Author Topic: EMdrive Developments working in visible and infrared light regime.  (Read 80354 times)

Offline 1

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Please correct me if I'm wrong, but from what I understand (not being trained in university physics), meberbs thinks the photon force on all the walls of the cavity theoretically cancel each other out.

Assuming I'm summarising meberbs correctly, do other people agree with that? And if not, why not?

Not speaking for meberbs, but in general, this is correct for a completely enclosed cavity. (If you're missing a wall such that your beam can ultimately escape, then what you've constructed is a photon rocket. Monomorphic's build is currently closer to the latter, but it's still quite early. Give him time.)

That said, the nature of the cancelling forces could probably use some clarification as I'm seeing a lot of thought experiments that are mixing transient effects with steady state effects; which is a great way to arrive at a non-physical conclusion.

The main issue is that a phrases such as "the photon transfers momentum to the cavity" are actually very ill-defined because an incident photon cannot interact with the entire cavity all at once. At best, it can only interact with a handfull of atoms at a time. These initial interactions will eventually propagate to the rest of the cavity structure, but that takes time. Specifically, those propagations travel at about the speed of sound through the cavity material; compared to a reflecting photon that travels at the speed of light. This effectively means that a photon will bounce back and forth hundreds of thousands of times before the "impact" of any one bounce reaches the other side of the cavity. Thus, due to the drastic difference in propagation velocities, even the very first photon entering and bouncing aroundthe cavity ultimately results in a force outward, not forward.

The red shift / blue shift tug of war is not due to translational movement of the cavity as a whole, but instead due to expansion vs compresson of the cavity walls due to internal photonic pressure. The outward pressure due to a photons initial reflections cause the cavity to expand slighty, placing the whole system in tension; not unlike an (infinitessimally) inflated balloon. Soon, the photon is no longer energetic enough to maintain that outward pressure, and the cavity contracts; transferring energy back to the reflecting photon.

In the real world, there are many other kinds of energy loss that will eventually completely consume a photon. But if we continually replace lost photons with new ones such that the internal photonic pressure is maintained, then the system will settle to an equilibrium where, on average, reflecting photons impart no momentum to the cavity walls.



Offline Monomorphic

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I switched out the regular mirrors for some acrylic first surface material that was recommended by Hakasays previously.

It seems to work as well if not slightly better than regular mirrors, but you can see that some of the laser is passing through the thin mylar coating into the acrylic and 3D printed material behind. However, I have serious doubt that the acrylic mirror can stand up to a 7 watt laser.
« Last Edit: 06/22/2020 05:33 pm by Monomorphic »

Offline Monomorphic

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The new 7 watt laser and heatsink arrived today. After some tests, it looks like i'm going to top out at 4 to 5 watts driving it with the equipment I have.  Even at those power levels, this thing is a beast. It will instantly cut through sandpaper and wood.

I was correct that the acrylic mirror isn't going to work. It is fine for low power applications, but you can see the damage done to the surface by using less than 1 watt.

 

Offline Monomorphic

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The sales people with the first surface mirror company could not provide me with the laser breakdown threshold for their 1/4 inch 1λ mirrors. They recommended that I order a sample for testing, which I did. The sample arrives Tuesday.

Offline Monomorphic

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Very glad I ordered the sample mirror as the piece they sent (15cm x 15cm) is large enough to cut the three mirrors I need out of it. There is very little margin for an error in cutting, but even ordering another sample piece is a lot cheaper than ordering the three custom pieces.  Sample piece was $14 plus $9 shipping. Three custom cut pieces at 4cm x 10cm is $105 plus $9 shipping. 

One small issue is that I did not anticipate the glass being 1/4 inch (6mm) thick in the initial design. I will need to make a minor adjustment to how the two side mirrors are mounted to the supports to make sure there is enough room for the back mirror.

EDIT:  Just tried cutting this mirror and it is very difficult.  The side crushes before it breaks.  Looks like I will have to order custom cut pieces.  At least I can see if this mirror holds up to the laser as originally planned.

« Last Edit: 06/30/2020 08:43 pm by Monomorphic »

Offline Monomorphic

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No obvious damage to the first surface mirror from ~4.5 watts of laser. After at least 20 seconds of continuous wave with the laser as focused as I could get it at the surface of the mirror, I could see no damage to the mirror with the naked eye. But then upon inspection with a flashlight from behind, I can see tiny holes in the mirror.

After messing with the focus of the laser so it is not so focused on the first bounce, then the mirror appears to sustain no damage whatsoever.  Just to be safe, I will probably limit power on the first tests to ~2 watts or so.

The last image below shows the ~3% of the laser that passes through the mirror. This does not damage the mirror unless the beam is very focused and at full power.
« Last Edit: 06/30/2020 09:03 pm by Monomorphic »

Offline Monomorphic

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Custom-sized first surface 1λ mirrors arrived more quickly than I anticipated. Whoever cut these did a much better job than I ever could have. The side seen in the image below is the regular mirror side. The first surface mirror is on the reverse side and still protected by a removable plastic film.

Everything is in place now to run some experiments. I just need to do a little soldering on the two DC power leads, make sure they are twisted, and change a couple of wires on the ADC to detect when the laser is on and off. There should be some preliminary results this weekend.   ;D
« Last Edit: 07/02/2020 09:42 pm by Monomorphic »

Offline Monomorphic

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First surface mirrors attached to adjustable mounts with protective film visible. I will remove the film once I have finished soldering and twisting the two power leads.

I added white electrical tape to the ends of the two side mirrors so if/when they touch the back mirror, they do not cause any damage to the delicate metal surface.
« Last Edit: 07/02/2020 11:01 pm by Monomorphic »

Offline Monomorphic

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After finishing up on another experiment yesterday, I was able to mount the new laser cavity and laser assembly to the thrust balance.  The experiment weighs in at 550 grams, and since one has to add an equal counterweight to the other side, that brings the total added mass to 1100 grams!  Adding the mass of the aluminum arm, damping, and other parts, the total mass of the torsional pendulum is ~1450 grams.  That is 3.2 lbs. 

Each of the flexure bearings has a load capacity of 3.6 lbs (1630 g). Since there are two of them, that comes to 7.2 lbs (3260 g). So I am very near half the load capacity of the bearings. 

With the added mass, the moment of inertia increased substantially.  Damping had to be increased quite a bit to compensate.  All this increases the period of the balance. So when it was ~7 seconds, it will be probably double that, if not more.  I adjusted the damping today, but forgot to measure the oscillation period. We will see what that is when I run a few calibration pulses later.

The procedure for testing will be to make all major adjustments and changes to the laser cavity on the work bench, and then when that is complete, move the cavity assembly to the torsional pendulum and simply connect the two wires. Then make any last minute adjustments on the pendulum and then ~2W powered tests.
« Last Edit: 07/05/2020 03:22 pm by Monomorphic »

Offline crow_kraehe

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After finishing up on another experiment yesterday, I was able to mount the new laser cavity and laser assembly to the thrust balance.  The experiment weighs in at 550 grams, and since one has to add an equal counterweight to the other side, that brings the total added mass to 1100 grams!  Adding the mass of the aluminum arm, damping, and other parts, the total mass of the torsional pendulum is ~1450 grams.  That is 3.2 lbs. 

Each of the flexure bearings has a load capacity of 3.6 lbs (1630 g). Since there are two of them, that comes to 7.2 lbs (3260 g). So I am very near half the load capacity of the bearings. 

With the added mass, the moment of inertia increased substantially.  Damping had to be increased quite a bit to compensate.  All this increases the period of the balance. So when it was ~7 seconds, it will be probably double that, if not more.  I adjusted the damping today, but forgot to measure the oscillation period. We will see what that is when I run a few calibration pulses later.

The procedure for testing will be to make all major adjustments and changes to the laser cavity on the work bench, and then when that is complete, move the cavity assembly to the torsional pendulum and simply connect the two wires. Then make any last minute adjustments on the pendulum and then ~2W powered tests.

Is the purpose of this experiment to test a visible light version of the EM drive concept using lasers? Are you looking for thrust? And is it not required that one uses a spherical wave source, not lasers? And if you are looking for thrust (I don't know) Are you not concerned about leaks since your cavity is not closed?

Offline Monomorphic

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Is the purpose of this experiment to test a visible light version of the EM drive concept using lasers?

Yes.

Are you looking for thrust?

Yes.

And is it not required that one uses a spherical wave source, not lasers?

Not according to McCulloch.

And if you are looking for thrust (I don't know) Are you not concerned about leaks since your cavity is not closed?

It was shown previously in simulations that the laser can bounce an arbitrarily large number times using special arrangements of mirrors.  However, after 30 - 40 bounces, most of the laser energy is lost because the mirrors are not perfect.  The hope is that an anomalous effect can be detected within the first 30 - 40 bounces if the laser energy is high enough.
« Last Edit: 07/08/2020 01:08 am by Monomorphic »

Offline Mark7777777

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Please correct me if I'm wrong, but from what I understand (not being trained in university physics), meberbs thinks the photon force on all the walls of the cavity theoretically cancel each other out.

Assuming I'm summarising meberbs correctly, do other people agree with that? And if not, why not?

Not speaking for meberbs, but in general, this is correct for a completely enclosed cavity. (If you're missing a wall such that your beam can ultimately escape, then what you've constructed is a photon rocket. Monomorphic's build is currently closer to the latter, but it's still quite early. Give him time.)

That said, the nature of the cancelling forces could probably use some clarification as I'm seeing a lot of thought experiments that are mixing transient effects with steady state effects; which is a great way to arrive at a non-physical conclusion.

The main issue is that a phrases such as "the photon transfers momentum to the cavity" are actually very ill-defined because an incident photon cannot interact with the entire cavity all at once. At best, it can only interact with a handfull of atoms at a time. These initial interactions will eventually propagate to the rest of the cavity structure, but that takes time. Specifically, those propagations travel at about the speed of sound through the cavity material; compared to a reflecting photon that travels at the speed of light. This effectively means that a photon will bounce back and forth hundreds of thousands of times before the "impact" of any one bounce reaches the other side of the cavity. Thus, due to the drastic difference in propagation velocities, even the very first photon entering and bouncing aroundthe cavity ultimately results in a force outward, not forward.

The red shift / blue shift tug of war is not due to translational movement of the cavity as a whole, but instead due to expansion vs compresson of the cavity walls due to internal photonic pressure. The outward pressure due to a photons initial reflections cause the cavity to expand slighty, placing the whole system in tension; not unlike an (infinitessimally) inflated balloon. Soon, the photon is no longer energetic enough to maintain that outward pressure, and the cavity contracts; transferring energy back to the reflecting photon.

In the real world, there are many other kinds of energy loss that will eventually completely consume a photon. But if we continually replace lost photons with new ones such that the internal photonic pressure is maintained, then the system will settle to an equilibrium where, on average, reflecting photons impart no momentum to the cavity walls.

I've just realised, after reading:

https://www.vice.com/en_us/article/7x3ed9/darpa-is-researching-quantized-inertia-a-theory-of-physics-many-think-is-pseudoscience

that I may have misunderstood Mike McCulloch's explanation as to why an asymmetric laser cavity should move.

From my understanding, it's not the photons bouncing off the cavity walls that would produce thrust, but rather the warm Unruh radiation pressure in the larger section of the cavity compared to the narrower section.

If that's the case I'm not sure about photon acceleration though. Mike says that velocity won't cause a horizon, but rather only acceleration. I thought photons reached the speed of light instantly so there is no acceleration in them. And therefore the laser beam just goes bouncing around the cavity at a constant velocity (c), but with no acceleration.
 
« Last Edit: 07/08/2020 06:26 am by Mark7777777 »

Offline meberbs

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If that's the case I'm not sure about photon acceleration though. Mike says that velocity won't cause a horizon, but rather only acceleration. I thought photons reached the speed of light instantly so there is no acceleration in them. And therefore the laser beam just goes bouncing around the cavity at a constant velocity (c), but with no acceleration.
Reminder for when reading this reply, velocity and momentum are both vector quantities.

There is technically an impulse force when a photon bounces off of a mirror, which means that there is acceleration, but in the model of a single particle photon, it becomes a divide by zero, since it is instantaneous. In reality, a single photon does not have a well defined position, so while it can only travel at c, there is a period of time where the quantum distribution representing the photon is in a partially reflected state. This corresponds to finite force and acceleration (rate of change of the expectation value of the vector momentum quantity) of the photon, even though any velocity eigenstate of the photon has velocity c. (not sure that velocity eigenstate is actually a valid concept in this situation, but it communicates the idea.)

Don't bother to try to work out what that means in McCulloch's theory though, since most of what he does is handwaving to work around the fundamental inconsistencies in his theory.

Offline Bob012345

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Is the purpose of this experiment to test a visible light version of the EM drive concept using lasers?

Yes.

Are you looking for thrust?

Yes.

And is it not required that one uses a spherical wave source, not lasers?

Not according to McCulloch.

And if you are looking for thrust (I don't know) Are you not concerned about leaks since your cavity is not closed?

It was shown previously in simulations that the laser can bounce an arbitrarily large number times using special arrangements of mirrors.  However, after 30 - 40 bounces, most of the laser energy is lost because the mirrors are not perfect.  The hope is that an anomalous effect can be detected within the first 30 - 40 bounces if the laser energy is high enough.


I read through this thread but it's still not clear to me what your experimental design is. Are you in contact with Mike McCulloch? Or, are you in contact with Tajmar who is actually is testing McCulloch's concept? Thanks.


Also,

Are your mirrors dielectric?

Here are videos from Young Bae's Photonic Laser Thruster (I know, that's a different thing) but the reason I am pointing these out is if there is some information you can get from the optics system they use. They get 1500 bounces now.



« Last Edit: 07/08/2020 08:33 pm by Bob012345 »

Offline Bob Woods

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Is this the same BAE Corp that partnered with Shawyer?

Offline Bob012345

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Is this the same BAE Corp that partnered with Shawyer?

I do not know.

I looked into that.  It seems clear the answer is no. Roger Shawyer contracted with the British firm BAE Systems and the Photonic Laser Thruster is the brainchild of Y.K. Bae of Y.K. Bae Corp. a small outfit in Tustin California.
« Last Edit: 07/09/2020 04:11 pm by Bob012345 »

Offline Monomorphic

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Are you in contact with Mike McCulloch? Or, are you in contact with Tajmar who is actually is testing McCulloch's concept?

I am in contact with McCulloch and Tajmar on this matter.  McCulloch was kind enough to estimate for me the thrust he would expect, which is 0.1 uN at 2 watts.  Tajmar was already aware of the experiment from seeing it here when I emailed him about it. He said he was looking forward to the results.
« Last Edit: 07/10/2020 10:04 pm by Monomorphic »

Offline Bob012345

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Are you in contact with Mike McCulloch? Or, are you in contact with Tajmar who is actually is testing McCulloch's concept?

I am in contact with McCulloch and Tajmar on this matter.  McCulloch was kind enough to estimate for me the thrust he would expect, which is 0.1 uN at 2 watts.  Tajmar was already aware of the experiment from seeing it here when I emailed him about it. He said he was looking forward to the results.

Thanks. I wish you good luck with the experiment!

Offline meberbs

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Are you in contact with Mike McCulloch? Or, are you in contact with Tajmar who is actually is testing McCulloch's concept?

I am in contact with McCulloch and Tajmar on this matter.  McCulloch was kind enough to estimate for me the thrust he would expect, which is 0.1 uN at 2 watts.  Tajmar was already aware of the experiment from seeing it here when I emailed him about it. He said he was looking forward to the results.
Is your setup sensitive to that level of force? What is the amount of noise or other errors that you expect? Because if you mounted the laser external to the pendulum, and just bounced it off one mirror, I would expect 0.013 uN of force from a 2 W laser. Which is about one-eighth of McCulloch's prediction. If you had the equipment to drive the laser at a full 7 W (and the mirror could take it) It would be up to 0.047 uN expected.

I know that your current setup has the laser attached, and the beam exit is at an angle, but I find these comparisons helpful for considering what needs to be accounted for. These cases may also serve a purpose as a null test, if you can measure them, they can confirm your calibration, and even if they are too small to be measured, it could confirm that there are no other errors. (The laser being attached to the beam halves the force, and angled beams can be accounted for too.)

Offline Monomorphic

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McCulloch is developing a program to calculate the predicted thrust from so-called, Horizon Drives. As of now, the app can only calculate for silver, copper, and gold cavities.  Fortunately, at 450nm, aluminum and silver have very similar reflectivity. So here we have used the properties for silver to come up with the 0.1uN at 2 watt estimation.


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