Far out cosmology: expanding universe will not tear apart (Introduction)

by David Turell , Tuesday, January 09, 2024, 19:59 (108 days ago) @ David Turell

Latest conclusion from a ten-year study:

https://www.sciencealert.com/most-precise-measure-of-dark-energy-confirms-universe-wont...

"The announcement in New Orleans may take us closer to a better understanding of this form of energy. Among other things, it gives us the opportunity to test our observations against an idea called the cosmological constant that was introduced by Albert Einstein in 1917 as a way of counteracting the effects of gravity in his equations to achieve a Universe that was neither expanding nor contracting. Einstein later removed it from his calculations.

***

"The DES results are the culmination of decades of work by researchers around the globe and provide one of the best measurements yet of an elusive parameter called "w", which stands for the "equation of state" of dark energy. Since the discovery of dark energy in 1998, the value of its equation of state has been a fundamental question.

"This state describes the ratio of pressure over energy density for a substance. Everything in the Universe has an equation of state.

"Its value tells you whether a substance is gas-like, relativistic (described by Einstein's theory of relativity) or not, or if it behaves like a fluid. Working out this figure is the first step to really understanding the true nature of dark energy.

"Our best theory for w predicts that it should be exactly minus one (w=-1). This prediction also assumes that dark energy is the cosmological constant proposed by Einstein.

"An equation of state of minus one tells us that as the energy density of dark energy increases, so the negative pressure also increases. The more energy density in the Universe, the more repulsion there is – in other words, matter pushes against other matter. This leads to an ever-expanding accelerating Universe. It might sound a bit bizarre, as it is counterintuitive to everything we experience on Earth.

***

"..this measurement may signal the end of "Big Rip" models which have equations of state that are more negative than one. In such models the Universe would expand indefinitely at a faster and faster rate – eventually pulling apart galaxies, planetary systems and even space-time itself. That's a relief.

Comment: that's a relief if correct. An ever-expanding universe at an ever-increasing rate certainly suggests it could tear up.