Why big bang happened anyway?
The repulsion of condensed energy and availability of ether which is nothing actually.
How big bang happened? If time had a start, then we know it has end because something that has start must have end.
The popular myth of explosion and tiny fireball both are null and void. Rather, the universe is still expanding at a horrendous rate. Back calculation suggests Singularity existed during the start of universe. The CMB recognition supports the heat that caused the expansion, also the evidence of light elements in observable universe give enough proof of Big Bang.
Do you think that, all brains of all time put together can assume Allah without Allah's will?
To answer this first you need to answer, do you believe in Allah. Allah is only believed by a handful of people in a 700 crore homo sapiens that exist on earth. Now as a believer of Allah, you must follow Quran. The holy book suggest nothing is stronger than Allah in any context so the response would be negative for any believer alike.
what is "nothing" and what is "exist"?
This question is invalid in terms of theoretical physics, in science 'nothing' does not exist so 'exist' does not reciprocate nothing as a word in question.
When Allah created something, eg time, space, beginning or end or bigbang, then Allah can't be dependent on any of it. What do u think?
This is a fundamental truth for a believer of Islam. So, question like this becomes invalid for the specific group termed as Muslims as Allah is the supreme power, faith will be questioned if any dependence is indicated in this regard.
Now my question to you:
Why are you mixing up religion and science and also starting the thread about something quantum and then asking primitive big bang questions? I am confused about the motive of this thread.