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How To Build a Quantum Propulsion Machine
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."
I bet this could be done even easier with cats, but the ASPCA people won't like it.
Well.
A non-reaction mass drive. That makes my head hurt. It just gave a slight air of plausibility to a few million bad SF novels.
John Walker called such a device a vacuum propeller. He didn't have any particular ideas about how the device would work, but he does have a nice analogy involving propellers.
You don't need to vacuum if there are no particles.
If you, you know, read the article, you'd know they're changing the momentum of the electromagnetic fields in a quantum vacuum. Thus, momentum is conserved.
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
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Is dumping momentum into the quantum vacuum different from emitting photons carrying the same momentum? If not, this is just a photon drive, which is a well known concept, has brilliant specific impulse but is incredibly energy-inefficient except at high relatavistic velocities.
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).
Well you're not going to get to a decent fraction of light speed if you need to squirt stuff out of the back of a rocket. A propulsion system that doesn't depend on squirting stuff out of the back of the ship opens up all sorts of possibilities.
E.g. a spaceship that could accelerate at 1g would have all sorts of useful properties. Firstly 1g feels like gravity. Secondly you could zip around the solar system pretty quickly. Last but not least, due to time dilation you could circumnavigate the known universe in 50 to 100 years ship time. Of course back on Earth millions of years would pass so the trip would be one way. Still you could imagine making decades long (I guess, I'm too lazy to do the math) trips to a star like Sirius.
Actually I like the idea of sending out a plague of self replicating machines in devices like these, to bring the Word Of Dawkins to the stars and troll the inhabitants of other star systems.
echo -e 'global _start\n _start:\n mov eax, 2\n int 80h\n jmp _start' > a.asm; nasm a.asm -f elf; ld a.o -o a;
Does it mean that I am old because I look around every day and it feels like I am living in a surreal sci-fi story?
Reactionless drives, energy weapons, smart phones, robotic killing machines, genetically engineered super species? At this rate I wonder if I would be surprised when practical AI or faster than light travel becomes an option.
You can't change the momentum of the vacuum.
"You can't see moons around Jupiter. If there were, it would mean the Earth isn't the center of the universe." (Galileo's critics really said this.)
"You can't sail across the Atlantic to China. If you could, it would mean the Earth was round" (many, many errors on all sides of that statement!)
"Anyone who is talks about the practical uses of nuclear power is talking moonshine" (Rutherford in 1920, more-or-less.)
Scientific progress is the process of tearing down previously believed truths as well as discovering new, hopefully somewhat less contingent truths (although of course non-zero contingency always remains, which is a big deal to philosophers,mathematicians and other insane people, but not something anyone else cares very much about.)
People who have done actual calculations, rather than an arm-chair analysis on /., think that it is possible to change the momentum of vacuum modes, thereby making them non-vacuum modes (one would presume) by introducing asymmetries from rotating magneto-electric materials and in various other ways.
Introducing asymmetries has long been know to produce real particles from the vacuum. One of the most dramatic theoretical instances of this is a step-function potential with more than twice the electron mass. If you solve the Dirac equation in this situation you get weird phenomena like negative transmission and reflection coefficients that are negative or greater than unity.
The explanation is that such a large potential (so long as the step occurs over a scale of less than the Compton wavelength of the electron, which is about a pico-metre) has the ability to separate the virtual pairs that make up the "Dirac sea", thus turning them into actual particles (at the cost of the required amount of energy). If you could actualize this you could then accelerate the electron and positron to fire them off in the same direction, giving your apparatus a push in the process. At the most abstract level, what these guys are proposing is no different from that.
Blasphemy is a human right. Blasphemophobia kills.
This is exactly what they're saying. A quantum propeller.
You push off of stuff that already exists in space to move forward, instead of having to throw stuff backwards to move forward.
The KEY is that space is not a true vacuum. It is a "working fluid" in the sense that you can push at it with magnetic fields. It can be interacted with.
With the first link, the chain is forged.
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.
I've fallen off your lawn, and I can't get up.
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.
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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.
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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. :)
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Yes it does. The field is generated from the virtual particles in the vacuum, not from the ship. It is that field that they add momentum to -- the article explicitly mentions doing this -- adding equal and opposite momentum to their ship. They aren't trying to 'drag' the quantum vacuum field along with them. That would be impossible, not a method of propulsion, and violate conservation of momentum. The actual idea, however, does not.
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