Why do two photons never collide I mean when two light rays intersect each other they do not form any resultant just passes each by ? Why and how ?

They do. But you need to have gamma photons with f.e. 510,999 eV energy each.

http://en.wikipedia.org/wiki/Two-photon_physics

 

Result is matter production

http://en.wikipedia.org/wiki/Pair_production

 

http://en.wikipedia.org/wiki/Matter_creation

 

y + y -> e+ + e-

OK but why do not simple photons of visible spectrum collide ?

As photons are not electrically charged they are not going to directly interact with each other.

OK thanks

I have not heard of two photons creating an electron-positron pair. Only one single photon carrying two electron mass at least, and near a heavy nucleus. This is also what the Wiki article seems to suggest:

http://en.wikipedia.org/wiki/Pair_production#Energy

 

Though, as the annihilation of an electron-positron pair must be reversible, maybe the process with two photons can exist.

 

Could it be that the creation of a pair requires too much accuracy from the photons? Fun, this would resemble entropy, but with few particles.

 

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Apart from carrying no charge, photons are also bosons, which permits them to occupy the same state. Electrons couldn't, for being fermions.

I thought I read that photons were their own anti-particle...and that they usually don't interact as they carry no charge and seldom get close enough to interact, but if they do happen to collide, they anniliate into heat....edd

What shall mean "heat" for two particles becoming none?

What do you call "close enough" for photons? The ones we receive from distant stars are square light years wide.

More generally: why formulate wild assumptions as claims?

"annihilate into heat" makes no sense. Heat isn't a substance, it's a process.