In simple terms, why do general relativity and quantum mechanics not work together?

I am not trying to completely understand both theory's, as i don't think any one completely does, but i was watching a documentary that said general relativity and quantum mechanics don't work together, then then started saying some stuff about why that went totally over my head, can any one explain in simple terms as to why the two don't work together.|||Because general relativity explains the universe and large objects that we see but quantum mechanics describes very small particles that make up atoms and very small particles behave differently to larger objects that we are used to seeing.


Apparently with general relativity the equations are solved for a universe that is static but Einstein had to change the equations for an expanding universe so he had to put something called the cosmological constant into the equations so they work with an expanding universe. Quantum mechanics doesn't use the cosmological constant instead it uses something called the uncertainty principle where the equations cannot be solved with certainty because particles move with quantum fluctuations which says something about position of a particle cannot be measured exactly because atomic and sub-atomic particles are always moving-- they are never still like objects we see usually are. I found Stephen Hawkings A Briefer History of Time to be of help which is basically A brief history of time simplified so people who are not physicists can understand the laws of the universe.


I'm not sure if this is what you are looking for but I hope it is of some help to you. I am not a physicist.|||General Relativity assumes that quantum behaviors are some Universal constants, and that the entire Universe is infinitely differentiable... so that we can use differential equations, and integration to solve problems. So it paves over everything that Quantum Mechanics is about... because that is all our tools allow us to do. And why GR is called a "classical" theory, and really talks more to "population dynamics".





Quantum Mechanics assumes the entire Universe is some local effect to the interactions of two or three particles. It is extremely accurate. It paves over the entire Universe, and could not be used to solve a softball-sized problem in finite time. And this is done because this is all our tools allow us to do.





Think of GR as Sociology or perhaps History, to QM's Abnormal Psychology.