## NASA's Warp Drive Question

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Mondo Bandeenie
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### NASA's Warp Drive Question

I was intrigued by the possibility of NASA creating a warp drive, through expanding space time behind the craft and contracting space-time in front of it. This doesn't seem to work to me: as the ship moves into the contracted space-time, wouldn't it also contract, and therefore travel relatively at the same speed? Or do they uncouple the ship from space-time?!

As you can probably tell, I'm not a physicist! So there might be something wrong with the way I'm understanding the process, or the way that the layman's press is reporting it, but any clarification would be super-duper.

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### Re: NASA's Warp Drive Question

Mondo Bandeenie
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### Re: NASA's Warp Drive Question

Yes, I was.

AvatarIII
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### Re: NASA's Warp Drive Question

In terms of the engine's mechanics, a spheroid object would be placed between two regions of space-time (one expanding and one contracting). A "warp bubble" would then be generated that moves space-time around the object, effectively repositioning it — the end result being faster-than-light travel without the spheroid (or spacecraft) having to move with respect to its local frame of reference.

yes, basically the space-time around the ship is "decoupled" from the rest of space-time.

If anything about it doesn't make sense to me, it's the fact that they say that it will use a certain, exact amount of energy.
Is that amount the minimum to get a tiny amount of space-time warping? if so you would need a lot more for a lot of space-time warping.
Or does the amount you warp space-time have no bearing on the energy put in? that doesn't really make sense
Or is that amount of energy the amount you need for practical FTL space-flight? If so, surely you could prove the concept using a much smaller amount of energy and space-time distortion in the lab right? I assume the 3rd option is correct right? Since the end of the article talks about "the Chicago pile moment" implying that getting a proof on concept on a small scale is the major step, followed by simple up-scaling.

gmalivuk
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### Re: NASA's Warp Drive Question

AvatarIII wrote:Or is that amount of energy the amount you need for practical FTL space-flight?
Wikipedia describes it as the energy required for "a macroscopic" ship, so yes.
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Spambot5546
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### Re: NASA's Warp Drive Question

Isn't this kind of thing supposed to be impossible regardless of your local reference frame? Something about time travel paradoxes?
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gmalivuk
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### Re: NASA's Warp Drive Question

The center of the bubble is causally disconnected from the rest of the universe, which among other things means you can't break causality with the Alcubierre drive.
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doogly
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### Re: NASA's Warp Drive Question

It also means you can't enter or exit the bubble, so using it as a means of transportation seems a bit odd.
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Gigano
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### Re: NASA's Warp Drive Question

doogly wrote:It also means you can't enter or exit the bubble, so using it as a means of transportation seems a bit odd.

If that is trulely so, then using it can be seen as a one-way-trip. This makes the effect of using it a little too permanent for my taste, but it could still be useful.

However, isn't the ship or whatever is in inside the Alcubierre field only causally disconnected from the rest of the universe IF and WHEN the field is 'active', shall we say? Isn't it simply a matter of turning the drive on, becoming causally disconnected, travel for some desired distance, turn it off and then be (as it were) re-integrated into the rest of the universe? Or is this last action not possible?
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PM 2Ring
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### Re: NASA's Warp Drive Question

Gigano wrote:Isn't it simply a matter of turning the drive on, becoming causally disconnected, travel for some desired distance, turn it off and then be (as it were) re-integrated into the rest of the universe? Or is this last action not possible?

Those are the big questions. Even if you can create a conveniently-sized Alcubierre field without needing exotic negative energy matter (which probably cannot exist) and a ridiculously vast amount of energy, it may not be safe to be in the vicinity when you torture spacetime to such an extreme degree. Similar considerations apply to turning it off. Actually, it'd be nice to know if the field can be turned off once it's formed, and whether it's possible to do so from inside the bubble.

Other problems with the Alcubierre drive include the difficulty of steering it and controlling its motion. Also, it may create enormous amounts of high temperature Hawking radiation inside the bubble if you try to travel at superluminal speeds.

Tchebu
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### Re: NASA's Warp Drive Question

I find it really hard to believe that such configurations of spacetime can be made from nearly flat spacetime and back into flat spacetime in finite time and not have such processes invade microscopic physics on a noticeable level...

But I haven't seen any of the math, so what do I know...
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Mondo Bandeenie
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### Re: NASA's Warp Drive Question

gmalivuk wrote:The center of the bubble is causally disconnected from the rest of the universe, which among other things means you can't break causality with the Alcubierre drive.

AvatarIII wrote:yes, basically the space-time around the ship is "decoupled" from the rest of space-time.

This is the bit that I have trouble with! If this is possible, does that mean we've already causally disconnected things from the universe? What would happen if these became a common spaceship feature: would overlapping bubbles affect each other? Would FTL communication be possible over these bubbles?

Mondo

AvatarIII
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### Re: NASA's Warp Drive Question

Mondo Bandeenie wrote:
gmalivuk wrote:The center of the bubble is causally disconnected from the rest of the universe, which among other things means you can't break causality with the Alcubierre drive.

AvatarIII wrote:yes, basically the space-time around the ship is "decoupled" from the rest of space-time.

This is the bit that I have trouble with! If this is possible, does that mean we've already causally disconnected things from the universe? What would happen if these became a common spaceship feature: would overlapping bubbles affect each other? Would FTL communication be possible over these bubbles?

Mondo

God knows, but if science fiction has taught me anything, when FTL drives go wrong, they open holes to hellish dimensions. so yeah, don't do that.

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### Re: NASA's Warp Drive Question

That'd be because a film about astronauts getting quickly fried by various forms of radiation wouldn't make for much of a horror.

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### Re: NASA's Warp Drive Question

Mondo Bandeenie wrote:
gmalivuk wrote:The center of the bubble is causally disconnected from the rest of the universe, which among other things means you can't break causality with the Alcubierre drive.

AvatarIII wrote:yes, basically the space-time around the ship is "decoupled" from the rest of space-time.

This is the bit that I have trouble with! If this is possible, does that mean we've already causally disconnected things from the universe? What would happen if these became a common spaceship feature: would overlapping bubbles affect each other? Would FTL communication be possible over these bubbles?

Mondo

No, because such a device has never been built and is, in all likelihood impossible to build. I don't know enough about the exact mechanics of the bubbles (if such things are actually possible), but it seems to me that, like event horizons, if they get close enough they should simply merge.
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snowyowl
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### Re: NASA's Warp Drive Question

eSOANEM wrote:No, because such a device has never been built and is, in all likelihood impossible to build.
eSOANEM wrote:I don't know enough about the exact mechanics of the bubbles

So... [citation needed].
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### Re: NASA's Warp Drive Question

snowyowl wrote:
eSOANEM wrote:No, because such a device has never been built and is, in all likelihood impossible to build.
eSOANEM wrote:I don't know enough about the exact mechanics of the bubbles

So... [citation needed].

Knowing the exact mechanics of the bubbles requires solving a system of 10 non-linear partial differential equations. As such it is well beyond the scope of a forum post.

It does not however require any knowledge of the bubble mechanics to see that they are almost certainly impossible. This follows simply from the fact that the Albubierre solution requires significant negative energy density (whereas, with the exception of the Casimir effect and a few other quantum phenomena which only generate small amounts at scales far too small to be exploited for a warp drive, energy density is always positive).

Some calculations have been done showing that it would require -10^64kg worth of energy to transport a reasonably sized ship across the milky way, this being vastly greater than the estimated mass of the universe.
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doogly
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### Re: NASA's Warp Drive Question

Almost certainly. Quantum field theory in curved space is weird though. It is very hard to actually prove wormholes, warp drives and time machines are impossible.
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gmalivuk
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### Re: NASA's Warp Drive Question

Yes, and there are other calculations suggesting a negative energy requirement of only a few milligrams, and positive energy of about one metric ton.
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### Re: NASA's Warp Drive Question

The real way to address the possibility of these things is based on the requirement that you achieve some net or average negative energy across a complete null geodesic. That is what seems like it might be difficult.
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Frenetic Pony
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### Re: NASA's Warp Drive Question

eSOANEM wrote:
snowyowl wrote:
eSOANEM wrote:No, because such a device has never been built and is, in all likelihood impossible to build.
eSOANEM wrote:I don't know enough about the exact mechanics of the bubbles

So... [citation needed].

Knowing the exact mechanics of the bubbles requires solving a system of 10 non-linear partial differential equations. As such it is well beyond the scope of a forum post.

It does not however require any knowledge of the bubble mechanics to see that they are almost certainly impossible. This follows simply from the fact that the Albubierre solution requires significant negative energy density (whereas, with the exception of the Casimir effect and a few other quantum phenomena which only generate small amounts at scales far too small to be exploited for a warp drive, energy density is always positive).

Some calculations have been done showing that it would require -10^64kg worth of energy to transport a reasonably sized ship across the milky way, this being vastly greater than the estimated mass of the universe.

The entire point of this story working it's way around the internet was a new paper, I wish I remembered where, showing the energy requirements for such a drive to be far less than was first assumed by Alcubier. Regardless, I do specifically remember it being shown to be quite physically possible to get those energies in practical terms we might be able to achieve. Now to just find the paper...

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### Re: NASA's Warp Drive Question

Frenetic Pony wrote:The entire point of this story working it's way around the internet was a new paper, I wish I remembered where, showing the energy requirements for such a drive to be far less than was first assumed by Alcubier. Regardless, I do specifically remember it being shown to be quite physically possible to get those energies in practical terms we might be able to achieve. Now to just find the paper...

Here you go. It's something of an astonishing result on the face of it. I'd like to see what the reaction among the experts is before I get too excited. Anyway, there's still the problem of how to continuously get from a flat spacetime into the "warp bubble" and then out again.

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eSOANEM
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### Re: NASA's Warp Drive Question

Frenetic Pony wrote:The entire point of this story working it's way around the internet was a new paper, I wish I remembered where, showing the energy requirements for such a drive to be far less than was first assumed by Alcubier. Regardless, I do specifically remember it being shown to be quite physically possible to get those energies in practical terms we might be able to achieve. Now to just find the paper...

I may have overstated the case, however the main thrust of my post was simply that "such a device has never been built" in response to Mondo Bandeenie's question as to whether we had already causally separated regions of spacetime.

Furthermore, like AvatarIII says, we still don't know of any way to turn a flat spacetime into an Alcubierre-like one and, let alone any way of creating a bubble around something (as opposed to growing the bubble from a point).
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