Relativity drive

[modest]

Does a laser exhibit recoil?

 

Yes.

 

 

In stimulated emission an excited state atom emits a photon in the direction of an incident photon and returns to the ground state. The incident photon causes no recoil in the atom but the emitted photon causes a recoil opposite the incident photon. Figure 1.4 shows conservation of momentum in stimulated emission. We can see that although the total momentum of the system is zero the atom has a recoil opposite the incident photon.

 

Section I: Theoretical Principles

 

Is this what you were thinking?

 

~modest

[wade_b]

Yes.

 

Is this what you were thinking?

 

~modest

That is interesting but expected behavior on the particle level.

 

The real question: is that recoil measurable in the laser itself, and does it follow the rules of Newtonian physics?

 

I'm searching really for a good abstraction for the relativistic notion of an "open system" as applied to the emission device in the tuned cavity.

[wade_b]

This really does seem impossible, even when applying the Einstein Elevator and changing the reference frame.

 

If I understand correctly, the law of conservation of momentum still applies inside the elevator.

 

The model I studied shows a force vector being applied from outside the elevator; the perception of momentum inside the elevator would be 0.

 

So I'm not quite seeing how a force generated inside the elevator could translate into momentum measured outside of it?

[modest]

That is interesting but expected behavior on the particle level.

I think so too.

The real question: is that recoil measurable in the laser itself, and does it follow the rules of Newtonian physics?

Not sure exactly what you mean by Newtonian physics, but lasers surely follow conservation of momentum. They follow Newton's first law - the law of inertia. They do recoil.

I'm searching really for a good abstraction for the relativistic notion of an "open system" as applied to the emission device in the tuned cavity.

Once again, I'm a bit confused by what you mean. When you say "open system" do you mean a "relativity drive" that looses photons into open space? If so, that is a perfectly normal thing to consider as a rocket engine. Qfwfq touched on that earlier in post #10. A well-focused laser could essentially work as a rocket engine. The laser does have recoil equal to the momentum of the photons leaving the craft.

This really does seem impossible, even when applying the Einstein Elevator and changing the reference frame.

That surely seems to be the consensus of the thread.

If I understand correctly, the law of conservation of momentum still applies inside the elevator.

I think it's a safe bet that conservation laws always apply.

The model I studied shows a force vector being applied from outside the elevator; the perception of momentum inside the elevator would be 0.

 

So I'm not quite seeing how a force generated inside the elevator could translate into momentum measured outside of it? :confused:

I don't see how it would work either. As Will said, there's nothing you can do inside the elevator to move its center of mass. So, it's not going to accelerate. Unless some mass leaves the craft or some force acts on the craft - it's not going to accelerate.

 

~modest

[wade_b]

I don't see how it would work either. As Will said, there's nothing you can do inside the elevator to move its center of mass. So, it's not going to accelerate. Unless some mass leaves the craft or some force acts on the craft - it's not going to accelerate.

~modest

I'm guessing that some mass is leaving the craft somehow; I don't really doubt that the engine works, I just have doubt that the engine works as he describes it.

 

In the end, this drive may still prove to be a viable replacement for ion thrusters.

 

My other comments were I suppose feeble attempts to understand Shawyer's rationale of his device as an open system; he is essentially viewing the emitter as not attached to the mass of the device itself, which SEEMS (to me) to be the basis of his insistence that this device does not break existing laws of physics.

 

Thanks for your patience with me - I'm still learning....

[wade_b]

But what of the laser gyro?

 

I mean - if I understand correctly, if the rotation of the laser gyroscope is in the opposite direction to the beam of light contained within, that beam of light takes correspondingly longer to reach the fixed target within the ring. :confused:

 

This seems to somewhat defy the simple Einstein elevator model...

 

In fact, could it not be deduced that the laser beam is not confined to the elevator?

 

My head is spinning. :phones:

[wade_b]

I think this is what I was grasping for when asking about the recoil as seen by the laser apparatus: (from wikipedia's page "Newton's_laws_of_motion" I'm not allowed to post URL's...)

 

 

Newton used the third law to derive the law of conservation of momentum;[24] however from a deeper perspective, conservation of momentum is the more fundamental idea (derived via Noether's theorem from Galilean invariance), and holds in cases where Newton's third law appears to fail, for instance when force fields as well as particles carry momentum, and in quantum mechanics.

[CraigD]

Does a laser exhibit recoil?

The real question: is that recoil measurable in the laser itself, and does it follow the rules of Newtonian physics?

Yes.

 

The momentum of light, be it from a lightbulb, a laser, a microwave or radio antenna, etc, is easy to describe. It’s energy divided by the speed of light. Force = momentum/time and Power = energy/time, so the force of light is Power/c

 

A couple of examples:

• A typical laser pointer (I use one of these as a cat toy)
  
  • Power: <0.001 W
  • Force: 0.001 / c = about 3e-12 N
  • Mass: about 0.005 kg
  • Acceleration: Force / Mass = about 6e-10 m/s/s
    
  • Example consequence: Left turned on free-floating in space for about 53 years, if pointed the same direction, my cat-toy laser pointer would increase its velocity in the opposite direction by about 1 m/s, a slow walking speed. (It’s batteries don’t last nearly that long, I can attest :confused:)
    

  [*]A weak old microwave oven (Like nearly every American, I have one of these)

  • 100 W (output power, not input)
  • Force: about 3e-6 N
  • Mass: about 10 kg
  • Acceleration: about 6e-7 m/s/s
    
  • Example consequence: If you cut its side off (my microwave emits photons from the side of its interior where the buttons are), it would accelerate itself to 1 m/s in about 19 days. However, when you throw in the necessary hardware to keep it supplied with power for 19 days, the system becomes much more massive
    

As best I can tell, what Shawyer’s proposing is similar to my microwave oven example, but without cutting the side open. This results in just a microwave oven, which will accelerate slightly in the opposite direction of any leaks in its oven compartment (I understand the window and door edges leak a little on most of them), an unintentional effect which I assume Shawyer’s system wouldn’t have, being sealed better than a microwave oven.

 

A more mundane example is a person standing on a sled on an frozen lake, propelling himself by pitching softballs. Shawyer’s proposes that you can propel the sled using just one softball that you pitch repeatedly to a friend also standing on the sled, if he has a catcher’s mitt that’s designed a special way.

[wade_b]

What about this (from physorg.com)

 

One of the interesting phenomena present in quantum mechanics is the Aharonov-Bohm (AB) effect. The AB effect predicts that a charged particle, usually an electron in experiments, shows effects from electromagnetic fields in regions where the particle is excluded. This leads to the interesting fact that, in electromagnetism, Newton’s Third Law of Motion doesn’t always hold true.

 

Herman Batelaan explains to PhysOrg.com: “If you want to move anything in the world around you, you need forces. But in the Aharonov-Bohm effect, the electron reacts without any forces. There is no force, but something happens.”

 

Batelaan, a scientist at the University of Nebraska-Lincoln oversaw an experiment done by graduate student, Adam Caprez, and Brett Barwick to demonstrate the absence of forces in the AB effect. A description of the experiment, and their results, is available in Physical Review Letters: “Macroscopic Test of the Aharonov-Bohm Effect.”

 

“The interesting thing,” Batelaan says, “is that experimentally scientists have detected evidence of this effect, and it is mentioned in textbooks. But nobody had shown that no forces are there.” The experiment performed at the University of Nebraska-Lincoln constitutes the first demonstration of a lack of forces. “We know the effects, and this is expected.” Batelaan continues. “Theoretically, scientist predicted this, but we want to see this. Now we have it.”

 

Experimental demonstrations of the AB effect usually include carefully controlled electrons using a distant electromagnetic field. “We understand the physics of this, such that we can take electrons and control them so well that we can see quantum mechanics happening,” Batelaan says. In order to perform the current experiment, the team used a pulse laser to hit a metal needle, a method developed at Stanford.

[wade_b]

I'm also currently trying to wrap my head around Minkowski forces; as described by Gary L. Mathis (and no doubt others), the Minkowski force associated with the center of mass of a system does not represent the total force acting on a system.

 

Perhaps the "impossible drive" is truly possible. :confused:

[wade_b]

If the emdrive works as described, I believe it would be a practical application of Einstein's box:

 

Google: 2005_dissertation_The_Abraham-Minkowski_Controversy.pdf

Google: Einstein's box

 

Can the emdrive possibly be a real implementation of Einstein's box?

 

Discuss?

[CraigD]

What about this (from physorg.com)

One of the interesting phenomena present in quantum mechanics is the Aharonov-Bohm (AB) effect. The AB effect predicts that a charged particle, usually an electron in experiments, shows effects from electromagnetic fields in regions where the particle is excluded. This leads to the interesting fact that, in electromagnetism, Newton’s Third Law of Motion doesn’t always hold true.

 

Herman Batelaan explains …

Caprez, Barwick, and Batelaan’s 8/17/07 “A macroscopic test of the Aharonov-Bohm effect” describes an experiment that further confirms that the quantum waves of an electrons in a stream, which are predicted to be affected in the absence of an interaction analogous to classical electromagnetic force, are not actually being affected by an unexpected interaction analogous to a classical electromagnetic force.

 

What is changed by the AB effect is the phase of electrons’ waves, resulting in a detectable change in the interference pattern produced by passing a stream of electrons through two slits – the famous two-slit experiment. Their masses and velocities are unaffected. Newton’s 3rd Law of Motion describes forces, masses, and velocities, not the wave nature of particles, I think the tagline “in electromagnetism, Newton’s Third Law of Motion doesn’t always hold true”, while catchy, isn’t accurate. It plays on different uses of the word “reaction”: in classical physics, where reactions are changes in momenta, vs. in quantum physics, where “reaction” can be a rarely-used synonym for “interaction”, which can involve changes other than to momenta The word “reaction” appears nowhere in Caprez, Barwick, and Batelaan’s paper.

 

The AB effect expressly doesn’t change momenta, so I can see no way that it can be used for propulsion.

[wade_b]

Caprez, Barwick, and Batelaan’s 8/17/07 “A macroscopic test of the Aharonov-Bohm effect” describes an experiment that further confirms that the quantum waves of an electrons in a stream, which are predicted to be affected in the absence of an interaction analogous to classical electromagnetic force, are not actually being affected by an unexpected interaction analogous to a classical electromagnetic force.

 

What is changed by the AB effect is the phase of electrons’ waves, resulting in a detectable change in the interference pattern produced by passing a stream of electrons through two slits – the famous two-slit experiment. Their masses and velocities are unaffected. Newton’s 3rd Law of Motion describes forces, masses, and velocities, not the wave nature of particles, I think the tagline “in electromagnetism, Newton’s Third Law of Motion doesn’t always hold true”, while catchy, isn’t accurate. It plays on different uses of the word “reaction”: in classical physics, where reactions are changes in momenta, vs. in quantum physics, where “reaction” can be a rarely-used synonym for “interaction”, which can involve changes other than to momenta The word “reaction” appears nowhere in Caprez, Barwick, and Batelaan’s paper.

 

The AB effect expressly doesn’t change momenta, so I can see no way that it can be used for propulsion.

Thanks for the explanation - I came to a similar conclusion after reading more data on that effect. AB is a phase change then...

 

What to make of Einstein's box?

 

I can only understand the first cycle, which shows the "recoil" from the emitted particle being transferred to the cylinder (v = e/Mc); then when the particle hits the far wall the cylinder comes to rest, due to energy to matter conversion: m = E/C(squared). (Feel free to correct me - I'm still learning :D)

 

What floors me though is the reference to energy absorption on Wall B and the massless carrier required to return energy to Wall A, and the assertion that such transference will NOT result in a change of position of the cylinder. :eek:

[CraigD]

What to make of Einstein's box? ...

Here’s a summary of the “Einstein’s box paradox”, and its resolution.

 

The paradox:

• The box has mass [math]M[/math] and a left and a right wall separated by distance [math]D[/math].
  
• Start with the box stationary, that is, its momentum is 0
  
• The “gun” on the left wall of the box emits a photon of momentum [math]p[/math].
  
• Per conservation of momentum, the box has a momentum of [math]–p[/math], and therefore, a velocity [math]\frac{–p}{M}[/math].
  
• The photon is absorbed by the right wall after time [math]\frac{D}{c}[/math].
  
• The box has traveled [math]\frac{–pD}{cM}[/math] in that time.
  
• Its momentum is again 0.
  

Therefore, it has shifted its position [math]\frac{–pD}{cM}[/math], without having been subject to an external force, violating the 3rd law of motion.

 

The resolution of the paradox is that, when the left wall emitted the photon, its mass decreased by the mass equivalent of the energy of the photon, [math]pc[/math]. When the right wall absorbed it, its mass increased by the same amount.

[math]pc = E = mc^2[/math], so [math]m_{\gamma}= \frac{pc}{c^2} = \frac{p}{c}[/math].

 

Center of mass equations are similar to torque equations.

Assuming the left and right walls were initially of equal mass, the initial center is [math]\frac{D}2[/math].

The new center of mass [math]d_1[/math] is given by the equation

[math]\left(\frac{D}2-\frac{p}{c}\right) \left(D-d_1 \right) = \left(\frac{D}2-\frac{p}{c}\right)d_1[/math]

which gives

[math]d_1 = \left( \frac{M}2 -\frac{p}{c}\right)\frac{D}{M} = \frac{D}2 -\frac{pD}{cM}[/math]

 

So the change in center of mass is equal to the shift in position, resolving the paradox.

[wade_b]

Here’s a summary of the “Einstein’s box paradox”, and its resolution.

 

The paradox:

• The box has mass [math]M[/math] and a left and a right wall separated by distance [math]D[/math].
  
• Start with the box stationary, that is, its momentum is 0
  
• The “gun” on the left wall of the box emits a photon of momentum [math]p[/math].
  
• Per conservation of momentum, the box has a momentum of [math]–p[/math], and therefore, a velocity [math]\frac{–p}{M}[/math].
  
• The photon is absorbed by the right wall after time [math]\frac{D}{c}[/math].
  
• The box has traveled [math]\frac{–pD}{cM}[/math] in that time.
  
• Its momentum is again 0.
  

Therefore, it has shifted its position [math]\frac{–pD}{cM}[/math], without having been subject to an external force, violating the 3rd law of motion.

 

The resolution of the paradox is that, when the left wall emitted the photon, its mass decreased by the mass equivalent of the energy of the photon, [math]pc[/math]. When the right wall absorbed it, its mass increased by the same amount.

[math]pc = E = mc^2[/math], so [math]m_{\gamma}= \frac{pc}{c^2} = \frac{p}{c}[/math].

 

Center of mass equations are similar to torque equations.

Assuming the left and right walls were initially of equal mass, the initial center is [math]\frac{D}2[/math].

The new center of mass [math]d_1[/math] is given by the equation

[math]\left(\frac{D}2-\frac{p}{c}\right) \left(D-d_1 \right) = \left(\frac{D}2-\frac{p}{c}\right)d_1[/math]

which gives

[math]d_1 = \left( \frac{M}2 -\frac{p}{c}\right)\frac{D}{M} = \frac{D}2 -\frac{pD}{cM}[/math]

 

So the change in center of mass is equal to the shift in position, resolving the paradox.

 

Which sounds like it COULD apply to the emdrive? :shrug:

[CraigD]

Which sounds like it [Einstein’s box] COULD apply to the emdrive? :hyper:

No, not according to a usual resolution such as the one in post #31

 

The Einstein’s box thought experiment (this particular one – there are actually several that commonly go by the name) – which can, with very precise equipment and instrumentation, by physically performed – is exactly analogous to the simpler example of a box inside a freely moving box, which I’ve sketched in the image attached below. It moves the outer box a fixed distance, then the system is “used up”, and before it can be used again, must either be reset, which returns it to exactly its starting position, or mass removed and added to it from outside, which defeats the premise of it being a closed system.

 

What makes Einstein’s box a trickier riddle is that it’s less intuitive that shining emitting light from one object onto another which absorbs the light (a more difficult feat than it sounds at first hearing, as most objects ultimately emit about the same amount of light they absorb) actually transfers mass between them, than it is that moving a small massive box from one end to another of a large hollow box transfers mass within it.

[Karnuvap]

At first I thought that this was just a spaceship with an open ended microwave cavity on the back thus microwaves out the back = thrust towards the front and thus acceleration (however slight) that would eventually build-up to pretty decent speeds.

But, on closer inspection, the cavity is sealed at the back too and it relies on the fallacious assumption that because the wall at the 'back' has a different surface area then the wall near the 'front' there would be more 'pressure' on the back than at the front. OK that is slightly an oversimplification of what they are trying to achieve and the reality of their theory is slightly more subtle.

 

The real secret to where they are bamboozling us lies in the expression "Group Velocity". This is not a real velocity that should be used in the subsequent equations. It is a mathematical construct to help solve the equations and not anything real. To give you a clue as to why group velocity isn't anything like real velocity - it is perfectly possible to have a group velocity faster than that of the light photons or waves that make it up (which, obviously, travel at the speed of light themselves).

 

So, unless something is emitted out of the back of your spacecraft it cannot accelerate.

 

Of course I might be wrong and it could be that the microwave photons are selectively destructively interfered at one end of the chamber (and, presumably) they constructively interfere at the other end. The destructively destroyed photons re-appear at infinity - or so my physics lecturer told me when I asked him where they would go if I shined two identical frequency lasers at a single point on a screen and then adjusted one of them so that it was precisely one half wavelength further away from the screen than the other. Where would the light go in this perfect destructive interference set-up? - they disappear and re-appear at infinity was his reply. I'd love to know what the real answer was.