Tyson doesn't actually answer these questions. His mission, this entire season, has been to show that answers are out there, for anyone willing to put in the time, and the thought to answering them. Tyson takes us through one last look at science's history, before ending the season (but hopefully not the series!) by repeating his five basic rules for determining what is true, and telling us to go find our own mysteries to solve.
Tyson asks us to think about a distant star. With a few planets orbiting. Now, imagine that one of these planets contained a species capable of abstract thinking. But, that species thought that they were the center of a universe made specifically for them. And that a book written in the dawn of their species' writing contained all the answers about the universe. How seriously would we take this species? And would we recognize ourselves, only a few centuries ago, in this species? Tyson points out that, up until a few centuries ago, Europeans didn't even think North or South America existed. And the Americas' indigenous peoples didn't even wonder if Europe existed. How could humanity be so ignorant, up until so recently in our species' history?
We start in Alexandria, which supported the most impressive library between about 200 BCE and 391 CE. The Library at Alexandria was a vast academic resource, famous for raiding ships and other lands for... books. Which would be copied, and the copies stored in Alexandria. Supported by the royal family, the Ptolemaic Dynasty of Egypt, the Library at Alexandria supported ancient academics for centuries.
Library fines were in ears of corn
Notable faculty included: Euclid, enemy of 10th grade geometry students everywhere; Archimedes, all-around best scientist and engineer: Eratosthenes, who first calculated the circumference of the Earth and the tilt of the Earth's axis; the mathematicians Theon and his daughter, Hypatia; and Aristarchus, who proposed that the Sun was at the center of the known universe, with the Earth orbiting it.
So what happened? Well, we know it was destroyed, in various phases, from multiple wars and conquests, starting in about 48 BCE by Julius Caesar invading. In about 270 CE, Emperor Aurelian invaded, destroying more and taking some scrolls for himself in Constantinople. Emperor Theodosius, in 390 CE, may have ordered what little remained destroyed when Christianity became the only legal religion of Rome. And, ibn al Aas may have finished the job in about 642 CE. Different parties blame each other, making it extremely difficult to know who did what. What we do know, is that vast troves of ancient knowledge were lost, and Europe entered the Dark Ages. Tyson's point is that knowledge can only be preserved if we make an effort to preserve it.
So, what happens when knowledge is preserved for future generations? Tyson then takes for a hot air balloon ride. With a man named Victor Hess, in 1912. At the time, radioactive energy had been discovered, usually emanating from sources such as uranium. Since these were all rocks on Earth, the theory at the time was that radioactive energy came from the Earth. So, Hess tested that theory by measuring levels of radioactive energy at different levels in the atmosphere, in a hot air balloon.
Also discovered the Fifth Dimension singing that balloon song
If radiation was coming from the Earth, the radiation levels would decrease with height. And they did, until about half a mile up. After that, the radiation levels rose dramatically, the opposite of what was expected. And Hess measured as far up as about 3 miles, which is about half the elevation of a cruising jet plane. Was radiation coming from our Sun? It seemed a likely culprit, so Hess conducted his radiation measurements, still in a balloon, during a solar eclipse. And at night. Still, a constant stream of radiation. Earth was awash in cosmic radiation all the time. But where did it come from?
Stars blowing up. In the 1930s, Fritz Zwicky, working with his partner, Walter Baade, spent years finding supernova explosions, which is where a star with no fuel reserves has finally collapsed under its weight, and the resulting bounce back out is a giant explosion (remember this episode?). Zwicky and Baade coined the term supernova, and proposed that supernova explosions were propelling the subatomic particles that made up radioactive energy into space, and called them a source of cosmic rays. Other scientists made their own proposals, or hypotheses, about where the cosmic rays were coming from. It took until 2013, for another team of scientists to confirm this, using the Fermi Gamma-ray Space Telescope. It's name is pretty much what it does, it examines gamma rays throughout the universe. We can document bursts of gamma ray energy with it, and even search for one of our universe's great mysteries.
Sometimes, you're even more right than you know
Wait, our universe is still mysterious? Even more than you can know at this time. Mass exerts a gravitational field on other masses (remember this episode?). The closer objects are, and the more massive they are, the more gravity exists between them. Let's look at our own Solar System for a second. Mercury, closest to the Sun, orbits the Sun at about 42,000 miles per hour. Neptune, way out from the Sun, orbits at about 4,900 miles per hour. So... why doesn't our galaxy, or any other galaxy behave this way? At the center of our galaxy, as well as most spirals, is a massive black hole (remember this episode?), with a gravitational pull on the stars and gasses of the galaxy, similar to our Sun working on the planets of our Solar System. By applying the theory of gravity, shouldn't stars near the edges of galaxies be moving more slowly than stars near the center?
That's what Vera Rubin thought. A pioneer for women in science, she was the first woman allowed to use astronomical instruments the Palomar Observatory in the mid 1960s. Literally, women were banned from using a space observatory until the 1960s.
To be fair, we leave our girl cooties everywhere.
Rubin spent her early career making galaxy rotation curves, which is a kind of graph. She started with the Andromeda Galaxy, one of our nearest neighbors. For her graph, one side has the speed of the star as it orbits around the center of the galaxy. One side has the star's distance from the galaxy's center. Rubin, like everybody else, expected a curve showing that speed decreased with distance. She got a huge surprise; star speeds stayed pretty constant despite distance from the galaxy's center. The"A" curve is what she expected. The "B" curve is what she got.
Call the cops, the Andromeda Galaxy's breaking the law of gravity!
But that's not all Rubin realized. Stars were orbiting around the galaxy's center so fast, they should have been breaking their orbits and breaking up the galaxy. But they weren't, and there was no indication they would. So, where was the gravity necessary to keep a galaxy together? Rubin repeated her observations for multiple galaxies, with the same results. We live in a universe of law-breaking galaxies. Rubin's math indicated that the Andromeda Galaxy's stars needed about 10 times more mass than they currently had in order to stay together. She stumped everyone. In order to solve the mystery that she uncovered, scientists had to go back to Zwicky.
Back in the 1930s, Zwicky was studying the Coma Cluster of Galaxies, which is like a mall, but at the scale of galaxies are bunched together. He went about calculating the mass of the Coma Cluster based on it's gravitational field, and noticed that it was about, oh... 400 fucking times more massive than the detectable stars of the galaxies (based on the luminosity of the galaxies overall) would indicate. In other words, the stars of the galaxies in the Coma Cluster were only a paltry amount of the matter necessary to generate the gravity required to hold the Cluster together. He called it Dunkle Materie. Which does not translate to Dunkin Donuts, but to Dark Matter. Dark matter isn't necessarily black, or even charcoal gray. It's called dark because it's almost completely undetectable, except for the effect is has on gravity. And the effect that gravity has on light, called gravitational lensing. As predicted by Einstein, if a cluster of galaxies is between me and a more distant background galaxy, dark matter will produce enough gravity to distort the light traveling from the distant background galaxy to me, distorting the image too. Zwicky predicted that Einstein's gravitational lensing was caused by dark matter, and we confirmed it does happen in 1979.
Dark matter is estimated to make up about 85% of all matter in the known universe. And we can barely even detect it. We don't know what particles it's made of. We can't even confirm it's made of a sub-atomic particle yet. But see the pattern- someone's way-out-there data has to be found, usually while answering some other question. The data that surprises and puzzles scientists then gets several proposed explanations, before one emerges, based on decades of collecting data and improved methods of collecting data that supports one explanation (hypothesis) better than any other. Over time, and repeated testing, that hypothesis graduates into theory. Like gravity. Or germs spreading diseases. Or evolution by natural selection. Or relativity. These were all mysteries, with first philosophers, then naturalists, then scientists, trying to just figure out the mystery to be solved in the first place, and then solving it, based on the preservation of knowledge.
In the 1920s, Edwin Hubble (yes, the telescope is named after him) got his hands on the biggest telescope of the time, the Hooker Telescope at Mount Wilson, California. And he wanted to test the theory of the time, that the Milky Way, our galaxy, was the only galaxy. And that all the universe was contained in our galaxy. Hubble shocked the astronomy world by insisting that he had used supernova explosions' constant brightness to accurately measure the distance to the nebula containing it, and that the nebula was too far away to be in the Milky Way Galaxy. But, how do supernovae tell us how far away stuff is?
Once again, we go back Zwicky's partner Walter Baade. Usually, when a star goes supernova, it's one star, and after the explosion of gas that becomes a surrounding nebula, the star shrinks into a neutron star. These stars, too small to become black holes and too big to become white dwarfs, can and do spin. Rapidly. As they rotate, they emit electromagnetic radiation that varies, like a rotating light on a cop car. The radiation, and resulting light, reaches us as a pulse. So, we call some neutron stars pulsars.
But stars can go supernova in pairs. When a dwarf star and a giant, paired by gravity, start to die, the dwarf starts absorbing gasses from the giant, literally sucking them away. When the gasses add too much weight for the dwarf star's core to handle, the dwarf literally collapses in on itself and explodes, causing a supernova with a constant, known light output. We call these 1a Supernovae, but Baade called them standard candles. Since we know their brightness, and that the light output is constant, we can find and distinguish them easily. And, knowing the relationship between apparent and actual brightness, based on distance, we can calculate the distance from Earth to all of the universe's type 1a Supernovae.
Hubble identified some 1a Supernovae, and a few Cepheid variable stars, just hanging out in various nebulae of gasses, and calculated their distances from Earth. Since other scientists had already estimated the size of the Milky Way Galaxy, Hubble could show that the immense distances to these objects, now more clearly seen in his newer telescope, were too far away to be a part of the Milky Way Galaxy. Our universe got millions of times bigger immediately.
And Hubble wasn't done. Working at about the same time as Georges Lemaitre, the two men discovered, during the late 1920s, that the universe's known matter is actually moving away from each other. Hubble worked with two previous discoveries: that of the varying luminosity of Cepheid Variable stars, and the red shift. Short story, the red shift is the Doppler Effect: the transition from high frequency waves to low frequency waves, depending on whether something is moving towards you or away from you. We usually apply this to sound, especially sirens or train whistles, but it works with light as well. Basically, objects in space moving away from you will emit lower-frequency wavelengths of light, appearing red (hence, red-shift). Hubble plotted the possible locations of other galaxies based on their red-shift appearances, and then plotted these locations over time. And he discovered that the red-shift was increasing. And the increase was even more pronounced for galaxies that were already farther away. In other words, he found that the universe is expanding. Even though he discovered this after Lemaitre, we still call it Hubble's Law. Basically, the universe is expanding, and the farther away objects are from each other, the faster they move away from each other.
Hubble's Law, together with the Big Bang, suggest a universe that expands, reaches a point where expansion is no longer possible, then starts contracting again due to the gravity of both stars and dark matter in the universe. But in the 1990s, scientists observed that the rate of expansion had actually been speeding up since Hubble first measured it. Dark matter was fucked up enough, but now there was something out there, also undetectable, that was fucking with dark matter. Probably out of sheer laziness, it was called dark energy. In other words, we determined dark matter must exist because things held together even when we didn't expect them to. We determined dark energy must exist because the universe is expanding faster than the expected gravity of all that dark matter would let it.
Future generations may discover, based on our current attempts to detect both dark matter and energy, some new relationship between the two, or that they're two aspects of something bigger. I don't know. And neither, by his own admission, does Tyson. What we do know, is that we actually don't know that much about our universe. We've managed to figure out that there are a lot of other mysteries out there. Yay for us! And yay for science!
So, our universe is much bigger than we originally thought. How do we get out there, beyond our Sun's reach, maybe even get to the closest stars? For now, we don't. Our messengers, Voyager 1 and 2, launched in 1977, do that for us. They've been traveling at 40,000 mph for about 37 years now, and at least one has already crossed out of our Solar System's fence, into the great interstellar gasses beyond. How do we know? The sun releases charged particles, circulating throughout the Solar System as "solar wind". Solar wind creates a kind of force field around our Solar System, usually way past Pluto, called the heliosphere. It's immensely useful at repelling cosmic rays from nearby supernovae before those gamma rays can hit Earth and mess up life here. When there's a lot of cosmic ray activity, it can push against the heliosphere. Depending on how close and powerful a supernova and it's resulting cosmic radiation are, the heliosphere can actually be pushed in, so that Earth is actually outside of it, exposing us to the cosmic rays. Notice, I said "can be". It hasn't actually happened for about 2 million years.
Once again, how do we know? Little rocks lining huge chunks of ocean floors called manganese nodules. Hidden in these guys are iron isotopes that would have had to come from a supernova. Yes, we can estimate the history of supernovae in our cosmic neighborhood from rocks on our ocean floors. Notice, that throughout the season, Tyson has demonstrate how the very small, even sub-atomic, can create phenomena that can be detected light years away.
Back to Voyager 1. Without the protection of our heliosphere, pressure builds up quite a bit past it from instellar gasses moving around outside our Solar System. Sometime in 2012, Voyager 1 began sending back info from its plasma wave instrument, indicating that the pressure of insterstellar gasses had gone up. Which means that Voyager 1 is in the great unknown. Voyager 2 has yet to catch up.
The spacecraft are expected to send information back for about another ten years. After that, they'll stop collecting information and primarily bear it. To others. On both Voyager 1 and 2, is a copy of the Voyager Golden Record. It contains: a stellar map to Earth using some local 14 pulsars (and their identifying frequencies) that can be triangulated from; greetings in 59 human languages, plus a recording of whales saying whatever they say. The record plays a video as well as audio, and we've included graphic instructions for playing it.
Like Ikea's instructions, it helps to be a genius to get it right the first time.
At the bottom, on the right, are representations of a hydrogen atom, showing the two states of its lone electron switching rotation. The time interval of this switch is considered the default measure of time for the information presented on the record and how to play the record.
Voyager 1 gave us one more present: a view of ourselves, as we look, from Neptune. In 1990, Carl Sagan convinced NASA to turn the craft's camera around, for one last photo of ourselves.
We hate the way our hair looks in this picture
We are, literally, a Pale Blue Dot. Sagan, in his 1994 book called Pale Blue Dot, reminded us that our entire history as a planet and species, takes place on what is, essentially, a speck of dust and water in a universe that can't even make us out from outside the Solar System. Any importance we assign to ourselves is self-assigned. And the vast interstellar oceans between us and any other intelligent life renders us, essentially, alone. No one is coming to save humanity from itself. Sagan: "The Earth is where we make our stand." If we want to live here until the Sun goes out, we will have to figure out some way for all of us to live here responsibly. Or we will perish together.
Tyson's getting into his end game here. He reminds us of the rules of science he first taught us in the premiere:
1- Question authority: remember Nullius in verba?
2- Question yourself: what are you assuming? In other words, make sure you know how you came to know what you think you know.
3- Don't accept something as true because it's what you want to think.
4- Test ideas with observation and experiment. Follow the evidence. It might confuse you for a while, but whatever happens usually leaves a mark that can be found. Reserve judgement until you've got some evidence.
5- Remember, you could be wrong. Especially if you skipped any of the steps above.
Is science perfect? No, and Tyson admits this. Scientists developed the nuclear bomb. Scientists told us lead in the air was safe. Which is why you always go back to the rules above. Is the science telling us what we want to hear, based on assumptions? You could be wrong, and need to go back for more observations, then. Science also has one advantage in the battle to help humanity- it's not owned by anyone. No one's got a patent on the scientific method. We can all use it. When we support science together, it's owned collectively, making scientists accountable to us collectively. Making science accountable, both to stick to observable truth, and work for the benefit of those supporting it, is the best we've got. But that best has gotten us out of the Solar System. That best has produced electrical power and agriculture, enabling our populations to explode. That best has enabled knowledge to live forever, as long as we're willing to preserve it.
Now, go discover something.
Tyson ends with what we don't know: what happened (or what existed) before the Big Bang? Is anything beyond our cosmic horizon? How did life begin on Earth? Or any other living planet? Tyson, standing on the beach he started the season on, reminds us that science, like life is a chain that connects generations. He stays on the beach while Imagination, powered by science and wonder, fades back into space, drifting through the stars.
Second star to the right, then straight on til morning...
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