B Why does light not have infinite mass?

[Allen_Wolf]

I have read in the book 'A Brief History Of Time' that other bodies can't reach the speed of light because as its speed gets near the speed of light, it gets infinite mass and requires infinite energy to reach the speed of light. So light itself should be having infinite mass and would be requiring infinite amount of energy. But it does not have these properties. Why?

 

[jedishrfu]

Light has zero rest mass so that notion doesn't apply. Light does have momentum.

https://en.wikipedia.org/wiki/Light

They estimate that you would need 30 billion laser pointers hitting a penny to have enough force to move it.

Due to the magnitude of c, the effect of light pressure is negligible for everyday objects. For example, a one-milliwattlaser pointer exerts a force of about 3.3 picoNewtons on the object being illuminated; thus, one could lift a U.S. penny with laser pointers, but doing so would require about 30 billion 1-mW laser pointers.[19]

 

[Borg]

Take a look at the physical properties of a photon. In particular, the full version of the relativistic equation

As jedishrfu stated, light doesn't have mass. It's energy is just E = pc.

 

[Allen_Wolf]

So photons doesn't have mass right?

 

[PeroK]

I have read in the book 'A Brief History Of Time' that other bodies can't reach the speed of light because as its speed gets near the speed of light, it gets infinite mass and requires infinite energy to reach the speed of light. So light itself should be having infinite mass and would be requiring infinite amount of energy. But it does not have these properties. Why?

There's no such thing as infinite mass or infinite energy.

 

[Allen_Wolf]

There's no such thing as infinite mass or infinite energy.

So what does it actually mean or state, sir?

 

[newjerseyrunner]

Instead of thinking about motionlessness being the default state and energy being required to move, think of it more like this: light speed is the default state, and things with mass experience drag. No matter how hard you push against something, you can never remove the effects of the drag, just keep adding more power until that drag is negligible, so you can never move as easily as something that does not experience that drag.

This is not unlike reality, in fact, there was a brief point in time where everything: photons, gravity, quarks, electrons, all moved at the speed of light. The Higgs field hadn't settled yet, so nothing had mass. Since the Higgs field turned on however, everything with mass have been dragging along through it.

 

[PeroK]

So what does it actually mean or state, sir?

You could say that no finite amount of energy would accelerate a particle to the speed of light. Which is equivalent to saying it is physically impossible.

 

[Chalnoth]

Take a look at the physical properties of a photon. In particular, the full version of the relativistic equation

As jedishrfu stated, light doesn't have mass. It's energy is just E = pc.

Yup.

And furthermore, the speed of anything is just:

v = {pc^2 \over E}

Since E = pc for photons, v = c. For anything with mass, though the energy is always greater than pc, so it always has a speed less than that of light.