Neil deGrasse Tyson

No one is in the streets, no one is in the parks, and when they walk in the streets, they walk on the side of the street that's shadowed, and they only follow shadows around.

The universe is not pancake shaped.

So, next question.

It's waffle sink.

No, but to the point, galaxy motions are mostly random.

Okay.

And what I mean by random is they're not coordinated in some big way unless you're part of a galaxy cluster.

Okay.

And then there's some ballet of movement.

However, some structures in the universe are so large that the average speed...

of the galaxy moving among other galaxies in that cluster is insufficient for the galaxy to have made one complete loop through that cluster.

Okay.

So that has significant consequences to what's going on there.

It's called, it's not virulized.

A virulized cluster is a cluster that has a very mature shape where, like a beehive, all the galaxies are moving around.

You step back, it has a spherical kind of envelope that contains them.

Gotcha.

But if it's kind of ratty, like that, it's not yet virulized.

It comes from what's called the virial theorem, which talks about

how energy can be transmitted, shared, from objects with high energy to objects with lower energy, so that everybody has approximately the same energy at the end of the process.