Mass of Light?

[unclebabar]

>If that is true, mass and energy are interchangeable...

That's true, mass and energy are interchangable, at least in one direction, according to E=mc^2. At least for physicists.

Things are different for scientists and normal people. Just like zzzz mentioned, to an ordinary person, light means that thin band of radiation from 400?-750? nm, while light to a physical scientist more than likely means the whole electromagnetic spectrum. A physicist can get energy from mass. Normal people can't. You split some plutonium up and you get uranium + a bundle of energy. You mush some deuterium together and you get helium and a bundle of energy. However, as a normal person (non-physicist), you can't take a block of cheese to the power company and ask for a terawatt-hour. Well, you can, but they just laughted at me when I did it.

 

[Sahakiel]

Originally posted by: unclebabar
>However, as a normal person (non-physicist), you can't take a block of cheese to the power company and ask for a terawatt-hour. Well, you can, but they just laughted at me when I did it.

You too? And here I was taking it all personal and stuff. Guess I won't need that microwave cannon, anymore...

On a side note, I've found it relatively convenient so far in basic physics to think of mass as not a measure of matter, but more of a measure of the resistence to changing velocity. Especially since with this matter/wave duality crap, I've decided everything is a wave, multidimensional or otherwise (There's what, 11 to choose from?) and what we perceive as matter in the traditional sense doesn't exist. It sounds so wrong, but if you're not going too deep into physics, it seems to help squeak you by.

Hm... I wonder if mass can be seen as a measure of temporal velocity in the object's frame of reference... Some trekkie help me out, plz..

 

[heliomphalodon]

Originally posted by: Sahakiel
I've found it relatively convenient so far in basic physics to think of mass as not a measure of matter, but more of a measure of the resistence to changing velocity.

That's a great way to look at it, and it leads to the idea of the equivalence of inertial mass and gravitational mass that underlies General Relativity.

 

[BumJCRules]

I agree... That is a good way of thinking about it.

 

[RossGr]

E=mc^2 is a very nice equation but it tends to get misapplied alot. It is simply the energy equivelence of mass, it is not used to determine the mass of a moving particle. The key relationship from Special Relativity is called gamma = 1/(1-(v/c)^2). This factor is used to compute, length contraction L = L0/ (gamma), Time Dilation T=T0/(gamma), and the increase in mass m = m0*(gamma).

If you look at the behavior of gamma, you can see that if v is much smaller then c then gamma~ 1 so for the velocities which we normally experiance there is not a significant change in, time, length or mass, but as v-> c, Gamma << 1 thus becomes a significant factor.

An interesting view point is to compute times and lengths from the frame of a photon, since v=c time and length both shrink to zero, so a photon does not experiance time or distance, as far as the photon is concerned it is adsorped as soon as it is emitted but that is ok, because it traveled no distance in doing so. This is as true for a photon we observe from the most distant points in the universe as it is for the photons which light the room you are sitting in.

Now it is not necessary to say that you cannot accelerate a body to the speed of light because its mass increases to infinity. Consider yourself on a spaceship, you acclerate away from some referance until your velocity with respect to that reference point is .5c, now you coast at that velocity and do some experiments measureing the fundamental constants of space (e0 and mu0) and the speed of light, the relationships hold c =1/(e0 * mu0) and indeed you measure c to be c. Now again you leave a referance at this velocity and accelerate to .5c, you can now measure the velocity of your original referance point but will find that it is somewhat less then c, do your experiments again with the same result, for all the energy you have expended you are no closer to the speed of light then when you have started. You can expend as much energy as you wish and you will NEVER achive even a fraction of the speed of light as you will always measure it to be c, no matter how fast you are moving with respect to any other point in space. Now if you were to step onto a scale you could not measure any increase in your mass or the mass of your ship. The mass increase is only observed from one frame of referance to another, neither it , nor time dilation, nor length contraction are observed in the moveing frame by those moveing.