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Tetris

Sat Mar 02 2013, 05:48PM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

One of the guys I follow on FurAffinity (that also is from 4HV) shared something interesting.

--

Disclaimer: Non-furry nerd stuff follows.

Ok, so I will assume everyone has seen a shuttle/rocket lift off. And you know basically what's going on in terms of the physics involved. Get a bunch of gases really hot, they expand and fly out the back. Everything that isn't flying out the back gets shoved forward and the result is called 'thrust'. It's Newton's law of "equal and opposite reaction".

Pretty much everything thing that moves follows this law in some way.
Well, almost everything.

This immediately screamed pseudo-science BS when I first caught wind of it;
It's a device that produces a thrust and can accelerate itself without expelling reaction mass or affecting its environment in any way.
...Then I realized there was actual math backing it up, the inventor was not trying to conceal what was making it possible, working models exist and China recently sent a prototype into space (edit: correction- China has a functional device built, has been tested but not launched yet ).

There's nothing spectacular about the first-gen models that have been built. It's a magnetron spitting microwaves into a closed, cone-shaped copper chamber. Input power is around 1 kilowatt, net thrust is a few ounces at most. It would be possible to build a similar proof-of-concept model in your garage with a modest budget.

'Second-gen' systems are where things will supposedly start getting weird. In a relative sense, copper is not a great conductor. You can't push electrons through it without some level of resistance, which turns into waste-heat. This is where a large amount of energy is being lost in prototype models. Superconductors (which are expensive but readily available) are proposed for useful real-world applications because they have no measurable resistance.

The efficiency jump here works out to something like 0.001% to 99.99% efficient. The power an incandescent lightbulb consumes is suddenly enough to levitate a person. The power output of a typical car engine becomes enough to levitate a house.

I'll leave it up to those of you that are interested to research the details and scrutinize current studies. There's always room for this type of claim to end up being a scam, but after years of laughing at crackpots like Hutchison and Rossi, this this is the first time I've felt it was worth my time to raise awareness about something which appears impossible but also completely legitimate.

It's probably worth keeping an eye on, anyway.

TL;DR
You *might* own a Flying Saucer in your lifetime.

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He speaks of using photon acceleration to build flying saucers and says a proof of concept model could be built in a garage. Has anyone here built one--if it's even possible?

Dr. Slack

Sat Mar 02 2013, 06:18PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Quote from the wikipedia article - "Any claim of a reactionless drive is treated with skepticism by the physics community, since reactionless drives violate the well-established principle of the conservation of momentum, which has enormous experimental support. Shawyer claims that his drive does not violate the conservation of momentum"

But that's just scientists. However if a furry thinks it works ...

Ash Small

Sat Mar 02 2013, 06:44PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Any results could be attributed to the larger end of the cone radiating more heat than the smaller end.

In my opinion, any conclusive tests would need to be carried out in a vacuum.

I've only read the Wikipedia article so far, though.

Tetris

Sat Mar 02 2013, 06:51PM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

Dr. Slack wrote ...

Quote from the wikipedia article - "Any claim of a reactionless drive is treated with skepticism by the physics community, since reactionless drives violate the well-established principle of the conservation of momentum, which has enormous experimental support. Shawyer claims that his drive does not violate the conservation of momentum"

But that's just scientists. However if a furry thinks it works ...

But then how do solar sails work? Momentum = mass * velocity and photons have no mass. Yet there's still acceleration using solar sails.

Ash Small

Sat Mar 02 2013, 07:15PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

HighVoltageChick wrote ...

But then how do solar sails work? Momentum = mass * velocity and photons have no mass. Yet there's still acceleration using solar sails.

I think, and I'm not certain, that either relativity or special relativity states that photons have no mass when at rest. I don't fully understand this either.

Maybe someone else here can add something?

EDIT: I found this on the Wikipedia page on photons: "Sharper upper limits have been obtained in experiments designed to detect effects caused by the galactic vector potential. Although the galactic vector potential is very large because the galactic magnetic field exists on very long length scales, only the magnetic field is observable if the photon is massless. In case of a massive photon, the mass term would affect the galactic plasma. The fact that no such effects are seen implies an upper bound on the photon mass of m < 3Ã—10âˆ’27 eV/c2.[24] The galactic vector potential can also be probed directly by measuring the torque exerted on a magnetized ring.[25] Such methods were used to obtain the sharper upper limit of 10âˆ’18eV/c2 (the equivalent of 1.07Ã—10âˆ’27 atomic mass units) given by the Particle Data Group.[26]

These sharp limits from the non-observation of the effects caused by the galactic vector potential have been shown to be model dependent.[27] If the photon mass is generated via the Higgs mechanism then the upper limit of mâ‰²10âˆ’14 eV/c2 from the test of Coulomb's law is valid.

Photons inside superconductors do develop a nonzero effective rest mass; as a result, electromagnetic forces become short-range inside superconductors.[28]"

BigBad

Sat Mar 02 2013, 07:17PM

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

It seems difficult to see how this could work.

If you could turn it on, and then off, and you've gained speed then that violates conservation of energy.

Photons have no rest mass, but they do have momentum and energy

E = p c

where p is the momentum, and E= h v where v is the frequency

Dr. Slack

Sun Mar 03 2013, 06:22AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

HighVoltageChick wrote ...

But then how do solar sails work? Momentum = mass * velocity and photons have no mass. Yet there's still acceleration using solar sails.

Photons have a measured momentum. The momentum due to rest mass * velocity is covered by the equation above. The momentum due to energy at light speed is not. You can't really use Newtonian mechanics to work with entities that don't have a rest mass because they are never at rest.

Let's say the photon has momentum right to left as it comes in, then left to right as it leaves after pinging off the sail. That's an impulse to the sail of twice the photon momentum. Even if it was absorbed as heat, it will be from time to time, the sail still gets a momentum change of one times the photon momentum.

The point is that entities bearing momentum are arriving at and/or leaving the sail system. The whole point of the EmDrive as proposed by Shaywer is that nothing leaves the system.

Now if he shone an ffing big searchlight out of the back of the engine, that would all be fine. The problem with that is that photons don't have much momentum, the drive would be very inefficient. What Shawyer is trying to do with a high Q cavity is get 1000s more photons (more momentum) stored in the volume for the same energy input = more efficiency. Unfortunately, the internal pressure on the cavity cancels on all sides. There's no net momentum gain unless you let some out. He uses a cone-shaped cavity to confuse the math, and then throws in a bit of relativistic fruit-loopery. Read Costella's rebuttal.

Conundrum

Sun Mar 03 2013, 09:45AM

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

Maybe we should get together and make a prototype

That would answer the issue once and for all, while also allowing 4HV to get credit due if it does work.

Re. superconductors, I am working on this too.
The problem is making a cavity (MgB2 maybe?) as ceramic materials such as BSCCO really do not like being wound into cone shaped cavities.

The way around the problem would be to make a chamber with say copper on the outside, an intermediate layer of silicon carbide and an inner layer of YBCO etc.

to complicate things, lets say that the microwave energy heats up the superconductor and quenches it.
This will result in a pulsed drive rather than continuous thrust so you'd need a spinning arrangement like the one on "2010: The Year we made Contact"...

Pinky's Brain

Sun Mar 03 2013, 09:56AM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

A photonic drive can work, but provides minute amounts of thrust ... even by space ship standards.

It's more efficient to accelerate used up fuel, gets you more thrust. Only with matter/anti-matter fuel does a photonic drive become interesting.

As for satellite control, there is nothing you could do with solar panels and a photonic drive you couldn't more efficiently do with a solar sail.

2Spoons

Mon Mar 04 2013, 01:38AM

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

BigBad wrote ...

If you could turn it on, and then off, and you've gained speed then that violates conservation of energy.

No, the kinetic energy gained is extracted from the resonator cavity, and originally comes from the microwave input.

It's not just a case of making a superconducting waveguide - the microwave source it going to have to be something special too, as an ordinary magnetron also loads the cavity (power flows both ways!). Something akin to a Class C amplifier, maybe.

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