Big Bang Theory: Force & Surface Questions

[Mohamad&Issa]

Hi,
The theory about big ban says that there were high temp. and high pressure.
But pressure=force/surface
I want to ask about the the force. Force of what? Is it the force of gravity?
And is the surface for the atoms?
Thanks.

 

[Drakkith]

It's not just a physical surface, but any area. For example, inside a closed container of gas the molecules exert pressure on themselves equal to the pressure they exert on the container walls. Any square centimeter area inside the gas has equal pressure to any square centimeter of the container wall. The force is the force of the molecules impacting each other.