Speed of light question

[likephysics]

Main Question or Discussion Point

simple question - Can light or anything else, travel faster than 3x10^5 km/sec?
If not, why is there a limit on max speed particles/photos can travel at?

 

[BryanP]

From wikipedia on Special Relativity:

Special relativity reveals that c is not just the velocity of a certain phenomenon, namely the propagation of electromagnetic radiation (light) - but rather a fundamental feature of the way space and time are unified as spacetime. A consequence of this is that it is impossible for any particle that has mass to be accelerated to the speed of light.

 

[michael879]

A good way to think about it that I recently came across is that everything is moving at a constant speed. That is, every object has a 4-velocity and a 4-speed of c (speed of light). A 4-velocity is a 4-dimensional vector where the first index is time and the last three are space.

Examples:
Object at rest: v = (c,0,0,0)
Photon: v=(0,c,0,0) *or any vector where the length of the spatial part is c and time is 0

So the question isn't "why is there a maximum speed?", its really "why is everything moving through space-time at a constant speed?".

 

[robphy]

A good way to think about it that I recently came across is that everything is moving at a constant speed. That is, every object has a 4-velocity and a 4-speed of c (speed of light). A 4-velocity is a 4-dimensional vector where the first index is time and the last three are space.

Examples:
Object at rest: v = (c,0,0,0)
Photon: v=(0,c,0,0) *or any vector where the length of the spatial part is c and time is 0

So the question isn't "why is there a maximum speed?", its really "why is everything moving through space-time at a constant speed?".

For a photon, its tangent vector has the form
Photon: v=(c,c,0,0), for example, so that $$c^2-(c^2+0^2+0^2)=0^2$$.

Here's my comment on the "speed through spacetime" idea:
https://www.physicsforums.com/showthread.php?p=565681#post565681

 

[michael879]

For a photon, its tangent vector has the form
Photon: v=(c,c,0,0), for example, so that $$c^2-(c^2+0^2+0^2)=0^2$$.

Here's my comment on the "speed through spacetime" idea:
https://www.physicsforums.com/showthread.php?p=565681#post565681

my bad, I forgot that detail: mass-less particles have 4-speed of 0 while massive particles have 4-speed of c.

 

[superdirt]

I read this today:

http://en.wikipedia.org/wiki/Variable_speed_of_light#Varying_c_in_quantum_theory

Scott