Gravitational waves are not light; they are emitted in the rippling of spacetime and can be likened to sound, as they can be detected in the human auditory range if one is close enough to colliding black holes.

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

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.

Gravitational waves are created when massive objects like black holes move, causing ripples in the fabric of spacetime that can be detected on Earth.

On September 14, 2015, after years of work, LIGO detected its first gravitational wave, a signal from a collision of black holes that occurred over a billion years ago.

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.

LIGO is like a gigantic musical instrument designed to record the shape of the ringing drum of spacetime, allowing scientists to listen to gravitational waves rather than just taking snapshots of them.

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.

One of the most incredible things humans have accomplished is detecting gravitational waves through LIGO, which allows us to observe events from the early universe.