Warp drive, then where are we?

[SpaceTiger]

But, of course, no system can be 100% efficient in converting matter to energy.

You're absolutely right and I should have included a little remark about that. In a hypothetical futuristic warp drive, however, we can probably consider this factor to be of order unity (i.e. less than an order of magnitude from 100%).

 

[ohwilleke]

A variant on a warp drive which poses considerably fewer engineering challenges would be essentialy an extremely powerful slingshot. You would put your payload in some sort of large ring and slowly power them up to nearly "c" with an external power source, and you would use gravitational braking (and perhaps space dust and interstellar radiation) to bring the amount of energy you need to carry as fuel to slow down to considerably less than $$E_k$$ for the payload, which would still be predominantly fuel, but perhaps not nearly so impossible as a ship that needed to speed itself up and slow itself down.

Of course, once the first crew gets to the destination, they then build the starship equivalent of an aircraft carrier tail hook system to move as much as possible of the braking energy off the ship as possible (e.g. with a series of targetted electromagnetic beams directed in such a way as to decellerate the ship at a tolerable rate). A shift from a $$2E_k$$ carried energy requirement to a $$0.8E_k$$ energy requirement dramatically reduces the engineering challenges involved.

Naturally, the first crew also has to build its own slingshot to return, and when they return, they find the planet they left is 100,000+ years older.

Also, given the immense energy cost you are paying to shorten the ride for the passengers with special relativity, it would probably be more likely that any such ship would either rely on some form of biostasis (essentially hibernating the people on board for a very long time), or would be multi-generational carrying a community in which the original crew's descendants, perhaps many generations later, are the ones who actually arrive at their destination.

 

[matt.o]

SpaceTiger, I too have had the problem of people asking about special relativity and why you can't travel faster than the speed of light. I have found that if you explain that the constancy of the speed of light was observed experimentally by the Michelson-Morley experiment, then normally this is enough.

I think a common misconception with the general public (and some physicists) is the belief that Einstein came up with SR and GR out of no where (complete with a light bulb above his head!), when in fact he was just attempting to explain some observed phenomena.

 

[AcEY]

FTL travel would surely be possible if we found a way to create a weightless material. Unfortunatly that's impossible (although if i believed quantum mechanics then if i kept trying eventually it may happen). I was thinking, maybe we could create some kind of bubble that would make us weightless, but in technology terms its far into the future for something like that. And Dave on the making worm holes into a time machine, i believe that you somehow connect one end to your ship and fly at sub-light speeds (but close to light speed) so that time dilation occurs and one end is older than the other - like the "Twin Paradox" (Being that if one twin went on a ship and flew at close to light speed then came back, due to length contraction - not time dilation as both twins would age the same amount - be different ages). But some theorise that when you bring the end of the wormhole back together with the other end (to have them close enough to be a wormhole) a light feed back loop would occur (light would go in one end and come out the other, because one end is in the past the light could then go back in at the same time as it originally went in and keep doubling up) until it exploded.

 

[SpaceTiger]

FTL travel would surely be possible if we found a way to create a weightless material.

Actually, a massless object would move at the speed of light.

 

[AcEY]

hrm ok, well anyway. If we found a way to travel faster than the speed of light, I am guessing at this point we would also find a way to get from FTL to sub-light which is apparently impossible as well, and you didnt travel into the past then we could level journeys out so that when we arrived it would be the same time as we left, imagine never having to leave 30 mins before work starts, you could just be there when you leave.

sorry i meant to point out that traveling into the past would be more useful, but would probably be illegal due to paradoxes.

 

[JesseM]

Against wormholes:

http://www.arxiv.org/abs/gr-qc/0503097

Date (revised v3): Fri, 8 Apr 2005 19:54:25 GMT (6kb)

Wormholes and Time Travel? Not Likely
Authors: Leonard Susskind
Comments: 5 pages, remark added about time delay in identification. Reference added

Wormholes have been advanced as both a method for circumventing the limitations of the speed of light as well as a means for building a time machine (to travel to the past). Thus it is argued that General Relativity may allow both of these possibilities. In this note I argue that traversable wormholes connecting otherwise causally disconnected regions, violate two of the most fundamental principles physics, namely local energy conservation and the energy-time uncertainty principle.

Susskind later realized that that paper contained some elementary errors and basically retracted the whole argument:

http://www.arxiv.org/abs/gr-qc/0504039

Rebuttal to a Paper on Wormholes
Authors: Leonard Susskind

In a recent paper on wormholes (gr-qc/0503097), the author of that paper demonstrated that he didn't know what he was talking about. In this paper I correct the author's naive erroneous misconceptions.

 

[ohwilleke]

Susskind later realized that that paper contained some elementary errors and basically retracted the whole argument:

http://www.arxiv.org/abs/gr-qc/0504039

I'd seen the pair, but hadn't caught the sweet irony that the reply and the original were by the same person.