(ORDO NEWS) — From the smallest bacterium to the largest galaxy: death looms on the horizon; even if, on a cosmic scale, the timescales are too large for us to truly understand.
In the end, even the universe itself must come to an end – when the last light goes out, and only cold, dense lumps of dead stars remain.
At least that’s how it is. Modern cosmological models. What if our universe does not die a cold death, but collapses, inflates and collapses again, again and again, like a giant cosmic lung?
This is not a completely accepted theory, but for some cosmologists, our universe may be just one of a long series of births, deaths and rebirths that has no beginning or end – not a Big Bang, but a Big Rebound.
Now, physicists have shown that the latest iteration of the Big Bounce Hypothesis, which solved serious problems with previous iterations, still has some pretty serious limitations.
“People have suggested discarding universes to make the universe infinite in the past, but we show that one of the newest types of these models doesn’t work,” said physicist Will Kinney of the University at Buffalo.
“In this new type of model that solves problems with entropy, even if the universe has cycles, it must still have a beginning.”
Currently, the most accepted model of our universe suggests that it emerges from a point of origin called a singularity. About 13.8 billion years ago, the Universe as we know it began to expand out of an incredibly dense chunk of time and space… for some reason.
Unfortunately, the models that support the Big Bang explanation have little to say about what such a singularity might look like.
The big bounce hypothesis, alternatively, could sidestep the singularity problem by abandoning it entirely. Instead, the collapsing universe will recover before it even reaches the moment that destroys the model.
However, this hypothesis has its own problems. An infinitely “bouncing” Universe must also have an infinitely increasing entropy, a measure of disorder in the Universe.
If the Big Bang was just one of an eternal series of explosions, then the entropy must have been really high; but it is not. In fact, if the universe had had high entropy at the time of the Big Bang, it could not have existed as we know it.
In 2019, the Big Bounce received a reprieve when a revised model was published that contained a solution to this major hurdle that had stymied the hypothesis for decades.
The researchers found that the expansion of the universe with each cycle dilutes the entropy enough to return the universe to its original state before the next bounce.
It was a huge deal, apparently bringing the Big Bounce back on the table as a plausible cosmological model; but now other scientists have done what they do best. They made a new hole in the revised model.
Kinney and his colleague, physicist Nina Stein, also at the University at Buffalo, performed a series of calculations and found that a cyclic universe cannot stretch. endless return to the past.
“In short, we showed that when you solve the entropy problem, you create a situation where the universe should have a beginning,” Kinney explained.
“Our proof as a whole shows that any cyclic model that eliminates entropy by expansion must have a beginning.”
This does not mean that the cyclical universe is dead in water. The team notes that their work does not apply to physicist Roger Penrose’s model of a cyclic universe, called conformal cyclic cosmology.
According to his version of the repeating universe, each cycle expands indefinitely without a contraction period. This is quite a complex thing, and it will require further elaboration.
For now, however, it seems like the Big Rebound will at least require a bit more thought to remain viable.
“The idea that there was a point in time before which there was nothing, there was no time, worries us, and we want to know what was before that, including scientists,” Stein said.
“But as far as we can tell, there had to be a ‘beginning’. There is a point for which there is no answer to the question “What was before this?”
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