Roryrai, you've studied GR, so this is mainly asking for your thoughts; but anyone else, feel free to chip in.
Anyway...
So I was thinking about General Relativity. Specifically, its relevance to gravity, and to quantum mechanics.
We treat gravity as a force. But does it act like one? Not really. The effect is similar - then again, the effect of gravity is also similar to electromagnetism, but that doesn't make them the same thing. A typical force is as such: two objects with a certain charge in a certain force exchange a force carrier, and are attracted or repelled. A proton exchanges a photon with an electron and they're attracted to each other. That's all there is to it.
If we now turn around and look at gravity...
A force carrier may be involved. We don't know. We think there is because it fits the standard model. But we've never seen a graviton. And it doesn't need to exist - gravity already has a medium, spacetime itself, whereas electromagnetism and the nuclear forces do not.
Gravity, instead, works by warping spacetime, and that warp causes objects to change their course. Hell, Earth doesn't even act directly on me (unlike a proton on an electron) - Earth acts on spacetime, and spacetime acts on me. Well, Earth doesn't act on spacetime, really; spacetime reacts to Earth's mass. So there's really no direct interaction between Earth and me. Unlike a force.
The warping, too, is unique. Electromagnetism was demonstrated to potentially be a spacetime warp, like gravity, by the Kaluza-Klein theory which added an extra dimension. However, this fifth dimension couldn't change shape, and was incompatible with GR. So that was discarded... leaving the result that no force, besides gravity, warps spacetime (if we consider gravity a force).
And we have the strength of gravity. The other forces vary considerably, true, but the difference between gravity and the others is vastly larger than any differences between the others themselves. Why is gravity so weak? Well, if it's not a force, there's no reason for it to be anywhere near the forces.
Now, let me present my strongest direct evidence...
An electromagnetic wave, or field, is photons. Photons are therefore equivalent to the force itself. Photons are electromagnetism.
A gravitational wave, or field, is spacetime itself. If we follow the same logic, spacetime is gravity. More accurately, gravity is a property of spacetime. Not a property of mass. Spacetime reacts to mass, not mass to spacetime. A force is a property of matter. Not of spacetime.
Gravity is spacetime. So unless we want to consider the very fabric of our universe to be a force, spacetime isn't one. And therefore, gravity isn't either.
Thoughts?
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