You are moving along at a rapid clip. Your Einstonian clock must be ticking slowly. You are indeed a fountain of knowledge, and efficient at finding your flow.
I am not being ironic and we will stay away from alternate universes.
You don't need to apply gravity to matter. It constantly applies itself to all matter. I say, and everyone can observe that gravity "pulls things together". Try jumping away from the earth and see that it pulls you back. Spew any fountain upward and watch the water cascade back to earth. Stop the orbital acceleration of the moon and watch it come crashing towards us. These things will happen. How does it happen? Not by quirky particles that impart a message "come to me"!
It is an attractive mechanism, and inverse theory allows us to visualize how it works quite logically.
As of recently, anti-energy has been defined. It is gravity. Time will acertain this.
As for the photon, your are right. Quanta implies-how much? And so each photon is different depending on the frequency and amplitude of the wave. From here I will skip to arguements in your follow up entitled Relativity and venture that the ether is not dead. Many scholars have not discounted it; the MM experiment only discounted it until Rutherford changed our understanding of the distance involved between subatomic particles.
Logic tells us that waves need a medium to move thru. Because we do not understand the medium or can not see it does not mean that it does not exist. I visualize waves in the medium causing spin in the ether proportional to their amplitude and wavelength. I visualize the photon and the graviton with opposite spin and vectors traveling in the same wave. One is energy, the other is anti-energy. The forces between these particles are perhaps more easily understood thru fluid mechanics than quantum mechanics.
Does E=mc2? Many people dispute this. Perhaps none so enthusiastically and tenaciously as Milan Pavlovic. His theory on the Elpotrin is very convincing to a dilettante in physics, such as I.
But it proved a good place to start from. I was intrigued to learn that Heavyside should be credited with E=mc2, if indeed it is the truth.
What is the evidence for gravity acting at superlight speeds? I suggest a website entitled "The speed of gravity - What the experiments say", by Tom Van Flandern
found at: http://www.ldolphin.org/vanFlandern/gravityspeed.html
Weekend is here. I will try to respond more to Relativity as opportunity permits.