Can someone explain why the universe is expanding at all? I've heard it said "it's the momentum from the Big Bang". That sounds reasonable, but then we're told that it's not that the galaxies are flying apart, it's that the "basic metric of space itself is expanding".
I can understand momentum from an explosion, but why would "space itself" expand because of an explosion?
> Can someone explain why the universe is expanding at all?
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.
If you can answer the why, then I think physicists around the world would really like to know. We "know" the universe is expanding because we can observe the effects (eg, red shift of further away stars/galaxies), but the "why" has been the big, fundamental question for as long as it was predicted and/or observed. It's almost certainly related to some property of physics that we don't yet understand, but ultimately, we may never know any reason beyond "that's just how it is".
Thanks. So it's not related to Einstein's General Theory? In discussions around the cosmological constant, static vs. expanding universe and energy of space, it feels like the expansion is a consequence of the General Theory, and that all we need is to fill in some constants, like the amount of matter in the universe, and the actual energy of space.
Is the theory missing in some more fundamental way, like the lack of unification of gravity and quantum mechanics?
Thing about the big bang is that, as current theories go, it wasn't really an "explosion".
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.
because some theorists ignored physical reality and got caught up in the beauty of their math instead. They let math dictate "reality" instead of vice-versa. And then they taught it in the schools as theory at first, and now seemingly as fact.
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.
While it seems that might be true of whatever the bottom level is, we're nowhere near that now. For instance, we know not just the how but why of Newtonian gravity; relavistic gravity! Of course, we have lots of unknowns about relavistic gravity, so on it goes.
Religion can't really explain things though. If I say a floating jellyfish did it all, and we are too stupid to ever know why, that doesn't give any clarity.
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'
The answer being “god” is not useful. You can’t use it to predict or measure (people have certainly tried for millennia) phenomena therefore it isn’t worthy of discussion outside the purely philosophical.
That's because it violates Occam's razor. That doesn't disprove the existence of a God, of course, but it makes it less likely if you accept Occam's razor to some degree.
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.
You're right. I'm also amazed how the Magic Unicorn hypothesis seems to not exist amongst the modern, smart tech world. It's hard to imagine why they ignore us.
> I’m amazed how the God hypothesis seems to not exist amongst the modern, smart tech world.
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.
I can understand momentum from an explosion, but why would "space itself" expand because of an explosion?