Already Vuniverse: Why some physicists think we could live in a Groundhog Day universe

Already Vuniverse: Why some physicists think we could live in a Groundhog Day universe

About 13.8 billion years ago, all the energy in the universe was condensed into a single point. Until suddenly it is no longer the case. The resulting detonation was the most massive explosion in the entire history of the universe, but from there energy was formed in all matter, atoms, molecules, planets and all life on Earth.

It’s the Big Bang theory, a model that explains much of what we observe when we look at the universe. Between all the stars, galaxies and gas clouds is the cosmic background radiation – a residual heat from the Big Bang, which is still faintly visible today, and is one of the strongest proofs obvious that the universe started from a single point. Measurements using several different tools, including satellites and telescopes, indicate that this residue is consistent with patterns of an explosive birth of our universe.

Even Albert Einstein toyed with the idea of ​​a universe that springs back and forth, dying and expanding, over and over again.

The universe is still expanding, at a rate of 73 kilometers per second per megaparsec, a metric known as the Hubble constant. You can imagine how it works by imagining two dots on a ball. As the balloon is inflated, the distance between the two points increases; fill the balloon with dots, and everything seems to drift away from everything else over time as the balloon inflates. If the universe is the ball and the dots are galaxies, that’s a good metaphor for how our universe changes over time.

Many scientists predict that in tens of thousands of billions of years the universe will eventually run out of steam and “freeze”. It will be the heat death of the universe. Also known as Big Freeze, this theory describes the ultimate fate of the universe as it approaches maximum entropy. When this threshold is reached, there is no more thermal energy or heat. Stars cannot undergo nuclear fusion, so no life can exist.

But an intriguing alternative, even if it doesn’t carry much scientific weight, is that before everything freezes over, the universe could fall back – all the galaxies clumping together, swirling closer and closer instead, until until it compacts again to a point. . Astronomers call it the Big Crunch. (Big Bang, Big Crunch… I sense a theme here.) In the distant future, as everything condenses, tightens more and more, it could once again create the conditions for a Big Bang.

This is the basic premise behind the theory of the cyclic or oscillating universe, which actually dates back to the 1930s. Even Albert Einstein toyed with the idea of ​​a universe that springs back and forth, dying and s extending again and again. Much like the 1993 romantic comedy “Groundhog Day,” starring Bill Murray as a weatherman stuck in a time loop, reliving the same day over and over again, our universe could cycle through different iterations over and over. Crunch, bang, crunch, bang.

At that time, Richard Chace Tolman, an American physicist and cosmologist, was the first to really popularize this idea, but he first sought to disprove it. At the beginning of the 20th century, the Big Bang theory was not common. Most people believed that the universe had always been there and always would be. In fact, for many years “Big Bang” was used with derision, a way of dismissing how ridiculous the idea was to astronomers. But Tolman noticed that the ratio of hydrogen and helium – the two most abundant elements in the universe – could not have happened in a static universe. An explosion probably kicked things off.

In 1934 Tolman published his book “Relativity, Thermodynamics and Cosmology”, inspired in part by descriptions of an expanding universe model first proposed by Edwin Hubble in 1929. He and Hubble actually published together once, an article describing the expansion of the universe. It is quite clear that stars and galaxies are unfolding as in our balloon metaphor. What was less clear to Tolman and other astronomers was whether or not gravity would eventually bring the universe together. “He took the possibility of an oscillating universe very seriously,” said a biography of Tolman.

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As the Big Bang became an accepted scientific theory, the oscillating universe theory faded away. But some physicists, like Paul Steinhardt and Neil Turok, took the idea, tweaked it somewhat, and breathed new life into it. A central part of the updated theory concerns dark energy, a mysterious and not fully understood aspect of the universe that is believed to be the driving force behind our expanding universe.

In their 2007 book “Endless Universe: Beyond the Big Bang”, Steinhardt and Turok describe how they came across this theory by postulating that dark energy could have existed before the Big Bang and is so powerful that it will eventually pull the universe together using a “spring-like” motion that stretches “branes”, a term used in theoretical physics to describe a type of structure in the universe.

If this were true, it means our universe is on a seemingly endless loop, a cosmic version of Groundhog Day on a rhythm spanning billions, if not trillions of years.

“Potential energy would only be noticeable again after nine billion years of expansion and the density of matter and radiation had fallen below the potential energy,” Steinhardt and Turok wrote. “Only then would the potential spring energy take over, just as it did before the bang. Once again, it would act as a source of dark energy that accelerates the stretching of the branes, exactly what we are witnessing today…”

“Of course, if it could happen once, nothing would prevent the whole process from happening again and again. The detonation could continue indefinitely,” Steinhardt and Turok continued. “Suddenly and inadvertently, we had revived an ancient idea that we had been taught was impossible: a cyclic universe.”

If this were true, it means our universe is on a seemingly endless loop, a cosmic version of Groundhog Day on a rhythm spanning billions, if not trillions of years. Nevertheless, the theory is not widely accepted in science. It would be quite difficult to test the oscillating universe theory, as no information would likely survive the cycle of a Big Bang or Big Crunch, although mathematical physicist Roger Penrose has argued that black holes from previous universes might have survived the transition.

There are many models of the universe, but for a model to be useful it must be testable. The Big Bang Theory is the best model we have of the entire universe, how it formed and where it is going. That could be totally wrong, but good luck disproving it. But until we know more about dark energy – arguably the most mysterious of the constituent matter and energy in the universe – we may not have enough evidence pointing to a repeating cycle. universal death and rebirth.

But curiously, there may be other universes with different fundamental constants that have a cyclical quality. Of course, the existence of other universes would require the multiverse theory to be real. Incidentally, while there are aspects of our universe that hint that we may be living in a multiverse, that too is not provable.

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