Thar was no 'original particle. The universe was the size of a particle at that time though
Then a sudden chain reaction caused it to expand, and viola! We haz the universe...lulz
Tis' still expanding to date...which is whaur the Big Crunch theory comes into play
Okay, but this still does not explain where the particle sized universe came from. I guess I can't critique the big bang theory for that reason........ because every theory there is cannot explain an ultimate beginning. Because what could be there to create an ultimate beginning, and what was there to create what created the ultimate beginning, and so on and so forth.
That's why it makes sense to me that there was no ultimate beginning. It just was there.