White claims to have calculated a way to substantially reduce the energy requirements to form a warp bubble, and without reading his papers I suppose I should provisionally believe him. But the required energy has to be negative (as he confirms here), and I have never, ever seen him or anyone else suggest how he plans to accomplish that. Negative vacuum energies like what he's relying on have never been observed in the universe (directly or indirectly), and would violate a number of "energy conditions" commonly believed to hold for realistic matter. It would be very exciting if those energy conditions really were violated, but it's an extraordinary claim that backed by zero evidence.
With that in mind, I continue to be puzzled by the amount of press that this story seems to receive.
That's a misconception I've come across a few times. It creates a negative energy density relative to the ambient energy density, not an absolute negative value. In other words if you consider ambient energy density to be zero the. The casimit effect gives rise to negative energy densities, but if course zero point vacuum energy means the ambient energy density is never zero. The casimir effect cannot lead to 'true' negative energy densities.
I haven't studied this in detail, but my understanding is that dark energy (whether from a cosmological constant or other sources) does not violate the "null energy condition" (roughly speaking, the condition that a light ray would never "see" a negative energy density). I don't recall exactly which energy conditions the Alcubierre drive violates, but my impression was generally "all of them". (His paper explicitly talks about violating the weak, dominant, and strong energy conditions, but doesn't mention null one way or the other.) There are quantum effects that seem to violate some of these, but my impression has been that the known examples do not violate them when averaged along an allowed trajectory in the spacetime, which the Alcubierre solution would.
That's getting near the boundaries of my technical knowledge of the subject, though, so I won't argue further. It would be awesome if this could work out, but as I've said elsewhere there are multiple Nobel-worthy steps between what we know today and actually creating any sort of warp bubble in the lab. If I were White, I'd be publishing my solutions to those first!
"With that in mind, I continue to be puzzled by the amount of press that this story seems to receive."
Let's make the supposition that a science idea has to meet some standard of plausibility in order to be publishable. The standard being applied to this is that it hasn't (yet) been categorically denied by any incontrovertible law of nature. Not much fails this test. If you postulate access to a source of negative energy or to the inside of a black hole, nothing is technically impossible.
As far as I know, negative energy is theoretically still sound; I may be quite mistaken though. What "energy conditions" would negative energy (or mass for that matter) be violating?
These conditions are widely believed to apply to all realistic matter configurations (to the extent that the less-restrictive ones get used as postulates in some theorems in relativity), though there are some exceptions due to quantum effects (which I believe are usually short-lived). Just for example, a cosmological constant or other dark energy source does not violate the null energy condition.
It would be really cool to see any of the energy conditions violated for an extended time in a lab! I'm pretty sure, though, that it has not yet been done.
Weak energy condition[1]. In general the energy conditions are useful for analysis of the Einstein equations, but general relativity does not demand them. So violating the energy conditions is somewhat theoretically sound, but one can only say so much about general relativity with violated energy conditions. ( For example a lot of stuff we know about black holes only holds, if some energy conditions are satisfied.)
Negative refraction is just as strange a concept, and we seem to be slowly getting there technologically. So I'm actually hopeful this will happen someday.
Unfortunately negative refraction a secondary effect where you have negative permittivity and permeability at the same time. Negative permittivity is no big deal, metals act like an electron plasma gas around certain frequencies and get all weird, something like the color transmitted thru thin films of gold and how weird gold, silver, copper act in the THz range and all that. The "magic" is creatively negating both .. At The Same Time. Then the negative refraction / metamaterial effects take hold.
Kind of like you can compress ammonia (a bit) and nothing terribly interesting happens, and you can cool ammonia gas (a bit) and nothing terribly interesting happens, but do both at the same time and you've invented liquid ammonia and refrigeration and all kinds of nifty stuff.
On the other hand energy/mass seems rather fundamental. There are no multiple "easily" negatable components you can play with mixing together. There's no "add a to b to get the mass" going on. So you can't get sneaky with combinations and initial conditions to magically make negative mass/energy. It's really a different kind of problem.
The whole topic is pretty interesting to me because the first metamaterial stuff was constructed out of printed circuit boards with weird etchings right around the ham radio microwave 6cm and 9cm bands, which is right up my alley (doing weird ham radio things involving PCBs and such around those frequencies) Unfortunately I have been unable to figure out any practical engineering demo (like, an antenna or a waveguide or some such) that would be ham radio applicable in a real world demonstration. I guess I could make a really weird lens and place it in front of a 6cm horn waveguide antenna, but I can make a much simpler microwave lens antenna using about 1940s tech. Lens antennas using plates of styrofoam and aluminum foil work pretty well at 10 GHz ham radio band for example, but I digress.
Metamaterials are kind of a solution in search of a problem right now, like lasers in 1960s or home computers in the 80s or whatever. Most likely, much like the examples, it would be pretty hard to predict today just how important they might be in the future. Or maybe we're seeing the next "magnetic bubble memory" or magnetic amplifier technology or fluidic analog computing or whatever. Hard to predict.
He mentions the 100YSS Symposium, which was conveniently held in my neck of the woods in 2011. It was exciting to be among a couple hundred smarter-than-average people who wouldn't so much as crack a smile when the word "starship" came up in conversation. Outside-the-box ideas, lessons taken from ISS, Orion, nuclear propulsion, radiation shielding, social engineering, violation of the 2nd Law, other cool stuff. It was a brainstorming excuse, and an opportunity to dream big. If you live near Houston, and you'd care to rub shoulders with some not-stupids who think seriously about this stuff, you might check this out. http://100yss.org/symposium/2013
Space exploration is not handicapped by technology, but by societal willpower in the absence of an existential crisis like the Cold War. The Alcubierre Drive is fine as a theoretically impossible physics plaything, but the expansion of the species beyond the Earth only requires funding to achieve using much more modest means. For every one space science mission that goes forward, our academic system produces 500 concepts that are judged too impractical or too expensive, and 50 that arrive at group consensus that it would be productive to move forward and submit proposals. 5 of them get funded into fully developed systems, and 4 are cancelled just shy of completion through because the JWST has cost overruns or the new Majority Leader / President wants to make his mark with an arbitrary decision like cancelling the 6 year old 20-year-plan for a Mars base in exchange for a 20-year-plan for a Moon base (that will be cancelled in six years).
The path is there, the end discoveries (relative to many other fields) relatively certain, we just don't like to make the effort in any concerted way, and our government is broken; Congress would prefer it if they could just run NASA on a soundstage.
I do agree with your overall premise, but societal willpower in this case is really just a proxy for cost. Space exploration is fantastically expensive. Of course it doesn't help that the Space Shuttle and therefore the ISS were hopelessly cost inefficient, but even without the shuttle tax space exploration is still very costly.
This is why SpaceX's plans for substantially reusable launch vehicles is so exciting. They have a credible roadmap towards cutting launch costs by a factor of ten or more. We're in one of those situations where yes, we could spend more billions on space exploration right now, but there's a very real chance that if we maintain current space spending for just a few years those extra billions could buy us a huge amount more. I bet projects like the planned asteroid mining venture are watching SpaceX's technology development program with bated breath.
It's the Alcubierre drive. First paper on the idea was published in 1994, and everybody seems to think it's legit according to relativity, though with large practical difficulties. http://en.wikipedia.org/wiki/Alcubierre_drive
Large theoretical difficulties, too! To the best of my knowledge, nobody has ever been able to write down a complete mathematical description where an Alcubierre bubble "turns on" or "turns off": instead, the math always seems to describe a scenario where the warp bubble exists (and is inaccessible from the outside) into the infinite past and infinite future. Also, all versions of Alcubierre's model that I am familiar with require forms of matter and energy with properties completely different from anything ever observed (and different from most mainstream ideas for possible new types of matter and energy as well): namely, they require violations of various "energy conditions". http://en.wikipedia.org/wiki/Energy_condition
The vast practical difficulties are in addition to the enormous theoretical challenges. I would absolutely love it if something like the Alcubierre drive could be made real, but there are multiple steps between here and there that would each deserve a Nobel prize. If I were White, I'd be talking about how I'd solved all of those problems (or any of them!) before jumping straight to trying to generate a warp bubble in the lab.
>If I were White, I'd be talking about how I'd solved all of those problems (or any of them!) before jumping straight to trying to generate a warp bubble in the lab.
Why not try to generate a bubble, if it works great, otherwise try formalize it in greater detail. If warp bubbles are possible than it may be that they are already being created through random chance at the micro-level in the natural world.
Missing the part from the paragraph about having no idea how to generate that condition, although if it existed in the past it would presumably be "sorta stable" in fact it would never be able to shut off as presently understood.
A good analogy would be trying to talk to the original Lada Ada about silicon based computers without the folks of that era knowing enough solid state physics to contemplate whats going on in a simple transistor. "So if you could magically understand how to create a transistor, which won't happen for a century, then logically it follows that such and such array of those magic devices would make a great full adder circuit to add binary numbers"
So what? Half of number theory (I don't know enough of it to say whether that _is_ an exaggeration) does right that: "If the generalized Riemann hypothesis is true, ..."
Its a more fundamental problem. Like "Wouldn't it be cool to be able to multiply. At least for reasonable small integers, if you could add, which you can't at this time, then you could multiply simply by repeated addition. But, of course, you can't add, so ...".
I just meant that the basic idea doesn't violate general relativity.
Your link mentions that negative energy density has been observed at very small scale as a result of the Casimir effect. It's difficult to see how that could be scaled up, but I suspect that's what White is using here.
"...some physicists have presented arguments to suggest that a theory of quantum gravity which merged the two theories would eliminate those solutions in general relativity which allow for backwards time travel (see the chronology protection conjecture), of which the Alcubierre drive is one" [emphasis added]
The thought experiment: imagine a billiard table with a wormhole which curves around and goes three seconds into the past. Roll a billiard ball into the wormhole such that it will emerge three seconds earlier and knock itself off the path, so it doesn't enter the wormhole.
Instead, the ball emerges along a slightly different path, striking itself merely a glancing blow that allows it to enter the wormhole.
And why did it emerge with an altered path? Because it was struck a glancing blow.
You do aim it so it hits dead on. Then it emerges at some different angle which knocks itself off that dead-on path that you so carefully aimed. Now it's traveling an altered path that makes it emerge at that different angle.
Why does it do that? I get why the principle demands that it does and I get why it's a stable solution once it's been made to happen, but how did it actually make the jump from "straight on" to "at an angle"? Presumably not every self-consistent causal loop materializes itself out of thin air just because it would work if it did.
Edit: possibly lame example, but in Terminator 2, we find out that terminators were a secret government project that went awry. Where did they get the technology? Well, a terminator from the future came back and died in Terminator 1 and the parts it left behind allowed engineers to get a head start on building one. So there's a similarly self-consistent causal loop. But it doesn't really answer the question of how there came to be terminators.
I can't say I fully understand it. One thing I've seen stressed is that there's only one timeline. There's never a time when the ball continues straight through into the wormhole, only to somehow emerge with an altered path. It only travels that path to the wormhole once, and when it does, it gets hit a glancing blow.
The wiki entry I linked is intriguing. It says in some cases there are an infinite number of consistent solutions. They found they could analyze those cases with quantum mechanics, doing a sum-over-histories that only includes the consistent solutions. That gave a probability for each particular outcome.
So maybe that's fundamentally how causation actually works in the universe, and in the absence of time loops it reduces to normal causality. Now I can't help speculate whether actual quantum mechanics involves time loops somehow. (And in fact, Cramer's transactional interpretation does involve waves travelling backwards in time.)
Another way to look at it, maybe, and take with a grain of salt because I came up with it myself: Imagine there isn't just one timeline. In the paradox the universe runs an infinite loop, the ball first going into the wormhole, then not, then it does, then it doesn't. But given quantum mechanics, the position and momentum of the ball is uncertain. Given a very large number of trials, it's eventually going to shift significantly. At some point, it hits on a consistent solution, and the looping finally stops.
I can only imagine this kind of thing happening in a reversible, constant entropy system and a system without intentional processes.
For example, imagine a programmable drone. It is programmed to enter the singularity if and only if nothing seems to emerge and to then avoid collision with anything once it emerges - and transmit a signal announcing it's emergence to boot. Maybe you could do setup a fancy scenario for not winding up with two (or no) drones at the "end". But things not longer seem very plausible.
And you could probably arrange for a thing to carry entropy backwards if you had a varying entropy a system. But that's left as an "exercise for the reader".
I think the problem with the warp drive is topological. His drive relies on expanding space behind you and contracting it in front. OK. But what happens when you turn the drive off? Assuming all this squashing and stretching doesn't involve discontinuities, at best you're back where you're started from. At worst, you're in some kind of weird messed up crappy nook in spacetime where you're a long way from your starting point and your destination.
I think that's why you still move the ship forward within the warp bubble (to borrow a Star Trek term). So you're compressing space in front of you, while moving forward into the compressed space.
Right. In a sense it operates on the same principle as why the known universe is larger than it is old (as space-time continues to expand and light has further to go)
> Assuming all this squashing and stretching doesn't involve discontinuities, at best you're back where you're started from.
Are we sure space is perfectly elastic? What if space is infinitely plastic? Then when you turn the drive off, for all observable data you would be sitting in normal space just short of your destination.
Wouldn't an Alcubierre drive just always take you into the past? If you leave Earth using this drive and get to some distant star at FTL using this mechanism, maybe you escape relativistic effects, but you'll still get there before light from our star arrives there. And then when you go back wouldn't you arrive before the light left? It doesn't seem to make sense to me. Maybe someone can explain away my misconception about how that works?
Say we are having a swimming race and both leave the same starting side at the same moment. I get to the other side of the pool and return to the starting position before you reach the opposite side of the pool. Just because I lap you doesn't mean I travel back in time.
Ok, that makes sense, but what happens to the light being emitted from your internal ship lighting. Are you traveling faster than that? How do you look around?
the wikipedia article linked above talks about this, saying that the "...This method of transport does not involve objects in motion at speeds faster than light with respect to the contents of the warp bubble; that is, a light beam within the warp bubble would still always move faster than the ship. As objects within the bubble are not moving (locally) faster than light..."
It's relativity; internal lighting will look the same because light in your ship will still be traveling at the speed of light relative to you (if I'm not mistaken).
No, you are confusing special and general relativity. In a flat spacetime your only chance at getting faster than light travel is by violating local Lorentz invariance. In general realtivity, you can essentially go faster than light in two different ways, either you win an honest race or you find a shortcut. The Alcubierre drive is of the second variety, so you do not get to create closed timelike curves ( the technical term for time travel), but you can still arrive at a distant point faster than a 'naive' measurement of the distance would suggest.
Essentially yes. Faster than Light travel is essentially equivalent to traveling to the pass changing the reference system. That's why I'm very skeptic.
But you need a more complex setup. If the two stars are static (or the relative velocity is 0) then in both trips you arrive later than the departure time, so there is no easy to spot paradox.
But let's suppose that the Sun is static and the other star is moving very fast (with a speed <c). In the first part of the travel, form the Sun point of view you are traveling forward in time with a speed than is greater than c (in spite allegedly you are in a "bubble" so you locally are traveling wit a speed smaller than c. The bubble and everything that is in it is traveling with speed >c.). From the other moving star point of view you (or the bubble) are traveling backwards in time. You reach there and then they see you approaching there.
We can compare this to sound of a supersonic plane, where the plane arrives first and then the sound arrives, but if you do the calculations the sound was emitted before the plane arrival time. But if you travel fast enough and the star is moving fast enough then the effect is different, with the correct standard calculations the light arrives later than the space ship, but the light "was" emitted after the ship arrival time. From their point of view the space ship was traveling backwards in time.
Once you are there, you only have to recalibrate all the systems to use the other star reference frame. All the inertial reference frames are equivalent, so this is easy.
And now you start the engines and travel forward in time with a speed > c in the other star reference frame. They don't see anything too special, only that you go too fast but they are unable to tell you that. But form the Sun's point of view you are now traveling backwards in time, so you arrive before you departure the other star!
So, let's peek the Sun's reference frame. You travel first forward in time and then backwards in time. Is the sum positive? If the other star is static then the sum is always positive an there are no surprises. But if the other star moves fast enough then the sum is negative and you arrive before you departure.
If you don't find a fast enough star then you can use a fast space station or a fast space ship as the other extreme in your journey. Or even use an abstract point traveling fast enough in the middle of the space.
You're arriving before the light arrives, not before it leaves. The light takes a certain amount of time to travel that distance: you take less time, not negative time.
Why would you arrive before the light left? You could arrive at your destination before light from your source got there, so it would make phoning ahead to let them know you're on your way very difficult, but you wouldn't truly be in the past.
I don't see anywhere in my post where I suggest that it did. I think though you could use this device to at least outrun light and then use a telescope to look into the past.
I mean – unless you have in mind some complicated relativistic effect, in which case my answer may be a bit naive, it feels a bit like you are overlooking the fact that, as you go back, you will kind of receive double your share of photons from the planet and play fast-forward on everything you missed on your way out.
As I said, I suspect this is not how it would end up happening, as I remember reading somewhere some weird stuff about how the speed of photons hitting you was always the same regardless of your speed.. But that gets too weird for me to comprehend.
Sounds like they need funding for 100 years. That's a lot of money! It's actually basic science like this that I think is a defensible form of public research spending.
I am often distressed by the time, energy, and resources people consume in an attempt to escape reality (i.e. video games, films, alcohol, and drugs). Reading about endeavors like this renews my optimism for the future.
I take issue with video games and film being a waste.
The entire idea of a warp-drive comes from science fiction and people daydreaming/trying to escape their current reality. The Hyperloop is directly out of Heinlein. Subterranean cannons on the moon as a public transport device... Without escapism we lose the essence of human creativity, imagining a future that is different from the present. Do you think we would have bothered to build rockets and go to space/the moon if science fiction hadn't whetted the public's curiosity?
If anything, the problem is that current escapism kind of sucks and we need to do it better.
People need a break, and video games, films, alcohol and drugs can provide those (just like hiking, gardening, and photography). There's nothing like a bit of downtime to let your mind turn things over in the background.
And with regard to film, alcohol, and drugs specifically - these can all be tools to gain a different perspective on reality, they're not necessarily mindless escapism.
I partially agree with you, especially in the case of documentary films; and would further add that books (of literature, fiction, and non-fiction), plays, and operas are very powerful tools for understanding the world. From what I can see, these tools are generally not being used to help people "gain a different perspective on reality", as large portions of the populace do not read a book, or try to understand what any character in fiction is experiencing. As to the drugs and alcohol, I need not point out that stumbling masses of people in the streets after midnight is more indicative of their use as a soma rather than an instrument of introspection.
Drugs can be used as a tool for introspection (psychoactive drugs for example. They can also be used as a means to counter the stress coming from other areas in life, if they are used with care (alcohol, nicotine, cannabis, maybe even cocaine, which is pushing it). And then there's the variety that acts like shocking your pleasure centrum (meth, crack, and various other hard hard drugs).
Aside from the third case, I'd argue against drugs being a waste of time. Unless you abuse them, they can actually increase your quality of life.
You shouldn't poo-poo escapism wholesale. Granted, the vast majority of them are used for complete non-productive rubbish, but recreation and inspiration can go hand-in-hand.
After all, film and video games (and, of course, the TV series that came before) were the inspiration for this as well, no?
They're not poo-pooing it wholesale. Recreation has its place, but some people clearly go too far and spend too much time on it. That's what GP is worried about.
Well, a lot of people still consider the whole notion of trying to warp space to get around the lightspeed issue as nothing more than an attempt at escaping reality. ;) Also some people really like doing math as much as other people like watching Game of Thrones.
One of my favorite points from Ira Glass's lecture: Ideas come from other ideas. There is no such thing as creativity in a vacuum. Your output of ideas is related to the quantity and quality of information you take in.
HN is a good bit better for that than reality TV, but not all resource consumption is bad. This endeavor in particular smells of a fairly cheesy "waste of time" low-budget, low-brow television show.
But the question remains. How did he drop the energy requirements by orders of magnitude, and from my fuzzy memory of such things, would that even be enough to make a warp drive practical?
If he's right, it would be at least, a step in the right direction....
He is only testing the ability to warp space. The setup is extremely simple actually. All he is doing is splitting a laser, one part goes through an extremely charged toroidal capacitor and the other goes through nothing. If the path lengths of these two lasers are the same, but the interferometer reads that the lasers are out of phase, then you have possible warping of space. Most of the cost is probably in the high-precision interferometer.
If you notice a discrepancy, isn't it more likely that one laser was "slowed down", rather than sped up? You'd get the same effect by shining the laser through a thick pane of glass: it arrives out of phase on the other end as if it were slowed down.
| In 2012, physicist Harold White and collaborators announced that modifying the geometry of exotic matter could reduce the mass–energy requirements for a macroscopic space ship from the equivalent of the planet Jupiter to that of the Voyager 1 spacecraft (~700 kg)[5] or less,[19] and stated their intent to perform small-scale experiments in constructing warp fields.[5] White proposed changing the shape of the warp bubble from a sphere to a doughnut shape.[20][21] Furthermore, if the intensity of the space warp can be oscillated over time, the energy required is reduced even more.[5] According to White, a modified Michelson-Morley interferometer could test the idea: one of the legs of the interferometer would appear to be a slightly different length when the test devices were energised.[19]
I don't understand physics to any degree, but I was under the assumption that EM fields also warped space (albeit orders of magnitude less). I found some explanations that are way above my head on Quora:
With that in mind, I continue to be puzzled by the amount of press that this story seems to receive.