There Are Only Impossible Things Left to Do

The idea that broke the room arrived on an ordinary afternoon, near the end of a seminar on space economics, from a student who had been quiet for most of the term.

We had been talking about cost curves — the unglamorous arithmetic of getting a kilogram off the surface of the Earth, which is the hidden tax on every dream anyone has ever had about the stars. Chemical rockets are magnificent and they are also, in a sense, a confession of failure: most of what you launch is fuel to launch the fuel. The numbers are punishing. Everyone in the room had spent weeks marinating in those numbers, and the mood had taken on the particular flatness of people who have been told, gently, that the universe is mostly closed for business.

Then the student raised a hand and proposed that we stop carrying the fuel altogether. Leave the engine on the ground. Build an enormous array of lasers, point it at a small spacecraft trailing a reflective sail, and push the thing across the solar system — and then, why not, across the gulf to another star — with nothing but concentrated light.

The room did what rooms do. Someone laughed. Someone else began, almost reflexively, to explain why it could not work — the power requirements, the pointing precision, the sheer absurdity of accelerating anything to a meaningful fraction of light speed with a flashlight, however large. The objections were not stupid. That is the thing I want to be honest about. The objections were, in fact, completely reasonable.

I smiled anyway. Not because the idea was correct. I had no way of knowing whether it was correct, and neither did the student. I smiled because the idea was impossible in the right way — impossible the way crossing an ocean in an afternoon was once impossible, rather than impossible the way a perpetual-motion machine is impossible. There is an enormous difference between the two, and the entire future turns on our ability to tell them apart.

Here I have to disarm something before it detonates. The impossible becomes possible. It is the most exhausted sentiment in the genre — the motivational-poster version of history, the thing said by men in vests at conferences. If I am going to ask you to take it seriously, I owe you more than the slogan. I owe you the mechanism.

So consider what the student actually stumbled into. Pushing spacecraft with light is a real research program with a real name. In 2016 a consortium of physicists and an unreasonable amount of money launched an effort called Breakthrough Starshot, whose stated ambition was to send gram-scale probes — chips with sails — toward Alpha Centauri at something like a fifth of the speed of light, propelled by a ground-based laser array. Stephen Hawking lent his name to it before he died. Serious people at serious universities have spent the better part of a decade working out the radiation pressure, the materials science of a sail that does not vaporize, the phased-array optics. It may not work. Most of the engineering remains genuinely unsolved. But it is not absurd. It sits on the correct side of the line — the side where the obstacle is difficulty, not law.

My student had reinvented, from first principles, in a Tuesday seminar, an idea that some of the best minds alive are quietly betting on. And the room laughed.

I am not telling this story to scold the room. I would have laughed too, at twenty. I am telling it because the reflex to laugh — and the closely related reflex to explain why something cannot be done — is the single most expensive habit our civilization has. We acquire it precisely as we acquire everything else we mistake for maturity.

Watch the sequence in a single human life and you will see the whole tragedy in miniature. A toddler reaches for the sky without first commissioning a feasibility study. A child imagines dragons without waiting for the market to validate them. Then, somewhere in the long sanding-down of growing up, we learn caution, and caution hardens into limits, and limits calcify into certainty, and — this is the fatal step — we begin to mistake certainty for wisdom. The person who can explain why a thing will not work sounds smarter than the person proposing it. Often he is smarter. He is also, frequently, wrong in the only way that matters, which is the way that forecloses the future.

It helps to remember what flight actually looked like before it happened. In October 1903, The New York Times opined that the development of a flying machine might be expected to require the combined efforts of mathematicians and mechanics over the next one to ten million years. Two brothers who fixed bicycles in Ohio managed it in about nine weeks. The Times was not being foolish; it was being reasonable, which is worse, because reasonableness is harder to argue with. The physics of flight had not changed between the editorial and Kitty Hawk. What changed was that two people declined to be reasonable on schedule.

And this is the part the slogans always skip. What separates the laser sail from the perpetual-motion machine is not optimism. It is physics. Light does carry momentum; you can, in principle, push on a mirror with a beam. That is a fact about the universe, not a wish about it. The discipline the moment demands is not the courage to ignore reality — any crank can do that, and most of them have podcasts — but the much rarer courage to find the ambition that reality permits and almost nobody has bothered to attempt. The frontier is not the place where the rules stop applying. It is the place where the rules still apply and no one has done the work.

We are, by any honest accounting, the most capable generation that has ever lived. We have machines that generate language and rockets that land themselves on their tails and telescopes that read the light of galaxies as they looked before the Earth existed. The toolkit would have looked like sorcery to anyone born before about 1950. And what do we mostly point it at?

We build slightly faster apps. We build slightly better systems for guessing which video you will watch next. We build, with some of the finest engineering talent in human history, marginally more persuasive advertisements. There is a kind of genius being spent, at scale, on the optimization of distraction, and it is the great quiet scandal of the age — not that we cannot do large things, but that we have aimed so much capacity at small ones, and called the aiming realism.

Meanwhile the oceans are barely mapped and the Moon is barely touched and Mars is an empty rumor and there are entire industries — orbital manufacturing, autonomous lunar mining, propulsion that does not require us to set fire to most of our payload — that do not exist for no better reason than that no one has yet been reckless enough to insist on them.

The next genuinely large company will, I suspect, sound ridiculous when it is founded. The next genuinely large discovery will look irrational right up until it looks inevitable. The fortunes of the coming decades will be made in the places today's experts are most confident are dead ends, because confidence about dead ends is, historically, where the money has always been left lying around.

The student stayed after class that day, half-expecting, I think, to be let down easy. Instead I told them to keep going — to do the math, find the flaw, and if the flaw was fatal, to find a more interesting impossibility. There are, after all, so many to choose from.

We have spent ten thousand years conquering the visible hills, the ones you could see from the valley floor, and we have done it so thoroughly that the comfortable work is mostly finished. What remains is the work that does not yet have a map. The frontier has gone invisible, and people keep telling me this is cause for despair.

I think it is the best news we have had in a long time.

It means the easy things are taken. It means the only assignments left are the ones that make investors nervous and experts patient and rooms full of clever people laugh. It means that the constraint on the next century is no longer, as it was for nearly all of human history, the limits of what we can build. The constraint is the limits of what we will let ourselves imagine.

There are only impossible things left to do.

Good. Let's get to work.