The End of Everything (Astrophysically Speaking)

by Katie Mack

“We are a way for the cosmos to know itself.”

getting higher pitched as the object emitting it moves toward you,

and dropping in pitch when it moves away.

8: Illustration of a Doppler shift. When the source of the sound is stationary, the frequency heard by two stationary observers is the same. When the source of the sound is moving, the sound is stretched out to lower frequencies for the observer the source is receding from and compressed to higher frequencies for the observer the sound is approaching. The former hears a low note, while the latter hears a high one.

There isn’t really a mechanism in general relativity to transition from an end-singularity to a beginning one, however.

Why doesn't it stay in motion?

The basic idea of this equilibrium version of de Sitter space is that the origin of our universe and everything that happens in it can be thought of as the result of random fluctuations out of an eternally expanding universe containing only a cosmological constant. From time to time, a universe fluctuates out of the heat bath into a very low entropy starting state, and then evolves forward (with increasing entropy) until it gets to its own Heat Death, decaying back into the background de Sitter universe. And from time to time, the fluctuation doesn’t produce a Big Bang, it just re-creates last Tuesday—specifically,

specifically, that moment when you stubbed your toe on the kitchen table and spilled an entire cup of coffee on the floor. That moment. And every other moment of your life. And everyone else’s.

The Gay Science

more likely to occur than a whole universe that, if we want to use random fluctuations to build our universe, we have to accept that we’re much more likely to be just imagining the whole thing.

This makes sense in a way, if every bit of space is automatically assigned a set amount of dark energy within it, but it’s still super weird, because it means that as space gets bigger, the amount of dark energy increases to keep the density constant.

It also means that if you draw a sphere of a given size anywhere in the universe and measure the amount of dark energy inside the sphere, and then do the same at some future time, you’ll always get the same number, regardless of how much the outside universe has expanded in the meantime.

a cosmological constant is just one possibility for dark energy.