Reading The Fate of the Universe. Astrophysicists are the prophets of the cosmos. They are already looking into a future in which the stars go out, the galaxies evaporate and matter breaks down. At the beginning there was the energy flash of the Big Bang - in the end there will be darkness. The universe will end either with a big bang or with a long whimpering - that was already clear in the 1920s when cosmologists applied Albert Einstein's theory of relativity to the cosmos as a whole. The experts speak of a temporally open or a closed universe. Either the universe will continue to expand for all eternity, or it will have enough mass to stop the expansion and reverse it. In this case, the universe becomes smaller, hotter, and denser until it engulfs itself in a final collapse that could be expected in about 100 to 200 billion years.

The first chapter of cosmic history, the epoch of inflation, lasted only a tiny moment-unimaginable 10 -32 seconds. At the beginning, our Universe came into being with the Big Bang and immediately ballooned - hence the name (the Latin "inflatio" means "self-inflating"). This was followed by the epoch of radiation that lasted about 300, 000 years. Light and matter were in close interaction at that time, so hot and impenetrable was the soup of the elementary particles. In the first three minutes of this era, the light atomic nuclei arose. When the temperature dropped to 3, 000 degrees due to the further expansion of the universe, the electrons with the atomic nuclei united into atoms. Only now was the radiation free: space became transparent. Now began the epoch of the stars - our epoch. Over the course of many millions of years, structures formed out of what was once an almost equally distributed source gas: stars, galaxies, as well as clusters and superclusters of galaxies. Through nuclear fusion processes, stars incubate heavier elements inside, exploding and thus providing the raw material for new stars. Thanks to the heavier elements, planets could also be created - and finally, on this planet, living beings like us, who think about the evolution of the universe.

Laughlin has calculated that in about 10 to 14 years - that is 10, 000 times more than the previous age of the universe - also the galactic gas and dust clouds are depleted, the raw material for the creation of new stars. Star formation and star evolution come to a standstill at about the same time. This is the end of the star era. Then literally the lights go out in the universe.

Now begins the fourth era, the epoch of decay. The cosmic structures begin to dissolve. Space expansion drives the supergalactic clusters apart to such an extent that hypothetical astronomers in the distant future, even with the best telescopes, could no longer observe other star-islands. The celestial bodies scatter in the darkness. display

These cosmic gravity traps are the only remaining macroscopic bodies that dominate the fifth era, the era of black holes. But their fate is already sealed by the laws of nature. As Stephen Hawking of the University of Cambridge has calculated, black holes radiate heat due to quantum mechanical effects and ultimately lose mass when their ambient temperature is sufficiently low. "Black holes are not that black, " Hawking writes in his famous book, "A Brief History of Time, " which in this case is not that short.

The periods in which this happens can no longer be illustrated. They can only be calculated and named: Stellar black holes blaze in the course of about 10 years high 66 years, galactic and supergalactic need 10 high 100 years and more. They are getting hotter and eventually explode in a sudden, blazing flash of gamma radiation - "a fleeting grave for the once-existing existence of a billion bright suns, " Davies says.

In the last era, the epoch of darkness, not much is happening. Some of the remaining electrons now and then find a positron, their anti-matter sibling particles, and blast it. Sooner or later, a continually expanding universe is an abandoned, bitter-cold and pitch-black arena.

Although some details of the cosmic drama are still speculative, one thing is certain: the future will be bleak. Only a few photons, neutrinos, and a few other elementary particles float quietly and eternally isolated from each other through the endless spaces of darkness. But as boring and black as this future may seem to us, time will not stop.

"The concept of time loses some of its meaning when applied to these distant stages of the universe, " says Jamal Isalm. "The only way in which time will then manifest will perhaps be the decreasing density and temperature of the cosmic background radiation approaching absolute zero, minus 273.15 degrees Celsius, but never quite reach it. "And he adds, " Even the most speculative life forms may look back to our times and to Earth as an ideal world of sunshine and energy for billions of years, a dream world that is over and never returns. "

The cosmologist Edward R. Harrison of the University of Massachusetts in Amherst chooses a metaphor: "Apart from the original glory of the Big Bang and a subsequent galactic era lasting a few tens of billions of years, the universe is an eternal whining of dark despair."

This whimpering in the ocean of emptiness becomes more and more silent, but never mute. For Freeman Dyson, who has probably advanced further into the physics of destiny than anyone else before him, that is no reason for sentimentality. "The laws of physics do not predict a last silence, but show us that something will always happen, that physical processes will not cease, as far as we always think in the future."

=== Rüdiger Vaas

© science.de

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