
Quantum vacuum plasma thruster - lelf
https://en.wikipedia.org/wiki/Quantum_vacuum_plasma_thruster
======
gus_massa
All the information about this is very confusing, and in some press report it
looks like a perpetual motion machine. I’ll try to explain what I had
understood trying to find an explanations that don’t break the physics laws.

You _must_ use some particles to carry the momentum. It’s not clear, but the
main candidates are photons (aka light). The quantization of the
electromagnetic field is the cause of the Casimir effect, and the name of the
particles that arrays due to the quantization of the electromagnetic is
photons. Some other explanations talk about a moving mirror, and an
oscillating mirror produces photons.

The number of photons is not conserved, so they can be created or destroyed
“out of thin air”. (Really you need another particle like and electron to
carry the difference of energy and momentum. The electron then bounce against
the ship to accelerate it forwards, and picks a little of energy to compensate
the energy that used to create the photon. It’s plenty of electrons, and you
can reuse them.)

So this is equivalent to pointing a laser backwards, so the spaceships
accelerate forwards. The discussion should be about efficiency. Is this more
efficient than a laser?

(Well, it’s not necessary to use a laser, a simple light bulb with a mirror
that reflect the light that tries to go forward will work. If it’s not
directional you will lost a lot of energy because the light that goes to the
sides doesn’t accelerate the ship (I don’t want to do the integrals now, but I
guest 1/3 of efficiency.) With a more directional setting, like the mirrors in
a flashlight the efficiency will improve.)

~~~
throwaway_yy2Di
This is inconsistent with the claimed "specific force performance of 0.1N/kW".
The ratio a photon's momentum to energy is fixed at _1 /c_, which is 3.3E-6
N/kW.

~~~
claudius
Which is why using the vacuum fluctuations makes sense – these are
particle/antiparticle pairs created randomly in the vacuum. Since these do
have finite masses, you can accelerate them to larger momenta than would be
possible with photons (which can also carry arbitrarily large momenta ℏω, but
creating these high-frequency photons is difficult).

~~~
throwaway_yy2Di
That doesn't solve anything, it only shifts the violation somewhere else? Of
course you can't keep the virtual particles, that's a net creation of mass-
energy.

" _which can also carry arbitrarily large momenta ℏω,_ "

With proportionally large energy. That's the concern here, not photon count.

(For anyone confused, it's ℏω/c in conventional units. Some unit systems
define c=1 for convenience)

~~~
scythe
See:
[https://en.wikipedia.org/wiki/Woodward_effect#Propellantless...](https://en.wikipedia.org/wiki/Woodward_effect#Propellantless_propulsion)

The claim appears to be that the momentum is transferred first to the local
stress-energy tensor, and then to celestial bodies. It almost sounds feasible
at a glance, but, well, it's quantum gravity.

I would say it certainly seems like there's something to be learnt by this,
though. A quantum effect with measurable gravitational consequences is...
almost unheard of.

~~~
gus_massa
There is not a complete Quantum Gravity Theory, so all what I will say are
only educated guess, supposing that the final theory will mix gracefully with
the current theories for the other forces.

> _[...] thereby producing a propulsive force thereon without having to expel
> propellant from the object. [...] Local momentum conservation is preserved
> by the flux of momentum in the gravity field that is chiefly exchanged with
> the distant matter in the universe._

The gravity field should be quantized, and the associated particles are the
gravitons. So in this effect they are using a jet of gravitons instead of a
jet of photons (like in my example) or a jet of atoms/ions (like in a
conventional rocket).

The exact quote can be used to describe how the “laser motor” works:

(modified quote) [...] thereby producing a propulsive force thereon “without”
having to expel “propellant” from the object. [...] Local momentum
conservation is preserved by the flux of momentum in the _electromagnetic_
field that is chiefly exchanged with the distant matter in the universe.

The correctness of this phrase depends on if you count the photons/gravitons
as propellant or not.

The graviton shold be massless, because the gravity force has unlimited range.
The relation of the energy-momentum in a graviton should be a cuadrivector, or
in more simple terms, the formula in my other comment should be valid, with a
“rest mass” m = 0.

So the formula can be simplified and you get the same p = E/c relation of the
photons, with is very small as throwaway_yy2Di noted.

------
zackmorris
The reason this is important (if it works) is that currently there is no known
propellantless rocket that produces more thrust than light pressure. Light
pressure is incredibly weak:

[https://en.wikipedia.org/wiki/Light#Light_pressure](https://en.wikipedia.org/wiki/Light#Light_pressure)

The formula is F = P/c so 1 watt of power (say, from a laser) only results in
a force of 3.33 nano newtons or 0.75 nano pounds. In other words 1 kW (a
little over 1 horsepower) results in about 1 micro newton or 1 micro pound of
force. A craft that used light pressure for propulsion would use up most of
its mass (even with fusion or antimatter fuel) to get to some fraction of the
speed of light.

So if this effect is real and has a performance higher than 3.33 nano newtons
per watt, to me it's one of the greatest breakthroughs in the history of
propulsion. It would have all kinds of ramifications for science because even
though it doesn't break any laws of physics, it means that we can no longer
assume that motion only comes from reactions with other matter or light. It
would basically open the door to modifying the mass and energy of empty space.
So I will remain highly skeptical until someone reproduces the claimed
results, but I would love it if they did!

------
stcredzero
Basically a plausible sounding mechanic for "thrusters" from Larry Niven's
Known Space. Lots of Sci-Fi ships as portrayed in media would be implausible
if they actually had to carry reaction mass. Even antimatter fueled ships need
mass fractions over 50% for intra-solar system missions. (Up to 80%, but for
some reason, never over 80%. Robert Forward covered this in _Mirror Matter_ )

One thing I'm confused over, however, is what happens to the momentum? Is this
like magically creating particles that carry momentum? (So you can carry
momentum in the opposite direction.)

------
Morendil
No, Wikipedia, in the context of space missions a DTO is _not_ a Data Transfer
Object.

(Fixed, so see
[https://en.wikipedia.org/w/index.php?title=Quantum_vacuum_pl...](https://en.wikipedia.org/w/index.php?title=Quantum_vacuum_plasma_thruster&oldid=589440802)
for the lulz.)

------
moocowduckquack
This reference looks interesting:

 _" A net unidirectional and reversible force on the order of ± 3.14
milli‐Newton or 0.069% of the suspended test article mass was recorded by us
in our first high frequency 2.2 MHz test article. The authors also developed a
W‐E model that integrates the various engineering parameters affecting the
design, construction, and performance of W‐E based MLTs for the next
generation of systems. When Woodward’s (2004a, 2004b, 2005) and our test
results were compared with the model’s predictions, the test results exceeded
predictions by one to two orders of magnitude. Efforts are underway to
understand the discrepancies and update the model. The test results imply that
these devices, when fully developed, could be competitive with ion engines
intended for use on satellite station keeping and/or orbital transfers."_

[http://scitation.aip.org/content/aip/proceeding/aipcp/10.106...](http://scitation.aip.org/content/aip/proceeding/aipcp/10.1063/1.2169317)

~~~
DennisP
Woodward's idea is something different though. It's based on general
relativity.
[https://en.wikipedia.org/wiki/Woodward_effect](https://en.wikipedia.org/wiki/Woodward_effect)

~~~
moocowduckquack
Sorry, I sort of ignored the article and just had a look at the references
instead.

------
baq
> equivalent specific impulse of ~1x10^12 seconds

this is so much more than pretty much anything else it's hard to comprehend
why there hasn't been a billion dollars put into it just to rule out the
possibility that it could work.

~~~
valarauca1
Most likely because of the 0.1N/kW. The best current made RTG's generate about
2.8 watts per kilogram. [source Wikipedia]

Which means based on these current numbers well need 3500 kilograms per Newton
of thrusts. This would generate a acceleration of 0.00002 m/s^2 of
acceleration. This would take about an hour, and a half to make a 1m/s delta-v
course change.

And that's without the drive, communication, heating, or scientific
instruments. The drive is VERY low powered. Also specific impulse means little
if you don't have fuel, since it determines your efficiency, but this rocket
already has 100% efficiency since it has no on-board fuel.

~~~
wcoenen
With a TOPAZ reactor you can get 15 watts per kilogram.

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dsr_
Chocolate Frosted Sugar Bombs.

Proof that anyone can edit Wikipedia, and frequently does.

~~~
unpointfulness
It's just a redirect man.

[https://en.wikipedia.org/wiki/Chocolate_Frosted_Sugar_Bombs](https://en.wikipedia.org/wiki/Chocolate_Frosted_Sugar_Bombs)

------
victorquinn
This sounds a lot like a perpetual motion machine...

~~~
slacka
Did you even read the article or just feel like spamming HN with some
uninformed snarky comment? I also am skeptical about this and don't fully
understand the physics behind it. But I did RTFA and all of the references
checked out.

