[Coda]

Originally Posted by Potironette

Woah! So energy is mass..? Or most of mass is energy?

That's exactly what E = mc² means!

Doesn't that mean mass is literally energy bunched up together O_o? And that what's happening at nuclear power plants is more or less spreading that locked and bunched together energy out?

You could look at it that way!

Ohh woops. When energy is released mass is lost, and taking the stuff apart means releasing all the energy. But then again protons and electrons aren't even masses either (I forgot quarks existed, well I never knew what they were until now ^^;;)...What even is mass, it seems that literally everything might as well be internal forces o_o.

I think the bulb may have just lit up. :D

I'll point out that particle physicists measure mass in electron-volts (1 eV = 1.6x10^-19 J) instead of some unit derived from the gram.

Oh! But why do quarks count as rest mass? Aren't they energy as well x'D.

They count as rest mass from the perspective of separating binding energy from everything else, but you're right: that rest mass itself is made of energy! That energy has a charge and a spin and other properties, and it's got the same wave/particle duality that photons have, but it's turtles all the way down.

The internal forces aren't accounted for is because the internal forces are part of the rest mass..? And they, because of Newton's third law, aren't going to suddenly change the object's rest mass?

Strictly speaking, it's not the forces themselves, it's the energy resulting from the forces interacting. But basically, yes.

I say basically because radioactivity violates the simplistic reading. The mass has changed, but no outside force has acted upon an atom to make it give off alpha or beta particles; it's one of the things that currently appear to be truly spontaneous in physics. But the system taken as a whole, if you look at everything as energy equivalence instead of distinguishing between mass and energy, obeys it -- adding up the nucleus, the photon of energy, and the emitted particle means the final system has the same mass-energy as the initial one.