Neil deGrasse Tyson: Bring Out The Aliens! | The Diary Of A CEO Transcript

Neil deGrasse Tyson discusses aliens, black holes, the simulation hypothesis, and the meaning of life with Steven Bartlett

Steven Bartlett interviews astrophysicist Neil deGrasse Tyson on The Diary of a CEO.

Summary

Steven Bartlett interviews Neil deGrasse Tyson, astrophysicist and author of Take Me to Your Leader: Perspectives on Your First Alien Encounter. Tyson argues that intelligent life elsewhere in the universe is highly probable given its size, age, and the speed with which life emerged on early Earth, but insists that extraordinary claims — such as government possession of alien bodies — require extraordinary evidence: "Bring out the alien." He addresses the simulation hypothesis at length, arguing that humanity's current inability to simulate other universes actually improves the odds that we are either the original universe or the last in a chain — reducing the probability from astronomical to roughly one in two. Tyson also explains what physically happens to a human body falling into a black hole, discusses the geopolitical rather than scientific motivations behind the return to the moon, and closes with a reflection on meaning, education, and his chosen epitaph from the educator Horace Mann: "Be ashamed to die until you have won some victory for humanity."

Key Takeaways

FULL TRANSCRIPT

What draws humans to questions about the universe

Steven Bartlett: Neil deGrasse Tyson, people come to you to try and understand the universe. What is the most pressing question people are asking you right now about the universe?

Neil deGrasse Tyson: Are we alone in the universe? And that's influenced by pop culture. I'll give an example. When the movie Ghost came out, polls showed that more people believed in ghosts after that movie than before the movie. So pop culture is a huge force of influence on our thoughts and feelings and attitudes and what we believe is or is not true. So when you say what is the most pressing question, it's: are we alone in the universe? Then they say, "Have we been visited?" And, "How will it all end?" That's another one. Usually God shows up in there. Is there a God?

There's an assumption — I think it's a naive assumption, but an interesting one nonetheless — that people who study the universe might stumble upon God, because we're told, or at least in our artwork, gods live in the sky. So people then study the sky. When the Apollo astronauts came back, people said, "Did you see God? Did you see heaven?" What is the essence of why people are so curious about these subjects?

My best speculation — and this is a wild speculation, and my ego is not based on whether this is true — but it's fascinating for me to think about the fact that we are completely comfortable sleeping on our backs. Ask yourself how many other animals do that at all. Does a beetle say, "I'm going to turn over and go on my back"? Do spiders just go on their back? Think about it. That's quite vulnerable. You're asleep and your belly is exposed.

We sleep at night typically. If you're outdoors and you sleep on your back at night and you wake up, what's the first thing you see? The universe. The sky. You'll see comets and meteors and the moon and brighter stars, which we call planets eventually. And from night to night — wait a minute, the moon had one shape and now it's a different shape and it's a different part of the sky. And these lights are moving. How could we not be curious when in the middle of the night you wake up and the universe presents itself to you? So I think that's sort of in our DNA, the curiosity about the night sky.

I didn't make people interested in the universe. In fact, when I was a kid, my first encounter with the night sky was a planetarium — the Hayden Planetarium here in New York City. I said, "Wow, I want to study the universe, but the universe is so interesting, everybody's going to want to study the universe. There'll be no room for me." As I got older, I realized there are other things people are interested in. Not everybody wants to study the universe professionally. However, whatever you choose as a profession, it doesn't change the fact that somewhere in you, you're going to look up and say, "What does that represent in the universe?"

Steven Bartlett: I thought you were going to say, when you talked about sleeping on their backs, that we are now so comfortable being the apex predator that we're able to sleep on our backs — and actually we're so interested in aliens because it's the only thing that would threaten our place as the apex predator.

Neil deGrasse Tyson: I don't know that ancient people were dreaming up aliens. It's just the night sky itself. Well, let's not use the term alien. Let's just use the term gods. Where are most people's gods? They're in the sky. Even in ancient Greece, they're on Mount Olympus — not in the sky, but in high places. You look at posters with religious sayings on them. Typically it's sunbeams coming through clouds and a beautiful landscape. You're looking at the sky.

And by the way, what are our images of deity? Many of them could pass for aliens. The Gorgons, for example — look at Medusa. Snakes for hair. That's as alien as anything you would ever conjure. Images of Jesus: he's floating, he's got beams coming out of him. If he's not floating, he's walking on water. These are things that go beyond anything that's earthly. So now people imagine aliens with all these same powers and weirdnesses. I don't know that "alien" is something specific that's in our DNA to think about, but to imagine things beyond ourselves — I would lump them together in that respect.

How small are we in the universe?

Steven Bartlett: One of the things that made me more curious about aliens and meaning and purpose and gods and all these things was watching Cosmos — which was your series about the universe.

Neil deGrasse Tyson: Carl Sagan did it first. My series is one I happen to host. Yes.

Steven Bartlett: Well, I watched both. They both had the same impact on me, which was they made me feel insignificant in the grand scheme of the cosmos. I almost feel called to fill it with something. Just how small are we, Neil, in the grand scheme of the universe?

Neil deGrasse Tyson: Well, if you don't think in terms of metric size — how big are you? If you think in terms of powers of ten. The things ten times bigger than us, ten times bigger than that, ten times bigger than that. Just keep doing that. We're small compared with the universe, but we're huge compared with atoms and molecules. Instead of going ten times bigger, go ten times smaller — one tenth to be precise. You keep going down, you enter the realm of molecules and then atoms and then particles.

There are things much smaller than we are. In fact, I addressed some of that in a book I wrote recently, Take Me to Your Leader. There's a lot in there about changing your perspective on what you might expect life forms to be like out there. So you can ask the question: are the life forms the size of a galaxy? Or are the life forms the size of atoms? Are we just biased by what our senses can drink in from our own size scale?

You know who would feel small? If you were a life form the size of molecules. There's not much smaller than you if you're molecularised life. Now, we don't know how you would make that, because life by our own understandings and definitions has a metabolism. You ask a biologist what is life, they'll give you a list of criteria which are hard if not impossible to be fulfilled by life that's extremely small. They still debate whether viruses are alive based on some criteria. But some have speculated that life could be the size of nucleons — the size of the particles in the nucleus of an atom. Things happen very quickly on that scale. So they might wonder how it is that we live so slowly.

Inverting your expectations is a time-honoured exercise in keeping you honest, keeping your ego in check. You can go the other way — this whole universe could be something in another life form's gut microbiome.

Steven Bartlett: Yeah.

Neil deGrasse Tyson: That was briefly addressed in the film Men in Black. What I can say is the laws of physics manifest differently on different scales. So you can't just scale everything up. Which is why you don't have human-sized insects — their legs would break under their own weight. It's why heavy animals have thick chunky legs. It's why if you fell off the roof, you're dead, but an ant can just land and keep walking. Forces don't interact in the same way depending on your scale.

One of my favourite scenes is in the film A Bug's Life — I think that was a Pixar film. Pixar must have a room full of scientists working for them. There's a mosquito at a bar. The mosquito orders a drink. What drink does he order?

Steven Bartlett: A mojito? I don't know.

Neil deGrasse Tyson: A Bloody Mary, of course. How big is a mosquito? It's this big. And it's an insect bar. The bartender brings over the Bloody Mary and just puts a blob of the liquid in front of it — not in a glass, not in a jug. It's just there. Because surface tension is something that manifests in ways that insects care about greatly and we don't. Unless you're waxing your car and water beads up on it.

Surface tension is a property of fluid liquids where the outer surface molecules are a little more tightly gathered because they don't have forces above them to pull them into the solution. So transitioning from the liquid itself into air creates a kind of film. It holds the liquid in place. Unless there's too much liquid, then gravity becomes stronger than the surface tension and it flows. But below a certain amount, the surface tension is greater than the gravity and it beads up. They knew this in that movie, and I thought that was brilliant.

My only point is to communicate that you can't just scale things up and expect everything to behave in exactly the same way.

But I want to get back to your point when you said you felt small after you saw Cosmos. You only felt small because you went in there with an ego that was unjustifiably too large to begin with.

Steven Bartlett: Probably.

Neil deGrasse Tyson: I'm accusing you of that. However, I go in there with no such ego. I look up at the stars and I learn from modern astrophysics that the elements in our body were forged in stars that exploded — the oxygen, the carbon, the nitrogen, the iron that courses through our blood was forged in stars that at the end of their lives exploded, scattering that enrichment into the galaxy, out of which the next generations of stars and planets are formed. Early in the universe, we didn't have these ingredients. We could not exist in our current form.

So when I look up, I don't feel small. I feel large, because I'm connected to the cosmos chemically. Not only are we alive in this universe — the universe is alive within us. And that fact borders on the spiritual. It is an astrophysical fact that gives you a pathway of relevance to the universe. We are part of this great unfolding cosmic story.

Next time you go out and look up, I want you to feel large, not small. Because we are not only made of what stars have produced — we are solar powered. If you're omnivorous, maybe you had a steak last night. That steak was once a cow. What did the cow eat? Grass. What do plants eat? Well, they don't eat — they just sit there and receive sunlight. I said this once on the internet and freaked people out, but I should not shy away from speaking truth just because it freaks you out. A cow is a machine that we invented — cows don't exist in the wild, it's a domesticated animal — a machine that we invented to turn grass into steak. Because at the end of that chain is grass that has photosynthesis, essentially 100% of our caloric value is traceable to the sun. So you are solar powered and the universe is alive within you. So don't ever sit across from me again and say you feel small in the universe.

Religion, God, and the Big Bang

Steven Bartlett: It's strange, isn't it, this idea of significance as a concept — trying to understand one's significance. I think religion often gives us a sense of significance.

Neil deGrasse Tyson: Well, it does. Yes, of course. Hence its value to people and its persistence throughout time and across cultures. Has your view of religion changed through all that you've learned about the universe?

Steven Bartlett: I've got this photo of you as a young man. This one here — I love that one.

Neil deGrasse Tyson: My hair was like this when I was that age. So this one was my first telescope and that's my father helping me put it together. If I think about this young man here and what he thought about religion —

Steven Bartlett: Are you more religious, less religious? If so, why?

Neil deGrasse Tyson: By the time I was eight, nothing was making sense that people were telling me about religion. What I didn't know is that belief systems don't have to make sense. That's why they're belief systems. If they made complete sense, they would just be objectively true. If it's a belief system, then it's beyond critical analysis. It's just a belief system. So when I say beyond critical analysis, what I mean is: if something in your belief system lends itself to be tested, we can test it. And if what we test shows that what you believe is false, are you going to stop believing? Generally not, because it's a belief system.

Most people want to engage me ultimately with some kind of spiritual or religious conversation. I have found, especially given my access to the universe, that in the early days there were easy answers — this is religion, go ahead, I'm doing science here. Then I thought I owe people who are religious a more informed and nuanced engagement, because of the power and force that religion has exercised on the history of the world. It's not just cultural — it's political, it's economic. So I started reading religious tracts, and now when I'm engaged in a conversation, I have a full conversation with people on their beliefs, whatever intersection, if any, with the objective universe, and what those beliefs do for the person who holds them.

There are many places on the internet that claim me as an atheist, and I've never embraced that title. The only thing I am is a scientist. Titles are lazy. Once you hand a title to someone, that gives you licence to not have to think anymore about who and what that person is regarding that subject. And that has never ended well in my experience.

It's odd that such a word as "atheist" exists at all. Think about it. It's a word that says what you're not. Is there a word for non-golfers? Ask yourself how many things we have words for that are defined by what they're not. Very few. And so this exercise of saying you're either with us or you're against us — and if you're against us, I have this word for you that says you're not this — that never ends well. It ends in war and bloodshed.

Leading atheists today who write books on this — Richard Dawkins is among them. He wrote a book called The God Delusion. That's fighting words if there ever were any. These are people who reject God, reject its influence on politics and society and lives, and would just as soon see a world without it. I'm not that guy. I have behaviour that would be rejected by any modern atheist thinker.

So what am I? The next word would be agnostic.

Steven Bartlett: Okay. I would consider myself to be agnostic as well.

Neil deGrasse Tyson: Agnostic. Sure. I just don't know. What's your leading view of where all of this stuff came from?

Steven Bartlett: What is the Big Bang?

Neil deGrasse Tyson: It's consistent with observations and experiment. The Big Bang. It is so thoroughly supported. As fantastical as it is.

Steven Bartlett: Explain the Big Bang to me like I'm 15.

Neil deGrasse Tyson: I'll explain it to you like you're 12. Approximately 13.8 billion years ago, everything that you see and interact with in this universe began in an infinitely small point. That is the birth of the space and time of our universe. We have been expanding ever since.

Now, how does something that big ever become that small? Well, it's not matter trying to occupy the same space as itself. Energy can be essentially any size compacted, and you can measure what's there by what the temperature is. So it's a very hot fireball, basically, and as it expands it cools, and the cooling energy makes matter. It's E=mc² — energy on one side, mass on the other side. The c² is just the speed of light, just a constant. Einstein came up with this in 1905 and it made so much of the universe make sense. And it would take a while — we expand, we cool enough to make stars and galaxies, and we're still expanding to this day.

There are mysterious forces operating that we don't yet understand. What we call dark energy is a pressure in the vacuum of space making us expand faster than what would be allowed by the collective gravity of all the galaxies. That's a frontier question not yet resolved. Then there are sources of gravity that we don't know what's causing them. We call that dark matter. If you add up dark matter and dark energy, it's 95% of what's driving the universe. So everything you and I know and love about biology, chemistry, physics, astrophysics, forces, food, calories, molecules, solids, liquids, gas — it's 5% of what's going on in the universe.

This is why I said earlier that sometimes I wonder whether we are smart enough to figure out the entirety of the universe, or whether we just figure out our little fraction of it and live happily ever after within it.

Now, you have full rights to ask what was around before that. So ask me that.

Steven Bartlett: What was around before the Big Bang?

Neil deGrasse Tyson: We have no idea. We have suspicions there might have been a multiverse, which has come out of latter-day mathematics related to quantum physics and Einstein's relativity. What comes out of those equations is a multiverse.

Steven Bartlett: What's a multiverse?

Neil deGrasse Tyson: It's a medium that is pumping out universes. We are just one of them.

Steven Bartlett: What caused the multiverse?

Neil deGrasse Tyson: We don't know. It's a frontier. There's no crime in asking the question at the frontier of our knowledge. There are people who have to have answers — they don't make good scientists. The urge to have an answer can be influenced by their bias, by their culture. Just take a look at origin stories all around the world. They flow out of the cultures from which they emanated.

When you confront the unknown, you write the recipe for more data. That's all it is.

Steven Bartlett: And what are those recipes that you've written?

Neil deGrasse Tyson: We need telescopes. We have telescopes specifically designed right now to get a better understanding of dark energy and its manifestation throughout time in the history of the universe.

Steven Bartlett: Explain dark energy to me.

Neil deGrasse Tyson: It's something in the vacuum of space that's making the universe accelerate in its expansion. From that original explosion, we have all the galaxies, all the matter, all the gravity. You expect the expansion to be slowing down at some rate based on the gravity — like tossing something in the air. Gravity slows it down and actually makes it reverse. So we expected that. We went to make that measurement and we got the opposite answer. The universe is accelerating. That won a Nobel Prize in 1998.

It's a term in Einstein's equation that he himself rejected. He said there can't be a negative gravity — its value in his equation must equal zero. And so he moved on. Then we discovered it. We came up with a term for it. I think it's a bad term. We don't know what it is at all. So don't call it dark and don't call it energy. Call it Fred. And dark matter — we don't know what that is either. Let's call that Wilma. We've got Fred and Wilma. We don't know what either of them is.

Obama, Trump, and the UFO files

Steven Bartlett: The key question that people are talking about at this moment in time — you had Obama make those comments in that interview saying he'd never seen aliens.

Neil deGrasse Tyson: No, no, no, no. First of all, Obama is scientifically literate. He said — because he's scientifically literate — what is scientifically defensible: that there are probably aliens in the universe. Anyone who has studied that problem will arrive at that conclusion.

Steven Bartlett: "They're real, but I haven't seen them, and they're not being kept in Area 51 —"

Neil deGrasse Tyson: — unless there's this enormous conspiracy and they hid it from the President of the United States. That's what he said. But as a former president of the United States, in our alien-adjacent culture, it became: "Oh, that must mean there are aliens in the basement of the White House or somewhere in government custody." They took his statement that sure, there are aliens out there, and turned it into a claim about the US government. When I heard his comments, that's exactly what any scientifically literate person would say. What people did with that information — he then had to come back and explain. I didn't even think that was necessary, but apparently it was.

Steven Bartlett: And then Trump responded —

Neil deGrasse Tyson: Trump responded on Air Force One in an interview and said, "He gave classified information. He's not supposed to be doing that. He made a big mistake. He took it out of classified information."

Steven Bartlett: Trump seemed to stoke the idea that there are aliens. And then from that, shortly after, we had the UFO files announcement.

Neil deGrasse Tyson: Sure, great. Bring them out. I love it. They were going to release the UFO files. And now we find ourselves at a place where the general public is again really, really curious about the subject of aliens.

Do you believe in intelligent life in the universe?

Steven Bartlett: So my question to you is about this central question: do you believe there's intelligent life in the universe?

Neil deGrasse Tyson: One of those peaks in the Google trend data was in part because there were files released that week by the Pentagon — and dare I suggest my book was released in May on May 12th. Good timing. It just turned out that way.

I decided to put a foot into the ring when I saw these high-ranking whistleblowers come forward in Congress — sworn testimonies, former intelligence officers, former military folk. I said, "All right, it's time to jump in, because no longer can you discount the testimony the way you might have done before with the farmer in the back 40 who saw something and is talking about it but didn't take a picture of it." Now, when official government people are doing it under oath, it's time to take it up a notch.

And what do I mean by that? Bring out the alien. If you're saying you've got an alien in the shed in the back 40, just bring it out. And the moment you do that, no one will ever have to ask again, "Do you believe in aliens?" No one has ever asked me, "Do you believe in elephants?" Why? Because we've shown elephants. We have elephants. We've seen elephants.

But do I think there's intelligent life in the universe? I don't see why there wouldn't be, given the size of the universe, the age of the universe, and the ingredients of the universe. Think about it. The early Earth — life got underway within 100 million years of as early as it possibly could have. That sounds like a long time, and it is, but that's small compared with the timeline of Earth itself. It's like 5% of the timeline of the Earth. Almost as fast as it could possibly happen, the basic ingredients on Earth — which matched the basic ingredients of the universe — went from organic molecules to self-replicating life. Whatever our challenges in the lab, Earth didn't seem to have a problem accomplishing it.

Yes, it would take much longer to generate what we're calling intelligent life. But given how many planets are likely in the galaxy — our catalogues now have 6,000 exoplanets in them, and that's just in a tiny little area —

Steven Bartlett: What's an exoplanet?

Neil deGrasse Tyson: A planet orbiting another star. We've catalogued 6,000. In 1995 — what year were you born?

Steven Bartlett: '92.

Neil deGrasse Tyson: So you were three years old when we discovered our first exoplanet. And now we're rising through 6,000. If life happened on Earth as swiftly as it did, no one among us who has studied the problem is given reason to doubt that it couldn't happen frequently elsewhere in our galaxy or in the trillion other galaxies in the universe.

Steven Bartlett: This is one galaxy, right?

Neil deGrasse Tyson: One galaxy containing hundreds of billions of stars. This cloudy thing — you cannot resolve the cloud into individual stars. Galileo did this. He said, "I wonder what that Milky Way is. Is that just a cloud?" He took his telescope, put it on the Milky Way, and saw individual stars.

Steven Bartlett: And how many galaxies are there in the universe?

Neil deGrasse Tyson: At least 100 billion galaxies in the observable universe. Let's quantify what it is to not know. Things range over such a huge scale that if you're off by a factor of two — which sounds significant in most everyday life — but if things range over factors of trillions, then if you can get an answer within a factor of two, you're doing really well. Our galaxy has several hundred billion stars in it. We don't have an exact count, but that's a very good estimate because we know the total mass of the galaxy and we know how much mass a star occupies. We know how much dark matter there is. So we can calculate the likely number of stars.

Given our data on planets, we have many star systems with multiple planets, and that's just in our neighbourhood. If that's representative, you just scale that up. You end up with millions of planets, possibly billions across the galaxy.

Steven Bartlett: And there might be hundreds of billions of galaxies.

Neil deGrasse Tyson: Not just might be. There's at least that many in the observable universe. The actual universe goes beyond our horizon, in the same way that for a ship at sea you have a horizon. You're not saying, "Oh, that's the edge of the ocean." You keep sailing and more ocean comes into view. Is it infinite?

Steven Bartlett: It might be. We don't know.

Neil deGrasse Tyson: I'm not going to put a prerequisite on the universe just because infinity is kind of hard for the human brain to wrap its head around. We've made assumptions about the universe just to be consistent with our own philosophies that just turn out to be flat wrong. Copernicus, a religious man, comes up with the idea that maybe the sun is at the centre of the known universe and not Earth. We go from geocentric to heliocentric. If you do that, then we don't have epicycles — we just have simple orbits around the sun. Well, he did that, but it didn't match the observations as well as the epicycles did. We would learn later, 50 years later, that the orbits are not perfect circles. He made them perfect circles because God created the universe, God is perfect, the circle is a perfect geometric shape — clearly anything moving in the universe is going to be in a perfect circle. That was an assumption placed on the universe derived from a religiously philosophical proclivity.

So given this failed exercise in the history of science — of which there are many examples — I will not say that the universe can't be infinite.

What's at the centre of the galaxy — and what is a black hole?

Steven Bartlett: What's in the middle of the galaxy? Because it looks like a light.

Neil deGrasse Tyson: There's a black hole. Well, in this picture, the density of stars is way higher in the middle of the galaxy than out here. We think in the formation scenario of the galaxy that most of the mass is near the centre and it gets thinner as it comes out. So we're going to have the most stars where the most mass is. And in the exact centre is a supermassive black hole, which we've measured to be there. A Nobel Prize was given for that measurement.

Steven Bartlett: Can you explain what a black hole is — like I'm 12?

Neil deGrasse Tyson: You've got to respect black holes. Don't ever diss a black hole, because you will lose.

So we're here on Earth and the old adage is what goes up must come down. By the time I was 10 years old, we walked on the moon and then left rocket parts on the moon. Those are never coming back to Earth. So there are things that went up that never came back.

Well, if you take something and toss it, it slows down, comes to a stop, and then speeds up and comes down again — it's captured by Earth's gravity. But there is a speed with which I can throw something so that it never comes back. If I throw it a little faster, it goes higher before it comes back. Even faster, it gets higher and higher. You can calculate using physics and gravity equations that there's a speed with which this will go so high it'll reach infinity. If it reaches infinity, it's not coming back. That's called the escape velocity for Earth. It's really fast — 7 miles per second. If I throw something at 7 miles per second, it'll reach the edge of the universe and never come back to Earth.

Suppose Earth had more gravity than it currently does. Does it make sense that the escape velocity would be greater than 7 miles per second? If Earth's gravity were stronger, it might be 10 miles per second, 100 miles per second. Keep up this exercise and you'll reach a point where your object has an escape velocity that equals the speed of light. The moment it achieves that, light cannot escape — it's not moving fast enough. And if light can't get out, it's black. If you fall in, you are never coming out, because you can never reach the speed of light. There's no greater definition of a hole than that. Hence, black hole.

Einstein could have predicted them, but it was too weird for him to go there with his equations. We would learn about black holes mathematically in the 1960s, make our first discovery of one in the 1970s — a famous source of X-ray energy called Cygnus X-1. And now they're common. We've even discovered them in the centres of galaxies — supermassive, a million times the mass of the sun. Monstrous black holes dining on anything that comes close.

Steven Bartlett: Just things that come close?

Neil deGrasse Tyson: Yeah. It's not going to reach out. So if the sun were to become a black hole now — it won't — it wouldn't reach out and grab us and suck us in. It would have the same gravity as a black hole as it does as a star. But if you get close —

Steven Bartlett: Is there a certain distance?

Neil deGrasse Tyson: There's a distance around every black hole — I think it's called the ergosphere — where there are no stable orbits. If you get closer than that, you will fall in no matter what. Whereas beyond it, you can maintain a stable orbit and look at the black hole from a distance.

Steven Bartlett: And where do you go if you get sucked in?

Neil deGrasse Tyson: Well, it depends how big the black hole is. Small black holes — that's all she wrote.

There are books — I have one on my shelf and I've even read it — a graduate textbook that describes the mathematics of space and time on the other side of a black hole. It shows that a whole new spacetime opens up in front of you. Inside the black hole, the math shows that given the general theory of relativity, which gives us black holes in the first place, if you follow the math, you get a whole spacetime that opens up inside the black hole. And as you fall in, your time changes. Time ticks more slowly for you relative to the universe. It's called time dilation. And so as you look out at the universe, the universe will unfold faster and faster and faster. You will see the entire future history of the universe unfold as you descend into the black hole.

Steven Bartlett: When you say descend — I thought if you go close to a black hole, you're going to be crushed into a small mass.

Neil deGrasse Tyson: I didn't get to that part yet. I'm describing what happens to space and time as you descend through what's called the event horizon. That's the region out of which you don't escape. That's the functional size we give to black holes. It has taken the fabric of space and time and folded it back on itself. There's no pathway you can take to get out. You're in there forever.

For the small black holes, here's an interesting fact. When you stand, your feet are closer to Earth's centre than your head is. You can calculate what the force of Earth's gravity is at your feet and at your head, and you'll get two different numbers. They're very close to each other, so we don't think about this. But as you descend into a black hole, the difference in gravity between your feet and your head gets greater and greater and greater. They're called tidal forces, and they end up stretching you head to toe. Initially it probably feels good — you sort of stretch. And then you realise, oh my gosh, this is unrelenting and it's getting stronger. Eventually you'll snap into two pieces, likely separated at the base of your spine, if you look at the structural integrity of human physiology. And then you're still falling, and now those same tidal forces will operate on your torso and on your lower half. They'll stretch and snap into two pieces. So you go from one to two to four to eight to sixteen, and you'll bifurcate in pieces all the way down to the centre of the black hole.

The worst part — or maybe equally as bad — is that you are occupying a narrower and narrower volume of spacetime as you go down to the singularity that is the centre of the black hole. So not only are you getting stretched head to toe, you're getting extruded through the fabric of space like toothpaste through a tube. Have a nice day.

Steven Bartlett: So you don't want to test that.

Neil deGrasse Tyson: All of our equations tell us that's what'll happen to you.

Steven Bartlett: What's at the heart of the black hole?

Neil deGrasse Tyson: We don't know. General relativity, which gives us the black hole in the first place — if you follow the equations, the centre of the black hole is infinitely dense and infinitely small. How does that even happen? We don't know. Maybe something prevents that, but that is the limit of Einstein's general theory of relativity.

The UFO footage and alien archetypes

Steven Bartlett: I'm presuming you've seen all the footage that's been released. Was any of it compelling to you?

Neil deGrasse Tyson: No. It's something that we don't know what it is. Let's back up. Even UFO enthusiasts of the most severe kind would agree that most sightings of what we call UFOs have natural explanations that you just didn't know what you were looking at and then figure out later. Is it a cloud formation? Is it lightning? Is it twilight conditions? Sure. But then there's some that no one knows how to explain. I don't have a problem with that.

I like the Tic Tac. The Tic Tac is fun.

Steven Bartlett: What's interesting about that?

Neil deGrasse Tyson: I don't know what it is. I'm a scientist. We are attracted to things we don't know or understand. And you can see it move in one of the frames, and you can see it sort of gimbal in one of the frames. Of course, it's combined with the statements of the pilots, how shocked and surprised they are. It looks like one of the alien spacecraft that Steven Spielberg showed in Close Encounters of the Third Kind, but that's not what intrigues me.

What intrigues me is we have whistleblowers saying we have actual aliens. Give me the actual alien. Do you think if we did, we would tell the public?

People have testified we have aliens, that we have alien crash parts, that we have reverse-engineered alien technology. And somebody says, "Oh, we're not ready to see an actual alien." Of course we're ready. Hollywood has prepped us for decades for this day. I think it'll be charming.

What would surprise me most is if the alien were humanoid. Most Hollywood renderings of aliens are humanoid — a head, two eyes, a nose, a mouth, ears. Oh, they're bald. Or they have pointy ears. But they're still walking, they still have elbows and fingers and knees. I would be most surprised if the alien was humanoid.

Steven Bartlett: What would you expect them to be, based on the atmosphere of the universe?

Neil deGrasse Tyson: I would expect it to not be humanoid. Most life on Earth is not humanoid. We have DNA in common with all life on Earth, and most life is not human. Oak trees, worms, lobsters — none of those life forms are humanoid. The xenomorph is not building spaceships. So if this comes to Earth, it's because we brought it here, not because it flew. Based on its conduct, it looks like it just wants to be parasitic. ET has fingers and looks like it can build a spaceship. And the predator — notice that its eyes are even the same separation as our eyes. There's an actor in that costume, and the actor is human. That's really what this comes down to.

In the book, I stumbled on the fact that people who care about alien sightings — not UFO sightings, but alien sightings, people who have said they've seen aliens — divide into archetypes. Little green men — we had a lot of those back in the 50s and 60s. And the fact that we would even use the adjective "men" meant they're humanoid. Another one, much more common today: the grays. The gray alien. These also tend to be bald. And then there are others — Arcturans, from the star Arcturus. Lyrans, from the constellation Lyra, the harp in the sky. Sirians, from the star system Sirius. In my book there's a dozen of them. The tall whites. Insectoids — I love this one, because we hate insects. Insects are ugly to most humans. So if you have a creature that resembles an insect, you don't want to become friends with it.

Steven Bartlett: If you listen to people that have done DMT, they often cite seeing or meeting these types of beings.

Neil deGrasse Tyson: The commonality of that is intriguing. Rather than jump to a conclusion that they're all having some common interdimensional experience, it's easier for me to think that they all have human brains and the chemical is exciting the same part of each one of their brains, thereby sharing in some experience. Plus, I don't know if they've done this across cultures, but English-speaking cultures have reported many more alien sightings than other cultures — vastly more sightings. Which is a little weird. So either aliens just like visiting English-speaking countries, or we just know better how to report what we see, which is probably what it is. But you go to other countries and they don't have this alien fixation.

Psychedelics, reality, and objective truth

Steven Bartlett: Have you ever done psychedelics?

Neil deGrasse Tyson: Never.

Steven Bartlett: Are you curious about it?

Neil deGrasse Tyson: Not really. Because the human brain barely works as it is. Just open any book of optical illusions. Turn to any page. Is it bigger? Is it smaller? Is the line in the page or out of the page? Simple drawings confound your perceptions of reality.

Steven Bartlett: But doesn't that mean reality is fragile?

Neil deGrasse Tyson: Yes. And so if I want to now stir chemicals into my brain — as a scientist who values what is objectively true, since my brain barely works as it is — to put in chemicals, it's not clear to me that that gets me closer to any reality at all. And it's reality that I value in this world. That's why I haven't done psychedelics.

Steven Bartlett: What I think about is: if I can inhale something and suddenly my subjective experience of reality is entirely different — it's 4K and I'm somewhere else — does that not then mean that my current subjective experience of reality is as fragile as an inhale?

Neil deGrasse Tyson: Sure. It's chemicals. It's a reminder that your brain functions based on electrochemical signals. And to put some other chemicals in there to disrupt it — the sky is the limit.

Steven Bartlett: But does that mean that reality itself is just a bunch of chemicals?

Neil deGrasse Tyson: There are philosophers who like thinking about that and debating it. I tend to be way more practically minded in that conversation. I can perform an experiment outside of your five senses and it will get a result that everyone coming together to look at that result will agree on.

Steven Bartlett: That's one of my senses though — looking.

Neil deGrasse Tyson: Sure. But I can create a measurement of ultraviolet light. You can't see ultraviolet light, but I have a detector that fires and you can look at the detector firing. I've measured ultraviolet light and I didn't need your eyes, your retina, or your brain to make that measurement. So when Einstein said E=mc² and that became the foundation of atomic weapons that we then dropped in warfare killing hundreds of thousands of people — you can't tell me that's just our imagination or just chemical things. That is a real phenomenon based on real physics drawn from an objective reality that we established while not doing drugs. That's why it took so long to develop science — to separate measurements of an objective reality from the neurochemical synapses of your brain.

Steven Bartlett: Isn't observation the rule? Isn't that what science is?

Neil deGrasse Tyson: Yeah. So if I can have a device that makes a measurement and most people looking at it can agree what that thing is, if I'm a betting person, I would bet that that is a representation of objective reality. If I bring a completely crazy person to it, they're not going to know how to interpret it. And so how do I value their interpretation of the data? These are legitimate questions, but they're answerable using the methods and tools of science for what is repeatable in this world and what is not.

Steven Bartlett: A physicist came on and said that we can only see that which we need to see in order to survive. So there could theoretically be spirits in this room now, but because they're inconsequential to my survival, I actually don't even need to be able to see them. I didn't need to develop the senses to be able to know that they were here.

Neil deGrasse Tyson: That's why science has dozens of senses. We've gone beyond human physiology in the sciences. So that's why I don't have to have that conversation about my reality versus any other alternative reality and which one is real. That's why science exists. We have the microscope that gets us into the realm of the small, the telescope that gets us to the realm of the large. Your senses have no access to either of those places.

The Dead Sea in the Middle East was called dead because there were no macroscopic fish there — the salt level is so high. But there are microbes doing the backstroke. Salt-resistant microbes. They couldn't see those. So their reality missed something. Yes, your reality is going to miss things that are not otherwise going to put your health at risk evolutionarily. But science changed that forever.

Steven Bartlett: A lot of it's predicated on believing in my observable experience.

Neil deGrasse Tyson: You don't have to, because we have tools. That's why I can look in the sky, say, "Wow, what is that?" and pull out binoculars. Tools. "Oh my gosh, it's a drone." Now I can see it better with higher resolution. "What is that over there on the horizon?" I don't know. "Oh, it's a bear crawling on the side of the thing. It's not some alien." You bring out the tools, supplement your senses.

Steven Bartlett: But there are others that you can test things without observing them — you can look at what effect they have on something else. For example, if a couple of chemicals are responsible for this entire experience — the things that I feel, touch, smell, hear — is it plausible then that we are just a bunch of chemicals in a petri dish somewhere that are creating a subjective experience, and that subjective experience manifests as a universe that I can see? Because if chemicals are my entire subjective experience, it's way more likely that we are just a simulation.

Neil deGrasse Tyson: Yeah, I think we probably are a simulation. Based on what you just said, it's more likely that we're simulated by some snot-nosed kid in its alien parents' basement.

That was a biological simulation you described. The laws of physics are different on different scales. You can't just put us in a petri dish and have us behave the way microorganisms would behave. A petri dish is ideal-sized for bacteria, not for us. You can't just scale it up.

The simulation hypothesis

Steven Bartlett: Do you believe that we're in a simulation?

Neil deGrasse Tyson: I don't want to believe it.

Steven Bartlett: You don't want to believe it?

Neil deGrasse Tyson: I'm whiny about that. Nobody wants to be a simulation. My best argument that we're not — or rather my best way to improve the odds that we're not — is just to remind you how the simulation argument works.

You have some universe, and then they have computers that are very powerful. They simulate a world within the computer, and the life forms in that world believe they have free will. And then they say, "I'm bored. I'm going to make computers." So they invent computers and create a video game inside their computers. It's video games all the way down.

If I close my eyes and throw a dart, which universe am I most likely to hit? The one that started them all, or the 999 bajillion that followed? Probably one of the ones that were manufactured, which argues strongly that we're in a simulation.

However, the only universes that could create other worlds are the ones that have the capacity to create other worlds. So each one of these in this sequence had the computing power to create a whole other world. That's why it continued the sequence. We humans on Earth do not yet have the power to create an entire other universe with people in it who have what they believe is free will. We don't have that power yet. Because of that, we are not one of the ones in the sequence — because everyone in the sequence has the power to create another universe, and they did. We don't have that power. Which means we are either the very first universe in that sequence or the very last, which has yet to achieve the power of simulation. So we go from 100 bajillion to one likelihood that we are simulated, to maybe one in two. And I like those odds.

Steven Bartlett: Does this not assume that the creators of the simulation modelled their universe as a one-to-one copy of our own?

Neil deGrasse Tyson: No, they can make any kind of universe they want. This universe happens to have planets and stars and people in it. The other one could just be Mario characters.

Steven Bartlett: Probabilistically, I think I've heard Elon Musk say that he thinks probabilistically this is a simulation. He reasoned that there are three potential options: either humanity just blows themselves up before they get to this technological advancement, either this is a simulation, or this is base reality. And one would say being base reality is highly improbable.

Neil deGrasse Tyson: Why is that highly improbable?

Steven Bartlett: The size and scale of the universe and the speed in which we've gone from being like cavemen to being able to do large language models of vast intelligence and VR simulations. It's like this — Cosmos taught me this.

Neil deGrasse Tyson: Well, it's actually not like that. Can I explain why? It's simply exponential growth. If you plot Earth's population, you have a very common encounter with an exponential curve. You have a plot and you have time. Go back as far as you want and it's almost a flatline, and then it goes up. That is the plot of an exponential on a linear graph.

Here's what all exponentials have in common. If you truncated it somewhere — say, go back 20 years, 30 years, 50 years — and then replotted it, it would do the same thing. Go back again, replot it, it would do the same thing. Everybody in an exponential thinks they're living in special times. They think that all the greatest, most important discoveries happened recently. Yes, that is true. But it's true for everybody along the exponential.

When we invented the automobile, no one was saying, "Look how backwards we are." They were saying, "Look how advanced we are. We now have an automobile, and we have railroads that cross the lands, and we have steam ships that cross the ocean. Look how far we've come in just decades." If you imagine any rate of improvement at our current trajectory, we get to a point at some stage in the future where we can create simulations. We get there, but we're not there now. And since we're not there now, we're not one of these middle universes.

Steven Bartlett: But whether it's 100 years or a thousand years or 10,000 years, we eventually get there. And if you layer that over with what you said about there being 100 billion galaxies with 100 billion stars, it's conceivable that we are not at the front of that race. And if we're not at the front of that race, it means that someone else theoretically got there at some point, and therefore we might be their simulation.

Neil deGrasse Tyson: Yes, of course. Yes. We could be their simulation, but we can't simulate anybody within our world yet. That's why we are either the last one in that list — created by some other civilisation that can't yet create the next civilisation — or we're the first one that's authentic.

Steven Bartlett: Or it could be a tree. It could be like they did one, they did 500, then this person here did 300.

Neil deGrasse Tyson: Yes. I'm taking the very straight-line model. It could be fully branched out. All I'm saying is we're nowhere in the middle of that. We have to be at the end because we can't make another universe yet. So that greatly reduces the total number of universes your dart can hit when you toss it against the wall. Either the first universe or the last one.

Steven Bartlett: It could be the last of a tree. Like a family tree. You don't have to —

Neil deGrasse Tyson: That's fine. So how many would the last be? 500, a thousand, whatever that is. There are countless other ones that came before us leading up to that. And we could have cousin simulations that went on. But it seems more probable — I can't think of a singular argument that's more convincing — that if humans eventually get to technological advancement such that they could create their own simulation, then it's conceivable that in such a vast universe other intelligent life got there first. Do you agree that there's intelligent life in the universe? I think it's quite arrogant of us to think that we are the most technologically advanced in the universe.

Neil deGrasse Tyson: No one should be thinking that.

Steven Bartlett: So thus it's a simulation, Neil — unless we are not the simulation and we're the original universe that hasn't started the ball rolling yet.

Neil deGrasse Tyson: And could you imagine the odds of that? The simplest way — in the straight-line example, which we can spread out — we're either the starter universe who hasn't figured out how to make a universe yet, or we're the last in that line which has yet to evolve the capacity to make a universe, because it doesn't happen instantly. They have to invent computers and they have free will and so they're doing their thing.

However many universes are in between, it goes from that number of possible universes we could have been to a one-in-two chance that we're real. One in two. We're the original, or we're this one which is simulated. Now you have branches — fine. Once again, we are either the last one in a branch or we're the first one that started it all.

Steven Bartlett: Here's my drawing of how it might look. We could be that one, or we could be that one, that one, that one, that one. Why is that not plausible? It's kind of like a family tree. Some of them have kids.

Neil deGrasse Tyson: So in that case, only one of them evolved to make another universe. And this one here made ten, and only one of them made another universe. That's fine. So now two of them made another universe. You keep doing that. If we're early in the game, we could be any one of those at the edges of the line. But if all the rest make more universes, we know we're not them because we don't have that ability yet. So in your top row example, if one of them continues to not be able to make another universe and the others do, once again it's one out of three chance that we are real — that we're the starter universe — because you have two other places that have yet to make one.

In the simulation scenario, you could draw a whole crop of universes that are not simulating other universes. So it's not very fertile in the simulated universe universe.

Steven Bartlett: Maybe this is what the multiverse is. Maybe this is what infinity is. Maybe this is what the Big Bang was — a universe creating the next universe.

Neil deGrasse Tyson: Well, that's what we call the multiverse — creating universes.

Steven Bartlett: And maybe the point at which we as an advanced civilisation can come together with AI and build a new universe is the next Big Bang.

Neil deGrasse Tyson: Yeah, I mean, that would be interesting if they just summon it up at will. What's interesting though is that the laws of physics we measure on Earth apply across the universe and across time. Maybe that's just the programmer's rules for the universe they just created. I have no way to step to the side of that argument.

Steven Bartlett: So the difference is in our Big Bang we went through single-celled life, then multicellular organisms, then intelligence, then technology. In a simulation — are they starting you from the beginning of the universe? Is there a Big Bang in the simulation, or do people just show up fully formed as an intelligent species, maybe implanted with a memory that's not real?

Neil deGrasse Tyson: This is very Matrix-y.

The return to the moon — geopolitics, not science

Steven Bartlett: At the moment, it seems like there's a race to go to the moon. A lot of companies are interested in that. We've got the Artemis program happening. Why are people so interested in going to the moon, and is there merit in their motivations?

Neil deGrasse Tyson: Well, we could have stayed on the moon in 1972, but we didn't. Could have gone in 1980, but we didn't. 1990, we didn't. 2000? No. 2010? No. Well, what happened in the 2010s? We learned that China wants to put astronauts on the moon — taikonauts, they call them. We then say, "Hey, wouldn't it be good if we went back to the moon? That's an interesting idea. Let's do that." That happened under the first Trump administration. So the Artemis mission gets birthed. Artemis — do you remember who Artemis was in Greek mythology? Artemis is the twin sister of Apollo. So we say we're going to go back to the moon. My read of that landscape is that China put a flame under our ass. No different really from when Russia first launched the satellite — Sputnik — put a flame under our ass. Within a year, we created NASA.

By the way, it may take just such a thing to bring Congress together for a unified project. Do you remember when we had the testimonies in Congress of the whistleblowers? We had Republicans sitting right next to Democrats asking questions about aliens. I said, "Wow, Republicans and Democrats are agreed on some process in Washington." I thought that was a beautiful fact.

Steven Bartlett: So what are our motivations now to go to the moon? Is there an economic upside to it?

Neil deGrasse Tyson: No, it's geopolitical. China says they're going to the moon 50 years after we go to the moon, and we all of a sudden decide we want to go to the moon. Let's be real about that. And while that came out under Trump, Biden came in and we kept the program. Biden could have said, "This is a Trumpist thing, I don't want to do it" — and what would anyone have said? But he didn't, because NASA is a geopolitically responsive organisation.

Steven Bartlett: So what if China gets there first? Why does that matter?

Neil deGrasse Tyson: Geopolitical egos. Just ego. Did you see the hearings in Congress with the head of NASA when they were asking, "Why did China land on the far side of the moon? What do they know that's there that we don't?" These are the competitive urges that we have. And don't delude yourself into thinking we ever went to the moon for science — then or now.

Steven Bartlett: What about resources? Are there resources on the moon?

Neil deGrasse Tyson: We're looking for them. NASA has an entire branch called in-situ resource utilisation — ISRU. We think there's water at the South Pole. So you go get the water. Maybe if you get a 3D printer, you can take the silicates from the moon's surface, dump it in, and make tools. There's a whole piece of space exploration that concerns itself with that, because you can't take everything with you.

Steven Bartlett: Is it cold on the moon or hot?

Neil deGrasse Tyson: It depends on whether you're facing the sun or not. When you say "is it cold," you're generally referring to the temperature of the air around you. Where there is no air, your temperature comes from any source — or absence of a source — of energy. So if you face the sun, this side of you will burn up and the other side will freeze. So what we really need are rotisseries — or a highly insulated space suit.

Steven Bartlett: Don't you think that would be a great tourist destination? It's three days away, isn't it?

Neil deGrasse Tyson: Yeah. You can get there quicker, but the minimum energy to do so will take you three days.

Steven Bartlett: I would save up multiple years of vacation money to go to the moon. Yes. Completely.

Neil deGrasse Tyson: If you can bring the price of that down, make the moon our backyard. What I wanted to be clear about earlier — when you say is there an economic reason to go to the moon? Not initially, until you set up bases and hotels and restaurants. And if you have restaurants, there'd be really weird food that they would serve in moon gravity.

Space debris, Kessler syndrome, and space law

Steven Bartlett: I've wondered about this space debris thing because it seems that every nation is racing to throw tens of thousands of pieces of metal satellites into our orbit. Is it a problem?

Neil deGrasse Tyson: It's worse than you think. You have to ask: who is it a problem for? Is it a problem? Yes. Who is it a problem for? Not the people who want high-speed internet in the middle of the ocean or in the Arctic or in the middle of the desert, because these satellites — the SpaceX Starlink satellites — are providing that in these remote places of the world. So it's not a problem for them. It's a blessing.

It's a problem if you're just trying to observe the night sky the way we've done as astronomers since time immemorial. I'm trying to get images of the night sky and I see satellites crossing back and forth. This amounts to visual noise in my data. If I'm trying to track an asteroid that might be headed our way and I have thousands of other streaks of light in my image, there's a chance I might miss the asteroid. Also, if there's some object of interest and a satellite passes right in front of it, that will contaminate the data that I seek.

I don't know if this is reversible, but what it tells me is that the future of telescopes is going to have to be space-borne telescopes — which we've already made that transition to — or telescopes on the moon. They've launched roughly 5,000 satellites into orbit in 2025. We're on track to launch even more than that this year.

Steven Bartlett: That's correct. We're being recorded mid-year 2026. The last number I saw, SpaceX had 10,500 satellites. There'll be 100,000 active satellites in orbit by 2040.

Neil deGrasse Tyson: Probably more. This is the utility of space — not only for reconnaissance, for surveillance, basically military security, but also commerce. There is no Uber without GPS. It's not the value of the satellites themselves that matters here. It's the value of the economies that they enable. And that's why we have a Space Force now. A Space Force which had been percolating for decades. Trump in his first term decided, "Let's make this official." And so he did. People say, "Does that mean there's going to be like Star Wars?" There already was a space force. They didn't call it that. It was called the Air Force Space Command. It was a sector within the Air Force. You pull that out, and now the mission is a little more pure about what its goals are and what it needs to accomplish.

Steven Bartlett: Have you heard about Kessler syndrome?

Neil deGrasse Tyson: Oh yeah, of course.

Steven Bartlett: Could you explain it?

Neil deGrasse Tyson: In 1978, a physicist or mathematician named Kessler saw the increase in satellite launches that had been going on, did a calculation, and said: there must be some threshold of satellites orbiting the Earth where if one of them gets destroyed by any means — maybe two collide with each other, or one is intentionally taken out by a missile, which has happened three or four times now. China's done it, India's done it, Russia's done it, and we've done it to our own satellites. Which means: if you can do it to your own satellite, you can do it to anybody else's satellite. It's a demonstration of your sovereignty, of your power over what you might perceive as an aggressor.

If you destroy a satellite, let's say it breaks into ten pieces, each going at orbital speed. Orbital speed is 17,000 miles an hour — way faster than a rifle bullet. So little pieces of satellite can be far more devastating than a high-powered rifle bullet shot into another satellite. These pieces scatter. If any one of them hits another satellite, breaking it into ten pieces, you go from one to ten to a hundred to a thousand. Within just a few orbits, 100% of the satellites can be taken out, if you have enough satellites for that thresholding to take place.

In other words, if low Earth orbit is mostly empty and you destroy a satellite, the particles are not going to take out another satellite. They'll orbit harmlessly or fall to Earth harmlessly. But if you have another satellite in that path, then that destruction is going to take out other satellites. So he warned us of these thresholds. I don't think we're there yet, but we need to keep it on our radar. The movie Gravity portrays exactly that scenario.

Steven Bartlett: Objects in orbit travel at blistering speeds — 17,500 miles per hour. At that speed, even a fleck of paint carries the destructive power of a rifle bullet or an exploding grenade. A fleck of paint.

Neil deGrasse Tyson: Correct. And shrapnel is the best analogy to that, because it comes out and damages other things beyond the target that was intended.

Steven Bartlett: And there's no laws up there, is there?

Neil deGrasse Tyson: Space law is a wild west at this point. Forget orbit — it's like, you go to the moon. Who owns the moon? Who owns a plot of land on Mars? If I go to an asteroid and I want to mine it for its minerals, who owns those minerals?

Steven Bartlett: Isn't it just whoever gets there first?

Neil deGrasse Tyson: Yes. That's what I mean by the Wild West.

The meaning of life

Steven Bartlett: What is the point of life? What is the point of all of this stuff? You've got to live, I don't know, 80, 90, 100 years, whatever it is. What is the point, Neil?

Neil deGrasse Tyson: That question, asked by many people, will keep religion in business for a long time. For many, the purpose in life is to serve God. And that's a little odd to me, because if I created a universe, I would not need people to praise me. That just feels weird. I would just create it and have fun. Let me work on the next universe. It's odd that an all-powerful, all-knowing entity seeks your submission and obedience. I've never fully wrapped my head around that idea.

But the meaning in life — that's really what you're asking. What is meaning? I derive meaning from life. I create meaning from life. I don't look for meaning. Many people look for meaning — is it under a rock, behind a tree? I'm still in search of the meaning of life. You realise you have the power to create meaning. Create meaning. We all have the power to do so.

One way — this might not be the recipe for everyone — I want to learn something today that I didn't know yesterday. I want to learn something tomorrow that I didn't know today. Thus growing my awareness of the objective realities of the world. And as I grow my awareness, I have new, nuanced, informed perspectives. So you can grow in knowledge, wisdom, and insight that wouldn't otherwise be possible if you didn't keep learning.

Second, I want to do something today that lessens the suffering of others. Why? Because if I have the power to make the world a better place for me having lived in it, I value that. I value happiness because people apparently like being happy. Happiness is something I've valued my whole life. It brings joy to being alive at all.

In my podcast, humour is an important element. There's a braid of science, pop culture, and humour. People return to the podcast because they laughed, they smiled, they felt good at the time they learned something, and they want to reproduce that feeling. We should not be surprised that we want to do things that make us feel good.

Why does helping another person make me feel good? I don't do it for me. I do it for the person. I don't help the person across the street so that I feel good about myself. I help the person across the street so the person feels good that they made it across the street.

Steven Bartlett: Which in turn makes you feel good.

Neil deGrasse Tyson: Well, there are things that I could do that make me feel good that I don't do because it doesn't spread the goodness. I can live in my own little world — this feels good. But when you spread it, other people can share in your emotions. I don't do it so much for myself. I just do it because I think we should spread more joy in the world.

Here's a way to do that. Do someone a favour and they say, "Thanks. I really needed that. I'll repay that favour one day." And I'll say, "No, pass it forward. Do that favour for someone else. Ideally, a stranger. A stranger who will never remember your name." Do it for them. And you know what'll happen? That favour — and you tell them to pass it forward — will work its way through society, through cultures, through civilisation, never being closed back. The moment you say, "Hey, I'll repay you the favour," that closes it off and it's no longer available to anybody in civilisation. If you don't close it, send it forward. Then there are these tributaries of favours working their way through civilisation and everyone is better off for it.

Closing question — the epitaph

Steven Bartlett: Neil, we have a closing tradition where the last guest leaves a question for the next, not knowing who they're leaving it for. The question left for you is: what is it that you would like us to write on your gravestone if we were the authors of the message?

Neil deGrasse Tyson: Let me back into that by saying I don't want anything that memorialises my life, because as an educator, it's not about my life. It's about the life of those who I've touched. It's about their life. No statues, no plaques, nothing. I don't need that. I don't seek it. I've had photographers come up to me and say, "I photograph all these famous people. Do you want to be a part of that?" No. It's not about me. I don't need you to look at a picture of me in a book. What I want you to do is open up a book that I wrote and read what I wrote. You will learn from it. You'll be enlightened. Because as an educator, it's about you. It's not about the educator.

So I don't want memorials or anything. But I know what I want on my tombstone. There's the full quote, which I will begin with, but it's the end of the quote that fits the tombstone. It's by Horace Mann, the educator — an American educator of the early 19th century. He was a university president. Schools are named after him. For one of his farewell addresses at a university, he said:

"I beseech you to treasure up in your hearts these my parting words. Be ashamed to die until you have won some victory for humanity."

That's what I want on my tombstone. Be ashamed to die until you have won some victory for humanity. As an educator, that's my goal. Humanity is better off for me having been in this world. That's my goal. Because all too many — there are a few key people in the history of the world for whom the opposite is true. And if we can do our little bit to improve the world —

Steven Bartlett: You've most certainly done that. You've done it for arguably hundreds of millions of people. I think if I crystallised the net impact you've had on my life from all of the content and information and movies and books and documentaries that you've written, I'd say it's about curiosity — expanding my mind to wonder more.

Neil deGrasse Tyson: Unfortunately, that does not exist in most schools. The kids in their class can't wait until the end of the period. They see the clock. They can't wait till the end of the school day. They can't wait till it's Friday. They can't wait till it's vacation. They can't wait till school's over. They can't wait till graduation. All of these sentiments are: I don't want to keep learning anymore. It's a chore. I don't enjoy it. I don't like it. There's even a rock anthem celebrating that fact — Alice Cooper says, "School's out for the summer." School's out forever.

Steven Bartlett: I hated school.

Neil deGrasse Tyson: I don't blame the students. I'm blaming the system. You can't wait to get out of school, which means they're not teaching curiosity. Because if they did, staying in school would be fulfilling that. And if they did, leaving school would birth the rest of your life as a curious person where you continue to learn. That's what school should be about. And it's not.

Steven Bartlett: And that's what you're doing for others — expanding the curiosity, the aperture, and allowing them to wander beyond the narrowness of whatever. I want people to say, "Gee, I miss school."

Neil deGrasse Tyson: I absolutely don't miss school. But we have to make a distinction between school and education, or school and learning. We kind of conflate the two and think they're the same. School's got a bad name. It's a place where you go to have curiosity stoked and fulfilled. If all schools were that, imagine how different the world would be.

Steven Bartlett: We can only imagine. I have your book in front of me here. It's beautiful and the title is great. It's called Take Me to Your Leader: Perspectives on Your First Alien Encounter. Thank you so much. I'm going to link this book below. Anyone that's into the subject matter of aliens and wants to wonder and have some fun —

Neil deGrasse Tyson: If I can give you just my favourite example from the book. In the chapter "Alien to Us" — there's "alien to us" and "alien to them," whole chapters. Let's say you befriend the alien and then you say, "Excuse me. I have to lay down horizontally and go semicomatose for one third of Earth's rotation." They'll look at you and say, "What? You guys know sleep? What's sleep?" Be ready. The things we take for granted might not be obvious to an alien.

And another one: if the alien has some appendage, don't just reach and grab it and shake it. You don't know what part of the alien that is. And maybe you don't want to find out after you just shook it. Shaking hands is not even earthwide — in Asia, shaking hands is not as common as it is in the West. So don't take your own assumptions and apply them to the alien.

And the "alien to them" chapter — just imagine they landed in Los Angeles, in the median of the 405, and they're just looking around. I'm certain they would conclude that the dominant life form on Earth was the automobile. There they are just doing things. Then they'd see a car hauler go by and say, "That one's pregnant." They would see cars inside. If there's an accident, other automobiles come up to take it away and repair it. These automobile wheels go up to fast food establishments and people don't get out of their car to go in. They stay in their car, wait in a slow line to get fast food, have it handed to them through a window, and then eat it in the car. So the aliens would say, "Okay, the life form is the car, and the squishy things inside must be the squishy middle of this life form."

What this book tries to do is recast all of your assumptions about what an alien would think of us and about what we would think of an alien. And I try to have fun doing it along the way. Thank you for bringing it up.

Steven Bartlett: Thank you so much, Neil.