This paper claims to explain how the notoriously click-baity EmDrive could actually be working. If you've been living under a stone on Mars, the EmDrive is a magical copper tube that proponents claim will be able to get you back home to Earth in double-quick time without using any propellant. Everyone else says that's just silly because it means violating the conservation of momentum, which is tantamount to saying that a wizard did it.
There are two very positive aspects to this paper :
1) It wouldn't violate the conservation of momentum after all, thus saving the Universe from magical leprechauns and wicked pixies.
2) It makes a very clear and testable prediction that the thrust the device is supposedly producing could be reversed if the tube was made shorter.
I remain extremely skeptical in many senses of the word (http://astrorhysy.blogspot.cz/2015/09/skepticism.html) because there are also some very negative aspects of the paper, not least of which is that the idea behind it can also explain galaxy rotation without dark matter and the acceleration of the Universe without dark energy. That rather smacks of being too good to be true, and anyway it's not just galaxy rotation curves which suggest the need for dark matter.
Then there's the fact that it references few peer-reviewed journal articles (this article is itself not peer reviewed) and the acknowledgements section consists of : "Many thanks for Dr Jose Rodal and others on an NSF forum for estimating from photographs the proportions of the various experimental arrangements."
Yeah, really ? Some dudes on the internet looked at a photograph for you ?
None of which means the idea isn't true - I haven't gone through it properly. But "too good to be true" ideas with dodgy references have an awfully strong track record of being... well, too good to be true.
[The EM drive has been completely discredited by repeated tests that measured a small thrust even when turned off, indicating that this is a good old-fashioned low-significance measurement error.]
http://arxiv.org/abs/1604.03449
Hmmm... build one and put it in orbit and test it there? Someone once abused me on the internet for suggesting something along those lines. I wasn't even being snarky or anything.
ReplyDeleteIs NASA getting more funding to study it (the EM)?
ReplyDelete____________
Also...
"...the idea behind it can also explain galaxy rotation ..."
Hmmm. Would that make the rotation direction (CW/CCW) predictable in galaxy formation? Or is CW/CCW just an "above or below view" issue? How could you know?
Robert Hoyle As you say, it's an above or below issue. There's no standard against which to measure the rotation direction. Actually some galaxies have components which rotate in opposite directions :
ReplyDeletehttps://medium.com/starts-with-a-bang/messier-monday-an-elliptical-rotating-wrongly-m59-3228197387ac#.2h0no5i1v
As far as I can tell, this wouldn't necessarily cause any problems for this idea (or indeed most other ideas of gravity/inertia). It only predicts the speed of the rotation, not the direction. It's not obvious to me if this model has any fatal flaws from a galactic perspective, I have to think about it some more.
Tks Rhys Taylor,
ReplyDeleteI finally get a definitive answer on this rotation direction issue that has perplexed me for many years. Angular momentum is a curious creature. (Or, is it?)
So...on Ethan's M59 analysis -- there is something of a “whirlpool” effect when stars fall into a black-hole? And, that’s what’s causing the very faint spiral structure and "opposite direction" rotation near the core?
Nature is incredible. We have “whirlpools” here on Earth b/c of Coriolis "forces," etc — but there are analogs even in galexies. Amazing.
Finally, on the EM -- I so hope this all works out. But...it's my understanding that they need more research funding.