From his wiki page:
The beams have the appearance of red light (i.e., electromagnetic radiation in a red wavelength); however, they do not give off heat and instead deliver concussive force without recoil.
Considering that all photons exert a momentum change when they strike an object, Newton's laws insist that an equal and opposite change in momentum is required. Why is this not so?
From the same article:
Cyclops' eyes contain inter-dimensional apertures, releasing powerful energies from another dimension into his own via the beams. These later accounts state that his body naturally metabolizes ambient energy that is used to open and focus the apertures in his eyes. The energy of the beam itself originates from this other dimension.
Further,
Cyclops' body is naturally immune to the beams' force
Since the beam originates from another dimension, then it's not necessary that there be any recoil at all, in our dimension. Any recoil could be absorbed within the extradimensional space. (Also, since his body is immune even to a direct strike we can suppose he might be immune to the recoil too).
Cyclops' eyes contain inter-dimensional apertures, releasing powerful energies from another dimension into his own via the beams. His body naturally metabolizes ambient energy that is used to open and focus the apertures in his eyes. The energy of the beam itself originates from this other dimension. [source:wikipedia]
Theoretically, any recoil or force pushed back against the beams would affect this alternate dimension and not Cyclops himself. It is also possible that the optic blasts are subject to the physics of their home dimension and not the physics on Earth.
Per the Marvel Wiki article about Cyclops' visor:
The mask itself is made of high-impact cycolac plastic.
Cycolac plastic is an ABS: http://en.wikipedia.org/wiki/Acrylonitrile_butadiene_styrene
ABS has great shock absorption properties...it is commonly used in golf clubs to reduce the reverberating impact when the club makes contact with the ball.
Most likely the ABS plastic absorbs the kickback of the blast. Also, I'd imagine that his own physical strength and familiarity with the kickback of his powers lends itself to allowing him to not fall on his butt everytime he shoots optic beams, similar to getting used to the kickback of a shotgun or magnum.
