Atheists commonly object to premise 2 in the Kalam Cosmological Argument.
- Whatever begins to exist has a cause.
- The universe began to exist.
- Therefore, the universe has a cause.
There are various theories that atheists assert that result in a Universe with an eternal past.
- Oscillating Model – This theory asserts that the Universe has been expanding and contracting forever. Basically, the Universe goes through a period of expansion, then gravity slows down the expansion and leads to contraction. The Universe then contracts into a big crunch that leads to another Big Bang event followed by expansion.
- Steady State Model – In this theory, as galaxies travel apart from each other, new galaxies are created in the space between them. Basically new matter is created out of nothing so that the Universe is constantly expanding and has been forever.
- Quantum Gravity Model – In this theory the past is not eternal but there is no beginning to time.
- String Theory – Pre-big bang scenario – In this theory, the time prior to the Big Bang was an infinite state of contraction with the Big Bang being the pinnacle of the contraction. So while you travel forward in time, the Universe is constantly expanding. Traveling backward in time prior to the Big Bang the matter is constantly expanding to very small density.
What these various theories fail to take into account is that you can’t have an actual infinite set in reality. You could never arrive at “today” because there is no way to traverse an infinite number of days in the past. So the fact that “today” has arrived is proof enough that the past can not be eternal but rather began a finite time ago.
Additionally, in 2003, three philosophers (Borde, Guth, and Vilenkin), put together a theorem that establishes that ANY universe that has been in a cosmic state of expansion cannot be eternal in the past.