I can understand momentum from an explosion, but why would "space itself" expand because of an explosion?
I think the answer to this is “no”. If you could properly ascribe a “cause” to the universe’s expansion (and could prove it), you would definitely be first in line for a Nobel prize, at the very least.
And no, “dark energy” isn’t an answer; it’s a placeholder term for that which we don’t understand about the universe’s expansion.
The expansion of the universe, which is known since Hubble observations.Although interesting, it can be explained assuming the big bang (a big assumption of course, but with plenty of experimental evidence).
The second thing,, and the truly mind-blowing one, it is that not only the universe is expanding, but that the expansion is accelerating!! The usual date for this discovery is 1998. This is like throwing a baseball upwards and instead of it keeping its speed or de-accelarating (because of gravity and friction) the ball instead starts to move faster and faster. You would suspect the existence of an unknown energy that is powering this acceleration. That is what is called dark energy , which for all intents and purposes it is a giant black box with a question mark right now.
Is the theory missing in some more fundamental way, like the lack of unification of gravity and quantum mechanics?
Take a rubber band- one of those big wide ones- and draw two dots 1cm apart. Then stretch the rubber band. The dots aren't moving, but the distance between them is growing. That's the big bang.
During the big bang, the distance between things increased at speeds faster than the speed of light. They didn't move at all (no FTL movement), just new space existed between everything. Still happening now, just at a slower pace (but a pace that seems to be increasing?).
Why? Answer that definitively and you'll earn yourself a Nobel prize or two.
Tesla challenged the notion of "curved spacetime" as illogical. People should have listened to him.
Edwin Hubble, who discovered redshift disparity, in his later life questioned expansion as the cause. People should have listened to him.
Many "alternative" physicists over the years and still today deny expansion, dark, matter, dark energy, black holes, and other imaginary phenomena that were invented to patch mis-matches between observations and mathematical predictions.
But its like spitting in the wind against the force of inertia as everyone gets taught these fantasies in school as though they are fact.
Do yourself a favor and look into some alternative cosmology theories. I've posted a list elsewhere in this thread.
Tim Minchin has a great line about this in one of his songs[1]
'Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved'
God is not a hypothesis, but more of an theory in the analytical rather than scientific sense. That is, God is a conceptual framework by through which other information is interpreted, not a source of testable predictions.
The reason it violates Occam's razor is because it is the strongest possible axiom you can include in a system. Why does anything happen? Because God. That's not a very interesting theory in that it can predict anything without offering any reasons or insights.
Not to mention, we have no direct observational evidence of such an entity.