ATI Radeon HD 4000 Series discussion

[Telo]

I want to know about the physics part,is it actually better,how does it work, like will a x2 be crossfire physics?

If you meant Physx, then the answer is no. Nvidia did a smart thing by swallowing Ageia to get their hands on the Physx and make it available only to Nvidia users.
Only way for you to have Physx capabilities is to grab one of the old PCI Physx cards. And again, that is if you meant PHYSX not PHYSICS.