'Cosmos' episode 4: Speed, size and black holes in 'A Sky Full of Ghosts'

"Cosmos" would like you to know that the universe is big, fast and really weird. That's basically what "A Sky Full of Ghosts" is about. Considering that the "ghosts" in question are observations of stars whose light has traveled for hundreds and thousands of years, astronomy is essentially seeing into the past.

Which is pretty cool. Other cool things are in the recap below.

Congratulations! You are the center of the universe! (kind of)

Thanks to the Big Bang Theory and the idea that light has a definite and limited speed, you can now tell your parents that you are, in fact, the center of the universe. Just don't tell them that they are too. Every place in the universe actually appears to be the center and everything is moving away from every point.

What comes before/further than the 13.4 billion-light-years-away starlight? According to most theories, that's pretty much it: The beginning of time and the end of space.

We will conveniently ignore the fact that the "end of space" negates Giordano Bruno's concept of an infinite universe. "Cosmos" does -- mostly because the way around this involves mind-bending mathematics and theoretical physics. Scientists have trouble with that one too.

Everything in the universe is really big and really fast

Just remember that it can't be faster than the speed of light, and you're good.

That whole thing about Einstein picnicking in the Italian countryside pretty much boils down to the above statement. You can go super-fast, but you can't reach the speed of light. And lots of weird stuff happens at that speed too. For example, relative to people hanging out on Earth, you would age slowly. It's kind-of-sort-of time travel, only slightly more plausible.

Even if people can't go the speed of light, take comfort in the fact that we're zooming around the universe at millions of miles per hour. That's why you should like gravity -- spinning off into space at that speed wouldn't be much fun.

Everything needs to move really quickly though because the universe is insanely big. At the speed of light (which is 186,000 miles per second, aka really fast), it takes almost 9 minutes to get to the Sun, four hours to Neptune, 30 million years to get to the Sombrero Galaxy and 13.4 billion years to the oldest light observed in the universe.

Basically, the universe is really big. And because it's really big, it has to be really old (not just a few thousand years).

William Herschel tells weird ghost stories

No matter how much the man's voice sounds like Patrick Stewart's, William Herschel didn't quite get the point of a ghost story. Sure, the light from the most distant stars may be coming from some that are already dead, but where's the fear? Where are the campfire and smores?

We shouldn't get too mad at Herschel, little John or that colleague, John Michell, either. They did good science, and it wasn't their job to tell ghost stories. Instead, it's probably better to note that William Herschel a) discovered Uranus, b) wrote three books describing thousands of nebulas (which, at the time, included galaxies) and c) observed stars orbiting around each other (proving that gravity exists outside the solar system).

Michell, meanwhile, managed to measure gravity in a lab. He also made up stories about black holes and measuring red shifts.

One note here: No matter how much "Cosmos" likes to be all progressive and tell the stories of unheard-of astronomers, the Herschel story misses a perfect chance to note that women looked at the stars too. Caroline Herschel -- William's sister -- was a dedicated astronomical observer actually honored in her own time for her work.

"Cosmos" apparently isn't interested in her. But trust me -- she's awesome.

Black holes

Weird stuff happens when black holes are around. No matter how much Neil deGrasse Tyson talks about it, no one really knows what's going on in there anyway. Seriously, just make up your own theories -- they are just as valid as whatever the astrophysicist tells you.

Oh, and "the undiscovered country from which no traveler ever returns"? That's from Shakespeare ("Hamlet," to be precise) and it refers specifically and explicitly to death.

So you're totally going to die if you fall into a black hole. Try to avoid that.

Photo/Video credit: FOX