Are We Alone in the Universe?: A Conversation with Neil deGrasse Tyson (Episode #252)

Key Takeaway

Practice “assumption audits” when confronting a big unknown today. List the observations you actually have, then identify the Earth-centered assumptions shaping your conclusion—such as life requiring planets, starlight, or human-like intelligence. This habit will not answer whether life exists elsewhere, but it makes your reasoning more accurate by separating evidence from familiar-but-unproven intuitions.

Episode Overview

Sam Harris and astrophysicist Neil deGrasse Tyson explore whether life and technological civilizations may exist elsewhere in the universe. They discuss the Fermi paradox, the rapid appearance of life on Earth, the limits of Earth-based assumptions, exoplanet atmospheric biomarkers, and why intelligence may not be an inevitable product of evolution.

Full Transcript

Transcript of Are We Alone in the Universe?: A Conversation with Neil deGrasse Tyson (Episode #252) from Making Sense with Sam Harris. Auto-generated from episode audio; may contain minor errors.

Welcome to the Making Sense podcast. This is Sam Harris. Just a heads up: if you're listening to this, it's because you're not on our subscriber feed and will only hear the first part of this conversation. To access full episodes of the Making Sense podcast, you need to subscribe at samharris.org. There you will find our private RSS feed to add to your favorite podcast, along with other exclusive subscriber content. We don't run ads on the podcast, and therefore it's made possible thanks to the support of our subscribers.

So, if you like what we're doing here , consider becoming one. Today I'm speaking with Neil deGrasse Tyson. Neil probably needs no introduction. He's been on the podcast before, and he's been everywhere else before. He is an astrophysicist who hosts his own podcast, StarTalk Radio, as well as the Emmy-winning StarTalk and Cosmos programs for National Geographic. He is the author of more than a dozen books, including Astrophysics for People in a Hurry and, more recently, with his co-author James Trefil, Cosmic Queries, StarTalk's Guide to Who We Are, How We Got Here and Where We're Going.

He is also the director of the Hayden Planetarium in New York. Today we talked about our place in the universe. And we spend a good part of our time debating whether or not we are alone here. So, we discussed the famous Fermi problem, that is, where is everybody? And this naturally leads to a conversation about recent events on Earth, where a renewed interest in UFOs has captured a lot of public attention. We also touched on the public understanding of science, and the impossible existence of flat-Earthers who still live among us.

And then I try to steer Neil once again into a conversation about politics and the moral panics associated with it. And you can judge the results of that for yourselves. In any case, it's always great to talk to Neil. And I hope you enjoy the conversation as much as I do. And now I bring you Neil deGrasse Tyson. I'm back once again with Neil deGrasse Tyson. Neil, thank you for joining me. Yes, Sam. I mean, I love your show and I never think about participating in it .

So, when I'm in it, it's like: "Ooh, what am I going to talk about?" Because all your guests and all your conversations are, you know, everything I do as a scientist and science communicator, you raise the bar a little and end up getting involved in the most controversial things happening in society. And I'm just not that brave, you know? So, I feel like I shouldn't be on your show. I feel like that sometimes. Well, I hope I don't confirm that hypothesis, but I'm going to push you to the limit of your courage, and then you can pull me back.

Okay. But it's great to hear your voice, and before we continue, I want to talk a little about your book, because you've released a new book, Cosmic Queries, StarTalk's guide to who we are, how we got here, and where we're going. Let's start with the area of pure scientific interest, and then we can address controversial points, or not, as time goes on. But this is truly a beautiful book. It is published by National Geographic. So, it's very well illustrated. And while reading it, I confess I didn't read it all, but I read a lot, and it immediately occurred to me that this is the book you would want to give to an intelligent, curious teenager interested in science, you know, of any age, say, 14 years old and up.

It is perfectly suited to be a person's first book on science. Was that your intention when you wrote it? It's interesting that you say that because what I learned from my first book , which was many, many moons ago, was that I wrote a book and said, "Well, how am I going to write a book about science? I want to make sure everyone understands everything in it, right?" So , my first book was a question and answer book about the universe, and I wrote it in a fun way.

It was a pseudonym for Merlin, you understand? Dear Merlin, do you know how the universe works? And Merlin called for a conversation with Einstein. It was a fun and entertaining thing, and all the questions were asked by adults. When the book was released, I discovered that when adults read it and understood everything, they thought to themselves, "Well, this clearly isn't for me. This is for someone younger." And I said, "Wow." So, people are used to the fact that when they meet adults, when they find a science book, they expect part of it to be above their heads .

Yes. And then I said, "Oh, okay. So, my next book, which has two chapters, is sure to grab everyone's attention, and nobody thought to give it to children. But Cosmic Queries, I think, is a celebration of the deepest sources of curiosity that exist within us as humans. And all those cylinders, if you'll allow me to use an internal combustion engine reference, all those cylinders were firing for all of us when we were younger. Right? Every day is a 'what is this?'" "And it's a flower, a tree, a stone, and a" why this and that?

"And some of these questions are very profound. How did all this get here? And why are we all here? And are we alone? How will all this end? And so this deeper category of questions has been elevated and placed in this book. But the whole concept of Cosmic Queries is fed into our StarTalk podcast monthly . On StarTalk, we interview celebrities, and I have a comedian who co-hosts, so it's really cool that they have the strength of lightness in a show where the content can have its own gravitational pull.

Mhm. And I include them so that we have a consistent product every time. But one of the most successful variants on that show is called Cosmic Queries, where our fanbase simply asks us questions. And we select the deepest subset of them and put them in this book. So, I think for me it's a celebration of what it is to be human and to be on one side of knowledge and want to cross over to the other side of enlightenment. Mhm. And yes, it caters to curiosity, and that's all I think some adults have lost.

And so maybe it rekindles that." The embers rekindle, and perhaps it will reignite a flame once more, because you know it was there when you were younger. So, I think that's how you... That's why you were feeling that way about it. Because it makes you feel young again. And wide-eyed. And thank you for noticing the National Geographic DNA in the book. It's a beautiful book. And we don't just stop at the scientific illustrations. There's art too. Yes. Yes. Carefully chosen artwork that evokes the themes or ideas of the narrative.

So, yes, thank you for mentioning that. Right, so is it always an exciting time in astronomy and astrophysics? Or have there been periods of stagnation analogous to those in physics? I... You know, I have a feeling that in physics, certainly, in any generation, there's a striking sense of, at least on the theoretical side, just spinning the wheels and not necessarily making perceptible progress. But intuitively it seems that it could be different in astronomy and astrophysics. Is there? That's a perceptive point, and let me try to address it, regardless of whether I've fully answered it or not .

In Physics, what you're referring to, I think, is a kind of revolution or evolution of ideas. Right? And you don't have these things every day. You know, you have maybe once every generation. And every year in between they're filling in the gaps between these ideas. And they don't usually make headlines, even though they're inherently exciting for a physicist. So, in astrophysics, sometimes ideas matter deeply, yes. But what happens more often is that strange things are discovered. Right? Or interesting things. Water on the moon, in the craters of the moon.

A black hole in the galaxy, at the center of the galaxy, a photograph of the black hole at the center of the galaxy. I mean, things that exist in the universe because the universe is so vast and has so many different kinds of objects that in all our catalogs, we probably miss something that's one in a million or even one in a billion. And when that's discovered, it makes headlines. And so no, it doesn't rethink the whole field, but it's definitely fun to inventory, talk about it, characterize it, and try to figure it out.

Now, I did one thing for At one point, I was a postdoctoral fellow at Princeton, and Princeton has our flagship journal, the Astrophysical Journal, all on one wall. Right? From the very first issue, its first edition, 1895, the Astrophysical Journal, to the present. And I thought to myself, " Hmm, let me do this experiment." And I found the exact middle of that wall of all the periodicals. And I said, "What date will that be?" And that was 5 years ago. So, that would be the midpoint.

And as I did that, and kept having that, what I discovered is that the average time interval was 18 years. It fluctuated between 15 and 18 years. So, the total amount that was published doubled every 15 years. Now, not everything is quality. You understand that. I understand. But as a first measure of the pace of things, that was very enlightening to me. And it said that yes, I mean, when you're living on the exponential curve, every day feels like you 're living in special times. And I remember going back, I have a book about the sun written by an astronomer named Charles Young.

He was actually at Princeton at the time. I have two versions of the book. One that came out around 1880, the late 1880s, and another that came out in the 1890s. It was like the second edition. And like, you know, 5 or 8 years passed and You read the preface in the second edition and said, "Our advances are so great in our understanding of the sun." We had to launch another one. "And I was thinking, ' You have no idea what a huge breakthrough this is.'" "Yes, of course, that's what it looks like when you're on an exponential growth curve." Everyone feels like they are living in special times.

The biggest change, and once again, I have a layman's view of advances in astronomy, actually. To address the observational side of things for a moment. The biggest news of my life , I think—I mean, leaving aside very sensual things like gravitational waves—is simply the fact that we've gone from talking only about planets in our solar system to confirming their existence elsewhere. I mean, we famously lost Pluto , but we gained I don't know how many planets at this moment. How many extrasolar planets have been cataloged?

More than 4,000. Yes, and it's increasing rapidly. Yes. Yes. And so, I mean, what is the safe assumption now that our own galaxy has hundreds of billions of planets? I mean, and I mean, what is the number of planets, we do this calculation and you, in the section, you know, are we alone in the universe? But you can ask a different set of philosophical questions, something that might excite you. You can look at all the layers of bias that are inherent in how we answer these questions.

Because even in your statement, you said, "Well, how many planets?" Because the life you know and the life I know lives on one planet. But maybe life also lives on moons. Maybe it lives in the atmosphere. Maybe it lives in clouds of gas. So, we go through all the biases. There's a carbon bias, right? We are carbon-based life. Some of these biases, I think, are totally legitimate. But if you really want to search with the widest possible net, also consider the Goldilocks zone. Much has been written and spoken about for decades, since the 1950s and 1960s when this concept was first formulated, where we know that life thrives, needs, and thrives on liquid water.

So, if we put a planet in a star system, not too close, the water will evaporate. Not too far away, the water will freeze. So, there's this zone, this belt around any star where a planet would naturally have liquid water. And you need these atmospheric conditions to sustain it, of course, but You 're not fighting against it. It would happen naturally if conditions allowed. And then, we learn, wait a minute, the sun isn't the only energy source in town. Okay? Jupiter and its tidal stresses on the surrounding moons are an energy source.

So, one of Jupiter's moons , Io, is the most volcanically active place in the entire solar system because Jupiter is pumping it with energy. And then, now we have to think, if life needs the heat, the heating energy of a star, it only needs one energy source , why does it have to have a star? And then, you go on and then we learn, every model of the solar system that we build, of any star system when it's born, most of the planets that form are unstable orbits, and they fly off into interstellar space.

There may be more rogue planets than planets bound to their local star systems. So, you say, " Well, that's not a good prospect for life." "However, the Earth still has energy sources in its core. Yes. That's how volcanoes arise and all those vents in the middle of the sea that pump very hot water to the bottom of the oceans. If you're a life form thriving on that, you don't even care if you've ever orbited the sun. You could be the bed of a frozen lake on top of frozen ice, but down there, you could be swimming on your back in your heated hot tub .

So, this notion that we want to look for a habitable zone with the Goldilocks zone can be unnecessarily restrictive as we move forward. Mhm. So, now, how have your intuitions been influenced regarding the prospect that we are alone versus the seemingly equally surprising prospect that the galaxy and the universe are teeming with life? Have you had changes in how you weigh these probabilities throughout your life? Yes, that's a great way to ask that question. I would say the probabilities have changed, as they have changed only because we've learned new things, but not because I've had to reassess what I already knew." I was thinking.

I've always been very open to the possibilities of the universe, given its size, the diversity of objects, and its age. Practically anything you can imagine being possible, we think is possible. But there are other very good reasons for some of the biases we're invoking here. For example, there's a famous episode of the original Star Trek where they find a life form that's basically made of rock and moves through it like we move through the air. It's rock-based life, and an active ingredient in many minerals is silicon.

So, it's silicon-based life, and that was their attempt at it in the 1960s. It was silicon-based life , rather than carbon-based life . Well, they didn't pull silicon out of their asses, did they? Why do people think about silicon-based life ? If you go back to the periodic table and remember why the elements form columns, the columns have similar valence electrons , which means that if you're above or below another element in a table in the periodic table, you can make similar molecules with all the same other atoms.

Mhm. Okay, let's find carbon. Well, there it is at the top of the chart, number 12. What's directly below it? Silicon. So, every atom you can make with carbon , you can make with silicon. So , why not create an entire parallel life system where silicon is the basis instead of carbon? And so, that 's a perfectly legitimate chemical extension of your bias as you do the research. My rebuttal to that is that you don't need to do that because, first, carbon is extremely sticky. It clings to itself in multiple bonds, and so does silicon, but what you really get is that carbon, depending on exactly where you are in the universe, is between five and 10 times more abundant.

So, carbon will already be added before silicon, you know, figures out how to put on its pants in the morning. And so, I don't need to really think about life forms based on an isotope of bismuth or even silicon. So, I think carbon is the way to go here. Given the diversity of chemical elements it offers us . And I don't know If I answered your question directly. Oh, did I change any of my assessments? Yes. So, the Fermi paradox is what you're discussing there. And I want to clarify the Fermi paradox because I think most people who invoke it don't know the full weight it carries.

Okay. So, you can do the thought experiment. So, the physicist Enrico Fermi famously said: "If there is life in the galaxy, then it should be teeming with life and they would have already visited us." Where are they? "Okay? So maybe they're not even there. Perhaps it's worth explaining why this seems so logical. I mean, just in relation to any kind of time and which one exactly. So, you might ask yourself: 'Well, what is the width of the galaxy?'" "So, 100,000 light-years." Okay. So, this seems intractable.

So, let's say you never reach the speed of light. But let's say we reach 20% of the speed of light. Well, that means you could cross the galaxy in 500,000 years. All good. But most stars are not within a galaxy's diameter of each other. They are much closer. So, for example, the Alpha Centauri system from Earth, four light-years away, at 20% of the speed of light, you get there in 20 years. Right? And you can jump from star to star. So, imagine this is one of those machines whose name I've forgotten.

You go to a planet and then use a robot, and then the robot builds two copies of itself, and then they are launched to other planets. Right? And then there are either people or aliens. So, they arrive on a planet and then say, "Okay, time to go to more planets." And now you go from one planet to two, to four, to eight star systems. It turns out that if you did that, going to two only when you landed on one, you could reach two raised to the nth power, right?

So, no matter how many years are carried over into your n, you can easily populate the entire galaxy on an evolutionary timescale. Mmm. Easily. Yes. And just like you can do that in some, you know, tens of millions of years. But the planet has existed for billions of years. So, where is everyone? That's the question. And the other intuition here, the other element of this image, is that if complex life is ubiquitous, you would expect certain civilizations to be millions of years ahead of us. I mean, given, you know, almost 14 billion years to begin this experiment, it would be a miracle if all complex life were at precisely the same point in its technological evolution.

Therefore, finding ourselves not surrounded by evidence of technological alien life suggests that it may not exist. Because, you know, again, where is everyone? Yes, and you're right. We are very behind in this. First, you have the age of the universe, which is 14 billion years. So, you have the solar system that is five, four, and a half billion years old. So, ask yourself, how old is the branch of the tree of life called primates? Okay, if primates were your best chance, or mammals, let's say, your best chance at, quote, intelligence on Earth, we didn't really start until after the dinosaurs, and that was basically yesterday, 65 million years ago.

And the Earth had already existed for hundreds of millions of years, generating life. So, imagine a planetary system that was a billion years ahead of us. Yes. If there were any driving force behind intelligence, we would be overshadowed by any intelligence that manifested itself. And the comparison I like to make, and I'll come back to Fermi in a moment, is that comparison you always hear about DNA between a chimpanzee and a bonobo, say, and a human. You know, it's something around 90, 99, I don't know, percent identical DNA.

And people who want to continue thinking that humans are special will say, "But what difference does that half percent make?" And they huddle together in that middle percent and celebrate everything that we are and that chimpanzees are not. But I prefer to put the question a little differently and say: "Suppose the difference between humans and chimpanzees is as small as half a percent of DNA in the intelligence vector, whatever that vector may be. Suppose it's that small." Well, do it... Well, what do you mean? We have the Hubble telescope, poetry, and philosophy.

And they stick a branch into a hole to get rid of termites. And I say: well, maybe the difference between them is small. You don't want to think about it that way, but imagine. So now let's imagine an alien that is 5% along that same vector beyond us, beyond the chimpanzee. What would we look like to them? There is no reason to think that we would not appear different to them than chimpanzees appear to us. Because an intelligent chimpanzee can stack boxes and reach a banana.

This is what a small child can do. So, what does an intelligent human being do? Well, we can, you know, consider Stephen Hawking to be an intelligent human being. And they 'll laugh and say, "Oh, he's theorizing about black holes in the brain, just like little Timmy here who just got home from preschool." So, that's half a percent. So now imagine 5 %, 10%. And the simplest expression of an idea would transcend our most intelligent capacity for understanding. Just like when you approach a chimpanzee and say, " What time is it?" He has no idea what you're talking about: "Do you want a cup of coffee at Starbucks?

Are you going to catch a plane? Do you want to go to the library? " None of that makes sense to them, and those are our simplest sentences. So, I think about this all the time, which makes me wonder if the search for intelligent life, SETI, isn't itself a bit arrogant because it presupposes that some other species has our intelligence and not something so far beyond us that it wouldn't be interested in who and what we are. One solution to the Fermi-Fermi paradox is that we are to aliens what earthworms are to us.

You don't walk down the street and a worm crawls out of the damp soil, and you don't say, "Wow, is that worm thinking? Let me figure that out ." Unless you're a dewormer, no, you're not thinking that. So, one of them is that they studied Earth and there's no sign of intelligent life that interests them. But I have my favorite explanation for the Fermi paradox. And forgive me for not remembering who to give credit to for this, but I don't claim this idea as my own.

Whatever the necessary impetus is for you to want to, say, colonize planets with ease, right? You go to a planet, have children, they colonize two planets and then go to other planets. Whatever that desire may be, it contains the seeds of its own destruction . What happens when planets start to become scarce? Your desire to do this, risking your life and limbs, means it's deep within you. You need that planet. You want that planet. And then you go out and then there's someone else trying to claim the planet and then you have an interstellar war.

Competing for the limited space of planets in the galaxy. Yes. And then you think to yourself, " Well, we are..." It's a version of the big filter argument that I believe originated with Nick Bostrom. He certainly talked a lot about it. He may have learned it from someone else, but I think it 's Bostrom, but I mean the more general idea here is that this places most of the onus on the technology. The thing is, when you become technically sophisticated enough, you've almost certainly built a destructive technology, and you know, whether it's specifically weapons of war or artificial intelligence or something that escapes you and with enough technical skill to colonize the galaxy, it becomes self-destructive, but almost by definition.

I mean, there are many ways to kill yourself, and having all your incentives as a species misaligned means you simply self-extinguish. So, I would say that this would be a subcategory, or perhaps both are categories, of the phenomenon of self-destruction in highly intelligent creatures. Because what this specifically implies are the same impulses that instilled in colonial Europe. Right? So here we have Spain, Portugal, England, and the Netherlands. And they all want to conquer the world. So, initially, they have their own territory. But then they meet.

And then the whole system implodes because they can't share it because they want to own it. And this notion has already manifested itself in this world. And that was the implosion of Europe and its colonial customs, from the era of the great explorers to the era of the great collapse of colonial empires. Therefore, it is not difficult to imagine this as a fundamental truth without having to analyze the alien's psychological profile. It's just one of those basic and simple facts that can manifest themselves regardless of the form of life.

Well, going back a second and returning to Fermi, how has your perception of the proliferation of life, or the lack thereof, changed after we discovered things like amino acids in meteorites and in comet tails, which are the building blocks of life that seem quite ubiquitous? Yes, and that's part of what we find encouraging for those who are hoping for life elsewhere, because I can summarize that statement in one simple fact. If you were to rank the abundance of chemical elements in the universe, element number one is hydrogen, number two is chemically active, number two is helium, which is not chemically active, but it's there, but it's a large number two.

The number three is oxygen. The number four is carbon. The number five is nitrogen . Oh my God. Yes. So, everything is on the menu. Of the five main elements of the universe, the seventh is a ham sandwich. They are contained within what we call biochemistry. And that's why, as I said, if we were made of something exotic, like, I said, an isotope of bismuth, you could have an argument to say that God made something special on Earth because this thing cannot be found anywhere else.

But if we...Then, if there's anything to it, life is opportunistic, right? She makes very good use of what she has and...Another fact , which is not often mentioned, but has to be in the equation is, uh, you know, the oldest fossil evidence comes from life, from about 3.8 billion years ago. And the Earth began 4.5, 4.6. So, for a long time, for decades, people subtracted those two numbers and said, "Okay, life took 600 million years." That's still pretty fast, considering we've been around for 4.5 billion years.

Right? It 's still quite fast. It's small compared to the life expectancy on Earth. But it's even better than that. Again, I'm assessing the speed of this. Because early Earth was subjected to what we call a period of heavy bombardment. There were two such periods. Heavy bombardment, the Earth is still, to put it politely , accumulating matter from the nascent solar system . The most blunt way to put it is that it is constantly being hit by comets and asteroids because it has strong gravity in its region.

It's clearing its orbit, and all that material ends up going somewhere and landing back on Earth. And so the Earth is gaining mass, and as it gains mass, it gains even more gravity, it gets even better at it, and over that time, the Earth's surface is sufficiently affected that the temperatures prevent the formation of complex molecules. Because under high temperatures, the molecular bonds break, and every time you try to experiment with them, they fall apart. Therefore , it is not conducive to life experiences. Therefore, if you want to start the timer, wait until the heavy bombardment period is over.

That was 4 billion years ago, not 4.6. So now you start the timer. The Earth has a chance to cool down and produce complex molecules and initiate the birth of biochemistry, and there you have it . The Earth transitioned from organic molecules to self-replicating life in a period between 1 and 200 million years ago, during the early universe and on primitive Earth. And that's amazing. So, if this happened so quickly using native ingredients on a planet that just formed like any other planet, then nobody who has studied this problem goes around saying that we are alone in the universe.

Although there is the added improbability , whatever it may be, of transitioning from a single-celled and, I suppose, multi-celled life form to a technologically advanced civilization. I mean, you could argue that we barely manage it and there's really no sign of it, but for us, there's no sign of natural selection producing anything resembling civilization without us. So, again, we have...we're collecting samples of this in a very narrow time window, and who knows what the next few million years might bring. But I think it'll... I mean , just sharpen your Fermi intuition here.

If you had to bet or assign a probability to one of two outcomes or to one of two states of affairs, one where alone with respect to complex life or to sentient technological civilization building life . So, there may be microbes elsewhere in the galaxy, but there 's nothing like us yearning for other star systems versus the galaxy that was or is teeming with advanced life, and we don't see it, and for whatever reason, we don't see it, which seems less surprising to you or less improbable.

Yes, no...I have to think about it the way you phrased it, but let me...it's because I don't entirely agree with that part of your premise. So, look at beavers . Okay, beavers are mammals , they have large brains relative to other branches of the tree of life, and they fully exploit the resources in their environment. Ah, there's a tree over there. I'm going to use this tree to dam this river, and I'm going to build an underground dam. Right? Is this different from that? We use trees, well, first we use grass to make huts.

This was available, then we used trees. That's very convenient. Then we found metal. Oh my God, let's use this. Okay. And then we learned how to make alloys. Let's do this. And then we learned chemistry. Let's do this. So yes , certain levels of intelligence are needed to further explore one 's environment, but the simple act of exploring an environment is not unique to humans. That's my first point . Secondly, the Romans were no less intelligent than anyone who followed them. Right? Intelligent in terms of what their brains could figure out .

But they didn't have alien communication technologies. They didn't have radio telescopes. They weren't going to space. So imagine the Roman Empire and the aliens are waiting for a signal to return through space. And there is no sign of a return. Then they will say there is no space. They are still trying to do arithmetic with their Roman numerals . That was the problem. Yes, they needed Arabic numerals for that. Yes, but people forget that Roman numerals don't have a zero. Yes. You can't represent zero with Roman numerals, and that's why the calendar—the Christian calendar, the Gregorian calendar, and the Julian calendar—doesn't have a year zero.

It spans from 1 BC to 1 AD. And since they didn't have it , nobody could understand it. So yes, arithmetic is difficult. I think they would have discovered something. I think they were intelligent people . In the fullness of time. You know, I mean , I understand your point, and we should feel humbled by how much change can occur on such large timescales, right? I mean, you look at the rest of what's on Earth with us now, and it's hard to imagine anything evolving into the kind of species that could do more than we're managing to do, but we're only looking at asynchronous lines of evolution, right?

And given the millions of years, basically everything is potentially available. And millions is a small number compared to billions, right? One billion is 1,000 times greater than one million. And here we were, some kind of shrew the size of a fist or smaller, or some kind of rodent scurrying underfoot trying to avoid becoming appetizers for the T-Rex. And this is how it would have turned out if the dinosaurs hadn't been unlucky. And an asteroid carries them out, opening up the niche, an ecological niche that allows mammals to evolve into something more ambitious than a rodent.

Meanwhile , rodents are still among us. So, I want to show people , in case they haven't understood, that we went from rodents to humans in 65 million years, and that's an extremely small fraction of a billion years, and the Earth has existed for 4 billion years. So now comes the tricky part. If you align it— this is a little thought experiment— if you simply place the Earth's timeline on the wall from left to right, from beginning to end. And then you blindfold yourself, like, tie the tail to the donkey.

And then you walk up to him. You don't know where you are, and you get caught in the crossfire. In most places in that timeline you're considering, Earth only had single-celled life. Complex life arrived relatively late, lasting half a billion years. Mmm. And then there's what we call intelligent life and large-brained mammals , even smaller than that. The point is, if Earth is any indication, if it ever comes to that , then it will happen quickly. So imagine if he had arrived sooner. Or, on the other hand, imagine that the asteroid had never arrived.

There would still be dinosaurs here today. Do you know how I know this? Because dinosaurs existed as a community for 300 million years before the dinosaurs, before the asteroid. So, what are 65 more than 300? They would still be here . So what this tells us is that what we consider intelligence is clearly not important for survival. Otherwise, cockroaches would have really big brains, right? So perhaps the biggest mistake here is thinking that intelligence is an inevitable consequence of evolution, when all that would be needed is a broken branch.

Within it, all mammals could have been removed from the vertebrate food chain, and then we would have nothing as we consider intelligent creatures today. Yes, but if you run this experiment billions and billions of times, well, there you have it. That's the answer. As long as we assume that we are by no means unique, and that we are a species of Earth, and if multicellular life is ubiquitous in the galaxy or the universe and you only have these hundreds of billions, ultimately trillions of similar experiments to run, then it is very difficult to imagine that you don't have at least tens of millions of instances of technologically advanced life.

That's how you end up winning the argument in the end. You say, "Oh, what are the chances of that happening ? One in a million? Right, one in a million, and there are a hundred billion star systems out there." So, do the math. Nobody thinks we're alone. Yes, well, but is that really the opinion in the field? If you gathered people at a conference of physicists, astrophysicists, and astronomers, do you think a large majority would say that advanced life is ubiquitous in the universe? I think the only sensible way to do this is to have a sample from one person, so let's start with that and ask in what fraction of Earth's total timeline Earth has had what we would call intelligent life?

Or life with a big brain. Yes. And in what fraction of that period did it have intelligent life? Ah, it's the Drake equation. And in what fraction of that period did it have intelligent life with technology? So, if you do that, you'll have a set of fractions that you can layer onto the entire stellar population of the galaxy. Even using highly conservative estimates, you don't arrive at the conclusion that we are the only life form out there. And as I said, if you look at the actual map of the galaxy where we find these 4,000 exoplanets, that little circle around the star has to be close enough to know if there's another planet nearby.

Mmm. And you say to yourself, "Wow, that's what leads to the analogy that comes from the SETI Institute with Jill Tarter and Seth Shostak, where they say: if you're going to say, 'Well, how could we have found life?'" "We haven't found life yet. And that's like taking a cup, emptying a glass, throwing it into the ocean, pulling it out and saying: the ocean doesn't have whales, from that small sample of the vast ocean that you know you still need to explore. Mhm, yeah. What do you think is the limit to getting a really optical view of an exoplanet?

I mean, any of these big telescopes that you describe in your book that are available online, how close are we to seeing something of interest in another solar system? Yes, that's a great question. So, you can ask. Let's ask again. If you 're on the Moon, how well can you see the cities of Earth? Not very well. Those images you see on screensavers, where you have the space station orbiting, you know, they've increased the brightness of those cities so that they can stand out as beautifully as they are.

But if you go a quarter of a million miles away from them and stay on the Moon, they become much less visible. And that 's our closest neighbor in space. And let me quantify that. Imagine a globe of Earth of..." Classroom. And I always get sad because they're always color-coded. And then, you think of Earth as a place divided by countries, not unified by land, water, and atmosphere. That's just me getting sentimentally cosmic about it. But, you might ask, "Well, at what altitude above this globe would you find the International Space Station?" " Half of the people I asked move away about 30 cm." No, it sits 3/8 of an inch above the surface.

All good. So, where would the moon be? Well, we're so tired of seeing the Earth and the moon drawn in a textbook that people tend to place the moon maybe 30 or 20 cm away. No, the moon is 9 meters away. Where would Mars be located ? 1.6 km away. The space is vast. So, to get a direct image of a planet, well, yes, it might be on our horizon, but to get an image in a way that we see roads and cities, I don't think that's unrealistic.

But I have one... I say this, but smiling because I know what we're already doing. All good. You want to see life forms waving back at you. What I want to see is any evidence in the atmosphere that someone is alive on the surface of that planet. Yes. And these, we collectively call biomarkers . Right? So, if you... Well, I did n't know that. I had to figure one of those things out on my own, which I learned as I got older, wiser, and more intelligent.

So, you grow up and see these science fiction stories and pick up Star Trek again , for example. You know, they never wore spacesuits. You know? Have you ever wondered about that? Never. Never. They roamed around on all sorts of planets. No space at all. Okay. I also wonder about the clothes they wore, but it doesn't matter. That was in the 60s. You were very young. Okay, I remember. All good. So, I can use my age to brag. Yes. So, they never wear spacesuits. Why? Because they have sensors and they say, "Captain, it's an atmosphere of oxygen and nitrogen.

Okay, let's go down." If you did enough research, you would simply find atmospheres of oxygen and nitrogen. What I didn't know at the time, and I think they didn't know either, is that we only have oxygen because we have life. Okay. That's the only reason. And not just because we have life, but life is constantly producing oxygen. Because oxygen is chemically highly reactive. So, if you start with a planet that was born with oxygen, it will disappear. He will react to all sorts of things and will reach zero in a very short time.

So, the fact that we have an active fraction of 20 to 21% of oxygen in the air tells you that something is constantly producing it, and that is photosynthesis in plant life. So, if you find a planet that has a stable supply of oxygen, oh my God, put that at the top of your list . And there are other unstable molecules, such as methane, although there are other ways to produce methane. But the people who are in the business of studying the chemistry of atmospheres have a long list of chemical molecules that will be the product of all the types of life that we know occur here on Earth.

And one of them was phosphine. You should remember the news. They found phosphine in the atmosphere of Venus. It's not so hot, scorching on the surface, but as you go up a bit, it's a little cooler. Phosphine, no one can figure out how you produce phosphine except through the natural chemistry of life itself. So, that made it headline news . Perhaps it has been questioned for other reasons since then, but we have this cottage industry of people studying the atmospheres of exoplanets. Now that we have the exoplanet catalogs ready for our analysis.

And I think that's where the answers will come from. Mmm. And what... One last point about this is that I joke that if you find a planet that has hydrocarbons in its atmosphere, but also pollution, soot, and other things, that would be the surest sign of the absence of intelligent life. Yes. By polluting their own air. And one last thing I'll say about the atmosphere is that the thickness of our atmosphere is to Earth what the peel of an apple is to an apple. Okay. So we think of it as a huge ocean above us, but it's not, and in fact it's quite fragile.

So, this ties in very well with the recent news about aliens among us. And I imagine you were bombarded with all sorts of human-origin communication about this behind the scenes because, well, even I was, and this isn't my area of ​​expertise. But then, what we had, or you know, we're recording this in the second week of June. And then, we had recent revelations in the press that the Pentagon and the Office of Naval Intelligence, primarily, gave up and admitted that we are in the presence of technology that they cannot explain.

And they presented some confidential evidence, apparently, that is supposedly better than the things that leaked and the media seized upon, and they've been really important stories that weren't at all skeptical, uh , and didn't build any legacy of, you know, skeptical debunking of that kind of material, uh, in their reporting. And then we have 60 Minutes and the Washington Post and the New Yorker, the New York Times, I mean, really more or less everyone in sight gave a very fair and, one might even say, credulous audience to these reports.

In my eyes, it's not really clear what's going on . I said this on someone else's podcast , on Lex Fridman's podcast, that I received a sort of advance communication—advance in terms of the timeline, not the details— that this was coming. And you know, I was urged to prepare my brain to receive these startling revelations so that I could help shape a public conversation about it. The new consensus, which was intended to be...once again, it seems to me that the bomb never dropped and...I want to know your opinion on this, but what I was asked to anticipate was that the people who are in the best position to assess the evidence, the people who have the radar evidence, the Navy pilots who have the dashcam video, the analysts who have analyzed this data for several decades, have formed a consensus that there is no way what they are seeing is a mere artifact of glitches in our technology.

This leaves no room for any truly skeptical interpretation. No, we are dealing with a technology so advanced that it could not possibly be of human origin, and we don't know what to make of that fact. I think my first question before we receive your full download, Neil, was: did someone contact you and ask you to prepare yourself for what was coming? Yes, I've been interviewed at least a dozen times in the last 10 days. Most recently, a few hours ago , for ABC's daytime program, The View.

So, you were right to recognize that. If you want to continue listening to this conversation, you will need to subscribe at samharris.org. After doing this, you'll have access to all full episodes of the Making Sense podcast, along with other exclusive subscriber content, including bonus episodes and AMAs, as well as the conversations I've had on the Waking Up app. The Making Sense podcast is ad-free and relies entirely on listener support. And you can sign up now at samharris.org.