Slymodi wrote:Why does the predicted mass of the quantum vacuum have little effect on the expansion of the universe?
Because the predicted mass of the quantum vacuum is wrong. The expansions of the universe in fact gives you a fairly good estimate of what the correct mass should be, and is thus one of the indications that the Standard Model is incomplete, since each particle has an impact on the mass, and thus extra particles could bring the mass to the correct value.
As to what exactly is wrong with the standard model, well, if I knew that I'd be ready to collect my Nobel prize soon
IronDuke wrote:What's the difference between a coilgun, a railgun, and a Gauss cannon?
In short, what narwhalz said.
In more detail:
Coilgun:
One electromagnet or a series of electromagnets (consisting of coils, as electromagnets are) set up in such a way that a projectile can pass through the center. The projectile is accelerated by turning on the magnet, so the projectile is attracted to it, and then turning it off when the projectile passes through the magnet, so the projectile keeps its momentum and flies out again at high speed.
This only works if the projectile is made of a ferromagnetic material and is fairly hard to make (for high velocity bullets your magnets have to switch on and off very quickly)
Railgun:
An electrical circuit consisting of 2 rails (hence the name) connected to the power source, and a projectile that slides between the two, connecting them electrically. If you put a strong current on this circuit, it also produces a strong magnetic field. (It's essentially one loop of an electromagnet)
Now, a magnetic field exerts a force on a wire through which a current is flowing. In this case, the force push the projectile forward in the rails, accelerating it.
This is partically easier to build, and can accelerate projectiles to immense velocities, but the friction also puts an immense stress on the rails.
Gauss cannon or gauss gun:
is normally a synonym for coilgun, except in the numerous cases where the name is used by people who don't know the difference between the two