Special Relativity

[shoelevy]

Well, does e=mc^2 apply to massless objects? If your statement is right, then photons are also massless, which means that photons themselves can't even reach c?

the actual equation as derived from lorentz tranformations as according to einstein's method is E^2=(m^2) (c^4) + (p^2)(c^2)
in the case of photos, m=0 so the equation reduces itself to +/-E=pc where p is the momentum of the photon
ignore the negative sign for it represents the antiphoton and what you get is E=pc which implies that photons have momentum and energy

[weixing]

Hi,
Normally, photon is consider to have no mass.

Question to think about (saw this on one website, quite interesting):
A higher frequency photon have more energy than a lower frequency photon, so can we say that a higher frequency photon is more "massive" than a lower frequency photon??

Have a nice day.

[shoelevy]

Some discrepancy though, photons have mass that are so small that we refer them to as massless. Try thinking photons as pure energy and not matter.

Regards,
Sam

in relativity, the mass you state must be specified as rest mass or relativistic mass
so when u say photons have mass that are so small we refer to them as massless, you are wrong. photons are described as massless means they have no REST mass. but they have relativistic mass.
this is very easy to understand.
1)if they had rest mass, then they can't travel at the speed of c.
2)from the above post by me, you can easily see from the equation that a photon has momentum. as a result, it behaves like a particle and when it hits something, it'll transfer some momentum to the target object. therefore, a photon behaves as though it has mass. so, to makes things coherent, physicists asign photons with a mass specifically called imaginary mass or relativistic mass. its called relativistic mass because its mass is a result of relativity

[shoelevy]

Hi,
Normally, photon is consider to have no mass.

Question to think about (saw this on one website, quite interesting):
A higher frequency photon have more energy than a lower frequency photon, so can we say that a higher frequency photon is more "massive" than a lower frequency photon??

Have a nice day.

yes, normally a photon is considered to have no mass but when dealing with its particle properties, it behaves as though it has mass so when dealing with such rare situations, a photon is considered to have mass.

and regarding "A higher frequency photon have more energy than a lower frequency photon, so can we say that a higher frequency photon is more "massive" than a lower frequency photon??"
this is true.
a beam of blue light carries with it more momentum that a beam of red light. as a result, higher freq photons behave as if they were more "massive"

[[BPST]FerMIons&BOsOns]

lol i dont understand...

[shoelevy]

its more of a physics thing than astro thing

[ChaosKnight]

Someone sent me this link: http://math.ucr.edu/home/baez/physics/R ... ocket.html

It contains equations for acceleration, but the conditions for derivation are different. The final equations are therefore also different.

[shoelevy]

different as compared to equations from where?

[Destructos]

different as in the conditions at which the variables are measured... probably due to the uncertainty principle where it is stated that the exact velocity and position of the particle cannot be observed at the same time, therefore preventing the possibility of predicting the future... or something...

[Destructos]

i'm not in too deep into astro physics to the point where i would purchase Principia Mathematica(i cant afford the damn thing...), so i'm guessing the difference could be referring to the difference of the equations between special and general relativity... just guessing...