Alcubierre drive

mnielsen1

Amen

mnielsen1

Looking at PF i do see that, love the conversation

George Jones

See also the review

http://arxiv.org/abs/0710.4474.

mnielsen1

So, any idea what this "exotic matter" is or might be? Whatever works?

PAllen

There is no known form of it or place for it in current theories except in very limited quantities. For example. look up the Casimir effect for a limited case known from theory and experiment. So you would be looking to to somehow do this on a very large scale.

djg1508

Supposing the energy problem had been solved and your ship had all the energy it needed at its disposal. My question is; "What would you do with the energy?"
How would it be expended? How would it be radiated? - If this was just an engineering problem, what would be the solution?
Would it be channelled as electricity through metal coils to generate intense electo-magnetic fields? Or would it need to be used in some other way?

Sorry if its a basic question, but all the talk seems to be about generating the energy and not how you would use it!

Simon Bridge

Welcome to PF;
Once you have the energy - finding uses for it (guessing you mean: "when it isn't being used for the drive") usually takes care of itself. I imagine the military may want to release it all in one go at the destination for example.

A lot of the answer will depend on what form the energy takes and how much there is.
Without that information - there is no way to answer.

PAllen

I hope you realize that what is needed for all these devices is 'exotic matter' not normal mass/energy. This exists, so far, only in tiny quantities due to quantum effects. I don't think anyone knows how, if it existed in large quantities, how it could be maniputated or would behave.

djg1508

Thankyou Simon.

No, I think you misunderstand me (probably because I didnt explain itvery well)
What I mean is; What do you do with the energy in order to make it create a warp-bubble?

If you had tonnes of anti-matter and tonnes of matter - all contained and ready to be borught into contact to generate energy the the energy generated would be in the form of photons - essentially heat & light - how would you then use this (electromagnetic) energy to create a warp bubble?

PAllen

You continue to misunderstand that you can't make a warp bubble at all from normal matter or energy. You need 'exotic matter', which means matter with properties unlike any known matter or energy (except or tiny regions like the Casimir effect).

djg1508

So why is it that all of the posts and articles refer to "not having enough energy"

If it is 'exotic matter' you need and not energy then I re-phrase my question; "What would you do with the exotic matter to make a warp bubble"?

PAllen

Exotic matter has an energy equivalent; the problem is worse, the more you need. The scholarly articles do mention it, but don't always highlight it because it is one of those obvious things the intended audience doesn't need to be reminded of. As for popular articles, they are simply quite commonly erroneous.

I am not aware of any theoretically well motivated approaches for building a warp bubble. The main effort in such theoretical investigations is simply to reduce the required amount of exotic matter.

Please see the abstract [also, the contents if you want more detail] of the review paper posted by George Jones above:

http://arxiv.org/abs/0710.4474

There are also analyses of the what would happen to the occupant of a warp bubble, and to the planet they got near. These show the occupants would be vaporized, and the destination would be vaporized. It is fun to speculate on these ideas, but it is wildly unlikely anything will come of it. In pop sci speculative mode, or sci fi stories, you ignore or minimize the problems.

Simon Bridge

I did, indeed, misunderstand you :) Let's see if I have you now: PAllen has already explained that the energy is a special kind - it's negative. This implies that the matter is "exotic" - i.e. it has a negative mass.
http://en.wikipedia.org/wiki/Exotic_...#Negative_mass

To get a warp-envelope, you have to make your exotic matter into a particular shape. That's in the articles... some sort of torus is favorite.
Probably the simplest way to think of this is that you are trying to make a gravitational field that is a very unusual shape. In GR, gravity is described by curving space-time - and space-time curves in response to energy distributions... which is why there is all this talk about energy requirements: matter has mass which is very dense energy - so it is handy for making gravity.

Unfortunately the gravitationat field needed to go FTL without breaking any of the Rules is so weird that the matter/energy needed may not even exist (up until recently, imaginary matter would mean that the situation is certainly not possible!) but the investigation may tell us something about the relationship between GR and QM.

That help?

djg1508

Thanks for sticking with me on this!

So to bring it back to a 'hypothetical' question of engineering;

Assuming you had access to the right kinds and amounts of exotic matter, you would simply put one kind of matter at the front of the ship and the opposite kind of matter at the rear of the ship to make it go?

Or, in terms of energy;

Emit the right kind of particles at the front and the right kind of particles at the rear?

Simon Bridge

No - you need it to be the right shape as well.
But that's the basic concept... very very basic.

You also need to revise your ideas about the relationship between particles and energy.

djg1508

In what way "revise"?
I'm just interested in what set of physical\mechanical attributes and their distribution in relation the vessel would need to exist in order for the vessel to begin to create the space-time distribution around itself that would propel it in a given direction.

The emphasis has so far been on the impracticalities of;
Producing the energy required
Obtaining right kinds of 'exotic' matter
Handling the amounts of 'exotic maater'
The radiation problems
The problems of destroying your destination etc...

I'm aware of all those issues and im not really interested in those issues, as I realise this ship isnt going to get built any time soon.

I was just wondering, theoretically, what you would have construct (schematicallY0 from an engineering point of view in order for the vessell to to go! Or rather space-time go around it.

So far the diagrams show the shape of the warp bubble and how space-time would need to be warped around with a dip at one side and a peak at the other etc... but I cant see any indication of what (mechanically) the ship would need to be doing to create this shape. (theoretically of course)

1977ub

If you could go FTL, you could go backwards in time. That in itself may be the most damning bit of evidence against the possibility.