… and how do they theorise how energy was created?
There’s a theory that the universe oscillates between expansion and contraction in an infinite series of “Big Bangs” and “Big Crunches”. Under this theory, the universe and all its matter and energy always existed and always will exist. There is no beginning and no end.
They are interchangable using the good old E=MC[sup]2[/sup] equation.
When you are at the densities and energies of the extremely early Universe (immediately post Big Bang) all four forces were wrapped up into one super force. As the universe expanded and cooled this super force degenerated into the four component forces we are aware of today (strong and weak nuclear, electromagnetic and gravity and they spilt off very quickly post Big Bang…far far less than a second). What the physics were of the plasma/energy/whatever you want to call it prior to the forces splitting off is anybodies guess. Indeed, it is just this sort of thing that physicists are tackling today (gravity stubbornly refuses to be wrapped up with the other three forces). Once the four forces did separate you get your quarks and gluons forming protons and neutrons and so on till you have a universe filled with matter.
As to where all this energy came from pre-Big Bang is a question that can’t be answered. God created it. The Universe has always been here with no beginning and no end. Some kid in a higher dimension whipped up our Universe as a high school lab experiment. Take your pick.
I think this theory has fallen out of favor. Recent observations suggest the Universe is flat and will continue to expand forever. Under that theory the Universe will die a heat death and will be a lonely, uninteresting place.
Additionally, the Big Bang/Big Crunch model had some problems with it. Notably that entropy would increase each time the Universe did this. Sooner or later it gets pretty hard to imagine how a Universe would work at all with an exceedingly high entropy (killing the notion of an infinite series of expansion and contraction).
However, some scientists have recently come up with a new idea for a Cyclic Universe that would allow the Universe to ‘recycle’ itself ever few trillion years or so. Our Universe will still die a heat death (so no one will be around to see this) but sooner or later a sort of Big Bang will occur again and a new Universe will pop into existence. This theory is pretty new however and has a long way to go to prove itself but there seems to be enough there to keep scientists looking at it as a possibility.
Thanks for the clarification, Whack-a-Mole. I vaguely remember hearing recently about the new “cyclic universe” theory, and conflated it with the old bang-crunch model in my walnut brain, causing me to think I was on top of things!