Question

What evidence do scientists have that nothing existed before the Big Bang occurred?

Answer 1

There is no 'before' the big bang

Explanation:

As space-time began with the big bang, there is no 'before' the big bang, neither is there a 'where'. That is of course only the case if the big bang wasn't the result of another universe collapsing, in which case those assumptions would be incorrect and there would have, indeed, been a 'when' and 'where' before the big bang.
Saying that nothing existed before the big bang is like saying nothing exists outside the boundaries of the universe (if there are any).

Hope that helps a bit

Answer 2

Some Scientists believe that nothing existed before space and time came into existence at the Big Bang.

Explanation:

The belief that nothing existed before the Big Bang is based on the evidence that before the Big Bang there was no space nor time. Without space and time it is hard to understand how matter and energy could exist. Therefore some scientists believe before the beginning of the universe there was nothing.

The evidence that neither space nor time existed before the Big Bang the rapid beginning of the universe creates some philosophical problems. If nothing existed before the beginning of the universe, where and how did the universe come from and come into being?

The standard answer has been the oscillating universe theories. The idea that this universe came from a previously existing universe. This belief has been damaged by evidence that the rate of the expansion of the universe is increasing not decreasing as predicted by the oscillating universe theory. ( See Supernova studies 1997) These studies indicate that the universe will have an ending and not recycle.

A novel answer is that the universe is part of a multiverse system. The Multi universe theory can be pictured like an old lava lamp with new universes being spun off or born from an eternal reservoir of matter and energy. There is no possibility of empirically verifying this proposal being outside of the realm of observation.

The traditional answer is a supernatural source. "In the Beginning God created" As science is limited to natural causes this answer is not at all satisfying to most scientists.

There is evidence to belief that before the Big Bang the beginning of the universe there was nothing. Believing that nothing existed before the Big Bang creates the need for belief in something outside of the present universe.