# Warp theory vs causality

1. Jan 24, 2014

### Dhruva Patil

I have heard many physicists (ex:- Michio Kaku) saying "Warp speed" from Star Trek doesn't violate any known physical laws. But doesn't it violate causality?
Say, we make warp speed possible and get on it and travel towards Alpha Centauri (4.22 light years away) in warp speed and reach there, say, within a year (+/- few months) and blow it up. Now using Special Relativity, we could devise a frame of reference where in the observer would see the star blow up before we ever left planet Earth. Wouldn't that violate causality and make warp speeds unattainable?

2. Jan 24, 2014

### ghwellsjr

Here's where he discusses the issue (on the next page of the article):

Sure we can do it, if only we had some negative matter, which we don't.

3. Jan 24, 2014

### yuiop

So given some negative matter and a suitable folding of space we can have superluminal transport without violating any known physical laws ... as long as we don't count causality conservation as a physical law?

4. Jan 24, 2014

### Dhruva Patil

That is not the question. I know we need Negative matter/energy which we do not have or know how to create. But if we did, could we really be able to travel at Warp Speed? Wouldn't it violate causality?

5. Jan 25, 2014

### FactChecker

If you assume that we traveled faster than light, then it's hard to figure out how much of special relativity still applies. In general though, here is something to consider. Simultaneity of events at widely separated points is different for different reference frames. So the times that things happen depend on the reference frame. For events A on the earth and B the star, it would be hard to agree if A and B were simultaneous, A before B, or B before A. The observer would agree that we blew up the star but he would not agree with us about when we left the earth.

Last edited: Jan 25, 2014
6. Jan 25, 2014

### Staff: Mentor

You can't use SR in this scenario. The process of creating the "warp bubble" and expanding and contracting space would also expand and contract time; you simply would not be able to construct an SR-style inertial frame, even an approximate one, that included all of the events in question.

7. Jan 26, 2014

### JesseM

Maybe it would depend on what's meant by "approximate one", but since the Alcubierre metric is asymptotically flat (as mentioned on the first page here), doesn't that mean that if you "zoom out" to sufficiently large scales of space and time, the warp bubble behaves like a small localized disturbance moving on a flat spacetime? If so, then if it moves faster than light, with multiple such warp bubbles moving in different directions it seems like you should be able to construct a causality paradox similar to the tachyonic antitelephone. And it has been shown that a system of multiple "warp bubbles" moving in different directions can give rise to closed timelike curves in general relativity, see the paper at http://exvacuo.free.fr/div/Sciences...tt - Warp drive and causality - prd950914.pdf.