10 Things We Learned From Neil deGrasse Tyson's "The Inexplicable Universe" Course

Over the past decade, famed astrophysicist and cosmologist Neil deGrasse Tyson has made the universe cool again. Like Carl Sagan before him, Tyson uses his infectious charm and passion for science to teach people from all walks of life about the great beyond without any of the intimidation of your high school physics class.

In a lecture series available exclusively on The Great Courses Plus, Tyson takes a deep dive into the early history of cosmology, the origins of planets, the spooky side of our universe, and more. Here are just a few things we learned by watching Tyson's talks. The best part? We didn't even have to leave the couch.

1. CELESTIAL MECHANICS PREDICTED NEPTUNE’S EXISTENCE BEFORE WE ACTUALLY OBSERVED IT.

After Uranus was discovered by William Herschel in 1781, scientists decided to test whether or not Newton’s law of gravity was still applicable to an object that far out in the solar system. So over the first 70 years after Uranus was discovered, scientists observed its orbit around the sun (a full orbit would take 84 years). They soon discovered that something was a bit off. Uranus’s orbit wasn’t following Newton’s laws, leading scientists to believe that either the laws didn’t apply or that the gravitational pull of an unknown body was affecting its orbit.

Using the calculations astronomers made in regards to Uranus’s orbit, French mathematician Urbain Le Verrier not only deduced that another planet must exist; he assisted astronomer Johann Gottfried Galle in finding exactly when and where to find this mysterious object. Le Verrier, without ever having physically observed this unknown planet, managed to pinpoint its location (which was off by just a bit), simply by using the laws of physics. We now know this mysterious celestial body as Neptune.

2. VULCAN: THE PLANET THAT WASN'T.

After celestial mechanics helped discover Neptune, a similar problem cropped up with the orbit of Mercury. Calculations of the planet’s orbit just weren’t adding up, leading some to believe that there was a hidden body obstructing it. Again, Le Verrier stepped in, this time with the theory that an asteroid belt between Mercury and the Sun could be throwing the planet’s orbit off. But when an astronomer claimed to see a hidden planet between Mercury and the Sun, Le Verrier jumped at the opportunity, going so far as to give this mysterious planet a name: Vulcan.

Though astronomers with better telescopes came along to discredit the sighting of this phantom planet, for years plenty of scientists still believed that Vulcan was somewhere out there, throwing a wrench in Mercury’s orbit. The Vulcan question was put to rest when Einstein’s theory of general relativity explained that there was no unseen planet Vulcan; Mercury was simply following the curvature of space because of its vicinity to the Sun. This proves that Newton’s laws can be broken when dealing with an object the size of the Sun. As Tyson put it, “Mercury required an entire new branch of physics to be invented just to explain it.”

3. COPERNICUS KEPT HIS THEORY OF THE HELIOCENTRIC MODEL A SECRET UNTIL HE WAS ON HIS DEATHBED.

When Nicolaus Copernicus proposed the heliocentric model of our solar system—a model where the planets revolve around the Sun, as opposed to Earth being the center of the universe—he did so on his deathbed. That’s because back in the 16th century, governing bodies didn’t take too kindly to people coming along and redefining our world, especially if new ideas went against the church’s teachings.

Copernicus held these heliocentric ideas for years—with many people urging him to make them public—but he waited to release them until no retribution could be enacted upon him. Tyson explains that Copernicus’s idea of heliocentrism is right in almost every way, except he imagined all planetary orbits existing in perfect circles. Johannes Kepler (1571-1630) is generally credited with the discovery of planets’ elliptical orbits, a theory he arrived at after calculating the orbit of Mars.

4. YOU COULD TECHNICALLY SURVIVE A TRIP THROUGH A BLACK HOLE.

It would have to be a big one, though. The bigger the black hole, the smaller the tidal force is on your body, which—to put it simply—means you won’t end up being torn apart by the intense gravitational pull. And if you choose a spinning black hole with a donut-shaped singularity, you could, according to some theoretical physicists, actually fall through it and into a completely different universe from the one you traveled from on the other side. Somehow, that’s not the weirdest part.

When you’re in a black hole, time virtually stops. That means the lifespan of our universe will play out normally on the outside as you fall through this black hole and into this potential other space-time. As Tyson points out, though, although this all makes sense on paper, it’s not exactly the easiest experiment to try out in practice.

5. YOU’RE BEING BOMBARDED BY NEUTRINOS AS YOU READ THIS.

Neutrinos were predicted by scientists in 1930, but it would take another 26 years to officially discover them. These strange particles are birthed in abundance from nuclear reactions, like the ones from the Sun’s core and or from the deaths of stars. Once neutrinos are born, they immediately escape into space and travel throughout the universe. That’s not the most interesting part, though. Turns out we’re very familiar with neutrinos—we just don’t realize it.

According to Tyson, 65 billion neutrinos (billion…with a b) pass through every square centimeter of our skin, every second of every day. All of these neutrinos that we’re bombarded with are made in the Sun. They have no charge, almost no mass, and they move close to the speed of light. It’s no wonder they’ve been nicknamed “ghost particles.”

6. WE COULD ALL BE MARTIANS.

What if—untold billions of years ago—Mars was an oasis? And in that oasis existed countless microorganisms housed inside the rocky nooks and crannies that made up the planet’s surface. It turns out that plenty of Martian rocks have made the long journey to Earth after meteors collided with the Red Planet.

If microorganisms managed to stow away on those rocks and survive the journey, they could potentially have seeded life on Earth hundreds of millions of years ago, leading to our current form. Though it sounds like something out of a science-fiction movie, the theory that Earth was first populated by microorganisms from outer space, called Panspermia, has its supporters in the scientific community. Still, the only way we’ll know for sure is by actually discovering life on Mars and finding common DNA with it.

7. WE’RE CLUELESS ABOUT 96 PERCENT OF THE UNIVERSE.

For all of the voyages mankind has made into space, the probes we’ve sent to other planets, and the pictures we’ve taken of the cosmos, we actually only comprehend about 4 percent of what the universe is. The other 96 percent? We haven’t gotten quite that far yet.

Tyson points out that scientists have calculated that 70 percent of the universe is comprised of dark energy—the mysterious form of energy that virtually permeates space and is responsible for the accelerated expansion of our universe. Outside of that, not a whole lot of concrete data on dark energy exists.

The other mysterious 26 percent of the universe is made up of dark matter. Tyson explains that dark matter is basically the missing mass that binds galaxies together so they don’t become unglued when moving at their current speeds. This unknown matter accounts for galaxies having enough mass to hold their shape, even though they don’t appear to have enough mass to do so.

Those two factors—dark matter and dark energy—are the driving forces of the universe. And we’ve barely scratched the surface of what we need to learn about them.

8. WE CAN SEE OUR OWN FUTURE IN THE DESTRUCTION OF OTHER GALAXIES.

We can’t actually see the entirety of our own galaxy because, well, we’re in it. But that doesn’t mean we don’t have a good idea of what we look like. We get this information by observing the characteristics of the closest galaxy to us, the Andromeda galaxy. Both the Milky Way and Andromeda are spiral galaxies, meaning they’re a close approximation of each other, allowing us to get a better sense of ourselves. There’s only one downside to having a galaxy close enough to observe: We’re slowly hurtling towards each other.

What is our eventual collision with Andromeda going to look like? Well, we can see that too, to an extent. There are other galaxies out there with disturbed or irregular structures, and astronomers believe them to be the result of their own collisions with their neighboring galaxies. It’s a bit like looking into the future of what the inevitable Milky Way-Andromeda impact will look like. If it makes you feel any better, this impact will happen well after our sun burns out, so Earth will be nothing but embers by that point anyway.

9. THEY MAY BE HYPOTHETICAL, BUT TACHYON PARTICLES ARE FASCINATING.

Tachyon particles have been the go-to for science fiction writers looking to explain time travel for years. But despite showing up in Star Trek and comic books, there’s no proof that they exist. Tachyon is a generic name for a hypothetical particle that scientists theorize could move faster than the speed of light—something we have no concrete proof is even possible.

There is one exception to that rule: Einstein explained that you can’t accelerate an object faster than the speed of light, so tachyons are theorized as particles that simply exist faster than the speed of light—meaning they always have and always will be traveling faster than the speed of light. In fact, it would take an infinite amount of energy just to slow them down to light speed. This doesn’t necessarily go against what Einstein was saying, which allows scientists to do all sorts of calculations about the hypothetical tachyons.

Technically tachyons live backwards through time. Einstein established that time moves more slowly as you approach the speed of light, so once you exceed it, you would (theoretically, of course) be able to travel backwards in time. This all sounds good on an episode of The Flash, but as Tyson explains, the tachyon is simply an “intellectual curiosity” right now.

10. THE DISTANT FUTURE DOESN'T SOUND TOO GREAT.

The end of our galaxy—and other galaxies like ours—won’t be pretty, according to Tyson. Eventually, the Milky Way will run out of gas to create new stars, leaving nothing to illuminate the sky once the existing ones burn out. Orbits will decay, eventually piling planets and stars into the Milky Way’s central black hole—the black hole that every galaxy theoretically has at its center.

As the same fate befalls every other galaxy, the universe will be littered with these black holes, which will eventually evaporate. From there, Tyson explains, with no stars or planets or galaxies, our now barren universe will begin to cool as it marches towards absolute zero, the lowest temperature possible.