NYTimes.com: A Tantalizing ‘Hint’ That Astronomers Got Dark Energy All Wrong

[John Clark]

Explore this gift article from The New York Times. You can read it for free without a subscription.

A Tantalizing ‘Hint’ That Astronomers Got Dark Energy All Wrong

Scientists may have discovered a major flaw in their understanding of that mysterious cosmic force. That could be good news for the fate of the universe.

https://www.nytimes.com/2024/04/04/science/space/astronomy-universe-dark-energy.html?unlocked_article_code=1.h00.5Kdw.QJDXLL_Dk5fk&smid=em-share

[Brent Meeker]

"If the work of dark energy were constant over time, it would eventually push all the stars and galaxies so far apart that even atoms would be torn asunder,..."

That's not true.  The estimated strength of dark energy, w=-1,  implied that galaxy clusters and any smaller groups would still be held together by gravity, to say nothing of EM and nuclear forces.

Still an interesting.  The next question will be what causes DE to change?  When it was just the cosmological constant there was no change to be explained.

Brent

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[John Clark]

On Thu, Apr 4, 2024 at 6:00 PM Brent Meeker <meeke...@gmail.com> wrote:

 > "The next question will be what causes DE to change?"

That is a very good question but nobody has a very good answer, but at least now we know that's the correct question to ask. Assuming of course this result holds up and dark energy has really been getting weaker over time, if it turns out to be true then the people who discovered this are almost guaranteed to get a Nobel prize, they would certainly deserve it.  It opens up the possibility that dark energy might eventually drop to zero or even become negative and the universe could end in a big crunch.

> "When it was just the cosmological constant there was no change to be explained."

Actually I think it makes a theoretical physicist job a little easier. If as previously thought, dark energy was an intrinsic part of empty space and you use quantum mechanics to figure out how large it will be you get a value at least 10^120 times larger than what is actually observed. If the value was exactly zero there is hope that when we know more about quantum mechanics than we do now somebody will figure out how things cancel out and we get exactly zero, but if the value is ridiculously tiny but not zero then you have to figure out how to cancel out everything EXCEPT for one part in 10^120. How in the world do you do that?!  But if dark matter is not an intrinsic part of empty space then it must be caused by a field, sort of like the inflation field that caused everything to expand enormously just 10^-36  seconds after the big bang and ended about 10^-33  seconds after the big bang. But the dark matter field would be MUCH weaker than the inflation field.  

John K Clark    See what's on my new list at  Extropolis

dmf

[Jesse Mazer]

The article at https://arstechnica.com/science/2024/04/dark-energy-might-not-be-constant-after-all/ says: 'One alternative theory proposes that the universe may be filled with a fluctuating form of dark energy dubbed “quintessence.” There are also several other alternative models that assume the density of dark energy has varied over the history of the universe.'

I'd heard of "quintessence" (a dynamical scalar field throughout space) as an alternative to a cosmological constant, does anyone know what the "several other alternative models" with variable dark energy might be?

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[John Clark]

On Sun, Apr 14, 2024 at 5:53 PM Jesse Mazer <laser...@gmail.com> wrote:

> "The article at https://arstechnica.com/science/2024/04/dark-energy-might-not-be-constant-after-all/ says: 'One alternative theory proposes that the universe may be filled with a fluctuating form of dark energy dubbed “quintessence.” There are also several other alternative models that assume the density of dark energy has varied over the history of the universe.'I'd heard of "quintessence" (a dynamical scalar field throughout space) as an alternative to a cosmological constant, does anyone know what the "several other alternative models" with variable dark energy might be?"

The word "Quintessence"covers a lot of ground, it's just a placeholder name for a hypothetical fifth fundamental force of nature that produces a field with a negative pressure (stress) and thus, according to Einstein's General Relativity, would cause the universe to accelerate. If the recent observations made by the Dark Energy Spectroscopic Instrument (DESI) in Arizona about the expansion of the universe turn out to be valid (it only has a 3 sigma and you need a 5 sigma or more to claim a discovery) and the strength of Dark Energy really does change over time, then it cannot be an inherent property of space itself as most had thought. So it must be caused by some form of Quintessence.

One very popular type of Quintessence is called, for reasons not entirely clear to me, "Phantom Dark Energy"; it hypothesizes that Dark Energy is a field that contains negative kinetic energy.  But there are problems with this idea, it is very difficult to reconcile negative kinetic energy with standard Quantum Mechanics. And in the lab nobody has ever found anything that has negative kinetic energy. And if the DESI observations turn out to be true then Dark Energy is getting weaker overtime, but Phantom Dark Energy predicts it should get stronger leading eventually to the Big Rip.

John K Clark    See what's on my new list at  Extropolis

edp