Physics question that might interest some people here

[sandorski]

Hmm, maybe that's why my teeth hurt. Anyone wanna buy a used Microwave? It's got a turntable and everything!

 

[dxkj]

why dont we just use lasers to push the half as heavy microwave powered spacecrafts into orbit?

 

[Eeezee]

Originally posted by: sandorski
Hmm, maybe that's why my teeth hurt. Anyone wanna buy a used Microwave? It's got a turntable and everything!

Usually microwaves don't actually leave your microwave oven unless there is something seriously wrong with it. Microwaves are send down a waveguide into the cooking chamber, and they actually can't leave that chamber.

 

[newmachineoverlord]

Yes, light exerts pressure on things, yes photons have momentum, yes solar sails should work in theory.

If you have light trapped in a bottle, and the bottle moves, then relativistic effects will mean that to the bottle, the light has a higher frequency on on end than on the other. Momentum for light is proportional to frequency, so this gives us our net force, but this net force is always in the direction opposing the motion of the bottle. Thus this idea could be used to decelerate spacecraft once they were more than halfway to their destination, but it couldn't be used to increase velocity, unless there's a clever frame of reference trick I'm not seeing, or microwaves are allowed to leak from one end and not the other (costing energy.) The deceleration usage still seems like a violation of conservation of energy hax, but at least it should only work at relativistic speeds or very high energy flux. OMFG I just got it, he must be using a refractive medium so that when light goes in one direction, it bends its path to turn around instead of being reflected. Actual momentum transfers only in the case of reflection, not refraction. In this case I must admit this is an uber physics hax. Except that wasn't described in the article, so maybe I should go patent it real quick.

http://83.219.63.174/Articles/295931/Microwave%20engine%20gets%20a%20boost.htm
Shawyer cautions that the calculations only work for static thrusts. ?You can?t beat the laws of physics. If it is used to accelerate, the Q value drops. It is best used to lift a body and oppose a force, for instance to counteract gravity. It cannot be used to accelerate further.?

 

[MikeMike]

my head hurts

 

[TheBDB]

Originally posted by: everman
It all seems to depend on this being true:

How can photons confined inside a cavity make the cavity move? This is where relativity and the strange nature of light come in. Since the microwave photons in the waveguide are travelling close to the speed of light, any attempt to resolve the forces they generate must take account of Einstein's special theory of relativity. This says that the microwaves move in their own frame of reference. In other words they move independently of the cavity - as if they are outside it. As a result, the microwaves themselves exert a push on the cavity.?

Shouldn't they be at the speed of light?

 

[Eeezee]

Originally posted by: TheBDB

Originally posted by: everman
It all seems to depend on this being true:

How can photons confined inside a cavity make the cavity move? This is where relativity and the strange nature of light come in. Since the microwave photons in the waveguide are travelling close to the speed of light, any attempt to resolve the forces they generate must take account of Einstein's special theory of relativity. This says that the microwaves move in their own frame of reference. In other words they move independently of the cavity - as if they are outside it. As a result, the microwaves themselves exert a push on the cavity.?

Shouldn't they be at the speed of light?

Technically, yes, but the article meant "they are near the speed of light in a vacuum." The photons in the chamber would be moving at the speed of light in air, which is just barely slower.

In the water they use at nuclear reactors, a mysterious blue glowing effect can be seen because some of the electrons are moving faster than the speed of light in the water.

 

[Heisenberg]

Originally posted by: Eeezee

Originally posted by: TheBDB

Originally posted by: everman
It all seems to depend on this being true:

How can photons confined inside a cavity make the cavity move? This is where relativity and the strange nature of light come in. Since the microwave photons in the waveguide are travelling close to the speed of light, any attempt to resolve the forces they generate must take account of Einstein's special theory of relativity. This says that the microwaves move in their own frame of reference. In other words they move independently of the cavity - as if they are outside it. As a result, the microwaves themselves exert a push on the cavity.?

Shouldn't they be at the speed of light?

Technically, yes, but the article meant "they are near the speed of light in a vacuum." The photons in the chamber would be moving at the speed of light in air, which is just barely slower.

In the water they use at nuclear reactors, a mysterious blue glowing effect can be seen because some of the electrons are moving faster than the speed of light in the water.

Just an FYI - the blue glow seen in reactors is Cherenkov radiation. It's actually well understood and is used in cosmic ray and neutrino detectors.

 

[madeupfacts]

arc!

 

[cytg111]

emdrive confirmed : http://forum.nasaspaceflight.com/index.php?topic=38577.0

Some 10 years later it seems that (pun incoming) the emdrive is taking off. And if this (well, these, cause there's several DIY builders outthere) is doable in some guys garage, with that level of quality to the experiment, then shit has GOT to be going down behind the curtains. This shit is too big for oil-invested interrests to be covering up. The next few years should be interresting (10 years from now, can we have our flying cars please?)

 

[Paratus]

emdrive confirmed : http://forum.nasaspaceflight.com/index.php?topic=38577.0

Some 10 years later it seems that (pun incoming) the emdrive is taking off. And if this (well, these, cause there's several DIY builders outthere) is doable in some guys garage, with that level of quality to the experiment, then shit has GOT to be going down behind the curtains. This shit is too big for oil-invested interrests to be covering up. The next few years should be interresting (10 years from now, can we have our flying cars please?)

It's not confirmed yet. It has however been tested by other groups including NASA and they haven't been able to disprove it. So testing by various groups continues.

We've had a newer thread about this topic for about a year.

http://forums.anandtech.com/showthread.php?t=2393507&highlight=thruster