Thursday, April 30, 2015

Bad science, bad science journalism: the EmDrive

No, NASA has not discovered warp drive.  There is a huge amount of media attention (here, here, here, for examples of relatively mainstream media) being given to a claim that a NASA team has successfully tested a gadget called the EmDrive.  The claim is that one can take a conical microwave resonator (picture the cavity that is your microwave oven, only shaped like a truncated cone rather than a rectangular box), fire up microwaves to drive the resonant modes, and the cone will experience a steady thrust in one direction (the direction of the fat end of the cavity).  There are multiple alleged explanations for this, ranging from botched thinking about special relativity to really bizarre word-salad about virtual particles, the quantum vacuum, and "warp fields".

Let me explain why this is bad science, terrible science journalism, and highly problematic.

First, the science.  Our theory of electricity and magnetism is arguably the best understood, most precisely tested theory we have, both in its classical limit (the limit relevant for your microwave oven) and in its quantum limit (the limit relevant for things like calculating the magnetic moment of the electron, something that we can do to more than 14 decimal places!  According to that theory, a closed microwave resonator does not generate thrust (surprise surprise).  Given over 100 years of tests of classical E&M, it's going to take more than one poorly documented experiment, not published, to convince scientists that something exotic is going on.  Extraordinary claims require extraordinary evidence, and this just isn't it.  Moreover, claims that exotic quantum vacuum effects or "warp fields" are somehow relevant here are just on their face absurd!  The energy densities, the materials involved, none of this couples to exotic quantum vacuum physics any more than my microwave oven does.  This is like arguing that by accelerating a simple dielectric like a piece of plastic, I should see electron-positron pair production and warped spacetime.  It's nonsense.

What would it take to convince me?  How about a thoroughly documented experiment done by someone with credibility in precision measurement, for a start.

As for science journalism:  The number of outlets who uncritically pass along something like this is appalling.  What's worse, they distort it even more - the third link up top not only claims that this is a reactionless drive, but that it will allow faster-than-light travel.  What the hell?  (Yes, I know that the Daily Fail is third-rate fish-wrap.)  I fully expect to see a CNN story about this, and it will be terrible.  This will propagate in the media for several days, and they will portray it as some underdog inventors showing that the Scientific Establishment is wrong, or they'll present this as an actual scientific controversy, when in fact the burden is all on the experimenters to show that their work (which flies in the face of decades of contrary evidence) is right.  Hey, IFLS:  You should be ashamed of yourselves for your coverage of this.  Good grief - I thought part of your message was that people should, I don't know, think critically!

Why is this problematic?  It's an issue because people don't trust science, in part because they end up reading uncritical bull like this and come away thinking that science is either a dodge, a scam, or entirely a matter of opinion, when in fact it's an approach to thinking critically about the world that has made possible all of modern technology and medicine.

16 comments:

Michael Baldwin said...

I also don't like buzzwords like "quantum vacuum" etc, but the fact remains: This drive has been independently tested, in numerous countries around the world and has been found to produce thrust by some means. This is not arguable. The terms may be.

Steve said...

Thank you for posting this. I've seen warp-drive-garbage coming out of NASA for several years now and I was hoping someone would take them to task. It is a bit depressing that taxpayer money is being used for such crap. It is also depressing that news outlets don't bother to ask anyone who has any knowledge of the field whether this is at all meaningful.

Carolyn said...

What if any are the differences between the EmDrive and Cannae drives? There is an actual company http://cannae.com/

Douglas Natelson said...

Michael - "numerous" = 2 if we're going beyond anecdotes, and the fact is that doing a serious, careful experiment on this is very difficult for several reasons. Mounting a high-power microwave resonator so that there are no small unintended forces due to, e.g., the currents flowing in the input or the cavity walls, or thermally produced forces due to temperature gradients in the fixturing, etc. is hard. The reported forces are also small. They may well be measuring something, but there is no way that it's something that (apparently) violates conservation of momentum via relativistic reasons, the quantum vacuum, virtual particles, or big foot.

Carolyn, it looks like they're very similar.

Believe me, I'd love to see a genuine breakthrough in propulsion technology - I'm a huge SF fan. However, this isn't it.

I truly don't understand the apparent uptick in claims that somehow classical E&M systems (like these microwave cavities, or in the case of "Sonny" White's "Mach effect" gadget that involves charging and discharging capacitors) are a gateway to exotic physics (the quantum vacuum, gravitational radiation to carry away momentum, etc.). There is plenty of exciting exotic physics (dark matter? dark energy? matter/antimatter asymmetry?) - trying to get there via a theory that is known to be accurate to 15 decimal places without any of that stuff seems like a bad strategy.

Sean Nelson said...

What I hate is the blog/news reports that the laser went FTL when the opposite was observed. In this laser interfermeter experiment light was slower than it should have been. The explanation they're going with was, if we know it's speed was constant, and the time was longer, it must have traveled a greater distance so there appeared to be space expansion no length contraction so its 1/2 the Alcubierre metric (ergo 1/2 'warp bubble') Don't get me wrong if that happened its a breakthru but you need the length contraction too to 'spoof' FTL. Looking at this graph there was no negitive dip http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=36313.0;attach=825620;image Next laser test will be done in a vacuum to try to repeat the results ( or disprove them possibley because of gas refraction in the first test )

Peter Morgan said...

On the face of it, 0.4 Newtons/kW doesn't need a lot of precision. OTOH, the figure for electromagnetism ought to be of order 1/speed-of-light = 3e-6 Newtons/kW.

Anonymous said...

On the other hand, physics has been so unproductive in the past 30 years that its primary economic impact is in writing popular science books.

JasonDeibel said...

Dear Anonymous @ 1:39 AM,

If you are enjoying posting to blogs from your computer that has increased in performance, memory, and hard drive space by orders of magnitude in the last 30 years and don't get how physics has impacted societies and economies, then I suggest that you read more physics blogs. By the way, before you counter with that all of this was done by engineers, know that all of it was started with both basic and applied research done by physicists. You are also welcome for developments in security, medicine, renewable energy, etc.
Jason Deibel

Douglas Natelson said...

Anon, you must've missed the multibillion dollar GMR/TMR hard drive industry that lead to cloud storage. Since the primary purpose of science is not to have economic impact, that's a pretty good collateral benefit.

Zach said...

Huh. Looks like Harold White, one of the proponents of this whole thing, has a Ph.D. In Physics from Rice. Truly a credit to his alma mater.

Douglas Natelson said...

I was actually on Harold White's thesis committee. His thesis ended up being about lightning on Venus as studied via data from the Magellan spacecraft.

photofunia said...

Thank you for posting this. I've seen warp-drive-garbage coming out of NASA for several years now and I was hoping someone would take them to task. It is a bit depressing that taxpayer money is being used for such crap. It is also depressing that news outlets don't bother to ask anyone who has any knowledge of the field whether this is at all meaningful.

Anonymous said...

No laws are broken, the warp fields created within the resonance chamber pull space/time into them and push them back out. Remember even in a vacuum space/time exists. This resembles a type of gravitational pull on matter ahead of the warp including the body of the engine toward the warped space/time area. this can be imagined like a space/time compressor inducing velocity. what this means is space/time warps are created by low power microwave resonance... at the moment the warp is contained within the body of the resonator but it may be possible to project the warp outside the body of the engine enabling the whole engine to travel within the warped space/time at FTL speeds. this doesn't break any laws because space/time is warped. the attribution to quark vacuums or lenz effect is wrong. it's simply that no-one ever noticed that microwave resonance warps space/time before

Douglas Natelson said...

Anon@10:18 - You throw around lots of buzzwords, but there is simply zero evidence that microwave fields nontrivially warp space-time. People have been doing high power microwave experiments for seventy years, often in close proximity or direct contact with, e.g., beams of relativistic charged particles that would be extremely sensitive to anything exotic. No one has ever seen anything remotely like this, period. Occam's razor: What's more likely - (1) that moderate power microwave cavities (like your microwave oven!) warp space-time for a reason completely overlooked by one of the most precisely tested theories ever, and no one ever noticed this before despite decades of experiments; (2) these people who want to believe so badly have made a mistake somewhere.

Daniele Sicoli said...

Dear Douglas Natelson,
in your article you said that QED is the quantum limit of our theory of electricity and magnetism (Did you mean Maxwell's equations?)
This is wrong since QED is more fundamental than Maxwell's theory, which is the classical limit of QED.
Maxwell's theory says that the EM drive cannot exist. QED does not.
Actually I do not know wheter or not QED says something about it. Then maybe this is allowed at a quantum level.
I think experiments are more important than theory and I would be very interested in seeing the results of such an experiment. Maybe we should change something of maxwell's theory, maybe in the standard model. Maybe EM-drive is a fake.
I would like to know.
Why shouldn't the Higgs potential, which is defined all around us, be able to cause tangible effects?

Daniele Sicoli said...

I used the Higgs potential as an example, there may be an infinite number of things that can make it possible, maybe the mechanism which gives mass to neutrinos, why not? So I don't understand why we don't do other and more accurate experiments.