*Originally posted by vivify*

**http://science.howstuffworks.com/science-vs-myth/what-if/what-if-faster-than-speed-of-light.htm
**

The article in the link above mentions that the mass of an object approaching C starts to have an infinite mass. The energy needed to move such an object at C is infinite, making it impossible to pass C.

You guys already know that. A few questions:

1) Do ...[text shortened]... y is only light capable of this speed?

If anyone could help, I'd very much appreciate it.

It's important to be clear about what is meant by mass. In the early days of relativity they used to distinguish between rest mass and a quantity called equivalent mass. A body with rest mass m travelling with velocity v would have equivalent mass M given by:

M = m / sqrt(1 - (v/c)^2)

However it was realised that M is a redundant variable. Take the equation E = mc^2 and use units where c = 1. The the energy at rest is E = m. The energy when moving at a speed v (as a fraction of the speed of light) is

E = m / sqrt(1 - v^2) = M

So the equivalent mass is just the energy in these units. So we now do not talk about equivalent mass and drop the "rest" from rest mass and just talk about mass.

A photon has zero mass, which means it does not have a rest frame and is constrained to move at the upper bound for speeds in relativity, which is why that upper bound is called the speed of light.

So the article you were reading is out of date. They should not be talking about the rest mass, just the mass. The energy diverges as the speed of a massive particle relative to an observer approaches the speed of light.

1) Light has zero mass. Using the old concepts it has zero rest mass and finite equivalent mass given by humy's formula M = hf/c^2.

2) No a photon has finite energy, to have infinite energy it would need infinite frequency.

3) Gluons, the force carriers of the strong nuclear force, are also massless. Because of the way the strong interaction works it is not possible to see a bare gluon, there are hypothetical particles made up of them called glueballs which would have a mass as QCD is expected to generate a mass gap. All other particles couple to the Higgs field which is one of the two mass generating mechanisms in the Standard Model.

So the reason the photon is massless is because it doesn't interact with the Higgs boson and because it doesn't interact with the strong force. All other particles interact with the Higgs and composites like hadrons gain additional mass due to the strong force.