Undergrad Why there's No Unified Theory ?

[Arman777]

What's the main reason that we cannot unify QED and Gravity or with other foces ?

 

[Lukeblackhill]

@Arman777 , our current unified fiel theory comprises electromagnetism, the week nuclear force and the strong nuclear force. The problem of gravity is, first...its order of strength is much smaller than the other ones. That means that, on atomic and subatomic scales (where the other forces may compete, interact and compose), gravity seems to have no part due to the small masses involved. Einstein theorized that gravity could be the reason why the different "repelling parts" of an electron are held together, but that electrons even have parts, we haven't be able to demonstrate. At the same time, the best description of gravity doesn't use quantum methods, where we suppose the natural forces as virtual particles and whose interaction can be worked out by Feynman diagrams. Gravity is described by differential geometry, and effects on the topology of space time. So, it's both the incompatibility in scales of action and in methods of explanation. We do believe that, as we increase on the scales of energy, we may see gravity merge with the other forces. There are some theories who try to make that to work out, like string theory or quantum loops. But so far, nothing could be definitely proved.

 

[jtbell]

What's the main reason that we cannot unify QED and Gravity or with other foces ?

Because no one has been smart enough to be able to do it yet.

 

[Arman777]

Because no one has been smart enough to be able to do it yet.

Thats an another point of view.

Maybe we need to learn more so we can unify them

Interestingly, the idea of constant speed of light is the basis of SR and hence GR while light is about electromagnetism so it seems awkward..In Newtonian view we can't talk about the speed of light but only masses and forces and etc.as Luka said..I remember a diagram that we need a lot of GeV to unify them or it was something like.

Here it's

How is energy related to unifying them ?

As in the beginning of the universe like $10^-39$ second or less there was only energy and nothing else and the universe was really small..Its really hard to believe that a theory will explain how matter behaves in that era.