Cosmologic philosophy: cyclical universe (Introduction)

by David Turell , Saturday, August 06, 2022, 19:59 (840 days ago) @ David Turell

An endless cycle of bouncing back after contracting and then expanding. Ths articlc says it douesn't exist:

https://phys.org/news/2022-08-universes.html

"In trying to understand the nature of the cosmos, some theorists propose that the universe expands and contracts in endless cycles.

"Because this behavior is hypothesized to be perpetual, the universe should have no beginning and no end—only eternal cycles of growing and shrinking that extend forever into the future, and forever into the past.

"It's an appealing concept in part because it removes the need for a state called a singularity that corresponds to "beginning of time" in other models.

"But a new study by University at Buffalo physicists Will Kinney and Nina Stein highlights one way that cyclic or "bouncing" cosmologies fall flat.

***

"'People proposed bouncing universes to make the universe infinite into the past, but what we show is that one of the newest types of these models doesn't work," says Kinney, Ph.D., professor of physics in the UB College of Arts and Sciences. "In this new type of model, which addresses problems with entropy, even if the universe has cycles, it still has to have a beginning."

***

"'Unfortunately, it's been known for almost 100 years that these cyclic models don't work because disorder, or entropy, builds up in the universe over time, so each cycle is different from the last one. It's not truly cyclic," Kinney says. "A recent cyclic model gets around this entropy build-up problem by proposing that the universe expands a whole bunch with each cycle, diluting the entropy. You stretch everything out to get rid of cosmic structures such as black holes, which returns the universe to its original homogenous state before another bounce begins."

"'But," he adds, "long story short, we showed that in solving the entropy problem, you create a situation where the universe had to have a beginning. Our proof shows in general that any cyclic model which removes entropy by expansion must have a beginning."

"'Unfortunately, it's been known for almost 100 years that these cyclic models don't work because disorder, or entropy, builds up in the universe over time, so each cycle is different from the last one. It's not truly cyclic," Kinney says. "A recent cyclic model gets around this entropy build-up problem by proposing that the universe expands a whole bunch with each cycle, diluting the entropy. You stretch everything out to get rid of cosmic structures such as black holes, which returns the universe to its original homogenous state before another bounce begins."

"'But," he adds, "long story short, we showed that in solving the entropy problem, you create a situation where the universe had to have a beginning. Our proof shows in general that any cyclic model which removes entropy by expansion must have a beginning.'"

Comment: some old battle. For me. A much more telling point is the state of space. All evidence points to it being flat, which means it will expand until it dies. It can be cyclic only if space is curved and will come back to itself as a single point.