Alcubierre warp drive

[doctorevilbrain]

Then why was shrinking the ship and going into it mentioned?

[Andrew Hackard]

I just removed an off-topic tangent that was bordering on personal attack territory. I strongly recommend NOT going back down that road.

[Anaraxes]

Originally Posted by doctorevilbrain

Then why was shrinking the ship and going into it mentioned?

Because that's one approach to envisioning the effects of the math in a later paper -- not Alcubierre's original one, so Alcubierre wouldn't have mentioned it, but follow-up work done by others*, inspired by Alcubierre's result. That paper showed a dramatic decrease in the amount of energy (or mass, if you prefer) required to form a warp by using a shape of spacetime that has that wormhole mentioned earlier in the thread. A tiny wormhole works better than a larger one for the purpose of warping, apparently the tinier the better as long as it still exists. But that leaves you with the problem of how to get the ship through that tiny wormhole.


--
* Chris van der Broeck, "A `warp drive' with more reasonable total energy requirements". Sergui Krasnikov followed up that paper with a modification that reduced the requirement to a few milligrams. The infamous Harold White also had a paper that showed a reduction in matter requirements down to about 1000 kg.

[doctorevilbrain]

Harold White is infamous? Why? I've read about him.

[MrTim]

Originally Posted by doctorevilbrain

Harold White is infamous? Why? I've read about him.

His EM Drive would be a dramatic game changer if it works, but very few in the field seem to believe it works.

[Varyon]

Originally Posted by doctorevilbrain

Harold White is infamous? Why? I've read about him.

Infamous means being well known for something bad (in this case, controversial claims of creating a reactionless drive), it doesn’t mean “not famous.”

And this is an interesting thread, going to reread Luke’s post to see if it finally helps me understand the whole “FTL = time travel” idea.

[Phantasm]

Originally Posted by Varyon

And this is an interesting thread, going to reread Luke’s post to see if it finally helps me understand the whole “FTL = time travel” idea.

Near as I can tell (I'm not a physicist; my sister has a double masters in Math and Physics, though), the whole "FTL = time travel" idea comes from Einsteinian physics and time dilation where as you approach the speed of light in a vacuum (c), observed time (t)slows down. Exceeding c (such as with the hypothetical tachyon particles) means that t is a negative. How that meshes with quantum mechanics or the proposed Alcubierre drive, I have no clue.

And there's also the idea that plotting a wormhole means that you're creating a pathway between points A and B means putting B where you can observe it, not where you calculate it to really be. For example, calculating a wormhole between Earth and Alpha Centauri means making a 4.3 lightyear trip, which at c takes 4.3 years, but puts you where Alpha Centauri is in the sky, or where it was 4.3 years ago, and hence putting you 4.3 years in the past.

Of course, some settings can (and should!) ignore this by saying that computations of the destination include taking proper motion and radial velocity of the target location into account, so that when you reach Alpha Centauri you are roughly where it really is when or after you left, or will be when the trip ends (if said trip is to take 3 years, where it will be three years from departure).

[Agemegos]

Originally Posted by Phantasm

Near as I can tell (I'm not a physicist; my sister has a double masters in Math and Physics, though), the whole "FTL = time travel" idea comes from Einsteinian physics and time dilation where as you approach the speed of light in a vacuum (c), observed time (t)slows down. Exceeding c (such as with the hypothetical tachyon particles) means that t is a negative.

Not quite. It comes from the offset term in the Lorenz transformation for t, not from the time dilatation term. It's easiest to explain with simple algebra or a space-time diagram, and you have to familiarise yourself with the Lorenz transformations first.

It's best not to try to guess what the physics is here. With all due respect, if you haven't studied it, please don't try to explain it.

[Anaraxes]

Originally Posted by Varyon

see if it finally helps me understand the whole “FTL = time travel” idea.

Give this page a try. It has some space-time diagrams that show how to construct a causality-violating loop given FTL comms.

[Anthony]

Originally Posted by Varyon

And this is an interesting thread, going to reread Luke’s post to see if it finally helps me understand the whole “FTL = time travel” idea.

It's basically a side effect of frame invariance. In relativity, if two events occur at different locations, two different inertial reference frames can disagree about which event came first. Thus, if you have a means of changing from one reference frame to the other, and you can travel between those two locations in less time than the disagreement, you can travel backwards in time. The disagreement, if you pick your frames correctly, can be any value less than the time it takes for light to travel between the two locations.