Alcubierre Warp Drive

Rxke · 2004-04-25 13:26:20

The Alcubierre name rang a bell, I read about it before and i went searching... And found it back in a topic called 'Dark Energy' on the great Everything Space Messageboards, boardmember engaaraa explains why he thinks it is impossible... It *does* seem to break some physics laws, but he doesn't go into much details, maybe invite him over for a chat?

(The guys run their boards on a pretty old, so sometimes slow server, so be patient if it doesn't seem to load rightaway....)

http://www.everything-space.com/yabbse/ … ...did=636

Rxke · 2004-04-25 14:00:35

I don't know if i'll get around reading all the papers, my grasp of physics is, errr... shakey, to say the least, still have tremendeous problems with getting an overall grasp of quantum physics, but so did Einstein, heh...

Not that i don't like to read about it, but i surely can't claim i understand the finesses... at all.

Trebuchet · 2004-04-26 04:49:29

Ahh, Alcubierre's warp drive. Taking advantage of the fact that what Special Relativity takes away, General Relativity gives back.

Alcubierre's idea basically works by cheating and moving the chunk of spacetime the craft is in rather than the craft. The problem - the main problem - is that it requires more energy than exists in the universe. Someone came up with a variation on his topology which skirts this problem, but the energy requirements were still awe-inspiring in scope.

What can I say... probably something to occupy the engineers and drain budgets a few centuries from now.

clark · 2004-04-26 09:38:09

Okay, let's say the energy required wouldn't "break the bank".

I would imagine that having the neccessary power generation on the ship would just increase the mass size that has to be sling shoted, right?

The reason I ask is because I think if this were doable, then it would only be realisitic to have something of a "gate", where the power geneartion is located exterior to the ship. If that is the case, wouldn't the trip be one way?

Communication with any probe or ship would still be limited by the speed of light constraints (unless you fold space to send communications, but that requires power to begin with!).

I would also imagine that if we are able to bend space-time, we're dealing with gravity on some level- wouldn't any fold in space also fold the ship? Squished ship, no?

Wouldn't the folded space (i.e. the destination) be linked back to the starting point too? That means whatever is on the other side, could come flooding into our local area... folding space to jump a few light years might create a gravitational ripple effect that causes any nearby stellar object to be affected (even our sun dosen't 'fold' space) since we're dealing with the creation of an artifical mass via energy to fold space in on itself.

I am no expert by any stretch of the imgaination on this one, just asking lame questions based on my limited understanding of physics, so take this for what it's worth.

Shaun Barrett · 2004-04-26 20:55:09

Hi BGD!
I was interested to see your reference to the so-called Zero Point Energy in your last post. I've just finished reading "The Hunt for Zero Point", a book by a "Jane's Defence Weekly" Aerospace Consultant called Nick Cook. (For those new to this jargon, Zero Point refers to quantum vacuum fluctuations, whose existence has been experimentally verified by the Casimir Effect. Empty space isn't actually empty. Untold numbers of virtual particles spring into and out of existence every second in every cubic centimetre of space - a seething foam of potentially accessible energy.)
According to Cook's research, the Nazis had a secret weapons program in the closing years of WWII, which had been subsumed into the jurisdiction of the SS. Although nominally under Himmler's control, the program was actually run by a guy called Kammler, an SS general who was using jewish scientists selected from the concentration camps to help develop anti-gravity propulsion and weaponry based on the theories of an Austrian called Schauberger.
I don't know whether I should continue describing the main thrust of the book, since some of you may want to read it for yourselves and I'm not sure if I'm breaking some kind of copyright law! (I guess a broad precis is O.K., though.)

Anyhow, Cook makes it look very much as though there's been a 'black' anti-gravity propulsion program going on in America since the late forties. Kammler, among others, was never called to account at Nuremburg and nobody ever tried to trace him. This, despite his involvement in slave labour programs and having been instrumental in the massacre of 62 scientists, in early 1945, who had worked on his secret weapons agenda. It looks as though Kammler may have bought safe passage to the U.S. using his experimental results in anti-gravity as his ticket.
It's a great book and the author's background in high-tech military aircraft, together with his professional contacts within the aerospace industry, make the story very believable. I recommend it to anyone interested in the new concepts emerging now in the world of physics.

Anyway, my point is this ("Thank God, he's getting to the point at last!", I hear you all cry. ): It's fascinating that Alcubierre and others have shown that warp drive is at least hypothetically possible, without breaking any laws of physics, although it requires staggering amounts of energy. But then, coincidentally, it's becoming less and less heretical to discuss the distinct possibility that quantum vacuum fluctuations might be the source of unimaginable amounts of just what warp drive needs .. energy.
And in the background, we have stories about 'black' programs within the U.S. military to create gravitational propulsion and we have people like Podkletnov and Ning Li, who have done promising work, both practical and theoretical, into electro-gravitics in recent years.

Could all this represent some kind of serendipitous convergence of ideas? Might we be on the threshold of an enormous leap forward in technology and clean cheap energy for all?
Something's definitely going on. It's in the air ... I can feel it in my bones!

Euler · 2004-04-26 22:21:01

Wouldn't FTL travel violate causality?

Trebuchet · 2004-04-27 01:13:22

Yes, space around the ship, in Alcubierre's warp drive, is distorted. The front edge is shrunk, or contracted, or however you want to call it, and the back is expanded. Using the usual dents-on-a-rubber sheet analogy, the space in front of the ship is a deep, narrow canyon, and the space behind it is a hill. The net result is that the bubble of spacetime that the ship is in 'falls' forward endlessly. The ship never exceeds its own local speed of light, nor does it experience time dilation or any other relativistic effects, nor does anything else in the bubble of space within the front and rear distortions of space propelling the craft. That's why I'm calling it 'cheating and moving a bubble of spacetime'.

As for zero-point energy, the problem with Alcubierre's engine is that it needs more juice than the universe has to offer... even including zero-point energy. That's one hell of an energy budget needed, especially considering that your coffee cup statement is true. There are, however, shapes of space-time distortions which other people thinking about Alcubierre's idea devised which do not have the problem of requiring more energy than the whole universe contains to work. The energy required is still mind bogglingly huge, more than whole galazies. My statement about a few centuries from now is quite justified; I'm *expecting* our descendants to make some dramatic advances. But there is no way in hell anything remotely like the energies needed will be available in my lifetime... even if someone went and invented a safe, reliable way to tap zero-point energy in huge amounts. Even if angels descended from on high with blueprints, diagrams, and God's Guide To Nearby Planetary Systems I would predict we'd spand a few decades colonizing the whole damn solar system with that sort of power before actually bothering to move to FTL interstellar flight. And I don't forsee divine intervention.

Josh Cryer · 2004-04-27 01:35:34

Trebuchet, hehe, your last post gave me a well needed chuckle, thanks for that.

I got around to reading the original paper, and some other papers linked on that site about the impossiblity of the drive (which is good of that site to provide, this is how we know they're not really talking smack; they admit that it would take all the energy in the known universe, etc).

I remain a skeptic, but it's really nice to see that serious theoreists (as far as I can tell, they're not nutcases) aren't throwing out the FTL question without giving it a second thought. Then again, perhaps this is just a polite way of throwing it out.

Palomar · 2004-04-27 08:24:29

BTW, faster than light travel is possible and known of: see the quantum tunneling efect, which is something widely accepted.

*Well, I've read (IIRC, in a book entitled _Introducing Stephen Hawking_) that traveling faster than the speed of light *isn't* possible, because the faster [closer to the speed of light] a spacecraft (or any object) travels, the more the fabric of space-time "bunches up." Eventually the "fabric" of space-time builds up so greatly [at the point of the vessel reaching light speed] that it would stop the vessel.

That's just what I've read. I'm very certain I'm relating that material correctly.

And I'm admittedly not extremely (::polite cough::) knowledgeable about this stuff.

--Cindy

Euler · 2004-04-27 10:50:05

What I meant was that if you are going faster than light in one reference frame, you will be going back in time in another reference frame. This means that you can arrive somewhere before you left somewhere else. You should also be able to go somewhere and come back to your starting point before you left. This would allow you to go back in time and change the past, causing a lot of paradoxes and violating causality.

clark · 2004-04-27 10:58:15

I never understood fully this whole faster than light causes you to go back in time stuff.

Isn't the speed of light simply an observation of the upper speed limit on the observable universe? In other words, it would be like saying, "you can't go faster than a car, cause the car is the fastest (sorry) anything can go."

Based on our understandings, light has no mass, and something with no mass can travel no faster than the speed of light.

So what if we figure out a way to neturlize "mass" as an inhibtor of speed? Let me make up a word- an anti-mass field, whereby the actual mass of an object is reduced to minus zero. Wouldn't that allow us to effectively skirt the current phyics model?

Can something be given a negative mass? Or have I been smoking too long?

Euler · 2004-04-27 13:05:47

I never understood fully this whole faster than light causes you to go back in time stuff.

Events that are simultaneous in one reference frame will not be simultaneous in another reference frame. Observer 1 might find that events A and B happen at the same time, while observer 2 (moving with respect to 1) would say that A happens before B, and observer 3 (moving in the other direction) would say that B happens before A. They are all equally correct, and you cannot say that one event is absolutely before the other because light from one will not reach the other before it happens. However, in observer 2's reference frame, if A sends an FTL signal to B, it can arrive before event B happens. In observer 3's reference frame, B can send an FTL signal that arrives before A happens. This leads to all sorts of paradoxes.

clark · 2004-04-27 13:23:46

How can something be observed before it happens? That's silly.

If A, then B.

Observer 1 would see A (cause), then B (effect).
Observer 2 would see A, then B.
Observer 3 would see A, then B.

At no time is it possible for B to preceed A, no matter the refrence point. What am I missing here?

Now, let's say Observer 1 is sending a FTL message from Point A to Point B. No matter how you look at it, Point B will not receive, nor will it respond, until such time as it receives the FTL messgae from Point A. You cannot violate causality. The cause is Point A, nothing happens until Point A triggers the FTL message. Point B cannot respond until it receives the FTL message (effect). A will not receive a response from B until B replies. There is no way that B can send a message prior to the intiating A message. To do otherwise is to violate the cause-effect relationship, and then you end up with your parrallel-universe-collapsing-time-continuim-headache.

Light is the fastest observable "thing" in our universe, so we assume nothing can go faster. Then we confuse the issue by looking at this upper limit of speed and the effect it has on seperate refrence points. But that's all beside the point.

Speed is a function of time and distance, right? In other words, your speed is the result of how far you have gone in a set time frame. Even if we go faster, that dosen't change.

I look forward to being shown utterly ignorant here.

Euler · 2004-04-27 14:13:43

Say you have a space time diagram. Time is on the y-axis (measured in seconds), and space is on the x-axis(measured in light seconds). For a motionless observer, things that happen with the same y-value happen at the same time. A moving object is a line on the graph with slope c/velocity. However, any observer that moves with constant velocity will believe that he is stationary and that the graph is moving instead. For a moving observer, things that happen on a line perpendicular to his velocity line happen at the same time. So observers moving relative to each other will have different standards of what they consider to be simultaneous.

How can something be observed before it happens? That's silly.

Yes, that is a big problem with FTL travel/communication.

If A, then B.
Observer 1 would see A (cause), then B (effect).
Observer 2 would see A, then B.
Observer 3 would see A, then B.
At no time is it possible for B to preceed A, no matter the refrence point. What am I missing here?

No, A and B happen at different places. Both happen before they can observe the other one happening.

A and B both happen in different places.
Observer 1 would see A and B happening at the same time
Observer 2 would see A then B
Observer 3 would see B then A

In a universe limited by the speed of light, neither A nor B can cause the other. However, FTL would change all that and cause the "parrallel-universe-collapsing-time-continuim-headache."

I know that there are some quantum phenomena that seem to transmit information faster than light, but my understanding is that they are not "really" FTL, they just appear to be.

clark · 2004-04-27 14:24:18

Please be patient...

Okay, try some different metaphors, I'm pretty bad with graphs and diagrams. I'll try to understand those, but if you've got another angle, I sure would appreciate it.

What you seem to be describing is the effect of the refrence point and how it affefts observable events. However, what seems to be skirted is "causality". Cause and effect relationships establish the forward progression of time.

Think of some domino's (not the game). The domino's stacked in a line, each falling after the preceeding one falls upon it. Cause would be you pushing the first one, thus causing all remaining domino's to fall after the one before it (but after the first one you pushed!) fall. No matter how it looks from different vantage points, or different speeds, the domino's may only fall in a cause-effect relationship.

Going faster than light will not violate casuality- it only means we go faster than light. It's a speed, not something that leads to time travel.

In a universe limited by the speed of light, neither A nor B can cause the other. However, FTL would change all that and cause the "parrallel-universe-collapsing-time-continuim-headache."

No. A star goes super nova (A), we see the light of said super nova and study it (B). Cause and effect. Now, let's say we had somebody right next to the star that was about to go Super Nova. Let's say we have FTL communication. We will not observe and study the Super Nova until that somebody next to the super nova calls and tells us. FTL is a speed, not time travel. There still needs to be an intiating force for effect. Effect cannot preceed the cause.

Euler · 2004-04-27 15:03:25

In special relativity there are 3 space-time regions- the absolute past, the absolute future, and a sort of ambiguous "possibly past, possibly future." Something is in the absolute past if you can observe it(or be influenced by it). Something is in the absolute future if it can observe you. The ambiguous region is everything that is far enough away(in space) and near enough (in time) that light from it has not yet reached you and light from you has not yet reached it. The absolute past and the absolute future are absolute because of causality. The ambiguous region is ambiguous because a cause and effect relationship cannot be established for it, and whether things in that region are in the past or the future changes depending on reference frame.

No. A star goes super nova (A), we see the light of said super nova and study it (B). Cause and effect. Now, let's say we had somebody right next to the star that was about to go Super Nova. Let's say we have FTL communication. We will not observe and study the Super Nova until that somebody next to the super nova calls and tells us. FTL is a speed, not time travel. There still needs to be an intiating force for effect. Effect cannot preceed the cause.

A star goes supernova (A). Another star also goes supernova (B). Assuming they are in the ambiguous region with respect to each other, which one went supernova first? That depends on your reference frame.

Now add in FTL. Suddenly, they are no longer in the ambiguous region with respect to each other. The problem is that the different observers still disagree over which one happened first. Now some observers will say that A caused B, and some will say that B caused A, and I don't know of any easy solution to this paradox.

clark · 2004-04-27 15:13:38

Okay, "light-cones". I get that (relationship of causality).

However, what we are discussing is refrence points in relation to observations made within the ambigous regions of a light-cone. That ain't time travel, that's an argument. :laugh:

So one person says that both stars went super nova at the same time, another says A went first, then B; and another says B, then A- all depending on where they are sitting and how fast they are going at the time.

Sounds like your average Football game.

I'm looking into this "Lorentz Symmetry" which kind of tackles the issue of refrence frames and causality. It seems more research is needed in this area (those Einstien sats!) to figure out if there is a violation of Symmetry (something about the laws of physics being the same for everyone, everywhere...well, the same for all inertial observors)

And I think there in lies an answer. I wouldn't be surprised if Lorentz Symmetry is violated, as that would reaffirm that just becuase you go faster than light, dosen't mean you go back in time. I think this all gets muddled because of the issue of refrence points- the inertial observors. The point I haven't seen made yet (due to my own lack of exploration in this subject) is that the effects of speed on inertial obervors does not actually effect causality, but merely how causality is observed.

C M Edwards · 2004-04-27 16:03:37

So, there needn't be any causality violation.

Third: Why does it have to be faster than light? The whole messy problem could be avoided altogether if we were just willing to settle for sublight speeds.

Second: I've seen some interesting speculations that an absolute reference frame could exist. Relativity allows for something of the sort with rotating objects, leaving the door open for the existance of an absolute reference frame (if certain violations of conservation of angular momentum are possible). An absolute reference frame would allow FTL travel without causality violation.

First: In strictest terms, the speed of light was never proven, per se, to be the fastest speed in the universe. This was simply assumed as a postulate in the derivation of Relativity, and all the predictions derived from that assumption have proven true so far. So far, the supremacy of light in the fast lane is an inductive conclusion, not a deductive one.

clark · 2004-04-27 16:24:14

CM, too funny. :laugh:

I want to go faster for the same reason that I don't obey the posted speed limit, ticket be damned!

An absolute refrence frame is possible, and indeed, that's my point in suggesting that Lorentz Symmetry will be violated. If the symmetry is violated, then physics isn't the same for all observors. However, what I see in the explanations is this kind of warm fuzzy theoritcal premise that effects can preceed cause based on the choice of mathmatical formula that postulates a negative time result. I think it's bunk.

If we assume an absolute refrence frame for the duration of the mathmatical formula that describes this stuff, we end up with a positive time result between any number of refrence points. However, with special relativity, it seems that both refrence frames are used in deriving time results, which results in a counter intuitive conclusion that effect can preceed cause. The refrence frames of two observeros should not be comingled to determine the time results, it leads to the time paradox that is, well, silly.

Josh Cryer · 2004-04-28 01:46:30

I intended to post here about causality but clark had beaten me to it. Perhaps Godel's theorem comes into play here. What we're trying to do is explain the universe from the inside out, rather the outside in, so we wind up having these time paradoxes here. If we were to, as clark talks about, imagine a fixed reference frame, that is, something outside of what we can observe, maybe we can just discover a FTL method.

Granted, in reality FTL isn't really necessary, as we could just lengthen lifespans to many millions of years or whatever. But it would mean basically being stuck to our galactic cluster, and that's really what annoys me more than anything. Speed limits don't matter if you're going down side streets in your town (ie, the galactic cluster), but they tend to get in the way when you want go to a really long way.

Algol · 2004-04-28 06:13:18

I always though there was an absolute reference frame anyway!?!?! To me the speed of light has always been a limit on the speed of observations.

Sorry, ill try and expalin what i mean (feel free to shoot me down and torture me for military secrets btw)

Three stars A,C,E; equi-distant from one another at 4 light years, and three friends algol, clark and euler (at their respective stars)

I'm algol (at A). I jump in my FTL ship and fly to C in two years to visit clark. I arrive at C before clark sees me even leaving A (this will not happen for 2 years), i phone euler on my FTL (lets say for the sake of argument that its instant)phone and tell him im visting clark and he also cannot see that i have left yet.

Now, the moment my ship arrives at C (clark will not have seen it coming) it will appear to instantly travel backwards (as all the light from the ship during the trip catches up with the ship and C, it will appear to travel backwards for 2 years until the light from when i left reaches C.

However to euler at E, the ship will appear to leave A two years after the call (4 years after i left) and he will be able to watch me make the transit from A to C in two years (because he is observing the trip perpendicular to the FTL travel. He could call someone (on the inst-phone) at A to check, but i would be long gone despite what he could see.

Now, if i left a friend behind on A, because i am travelling directly away from him, he would not see me arrive on C for 6 years.

Now, this is the fun bit.

If i left C as soon as i got there (after the phone call to E) and went home (in two years again) i would once again arrive back in A without my friend seeing me coming. As soon as my ship arrived my friend (and I) would see the light from the trip catching up with A and appearing to show my craft travelling backwards back to C (this would again last 2 years - the trip time) Interestingly though i would see two images of my craft, one from the outbound (to C) journey and one from the inbound journey arrive at C at the same time.

Anyway, what im saying is that you may be able to arrive somewhere before you apper to have left but there is no way to circuvent causality.

Apologes to the board for the worst explanation of anything. Ever.

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