# What is 'mass'?

1. Jul 17, 2004

### Reflector

Things would need to have 'mass' in order to have inertia and be defined somewhere in space-time? If 'charges' did not have mass where would they exist (relative to each other)? More mass = more inertia (harder to change position). Order the position of charges with mass to allow them to interact. You can't have one giant planet for some reason. You need lots. If you had one giant planet 'where' would it exist?

2. Jul 17, 2004

### HallsofIvy

No, things do not have to have mass in order to "be defined". Light has no mass and there are several fundamental particals that MIGHT have no mass. I don't understand what you mean by " Order the position of charges with mass to allow them to interact".

I would think one "giant planet" could exist where ever it wanted! Could you explain your " 'where' would it exist"?

3. Jul 17, 2004

### Reflector

If there was only one giant planet, the surrounding space would be infinite, therefore the planet's position would be anything, everywhere, infinite. That's what I mean. It could not exist anywhere because it could exist anywhere else... The other point is that if charges did not have mass they could not exist anywhere relative to each other. Has there ever been a massless charged particle in a vacuum? I could be wrong. This is just is just the way I make sense of it. I'm looking for replies also to see what other people think.

Last edited: Jul 18, 2004
4. Jul 19, 2004

### yogi

Virtual particles may no have mass in the conventional sense - and there is the neutrino that exhibits such a small mass that it is undetectable - yet it carries a large angular momentum that is normally associated with rotating masses in classical physics

5. Jul 20, 2004