New paper claims that the EM Drive doesn't defy Newton's 3rd law after all

[n2doc]

Physicists have just published a new paper that suggests the controversial EM drive - or electromagnetic drive - could actually work, and doesn't defy Newton's third law after all.

In case you've missed the hype, here's a quick catch-up: a lot of space lovers are freaking out about the EM drive because of claims it could get humans to Mars in just 10 weeks, but just as many are sick of hearing about it, because, on paper at least, it doesn't work within the laws of physics.

Despite that not-insignificant setback, the EM drive shows no signs of quitting, and test after test - including trials by NASA scientists at the Eagleworks lab, and an independent researcher in Germany - has conceded that the propulsion system, somehow, does produce thrust.

Why is that so surprising? That's because of how the EM drive is supposed to work, in theory at least. First designed by British scientist Roger Shawyer back in 1999, the EM drive uses electromagnetic waves as fuel, and creates thrust by bouncing those microwaves back and forth within a metal cavity to trigger motion.

more
http://www.sciencealert.com/new-paper-claims-that-the-em-drive-doesn-t-defy-newton-s-3rd-law-after-all

[tonyt53]

1. Been keeping up with that thing, It is intriguing. I wonder how strong gravity would affect it

[itsrobert]

2. Magnets?

What happens when it flys by a cloaked alien spaceship? Will the alien ship get pulled into its magnetic field?

[TexasProgresive]

3. I know you are being snarky

But what do magnets have to do with this drive? Light, heat and radio waves are in the electro-magnetic spectrum.

[longship]

4. Why doesn't my car move forward when I push on the steering wheel?

That's why the EM drive cannot work.

Pretty simple, actually.

[Warpy]

5. Yeah, except that it does

[longship]

6. That would violate all sorts of physics.

It doesn't. It just fucking doesn't.

So, there's that.

[Warpy]

7. Did you read the article?

What I want to see is if it works in a vacuum.

[longship]

8. I am aware of the EM drive.

It's bollocks.

And being in a vacuum or not is irrelevant as anybody who understands symmetry in physics would understand.

The operative principle here is the conservation of momentum, Newton's first law.

This is physics 101.

[Warpy]

9. Of course it is. Now read the article

You can do it. I know you can.

[longship]

10. I read it. It's still bollocks.

And if it is emitting photons, that is the origin of its thrust. But the whole deal is that the EM drive has always been pitched as a reactionless drive, one which has no emissions. And it is bollocks, no matter if somebody has figured out, by some hand waving, that it after all has some emissions.

It is not nice to fool Mother Nature.

I stand by my posts here.

[muriel_volestrangler]

15. No, people aren't interested because it "has no emissions"

They are interested because it doesn't need to carry reaction mass. If the 'exhaust' is photons, without mass but with momentum, then it changes the rocket equations, potentially in our favour.

[longship]

16. The rocket equation is pretty simple.

It's Newton's laws, conservation of momentum.

It is not nice to fool Mother Nature.

I'll leave it there.

[muriel_volestrangler]

17. No, it's not just Newton's Laws. Propellant mass is key to it

https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation

(yes, it's all derived from Newton's laws, but it involves the mass of propellant you have to accelerate with your actual payload before ejecting it as exhaust)

[cstanleytech]

18. So in other words it doesnt violate any laws because the particles its emitting (?) or

whatever its doing still have mass even though it might be an extremely small amount of mass?

[muriel_volestrangler]

20. Light has momentum, but no mass

This may seem an odd situation in classical physics, but was worked out when James Clerk Maxwell determined it is an electromagnetic wave. This is also the principle behind solar sails.

[cstanleytech]

21. I thought that in the end everything had mass even light but if it doesnt have mass then how can it

be captured by a blackhole?

[muriel_volestrangler]

22. Light is affected by gravity, but it doesn't have mass of its own

The gravity of a black hole bends space so much that light cannot escape the volume around it.

[cstanleytech]

23. My heads hurting now, I think I need an iburprofen :P lol

[longship]

24. We'll, it's conservation of momentum.

Action... Reaction. The mass accelerated includes the fuel, of course. The good ol' rocket equation.

I don't see the problem here. This EM drive cannot work. Theoretical physicist Sean Carroll compared it to pushing on your steering wheel to move your car.

[muriel_volestrangler]

26. But photons don't have a mass, but do have momentum

See eg http://physics.stackexchange.com/questions/112866/if-im-floating-in-space-and-i-turn-on-a-flashlight-will-i-accelerate

[DetlefK]

11. Because your car is invariant to spatial coordinate-translations.

Whether it rolls forward or backward, it's the same.

But the trick of the EM-drive is that the two ends of the device are different. I also don't know how it works, but this violation of spatial invariance allows (in theory) something weird to happen with respect to momentum.

(Momentum and space are conjugated variables, just like energy and time, angular momentum and angle.)

[longship]

12. Absolute rubbish.

Momentum is conserved.
No matter how one twists things.

Conjugated variables????? That's nothing I learned in my physics degree. Sounds like rubbish to me.

As does the EM drive. There is no such thing as a reactionless space drive. Or a warp drive, for that matter.

Pushing on ones steering wheel does not propel ones car forward. Newton got that correct.

[DetlefK]

13. I'm sorry to say, but then your physics degree is a sham. You should demand your money back.

https://en.wikipedia.org/wiki/Conjugate_variables

If you don't know conjugated variables, how do you solve problems in hamiltonian mechanics?

How do you calculate spatial translations in quantum-mechanics?

How do you calculate the time-evolution of a quantum-mechanical state?

How could you possibly define intertial-systems apart from accelerated systems?

How do you establish a connection between the energy-momentum-tensor of a translation and the time-space-coordinates of a particle?

For all these things you need the concept of conjugated variables.




If you can tell me a way how to derive conservation of momentum without going back to translation-invariance, I will be very impressed and will take it all back.

[longship]

14. Heisenberg may have been here.

This has absolutely nothing to do with conservation of momentum, other than momentum is a conjugate to position in quantum theory, just like energy and time are conjugates.

That says nothing whatsoever about reactionless drives, which violate basic principles of physics.

I will stand by my posts here. Let me know when this thing you are promoting achieves any credibility. I'll settle for a peer reviewed journal entry.

My best to you.

[DetlefK]

27. Glad you took no offense.

These conjugated variables exist not only in quantum-mechanics but also in newtonian/hamiltonian mechanics.

Yes, this EM-Drive violates the principle of conservation of momentum, BUT if it ALSO violates the way normal space-time behaves, by not having this translation-invariance, then conservation of momentum is no longer enforcable.

Let's put it this way: The EM-Drive (if it works and if it works as I suppose) does not technically break the law. It found a legal loophole.

[longship]

28. It is being universally panned by physicists.

Sean Carroll ripped it apart.

[cstanleytech]

19. You're making my head hurt. nt

[longship]

25. Here's Sean Carroll on this rubbish.

http://www.preposterousuniverse.com/blog/2015/05/26/warp-drives-and-scientific-reasoning/

(As well as the so-called NASA warp drive.)
Both are utter bunkum.