# Timon and Pumba on photons

1. Aug 7, 2003

### ddr

Timon, Timon, I wonder howcome photons have no mass at rest and yet mass is their only property?
Pumba, Pumba, you wonder - I know. There are no photons at rest!
----------------------------------------------------------------
ha, ha, ha...ain't it funny?

2. Aug 7, 2003

### mathman

What do mean by that? Photons have energy, travel at the speed of light, have spin 1, and other properties.

3. Aug 8, 2003

### ddr

it is because...

the energy of the photon is E=mcc
the momentum p=mc
...
---------------------------
if m=0 (there is no m) then
E=0;p=0... too(there is no E,p...).

4. Aug 14, 2003

### neutroncount

Re: it is because...

Doesn't work that way.

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/relmom.html

If mass is 0, than energy is equal to momentum times c.

Think relativistically!

Last edited by a moderator: Aug 14, 2003
5. Aug 18, 2003

### ddr

Re: Re: it is because...

Ok, how much is the momentum then?

6. Aug 18, 2003

### McQueen

Obviously then the photon must have mass ,right ? And if we follow this statement through to its conclusion it means that energy must have mass ?

7. Aug 18, 2003

### neutroncount

Why must a photon has mass? Look at the equations again. Energy approximately equates to momentum with a zero rest mass particle (mass disappears at c/c in the equation). So its MOMENTUM that relates to energy with the photon, not mass.