How To Build a Quantum Propulsion Machine 392
KentuckyFC writes "According to quantum mechanics, a vacuum will be filled with electromagnetic waves leaping in and out of existence. It turns out that these waves can have various measurable effects, such as the Casimir-Polder force, which was first measured accurately in 1997. Just how to exploit this force is still not clear. Now, however, a researcher at an Israeli government lab suggests how it could be possible to generate propulsion using the quantum vacuum. The basic idea is that pushing on the electromagnetic fields in the vacuum should generate an equal and opposite force. The suggestion is that this can be done using nanoparticles that interact with the vacuum's electric and magnetic fields, generating the well-known Lorentz force. In most cases, the sum of Lorentz forces adds up to zero. But today's breakthrough is the discovery of various ways to break this symmetry and so use the quantum vacuum to generate a force. The simplest of these is simply to rotate the particles. So the blueprint for a quantum propulsion machine described in the paper is an array of addressable nanoparticles that can be rotated in the required way. Although such a machine will need a source of energy, it generates propulsion without any change in mass. As the research puts it with magesterial understatement, this might have practical implications."
Fourmilab (Score:5, Informative)
Re:Momentum Conservation (Score:5, Informative)
Re:So , , , (Score:3, Informative)
FTFY. Now queue the Spaceballs jokes.
Re:Call me pedantic but... (Score:5, Informative)
It turns out that there is no such thing as a classical vacuum. Instead, you have a state where particle/antiparticle pairs are spontaneously created and destroyed with typically net zero force. So, the definition of vacuum has been reformed.
-l
Re:what are we talking here?! (Score:5, Informative)
That's not at all connected. What you are thining of is as velocity of an object increases its mass will increase (this is actually a little more complicated. This is only true for things with positive rest mass. If you have zero rest mass for example then this doesn't happen, but you will always be traveling at the speed of light anyways. If you are a tachyon and hus have imaginary rest mass and move faster than the speed of light in a vacuum then what happens as you change velocity is more complicated). This will still happen. The key to this sort of drive is that you don't *lose* mass as part of your reaction. Rockets, ion engines, and pretty much every other method of moving things requires you to push against something else to move. A rocket works by sending out particles from one end and so conservation of mass forces it in the other direction. An ion engine works the same way but instead of using hot fast particles uses little ions accelerated by a magnetic field.
The key to this sort of engine is that it doesn't do that, It can accelerate without throwing off mass. But the object will still gain mass as it accelerates nearer to the speed of light. In practice, the second part really won't matter for any practical engine since we will be moving so much slower than the speed of light. The key idea at some level is that you don't need to lose fuel to accelerate (you just lose energy).
Re:Momentum Conservation (Score:3, Informative)
If you would read the article (a high order, I know), you would realize that, with quantum mechanics taken into consideration, there is no such thing as a classical vacuum. Hell, you could probaby get that just from reading the summary.
Re:Call me pedantic but... (Score:3, Informative)
Alternatively (if you're talking about the other particles), see the other response.
Re:Momentum Conservation (Score:3, Informative)
Quantum fluctuations of the position or of the magneto-electric constant of particles do not affect the average value of their momentum, as a consequence of the conservation of momentum law. A propulsion engine may be designed by using for instance an addressable array of small magneto-electric particles or wires. Rotating (see Fig. 1) or aggregating (see Fig. 2) these particles will result in velocity:
He brings up attitude control of satellites as an example because, I think, it's a situation where very small amounts of momentum do useful work (you only need to rotate the satellite by a degree or so a day, he says). He's definitely talks about propulsion in the body, not just orientation.
As reactionless drives are very much Weird Science, not mentioning propulsion in the abstract could well be entirely deliberate to make the article more publishable --- you may not that it's incredibly well referenced.
I hope someone tests this soon; it sounds easy to do, and if it's true, it'll be an incredible breakthrough. Apart from producing awesome space drives it would also provide a way of coupling energy to momentum. As energy has dimensionality MASS.DISTANCE^2.TIME^-2 and momentum has dimensionality MASS.DISTANCE.TIME^-1, that would open up whole new areas of science to pick apart.
Re:Implications? (Score:5, Informative)
If a spacecraft carries reaction mass, the total mass of the spacecraft is increased by the amount it is carrying at any one time. This mass must also be accelerated and decelerated. So the more you carry, the more you spend because you're carrying it. There are various side effects too, for instance, since the vehicle's mass changes over time, course change calculations have to keep track of that. Also, for every bit of mass you have to carry that is fuel, that's less cargo you can move from point A to point B.
If you have an energy source that is relatively mass constant - a nuclear reactor, or a set of solar panels - and you can piddle along without any tanks full of "stuff", you're going to be able to carry more payload; you're going to be able to go a lot longer without "refueling"; you're going to have more freedom and more range. Headed for asteroid X? Something interesting over there on Asteroid Y? No bothersome fuel constraints, you just go and take a look. That's the kind of benefit that has very positive ramifications.
The reason reaction mass is used in space is because in a vacuum, one has to push against something in order to move. That's the role of the reaction mass. You spend energy in X direction and get sent off in the -X direction with the same amount of energy.
Think of how a nuclear sub works underwater. Because it has something to push against (water), its ability to move is constrained only by the degree of push it can generate - it doesn't have to carry anything to push against, it's surrounded by water that will serve the purpose. The reactor provides a lot of energy to push with, using a propeller, which is designed so as to create a forward vectored force when spinning in the water. That's what the article suggests for space craft; that there is something there to push against, and therefore, one doesn't need to carry reaction mass. Spaceships using this method would be very much analogous to that nuclear submarine.
Re:Is this different from a photon drive (Score:5, Informative)
Red this short article about "vacuum propellers" (props to RedJesus for finding the article):
http://www.fourmilab.ch/documents/vprop/ [fourmilab.ch]
You don't have to "emit" anything, you just set up magnetic fields to push against the "vacuum" of space, which is not at all a true, classical vacuum (it contains little fields all over the place). It's like the ocean, a force that can be interacted with. A "working fluid".
And since we're talking electromagnetism, a really strong force in the grand scheme of things, maybe this will be a lot of energy efficient that simply throwing almost-massless particles out your rear.
Re:Conservation of M/E? (Score:3, Informative)
No. Think of the virtual particles as a loan that *must* be repaid. The more that is loaned, the quicker that it must be repaid. electron/positron virtual pairs exist for a loner time than say virtual proteon/antiproton pairs do. There is no way to use the creation of virtual pairs to create free energy or break the conservation laws.
Re:what are we talking here?! (Score:5, Informative)
Thanks for the thorough information. How does this throwing off mass thing relate to electric cars? Do electric cars accelerate without loosing mass?
It's not about losing mass necessarily, it's about Newton's 3rd Law / Conservation of Momentum. For something to accelerate forward, something else (the surface of the earth) must accelerate in the opposite direction such that momentum is conserved.
The concept of Conservation of Momentum and rocket propulsion is often explained using the analogy of a boat on the lake with a bunch of rocks in it. If you throw rocks off the back of the boat, conservation of momentum means your boat will be propelled forward. Now, that's a pretty silly way to propel a boat when you can just use a paddle or propeller to push the water backwards and your boat forward.
Rockets in space don't have that luxury. So they pretty much have to carry a bunch of "reaction mass" with them and throw it at high speed out the ass end of the rocket.
This invention, if it pans out, would be more like a propeller for spacecraft, pushed by and pushing against the short-lived particles that spring in and out of existence in vacuum. I have to imagine that the amount of thrust would be miniscule, but not having to carry reaction mass would be a huge advantage.
Re:Is this different from a photon drive (Score:3, Informative)
I did read that article. It didn't answer the question. The quantum vacuum consists of (at the energy levels we're dealing with) virtual photons. If we're giving net momentum to these virtual photons I think that is the same thing as there being real photons travelling in the appropriate direction. So, you move some charges and magnetic dipoles around, and you photons start moving -- how is this different from emitting something from an antenna?
And all electromagnetic forces are carried by photons so there isn't a difference in strength.
Re:Momentum Conservation (Score:5, Informative)
The issue with the theory is that it violates the Newtonian rule of conservation of momentum.
No it doesn't. As Maxwell figured out long ago, EM field can carry momentum.
The solution is simple... (Score:4, Informative)
Re:Doesn't sound exciting at all... (Score:3, Informative)
Your fuel source does not change its mass. The gas in your tank combines with the local air and releases pollutants into the air. Furthermore, it achieves actual movement by turning a wheel which interacts with the ground.
A spacecraft has no ground to interact with. Rockets produce movement by throwing away their mass. This engine (if it works) would not have to throw away its mass.
There are other ways to get around without throwing mass. Light sails produce it by interacting with photons that the sun (or a ground laser) throws at them. There's a plasma drive I can't quite remember the name of that interacts with the local magnetic field, in essence pushing on the sun from far away. The "flashlight rocket" (also called a "photon drive") mentioned just below this post throws photons away and achieves movement without losing mass. Ion drives don't count, because they do throw away mass -- tiny amounts of it, but they do.
Re:Momentum Conservation (Score:5, Informative)
An EM field can carry momentum, but this allows the momentum to go in only one direction.
If I emit an EM field, it is pushing back against me as it emits (albeit VERY gently). When the EM field hits something, it imparts some or all of that momentum to the object it hits. The conservation of momentum has been maintained, because there are equal and opposite forces.
Normally, drives do one of two things to move the object they are trying to move. They either eject mass at speed in the opposite direction (rockets) which involves the loss of mass or push against something like ground or air (wheels in a car, propellers on a plane) to pull themselves forward.
In a frictionless vacuum, the only known propulsion system that works is a mass-ejection system like a rocket. You have nothing to push against that a friction drive needs, so you have to bring your own mass and throw it out to gain momentum. As you use your propellant mass, you lose it, so you have to carry some sort of mass and some sort of way of throwing it out really fast so you make the most of every gram of mass you eject.
What this new theory is suggesting is that I can get the momentum for the cost of pure energy at one end, then use that momentum on the other end of the transaction for motion. Normally, I'd either have to have something to push against that would move back in the opposite direction as a result (or would be so huge that the opposing force would be negligible), or I'd have to eject mass.
This drive would do neither - it's like pulling yourself up by your own bootstraps (quite literally) then using the energy of your pulling to allow you to move through the air. The conservation of momentum, equal and opposite reactions, etc - poof - all gone. This is truly a non-Newtonian drive in that it appears to break fundamental laws of Newtonian physics.
Unless, of course, there is something that is "absorbing" the other side of the "equal and opposite" reaction, something outside our ability to perceive at this point, in which case this is a friction drive, we just haven't figured out what we are pushing against yet.
Or, alternatively, the theory may be complete crap. That's possible too. :)
Re:Is this different from a photon drive (Score:4, Informative)
Since it is a momentum-transfer (hence, reaction) drive, it would seem to face the same constraints as any such drive imposed by conservation of energy, so in the ideal case, it would perform exactly the same as an ideal photon drive. Of course, engineering efficiencies might, in practice, favor one over the other, but even an ideal photon drives has an enormous input power to thrust ratio on the order of 300MW per Newton of thrust.
QED (Score:3, Informative)
The existence of particles in a vacuum? That sounds exactly like the aether, a scientific theory that was abandoned about 200 years ago! [wikipedia.org]
I suggest you read this book: QED The Strange Theory of Light and Matter [wikipedia.org]
As the author of the introduction, Zee notes: "According to Feynman, to learn QED you have two choices: you can go through seven years of physics education or read this book"
This is the best book there is that I know of that will give you the grounding to get Quantum Electrodynamics. You will discover that particles do in fact, exist in a vacuum. The quantum world does not work anything like the macro world that we are used to. You have to get used to ideas like electrons traveling back in time and emitting a photon before they actually received a photon that caused them to emit said photon.
If you don't want to read that, then at the very least, read this: Vacuum Energy [wikipedia.org]
Re:Wait a minute... (Score:2, Informative)
Aether was intended to explain the propagation of light in a vacuum, before it was realized that light did not need a transmission medium. Up to that point scientists always figured you needed a medium to transmit energy. Once we dismissed that concept, the idea was thrown out. Proving that something might pervade vacuum is a little different than bringing back the theory of aether. ;-)
Re:Momentum Conservation (Score:3, Informative)
You're making an assumption -- that there is no effect on the ambient EM fields -- that the article does not support.
There is no reason to believe that the vacuum fields will be undisturbed by this process.
Re:I get the feeling (Score:3, Informative)
The computer you're typing on is a rather good example of quantum mechanics on an industrial scale. It's been estimated that quantum mechanics is in some way responsible for a large fraction (can't remember exactly - two thirds?) of our economy.
Re:Momentum Conservation (Score:3, Informative)
The main error being the claim that it was ever a serious criticism; a myth that appears to have been created by erroneous 19th century writings about Columbus. By the time anyone Europeans were looking for better trade routes to China and the Indies, both that the Earth was round and its rough diameter had been established for many centuries, and in fact navigation at that time relied on those quite heavily.
The criticism of Columbus's idea that he could reach (and, after his first trip, that he had reached, a claim he maintained until he died) the (East, now) Indies more quickly and efficiently by sailing across the Atlantic concerned the distance involved, since Columbus's plans required the Earth to be much smaller than the size it was generally accepted to be.
One should note that, in fact, Columbus was wrong and the criticism based on the generally-accepted results that he was challenging was right.
Re:Momentum Conservation (Score:3, Informative)
With a photon drive it takes 300MW to generate 1N of thrust. Perhaps this device will be more efficient?