# Why light is remains massless even if travelling w/ the fastest velocity?

1. Dec 1, 2011

### 121910marj

I got confused.. XD

"Under Einstein's theory of relativity, an object accelerated close to the speed of light gains a tremendous amount of mass.That is why no amount of energy can suffice to accelerate any object, even an elementary particle, to the speed of light - it becomes infinitely massive at the limit."

Photons are elementary particles that compose light. But as it travels at the speed of 3x10^8 m/s, i don't think it gain tremendous amount of mass, because light as we know is massless.

Thanks,
121910marj

2. Dec 1, 2011

### Staff: Mentor

Light doesn't accelerate to c. It starts at c and always travels at c. So even if you use the concept of relativistic mass (which modern physicists do not) the above quote doesn't apply to light.

3. Dec 1, 2011

### Pengwuino

Yes, the statement that an object's mass grows as it accelerates only applies to massive particles. Massless particles travel exclusively at the speed of light.

4. Dec 1, 2011

### 121910marj

DaleSpam & Pengwuino,
Thanks, it's all clear to me now..

5. Dec 1, 2011

### LGram16

I thought that the mass grew because it need an increasing amount of power. Think of it like this. A rocket ship needs a lot of fuel. If it wants to go faster, it needs more fuel. If it wants to go at the speed of light, it needs an infinite amount of fuel, therefore infinitely massive, therefore impossible. Something like that. Kind of.