Keldysh formalism

Keldysh formalism is a mathematical tool used to describe the behavior of an object over time. It is especially useful for studying the behavior of electrons and other small particles. It helps scientists understand how particles will interact with each other, or the environment, over time. In order to understand Keldysh formalism, we need to first understand something called quantum mechanics. Quantum mechanics is the science of how small particles like electrons behave. It says that particles can exist in many states at the same time, and that the states depend on their environment. This is where Keldysh formalism comes in—it is a mathematical way to describe the behavior of these particles over time. In a nutshell, Keldysh formalism is used to figure out how particles will interact with each other and the environment over time.