Does Light Have Infinite Mass When Traveling at the Speed of Light?

[demosthenes_001]

I recently heard something very interesting. For mass to go light speed, it must be infinite. It can be proved by breaking apart E=MC^2.

 

[Doc Al]

I highly doubt it.

 

[wlvanbesien]

For mass to go light speed, it must be infinite.

Even if it could, how could such a discovery in any way be significant?

 

[HallsofIvy]

On the contrary, for something to go light speed, its (rest) mass must be 0.

You may be thinking that, if an object with non-zero mass could go at light speed, according to the transformation formula, its mass would be infinite. What that does is prove, since there is no such thing as "infinite mass", that it is not possible for something with non-zero rest mass to go at light speed.

 

[demosthenes_001]

Exactly!

 

[dextercioby]

I recently heard something very interesting. For mass to go light speed, it must be infinite. It can be proved by breaking apart E=MC^2.

Simply because it's singular in the point v=c,the formula
$$m_{SR}=\frac{m_{0}}{\sqrt{1-\frac{v^{2}}{c^{2}}}}$$

cannot be used
This one can and it yields the correct results within the framework of SR
$$E^{2}=m_{0}c^{4}+p^{2}c^{2}$$

Try to make rest mass infinite and see that the total energy is also infinite.Ergo,unphysical situation.

Daniel.

 

[rahuld.exe]

$$m_{SR}=\frac{m_{0}}{\sqrt{1-\frac{v^{2}}{c^{2}}}}$$
according to this formula... anything that travels with speed of light will have infinite mass...

but light also travels like a matter... and so light(matter) obviously travels at the speed of light... doesn't it imply that light(as a matter) has infinite mass?

 

[Doc Al]

No. Anything traveling at light speed has zero mass (m₀).

 

[rahuld.exe]

yeah that is the rest mass... and light is never at rest
so isn't talking about the other mass a little more practical?
and 0/0 still is infinite right? so the other mass is infinite...
doesnt that mean that when light falls on me... i should be blown (no pun intended)?

PS: as you can judge by my no. of posts, i am new to this world... sorry if i sound stoopid or dumb...

 

[Doc Al]

yeah that is the rest mass... and light is never at rest
so isn't talking about the other mass a little more practical?

A better term than rest mass is invariant mass.

and 0/0 still is infinite right?

No, it isn't.

so the other mass is infinite...

No, it isn't.

That equation you used does not apply where m₀ = 0 or v = c. (As was pointed out in this thread over 6 years ago!)

doesnt that mean that when light falls on me... i should be blown (no pun intended)?

No, the energy and momentum of light are related by the second equation in post #6, which gives you: E = pc. Neither the energy nor momentum of light is infinite.

If you wanted to define the 'relativistic' mass of a photon, it would be E/c², which is also not infinite.

 

[rahuld.exe]

hmm... thank you for clearing it out!
what is 0/0 anyway? not defined?

 

[lightarrow]

hmm... thank you for clearing it out!
what is 0/0 anyway? not defined?

Not defined.

 

[rahuld.exe]

thank u!

 

[dextercioby]

$$m_{SR}=\frac{m_{0}}{\sqrt{1-\frac{v^{2}}{c^{2}}}}$$
according to this formula... anything that travels with speed of light will have infinite mass...

but light also travels like a matter... and so light(matter) obviously travels at the speed of light... doesn't it imply that light(as a matter) has infinite mass?

It's better to think of and use only one formula which is valid for all <particles> from special relativity.

$$E^{2}=m_{0}c^{4}+p^{2}c^{2}$$

With operators instead of scalar functions, this formula holds valid in quantum specially-relativistic theories as well. That's where the photons come from.