2. How can one refute the idea of an eternal universe?
That is an easy question. The kaalam cosmological argument is definitely the superior one. That is why it was proposed in the first place. Here is why. Here is a version of Aquinas’ cosmological argument: Premise #1 Everything that exists was caused. Premise #2 The universe exists. Conclusion: The universe was caused. I like this argument but people has successfully pointed out possible “holes” in the first premise.
For example, one can argue that the number 3 was not created. One can argue that the number pi or the number e were not created. One can argue that circles and squares were not created. There are mathematical things that clearly were not created–that were not caused. Now, in my opinion, despite this weakness, Aquinas’ cosmological argument is a valid and a strong one. But, the kalaam argument is significantly stronger. Here is why.
These things that were not caused (pi, the number 3, etc.) did not begin to exist. In fact, as far as I know, every single proposed “exception” to Aquinas’ argument did not begin to exist. They are logical necessities, and therefore did not begin to exist. (whether the number 3 or pi or the number e “exist” is debatable, which is why I believe Aquinas’ argument still holds, but…) This is why kaalam is better. Here it is:
Premise #1: Anything that begins to exist is caused. Premise #2: The universe began to exist. Conclusion: the universe was caused. The cause of the universe, almost by definition, is God. I like that argument.
Of course, this argument only works if it can be established that the universe began to exist, which brings you and me, naturally, to your second question.
That the universe began to exist is accepted as true by virtually all cosmologists. As recently as the 1970s and 1980s there was a small fringe of physicists who still defended the theory of continuous creation, also known as the steady state theory. In essence, they defended the idea of an eternal universe. But cosmologists must deal with three areas of evidence. These three items of evidence are the expanding universe, together with the cosmic microwave background radiation, combined with the apparent distribution of the elements. All of these are consistent with the big bang model. However, the second and third (background microwave radiation and element distribution) are certainly NOT consistent with the steady state theory. Here is how science works. Good theories are consistent with the evidence. By this standard, the big bang model is a god one, but the eternal universe is not. By the 1980s, belief in an eternal universe collapsed. As far as I know, there is no important or influential scientist, literally, in the entire world today who accepts the idea that the universe is eternal.
Add to this, there is the second law of thermodynamics. This law states that all spontaneous processes in the universe result in the increase of entropy. This is why the second law of thermodynamics is sometimes called time’s arrow. Things only go in one direction. The universe is running down. If this is true, and it is as far as has been observed, then if the universe were eternal, it should have reached the maximum possible state of entropy already, in which case the temperature of the universe would be zero and there certainly would be no active stars or life. The properties of the universe, as well as the triple threat of the expanding universe, cosmic microwave radiation and element distribution make the proposal of an eternal universe untenable. It is as close to disproven as any scientific proposal can be described as disproved.
If you have found someone who believes in an eternal universe you can be assured that they are not scientists and are not even scientifically literate. You can safely dismiss the eternal universe. Therefore the universe was created, and the kaalam cosmoligical argument is rock solid.