Will paralell light rays have a gravitational attraction to each other ?

Question

As we all know has gravitation an influence on photons, ligth rays; it can change the light rays direction. Thats why even light can't leave a black hole once behind the event horizon.
From my understanding of gravitstion if "things" can attract each other, both must have their own gravitational field. If this is true , also photons must have a very very small gravitational field and paralell light rays (photons) therfore will attracted each other and can't be paralell and the rays will cross each other and finally will join in one ray.

Or am I wrong ?

Answer 1

You are right.

Just to clear up a concept for other people answering or reading the answers: light, or photons, have zero **rest mass**, and this enables them to travel at the speed of light.

However, photons do have energy, and as such have an equivalent mass according to Einstein's famous equation,

E = m c^2
or
m = E / c^2

This is different than the "rest mass" (which is zero). And while it is not zero, it is a very small mass for most photons. As an example, for visible green light photons it is 4 x 10^-36 kilograms. That's a decimal point, followed by thirty-five zeroes, then the number four. Incredibly tiny.

So photons do have a gravitational attraction to each other, but because the masses involved are so small we could not detect the attraction with our current technology.

Answer 2

Nothing with mass can travel at the speed of light. This is a result of Einsteins' Theory of Relativity.

Photons travel at the speed of light. Therefore, they cannot have mass.

Gravity is a force that operates on mass. Since photons are massless, there is no gravitational attraction between light rays.

Regions of intense gravitational field will cause light rays to deviate, as in gravitational lensing which has been observed astronomically.

However, it is not gravity attracting light in that case, but gravity distorting space itself, the medium through which the light travels. From the perspective of an observer riding the light beam in this curved space environment, he would see the light traveling in a straight path.

Answer 3

Light, whether treated as a stream of particles or a wave, is massless (as are all energy carriers like photons). By definition a gravitational field can only be found around a mass. In the absense of mass, there is no gravitational field, just as there is not electric field around electrically-neutral particles.
So, two light rays cannot gravitationally attract each other.

Answer 4

thats a very good question and i like your thinking. light has been both described as a particle and a wave. technically if anything has mass it should have a gravitational influence. but with the duality of light, i think that the wave is used to describe this situation. the two light rays should not have a graviational effect on each other. even if you were to think of it as a particle, i dont think that photons actually have any mass since light is energy which would negate any ideas of gravity.

good thinking though

Answer 5

Per Einstein calculation on relativity theory light was shown to have bent in the presense of a gross mass.
Therefore light must have photinitos masses in order to respond to gravity field.

So based on this proof light has mass (what ever name any one choose to calle it=its mass)
It has been proven that it requires two masses for gravitational interaction to occur.
In the case of light the gravitational energy between the two light particle is very small compared to the kinetic energy of the light particle masse ,that path deviation is negligle.
However in the vicinity of a large mass the light rays will show significant deviation. If light rays were to collide we have a process of collision which will show interference pattern.

Answer 6

As one before me, light isn't a single ray or beam, it is a wave. It is drawn as a parallel ray at times, but it is constantly spreading out. Even the most advanced lasers in the world can't prevent this effect.

As far as black holes are concerned, no scientist can say for certain what is going on in them. Black matter is spread through out the universe, but there is no type of instrumentation that can even detect them. They can only detect the effects surrounding them, so they can't really describe with any accuracy what is the interaction between light and their gravity.

Answer 7

Light is made up of Photons which have mass. A very very small amount of mass. All mass is attracted to other mass. The partical beams will move closer to eachother as they travel.

Answer 8

If they did, I think we would see the light from stars not being uniformly distributed around them, but rather collapsed into columns of light by their mutual attraction. I don't think this has ever been observed, so the answer is likely no.

Might have something to do with rest mass vs kinetic mass too.....

Answer 9

Yes, they will.

The curvature of spacetime is related to the stress energy (the Ricci tensor). Light would contribute to this. But the contribution is mind bogglingly small, so two parallel rays would not be drawn together in the scale of this universe.

Answer 10

It takes mass and energy to form a gravitational field - c2 = E/m.