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'More than a hint' that dark energy isn't what astronomers thought

nytimes.com

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Re: 'More than a hint' that dark energy isn't what astronomers thought

#11

Post by mr_mitm »

timewizard wrote: post #6

> If dark energy really is Einstein’s constant, the standard model portends a bleak future: The universe will keep speeding up, forever, becoming darker and lonelier. Distant galaxies will eventually be too far away to see. All energy, life and thought will be sucked from the cosmos. The laws of thermodynamics pretty much guarantees this anyways does it not?

No, it could also end in a big crunch or big rip scenario. They'd have a finite lifetime of the universe.

Re: 'More than a hint' that dark energy isn't what astronomers thought

#13

Post by flowerthoughts »

timewizard wrote: post #6

> If dark energy really is Einstein’s constant, the standard model portends a bleak future: The universe will keep speeding up, forever, becoming darker and lonelier. Distant galaxies will eventually be too far away to see. All energy, life and thought will be sucked from the cosmos. The laws of thermodynamics pretty much guarantees this anyways does it not?

Thermodynamics says there will be equilibrium, not that it will be all dark. But all the visible stars will run out at some point, and since nothing new can get into that sphere, each place in space will be "dark" at some point.

What about the CMBR, I've never heard anyone say that's decaying, but surely it's not an infinite source of energy?

Re: 'More than a hint' that dark energy isn't what astronomers thought

#14

Post by adrianN »

flowerthoughts wrote: post #13
timewizard wrote: post #6

> If dark energy really is Einstein’s constant, the standard model portends a bleak future: The universe will keep speeding up, forever, becoming darker and lonelier. Distant galaxies will eventually be too far away to see. All energy, life and thought will be sucked from the cosmos. The laws of thermodynamics pretty much guarantees this anyways does it not?

Thermodynamics says there will be equilibrium, not that it will be all dark. But all the visible stars will run out at some point, and since nothing new can get into that sphere, each place in space will be "dark" at some point. What about the CMBR, I've never heard anyone say that's decaying, but surely it's not an infinite source of energy?

To harness energy you need a gradient. Once everything will be in equilibrium there is no gradient.

Re: 'More than a hint' that dark energy isn't what astronomers thought

#15

Post by ben_w »

flowerthoughts wrote: post #13
timewizard wrote: post #6

> If dark energy really is Einstein’s constant, the standard model portends a bleak future: The universe will keep speeding up, forever, becoming darker and lonelier. Distant galaxies will eventually be too far away to see. All energy, life and thought will be sucked from the cosmos. The laws of thermodynamics pretty much guarantees this anyways does it not?

Thermodynamics says there will be equilibrium, not that it will be all dark. But all the visible stars will run out at some point, and since nothing new can get into that sphere, each place in space will be "dark" at some point. What about the CMBR, I've never heard anyone say that's decaying, but surely it's not an infinite source of energy?

The CMB is red-shifting due to the expansion of the universe. If the big bang was infinite then the CMB is also infinite, but at some point it becomes so redshifted that photons from it have a wavelength larger than the Hubble volume.

Re: 'More than a hint' that dark energy isn't what astronomers thought

#16

Post by mr_mitm »

flowerthoughts wrote: post #13
timewizard wrote: post #6

> If dark energy really is Einstein’s constant, the standard model portends a bleak future: The universe will keep speeding up, forever, becoming darker and lonelier. Distant galaxies will eventually be too far away to see. All energy, life and thought will be sucked from the cosmos. The laws of thermodynamics pretty much guarantees this anyways does it not?

Thermodynamics says there will be equilibrium, not that it will be all dark. But all the visible stars will run out at some point, and since nothing new can get into that sphere, each place in space will be "dark" at some point. What about the CMBR, I've never heard anyone say that's decaying, but surely it's not an infinite source of energy?

In the standard model, the temperature of the CMBR evolves reciprocally with the scale factor, so it will go to zero.

Re: 'More than a hint' that dark energy isn't what astronomers thought

#17

Post by fedeb95 »

An interesting part from a different article mentioned here in the comments:

The results do not meet the so-called five-sigma threshold of statistical certainty that is the gold standard in physics for claiming a discovery. But many in the collaboration have shifted in recent months from a position of scepticism to confidently backing the finding.

Source: https://www.theguardian.com/science/2025/mar/19/dark-energy-...

Re: 'More than a hint' that dark energy isn't what astronomers thought

#18

Post by sigmoid10 »

fedeb95 wrote: post #17

An interesting part from a different article mentioned here in the comments: The results do not meet the so-called five-sigma threshold of statistical certainty that is the gold standard in physics for claiming a discovery. But many in the collaboration have shifted in recent months from a position of scepticism to confidently backing the finding. Source: https://www.theguardian.com/science/2025/mar/19/dark-energy-..…

If you combine it with other data it's from 2.8 to 4.2 sigma. Pretty strong and it has gone up since last year with more data. Nothing definite yet, but certainly intriguing.

Re: 'More than a hint' that dark energy isn't what astronomers thought

#19

Post by sigmoid10 »

mr_mitm wrote: post #4

I know it makes for a "better" headline, but don't be mislead by it thinking Astronomers actually thought dark energy was a cosmological constant, period. Read section 1.1 of the Euclid review paper from 2016 to get an impression straight from the horses mouth. > Why then is the cosmological constant not the end of the story as far as cosmic acceleration is concerned? There are at least three reasons. https://arxiv.o…

Don't confuse accelerated expansion with the cosmological constant. Accelerated expansion's origin is most likely the cosmological constant aka dark energy, but they are not the same thing. The cosmological constant itself arises naturally (kind of how an integration constant emerges for indefinite integrals) when you derive the field equations of general relativity. It is basically a geometric degree of freedom inherent to the Einstein-Hilbert action. Any astronomer who fit any model of the universe to some dataset in the past 25 years was fitting a constant. And even this new paper acknowledges that it will take some tremendous effort to convince people that this constant really is changing over time (which introduces a slew of theoretical issues that need to be explained). It will be particularly interesting to see how (if at all) this can be reconciled with measurements of things like the CMB, because stellar and galactic astrophysics is much less well understood.

Re: 'More than a hint' that dark energy isn't what astronomers thought

#20

Post by mr_mitm »

fedeb95 wrote: post #17

An interesting part from a different article mentioned here in the comments: The results do not meet the so-called five-sigma threshold of statistical certainty that is the gold standard in physics for claiming a discovery. But many in the collaboration have shifted in recent months from a position of scepticism to confidently backing the finding. Source: https://www.theguardian.com/science/2025/mar/19/dark-energy-..…

I think it's worth noting that the five sigma standard traditionally comes from particle physics, though. Cosmology doesn't have the luxury of being able to generate arbitrary amounts of data, and in fact has been a precise science for only sixty years or so. Hubble's first measurement of the expansion of the universe was off by a order of magnitude.
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