Einstein’s General Relativity Theory is also a gravitational theory. It is very theoretical, but he had no explanation why the universe didn’t collapse under gravity. So he introduced the cosmological constant, it was like a repulsive gravitational force over big distances. But Edwin Hubble looked in his telescope and discovered that the universe was expanding. Then Einstein called “the cosmological constant” his biggest blunder.
Hubble’s discovery gave rise to the Big Bang theory, where the General Relativity Theory is fundamental. Stephan Hawking wrote in his books that the universe could collapse or expand for ever, but it seems like it is exactly balanced in between, so it is hard to say how it would end. It is very unlikely, but it is crucial for galaxies with planetary systems to exist, with the possibility of life to exist.
Later they found that the universe will expand for ever and even accelerate.
Now it seems like the matter we see and know is only 5 % of what the universe consists of, 25 % is dark matter, that is needed for example to explain why Galaxies move like they do, most cosmologist are convinced that it exists. The rest, 70%, is dark energy, that is needed to explain why the expansion of the universe is accelerated. Like the cosmological constant.
The universe expands, without to expanding into any space outside it???? New space-time is created all time.
The Big Bang Theory includes an “inflation
theory”, that in a small fraction of the first second, it expanded very fast.
This “inflation theory” is like a brick that suits in a puzzle, but else there
is no scientific explanation for it. Roger Penrose calls it phantasy and in his
book “Fashion, Faith and Fantasy” he fantasies some more.
According to the Bible God created it all with his Word and holds it up with his Word. With faith we understand that it all was created with Gods word, so that what is visible came to be out of what was not visible. Since it is created by God’s Word, it is understandable. But how much do we understand?