One of my hobbies is physics. Yes, I'm a geek. It started, as best I can remember, with Carl Sagan's Cosmos. It was beautiful and clear. (The new one is even more message-heavy than the old one, and nowhere near as beautiful.) Stars are the way they are because of how atoms behave? The behaviors of the smallest and largest things are entwined? As Spock (pbuh) would have said, fascinating. So, I think about physics when I'm in the mood. And lately, I've been in the mood. I have time while riding the train back from work, you see. (Not on the way to work - that's nap time.)
Back when I was a teenager, I even wanted to be a physicist. My first year at university was as a declared physics major. I made the mistake of taking the accelerated courses, and trying to learn physics and the calculus behind it at the same time was just too much, too fast for me. So I dropped out and joined the Army to go fight the godless Communists. The point of this aside is to show that I have some background, but I am by no means a physicist or mathematician. I'm just a very bright geek.
I picked up a BD copy of Interstellar this weekend, and watched it last evening. It was as fantastic as I'd heard. I'm glad we saw it at home, with the subtitles on, as the background overwhelmed the dialog even more than is common with most movies. The I watched the special features, which includes a The Science Of section. Great stuff, and it clarified some things in my mind. Cue Moment Of Clarity. I now think I understand space-time and gravity. I'd been working on my theory of space for a while, since I worked out the existence of what turned out to be the Higgs field over the winter. I'll cut straight to the chase, and end this long-winded, stream of consciousness introduction.
Space-time is quantized. There is a smallest unit of space, as there is a smallest unit of time. Light travels at the rate of one space per unit time. That's why nothing can travel faster than it. Except gravity, of course, which has infinite speed. Why does gravity have infinite speed? Because it's not a property of matter, but a property of space-time itself. What is gravity? I propose (the truth according to my current opinion, subject to change) that gravity doesn't actually exist. What we perceive as gravity is more properly called vectored time. Mass 'warps' space. It does this by increasing space-time's density. The time dilation effects of near light-speed travel happen because the speed of the object makes it pass through more points of space, increasing its apparent density. Time dilation happens because time is directly related to the density of space. And time has a 3D vector component that we view as gravity. This vector increases as the density increases, or inversely to the distance between adjacent points of space-time, in a logarithmic fashion. After all, it takes quite a lot of mass to noticeably affect time to any degree - as it takes quite a lot of mass to affect other objects to any noticeable degree.
There is a smallest unit of space that matter can occupy - but the distance between any two points isn't fixed. It's variable, to a rather large degree, based on the influence of the presence of nearby mass. The more mass there is, the closer the bits of space-time get to each other, increasing space's density. Space can create more space. Gravity and time are related functions of space-time.
An object continues in a straight line unless a force acts upon it. Space-time gravity affects matter as a 3D vector to that motion - time itself is preferential in its relationship with mass. Yes, a rock floating in space continues in a straight line, as far as it knows. It's just that the forward direction of time is pulling it ever so slightly towards the nearest other mass, and that larger mass over there, and that enormous, bright mass over there... And the quote from the movie that spurred these thoughts - "Time inside the event horizon of a black hole points towards the center."
The initial period of greater-than-light-speed expansion happened because the enormous density of energy led to an enormous density of space, which then immediately spread out to a more "comfortable" distance from each other. Space is not constrained to light speed, because space is not matter. It is the background upon which matter and energy are overlain.
Why does light slow down when passing through water? It's more dense, and thus space-time is more dense. Why does light curve around a galaxy, or a black hole? It's more dense, and time is flowing towards the center. (Photons, being massless, don't directly react to traditional gravity. But they obviously curve around very massive objects.)
Thought experiment. What is the life span of a photon? Well, let's see. Photons travel at, you guessed it, the speed of light. Time slows down the closer you get to the speed of light. Obviously, when traveling at the speed of light, no time appears to pass at all. Therefore, subjectively, no time passes between the creation and destruction of a photon. Therefore, it can last indefinitely in the outer universe, as it doesn't actually age.
Space can create more space. That's why the universe can expand. In the absence of matter, space-time becomes much less dense, as the points spread apart. Once they cross a certain minimum density threshold, new points of space-time are created to 'fill in the gaps.' The space-time points then adjust position to reach local density equilibrium, and the cycle eventually repeats Thus, the more empty space you have, the faster that space will expand. And you never see it doing this locally, because the density of space-time in the presence of mass prevents it from doing so.
All this took so much longer to put into words and type than it did to think. I hope it makes any sense at all to somebody else. Like I say in my introduction, I'm not really good at communicating.