Why doesn't light bounce off of itself?

Question

It is a given that light has mass-- that's why it is affected by gravity.

It is also a given that light bounces off objects-- that's how we see objects.

But, with all this light bouncing off every object in all directions, why doesn't the light collide with itself and disolve into a field of visual static?

Answer 1

Because light's particle-wave duality is not observable with any experiment devised so far. By this, I mean that once light is observed to be a wave by an experiment, it cannot be seen as a particle by the same experiment.

Light bouncing off stuff can be considered an "experiment", and this event has been seen as a wave-nature experiment. So what happens is that photons are no longer involved in the visual process (up to the actual reception of light in the retina), and wave interference is what we observe.

Answer 2

first, light does not have mass. it is made of photons which are massless. it is pure energy.

some people will say that the photon has mass since it has energy, and energy is convertible to mass according to Einstein's formula E = mc2. They will say that the photon has "relativistic mass". "Relativistic mass" is an outdated term that means how much energy E is available to be converted into mass. But, once the photon is converted into mass, it is no longer a photon but another particle entirely. so, this term is misleading. in modern physics the mass of an object is its invariant mass which is always zero for a photon.

regarding its interaction with objects: when the photon strikes the surface of an object and is reflected, what really happens is the energy is transmitted to the surface of the object, agitating the molecules on the surface, which in turn spit out a new photon in the opposite direction. so, when you see the object you are not seeing the same beam of light that you shone on it, you are seeing a new beam of light caused by your shining the first beam of light on the object. and the interaction is caused by energy being absorbed, transmitted and ejected in a new photon, not by the photon bouncing off the object like a ball off the floor.

as to why light doesn't collide with itself, it does sometimes.
if light is trapped in a box with perfect mirrors so the beams of light are continually reflected back and forth in the box, it will appear pitch black, because the beams will cancel each other out. on the other hand, if you have two beams travelling on the same wavelength and frequency "doubling up", the light will appear twice as bright. if the multiple beams hit each other and they do not quite match up, it will create an interference pattern that will be brighter in some places and dimmer in other places.

Answer 3

No answers so far seem to get the gist of it.

Light - that is photons - do not have any rest mass. But they do have momentum, and hence contribute to the stress energy of space. This is what gravity affects, and is why light interacts through gravity.

There are two reasons that light does not bounce off itself. The first is that it does not interact by any force strongly enough. The second is that - in quantum terms - it is a boson and obeys bose einstein statistics. This means photons can all occupy a single state.

Light bounces off matter because it does interact via the electrostatic force with electrons.

Answer 4

The Speed At Which Light Is Traveling Causes Light To Interact Rather Than Deflect,Sort Of Like Liquids That Will Mix,Or Gas That Will Mix,The Physical Properties Of Light Will Mix Too

Answer 5

Ah, light does not actually have mass. It has energy. That energy itself can be interpreted as mass, and therefore subjected to the affects of gravity. Fun stuff.

The answer is found in the difference between gravitational and electro-magenetic fields. In gravitiational fields, all mass and energy is effected in the same manner. For example, let's take a satellite in orbit around the earth. It has mass, and is subject to the force of gravity. But this gives it additional energy, and that energy is also affected by gravity. So, a gravitational field is not gravitiational nuetral...the field produces another field itself. (This is part of general relativity.)

Magnetic and electric fields; however, are nuetral. This means that electromagnetic fields do not produce additional fields, which makes them a little simpler. Consider that photons are carriers of electromagnetic energy. When they meet each other, there are no additional photons produced to carry more electromagnetic forces. So they interfere, but do not deflect each other.

Simply put, light interferes each other like typical waves.

Answer 6

The interaction potential of a photon with a photon is zero unless there is a particle-antiparticle creation and destruction in the process. For low energy light, this is unlikely. Thus, there is little interaction between photons and other photons.

As for light having mass...this is wrong as usually interpreted. The equation for the energy of a relativistic particle is
E^2=m^2 c^4 +p^2 c^2.
Here, m is the rest mass of the particle, E is the energy, c is the speed of light and p is the momentum. For a particle at rest, p=0 and we get E=mc^2. For light, m=0 and we get E=pc.

Answer 7

Because its mass is not large enough to fill the space making collisions rare and then probably only glancing.

Light travels in straight lines so if it hit another ray of light head on something would happen but what. We have not got down tro that microscopic level yet so we can only guess but id light bounces of a mirror then it suggests in this example at least, it should bounce of itself.

Answer 8

Since light travels in a straight path at a constant speed, all the photons would travel parallel and at the same speed, eliminating the possibility of collisions.
By the way, gravity does not affect light directly but curves space, so it appears the path of light is bent by the gravitational force, while in fact it is still traveling in a straight line (which would be the shortest distance between 2 points).

Answer 9

Bounce may not be the correct word; reflect is more correct. With that said, lights/light sources - in a sense - do reflect off each other (i.e. light cannot absorb another source of light, like the "color" black and other shades/colors which are not white but are not as dark as black; also black, which is not a color at all, is actually the absence of light).
Light reflecting off another source of light will increase what the eye perceives as brightness, which is why two equal-wattage lightbulbs are much brighter than one. The reason that the amount of light is not twice as bright is because some of that light will be absorbed by varying objects of different colors/shades (as well as black) near thiose sources of light.
Check Wikipedia for more comprehensive (as well as a clearer) explanation of this.

Answer 10

Because of the distortion of space-time near objects that move at the speed of light.

When light approaches a surface, relative speeds are like both light and surface move at a half of the light speed, so no distotion occurs.

When two photones move toward each other, the relative speed is like one of them is static, and the other one moves twice as fast as the speed of light. Since it is not possible under any circumstances whatsoever, distortion of the space occurs, and the time prolonges (extends), and the end effect is that photones pass by each other.

The explanation is the following: due to the distorsion of space AND time, it appears that photones assume TWO positions at the same time - one is before the collision, and the other is after the collision (because of wave-like nature of light). So, two photones cannot even meet themselves, but they pass by each other.