Photons don't really have an anti-matter pair that we can observe afaik because anti-particles have the same mass and spin but opposite charge as their counterpart. Since photons have no charge, a photons anti-matter pair is just another photon. Furthermore, we know that anti-hydrogen has the same spectral lines as hydrogen so their electromagnetic interactions are the same.
Finding that anti-matter has anti-gravity would be world changing, though I'm setting my expectations very low. It would mean that we have access to the kind of exotic matter needed for a practical Alcubierre warp drive and could open up an entirely new field of space time engineering. It's just extremely unlikely, given all we know, that anti-matter has such properties.
That literally is light obeying gravity. Gravity interacts exclusively by the warping of space-time. Gravity and the Higgs field are completely 100% unrelated.
https://profmattstrassler.com/2012/10/15/why-the-higgs-and-g...
That is an incredible insight for me -- I never thought of it that way. So the thing that creates inertia (mass) is not the same as the thing that generates gravitational force -- they're just correlated in the types of matter that beings like us can interact with?
Are there anti-photons? (Presumably only anti-matter can make them.) Or is matter special because it matches photons gravitationally and thus answers the question of baryogenesis.
That second option leads to some very interesting implications for stars made of anti-matter. Any photons they make would be "shoved" away from the star - but where does that energy come from?
The first option means there are photons we can not detect (only anti-matter can make them, so only anti-matter can see them). That would imply there is an entire second universe out there overlayed on this one (at least photonically overlayed) that we have never seen, except gravitationally.
But during annihilation events which type of photon would be produced? Both? Randomly one or the other?
Finding that anti-matter has anti-gravity would open an absolutely enormous list of questions. It's not as simple, as OK, anti-gravity - every other part of physics would have to change as well.