Can Warp Drives Really Make Faster-Than-Light Travel Possible?

[tade]

Popular Science has been running an article about Sonny White, a prominent engineer at NASA's JSC.

White has been attempting to realize a warp drive as theorized by Miguel Alcubierre of UNAM in Mexico.


Warp Factor

Faster-Than-Light Drive


Negative energy, spacetime bubbles propelling a craft faster than light.

 

[1977ub]

Negative energy, spacetime bubbles propelling a craft faster than light.

... to boldly go into FTL causality violations.

 

[tade]

... to boldly go into FTL causality violations.

technically there are no CVs within the space time bubble.

 

[1977ub]

technically there are no CVs within the space time bubble.

"within the bubble" is not the problem. in the context of the surrounding universe, you are going FTL.

If you travel FTL "within the bubble" or if you do it by snapping your fingers, CV is implied. If you could fit the entire universe with you "within the bubble" then there'd be no problem CV-wise.

Here's a whole big jolly board discussion in which someone [who was a physics student at MIT] attempted to make this point and was rebutted with various assertions.
https://news.ycombinator.com/item?id=4536320

more with him:
https://news.ycombinator.com/item?id=4535481

The FAQ he refers to:
http://www.physicsguy.com/ftl/html/FTL_part4.html

You can work out a simple example with a train, a platform, and 2 FTL signaling devices which violates causality. You can arrange to be push a button and then shot with a laser beam before you pushed the button. It certainly makes no difference how the FTL signal gets there or whether causality is violated within the mechanism itself. Once you embed an intentional FTL event in a larger context, causality can easily be violated for observers/events in that larger context.

 

[cuberoot]

Yes, Alcubierre drives certainly do seem to allow causality violations and potential paradoxes. I posted about this in the other recent thread: https://www.physicsforums.com/showpost.php?p=4315097&postcount=38
Link to the paper that explains it: http://exvacuo.free.fr/div/Sciences...tt - Warp drive and causality - prd950914.pdf

 

[tade]

"within the bubble" is not the problem. in the context of the surrounding universe, you are going FTL.

If you travel FTL "within the bubble" or if you do it by snapping your fingers, CV is implied. If you could fit the entire universe with you "within the bubble" then there'd be no problem CV-wise.

Here's a whole big jolly board discussion in which someone [who was a physics student at MIT] attempted to make this point and was rebutted with various assertions.
https://news.ycombinator.com/item?id=4536320

more with him:
https://news.ycombinator.com/item?id=4535481

The FAQ he refers to:
http://www.physicsguy.com/ftl/html/FTL_part4.html

You can work out a simple example with a train, a platform, and 2 FTL signaling devices which violates causality. You can arrange to be push a button and then shot with a laser beam before you pushed the button. It certainly makes no difference how the FTL signal gets there or whether causality is violated within the mechanism itself. Once you embed an intentional FTL event in a larger context, causality can easily be violated for observers/events in that larger context.

There's a lot of confusion going on in that discussion.
On a side note, I've heard that Alcubierre's workings are perfectly valid within GR.


At least NASA is boldly going... "where no man has gone before".

 

[1977ub]

There's a lot of confusion going on in that discussion.
On a side note, I've heard that Alcubierre's workings are perfectly valid within GR.

At least NASA is boldly going... "where no man has gone before".

It seems pretty clear to me that the "confusion" exists on the part of individuals who are more enthusiastic and less educated :)

Who is the most educated person you can find who believes that FTL does not imply CV?

 

[tade]

It seems pretty clear to me that the "confusion" exists on the part of individuals who are more enthusiastic and less educated :)

Who is the most educated person you can find who believes that FTL does not imply CV?

Isn't it similar to recession velocities being FTL due to curved spacetime? I don't really know, I'm clueless on GR.


I'm new to PF, not familiar with many people yet.

 

[1977ub]

Isn't it similar to recession velocities being FTL due to curved spacetime? I don't really know, I'm clueless on GR.

I'm new to PF, not familiar with many people yet.

i was thinking in terms of scouring the internet, or reading the news. The enthusiasm that a warp drive can go FTL without raising CV issues seems to be an uninformed position.

 

[tade]

i was thinking in terms of scouring the internet, or reading the news. The enthusiasm that a warp drive can go FTL without raising CV issues seems to be an uninformed position.

True. Causality is an important principle.

But I'm not too worried about that. I hope that NASA will roll out some concrete preliminary tests soon.
It's probably a vain hope.

 

[cuberoot]

There's a lot of confusion going on in that discussion.
On a side note, I've heard that Alcubierre's workings are perfectly valid within GR.

It does not violate GR but it can be used to violate causality by making a round trip using two different bubbles. The paper I linked in post #5 here and in the other thread explains this in detail.

 

[tade]

It does not violate GR but it can be used to violate causality by making a round trip using two different bubbles. The paper I linked in post #5 here and in the other thread explains this in detail.

I guess it does. We'll just need to wait for NASA.

 

[Mordred]

I found this article fascinating on some hazards associated with the use of the alcubierre drive. If this is correct you may never want to use it.

http://arxiv.org/abs/1202.5708

 

[1977ub]

I guess it does. We'll just need to wait for NASA.

Perhaps the various interested parties at NASA are confident that some guardian angel will prevent CVs.

 

[tade]

Perhaps the various interested parties at NASA are confident that some guardian angel will prevent CVs.

Lol. If they cause CVs they might end up changing the fate of the human race or something like that.

Makes for good sci-fi at least.