Show me a source that states the big bang theory says there is nothing before it.
I thought I did. From Professsor Michael Woolfson's Time, Space, Stars, and Man: The Story of the Big Bang (Imperial College Press, 2009): "This observationally-based conclusion has led to the current theory that most, but not all, astronomers accept for the origin of the Universe- that at some point in the past all the energy in the Universe was concentrated at a point, a point with no volume that scientists refer to as a singuilarity. That is a challenging idea. The implication of it is that, at the instant the Universe came into being, space did not exist and time did not exist! Once again we are in the position that we cannot imagine or understand what this means. Try the following experiement- close your eyes and try to think of nothing- absolutely nothing. You can no more do this than we can properly understand- really understand- a Universe of zero volume in which time did not exists. This theory, called the Big Bang thoery, postulates that starting from the singularity the Universe expanded so creating space and time. Like any sensible person you will ask the question, "What was the state of affairs before the Big Bang?", to which you will receive the answer, "There is no such thing as before the Big Bang because time did not exist until the Big Bang occured." You might try again with the question, "Into what did the Universe expand?", to which the answer is, "There was no space for the Universe to expand into since the only space that existed was what it created as it expanded...Remember, once the Universe came into being and began to expand, then it is possible to talk about time" [italics in original, emphases added]. p.66
True but matter/energy were just in a different state at the moment the expansion began. Did you watch that video I posted? Is there something in that video I might be missing?
No I've read enough Stephen Hawking to know his views. From The Nature of Space and Time By Hawking and Penrose (Princeton University Press, 1996): "Indeed, almost everyone now believes that the universe, and time itself, had a beginning at the big bang." He (and Penrose) have both discussed other possibilities, including the existance of multiple singularities, multiple universes, etc. However, one then leaves the theory of the big bang behind.
We simply don't know. Your presuming there was nothing before it. Let me put it this way. At the very instant the expansion began there was something there to expand.
I'm not presuming it. That's the theory. And as Woolfson notes, it is hard to understand. The "something" which expanded, this singularity, was nothing. As Paul Lurquin puts it in his book Origins of Life and the Universe (Columbia University Press, 2003), this we are talking about "a universe beginning with a singularity characterized by zero space" So a point of zero space which isn't in space and neither space nor time exist. Norman Glennding titled the first chapter of his book Our Place in the Universe (World Scientific, 2007) "A Day without Yesterday" for a reason: "In an instant of creation about 14 billion years ago the universe burst forth, creating space where there was no space, and time when there was no time."
I'm not arguing that something couldn't have existed prior to the big bang. I'm simply stating what the big bang theory is. According to that theory, the universe began out of nothing, and when it began, space and time began with it.Time before the expansion began could easily have been very different which is what people contend that the laws of physics as we know it were very different before the universe formed.