I'm Amber and I'm from Ireland. This is a blog mostly about physics but with some other interesting things thrown in. So if you have an interest (as I do) in astrophysics, particle physics, theoretical physics, mathematics, technology and other science related topics, then I invite you to follow my blog.
Richard Dawkins (via imagineatoms)
If light has no mass how can it be affected by gravity?
Because it has momentum
But momentum is mass x velocity so how can it have momentum?
Because language can sometimes bring more problems than answers. Light does not obey the same laws as ordinary matter. To help show this I’ll use equations.
(this is the full version of the famous E=mc2 )
c=speed of light
So if we assume m=0 then we get E=Pc
We can find the energy of a photon by frequency x Planck’s constant (E=fh)
So if we know the energy and the speed of light (which is constant) then simple division will give us the momentum of the photon.
So gravity is related to momentum and not to mass?
Gravity is still determined by mass but in Relativity mass is determined by a stress-energy-momentum tensor. This tensor is what gives rise to the famous “curved spacetime”. If you would like to know about all of this and more in greater detail here is a fantastically well written Wikipedia article on General Relativity