快猫短视频

This story is part of our Cosmic Perspective special, in which we confront the staggering vastness of the cosmos and our place in it. Read the rest of the series聽here.

Since the opening act of the universe 13.8 billion years ago, a diverse set of characters have trod the boards 鈥� stars, planets, moons, quasars. But if you tend to get fidgety at the theatre, there is bad news: this cosmic performance has at least 100 billion years to go. Which raises a question: are we living at a special moment 鈥� the cliffhanger before the interval 鈥� or is this just an inconsequential moment in the mid-plot?

One hint that this is a special instant involves a swathe of observed properties of the universe known as fundamental constants. These include the strength of gravity, for example, and the fine-structure constant, known as alpha, which determines the way matter and light interact and thus how stars burn. If these numbers were just a shade different from how they are, then life might be impossible.

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Why is it all so perfect? One possible answer is that these constants aren鈥檛 so constant. Perhaps they have been gradually changing over the life of the universe and we happen to live at an auspicious blip in time. at the University of Cambridge has spent decades investigating this idea, in his case in relation to alpha. Based on precision measurements of the cosmos, Webb has claimed in the past that alpha has indeed morphed 鈥� although he now , thanks to systematic errors in the instruments used to gather data. 鈥淭he existing measurements are close to meaningless,鈥� he says.

Inconstant constants

Webb is optimistic that with artificial intelligence and new instruments, like the James Webb Space Telescope, it won鈥檛 be long before he has reliable data. However, it must be said that most physicists thumb their nose at the idea that the constants of nature have changed 鈥� and at the general notion of our universe being special. at Tufts University in Massachusetts has suggested that we follow the 鈥減rinciple of mediocrity鈥� and assume that there is nothing particularly special about us.

Still, there is a simpler sense in which we live at a special moment in cosmic history. Life as we know it couldn鈥檛 have formed before there were stars to fuel it and planets at a suitable distance from their star on which it could develop. Life also couldn鈥檛 arise as soon as stars appeared, because it requires elements heavier than the hydrogen and helium that made the first stars to support complex biochemistry. 鈥淪everal generations of stars are needed to build these [heavy elements] up to a level where you get planets and the chemistry of life,鈥� says at the University of Sydney, Australia. That means at least a few billion years after the big bang.

Star formation is slowing

Being intelligent enough to appreciate this also requires special conditions, says Lewis 鈥� and they are fast disappearing. That is because significant intelligence seems to take billions of years to develop 鈥� it did on Earth 鈥� and the star formation that can support it is slowing. Intelligence-supporting stars won鈥檛 be around for that long, relatively speaking. 鈥淢ore than 95 per cent of the stars that will ever exist have already been born,鈥� says Lewis. 鈥淪tar formation is winding down: in the future, stars like the sun will become rarer and rarer.鈥�

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In 100 trillion years, all stars will have died and the chances of habitability as we know it will have dwindled to nothing. That is the end of the show. Cue infinite darkness.

Practically speaking, we don鈥檛 even have that long. Before then, the mysterious repulsive force known as dark energy will probably drive the universe apart to the point that no light will be able to reach Earth from any other star. Even if life were still tenable, doing astronomy would be impossible. In that sense, at least, we are part of a singular generation of humans who can ask and answer questions of the cosmos. 鈥淲e truly live in a special time in the life of the universe,鈥� says Lewis.