The lecture begins about two and a half minutes in, and lasts twenty minutes.

Last Lecture (2018)

I was honored to be chosen by the senior class of 2018 to give their “last” lecture, which I gave at sunset on the steps of Morehead Planetarium and Science Center (in unusually chilly/windy conditions for April).

Here are a couple of links to news articles about the lecture:

University Gazette: Bold predictions on civilization’s momentum fill hopeful Last Lecture [also]

Daily Tar Heel: Professor Dan Reichart’s ‘Last Lecture’ focuses on human connection, outer space

Here is the text of the lecture:

Thank you everyone. 

When I got the ask to do this back in February, I was humbled.  In fact, it’s been a very humbling year.  And not in the negative way one might expect from someone who just got their ass blown up :)  But in everything that happened afterward…from the students who reacted quickly and collected water to keep my burns from deepening…to the emergency personnel and the amazing team of doctors and nurses who went above and beyond in their treatment of my wounds…to my colleagues who generously covered my classes.  And to my loving wife and family who did everything else until I was able to return to work in January. 

I of course expected this from my family, but the show of support that I received from across the UNC community – from students…many of whom I didn’t even know…right up through the Chancellor, and even the Governor – made me realize – perhaps for the first time in my 15 years here – that I was also part of a much larger family, and one that cares very deeply about its members.  As I said, the whole thing was a humbling experience, and in the best of possible ways.

And now I am once again humbled, and honored, to be giving the senior week last lecture.  Last lectures have been popular since even before Carnegie Mellon Professor Randy Pauch’s standout last lecture in 2007, and they’re supposed to be delivered with all of the wisdom and insight that only someone at the very end of their career should be able to convincingly muster :)

Well, I’m not there yet, hopefully anyway.  In fact, I did a quick back-of-the-envelope calculation and…assuming I can steer clear of any more explosive devices…and refrain from repeatedly kicking at them if I do come across one…it looks like I have almost 2,000 lectures to go…plus or minus :)

So let’s call it a mid-career lecture for me, but for you, the senior class 2018, this will of course be one of your last lectures, at least here at UNC. 


So, as you all know, I’m an astronomer.  And astronomers like to think big.  We think about space, on the largest scales imaginable.  And we think about time, going all the way back to the beginning, and as far forward as logic and reason are willing to carry us.

Now, thinking big spatially – that can also be humbling, and not necessarily in the best of possible ways. 

For hundreds, if not many thousands of years, humanity’s most learned scholars believed the Earth – and by association, us – to be…at the center of all things.  The sun and the planets orbited us…as did the stars, all fixed to a sphere that marked the outermost boundary of the universe – not far beyond Saturn :)  It was a small and tidy universe, and one in which we were clearly very special.

But with the development of new technologies, and with the solidification of scientific reasoning, by 400 years ago we were able to show that this happy view of the universe, with us at the center of all things, simply wasn’t factual:  Earth, it turned out, was just one of the planets, and all of the planets orbited the sun.  

Of course, it took a while to convince everyone of their now diminished place in the grand scheme of things, and frankly, if recent polling is to be believed, now, 400 years later, one quarter of American’s still don’t believe it!

But…that’s okay.  Facts don’t get offended if people choose to ignore them :)

And over the past 200 years, our expulsion from paradise only got worse.  We found that our sun was no more special than our planet, instead being just a star, no different than the countless many that fill the sky at night.

...except that they aren’t countless.  Our sun is one of a few hundred billion stars that form our Milky Way galaxy.  And our galaxy is but one of at least a hundred billion that span our universe…and that’s just the part of the universe we can see.  The true number may be infinite.

But that detail aside, let’s do the math:  That’s a hundred billion galaxies, for a total of over ten billion trillion stars…orbited by probably a hundred billion trillion planets.  And we’ve now studied enough planets to know that roughly a full billion trillion of these are Earth-like worlds, orbiting sun-like stars.  Just…like…us.

Now…that’s humbling.  Kind of makes you feel small and insignificant, and not very special at all.

Thinking big spatially can do that.  And consequently it’s probably not the best topic for what’s supposed to be an uplifting and inspiring last lecture…so let me try again :)


So, fine, we may not occupy a special place in space, but…I’ve become increasingly convinced that we occupy a special – even critical – moment in time.

The universe is 13.8 billion years old.  Our sun and the planets that orbit it are 4.6 billion years old.  And life, it arrived in our oceans almost as soon as our planet cooled down enough to have oceans, about 4.3 billion years ago.  Simple, single-celled life, after which it was a series of baby steps for the next three billion years.

But then, about a billion or so years ago, something amazing happened, and life became multicellular, allowing it to diversify into thousands, and eventually millions, of different species.  Shortly thereafter, life moved on to land.

Still, 99.8% of this billion-year span of time passed before the first humans arrived on the scene, about two to three million years ago.  And then 99% of this two-to-three-million-year span of time passed before our specific species of human – sapiens – emerged as the last one standing, about 40,000 years ago (though possibly later in Asia).

Even then, most of this time again passed before we started living in cities and recording our history, about 5,000 years ago. 

But despite the slow start, things have since been happening at an ever quickening pace.  Spurred by the agricultural revolution, our population started doubling every thousand years.  And with more people came more brains, and more connections between them – both spatially – through their close proximity in cities, and through increased travel to neighboring lands – and temporally – through the recording of ideas for future generations of brains to continue to mull over.

In both biology and computer science, a neural network consists of processing nodes, and connections between them along which information can flow.  If you want to build a better neural network, (1) you increase the number of processing nodes, (2) you increase the number of connections, or the rate that information can flow between them, and (3) you increase how much processed information you can store externally.  And this is exactly what the human race was doing, but at a meta level, with our brains as the processing nodes, and with our records and libraries as the external hard drive. 

Given this, perhaps the next leap in our evolution – not as individuals, but as a collection of networked individuals – was just a matter of time.

Humans have always had a penchant for trying to explain the unknown.  And we have a long history of preferring our own explanations – or our own group’s explanations – to those of other groups – and often to bloody ends.  But around 400 years ago, a new idea emerged from the network, and that idea was that instead of might always making right, sometimes we should just step back, and let the facts decide.

And so the scientific revolution was born.  Ideas that were contradicted by facts – no matter how cherished, no matter how desired – were discarded, making way for new ideas to take root.  And if these ideas eventually proved wrong, they would be discarded too.  This is the scientific method in a nutshell – Darwinian natural selection, applied not to organisms – but to ideas themselves. 

And this changed everything.  The scientific revolution spurred revolutions in industry and technology, in health and medicine, and driven by these new forces unleashed upon the world, in economics and politics – all revolutions that rage on to this very day.

Because of the revolutions in health and medicine, child mortality rates plummeted, and lifespans doubled, even tripled.  The time it took for humanity to double its population dropped from once every 1,000 years, to merely once every 50 years today.  The number of processing nodes in our meta neural network increased tenfold in only 400 years.

And because of the revolutions in industry and technology, the number of connections between these processing nodes, and hence the rate that information flows between us, also skyrocketed, in three ways:

(1) We have been reorganizing ourselves to be in closer proximity to one another, geometrically increasing the number of connections between us, with, as of 2006, over half of humanity now living in cities;

(2) We have dramatically improved the speed, safety, and expense of travel, which has proportionally increased the number of connections between distant regions;

Only to be surpassed by (3) a revolution in remote communication:  An exchange of ideas that used to take weeks, months, and even years by letter, can now be accomplished in minutes, and sometimes even seconds, by email, text, voice, or video. 

And increasingly, these real-time communications have been occurring not between pairs of people, but between interlocked networks of hundreds – and sometimes even thousands, and millions – of people at a time, through social media platforms.

The human neural network, as well as its external data repository – now in the form of the instantly accessible and instantly searchable Internet – are now vastly bigger, and vastly better networked than ever before, with some of the biggest advances in networking occurring just this past decade:  We are now, literally – all of us – connected at the hip.

To me, the most amazing outcome of the scientific revolution is that it’s resulted in a wild amplification of the very, underlying conditions that led to it the first place, and on which it continues to feed:  more brains, and more and better networking between them.  A perpetual feedback loop, which has been transforming humanity into something more than the sum of its parts, and which has been doing so at an accelerating, and now breakneck, rate. 

For lack of a better term, we have civilizational momentum. 

And where this momentum carries us next is anyone’s guess.  But since I’m giving the lecture…I’ll go ahead and make the guess :)


Over the next decade or two, humanity will begin to colonize the worlds around it, beginning with the moon and Mars.  It will be a novelty at first, but by the end of the century – which a few of you will see – and especially going into the next century, I imagine we’ll be sustaining sizable, and growing, populations off world.  And just when our population here on Earth will be maxing out.

But the moon and Mars, and the other worlds of the solar system, are by no means ideal.  Take Mars for example.  It’s small, cold, relatively atmosphereless, and geologically dead.  It’s not an Earth-like world.  It’s merely the thing that most closely resembles one within reach.

Now, with a lot of work, Mars can, and eventually probably will, be made Earth-like.  That said, we are now at the point in our history where we are beginning to discover truly Earth-like worlds, around the neighboring stars.  A similar, or even lesser, amount of work can probably get some of us there as well. 

How we do it will depend on the technology that we develop over the next couple centuries.  Perhaps we will use large, slow-going, generational ships.  Or perhaps we will use much smaller, fusion-powered craft that we’ll accelerate to near-light speeds.  By Einstein’s theory of relativity, the occupants could then travel for decades, but age only years, or even only months.

However we ultimately do it, with new worlds under our belt, the human neural network will be able to continue to grow, beyond the 10 or so billion brains that Earth alone can sustain.  And with 10 or so billion Earth-like worlds in our galaxy alone, humanity – or whatever we eventually evolve into – could eventually number not in the billions, but in the billions of billions.

It’s impossible to imagine what wondrous things, what depths of understanding about our existence, could emerge from such a neural definition:  We would have to have one to be able to imagine it :)


But despite not being able to see the future, the future will look back and see you, and I hope that they will do so with a sense of awe and wonder.

You will be the last generation to be confined to a single world – the generation that took the leap – and the generation that did so arguably at the most challenging, and consequential, time in our history, past or future.

When the oldest people alive today were born, the Earth was still sparsely populated.  When the youngest people alive today eventually die, the Earth will be at maximum capacity. 

This dramatic change…brought on by our scientific revolution…comes with all sorts of never-before-experienced, and frankly daunting, challenges – challenges that your generation has no choice but to face, and to solve, where future generations will need only copy, and perfect, what you come up with. 

How do we grow enough food to feed everyone?  From where do we harness enough energy to power everyone?  How do we manage our impact on the environment, now that we are sizable enough to have a significant one?  How do we educate enough people to solve these problems, or at least to make good choices when presented with solutions?

These are political and economic challenges as much as they are technical ones – challenges that many of you will be deeply involved in solving, but that all of you, as voters in a democratic society, will be responsible for acting on.

However, this is not all that we face.  In a world made ever smaller, both by dramatic increases in population and by dramatic advances in travel and communication, we increasingly face…each other.  Whether we like it or not, we are going to be increasingly in each other’s space, and in each other’s cyberspace. 

And there are a lot of people who very much don’t like it. 

A lot of people feel uneasy – even threatened – when confronted by others who don’t share their beliefs, be they religious, ideological, political, even conspiratorial.  And if they feel sufficiently threatened, they will band together and resist.  No number of well-reasoned arguments or strongly established facts can convince those who feel that their collective identity is being threatened.  If they can’t out-reason you, they will instead try to impugn you, and stir up others to do the same.  It’s a tribalistic response, and frankly, there’s no good solution for it in the short-term, except perhaps greater understanding and compassion…and systematic improvements to education in the long term.

But…these are not the only people who feel under siege.  Generally speaking, the world used to change more slowly than people lived.  But after 400 years of scientific revolution, this is no longer the case…and will never be again.  So many prepared for the world of their youth…a comparatively unchanging world…but now find themselves being run over by the very different and unexpected world of their present…and are downright terrified at what “civilizational momentum” will bring them next.

How we address these problems is every bit as important – and crucial to our species’ future – as how we address the more technical challenges of food and energy supply, climate change, and education.  In fact, these issues are all coupled, because in a democratic society, everyone decides.

I’m reminded of the old curse, “May you live in interesting times.”  And we do.  Interesting, exciting, unprecedented, frightening, challenging, and most importantly, consequential times.  A time in which our burgeoning population and technology…and finite space and resources…will – ready or not, like it or not – force us to pull together as a species, unlike at any prior time in our history. 

Simultaneously, it will be the last time we are all together as a species, as we prepare to take our first steps out into the universe, to neighboring worlds.

We often view ourselves, in the present, as standing at the pinnacle of history.  Rather, I think we’re merely at its beginning.  Thousands of years from now, our progeny, spread across the surrounding stars, will look back at your generation – the generation that took the reins at this, humanity’s most consequential, and unprecedented, moment – as one of legend, in a time of myth.

Class of 2018, you have spent your lives preparing…for these interesting times. 

With your mind on the lessons of the past…with your heart and your hands on the challenges of the present…and with your eyes agaze on the promise of the future…it’s time to go, and make it count.

Thank you very much.