Boldly going nowhere

To start out with the tl:dr -- no, despite what you may have heard, physicists do not have a working model of a warp drive.

Look, no one would love it more than me if we did.  I grew up on Star Trek and Star Wars, and the whole going-so-fast-the-stars-are-streaks thing is burned into my imagination.  (So, of course, is the weird trope from Lost in Space that if you go faster than light, time runs backwards.  I didn't say this stuff was all plausible.)

The reason we stargazers so desperately want a warp drive is because the distances involved in space travel are, well, astronomical.  Here's an analogy that will give you a feeling for it: imagine that the Sun (which is about 1.4 million kilometers in diameter) is shrunk down to the size of a marble, with a diameter of about 1.5 centimeters.

The Earth would be about the size of a grain of fine sand, and would be roughly a meter and a half away.  Jupiter would be eleven times larger in diameter, and over five times farther away.

You ready?  The closest star to the Sun, Proxima Centauri, would be a somewhat smaller marble, over four hundred kilometers away.  So if the marble-Sun was located in my living room, here in upstate New York, the marble-Proxima-Centauri would be somewhere around Baltimore, Maryland.

Everything in between is empty space.

Here's another way to think about it.  Voyager 1 -- the fastest human-made spacecraft ever created -- is traveling at about seventeen kilometers per second.  Which seems really fast, until you find out that at that speed, to get to Proxima Centauri would take seventy thousand years, if it was heading that way, which it's not.

So you can see why a warp drive would be nice.  How are we supposed to have a nice chat with the aliens when they're impossibly far away?

Well, if there's one thing I've learned, it's that the universe is under no compulsion to make me happy.  And at the moment, the current research -- led by Harold White of the Advanced Propulsion Laboratory -- doesn't make me happy at all.

The dozens of headlines in popular media I've seen claiming that the new paper has proposed an actual schematic for building a working warp drive aren't just exaggerations, they're outright fabrications.  Sabine Hossenfelder had a look at the paper, and for the first time I can ever recall, she (1) said the paper should never have been published in the first place, and (2) gave it a ten out of ten on her Bullshit Meter.  (She did not, however, do what I once saw her do, which is to print out the paper and then set fire to it, so I guess it could be worse.)  What all the hype is failing to tell you about is that White et al. have not actually created a "blueprint."  Here's Hossenfelder's take on it:

The way that they construct their so-called warp drive is that they postulate some curvature of spacetime and then postulate that it moves at a certain speed.  They then calculate the required energy from that.  That's their "engineering."  They postulate a shape, which they then plot.  The problem with this procedure is that it makes it entirely meaningless to say the warped space is a solution to Einstein's equations.  You see, you can take any, and I mean literally any, spacetime with any curvature, moving or not, and put it into the equations, and then just read off the source and call that a "solution."  The problem is that in general, there is no physically possible distribution of energies that gives you that source.  And of course, their so-called warp drive still needs negative energies.  Worse, they don't even mention the biggest problem with warp drives, which is that they still need to fulfill momentum conservation.  If you accelerate something going that way, you need to throw out stuff the other way.  This means that even with a warp drive, you still need a propulsion system.  

So, much as I hate to say it, this paper doesn't even get us incrementally closer to solving the faster-than-light travel problem.  We haven't discovered dilithium crystals or built warp field generators, or better still, seen any research by Zefram Cochrane.

I hate to throw cold water on anyone's excitement, but let's keep in mind that in this case, reality would have stepped in and done it sooner or later anyhow.

So that's today's rather short and disappointing foray into space.  Like I said, it's not that I'm happy about any of this.  At the moment, if there was a warp drive invented that could take us to distant star systems, I'd be the first in line.  For one thing, it'd be thrilling to see another planetary system close up.  For another, I'd finally be far enough away from Donald Trump.  But I'm afraid for now, we're stuck here on Earth, and probably will be for the foreseeable future.

Of course, I'm the same guy who told his students "adult tissue cloning is at least ten years in the future" exactly two weeks before Dolly the Sheep made headlines.  And in this case, if I'm wrong, I'd be somewhere beyond delighted to eat my words.

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Robustness, data, and the EmDrive

I get asked rather frequently why I put such trust in the scientific process.  Often, that question is framed even more pointedly; doesn't my belief in the reliability of science amount to religious faith -- something that I believe simply because I believe it?

It's an interesting subject, and it will probably come as no real surprise to my readers to hear that I think the answer to the latter question is "no."  When science is working as it should (and it doesn't always; as a human pursuit, it's subject to human fallibility, like anything else), we amass evidence, craft theories to explain said evidence, rule out ideas that aren't supported -- and in so doing, we get closer and closer to a theory that is self-consistent and explains all of the data we currently have.  Scientists call such a theory "robust."

And once we're there, the idea that something could come along and shatter the whole thing falls into the category of "possible, but extremely unlikely."  People like to cite Einstein and relativity as having destroyed the Newtonian view of the world, but this isn't really so; Newtonian physics works perfectly well at the speeds and masses we usually experience.  It is only at velocities near light speed, or masses with a big enough gravitational pull to warp spacetime significantly more than the Earth (or even the Sun) does, that we see a big enough relativistic effect to measure.  So Einstein was more of a refinement of Newton than an invalidation.

The reason all of this comes up is because of the recent news about the EmDrive, a propellant-less propulsion system that its creators claim uses quantum and relativistic effects to generate thrust from a closed system.  The drive, which uses microwave or radio wave generation inside a shielded shell, allegedly has been measured to produce a "few ounces" of thrust, and a paper describing the physics behind it has allegedly passed peer review and will be published this fall.

The problem is, the vast majority of the physicists -- i.e., the people who actually understand the intricacies of how the thing works, not to mention theories of propulsion, thermodynamics, quantum mechanics, and the rest -- are, in general, doubtful.  Physicist Sean Carroll, who writes passionately about the cutting-edge nature of modern physics research, and is up front about how much we don't know, was unequivocal:

There is no such thing as a ‘quantum vacuum virtual plasma,’ so that should be a tip-off right there.  There is a quantum vacuum, but it is nothing like a plasma.  In particular, it does not have a rest frame, so there is nothing to push against, so you can’t use it for propulsion.  The whole thing is just nonsense.  They claim to measure an incredibly tiny effect that could very easily be just noise.

Others have called the explanations given by EmDrive creator, engineer Roger Shawyer, as "Star Trek technobabble," or more simply, "bullshit."  (The latter from physicist John Carlos Baez of the University of California - Riverside.)  In order for a true exhaustless drive to work, it would have to overturn nearly everything we know about mechanics (quantum, Newtonian, relativistic, and otherwise).  In other words, it would point to a great big hole in our understanding of physics.

Once again: possible, but extremely unlikely.

Don't get me wrong -- no one would be more thrilled to have a potential interstellar drive system more than me.  If there was a spaceship that could get us to another star system in weeks or months (instead of tens of thousands of years) I would be elbowing people out of the way to get to the head of the line.  But the likelihood that the EmDrive is it seems slim to me, and the chance that what effect they've seen is simple experimental error or (as Carroll says) just noise nearly 100%.

Like any good skeptic, though, I'm perfectly willing to see the thing tested -- and I hope it does work. For one thing, if it did it would mean that there is a lot of physics out there that we don't understand, which is tremendously exciting.  For another, it would mean that we have a completely new way to power spacecraft, which is somewhere beyond tremendously exciting.  If the alleged peer-reviewed paper turns out to hold water, and tests of the thing -- data from which we should get in six months or so --  show that there is something to it, I will happily eat my words, publicly.  Look for a retraction right here in Skeptophilia -- should such an eventuality come to pass.