Theoretical physics is a branch of physics that employs mathematical models and abstractions of physical objects and systems to rationalize, explain and predict natural phenomena. This is in contrast to experimental physics, which uses experimental tools to probe these phenomena. 

The advancement of science generally depends on the interplay between experimental studies and theory. In some cases, theoretical physics adheres to standards of mathematical rigor while giving little weight to experiments and observations. For example, while developing special relativity, Albert Einstein was concerned with the Lorentz transformation which left Maxwell's equations invariant, but was apparently uninterested in the Michelson–Morley experiment on Earth's drift through a luminiferous ether. Conversely, Einstein was awarded the Nobel Prize for explaining the photoelectric effect, previously an experimental result lacking a theoretical formulation. 

A physical theory is a model of physical events. It is judged by the extent to which its predictions agree with empirical observations. The quality of a physical theory is also judged on its ability to make new predictions which can be verified by new observations. A physical theory differs from a mathematical theorem in that while both are based on some form of axioms, judgment of mathematical applicability is not based on agreement with any experimental results. A physical theory similarly differs from a mathematical theory, in the sense that the word "theory" has a different meaning in mathematical terms. A physical theory involves one or more relationships between various measurable quantities. Archimedes realized that a ship floats by displacing its mass of water, Pythagoras understood the relation between the length of a vibrating string and the musical tone it produces. Other examples include entropy as a measure of the uncertainty regarding the positions and motions of unseen particles and the quantum mechanical idea that (action and) energy are not continuously variable.
What is theoretical physics used to explain?
Can it also predict things?
What does it employ?
What part of physics is it different from?
What did Einstein develop?
What did he win for this?
What does a physical theory involve?
What keeps a boat above water?
Who figured this out?
Did he also study musical tone?
natural phenomena.
Theoretical physics is a branch of physics that employs mathematical models and abstractions of physical objects and systems to rationalize, explain and predict natural phenomena.
yes
Theoretical physics is a branch of physics that employs mathematical models and abstractions of physical objects and systems to rationalize, explain and predict natural phenomena.
matematical models
Theoretical physics is a branch of physics that employs mathematical models and abstractions of physical objects and systems to rationalize, explain and predict natural phenomena.
This is in contrast to experimental physics, which uses experimental tools to probe these phenomena.
This is in contrast to experimental physics, which uses experimental tools to probe these phenomena. 
an explanation of the photoelectric effect
 Conversely, Einstein was awarded the Nobel Prize for explaining the photoelectric effect
the Nobel prize
Conversely, Einstein was awarded the Nobel Prize for explaining the photoelectric effect,
it's a model of physical events/
A physical theory is a model of physical events. 
it displaces its mass of water
Archimedes realized that a ship floats by displacing its mass of water,
Archimedes
Archimedes realized that a ship floats by displacing its mass of water,
Pythagoras understood the relation between thno
Pythagoras understood the relation between the length of a vibrating string and the musical tone it produces