# How can warp drive not violate relativity?
**URL:** https://boards.straightdope.com/t/how-can-warp-drive-not-violate-relativity/642186
**Category:** Factual Questions
**Created:** [November 26, 2012, 7:13pm UTC](https://boards.straightdope.com/t/how-can-warp-drive-not-violate-relativity/642186 "2012-11-26T19:13:57Z")
**Posts on this page:** 13
**Page:** 3
### Author:  [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)
#### Post date: [December 3, 2012, 1:16am UTC](https://boards.straightdope.com/t/how-can-warp-drive-not-violate-relativity/642186/41 "2012-12-03T01:16:36Z")
> [@Chronos](#):
>
> This may seem like a nitpick, but that’s for a topologically-identified space, not for a closed space. Closed spaces of trivial topology still don’t quite have a preferred reference frame, although you can still end up with similar twin-paradox issues (the resolution is slightly more complicated than in the topologically-identified case, but similar).
I’m not sure what you mean by “topologically-identified space”. Looking around, I suspect it’s the difference between a universe being spatially a 3-sphere Vs. a 3-torus, with only the 3-torus version having a preferred frame. Is this basically it?
If so, I don’t think this is relevant to whether you can have a space which simultaneously has a topology with a preferred reference frame and which satisfies Special Relativity. I only need one example.
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### Author:  [@Lumpy](https://boards.straightdope.com/u/Lumpy)
#### Post date: [December 3, 2012, 1:56am UTC](https://boards.straightdope.com/t/how-can-warp-drive-not-violate-relativity/642186/42 "2012-12-03T01:56:12Z")
If you had a working Alcubierre Drive, and wanted to use it as a time machine instead of a FTL drive, how would you configure it?
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### Author:  [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)
#### Post date: [December 3, 2012, 2:24am UTC](https://boards.straightdope.com/t/how-can-warp-drive-not-violate-relativity/642186/43 "2012-12-03T02:24:52Z")
> [@Undo "Clear Fields", can it be done?](https://boards.straightdope.com/t/undo-clear-fields-can-it-be-done/5170/2):
>
> There could very well be a specific configuration of black holes, damned souls, and immersion blenders…
😃 Be sure to cool it with baboon’s blood.
> [@cmyk](#):
>
> A pure Doppler Shift is caused by the compression of waves between the discrete motions of objects relative to another in flat (or close/everyday) space.
>
> But, since spacetime is also expanding, there’s also a red-shift that is, for lack of a better word, accumulative. The farther away we observe something, the stronger the shift, even if the galaxies weren’t moving through space relative to each other.
>
> This would be like a train’s whistle changing pitch, because the earth and its atmosphere is expanding in size, despite the fact the train, nor you, are in motion relative to each other (imagining that all things situated on the planet would remain in their respective positions, like the dots on an inflating balloon analogy; as impossible as the planet doing this actually is, but hey… it’s an analogy)…
Thanks. I’ve seen this explained here many times, and I can never hear enough about the middle graf, the money graf.
But, as someone holding on to analogies with the skin of my teeth, in my 3-D physically perceived world, two objects on an expanding balloon _do_ have greater distances between them at t+_n_. Their addresses on the map stay the same and their distances are always proportionally the same relative to t_n_-1, but separate they do.
Fucking analogies.
ETA: “…their distances are always proportionally the same relative to t_n_-1” is a pretty loaded, and wrong, sentence, I think. Is it? Spacetime can change non-homogenously, right?
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### Author:  [@Zakalwe](https://boards.straightdope.com/u/Zakalwe)
#### Post date: [December 3, 2012, 3:25am UTC](https://boards.straightdope.com/t/how-can-warp-drive-not-violate-relativity/642186/44 "2012-12-03T03:25:55Z")
> [@Lumpy](#):
>
> If you had a working Alcubierre Drive, and wanted to use it as a time machine instead of a FTL drive, how would you configure it?
I would dial in the desired date and time on the little LED display, hit the gas, and try to get to 88 mph before I run into the photo development booth.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [December 3, 2012, 3:48am UTC](https://boards.straightdope.com/t/how-can-warp-drive-not-violate-relativity/642186/45 "2012-12-03T03:48:37Z")
> [@](#):
>
> If so, I don’t think this is relevant to whether you can have a space which simultaneously has a topology with a preferred reference frame and which satisfies Special Relativity. I only need one example.
Right, and I didn’t mean to imply otherwise. Strictly speaking, such a space does not _globally_ satisfy SR, but it does satisfy it locally, which is almost always all that one’s interested in.
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### Author:  [@jackdavinci](https://boards.straightdope.com/u/jackdavinci)
#### Post date: [December 3, 2012, 6:28pm UTC](https://boards.straightdope.com/t/how-can-warp-drive-not-violate-relativity/642186/46 "2012-12-03T18:28:39Z")
> [@moriah](#):
>
> Umm… [Begging the question - Wikipedia](http://en.wikipedia.org/wiki/Begging_the_question#Modern_usage)
I see what you’re saying, but I’d like it if Dopers, when correcting other Dopers, not only point out the mistake, but also suggest a better option.
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### Author:  [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)
#### Post date: [December 3, 2012, 6:35pm UTC](https://boards.straightdope.com/t/how-can-warp-drive-not-violate-relativity/642186/47 "2012-12-03T18:35:00Z")
Maybe we have different definitions of Special Relativity. To me, it means the constancy of the speed of light (plus, I guess, space being isotropic and homogeneous), and everything that then follows from that. The lack of a locally preferred reference frame then falls out it as an effect, not a starting requirement. The lack of a preferred reference frame that can only be found using global measurements doesn’t follow from that, so it doesn’t really make sense (to me) to say it doesn’t globally satisfy Special Relativity.
Going back to my earlier post, is it actually the case that if the universe is spatially closed as a 3-sphere, it wouldn’t have a preferred reference frame? Or is that not even what you were saying? It’s hard to visualize, obviously, but visualizing 2+1 dimensions, with space a 2-sphere and time radial, I would think you’d still have a single preferred frame. From there to a 3-sphere plus time doesn’t seem that big of a leap.
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### Author:  [@Lazlo](https://boards.straightdope.com/u/Lazlo)
#### Post date: [December 3, 2012, 9:29pm UTC](https://boards.straightdope.com/t/how-can-warp-drive-not-violate-relativity/642186/48 "2012-12-03T21:29:54Z")
> [@moriah](#):
>
> Umm… [Begging the question - Wikipedia](http://en.wikipedia.org/wiki/Begging_the_question#Modern_usage)
Yes, yes. Everyone who slept through Philosphy 101 knows that the OP used the colloquial definition.
Have a cookie.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [December 4, 2012, 1:42am UTC](https://boards.straightdope.com/t/how-can-warp-drive-not-violate-relativity/642186/49 "2012-12-04T01:42:02Z")
With the Universe as a 3-sphere, you could define something that behaved in some ways like a globally-preferred reference frame, but it would be really weird if you tried to interpret it that way. Basically, you’d be defining a reference frame for a higher-dimensional embedding space, not for our space itself.
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### Author:  [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)
#### Post date: [December 4, 2012, 5:59pm UTC](https://boards.straightdope.com/t/how-can-warp-drive-not-violate-relativity/642186/50 "2012-12-04T17:59:29Z")
> [@Chronos](#):
>
> With the Universe as a 3-sphere, you could define something that behaved in some ways like a globally-preferred reference frame, but it would be really weird if you tried to interpret it that way. Basically, you’d be defining a reference frame for a higher-dimensional embedding space, not for our space itself.
Can you point me to something that talks about this?
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### Author:  [@eburacum45](https://boards.straightdope.com/u/eburacum45)
#### Post date: [December 4, 2012, 11:03pm UTC](https://boards.straightdope.com/t/how-can-warp-drive-not-violate-relativity/642186/51 "2012-12-04T23:03:16Z")
> [@Lumpy](#):
>
> If you had a working Alcubierre Drive, and wanted to use it as a time machine instead of a FTL drive, how would you configure it?
This is a very important question, and deserves an answer from someone who knows more about this than I. But as far as I under stand it, the fact that the interior of the Alcubierre warp bubble is immune from time dilation doesn’t prevent the warp bubble as a whole from being used as a faster-than-light messaging system.
If you can communicate using a FTL messaging system between two observers who are both travelling slower than light but at significantly different velocities, then it could be possible for one observer to communicate with the past of the other one, and vice-versa. If you send the message back and forth at least once, you can end up communicating with your own past. The message you send could even be your own self, if the bubble is big enough.
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### Author:  [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)
#### Post date: [December 4, 2012, 11:19pm UTC](https://boards.straightdope.com/t/how-can-warp-drive-not-violate-relativity/642186/52 "2012-12-04T23:19:49Z")
> [@eburacum45](#):
>
> If you send the message back and forth at least once, you can end up communicating with your own past..
[Ursula K. Le Guin](http://en.wikipedia.org/wiki/Ansible) did not report this problem.
But the stock exchange…
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [December 5, 2012, 12:06am UTC](https://boards.straightdope.com/t/how-can-warp-drive-not-violate-relativity/642186/53 "2012-12-05T00:06:30Z")
The short answer to how to configure your warp-drive ship as a time machine is that your ship also needs to have conventional engines, and the top speed attainable by your regular engines times the top effective speed attainable by your FTL drive has to be greater than c^2. Then it’s just a matter of getting up to the right velocity using your conventional engines before engaging the warp drive.
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