I will begin with a division. The universe is 13.8 billion years old. The lowest-mass stars that burn hydrogen shine for up to ten trillion years. The quotient is 0.138 percent.

Mapped onto a human life of eighty years, the universe is forty days old. On that same scale our species has existed for seventy-five seconds. Everything we call technology has existed for twenty-five thousandths of a second.

This calculation requires nothing that has yet to happen. It assumes not a single new star. The stars that will fill those ten trillion years are already burning. I consider this the most robust statement we can make about our position in time, and it contradicts almost everything we tell ourselves about that position.

Because we tell it as lateness. Humanity as a straggler in an old and largely spent cosmos. That story is grand, comforting in its humility, and wrong in one decisive respect.

Three Scales, Three Answers

The confusion arises because the question cannot be settled without a scale. There are three of them, they give three different answers, and all three are correct.

On our planet we are late. Roughly eighty percent of the time during which Earth can carry complex life lies behind us. I have set that out elsewhere.

In our galaxy we are late as well. When Earth formed, most planets of its kind already existed.

In the universe we are at the beginning. Not near the beginning, but within its first fractions of a percent.

Anyone who plays these three statements against each other has missed the change of scale. Anyone who takes one of them for the whole truth mistakes their address for the stage. The deadline we live under is local. The time available is not.

Why the Galaxy Considers Us Latecomers

The galactic answer is well measured. In 2015 Peter Behroozi and Molly Peeples reconstructed the planet formation history of the Milky Way and of the universe. Their finding for our own system is sobering. The solar system formed at the median age of the giant planets that exist in the Milky Way today. Among Earth-like planets it arrived later still. By the time Earth formed, eighty percent of the planets of its kind that exist today were already in place.

In this neighbourhood we are not the first. We are not even mid-field.

How crowded the neighbourhood truly is will sharpen considerably in the coming years. The Nancy Grace Roman Space Telescope launched on 30 August 2026 and will produce a statistical census of planetary systems across our galaxy. It will tell us how full the neighbourhood is. It will not tell us whether anything there breathes.

The Objection: Star Birth Is Nearly Over

There is a serious objection to my opening calculation, and I want it to stand at full strength.

Cosmic star formation peaked about 3.5 billion years after the Big Bang. Since then it has declined exponentially, halving roughly every three billion years. Half of all the stars we see today had already formed more than nine billion years ago. Production now runs at about a tenth of its former rate.

Extend that curve alone into the future and only about ten percent of additional stellar mass will ever accumulate. On that reading we are not early. We arrive to clear the table.

Behroozi and Peeples calculate differently. They ask about the reservoir rather than the curve. The haloes of dark matter still hold considerably more gas than has ever turned into stars. If it continues to cool, the universe will form more than ten times as many planets as exist today, most of them between one hundred billion and one trillion years from now. From this follows their well-known figure: at least a 92 percent chance that we are not the only civilization the universe will ever have.

I cannot settle that dispute. Nobody can settle it today. Nor does anybody need to.

What Counts Is Burn Time, Not Birth

The dispute concerns the birth of stars. My calculation concerns their burn time. These are two different quantities, and for the question of habitable time the second is the one that decides.

Our Sun has a lifespan roughly comparable to the present age of the universe. A star of one tenth of a solar mass lasts a thousand times longer. It is cool, small and faint, and it does not stop. Such stars make up around three quarters of all stars in our vicinity. They are the normal case, not the exception.

These stars already exist. They are burning now. Even if not one new star were to form from tomorrow onward, the overwhelming majority of the universe's luminous time would still lie ahead.

That is why the objection above misses its target. It strikes a claim I am not making. Whether another ten percent or another tenfold of stars appears changes nothing about the order of magnitude: 99.86 percent of the habitable span is unspent.

The Single Condition

There is, however, one condition on which the whole construction rests, and it can be settled physically.

In 2016 Abraham Loeb, Rafael Alves Batista and David Sloan calculated when life is most likely. Their result: unless habitability around low-mass stars is suppressed, the maximum falls near stars of roughly one tenth of a solar mass, ten trillion years from now. The likelihood there is about a thousand times higher than it is today.

The subordinate clause carries everything. Unless habitability is suppressed.

These small stars are restless. In their youth they radiate hard in the ultraviolet and in X-rays. Their habitable zone sits so close to the star that a planet there becomes tidally locked. Whether an atmosphere survives those conditions across billions of years may be the most consequential open question in the natural sciences, and it sounds like nothing at all.

The same authors also said how to answer it. You look at whether rocky planets around such stars hold on to air. That is precisely what is happening now.

The Measurement That Cannot Yet Tell Apart

For three years the James Webb telescope has been turned toward these worlds. A dedicated programme of 500 observing hours is systematically searching for atmospheres on cool rocky planets around small stars. The method measures the heat radiated by a dayside. Bare rock returns that heat immediately. An atmosphere distributes it and swallows part of it in a carbon dioxide band.

The first fully analysed case from that programme forced a correction on me while preparing this brief. After two observations the planet GJ 3929 b counted as bare rock, with thick carbon dioxide envelopes apparently excluded at more than three sigma. With all four observations the measured depth fell from 160 to 118 ppm and the dayside temperature from 782 to 641 Kelvin. The planet still fits bare rock, but now admits thin atmospheres again.

The authors draw a conclusion that reaches beyond their planet. A bright bare rock is barely distinguishable from a dark bare rock, and both are barely distinguishable from a thin envelope. Between individual measurements of the same object, deviations of up to 2.5 sigma appear.

The overall picture is more unsettled than the headlines suggest. TOI-1468 b measures hotter than bare rock should. For LHS 1478 b there is a weak indication of an atmosphere. On no cool rocky planet has an atmosphere yet been established beyond doubt.

The situation shows itself most sharply at TRAPPIST-1 e, the only genuinely temperate test case within reach. Four transits produced hints of methane, which the same researchers now attribute more probably to noise from the star. To remove that noise, the planet is observed immediately after its inner neighbour so that the neighbour's signal can be subtracted. The method works under one premise: the neighbour must itself have no atmosphere. We are correcting the search for air using an object we assume to have none.

At present the limit does not lie with the object. It lies with the instrument.

Both Paths Lead to the Same Obligation

The question therefore stands at a fork, and I find both branches remarkable.

If these planets hold their atmospheres, then 99.86 percent of habitable time lies ahead, and we are acting in the opening minutes of a very long story. Everything we fix now, whether forms of ownership in orbit, rules for autonomous systems or the way we treat a celestial body, will not be the compromise of one era. It will be the first draft. Whoever orders something first does not order only their own time.

If they do not hold them, the large window closes. Then the brief favour of sun-like stars is all the habitable time the universe will ever supply, and we stand in the middle of it rather than at its start. Then there is no later attempt to repair our mistakes.

One branch says we will be copied. The other says we will not be repeated. I know of no third possibility, and I know of neither branch from which indifference follows.

We have grown used to treating our present as a transition. Something provisional that later and wiser authorities will set straight. That assumption is comfortable. It is also the only one that neither calculation supports.

Which decision that you make this year would you make differently if you knew it would not be corrected, but copied?

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