How is an Alcubierre drive FTL?

[1of6Billion]

OK, If I understand things well, the theorised Alcubierre drive works by contracting space in front of the spaceship and expanding space behind it. Right?

So, does this contracting of space not take time? I would assume that contracting business would obey the speed of light.

In that case it would take 1 year to shorten your trip 1 light year. Effectively cancelling your FTL.

I am no genius. And assumption is the mother of all F.U.'s. Where am I going wrong with this?

[NASAFanboy]

I don't think it takes time.

It simply contracts the space for an starship inside the "warp bubble", not for the general universe.

I'll admit it, I'm no physicist, but I think it requires faster than light contracting of space which most probably does obey the light speed law (As far as I know).

[SargeRho]

No, it doesn't work like that. It doesn't just contract the space so that you are "pulled" across the universe, it contracts and expands the space, comparable with a wave, or perhaps catterpilar tracks.

Instead it creates a bubble of spacetime that moves faster than light, apparently up to 10 times the speed of light. Because spacetime is a cheating scumbag, it can do that.

Edited March 24, 2014 by SargeRho

[Wahgineer]

It sort of slices and dices space-time, making a surfboard for its self, and a wave that the surfboard rides on. Since space-time doesn't have to obey the light speed limit, it can contract/move at superluminal speeds without causing time dilation. Since the ship doesn't move relative to its surfboard, it doesn't experience time dilation. (i.e., the ship is moving along with the surfboard of space time, so they don't move relative to each other.)

[1of6Billion]

It sort of slices and dices space-time, making a surfboard for its self, and a wave that the surfboard rides on. Since space-time doesn't have to obey the light speed limit, it can contract/move at superluminal speeds without causing time dilation. Since the ship doesn't move relative to its surfboard, it doesn't experience time dilation. (i.e., the ship is moving along with the surfboard of space time, so they don't move relative to each other.)

That's the part I have my doubts about.

[1of6Billion]

No, it doesn't work like that. It doesn't just contract the space so that you are "pulled" across the universe, it contracts and expands the space, comparable with a wave, or perhaps catterpilar tracks.

Instead it creates a bubble of spacetime that moves faster than light, apparently up to 10 times the speed of light. Because spacetime is a cheating scumbag, it can do that.

OK, you convinced me

[Skyler4856]

That's the part I have my doubts about.

There is sufficient evidence from cosmology to support his claims.

[Sillychris]

The idea is that nothing can exceed the speed of light while travelling through space-time (actually, if you study relativity more deeply you find that everything is moving at the exact same speed through space time when you factor in moving through time as a dimension, ie photons experience no passage of time or infinite time dilation, if you prefer).

Space time can't "travel" through itself. The speed limit applies only to things that exist in space-time. The cosmologists who are a lot smarter than me seem pretty confident that there is no reason to assume there is a limit on the expansion of space time. Also, how would you define the speed at which spacetime expands since you would have to measure it in reference to spacetime?

[Winter Man]

That's the part I have my doubts about.

The fact that we have a cosmological horizon (the edge of the visible universe) shows that one area of space can move faster than the speed of light relative to another, as it's the point at which objects are travelling away so fast as that their light will never reach us.

[Sillychris]

The fact that we have a cosmological horizon (the edge of the visible universe) shows that one area of space can move faster than the speed of light relative to another, as it's the point at which objects are travelling away so fast as that their light will never reach us.

Excellent point.

[1of6Billion]

The fact that we have a cosmological horizon (the edge of the visible universe) shows that one area of space can move faster than the speed of light relative to another, as it's the point at which objects are travelling away so fast as that their light will never reach us.

In dutch we say "Het kwartje valt!" meaning: "I get it!"

Space-time can contract and expand faster than light.

[Mazon Del]

Here is sort of the cliffs notes version of how the Alcubbiere drive works for FTL.

-Matter traveling through space cannot move at lightspeed (and because to move faster than lightspeed you must at some point ever be going lightspeed, which you cannot go, you therefor cannot travel faster than the speed of light), see relativity.

-Space is stretchy/bendy, see relativity.

-Space can stretch/bend faster than light can move. This has been theorized for a while, and with the recent discoveries pertaining to the Big Bang is mostly proven to be true with some estimates stating that during the moments after the Big Bang space stretched at speeds in excess of 10,000-100,000 times the speed of light.

-Matter inside of stretched/bent space (within reasonable amounts of stretched/bent, IE blackholes go too far!) is unaffected by this, except that it is dragged along for the ride, see gravity (sort of, it is a simplistic example).

-Because space stretching/bending pulls matter with it and because space can stretch/bend FTL, the matter therefor moves at FTL speed. However! The matter is only "moving" within its frame of reference at however fast it was moving before the drive was activated. IE, if you were going 10 kph and you activate the drive to go 10 times light speed, your speed (theoretically) should be 10 times light speed + 10 kph to an outside observer, but as far as relativity is concerned (with time dialation) you are only moving 10 kph.

Addendum.

10 times the speed of light is NOT a speed limit. To date as far as I am aware there is no known speed limit for the movement of space itself. The 10 times light speed comes from one of the recent papers by a scientist named Harold "Sonny" White (http://en.wikipedia.org/wiki/Harold_G._White_(NASA)) of NASA's White-Juday Micro Warp Field Interferometer Laboratory (http://en.wikipedia.org/wiki/White%E2%80%93Juday_warp-field_interferometer), when he designed a revision of Alcubierre's original warp drive. Alcubierre could achieve some amoung of FTL speed, at the cost of converting Jupiter into energy, infeasable. Sonny discovered that if you change the shape of the warp field from sphereical to more oval, you get dramatic energy reductions. His paper stated that to acheive 10 times the speed of light with a ship of X kilograms (I forget how many) it would take converting 1,600 lbs (roughly) of matter into energy. That is 'barely' outside our capabilities now (give it 40-50 years). For some reason most news outlets interpreted this to mean that the actual speed limit is 10c, which is not true. You can make a faster engine, the 10c engine was chosen because it was a nice round number.

Additionally, at the time of his first paper, he had not completed the calculations about a second idea he had (pulsing the engine on/off instead of always on), but insinuated that preliminary results indicated that adding this method of engine operation on top of his other change should result in a similar scale energy requirement drop. He later announced his calculations proved this to be correct. For some reason the news agencies never cared much about this second statement.

Current status of the warp-field interferometer: Results indicate a small, but non-zero effect achieved by the interferometer setup. To confirm and better quantify this, additional interference canceling and computational ability is required.

Enjoy!

Edited March 24, 2014 by Mazon Del

[Scotius]

So, there is hope that one day humanity will have FTL ships, right? Man, that would be crazy awesome if someone would say: "Yes. We can achieve this goal using this and that method."

[Mazon Del]

Tentatively yes. What this experiment shows is only one half of the equation, the part where we compress space (front of the drive). We know space compresses when loads of energy/matter are condensed into one spot. Right now we only have theories on how to expand space (back of the drive). These usually involve exotic matter/energy (of negative mass), which when condensed instead of forming a compression of space, forms an expansion of space. Thus far, exotic matter of this nature has never been observed or generated, though there are theories on how one might generate it.

However! Do not despair of this research. For two reasons. Firstly, even if we cannot figure out exotic matter, we can still use the front part of the drive as an STL engine capable of ridiculous accelerations. The second, in general if exotic matter can be synthesized and used for an Alcubierre style warp drive, the physics that allow this drive ALSO allow for wormholes. The two technologies intrinsically go hand in hand.

[Sillychris]

So, there is hope that one day humanity will have FTL ships, right? Man, that would be crazy awesome if someone would say: "Yes. We can achieve this goal using this and that method."

It is my opinion that if this lofty goal is not achieved we ultimately doom all life in the solar system to extinction.

We could possibly deploy deep space seeds, but the sheer distances involved in reaching a suitable extrasolar planet would be quite prohibitive to sublight travel.

[Mazon Del]

Fear not! For light-hugging ships (0.9999....c ships) should be possible with the front half of the warp drive. You just have to suck the time penalty encurred by time dialation via relativity.

Additionally, we have ever growing evidence of alternate universes. Who knows, maybe we can visit one?

[cantab]

Fear not! For light-hugging ships (0.9999....c ships) should be possible with the front half of the warp drive. You just have to suck the time penalty encurred by time dialation via relativity.

It's a benefit, not a penalty. The journey to alpha centauri would take about 4 years as measured from Earth, but considerably shorter for those on the ship.

[Mazon Del]

I sort of view the time desyncronization as a bit of a penalty, but honestly I can't explain why that is. Probably something subconcious left over from reading a certain Sci-fi book about a crew on the starship Envoy. It kept flashing back and forth between them, and the steadily growing differences between planet bound people and the families/communities that lived on board the FTL trade ships. In that story, relativitistic effects held true even through FTL travel.

[Moon Goddess]

Remember, just because relativity suggests that you could create a warp bubble if you have negative matter that we've never seen any suggestion exists, however all science we've seen suggests that nothing could ever survive inside said warp bubble.

And, of course then there's the fact that quantum physics is likely to show that negative matter doesn't exist, and even if it did wouldn't make a warp bubble.

The universe doesn't like cheaters.

[vger]

Kinda wish this discussion were about the Alcubierre's future (if any). Last I read, all recent lab tests on the whether or not the theory works, were deemed 'inconclusive.' After years of waiting for the result of those tests, I was not very enthused. Another dead-end in humanity's attempts to actually have a future?

[Mazon Del]

Moon Goddess, what evidence is it you are referring to? I have never seen any evidence to that effect. There are some issues with the warp bubble that are hazardous to people OUTSIDE the bubble, like the massive gamma burst that happens when you turn the engine off. But all that energy is directed 'forwards' away from the ship, so the ship is unaffected. The area where the ship exists would be a flat (or mostly so) area with neither crushing nor expansion happening. Nothing from the outside is getting in to harm the crew, and as far as they are concerned space-wise suddenly all the stars went out (though there is some argument over if the crew would see pitch black, or a uniform glow from the front).

Additionally, from what I have read there is relatively strong evidence to support that negative matter exists, or that something that fulfills its purpose for a warp drive does. Your statement of "And even if it did wouldn't make a warp bubble" seems to indicate you are saying that what current physics calculations (some supported by experiment data) say is the key to warp drive would not work "just because it wont". Why is it that you believe it would not work?

The universe doesn't like or dislike anything at all, it is a non-sentient 'thing'. So far scientific observation, calculation, and experimentation indicate it IS possible for a warp drive to work. One heavy part of this is the fact that they have shown from the recent data for the Big Bang, that rapid expansion (at FTL speeds) MUST have occured for our universe to exist the way it is.

-------------------

vger: The "inconclusive" result is a bit of a misnomer. I was observing the live stream when Sonny gave his results last year. He showed us a graph that measured the interference patterns in the laser for the experiment, they showed a definite spike where it was expected to be, but rather than jump up and down and shout "SEE! IT WORKS!" they are doing proper science and declaring that they need a more obvious result (which can only happen through greater noise cancelation, a greater signal, or greater computational power) as well as external varification. What most papers don't mention is that after they performed the experiment, their two grad/PHD interns went back to their universities and replicated the experiment attempting to find the desired result using two different methods (both different from Sonny's) and both of them had similar spikes in the data where they were expected to be. It is as a result of these three data points that NASA had granted them increased funding for the upcoming year to help them with their noise problem.

To put a little context into the noise problem they have. Their system is so sensitive to vibration, that the moving mass of a fully laden truck on the highway several miles away from their test facility was a detectable event. The big deal last year was that they had to move their lab into a special vibration canceling lab that NASA had constructed for use in the Apollo program. This helped out, but the vibration canceling equipment is the best we could make 30-40+ years ago, if they got the funding to construct a new system or upgrade the existing one, then they can cancel out more 'noise' and be able to see their spike better. Another method is very Kerbal in nature "Add moar boosters!", basically crank up the power on the capacitor they are using. Which is already operating at something like 20K volts. Either one of these methods (ideally both of them together) should result in the spike becoming more prominant and less likely to be a statistical anomaly brought on by the local area.

In the end, while the results so far have been labeled 'inconclusive' the more verbose answer they provided was something like "The results are inconclusive pending increased test capabilities, however we can state that there is SOMETHING going on."

Somewhere in the middle of that they also proved something called a Q Thruster was a viable engine. I don't understand exactly how this thing works because honestly it is somewhat magical. Ever hear of virtual particles? Little bits of matter and antimatter that pop into existence on super tiny scales, both heading towards a collision. An instant before collision they wink out of existence. These have been proven to exist and are one of the big parts of Hawking Radiation (how Black Holes dissolve). They are basically eveywhere at all times (even inside you, as I said super tiny scales here). A traditional engine works by pushing something out the back, either chemical, ion, or even just shining a really bright light. The Q thruster operates by 'pushing' off of virtual particles similar to how a submarine propellor pushes off of water. Just as the submarine is not throwing anything off of the boat to move, a ship with a Q thruster does not actually expend any mass to move, it is an entirely electrical system with nothing leaving the ship.

[SargeRho]

You could solve the forward facing gamma ray burst problem by "exiting" warp towards a star or a gas giant.

[Redjoker]

I may be thinking about this the wrong way. You don't actually go faster than the speed of light. This is because by compressing space you are shortening the distance that you will have to travel and not increasing your speed. It will only appear to the outside observer that you have travelled faster than light because the distance will appear the same to them. For example, you want to drive a 60 miles to your friends house, but want to do it in 30 minutes without breaking the 60 mph speedlimit. If you take a shortcut that is 30 miles long, then you will get there in 30 mins and it will appear to your friend that you drove 120mph on the way over.

Edit: "Also, this method of travel does not actually involve moving faster than light in a local sense, since a light beam within the bubble would still always move faster than the ship; it is only "faster than light" in the sense that, thanks to the contraction of the space in front of it, the ship could reach its destination faster than a light beam restricted to travelling outside the warp bubble. Thus, the Alcubierre drive does not contradict the conventional claim that relativity forbids a slower-than-light object to accelerate to faster-than-light speeds." from https://www.princeton.edu/~achaney/tmve/wiki100k/docs/Alcubierre_drive.html

Edited March 24, 2014 by Redjoker

[Dispatcher]

Yes, it seems that any comparison with the speed of light is not in the realm of this kind of propulsion. It would be incredible to know how such a drive actually effects the ship and external observers.

[vger]

vger: The "inconclusive" result is a bit of a misnomer. *snip*

Wow, nice. That paints a much more hopeful picture.

Given the sensationalism of modern media, I'm amazed this didn't get better coverage. When the first lab test was being set-up, there were news bytes about it everywhere. And I knew the schedule pretty well. After the fact, I didn't hear a peep about the results. I had to do a bit of digging to find any info, and the only tidbits I found were very discouraging. Strange how it went that quiet so quickly. Did that many journalists really just throw their arms up in the air and sigh, before they heard the whole story? I suppose that could happen, but it seems very out of character.