Illusions (A Sky Full of Ghosts): Cosmos Episode 4 Recap
The cosmos as revealed by science is stranger than we ever could have imagined. “Seeing is not believing,” we are told from the episode's outset. Even the stars are not what they appear to be.
“Light and time and space and gravity conspire to create realities which lie beyond human experience,” Druyan writes. The universe looks one way, but in reality is another, full of illusions.
Consider the following: many of the stars you see are ghosts, no longer there, just so far away that their light reaches us long after they’ve died.
The episode opens with British astronomer William Herschel explaining this fact to his child in a cartoon segment. Starlight, he tells his son John, travels really fast but it takes a long time to get here nonetheless because the stars are really far away.
I’ve heard some people complain that the show tends to be coddling. Maybe because of scenes like this, where the exposition is literally spoken to a child. But there’s something powerful in hearing complex ideas phrased simply. The ideas that science gives us are hard to figure out at first, but they can be understood, which is what this show is all about.
Guided by the light
This is an episode about illusions in space and how we’ve seen past them to the true nature they hide.
Even with our own star and planets, it took us a while to see through a couple of very powerful illusions:
The sun at sunrise or sun set isn’t actually at the end of your line of sight. The atmosphere bends it so, it’s technically below the horizon line.
Similarly, rising and setting are the illusion of relative motion. It’s the rotation of the earth that makes the sun appear to transit the sky.
The horizon itself isn’t really a boundary. The Earth keeps curving below it, we just lack the perspective to see that curvature.
Some of the illusions in the universe are because of our brains, but other important ones to science are because of light. The triumphs of modern physics — relativity and quantum mechanics—have come about because scientists better understood light.
So what do we know about it?
Light has a speed, as even Galileo suspected. Whether you measure it at 670 million miles per hour or 300,000 kilometers per second, it’s the fastest thing in the universe. Though it makes more sense to say that the moon is 238,000 miles away rather than one light minute, or that the Sun is 93 million miles away rather than 8 light minutes, when we get out beyond the solar system, the distance that light travels in a year becomes the most appropriate yardstick. Our nearest stellar neighbor, Proxima Centauri, is about four light years away, which means that it would take 80,000 years for the Voyager spacecraft—travelling at almost 35,000 miles per hour—to reach it.
The gorgeous Crab Nebula, the remnants of a star about ten times the size of the sun that blew up in a supernova is 6,500 light years away. That we can see things farther away than this pretty much kill the Biblical fundamentalist idea that the universe is between six and seven thousand years old. How else could we see anything else if that’s the age of the universe? “To believe in a universe as young as six or seven thousand is to extinguish the light from most of the galaxy. Not to mention all the other galaxies,” Tyson says. Unless, of course, the galaxies were put there by Satan, which thankfully is not something Tyson pauses to consider.
But could Satan have created something so beautiful? And if he had, might we consider worshipping him? Just look at how pretty they are! Seriously, I wish I could show you guys these images the Cosmos team has put together.
How old is the oldest light we can see? Tyson shows us a little red smudge, which is 13.4 billion year old starlight, taken by the Hubble Space Telescope. This too is another illusion. “We come to see what appears to be the end of space,” he says, ‘but actually it’s the beginning of time”
There are plenty more illusions in the universe.
Look out towards the cosmic horizon and you might conclude that you’re at the center of the universe. This is just a trick; we’re all at the center of the universe. “The cosmic horizon is no more real than the horizon at sea,” Tysons informs us.
And all those stars you see in the night sky? Most of them aren’t just one star, but two. Our friends Herschel discovered that many of the stars were actually binary star systems, where the two orbited each other. As cartoon Herschel tells his cartoon son, “most of the stars we see tonight dance with invisible partner,” proving that Newton’s gravity worked on the stars as well as the planets.
As much as he had pinned down the mathematics of gravity, Newton never could understand the physical mechanism that allowed it to work at such great distances. Newton famously offered “Hypothesis non fingo,” Latin for “I don’t have a fucking clue.” Space and time are actually just two aspects of space-time, and it took the monumental genius of Albert Einstein to finally see the universe for the cosmic hall of mirrors that it was. But before he could sort out his theory of general relativity, which introduced the world to the idea of space-time, Einstein had to consider some other illusions first, pertaining to the nature of light and its speed.
People have always measured speed of in reference to something else, presumably that was not moving. As Tyson rides his bike through the hills of Italy where Einstein lived as a young boy after the failure of his father’s business in Germany, the speed is measured relative to the ground. This of course ignores the rotation of the Earth around both its axis and the sun and so on. Until the late 1800s, most people thought that the speed of light moved relative to something, which they called the “ether,” which permeated the universe. But the Michelson-Morely experiment proved that this was most certainly not the case and left it to Einstein to invent a modern physics from the ruins of the classical.
Einstein’s thought experiments as a young boy, like what is it like to ride a beam of light led to his insights into the speed of light that became special relativity. The most important thing to consider is that there is a cosmic speed limit: the speed of light.
As Tyson walks his bike down an Italian road, a babe in black leather on a Ducati zooms by him. Soon, she has been teleported out into space to illustrate Einstein’s point. If she were to throw a dart from her motorcycle, the dart’s speed would be whatever the bike speed is plus the speed of the dart. But if she turns on her headlights, the light just zooms along at the speed of light, even if the bike is already travelling close to the speed of light.
“Thou shalt not add thy speed to the speed of light,” Tyson says, offering one of Nature’s commandments. And a lot of funny things happen if you do approach the speed of light: time slows down and distances get longer.
One illusion in astronomy is that all the important scientists were old white men. While this episode did not mention William Herschel’s sister Caroline, who collaborated often with her brother and was an accomplished astronomer in her own right, it makes up for it with the inclusion of John Michell, a black astronomer whom Tyson calls one of the “greatest scientists you never heard of.”
Working in Britain in the 18th century, Michell imagined a star so big so massive, not even light could escape it’s orbit, which he called a dark star. It could only be detected because of extreme gravity, shown by smaller, bright stars orbiting around it. This is exactly how the supermassive black hole at the center of the Milky Way was discovered. Michell’s dark star is of course what we call a black hole today.
Only one in 1,000 stars can become a black hole. When a giant star exhausts its fuel supply, it can no longer defend against its own gravity. For a long time these objects existed only as theories put for by people like Schwarschild and Chandrasekhar. But observation soon caught up.
The first black hole discovered is known as Cygnus X-1. It was discovered because of the x-rays glowed brilliantly emanating from a disk of matter swirling around the black hole. As Herschel showed, many stars have companions. Sometimes they can be black holes, sucks matter off the star onto what’s known as an accretion disk.
If you haven’t heard already, there are also supermassive black holes, thought to anchor the centers of most galaxies. Our Milky Way has one called Sagittarius A*, a dark region of space that stars whip around at 40 million kilometers per hour. Using Newton’s laws of gravity, scientists have calculated that the dark area must contain the mass of four million suns. Since we can’t see the light of four million suns, it must be a black hole.
At this point we reach the grand illusion in the episode, the one you’ve all been waiting for, where Tyson makes himself disappear into a black hole. The warped space-time, or at least his journey through it is best described as Kubrickian. What can we expect to find on the other side of a black hole’s event horizon? Are black holes wormholes, cosmic subway tunnels to other parts of the universe? Do they hold other universes in their entirety? As far as we know, he says, when a star collapses into a black hole it yields similar the conditions as those present at the big bang.
What are we to make of this episode? It contains all the best and worst of what we’ve seen Cosmos to be. There’s some great writing, explaining and visuals, and introduces us to some scientists we probably haven't heard of but it lacks the narrative tautness that the other episodes have so far delivered. And the episode stoops to coddling, where you have Herschel literally talking to a child on screen, and even forced sentiment, as Tyson reminisces about speaking with Carl Sagan at a bus stop while Michael Bolton-esque music plays us out of the episode.
It’s an ambitious episode, but it falls flat in many places. Having Tyson sail into a black hole probably seemed like a good idea around the writing table, but it’s little more than visual padding. Building up to something as important as Einstein, without offering an analysis of how important he was to our modern understanding of the Universe is a missed opportunity. I’m sure we haven’t seen the last of Uncle Al, but it’s now a deficit the show needs to make up.
Photo credit: NASA Goddard Space Flight Center via Flickr