So, what you just said is that the beams self-channel anyway.

So, if beams self-channel, this innovation does nothing, right? It's a complicated system of multiple beams to make the beam channel, which is to say, self-focus. But you just told me "self-focusing beams in air have been pretty well established at this point."

To the extent that air is not transparent, this doesn't work.

This does not address beam scattering. If the air is scattering the laser beam, it still scatters the beam.

It would reduce beam spread... except that the beams that create the channel are not themselves channeled.

on this we agree

My point is that from a surface-level analysis, it doesn't do anything useful.

Let me repeat. The beams that create the channel are not themselves channeled. So the channel itself... has the diffraction, scattering, and beam spread of an unchanneled beam. The net result can't be better than an unchanneled beam, because it is made out of an unchanneled beam.

I'm puzzled as to what this does or what it's good for, exactly.

1. Air already transmits light signals. It's transparent.
2. They haven't mentioned anything about amplifying light signals. This would be hard.

So, they are creating a "pipe" that can transmit light... but it doesn't stop beam spread (since the beams that make up the "pipe" still have diffraction-limited beam spread), and it can't bend light around corners. So, they now have a pipe that will funnel a laser beam along the path made by other laser beams, which take it exactly the same path that the beam would go without the pipe...

Right.

That was pointed out by Bondi in his 1957 paper introducing the concept.
http://journals.aps.org/rmp/ab...

Well, if you load your positive-mass vehicle up with an amount of negative mass, it will still fall downward, but it will have less overall mass and less weight. So it will only take a little amount of force to lift it or move it around.

The "if negative mass could be practically harnessed" is a big "if," though. Even aside from the fact that you have to figure out how to make negative mass.

Right

Right

You'd think, if it behaved like ordinary matter, that if it is attracted to positive matter, than it would conversely also attract positive matter. But no.

Negative matter particles attract each other, as you say, but repel normal matter. (They're attracted to it... but they repel it.)

The equations are: F = ma
and F = G mM/r^2

Fortunately, your happiness is not relevant to whether physics works.

No, this is one of the many examples where science depends on pure observation. The Pauli exclusion principle was first arrived at from observations, and only somewhat later was the theoretical basis-- the spin-statistics theorem-- worked out.

You're asking a lot, since we don't really know what the property of the particles are. A negative mass particle would curve in electric and magnetic fields (the usual way to determine what a particle is) just like a positive mass particle of the opposite charge. However, since negative mass particles also have negative kinetic energy, conservation of energy means that the remaining particles will have more energy coming out of the collision than they did going into it.

Positive mass particles emit positive energy and slow down. Negative mass particles emit positive energy and speed up. If you see unknown particles exiting the scene at high velocity, and leaving behind more energy the faster they go, that would be a negative mass particle.

Well, I already said negative matter is weird.

Robert Forward proposed that when positive matter and negative matter touch, they cancel each other out, and vanish:
  (+) + (-) --> 0 (vacuum)
The mass cancels, and you're left with nothing there.

Unfortunately, we know that this can't happen, because if it did, then the opposite reaction could occur:
  0 --> (+) + (-)
--vacuum spontaneously generating pairs of positive and negative mass. If this could happen, it would happen, everywhere, all the time. But it doesn't. So there are rules (presumably conservation laws) forbidding this from occurring.

Of course they can interpenetrate. The reason that you can't walk through a brick wall is because of Pauli exclusion: the electrons in your body can't occupy the same place (the same quantum state) as the electrons in the wall. But, whatever negative matter is, it's not electrons (nor any of the other particles that make up "solid" matter). So, yes, it would pass right through ordinary matter.

Nothing. Negative mass is weird.

What you're pointing out -- that a positive mass and a negative mass would chase each other-- was pointed out in 1957 in Bondi's paper about negative mass, "Negative Mass in General Relativity". Rev. Mod. Phys. 29 (3). Robert Forward, in 1990, then extended that analysis even further and pointed out that negative mass is even weirder than that.

A negative mass chasing a positive mass accelerates forever... but it doesn't violate conservation of energy, because the faster a negative mass moves, the more negative the kinetic energy, so the positive kinetic energy and the negative kinetic energy cancel out, leaving energy conserved.

There are weirder things than that, too.

If you think this is so weird that bulk negative mass can't exist... well, that's what Einstein thought (the "positive energy condition").

It's unrelated to dark matter (which has positive mass- that's how we know it's there), but dark energy is gravitationally negative (it causes expansion to accelerate: it's gravitationally repulsive)

You're in good company! If you did understand it, you could publish, and you should be getting a phone call from Stockholm soon.

It competes with the totalitarian principle, "everything that is not forbidden is compulsory."

Negative mass is very diferent from antimatter. Antimatter is opposite to normal matter in charge and quantum numbers (such as baryon number, etc.), but still has positive mass.

Negative mass reacts oppositely to both gravity and intertia. Oddly, that means that negative mass still falls down in a gravitational field: The gravitational force is opposite, but negative mass responds negatively to force (a=F/m, where both F and m are negative). So negative mass particles repel each other gravitationally, but are attracted to positive mass objects.

This has peculiar consequences. One consequence is that, for objects of negative mass, gravity and electrostatic charge switch. For normal mass objects, gravity is attractive, but like electrical charges repel. For negative matter, gravity is repulsive, but like electrical charges attract.

I wrote about this once, in the AIAA Journal of Propulsion and Power-- not a journal that physicists usually read, I'm afraid. If you have access to AIAA online, it's here: http://arc.aiaa.org/doi/pdf/10...

That's the way NASA currently does business: launch services are purchased.

SpaceX developed Falcon-9 on a NASA contract, specifically in order to be a vehicle that can be purchased for launch services. ("Commercial Orbital Transportation Services" was the name of the contract.)

That's a lot of aliens.

Well, since there are 100 to 200 billion galaxies in the observable universe, not so many. One burst per galaxy every 50,000 years or so.