# If you could make your mass=0, would you begin moving at c?

1. Jan 16, 2008

### Meatbot

Ok....we don't know of any way to do this, but let's assume we found a way for a second.

Would you require something to give you a push before you began moving at c or would you just instantly acquire that velocity? In what direction would you begin moving?

Must all zero-mass objects travel at c or can some travel slower, or be stationary? What if you were in an environment with no outside influences and you acquired zero mass? With nothing to push you, would you remain stationary? If you did, would you have zero energy?

Last edited: Jan 16, 2008
2. Jan 16, 2008

### Shooting Star

No, they all have to travel at c.

(If they are an imaginary particle, like a piece of classical vacuum, they can do whatever they want.)

3. Jan 16, 2008

### Shooting Star

That's a different ballgame altogether. Read up a bit on Mach's Principle, if you already haven't. Then we will discuss.

4. Jan 16, 2008

### Meatbot

I read up on it. Seems to me that if we imagine a universe in which the only object is one photon, then since there is no way to know if it is moving it can be said to be stationary. If a photon is massless and stationary then I would think it has no energy. I'm not sure how it can even be said to exist in that case. So I would think a photon can't exist unless there is something else in the universe with which to measure it's velocity against.

So I think that if a quark is alone in the universe and acquires zero mass it would cease to exist.

Last edited: Jan 16, 2008
5. Jan 16, 2008

### Shooting Star

Let's forget the photon for a while and say that an atom is there in a so called empty Universe. What about the speed of the atom, or the mass of the atom? Can it be said to exist in this case?

6. Jan 16, 2008

### Meatbot

Well, you couldn't tell if or whether it was moving since there's nothing to compare it to. I guess you can only tell the mass by it's effect on other mass or by trying to push it and see how it accelerates. But if you can't tell if it's moving since there's no other matter then you can't tell how it's accelerating. So I guess you can't *determine* the mass, but does that mean it's not there? I don't know but if it was still there it would still have energy so I think it could still be said to exist. I think a photon is different because it's defined as having no mass. No mass and no movement equals no energy. That would seem to indicate it's not there, or that it is there but has some other properties that we can't access.

Last edited: Jan 16, 2008
7. Jan 17, 2008

### Shooting Star

But in this case, there are constituents of the atom, and the motion of an electron may now be compared with that of the nucleus. This Universe is a bit different from the Universe with only a photon. The constituents may impose "mass" on one another, in a Machian way. The reason I wanted you think about an atom is that we know a bit about the structure of atoms, but not of the photons in the same sense.

> So I guess you can't *determine* the mass, but does that mean it's not there.

If it cannot be determined in principle, then it's not there.

What you are trying to say that a particle may exist in an empty Universe, even though we can't determine it's mass etc., but a photon cannot exist at all. Is that right?

>... or that it is there but has some other properties that we can't access.

That's a more constructive vein of thought.

8. Jan 17, 2008

### Meatbot

Yeah...that's the idea.