relativity question

All,
According to general relativity -- correct me if I am wrong -- as an object gets closer to the speed of light, it gains mass infinitely to the point that it requires infinite energy to continue accelerating that object. I would assume, based on this, that an object in motion must have mass. What about objects that don't have motion? Suppose it was possible to have an object be perfectly still. Would it have zero mass? Any thoughts?

-P

No, that's its rest mass! I don't think it's possible to have a completely still object, though, as it's going to exhibit some degree of Brownian motion.

If I'm not mistaken, I believe it's special relativity that deals with that; general relativity deals with gravity and space/time. Sorry to split hairs, but it is different.

As far as objects without mass, photons are a good example of that. They, by definition, travel at the speed of light. Also I think there are theorhetical particles called tachyons that supposedly travel faster than light. Their purpose and whether they've been officially proven or not I have no clue. That is an interesting question about having an object being perfectly still--even if the atoms and the subatomic particles are motionless. However, I think that such an object would still have mass, given that there's been experiments dealing with absolute zero (temperature) and I've never heard of zero mass being a result. I could be wrong though.

Photon's mass : P Question that a lot of people have different views on. IMO photons have mass as momentum and energy are functions of mass. Many people believe photons have zero rest mass and then 'create' mass as they go through the photoelectric effect.



explains very easy terms.
www.madsci.org...

I do not understand how anything can "gain" mass when it speeds up.

I understand that mass and energy are interchangeable, and that you cannot create energy, so how does one create mass without converting energy to mass?

I am probably missing something here, but from my point of view, it's like speeding up 1 brick to near the speed of light and ending up with the equivalent of two bricks...slow them down again and you have one brick again...whats that about?

Please explain....

Relativity is all about frames of reference.

It's impossible make an object perfectly still. It'll always be in motion from some frame of reference.

For instance, an object sitting still on the ground is still moving as the Earth rotates, and as the Earth orbits the Sun, and as the Sun moves through space, etc.

Originally posted by stumason
I do not understand how anything can "gain" mass when it speeds up.

That's a tricky subject, this is the most complete description i've ever come across (the bit below is in my own words, I had to type it out to try and get my head around it )

You can consider matter as a collection of charged particles. Taking the example of a single electron, when it is in motion it produces a magnetic field, the faster it goes, the greater the magnetic field. The magnetic field can be defined in terms of it's magnetic enegy and hence, the mass of the magnetic field. As the speed of the electron increases, the mass of its induced magnetic field increases which accounts for the observed increase in mass.

Relativity theory gives a relationship predicting the increase of mass of relativistic moving particles, but no physical model has been given to describe the fundamental physical mechanism responsible for the formation of that additional mass. We show here that this additional kinetic mass is explained by a well-known mechanism involving electromagnetic energy. This is demonstrated taking into account the magnetic field generated by a moving electric charge, calculated using the Biot-Savart equation.

Source

I know that it is physically impossible based on our laws of physics for something to be completely still. Stuff is always in motion. None of that is in question. I am posing this question about an impossible scenario because I am attempting to understand the true nature of what exactly everything is, or how it came to be. For instance, that brick that was mentioned, would it theoretically not exist? Would it exist as energy only? We are limited by what our perception tells us about what is around us. The whole idea of proposing this possibility is to test out something beyond our perception. Perhaps matter only exists in our dimenstion because whatever it was before is in motion. Who knows. I was just hoping that this would strike a cord with someone. Maybe to someone here, this is the missing-link that you have been looking for . . . I'm just putting it out there for people to add to.

If the brick was completely at rest it would still have a mass. The brick has a rest mass which is the mass of the brick when not in motion. That is what is commonly referred to as the mass of something because unless the object is travelling at a fair proportion of the speed of light the effect is completely neglible.

On a fairly related note... instead of just accelerating the brick and thus gaining momentum, there is the question of all the motions of particles within the brick; i.e. it's temperature.

When those particles get very very still... and hence cold, you can start to see some interesting effects.

the bose-einstein condensate is one of them; www.colorado.edu...

some materials become superfluid, others become superconductors, etc... so there really are interesting effects on particles/objects which are at rest; but they don't dissappear, or anything.