Physics professors often avoid discussing energy in General Relativity, similar to how a parent might skip the sex talk, because the topic is messy and unresolved.

Defining energy in general relativity is complex; pseudotensors can provide conservation but break covariance, while covariant definitions work under symmetry but fail in general spacetimes, hinting at a deeper structure yet to be universally interpreted.

The relationship between matter and curvature in Einstein's equations suggests that only matter energy is well-defined, leaving the nature of energy in general relativity still unresolved after over a century of inquiry.

Definitions of energy, such as mass in motion or the capacity to change, don't hold up in dynamically curved spacetime.

Einstein introduced the pseudotensor to represent the energy of the gravitational field, but it depends on chosen coordinates, which contradicts the principle of general covariance.

Most realistic cosmological spacetimes lack exact Killing vectors, limiting the applicability of the clean definition of energy in General Relativity.

In flat spacetime, energy-momentum conservation is straightforward, but in General Relativity, it becomes complex due to the need for a covariant derivative and additional machinery.

We haven't unified quantum mechanics and general relativity yet because we don't know what the fundamental objects are, and we need to rethink our notions of space and time.

Einstein viewed the universe as a vast library filled with mysteries, where he could only grasp the first page of knowledge.