#blackbody-radiation

#blackbody-radiation

Gravitational waves are a form of radiation, and while they have many similarities to light waves, there are some fundamental differences. This recognition is crucial for understanding how these waves behave in the universe.

General Relativity has yet to let us down. Its success rate is 100%, from tabletop experiments to gravitational lensing and the formation of the great cosmic web.

The way most people think about time is wrong. The notion that we share a 'common time' moving in a single direction is a useful illusion but, as physicists have understood since the discoveries of Albert Einstein, it doesn't comport with our understanding of the Universe. However, as the Italian theoretical physicist and writer Carlo Rovelli argues in this short documentary from Quanta Magazine, this doesn't mean we should abandon the concept of time altogether.

According to Einstein's General Relativity, for every black hole that exists within the Universe, there are only three properties that go into it that matter in any way: the black hole's total mass, the black hole's net electric charge, and the black hole's intrinsic angular momentum, and that's it. It doesn't matter what type of matter went into the black hole in order to form it; all that matters is its mass, charge, and angular momentum.

In terms of making things happen, energy is an indispensable consideration. Systems spontaneously tend towards the lowest-energy state. When a system reaches equilibrium, no further energy can be extracted. That maximum entropy, lowest energy state is the inevitable end-state of the Universe. But until that moment arrives, reactions of all kinds will occur, continuing to liberate energy. In our bodies, chemical bonds break and reform: releasing energy.

Star-formation will eventually end, and then the last shining stars will burn out. Galaxies will dissociate due to gravitational interactions, ejecting all masses and leaving only supermassive black holes behind. And then those black holes will decay via Hawking radiation, leaving only cold, stable, isolated bodies, from which no further energy can be extracted, all accelerating away from us within our dark energy-dominated Universe.

This system is truly extraordinary. We're seeing the radio equivalent of a laser halfway across the universe. Fundamentally, masers and lasers are focused beams of light in the same frequency. In the realm of astrophysics, these can arise from clouds of dust being excited into a higher energy state from the light emitted by other sources, like stars and black holes.