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Conundrum

Thu Mar 07 2013, 07:55PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

This demands to be replicated on the ISS..
Its not like it is a big experiment, just a few K$ worth of semiconductors to generate the microwaves, a Nicad battery for power and an accelerometer + cavity.
For extra points, try it with different shaped cavities to see what that does to the acceleration if any.

-A

BigBad

Fri Mar 08 2013, 02:27AM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
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Posts: 600

You're not listening.

Look, if this thing works, then something weighing 1kg can go from 10 m/s to 0 speed. It starts with 50 joules of kinetic energy, and ends up with 0.

Where does that energy go?

Meanwhile, in a different reference frame, the *same* object starts of with no energy, and ends up with 50 joules. Where does this energy come from, and how do you reconcile the fact that it both *gains* and *loses* energy.

The answer is, you can't.

Unlike rockets, which conserve energy by exchanging energy with their exhaust, this type of drive cannot and breaks well-known physical laws.

Conundrum

Fri Mar 08 2013, 06:44PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

My understanding is that energy is expended as heat within the cavity, magnetron etc.
Therefore energy IS being converted from one form to another, albeit with very low efficiency.
As an analogy, imagine a hypothetical solar motor which spins around on its axis when exposed to sunlight.
CoE is obviously valid as light energy is being converted into electromagnetic, and hence into kinetic energy.
Now imagine the same motor without the electromagnetic step...
Such a device is in fact possible, see the recent article on levitated pyrolytic graphite based light motors.

It is entirely possible that there is an as yet undiscovered force acting on the resonator, which is only seen under these specific conditions which suggests "new physics".
If so then CoE is still valid, as energy is being interchanged but without Newton's laws being observed directly.

BigBad

Sat Mar 09 2013, 03:10AM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
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Conundrum wrote ...

My understanding is that energy is expended as heat within the cavity, magnetron etc.
Therefore energy IS being converted from one form to another, albeit with very low efficiency.

Right, there will be energy losses. But I was able to show that the heat energy losses must be 100%; i.e. it cannot remain moving when you switch it off.

It wouldn't necessarily violate anything if it worked as a linear momentum wheel though (so you switch it off, and it goes back to moving as it was before you switched it on), but as something you can use to accelerate continuously in freespace, that cannot work without wholesale violation of conservation of energy.

Uspring

Sat Mar 09 2013, 08:00PM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
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BigBad wrote:

Look, if this thing works, then something weighing 1kg can go from 10 m/s to 0 speed. It starts with 50 joules of kinetic energy, and ends up with 0.

Where does that energy go?

Consider a setup, where your rocket is fixed, i.e. not moved by its thrust and some distance behind it a place, where the microwave beam hits. When you turn on the rocket, the same amount of energy, that the rocket emits, will hit the beam dump behind it.

Now assume that the rocket can move freely. It will accelerate away from the beam dump. This will cause a Doppler shift in the microwave frequency at the beam dump to lower frequencies. Since there are no photons lost and their frequency is lower, the energy dissipated in the beam dump is lower (Photon energy is proportional to its frequency). That difference in beam dump energy is exactly the one going into the kinetic energy of the rocket. For a rocket being braked, the argument is similar.

BigBad

Sun Mar 10 2013, 12:43AM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
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You may be unaware that the EMDrive design has a microwave source entering a completely sealed cavity, and none escapes; there is no beam.

If there was a beam, that would be a photon rocket, a completely different thing.

Mattski

Sun Mar 10 2013, 09:01AM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

In fact the efficiency with which energy is being converted to heat should be just about 100%, barring leaks. And the efficiency with which the microwave energy is being converted into kinetic energy is expected to be 0%, barring leaks.

wrote ...
As an analogy, imagine a hypothetical solar motor which spins around on its axis when exposed to sunlight.
CoE is obviously valid as light energy is being converted into electromagnetic, and hence into kinetic energy.

Light is already electromagnetic energy, no need for conversion of light into electromagnetic. Solar sails follow conservation of momentum as conventionally understood while EmDrive does not.

wrote ...

Now imagine the same motor without the electromagnetic step...
Such a device is in fact possible, see the recent article on levitated pyrolytic graphite based light motors.

Without the electromagnetic step? Light is electromagnetic. And why are you bringing graphite into the mix here I don't see how it's relevant to the Em Drive?

wrote ...
It is entirely possible that there is an as yet undiscovered force acting on the resonator, which is only seen under these specific conditions which suggests "new physics".
If so then CoE is still valid, as energy is being interchanged but without Newton's laws being observed directly.

But EmDrive's authors explain it's workings entirely within conventional physics, not new physics. The entire supposed theoretical basis for EmDrive is provided in a 1959 paper by Cullen, although the EmDrive's author(s) have made a critical error in applying the work of that paper to the EmDrive as I (and doubtless many others) already pointed out.

Uspring

Sun Mar 10 2013, 02:32PM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
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Posts: 711

BigBad wrote:

You may be unaware that the EMDrive design has a microwave source entering a completely sealed cavity, and none escapes; there is no beam.

Ooops, yes, I was unaware. It'd be interesting to know, where the momentum imparted to the rocket comes from. By conservation of momentum, it has to come from somewhere, i.e. somewhere outside the rocket the momentum has to be felt.

BigBad

Mon Mar 11 2013, 01:56AM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
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Posts: 600

Uspring wrote ...

BigBad wrote:

You may be unaware that the EMDrive design has a microwave source entering a completely sealed cavity, and none escapes; there is no beam.

Rockets? Rockets work by throwing their exhaust backwards very fast. The momentum is 'felt' by the exhaust.

In fact, if you turn a rocket on in space, the centre of mass of the rocket (including the propellant) doesn't move at all; the rocket goes one way, the exhaust goes the other, and the centre of mass stays put(!)

2Spoons

Mon Mar 11 2013, 02:04AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
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Posts: 615

Mattski wrote ...

But EmDrive's authors explain it's workings entirely within conventional physics, not new physics. The entire supposed theoretical basis for EmDrive is provided in a 1959 paper by Cullen, although the EmDrive's author(s) have made a critical error in applying the work of that paper to the EmDrive as I (and doubtless many others) already pointed out.

I would be interested to see the Cullen paper - do you have a ref? I'd also like to know where the error in application was.

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