Alcubierre Drives, Matter, Space and everything else.

Hi.
This thread was inspired by the debate taking place in this other thread:
Speedy neutrino mystery likely solved, relativity safe after all
There, the discussion touched aspects of relativity that made me remember an article I had read earlier, which is:
The Alcubierre Warp Drive
about the theoretical proposition by Miguel Alcubierre of a ship that would create a wave in space-time, essentially, and I quote:

Alcubierre's warp is constructed of hyperbolic tangent functions which create a very peculiar distortion of space at the edges of the flat-space volume. In effect, new space is rapidly being created (like an expanding universe) at the back side of the moving volume, and existing space is being annihilated (like a universe collapsing to a Big Crunch) at the front side of the moving volume. Thus, a space ship within the volume of the Alcubierre warp (and the volume itself) would be pushed forward by the expansion of space at its rear and the contraction of space in front.

Fancy cute pic:



Now, what made me remember this article was this commentary by CLPrime:

Originally posted by CLPrime

And my first point was that this is not actual velocity. Universal (metric) expansion is not motion. The space between objects is growing, objects are not moving farther apart.

I "understand"... expansion, as in, I can at least wrap my head around it if I ignore all the stuff inside....

But that article made me ask the question I always ask about this:

1) what effects would the creation of this "wave" in space-time have on the surrounding space and "stuff in space"?
and
2) What is the difference between matter and space?
(which I asked "off-topicly" in the cited thread so, sorry about that )
I know number 2 sounds stupid, but I could never see the real difference, beside the obvious...

I would apreciate any educated soul that lends me a hand on this.

Thanks

Drakus

1. I am unsure as to the effects of the warping of 4d space but the first thought that comes is that the expansion and compression would balance out, however upon further thought on it, the energy required to do both would be cumulative rather than cancelling each other. So I am unable to predict the effects especially regarding the conservation of energy principle and how it would affect net thrust.

2. I know exactly what you mean. In the Einstein model, matter and energy are interchangeable due to no area of space being 0K, hence having energy, and by transposition of e=mC2, mass. So in effect, the only difference between matter and space is the state of matter/energy.

Hope that made sense to someone other than me.

reply to post by Morgil


To complicate your thoughts, "space" is the container within which matter / energy occupy. So to create space, the matter / energy within would need dealt with and as they cannot be eliminated altogether, in my mind, the only way to do so would involve moving whats in front of the vessel to the rear. Theoretically, displacing such into a higher dimension then retrieving would be one way of accomplishing that. Perhaps some sort of "transporter" that permits quantum tunneling through the vessel could accomplish this as well.

reply to post by abecedarian


Aye, I see where you're coming from, but if you really want a headache, consider this; could space exist with the absence of matter or energy? If not, removing one or both from an area of space in front of the hypothetical craft could create a perfect compression at the forward edge (perhaps creating unlimited potential velocity?). However, if space can exist without energy/matter, then is it impossible to compress the space when there is 0 energy to remove or manipulate?

reply to post by Morgil


True. I suppose the questions needs answered: does space exist because of energy / matter, or does energy / matter exist because of space or are all one-in-the-same? And I fear we're now bordering on requiring "dark" energy / matter / aether, aren't we?

If they are mutually inclusive, perhaps the act of transposing the energy / matter from the front of the vessel to the rear would acheive a "vacuum" of sorts in front, pulling the vessel, and "pressure" behind, pushing the vessel.

reply to post by abecedarian


I do love a good physics debate.

I believe you are right about the expansion V compression component but my only concern is the net gain in reference to input energy. I do believe the Alcubierre drive has some promise, it's a matter of getting the output E > Input E

We need to come up with a power source that can accomodate that (vacuum energy?)

Originally posted by Morgil
reply to post by abecedarian

 

I do love a good physics debate.

I believe you are right about the expansion V compression component but my only concern is the net gain in reference to input energy. I do believe the Alcubierre drive has some promise, it's a matter of getting the output E > Input E

We need to come up with a power source that can accomodate that (vacuum energy?)

This isn't a debate; it's a discussion.
I do wish the OP was more involved though.

Motion always requires an energy source... confoundit.

Would it be possible to create a toroidal magnetic field with the center of the vessel wrapped around the center of the torus? Would the magnetic field then draw some matter/energy through the center of said vessel and deflect other matter/energy around the outside of said vessel? Should the magnetic field alternate polarity periodically, perhaps based on velocity, so matter/energy internal and external to the vessel would be drawn in / around the vessel, then repelled thus producing motion?

reply to post by abecedarian


I didn't mean the confrontational aspect of debate, more the productive discussion.

On the toroidal aspect, due to the toroidal model, there would be no inherent directional thrust without an outside force. Perhaps a toroidal model with a pulsed increase in power by some form to produce a net vectorial thrust?

Originally posted by Morgil
reply to post by abecedarian

 

I didn't mean the confrontatinal aspect of debate, more the productive discussion.

No qualms. I like thought discussions such as this.

On the toroidal aspect, due to the toroidal model, there would be no inherent directional thrust without an outside force. Perhaps a toroidal model with a pulsed increase in power by some form to produce a net vectorial thrust?

I think that if the magnetic field strength were increased, it would only increase the diameter of the torus, possibly putting the vessel in the center of the torus thus drawing matter / energy to the vessel, not through it instead of increasing the effective attraction / repulsive force. Perhaps multiple fields could be created which alternate polarity much like a centipede walking... say 5 fields where the first, third and fifth are "north" pole in the center and the second and fourth are "south" pole, then periodically, they all go neutral then reverse polarity in such a way that inertia keeps matter moving until poles reverse, and then become repulsive, ejecting matter / energy out the rear.

Make sense?

Originally posted by drakus

1) what effects would the creation of this "wave" in space-time have on the surrounding space and "stuff in space"?

As long as the wave (actually, more of a bubble from our perspective) is well-contained, it should have no effect. If the warping of space (so-to-speak) were significant enough outside to affect "stuff in space," then it would be significant enough inside to affect the ship riding inside it. This, obviously, is a rather undesired result... we want our ship to have a smooth ride inside the bubble, not become part of it. So, given this thin shell-like warping, there should be no affect whatsoever on "stuff in space". Unless, of course, you run into something as you're travelling - which is another matter entirely.

2) What is the difference between matter and space?

In General Relativity, spacetime is a tensor field, while, according to Quantum Mechanics, matter is a waveform (or a superposition of multiple waveforms) within (and affecting) that tensor field. If you need either, or both, of those explained further, I'll be more than happy to do so...tomorrow, when I'm more awake.

Originally posted by drakus
1) what effects would the creation of this "wave" in space-time have on the surrounding space and "stuff in space"?
and
2) What is the difference between matter and space?
(which I asked "off-topicly" in the cited thread so, sorry about that

)
I know number 2 sounds stupid, but I could never see the real difference, beside the obvious...

Thanks for starting a thread instead of going too far off topic in the other thread, I think they are interesting questions.

My short answer to both is I don't know, but I can give you some thoughts.

1. The warp drive isn't without some basis in physics, but it is sort of science fiction until we can confirm the concept. It's unclear if such a warp drive can be made, and if so, whether it would work.

I don't know if you ever watched Star Trek The Next Generation, but they must have used scientific consultants for the show because they explored this very question in one episode.

en.wikipedia.org...:_The_Next_Generation%29

"Force of Nature" is the 161st episode of the science fiction television series Star Trek: The Next Generation.
...
In this episode, a pair of sibling scientists show that warp drive propulsion is harming the very fabric of space.

Whether that could actually happen or not is anybody's guess. But I'm reminded of our air conditioning invention using freon that would have eventually damaged the ozone layer, possibly severely, thereby harming all life on Earth including us, so that's at least one example where we didn't do enough looking before we leapt. Warp drive tech would use some pretty powerful forces so the idea of unintended consequences isn't unthinkable. But I doubt anybody really knows. Until we can actually build it, it's pretty speculative and so therefore are any potential side effects.

2. This cosmology FAQ is pretty good. If I understand your question this may touch on an answer:

Are galaxies really moving away from us or is space just expanding?

This depends on how you measure things, or your choice of coordinates. In one view, the spatial positions of galaxies are changing, and this causes the redshift. In another view, the galaxies are at fixed coordinates, but the distance between fixed points increases with time, and this causes the redshift. General relativity explains how to transform from one view to the other, and the observable effects like the redshift are the same in both views. Part 3 of the tutorial shows space-time diagrams for the Universe drawn in both ways.

Is that what you were after?

Also see the next item, "Why doesn't the Solar System expand if the whole Universe is expanding?" that's somewhat related.

Another aspect we can comment on is the mathematical relationship between matter, energy, and space.

We know the relationship between mass and energy, it's E=mc^2. The relationship between matter and space is not known. We do kmow that space has energy, which could be considered a mass equivalent. But nobody is really sure how much. Here's a good explanation which looks at 5 different approaches for correlating energy with space, and if you know how much energy is in space, you know the mass equivalent in that space from E=mc^2:

What's the Energy Density of the Vacuum?

So, I've given you 5 answers to the same question:

VERY CLOSE TO ZERO
INFINITY
ENORMOUS BUT FINITE
ZERO
NOT DETERMINED

Which should you believe? I believe 1) because it is based on experiment and fairly conservative assumptions about general relativity and astronomy. Answers 2)-4) are based on somewhat naive theoretical calculations. Answer 5) is the best that quantum field theory can do right now. Reconciling answers 1) and 5) is one of the big tasks of any good theory of quantum gravity.

The moral is: for a question like this, you need to know not just the answer but also the assumptions and reasoning that went into the answer. Otherwise you can't make sense of why different people give different answers.

So that relationship is unknown. If we figure out the dark energy mystery, that may help answer the question.

I hope that helps, but if it's not what you were after just clarify your question.

reply to post by abecedarian


Aye, but would it produce a simultaneous increase to maintain magnitudes? or an increase in wavelength, thereby reducing amplitude?

How about opposing directional fields? They cancel out in a vector form, but in terms of flux density, it doubles leaving just a direction vector component requiring to be added. Is it possible to apply that to a propulsion theory?

Originally posted by Morgil
reply to post by abecedarian

 

Aye, but would it produce a simultaneous increase to maintain magnitudes? or an increase in wavelength, thereby reducing amplitude?

How about opposing directional fields? They cancel out in a vector form, but in terms of flux density, it doubles leaving just a direction vector component requiring to be added. Is it possible to apply that to a propulsion theory?

Now you have me thinking WWGRD... (What Would Gene Roddenberry Do.... )

As many materials are not affected by magnetic fields, seems my thought process is inherently flawed.

The next thing that jumps out at me would be simultaneously creating and destrying a singularity ahead of the vessel... but I'm sure there's something I haven't thought of (like how to destroy it for instance).

In General Relativity, spacetime is a tensor field, while, according to Quantum Mechanics, matter is a waveform (or a superposition of multiple waveforms) within (and affecting) that tensor field.

Not sure if I understand this. Spacetime a field? I'd call it a manifold (with a metric tensor). Which is a fancy way to say that it has dimension and a way to calculate distance between two points. But then I am not that much into differential geometry and General Relativity.

reply to post by moebius


Spacetime is certainly a manifold, but that manifold is a tensor field. And it is a metric tensor field, because, in 4-dimensional spacetime, the metric measures the curvature of that space, which is an indirect description of the forces acting on it - which, itself, is described by a separate tensor field (specifically, the stress-energy tensor).

reply to post by CLPrime


So, how would a ship create this "shell-like" wave-bubble in the "metric tensor field", and of sufficient thinness as to not be destructive to nearby matter, as described in the OP's linked article?

What would happen to external objects (space dust, rocks, other ships, asteroids, planets, ...) that happened to lie in the path of an Alcubierre ship and entered the region of distorted space-time at the leading edge of the warp, where space is rapidly being collapsed? The nuclei of any matter transiting that region would first experience enormous compressional forces, probably form a quark-gluon plasma reminiscent of the first microsecond of the Big Bang, and then explode in a flood of pi mesons and other fundamental particles when the compression forces were released, stealing energy from the warp field in the process.

reply to post by Larryman


That's the problem. Exotic matter is needed to warp space in such a way. A lot of it. At the moment, we don't even know if exotic matter exists, let alone being able to create it in such vast quantities.

Would it require 100 tons of exotic matter to create the wave-bubble around a 100-ton ship? Or is it like I've read... a planet Jupiter quanity of mass (exotic matter ?) to do it?

reply to post by Larryman


More in the range of a couple solar masses. Initial models gave amounts many times the mass of the observable universe.

reply to post by CLPrime


Ok, thanks. I'll stick with "Extended Heim Theory" then. I don't think it has such outrageous exotic matter requirements. It uses a different principle of operation for it's f-t-l travel - the elimination of mass from matter. It seems more acheivable to me, than warp drive.