1/4 impulse! light(literally) engines are here.

[insane_alien]

http://www.newscientisttech.com/article/mg19125681.400;jsessionid=NMGHKBGMCGMM

 

this guys figured out how to create thrust from microwaves in a closed off copper waveguide. I was skeptical at first (equal and opposite reaction and all that) but it looks ok and its in newscientist so i would gues that it has passed more than a few hurdles already.

 

i want the cool jet/hover car that it shows in the picture!

[[Tycho?]]

Yeah I saw this online a few weeks ago, I just read it on Slashdot now so checked back to see if anyone made a thread about it yet...

 

 

So yeah. Reactionless drives. Seems pretty sweet. I can't really judge the merits of such a device, but New Scientist usually isn't completely off the wall, especially since there is apparently a working prototype. It would be great for any kind of spacecraft. Hover cars would be way off in the distance, as you would need a ton of force to counteract gravity.

 

Still, I hope it all turns out well.

 

Here's a question though: I am learning relativity in university right now, and that it agrees with conservation of momentum. This drive seems to violate conservation of momentum. Does it really? Or is there a way around it using relativistic principals?

[insane_alien]

i have no idea. the physics of the thing is more than a bit beyond me i think. i know how photons transfer momentum but i don't know a thing about wave guides.

 

i'm sure if it was something as simple as that then newscientist would have spotted the mistake. the paper is on the site as well so have a read through it. you might be able to make more sense of it than i did.

[[Tycho?]]

Hmm, well the wikipedia article is extremely critical

 

http://en.wikipedia.org/wiki/Roger_Shawyer

 

Some guy named John Spiller was in charge of verifying if the thing worked, and he said it did. But... I have no idea who this guy is, so that doesn't really explain much. Nothing has been published in a peer reviewed journal, and New Scientist has recieved some flak for being so lax in what they report.

[swansont]

Here's the key:

 

"Then there is the issue of acceleration. Shawyer has calculated that as soon as the thruster starts to move, it will use up energy stored in the cavity, draining energy faster than it can be replaced. So while the thrust of a motionless emdrive is high, the faster the engine moves, the more the thrust falls. Shawyer now reckons the emdrive will be better suited to powering vehicles that hover rather than accelerate rapidly."

 

The high-Q cavity will store a large amount of energy, but it will take a long time to do so. Think of it as spinning up a flywheel, or charging a capacitor. So you may be able to get a large force, but it would have to dissipate insanely fast with displacement, so that energy conservation is not violated. Which is why I don't think it would work to make something hover.

 

The relevant value isn't the static force it can exert, it's the momentum it can exert over distance, and that's not going to exceed E/c. You'd do just as well overall sending the microwaves out of an open waveguide.

[YT2095]

You'd do just as well overall sending the microwaves out of an open waveguide.

 

I am SOoooo glad YOU said that instead of me, that`s exactly what I was thinking also, but didn`t dare post as I`m no Physics expert.

 

I thought of it as a quick release bucket of water being filled with a hose pipe, Whoosh! but then you`re still only left with the hose output

[rajama]

I thought the article was fairly neutral, appearing almost entirely a statement of claims made by the originator. Kind of careful.

 

It reminded me of an anti-gravity machine that appeared on national UK news some years ago - same storage of kinetic energy, but using a pair of gyroscopes.

 

This device used EM radiation - new twist...

 

Actually, more alarming than claims of a reactionless drive was the £1/4million funding from the DTI...

 

Ouch!

 

Question: the article claimed microwaves in the cavity were moving 'close to the speed of light' and had 'their own frame of reference', which I would imagine is just bull, but was this a reference to the group speed for EM in a cavity?

[Bluenoise]

Wouldn't this also apply force to the tapered walls of the cavity?

[[Tycho?]]

Wouldn't this also apply force to the tapered walls of the cavity?

 

I would think so, yes.

[J.C.MacSwell]

;304196']

 

Here's a question though: I am learning relativity in university right now' date=' and that it agrees with conservation of momentum. This drive seems to violate conservation of momentum. Does it really? Or is there a way around it using relativistic principals?[/quote']

 

Yes it violates conservation of momentum. No way around it using relativistic principals.

 

 

It won't work. If it did he would be smart enough to realize this. He would be saying he has a new drive that violates relativity instead of claiming he is using relativistic principals.

[padren]

Another side note:

 

Even if the whole microwaves bouncing back and forth deal worked - if your vessel did a 90 degree turn - wouldn't it loose all the stored energy?

 

The direction of the boucing microwaves would no longer be between the two ends, but bouncing off the internal sides of the tube. New microwaves entering the system from the immiter would be right - but the ones he has bouncing around already wouldn't do anything good at all.

[swansont]

Yes it violates conservation of momentum. No way around it using relativistic principals.

 

 

It won't work. If it did he would be smart enough to realize this. He would be saying he has a new drive that violates relativity instead of claiming he is using relativistic principals.

 

 

You do have a net momentum, though, if you look at it this way: you are using a buildup cavity. If you keep adding photons from one direction, you will have E/c more momentum in that direction for each photon you add. At any given time, then you will have something like E/c * Q (Q is going to be related to how many photons you can get onto the cavity) If you can use all of those photons for propulsion, you will get an instantaneous force like the guy has claimed, but only over a very short distance, because you'll drain the cavity in doing so. (and in a time of 2L/c, so a 15 cm cavity will drain in a nanosecond) The analogue would be (similar to what YT suggested) a pressurized container, like a bucket or hose, that is suddenly uncapped.

 

As I said before, it will not be any more of an impulse than ejecting the photons directly, since you will have losses over time in any cavity. There may be some practical reason to do it in one shot; all you are doing is storing up the energy.

[J.C.MacSwell]

You do have a net momentum, though, if you look at it this way: you are using a buildup cavity. If you keep adding photons from one direction, you will have E/c more momentum in that direction for each photon you add. At any given time, then you will have something like E/c * Q (Q is going to be related to how many photons you can get onto the cavity) If you can use all of those photons for propulsion, you will get an instantaneous force like the guy has claimed, but only over a very short distance, because you'll drain the cavity in doing so. (and in a time of 2L/c, so a 15 cm cavity will drain in a nanosecond) The analogue would be (similar to what YT suggested) a pressurized container, like a bucket or hose, that is suddenly uncapped.

 

As I said before, it will not be any more of an impulse than ejecting the photons directly, since you will have losses over time in any cavity. There may be some practical reason to do it in one shot; all you are doing is storing up the energy.

 

 

Understood, except I don't think that is what he is claiming. Also 99.99% of the energy leaves with the photons, not going into propulsion. Extremely inefficient.

 

I think he is claiming that the shape of the chamber influences the net rebound/impulse of the continuously resonating photons. An analogy would be putting a boat in the water and it moves forward because of it's shape.

[swansont]

Understood, except I don't think that is what he is claiming. Also 99.99% of the energy leaves with the photons, not going into propulsion. Extremely inefficient.

 

I think he is claiming that the shape of the chamber influences the net rebound/impulse of the continuously resonating photons. An analogy would be putting a boat in the water and it moves forward because of it's shape.

 

Oh, I agree that his explanation is BS. There is an effect, but it's easily explained with standard physics.

[Norman Albers]

i have no idea. the physics of the thing is more than a bit beyond me i think. i know how photons transfer momentum but i don't know a thing about wave guides.

I think of waveguides as mirrors, or rather a little hall of mirrors tuned to propagating a wavelength.

[JTM³]

So I guess this doesn't really work then?

[Rocket Man]

what speed does matter have to exit as the exhaust of a rocket for it to produce the same thrust of the mass energy as light?

if we could turn matter into energy we could have a fairly simple propulsion method (antimatter?)

[Norman Albers]

Your are only allowed one guess and I know mine!

[SmallIsPower]

I would bet against it......

 

Even if it did work, wouldn't relatistic forces rip it open?