The right way to think of this: the speed of light is not a speed limit, it's a speed reference. Everything is always moving at the speed of light through spacetime. When you "move" through space, you're not changing the magnitude of your velocity vector, only its direction. So the more you move through space, the less you move through time.
If you could move through space at the speed of light your velocity through time would be zero and you would appear (to yourself) to be moving infinitely fast, or equivalently, to be everywhere at once, or (again equivalently) that the universe had no spatial extent in your direction of travel due to an infinitely large Lorenz contraction.
This explanation is wrong, and is not what the article is talking about at all. This article is about creating a warp bubble using negative energy, which changes the distance between two points. You can think about it sort of like creating a kink in a piece of metal with a piece of dust inside of it, the kink then propagates through the metal by distorting the geometry of the larger object in such a way that the distance traveled by the piece of dust is less than the original distance between the start and end point of the kink. The reason this works has nothing to do with special relativity, it comes from the fact that if you plug negative energy into the equations of general relativity, you get warp bubble solutions which travels between two points faster than light could travel between the two points if there was no warp bubble.
A few years ago I actually read through most of the original paper[1], and worked out a lot of the equations.
Although I don't see it mentioned in the article, and I'm speculating here, the reason the approach described in the article might work out for photons is that negative energy has been discovered at the quantum scale in something called the Casimir effect[2]. The Casimir effect happens when you have two conducting plates which are placed very very very close to each other, then in the space between the plates, something which behaves exactly like negative energy exists[3], and it causes an attractive force to be exerted between the two plates.
A natural thing to try would be to harness this type of negative energy to create a tiny warp bubble, and try somehow to stick a quantum particle like a photon in it.
I will explain why lisper's explanation of light speed is wrong. The fundamental problem is that it violates the premise of relativity and is a classic example of appealing to an absolute frame.
Velocities are only measured relative to other objects. The explanation given by lisper requires an absolute reference frame. Otherwise, you have no way to figure out how much you're actually moving through space, and thus, through time because you can never figure out your "true" speed.
Relativity tells me that no matter what speed I travel at, I will experience time at the same rate. From my frame of reference, I will perceive things to happen in other reference frames at different rates. When we calculate time dilation and length contraction, we're determining that if something took time "t_a" in Frame A, it will appear to have taken time "t_b" to an observer in Frame B.
Furthermore, it's impossible under relativity to have a frame of reference that moves at the speed of light in any other frame.
That's a fantastic explanation. I did a Physics undergrad and masters, and somehow I never heard this particular metaphor for it, but using a velocity vector through spacetime makes for a very clear image of what's going on. Is that from general relativity? (I only did special relativity)
This is just special relativity (space need not be curved for this description to work).
Brian Greene's "Fabric of the Cosmos" gives a good layman's exposition of this idea, using a loaf-of-bread metaphor (this was the first time I saw it explained this way and it made a huge impact on my way of thinking about SR)
He does the same in "The Elegant Universe", using the metaphor of a car driving at a fixed speed (c) across field that is space in one direction and time in another. That was my big "aha" moment with special relativity: understanding that "space" and "time" are dimensions in essentially the same way that "length" and "width" are dimensions -- with the caveat that we always have this tremendous velocity (c) across one or the other.
Then you contemplate the kinetic energy that must be associated with c, and e=Mc^2 pops right out at you. Absolutely blew my mind when I first grokked that intuitively.
In the end, Greene failed to convince me that string theory was particularly interesting, but his descriptions of relativity are absolutely first-rate.
These are actually sometime the worst things to read if you actually want to understand stuff. The publishers of these kind of popular science books enforce the rule for authors that no equations should ever appear. If authors get really upset with that they allow printing one equation, usually, E=Mc^2. This leads even talented authors to water down everything with faulty and many time absurd metaphors. There is no real substitute to reading real physics books. On a lighter side, check this out: http://www.youtube.com/watch?v=w5VVEw4ZSRI
Well, having an intuitive understanding goes a long way too. Being able to derive formulae rather than just having them memorized is good. Of course, I don't want a book that doesn't include the formulae, but I want to know the "why" of it as well.
If you measure time in seconds, and speed in units of C, then vx^2+vy^2+vz^2+vt^2 is always a constant (in flat spacetime). So you have no choice over the matter. If you are stationary, time passes at a rate of 1 second / stationary second. If you move in space, rate of passage changes exactly by the amount required to compensate. So in a way, you always move at the same speed through spacetime, speed of light, and can only choose the direction.
The reason is that time dilation factor is the lorenz factor, (1-u^2/c^2). This is how much time will pass in your watch per one second of a stationary clock.
the minus sign in front of the vt is very important and gives the SR (hyperbolic) structure of flat spacetime. The rotating a vector thing is just an analogy to euclidean space rotations.
Yes it does. Gravity changes spacetime, so the locally flat spacetime at the bottom of a gravity well isn't the same as the locally flat spacetime at the top of a well, but it's still flat in both cases.
I really really want to understand this, but I can't get past your third sentence. No fault of your own, just me. But if you have anything I can read that explains it better I would be grateful!
The length of the red arrow is always the same. When your velocity is zero, your "time speed" is 1.0. As you begin to move faster, the arrow tilts towards the X axis, decreasing your "time speed".
The biggest issue is that the interchange between speed and time is not linear. So that graph doesn't make sense as displayed.
At a minimum you have to understand that the time scale on the side of the graph is not linear, but rather exponential. And graphs with exponential scales are not easy to understand.
Making it worse is that there are other things that can slow down time - namely acceleration.
I wasn't really criticizing you as much as the concept of describing relativity as a tradeoff between the two. I don't think that helps enough to overcome the misunderstandings it can cause.
If you were heading due north at 100m/s, then changed your bearing to head slightly east without changing your overall speed, then you'd now be heading a bit less than 100m/s north and a bit more than 0m/s east.
This is the same kind of thing, except that when "at rest" in space (relative to some fixed point) you're moving at the speed of light in a pure time direction. When you move in space, you divert some of that speed from the time direction into the space direction you're moving in. Overall you're still doing the speed of light, just in a different "direction".
Think of it like falling. If you fall straight down at your terminal velocity you always head for one point. If you are able to move side to side at a very large speed, you can theoretically fall towards all points under you at once. Or, if you will, 'stop' falling towards any one point at all.
I feel the same way. Every time I try to understand the speed of light and correlation between time/space, my brain just hits a dead end.
"When you "move" through space, you're not changing the magnitude of your velocity vector, only its direction. So the more you move through space, the less you move through time."
I can understand what is being said here word-by-word, but the concept as a whole does not make much sense to me.
What bugs me about this explanation is the following: aren't we moving quite a bit all the time? We go along the earth as it's rotating around itself, then revolving around the sun, then the solar system revolving around the milky way, then the milky way probably moving somehow and so on.
If we could somehow "get off" earth, "stand still" and let it "float away", would time would appear to move faster?
If we could somehow "get off" earth, "stand still" and let it "float away", would time would appear to move faster?
A qualified yes, but it depends which time you mean by "time would appear to move faster". If you were "still", then those observed in motion would appear to have time pass more slowly.
Astronauts who spend time on the international space station age slightly less than people on earth (by 0.007 seconds behind for every 6 months) - time on earth goes faster than for them relative to those of us "stationary" on earth.
When two observers are in relative uniform motion and uninfluenced by any gravitational mass, the point of view of each will be that the other's (moving) clock is ticking at a slower rate than the local clock. The faster the relative velocity, the greater the magnitude of time dilation. This case is sometimes called special relativistic time dilation.
In any given reference frame you have a velocity vector that's some part space and some part time but has magnitude 1. It's just rotated.
There's nowhere to "stand still" in the universe. But if you pick a reference frame where you're moving less fast in space your velocity has more of a time component to make up for it. If you pick one where you move very quickly in space (maybe one that doesn't follow the Earth's orbit) then you have less motion in time. That observer sees you experience less time.
And if they pick a reference frame where you move the speed of light - where your velocity vector is fully in space; with '1' for space and '0' for time - they don't see you experience any time.
There's no way to stand still per se, but we can tell the difference between someone who accelerates and someone who doesn't - that's the resolution of the "twin paradox". So if one person travels around in a circle and their twin stays still (by magically floating above the earth without following its rotation, or by staying suspended at a particular point in the earth's orbit for a year while the earth goes around), then they have accelerated less than their twin and should therefore have aged slightly more.
What I don't understand is: does this still apply under General Relativity, or does proximity to the massive earth redefine acceleration?
That's a nice explanation, but this hypothetical device doesn't move through space, it warps space. It's based on general relativity. It's gotten a lot of attention, and its practicality has been critiqued quite a bit, but everybody seems to agree that the math is right.
No argument there, just saying it doesn't seem to violate fundamental principles.
The exotic matter is negative mass. In theory there is such a thing, and a quantum effect produces it at a very small scale. Whether it will ever be possible to produce it in large quantities is another matter.
But at least the quantity required isn't quite as large as it used to be. The original configuration need a negative Jupiter mass. Now it's down to several tons.
Suppose all objects have an 'energy', whatever that is, given by a vector sum of two components: P and M. Now every object may be distinguished by the distribution among those components: if, for a given norm, the energy is all in P, we say it is spacelike, it's energy is all in the space component. If it's in M then it's timelike.
So for us massive timelike objects at rest, E=M (in natural units) and for spacelike objects, E=P. Then it becomes clear that, since the mass is an instrinsic property of objects, any given object with M>0 cannot be spacelike: the energy vector will always have a time component, and likewise light cannot be timelike. You can however increase the spacelike component of the object and make it approach spacelikeness, measured by, for instance, the angle teta=arctg(P/M) with diminishing returns for each unit of energy (if you visualize it, you'll se at the start the return is linear -- teta ~ P/M and then it becomes very hard).
So the explanation above is telling in the sense that if you could be spacelike things would be weird, but doesn't reveal why you can't have massive spacelike objects -- namely, because we have a finite supply of energy.
The problem with that explanation from a pedagogical point of view is that you have left the word "energy" deliberately undefined. Because it's undefined, your explanation is isomorphic to this one:
"Suppose all objects have a 'snorble' (whatever that is) give by a vector sum of two components..."
You also haven't defined M and P. I know you mean mass and momentum, but only because I already understand this stuff. If your target audience is someone who doesn't already understand it, you need to define your terms or your explanation won't be effective.
Based on my layman's understanding of relativity, I intuited this model on my own, but no physicist I've spoken with has verified it as a valid model. It just seemed so obvious to me based on the constraints. Thanks for verifying my intuition on the topic. :)
No. That is your normal state of affairs: when you're "sitting still" in space, you're "moving through time" at the speed of light. I'm using scare quotes here because, of course, there is no such thing as "sitting still in space" because all motion is relative. The point here is that "light is always moving at the speed of light relative to you (no matter how you're moving)" is the same as saying "you are always moving at the speed of light relative to light (no matter how you're moving)". The way that works is, as I said, that this constant speed is a measure of your motion through spacetime, not through space alone or time alone.
I get the space-time vector thing. You said that, when moving at the speed of light, one moves through time at a velocity of zero, thus giving the appearance of infinitely fast movement. So if one was able to achieve zero movement (which would probably require achieving zero energy?), wouldn't time also appear to be moving infinitely fast (even though it was actually moving at the speed of light).
> when moving at the speed of light, one moves through time at a velocity of zero
When moving through space at the speed of light one moves through time at speed zero. Likewise, when moving through space at speed zero one moves through time at the speed of light, which is one second per second. This is the normal state of affairs that you experience day to day. It is not possible to achieve zero movement through spacetime. In this universe, everything is always moving through spacetime at the speed of light. The only thing that changes is the direction of motion: more through space, less through time, and vice versa.
I read about this months ago, and it's an interesting idea. I'm not a physicist, but I spent some time trying to puzzle out how this fits in with my understanding of relativity. So please, correct any misunderstandings.
It's important to realize that the craft is never traveling faster than the speed of light through the space in front of it. But there's nothing in relativity that prevents objects from apparently traveling faster than the speed of light "after the fact". The farthest apart objects that we can see are significantly further apart in light-years than the estimated age of the universe, which is generally thought to be possible because of the expansion of space itself as objects were traveling apart at subluminal speed.
I don't think that apparent FTL travel violates causality because it doesn't allow you to actually reach anything outside of your light cone. It took me a while to understand this, but you can't really view the light cone as something that is statically determined at a given point in time, because it depends on the geometry of space as over time. So a craft capable of distorting space just ends up with a really funky-shaped light cone that's warped wider than normal out in its direction of travel and narrower in the opposite direction as it moves (if you had a way of externally viewing the curvature of spacetime, which you don't).
But one thing I could not really figure out is whether this so-called FTL travel has the potential to violate causality, because I don't fully understand how causality and FTL are related.
But one thing I could not really figure out is whether this so-called FTL travel has the potential to violate causality, because I don't fully understand how causality and FTL are related.
The relationship is that FTL in one reference frame is travel backwards in time in another.
If you're able to travel FTL in 2 different inertial reference frames, then you should be able to travel backwards in time and violate causality. Note that the "should" here is important - I can think of lots of possibilities for how that should could be prevented.
That said, I'd be much more optimistic about the plausibility of a proposed warp technology that only lets you go FTL relative to the implicit reference frame of the distant stars. Because that avoids any possibility of causality violation.
>That said, I'd be much more optimistic about the plausibility of a proposed warp technology that only lets you go FTL relative to the implicit reference frame of the distant stars. Because that avoids any possibility of causality violation.
I don't understand what you're getting at. It would be trivial for someone close by to match that reference frame, and then what?
I don't understand what you're getting at. It would be trivial for someone close by to match that reference frame, and then what?
And then nothing. :-)
My point is that being able to go FTL relative to distant stars does not allow time travel relative to distant stars, which means that there is no possibility of causality violation.
Being able to go FTL in 2 arbitrary reference frames leads to potential causality violation.
It's still not at all clear to me what you're saying.
Feel free to express yourself in more technically/mathematically: while GR is certainly not my field, I took classes in grad school that covered the material.
In SR, if A and B are two events and B is outside of the light cone of A, then reference frames can be found where A happens before B, A and B happen at the same time, and A happens after B. Therefore FTL travel in one reference frame is traveling backwards in time in another.
The ability to travel FTL in a single preferred reference frame is not sufficient to cause causality violations. That is because all trips move me forward in time according to the preferred reference frame, so I can't wind up at the same time and place that I (in my personal history) was at before. But if I can travel FTL in my choice of reference frame, in my choice of direction, then I can plan a trip from A to B which is FTL in one reference frame, then switch and travel from B to A FTL in a different reference frame. From the original reference frame I first traveled FTL, then backwards in time. In the second reference frame I first traveled backwards in time, then FTL. But both agree that two copies of me wound up at the same place at the same time, and I can try to violate causality.
Suppose that you go from SR to GR but are dealing with a large region that is approximately described by SR though locally it may look different. In my "warp drive" there is no local FTL. But the observations about SR, reference frames, and simultaneity still hold between two distant locations. The ability to warp as fast as I like but only relative to one "approximate SR reference frame" does not let me violate causality. But the ability to do it in any direction relative to any reference frame that I like, gives me the ability to construct "closed time-like loops". Which is what is required to try to violate causality.
Note that I say "try". It is possible that a unified theory of GR and QM could allow for closed timelike loops, but (thanks to quantum decoherence) would not allow you any meaningful interaction with the previous copy of you.
>It would be trivial for someone close by to match that reference frame, and then what?
all the machinery of the SR is valid only on the background of the fixed spacetime. Once you start to massage the spacetime itself, the SR is only approximation which is good only to the extent of how good fixed spacetime model is approximation of your real spacetime.
>I'd be much more optimistic about the plausibility of a proposed warp technology that only lets you go FTL relative to the implicit reference frame of the distant stars.
That sounds like a stationary ether; where there is some 'true' reference frame in the universe. The main intuition behind relativity is that there is no preferred reference frame.
My point is that the laws of physics can be have symmetries that do not exist in practice. For instance in the Standard Model there is nothing to say that protons need to be heavier than electrons. But thanks to the Higgs field, they are different everywhere that we see.
In the case of general relativity, even when there is no preferred reference frame in the theory, there is an obvious one that is still special. See http://en.wikipedia.org/wiki/Mach%27s_principle for more on that.
Reading the linked press release, it does not seem like they are claiming A->B->A. Rather, they are claiming a suppersistion of two states, (A->B) and (B->A). In the same way quantum mechanics allows a particle to be in two states at the same time, it allows the ordering of events to be two states at the same time.
Your third paragraph is a nice way to think about FTL. Actually it causes quite interesting problems to define FTL, since nothing special happens locally.
> But one thing I could not really figure out is whether this so-called FTL travel has the potential to violate causality, because I don't fully understand how causality and FTL are related.
They are not directly related, as I wrote above, nothing special happens except you find a 'shortcut.' So at every point there is still a nice lightcone ( locally) and every event is caused by events in its past lightcone. However, you can have global causality violation, that is closed timelike curves, a fancy way to talk about timetravel. The idea is, that you travel always forward in time and you reach the same space time point at which you started. Much in the same way that you can travel always forward on a tire (torus) and still reach your starting point. Something like this may or may not happen on a metric which permits FTL, for example the Alcubierre metric does not permit travel on such curves. [1] But it would actually be easy to perform the same analysis on a Godel solution [2], which would permit closed timelike curves.
Edith: Added the comment about the Godel solution.
I don't see how this can avoid violating causality. When analyzing this sort of thing, the method by which one travels faster than light doesn't matter at all. Warp drives, hyperspace, or magic carpet, it's all the same. The mere fact that one can do it is sufficient to violate causality. With any method, any method at all, that transmits information or objects faster than light, one can construct a scenario in which Event A precedes Event B in one reference frame but B precedes A in another reference frame. I'm sorry I don't have a brief example to post here, but everything I've ever read about this supports this view. I'd love to be wrong. I grew up looking at the stars from my back yard, watching Star Trek on its first run, and hoping that the stars would be in reach in my lifetime. But the Universe isn't here to please me and if FTL is really impossible, well, I'll live.
You are confusing special relativity and general relativity. In special relativity you are ( sort of) right. In general relativity you can find shortcuts in the way we measure distances. The trick is, that speed can either denote a local property, as measured by your speedometer, or a global property, that is distance traveled divided by time. And the light speed limit only applies to the local property. So if you can find a spacetime that contains a shortcut, then you can increase the distance traveled faster than the speed of light. ( And there is nothing in general relativity to stop you, since it only requires you to move locally slower than the speed of light.) An example for this would be a expanding universe ( and for simplicity let me assume that the expansion only starts a some time t1.) So you travel from t0 to t1 with constant velocity v < c. And you are then at some point x=v(t1-t0). Then you stop and expansion sets in. You stay in place at x, as measured relative to some point nearby, but the distance to your original starting point increases, since space itself is expanding. And there is nothing to stop this increase to be faster than the speed of light.
The other thing is the "sort of" parenthesis, the Lorentz transformation is directly linked to the causal structure of special relativity. A statement like "if* you could go faster than the speed of light, then you could violate causality" is somewhat nonesensical, since if you could go faster than the speed of light, then you would break local Lorentz invariance and therefore you break your very definition of causality.
Thank you for explaining the GR vs SR aspect of this. I was somewhat aware that the no-FTL rule was different in GR but I didn't really understand how. I'll have to look into this more and now I know where to start. I'm not sure I follow the second part, about Lorentz invariance, but my physics is decades old, so that's not surprising. Time to do more reading.
Sorry for the botched formatting (HN is for some reason not showing me a edit link :/ )
A quite interesting paper on the topic is McMonigal & al. [1], it is a bit technical but they discuss the Alcubierre warp drive quite nicely.
To elaborate on the second paragraph about special relativity, one way to define Lorentz transformations is, that they are the transformations which preserve the causal structure of Minkowsky space. On the other hand, the speed limit is a direct consequence of the Lorentz transformations. So the causal structure and the speed limit are directly related. To look again at the argument that a velocity larger than the speed of light implies causality violation: The moment you argue that a speed faster than the speed of light is possible, you implicitly change the meaning of causality. Then you use the Lorentz transformations to conclude that in on frame of reference event A precedes B and that event B precedes A in another. So you first deny the special status of the Lorentz transformation, just to go on and use Lorentz transformations. And my take on this is a strong maybe, the moment you start talking about local Lorentz invariance violation, anything goes. Perhaps there is causality violation, perhaps not, but this depends on your specific meaning of 'causality' and 'faster than light' and not very much on special relativity.
Nobody seems to have poked any holes in the math since Alcubierre first published, and it's not for lack of attention.
I'm not sure what they say about causality, but there's been some work suggesting causality doesn't have to be absolute. Imagine a billiard table, with a wormhole that curves and goes three seconds backward in time. You aim a billiard ball through the wormhole, such that it will emerge earlier and knock itself off the path, never entering the wormhole, and creating a paradox.
But what actually happens is, the ball emerges on a slightly altered trajectory, striking itself a glancing blow, and the ball enters the wormhole.
And why did it emerge with an altered trajectory? Because it was struck a glancing blow.
Physicists have worked out some math on this, and haven't managed to find any scenario that results in inconsistency.
There is a really good book called Time Travel in Einstein's Universe by Richard J. Gott (http://www.amazon.com/books/dp/B003L1ZYKG) that explores different concepts of time travel and violations of causality without violating Einstein's principles of relativity.
I hate to put a damper on the enthusiasm about this awesome topic, but this article doesn't even contain a hint of any reason to believe that the NASA scientist in question is making progress on any sort of FTL technology.
Alcubierre's work on "warp bubbles" has been known for years, but as even this article points out, there are enormous roadblocks to making it practical. For example, it requires matter with properties that have never been observed in the universe (namely, violations of the positive energy condition). If this NASA scientist thinks that he has a way to produce such matter, that would already be a bigger deal than any scientific finding in (conservatively) the past thirty years. Why hasn't he announced that?
Also, Alcubierre himself is quoted in the article pointing out that no signal from inside the warp bubble can ever reach the front of the bubble to "turn it on" in the first place. (As I recall, Alcubierre's equations describe an "eternal" warp bubble, moving forever with no beginning or end.) Has the NASA team found a way around that? The article doesn't give any hint that they have. (Nor that they haven't, but as a theoretical physicist myself I'd like to think that I'd have heard of a breakthrough like that.)
So what I want to know is, first, why did the NY Times decide this was worth reporting on (while leaving out any evidence that this NASA team is capable of making meaningful progress)? And second, why is NASA devoting multiple salary lines to this particular project? (There might be good answers, but they aren't evident here.)
>>For example, it requires matter with properties that have never been observed in the universe (namely, violations of the positive energy condition).
At first I thought about this, but then its for us to really ponder on a simple fact. You can achieve a X goal by doing Y, but to say you can achieve only by doing Y is wrong.
Scientific history is standing testimony to that. People have expressed skepticism about anything and everything, stuff like airplanes, nuclear energy, mobile phones, internet anything you name it. 50 years before they were all invented and put to use, they would have all seemed pointless directions of pursuit- yet all of it makes perfect sense today.
Yet some tangential line of thinking causes a major technology break through every now and then we are left wondering what we where thinking all along.
Skepticism in science is the right approach. Not blind, dogmatic skepticism of any idea that disagrees with orthodoxy, but informed skepticism that demands compelling evidence for surprising claims.
Maybe a computer analogy would be useful: Imagine reading an article about someone working on a revolutionary new image compression algorithm. He claims that it's lossless and that it can achieve at least 99.4% compression on arbitrary photographic input. But all he's willing to say about his technique is that it's based on wavelets, and he has no actual evidence to show. How excited would you be?
> You can achieve a X goal by doing Y, but to say you can achieve only by doing Y is wrong.
The trouble in this case is that the guy at NASA has said that his warp drive ideas are based on Alcubierre's work. Alcubierre's results are very explicitly constructed within the framework of general relativity, and that framework puts some pretty strict constraints on the content of space-time near an Alcubierre bubble. So it doesn't matter whether he's satisfying those constraints by doing X, Y, or Q: anything that met the necessary conditions would be one of the biggest scientific achievements in our lifetimes. (It would dwarf the Higgs discovery, just for instance.)
Remember that the people who make these discoveries are scientists. It's one thing for a person on the street to be skeptical it's another thing when a scientist in the field in question is skeptical.
Now these guys don't even have a hypothesis on how to turn the machine on. Forget the engineering. They can't get an idea to work. I'm with the GP, this is not very exciting. Even having a working idea on how all the parts may work would be more exciting than this article.
>> It's one thing for a person on the street to be skeptical it's another thing when a scientist in the field in question is skeptical.
No, Scientists are human beings too. And the fact is, a scientist's thoughts are biased based on what the person knows.
People co relate the events to happen in future on the basis of what they know right now. Which is the root cause of all problems. Though sometimes skepticism is perfectly valid.
>>Now these guys don't even have a hypothesis on how to turn the machine on.
These guys are not working on building the machine.
>>Forget the engineering.
Exactly. The first rockets were not built by directly opening up the lab and making the prototype in the first hour.
Even while building things like the first rocket, or the first viable airplane a lot of math and physics work had to be done. Which is what is happening now.
>>They can't get an idea to work.
Seems like they already have experimental test bed to verify their math.
>>I'm with the GP, this is not very exciting. Even having a working idea on how all the parts
I'm excited. Its not like software where you fire up your IDE and just get down to coding. That works with software because 100% of whatever we do is already done and proven by nearly everybody else. We just exercise the same to our domains of business.
Building some thing like a warp-drive may very well require some years of work on math and physics before any field trials are started. Basically nobody has done anything like this every before. No one knows the consequences, or the side effects or even the kind of effort such an endeavor would demand.
If you want an easy analogy, Alonzo Church died finishing his work on the lambda calculus before he could see a working electronic computer. Same could be told about Alan Turing. Yet these guys had mathematically demonstrated all they said was possible.
When the first gates were built, people expressed the same skepticism if the combination of these AND-OR-XOR gate will ever achieve something substantial. Or when the first brick was built, and when the first wheel was built.
The article indeed gave no indication of hope on the central problem, obtaining a violation of the weak energy condition. However, there is a relatively easy way to violate the weak energy condition using binding energy.
If one binds M_1 and M_2 with binding energy M_B such that M_B > M_1 + M_2, then one can violate the weak energy condition. I know for a fact that the above inequality is satisfied for some multi-brane configurations in M-Theory. So, there is hope.
Oh, I certainly won't argue that such progress must be absolutely impossible! The fact that Alcubierre's solution exists at all illustrates how unwise that would be. (I've also heard someone suggest that you might be able to produce an Alcubierre-like configuration if you could make a compact dimension's radius larger within some local region. No idea if there's any sort of duality to the brane configurations you're referring to.)
But the point is (and I don't think you'd disagree), if this guy wants to be taken seriously, he needs to tell someone what he's doing. If he thinks that he's creating a system with vast binding energy (greater than mc^2), that would be pretty easy for him to say. If he thinks he's constructing a bound state of branes or manipulating the size of an extra dimension, that would be easy to say, too. And even moderately convincing evidence for any one of those things would immediately make him one of the most famous and respected scientists on the planet: the warp drive aspirations aren't even necessary.
The complete lack of such details is a pretty compelling argument that he's not in that position.
> I've also heard someone suggest that you might be able to produce an Alcubierre-like configuration if you could make a compact dimension's radius larger within some local region.
Interesting, I hadn't heard of that one.
> But the point is (and I don't think you'd disagree), if this guy wants to be taken seriously, he needs to tell someone what he's doing.
I agree 100%.
PS: In the interest of full disclosure, a lifetime (AKA 14 years) ago, I did some research for NASA looking into such "negative mass solutions" in M-Theory that arise as a result of hep-th/9507022.
> I did some research for NASA looking into such "negative mass solutions" in M-Theory that arise as a result of hep-th/9507022.
Cool! The most informative thing about that to me is simply the knowledge that NASA has a history of investigating this sort of thing. Maybe it's a good thing if they keep a trickle of resources pointed in that direction, just in case there's something really there to be found. I hope they've got good people assessing whether it's worth it. (It's still odd for that sort of speculative work to be getting substantial press attention, though.)
I found the comparison of the iPhone to a "Star Trek" communicator a bit off topic. Even 40 years ago, I don't think anyone would have argued that something like an iPhone would be possible in the future. The idea didn't violate any known physics. Hand-held two-way radios were already commonplace. The fact that we achieved sufficient advances in circuit miniaturization and battery technology to build a hand-held smartphone does not in any way imply that we'll be able to build a warp drive for a spacecraft.
How about 60 years ago? 80? 100? At some point, if I explained to someone that I would be able to pick up a small black plate filled with electrical signals (ha!) flying around it many million times per second and use it to learn the answer to any question, talk to (AND SEE) any person in the world, in real time, how far back would you have to go to hear "that's impossible," because I guarantee you, at some point, someone thought that it was, even if not 40 years ago.
Hell, I remember explaining to my dad when I was a kid that someday there would be a way to watch whatever you wanted, whenever you wanted, simply because that's what people wanted to exist. In my mind, it was an inevitability, and he felt it would never happen. This was only a scant 20 or so years ago.
>At some point, if I explained to someone that I would be able to pick up a small black plate filled with electrical signals (ha!) flying around it many million times per second and use it to learn the answer to any question, talk to (AND SEE) any person in the world, in real time, how far back would you have to go to hear "that's impossible," because I guarantee you, at some point, someone thought that it was, even if not 40 years ago.
As soon as we have real science (i.e. post-Descartes) anything mechanistic seems possible. There was probably a point at which we had insufficient knowledge to say one way or another, but this isn't the kind of thing that's ruled out by physical law in the way that FTL travel is.
>Hell, I remember explaining to my dad when I was a kid that someday there would be a way to watch whatever you wanted, whenever you wanted, simply because that's what people wanted to exist. In my mind, it was an inevitability, and he felt it would never happen. This was only a scant 20 or so years ago.
You were lucky that time, but it's not a reliable heuristic. Plenty of people want to be immortal, but it hasn't happened yet. (OTOH, human immortality seems a lot more plausible than FTL travel - we can't see how it would work yet, but there's no law that rules it out - which puts it in the same category I think a phone would have seemed like in Newton's day).
*
How about 60 years ago? 80? 100? At some point, if I explained to someone that I would be able to pick up a small black plate filled with electrical signals (ha!) flying around it many million times per second and use it to learn the answer to any question, talk to (AND SEE) any person in the world, in real time, how far back would you have to go to hear "that's impossible," because I guarantee you, at some point, someone thought that it was, even if not 40 years ago.*
Pretty far back. Even Dick Tracy had a similar thing.
I think you would have to go back before Marconi and Tesla.
the idea that space expansion generates effect that looks like FTL in fixed space model doesn't violate any known physics - just look at the highly red-shifted galaxies.
>The fact that we achieved sufficient advances in circuit miniaturization and battery technology to build a hand-held smartphone does not in any way imply that we'll be able to build a warp drive for a spacecraft.
we just need sufficiently advance (increase) energy production and learn to focus it so that the density in a given volume will reach the "mass density of black hole multiplied by c-square" - that will be a good start to manage the shape of the spacetime
Actually, to argue the other side, "We have no evidence it's physically impossible" has never been a very good argument that anything will actually work.
Actually, hard scifi is loaded with stuff that falls under the category of "We can't yet prove it's physically impossible, but neither has anyone actually proposed viable non-crank theories on how it really works."
It's simultaneously infuriating and awe-inspiring that something that's visible to the naked eye - stars - could be so completely out of reach for us.
However, with the recent work of Drs Alcubierre and White, it's clear that cracks are forming in the Impossibility of FTL travel.
That leads me to believe the FTL is inevitable, because in the history of science, whenever we begin to see how maybe something could kinda, sorta, maybe exist, it's usually just a matter of time (perhaps centuries) until we crack it.
"because in the history of science, whenever we begin to see how maybe something could kinda, sorta, maybe exist, it's usually just a matter of time (perhaps centuries) until we crack it."
Like mermaids, magic, the halting problem, ESP, and religion?
LOL you got me. More specifically, proof of any example in the general category of one, and a solution to the other. Mix and match with the above how you'd like.
Wouldn't that imply that we couldn't prove/disprove God's extisnese. If we could prove it, we need only wait until we prove it, then return our answer.
To throw some fun fuel on the fire, which God, including conceptualizations that may not exist in our time yet.
If a missionary religion is the correct true religion, and FTL exists anywhere in the galaxy, then by definition we should have already been contacted by missionaries and "civilized". Yet we're clearly not civilized, so at minimum at least one must not exist. So its not looking good for the FTL hopefuls.
There is another fun one in that if an all powerful being exists, it seems a bit presumptuous for a mere moral to limit "it" to sublight. Therefore if the concept of FTL exists and an all powerful being exists, then FTL must exist in practice unless we're placing irrational limitations on an inherently unlimited being. Therefore if FTL can be imagined, but not implemented, that proves scientifically most conceptions of "god" do not exist; Or at least "it" is not all powerful. Unclear what impact that logic puzzler would have; probably just about none.
That would make a much more fun rabble rousing article than "yet another star trek communicator / iphone analogy"
You could have a non-missionary religion (like Judaism). You could have a missionary-religion that considers humans unsuitable for conversion. You could have a missionary-religion that puts some kind of restriction that says they have to wait for some trigger event before contacting humans.
As for God why do you assume God is inside this universe? God could be causing the universe. (Like God would be the computer and the program, and we the results of running the program.)
>If a missionary religion is the correct true religion, and FTL exists anywhere in the galaxy, then by definition we should have already been contacted by missionaries and "civilized". Yet we're clearly not civilized, so at minimum at least one must not exist. So its not looking good for the FTL hopefuls.
Not nessasarily. Assuming FTL does not imply time-travel, FTL still does not imply the ability to search the entire universe. The alien missionaries would still be limited by their sensors to scout X cubic-meters/year/ship. They would also have a limited supply of spaceships (that may grow exponentially with time).
If the being is all-powerful, it's not restricted by physics. We are.
Or you can say that the all-powerful being exists outside spacetime, and FTL is impossible to anything within spacetime.
So the all-powerful being sees all of spacetime laid out in front of it, like a canvas. The painter dabs paint on the left margin and they streak out toward the right in interesting patterns. The painter dabs paint here and there, the patterns respond, and he continues until he likes the picture.
Asimov had a concept like this in The End of Eternity.
If a missionary religion is the correct true religion, and FTL exists anywhere in the galaxy, then by definition we should have already been contacted by missionaries and "civilized".
Who says we weren't?
Yet we're clearly not civilized
Says... you?
Or it could just be that God adjusts His teachings to each sapient species's psychology, so having us contacted by Starfish Aliens would be kinda useless.
Or the true religion could be a non-missionary religion, like, as someone so astutely pointed out, Judaism.
That's odd, I could've sworn that he wrote -- and that you quoted him as having written -- "history of science" and also "could kinda, sorta, maybe exist".
It may be real, but it may also be inaccessible at human scale. That is, the accelerating recession of distant objects might someday be fully explained, but there might be no way to use that knowledge to go from place to place in our solar system or galaxy.
Lets have some fun with implications of FTL other than the usual cookie cutter "scifi" narrative. There's not much new in the article, lets cook up something really new here.
First of all FTL travel involving information transfer would have some interesting implications for the existing automated market high freq trading systems. Your proximity to the central clearing house no longer limits your profits. In fact the whole concept of HFT and a central clearing house and "A" individual market price might no longer have much meaning in that kind of economy. And that might be good, or bad, or not matter much.
Another aspect given ridiculous paranoid military industrial complex would be anything capable in theory of eventually delivering an a-bomb would be classified and hidden until an area defense exists. In fact a rational participant in MAD would immediately nuke any MAD member who got "close" to inventing actual FTL because they would insta-win any MAD scenario, therefore bomb them before they FTL bomb us. Aside from any direct weaponization of FTL "things" materializing in .mil owned reactor cores or .mil strategic targets. Shields materializing at FTL speeds in front of the laser beam headed toward the target. FTL drones to spy on people so quickly they're out of range before the target sees they were there. Yeah I think the first country to develop FTL will probably get nuked by everyone else, unless the discoverer is legendarily neutral (the swiss?) or ... Which would suck if the USA "wins" because it means I'd be getting toasty unless every other nation is suicidal and refuses to strike. Bummer for me and the rest of the usa. So I sincerely hope this dude fails.
Another interesting aspect vaguely hinted at in Ian Banks culture series is a FTL-ish universe culture by its very geography/technology inherently ends up much more libertarian than our own rapid descent into "1984". So there's interesting political issues where any group of modern "pilgrims" can at will escape the clutches of the evil empire. On the other hand small festering groups of true believers like to fanatically drink the koolaid, so I donno whats worse, one evil empire or a billion little clans of crazies all disconnected from each other.
Patent something and transmit the patent FTL such that you can deliver a cease and desist at FTL speeds before a non-FTL player even gets to see they've been checkmated?
This is like 50 steps ahead of anything that's actually happening, but I have to wonder what the potential destructive power of a warp-drive style FTL drive is. If you can create a spacetime distortion strong enough to move a ship around at FTL speeds, what happens when that distortion gets anywhere near the Earth? Will it cause some sort of total destruction to an enormous area? Change the orbit of the moon, the earth, asteroids? It would have a big effect on how any ships with such a drive are used. It could be sort of like SSBNs, where only major governments have them, and they only allow extremely senior and trusted people to operate them.
Yes, it would likely be very destructive - however, once you have massive, fast ships moving around the solar system the Earth will be in danger anyway, warp-tech or no. I think it's too early to speculate meaningfully about safe distances and danger levels when it comes to this technology, which as you correctly presumed doesn't exist yet.
The press is hugely missing the point when they steam ahead using nonsense StarTrek analogies without an apparent clue of what's (im)possible with today's technology, but neither are the people in here getting it who are stuck lecturing each other about causality violations. This is not about speed or acceleration, or even the transmission of information. It's about bending space time. Let's not forget the enormity of that concept, but let's also admire this potentially useful shortcut that might open up for us in the far future.
Current models are purely theoretical and work on a basis that is pretty similar to carrying a black hole around. Needless to say, in an age where we don't even have the energy to reach Earth orbit economically, the power requirements of such a technology are nothing but prohibitive.
But even if we had enough power (and hence mass) to warp space by brute force, it would be a huge event that needs to happen far away from planets. While the general principle is interesting, I think what we lack is a more sophisticated method of modifying the properties of space time, something that works on a smaller scale and can be more easily contained. "FTL" neutrinos were interesting for this exact reason (before they sadly turned out to be a measurement error) because they would have opened a door for us to access and manipulate space itself without having to resort to enormous and ultimately wasteful energies. I sure hope we'll discover how to do that in time.
That, and the potential for damage to space-time in general, were explored in Start Trek TNG. That's one of the things I liked about the series: the things that were invented as plot conveniences often had implications that themselves later became plot drivers. (Not always, of course. It was entertainment, not science. But often enough.)
Situation is largely similar to nuclear power. Though it had drastic implication for energy it could also be potentially a weapon and it is.
I believe it will be the case even with warp-drive technology too.
As always some people will always have something to fight on. I don't believe situation will change once we get access to colonizing the vast size of the universe. We will have everything(good and bad things) except that at the scale of universe now.
Kind of curious what other effects you might get if you localized a change in space-time. Given that the planet and the solar system are in motion would it deflect in the direction opposite that motion? If so could you put better numbers on how much inflation occurred post big bang?
I would dearly love to see FTL, but to paraphrase Fermi, where are the aliens? The first civilization that gets FTL would colonize the galaxy before any other developed. It's harder for me to accept that we are the first technological civilization than it is to believe that FTL is possible.
The universe is far too big. I mean its really really big. Even if we acquire FTL, lets say in the next decade(for assumption's sake) and start traveling. Its possible given our resources, time and required focus to achieve anything meaningful we may not even step out of milky way for several thousands of years from now.
The milky way has around 100 billion stars. Searching 100 billion stars for some meaningful results is not a Joke. Even if we do divide and conquer or do the equivalent of map-reduce approach to exploring space. There is no way we can get to meaningful results even in several thousands of years from now.
There fore the biggest challenge after the invention of FTL will be how quickly we can multiply spread and explore.
Trust me once we get FTL technology, the biggest challenge will be the dealing with overwhelming size of universe. In fact just within a few years we may even think FTL was an easy problem to solve. Our problems will be exploring the universe within human life timescales, multiplying fast enough to occupy and explore it.
So an alien civilization in some really far galaxies even with FTL technology possibly cannot search for us in the size the universe is.
Even given FTL, terraforming is a matter of applied planetary-scale ecology that's at least a century or two away from our current understanding. It could well be that, for instance, aliens looked at the Earth at some point, decided it was just never going to develop life as they knew it, and buggered off somewhere else.
Yeah, that's been my billionaire fantasy for a while now. The goal line could be just a design that a panel of esteemed physicists and engineers deems workable.
If you can transfer things/information faster than light, then link-state routing protocols no longer would have a meaning in a network containing at least some FTL links. Therefore some startup should create an internet scale distance-vector routing protocol. OSPF is dead, long live RIPv4 or whatever. Cisco would be an obvious candidate to purchase the startup. Obviously demand would depend on FTL deployment rates.
The question that occurs to me much later is what are the naturally occurring phenomena that hint toward these physics? As far as I know, as an interested layman, is that all experiments can be equated to events happening somewhere in the universe. Everything from black holes to supernovas act like massive particle accelerators. Are their any hypothetical situations that are similar?
Article seems a little misinformed. It claims you couldn't sent a signal to the front of the ship to turn the drive off, but the whole point of the drive is that, within the bubble, nothing is going faster than the speed of light. It is the stretching and compression of space time outside the bubble that moves the ship.
This has nothing to do with acceleration. The idea is that you bend space-time so that you experience movement of a relatively short distance but actually travel hundreds of light years. In order to do so you have to alter space-time as we know it. Just a few weeks ago, we found we don't even know what happens at the edge of our own solar system. How can you think that bending space and time will act the same way as driving faster in a car? Your experience could be movement in the range of a few KM, but in the end you could be light years away. The problem (and the reason you will surely perish if you try it) is that you need to change the way space and time fit. Go ahead and try it, just be a few hundred light years away first so you don't ruin our perfectly functional solar system.
And sometimes it is worth it. If someone shows plausible way to get to Pluto right now on a one way trip passing by Jupiter and Uranus - you will have no shortage of volunteers. Curiosity may have killed the cat, but sent the humanity to the moon.
Yeah, it would be worth it if you actually got to experience anything besides instantaneous death. Also, what makes you think there would be no danger to the surrounding system? Bending space and time within our own solar system sounds like a good way to mess up a pretty intricate balance. Of course, everyone else on HN can read the source code of the universe so they know how impossible any of that is...
Yes, I must be a real luddite... That's why I'm on HN. because I think technology is really awful. Also, thanks for letting me know when the first aircraft was invented. Since I consider the concept of bending time and space dangerous, I must not know anything about mechanized flight.
There is precisely one thing in this article that was scientifically interesting: pointing out that Nature has inflated space at apparently-superluminal speeds before.
I use a Firefox addon called RefControl so you can customise the referer that is sent on a per site basis. I have it configured to send the referer "http://www.google.com/" to nytimes.com which gets rid of the paywall.
> Harold G. White, a NASA physicist, gets ideas for his warp field from a Star Trek starship concept.
It is ridiculous to think that physicists get any ideas from science fiction. It happens the other way around. All he did was use it in a presentation. I'm nerd raging like hell here.
It would be more ridiculous to think they never got any ideas from science fiction. Or rock music. Or abstract art. Or obscure theatrical productions just off Broadway. Or stand up comedy. Or ancient religious texts. Physicists are not hermetically sealed away from the rest of culture in some kind of non-euclidian math-cave built of complex numbers.
I don't know how much inspiration Star Trek provided in this case, but it's not unheard of for scientists and engineers to find some inspiration in science fiction.
I'm reminded of a story about how the science fiction writer Katherine MacLean [1], who predicted the role of computers in communication and music in her 1947 novelette Incommunicado, accidentally stumbled into a conference of electrical engineers and found herself quickly surrounded by Bell Telephone researchers who were inspired by her ideas to build the next generation of communications equipment.
As a software engineer, I have to admit to being inspired by near-future software engineering fiction that explores new ideas, many of which are quite achievable.
I was generalizing too much when I said they don't get any ideas from science fiction.
I really just thought the original statement, that he "gets his ideas" for "a warp drive" from Star Trek, was kind of ridiculous. The author of the article actually edited it, so I guess they felt similarly.
> As a software engineer, I have to admit to being inspired by near-future software engineering fiction that explores new ideas, many of which are quite achievable.
What are some of your favorite examples of this genre?
My favorite examples are from several years ago -- Charles Stross's Halting State and Vernor Vinge's Rainbows End. The technology portrayed probably doesn't seem quite as amazing today in 2013, but I'm always reminded of how technology seems to be converging on those futures whenever I read over the latest APIs from the Khronos Group. More recently, Ramez Naam's _Nexus_ from earlier this year is pretty awesome, although a little more out there than the other two.
Why? SciFi is great fodder for the imagination. Sure his technical details are unrelated, but for SciFi to trigger the thinking that lead to them is awesome!
I would provide the counterexample of tech coexisting with scifi, that crude hang gliders were well within the technological reach of the ancients... however centuries of daydreaming about mechanical flapping bird wings kept them solidly on the ground.
Its entirely possible "something" going FTL will eventually happen. For some peculiar value of "something" and some peculiar value of FTL. However, it will probably resemble stereotypical deus ex machina sci fi reimaginings of classic WWII battleship and aircraft carrier movies about as closely as a modern helicopter resembles a really big hummingbird.
Unfortunately, much like flight, preconceived notions will probably hold back R+D in FTL until long past its possible start. Possibly if we'd just focus on "something else" then in 2013 we'd already be 50 years into practical FTL deployment.
All FTL is is the wish to travel to other worlds that we think exist in the sky. This inspiration pre-dates not just science fiction, but also science and probably writing.
If you could move through space at the speed of light your velocity through time would be zero and you would appear (to yourself) to be moving infinitely fast, or equivalently, to be everywhere at once, or (again equivalently) that the universe had no spatial extent in your direction of travel due to an infinitely large Lorenz contraction.