Why Isn't Dark Energy Considered a Fundamental Force?

[kuahji]

Basically what the title asks. I understand that there are four known forces, three of which have been unified, the other, gravity which simply doesn't want to integrate. But the reason I ask, is why isn't dark energy considered a force? I mean, if its thought to be causing the expansion of the universe, why then is it not a force? Is it simply because not enough is known about dark energy?

 

[Phrak]

In my understanding, it may as well be called a force, as much as gravity is called a force. Without knowing what 'it' is, it could just as easily be moved to the other side of Einstein's equations and be called 'dark gravity of the energy kind'. But 'dark energy' has a much better ring to it.

They don't seem to call relativity theory classical around here. You might get better answers if you posted in the relativity section.