

Ken G
2018-Sep-01, 04:57 PM
Papers like this are generally of interest mostly to people who care a lot more about general relativity than they care about the real world.

Quandry
2018-Sep-02, 10:37 AM
It is mathematically possible to have two apples in your hand and give away four, thereby not having two apples in your hand. It is totally impossible to determine the difference between not having two apples and not having four apples.

John Mendenhall
2018-Sep-03, 10:50 PM
It is mathematically possible to have two apples in your hand and give away four, thereby not having two apples in your hand. It is totally impossible to determine the difference between not having two apples and not having four apples.

Could you show your work, please?

Jens
2018-Sep-04, 12:04 AM
Could you show your work, please?

I think maybe what they meant to say is that you can not have two apples and you can not have four apples. In other words, you can have -2 apples or -4 apples, but in the real world that is meaningless. Well, it could be meaningful if you mean that somebody owes them to you.

Extravoice
2018-Sep-04, 01:04 AM
It It is totally impossible to determine the difference between not having two apples and not having four apples.

Try explaining that to the mortgage bank ;)


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DonM435
2018-Sep-04, 03:06 AM
What if you were standing on a scale, with a quantity of bricks (weight 2 lb. apiece) and a quantity of helium balloons (with 2 lb. lift each)? Tossing away the bricks would lessen your displayed weight. Letting go the balloons would increase your displayed weight. You could tell if you'd lost 4 balloons as opposed to just two, from the gain in the display.

Losing four balloons would demonstrate that (-4) x (-2) = +8 lbs gain, exactly the same as gaining four bricks (+4) x (+2) = +8.

WaxRubiks
2018-Sep-04, 06:42 AM
a problem I thought of with time travel: if someone gets into their Delorean in 2100, and goes back to 1980 for a while they will breath out CO2 which then mixes with all the other gases in the atmosphere, and later becomes part of a wheat plant and then becomes the flour in a pizza that this time traveller eats in 2100, and becomes part of the person's fat deposits, which he then goes back in time and breaths out.
So where would these looped carbon atoms have come from?

Jens
2018-Sep-04, 07:30 AM
a problem I thought of with time travel: if someone gets into their Delorean in 2100, and goes back to 1980 for a while they will breath out CO2 which then mixes with all the other gases in the atmosphere, and later becomes part of a wheat plant and then becomes the flour in a pizza that this time traveller eats in 2100, and becomes part of the person's fat deposits, which he then goes back in time and breaths out.
So where would these looped carbon atoms have come from?

I think you're making a formulation of a more general issue, which is, at the moment you go back in time, you have transported matter which already exists in the current world, so you have essentially added to the mass of the universe (in other words, the same atom exists twice). It seems to be a violation of the conservation of energy.

WaxRubiks
2018-Sep-04, 07:40 AM
I think you're making a formulation of a more general issue, which is, at the moment you go back in time, you have transported matter which already exists in the current world, so you have essentially added to the mass of the universe (in other words, the same atom exists twice). It seems to be a violation of the conservation of energy.

yes. I think to overcome this issue with time travel, only information would be transmitted, like a teleportation device which reformed the person and any associated objects using the energy that was present at that particular point in history.

JCoyote
2018-Sep-04, 05:49 PM
One of my fun scifi ideas has been the "loopback generator", a time machine that can only send a particle back a tiny fraction of a second. Pretty useless, right? Except you now had 2 particles, and can send both back, so you had 4 particles and can send both back, etc... so a failed time machine instead became a potent power source.

I would point out though, that conservation of mass/energy is a LOCAL phenomena, and that all versions of time travel and not so tangentially, warp engines, are non-local loopholes.