Warp Drives Revisited
massive errors and microscopic starships
This really does end up being about microscopic starships, but it gets there by way of a homily on what to do in the face of a mistake, which like most mistakes is an opportunity to reflect and learn.
I've written previously about the Alcubierre warp metric and the possibility of practical starships, and there has recently been a fascinating development that suggests a practical way to investigate the phenomenon, albeit at a very small scale.
Miguel Alcubierre is a Mexican physicist who realized that under very special circumstances there was a solution to Einstein's equations for General Relativity that would result in a "warp bubble", a travelling region of spacetime that moves by compressing space ahead of and stretching it out behind in a way that leaves a gap in the middle undisturbed. Because from the point of view of the universe nothing is actually moving, a bubble like this can travel at any speed.
The problem is that creating this situation requires producing a region of "negative energy", and I said at the time, "...no one knows how to create 'negative energy', or even what it means... if anything" which turns out to be false.
When you drop the ball completely like that it's always worth standing back and asking why. The non-analytical alternatives--beating yourself up over it, pretending it never happened, and so on--don't really do much. You can't learn anything from them, so what's the point, really?
In the case of saying something that isn't true, the first thing I ask myself is, "Did I or could I have known it was false?" Sometimes the answer is, "Nope. No way I could have known that." It's reasonable in those circumstances to poke around and ask if there might have been any clues I was missing information, or if I had some thinking on the back burner which if I'd brought it to the front might have helped.
This is an example of what I'll call "internal mindfulness", which is an awareness of little curious feelings we get that might be clues to work that would be useful to us. Sometimes an idea will kind of bug me for a while for reasons I don't understand. I've learned to ignore such feelings and wait for them to go away. If they don't do so after a few days, or if they come back a couple of weeks later, I take some time to pull on the thread they represent and see if it leads anywhere. Sometimes it does. Sometimes it doesn't. We don't have infinite amounts of time so we can't follow up on everything, but the popular heuristic of "eh, it's probably not important" is too extreme in the other direction: we wind up ignoring everything, and wandering through life in ignorance. I can't be having with that.
On the other hand, sometimes the answer to "Could I have known it was false?" is, "Oh, yeah." In those cases the problem is usually limited attention.
Attention is our scarcest and most powerful resource. What we pay attention to governs our lives, be it fear or joy or curiosity or love. What we don't pay attention to ceases to exist. We don't notice what we don't notice. We don't remember what we have forgotten.
We can only attend to between three and five things at once, and managing our limited attention well is one of the most challenging aspects of being human. I often feel deeply fortunate that I live after what Stephen Pinker calls the "Great Informalization", the revolution in the West in the 20th century where almost of the remaining social rituals washed away in the tide of war and upheaval and liberal democratic capitalism that swept the world. Societies that invest a lot in complex social rituals place high demands on the limited attention of their citizens. It's almost as if they want to leave nothing over that might be used to focus on anything else.
One of the most powerful tools for managing attention is reductionism: dividing and conquering complex topics by branching them into smaller and smaller sub-topics. Another is abstraction: lumping complexities together into generalities to keep the number of concepts we're juggling at once small enough to handle. Between the two of them we can get a lot done with the limited attention we have.
On the other side, the least functional approach to any problem is "holistic", which asks us to "pay attention to the whole", which we have as much chance of doing as lifting a thousand-pound weight. Sometimes we do have to step back and take a broader view, but we should never mistake that for a view of the whole. At best we can catch a glimpse of a few crude brush-strokes. It is a mistake to think we've absorbed the entire image.
All of which is a long-winded way of saying that of course I know what "negative energy"is. But that knowledge belongs on a different branch of the tree I use to organize my attention. I was writing about general relativity, and negative energy is a concept I keep stored over in quantum mechanics. It takes some time to wander over there and fish it out, but as soon as I read about the present work on the potential to build a tiny Alcubierre warp bubble I went, "Duh" and realized my attention had been elsewhere while writing about the topic originally.
This is not an indictment of reductionism or abstraction: they are the best tools we have to work with the limited attention that is available to us, and insisting we discard them because they don't Solve All The Things is like saying we should cease using a block-and-tackle and heft that thousand pound weight with our bare hands, just because a rope broke that one time.
So, negative energy works like this: imagine two ships anchored side-by-side, like the freighters that routinely anchor off my little island, waiting for berths in the Port of Vancouver. Here's a picture, looking end-on:
As the ocean tends to be rough, I've drawn in waves but notice there are waves with longer wavelengths in blue and shorter wavelengths in red. The space between the ships is too narrow for the longer wavelengths to fit, and this results in an absence of wave energy from those longer waves in that space. Because the outsides of the ships are still getting hit by waves of all wavelengths, and the insides are only getting hit by the waves with shorter wavelengths, this results in a slight force that tends to push the ships together.
In reality, this is never an issue: real freighter anchorages are well-spaced, but it turns out you can see this in a carefully constructed lab setup with two flat plates hung parallel to each other in a water bath that is set vibrating.
Now, the vacuum of space is actually full of electromagnetic waves and virtual particles, popping in and out of existence in a time that's too short to be observable. And because this is happening uniformly, everywhere, it has no effect... unless we put two perfect conductors very close together and exclude the longer wavelengths, in which case we get a tiny region of negative energy. It is "negative" relative to the surrounding vacuum, which is full of waves of all wavelengths.
This effect was predicted by Dutch physicist Hendrik Casimir in 1948, and detected unequivocally in 1998, although there had been suggestive experimental results prior to that. Our ability to make these measurements is fundamentally a result of advances in microfabrication that have come out of the semi-conductor industry in the past fifty years.
There are various potential uses of the Caismir force, including creating energy storage devices of extremely high energy density, so of course the US military is interested in it, and DARPA, the American defence research group that gave us the internet, is funding work on various more exotic configurations than simple parallel plates. As is usual in quantum mechanics, as soon as you deviate from the simplest geometry finding the solution goes from something a genius can work out with pencil and paper in 1948 to something that can only be solved approximately using a gigantic super-computer and a deep toolkit of incredibly clever tricks.
One of the geometries they were investigating resulted in a distribution of negative energy density that looked strangely familiar to the lead physicist, American Harold White, who has also been involved in work on the Alcubierre metric.
More detailed investigations followed, and the result is that there are plausible geometries on a micron scale in which the negative energy density created by the Casimir effect looks very much like that required to generate an Alcubierre warp bubble.
That's not exactly zooming through space on the bridge of the Enterprise, and the work thus far is entirely computational: no actual warp bubble has been created. Time and real experiments will tell. But these small steps may be taking us a giant leap closer to the stars.