How Cn Gravity Affect Light When Light Has No Mass?

[Rhondazvous]

And this explains why although photons existed before recombination, there was no matter and therefore no gravity to counter the dark energy pushing everything apart. only after things got so apart that they lost energy was the strong force able to bring quanta together to form atoms and then large bodies with measurable gravity.

I don’t believe that is accurate for two reasons:

1.  Recombination refers to electrons pairing up with protons.  They existed separately as ionized plasma before.   So there were matter before recombination, just not electrically neutral matter.
2.  Even if there were not electrons and protons, If there were photons, there were gravity.  Gravity is an artifact of energy in all forms, not just in matter form.   If I am not mistaken, most of the gravity of normal matter is not from the rest mass of the particles with rest mass, but from binding energy that holds These particles together.

In relation to this discussion, I must disagree with both your points.
1.Quanta is not matter but the constituent parts of matter, just as hydrogen and oxygen are the constituent parts of water. That's why quantum mechanics is different from classical mechanics because qunta doesn't follow the laws of matter. The smallest unit of matter is the atom. There are hydrogen atoms. There aren't any hydrogen protons.
2. subatomic particles are held together by the strong force (gluons) which is entirely different from gravity. Before quanta were brought together by the strong force during recombination, there were no atoms, ergo, no matter. Photons may have produced gravity but gravity is a weak force. It wan't enough to held quarks together.