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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

#81

Post by jandrese »

Sapere_Aude wrote: post #56

Why do people still waste time and money on these post hoc theories of Dark Matter / Dark Energy, which were invented to explain anomalies in the conventional cosmological model like galaxy rotation curves? We neither have direct evidence nor do we not have alternative explanations - to the contrary. They shouldn't even qualify as scientific theory, since they are neither falsifiable, have no predictive power or are…

People have been looking everywhere for a better solution than Dark Matter and especially Dark Energy for decades now without success. They may hate the theories, for good reason, but nothing better has materialized yet. Modified gravity always seems intriguing until you slam in a counterexamples for example.

This is a lingering sense that we have missed something big.

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

#82

Post by ben_w »

Timwi wrote: post #39
beeforpork wrote: post #31

Earlier quoted context omitted.

Why would you be concerned? Earth and everything living on it will be long dead by then, and probably gone and swallowed by the sun. And maybe the Sun dies before that, too. So what would be particularly concerning about merging of our galaxy with another one?

> Earth and everything living on it will be long dead by then How do you know? It's not far fetched to think that, if humans don't go extinct in the meantime, they will continue to find ways to shape the world according to their needs. By the time the Sun goes red giant, we may well have found a way to alter the orbit of Earth. By the time the Sun goes supernova, we may be able to move to another star. Who knows. But…

> How do you know? It's not far fetched to think that, if humans don't go extinct in the meantime, they will continue to find ways to shape the world according to their needs.

I'd say it's pretty far-fetched to imagine humans caring about things 7 generations into the future, let alone 3e7 generations.

> By the time the Sun goes red giant, we may well have found a way to alter the orbit of Earth. By the time the Sun goes supernova, we may be able to move to another star. Who knows.

We already know how to meaningfully alter Earth's orbit over such timescales[0], the sun won't go super-nova anyway (too small)[1], and we know what it would take to increase its lifetime by a few orders of magnitude even if organising ourselves on the numerical and time scales required is beyond us[2].

But even maximally extending the lifespan of Sol would take us to perhaps 100 trillion years if we're very lucky, and that's if we actually engage in the exact kind of long-term thinking that people currently criticise the Longtermism movement for even daring to consider.

[0] https://arxiv.org/abs/astro-ph/0102126

[1] https://en.wikipedia.org/wiki/Supernova#Core_collapse

[2] https://en.wikipedia.org/wiki/Star_lifting#Stellar_husbandry

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

#83

Post by IAmBroom »

drpossum wrote: post #60
Sharlin wrote: post #40

Earlier quoted context omitted.

In the end, to be fair, we measure both of them with photons (quite literally – GWs with laser interferometry and neutrinos by looking for Cherenkov flashes).

[flagged]

Wow, troll much?

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

#84

Post by cryptonector »

Sharlin wrote: post #68
AnimalMuppet wrote: post #66

Earlier quoted context omitted.

OK, but when I stepped on the scale this morning, I used photons to read what it said. That doesn't mean that I'm detecting EM rather than gravity.

A fair point, but it should be said that a scale also only measures a some sort of an EM-based proxy for gravity, typically the compression of a spring either mechanically moving a needle or being electronically detected with strain gauges[1]. I guess my point was that when we peer to the skies and detect EM radiation at various bands, that's also just a proxy for something else that we're actually interested in. The…

Nowadays it's all piezo.

It is useful to point out that everything we do is electronic in some way. All normal forces are really electronic forces. It just isn't the case that we can't observe forces other than EM, just that in the end everything has to become EM for us to be able to observe it, and... that's not too remarkable considering that we're made of electronic matter and are of such scales that nuclear forces are not relevant except in so far as they make chemistry possible.

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

#85

Post by cryptonector »

thom wrote: post #27

Were I to have a religion, it would be following the poor, stressed programmer tasked with creating (on some insane deadline) the universe we inhabit. To fix various performance bugs, he (I like to think he's called Colin) had to implement all sorts of hacky workarounds: lazy loading so some information is only calculated when it's observed, a maximum speed of information propagation to enable sharding, a system to i…

The standard model of cosmology is basically this but without making reference to something Prime Mover that caused it all to start, a Colin or God. The best science could do is show us that the universe just is, but even that wouldn't answer the question of why or where it came from even if the future and the past were infinitely long.

There will always be at least one turtle.

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

#86

Post by cryptonector »

wantoncl wrote: post #35
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?

> The laws of thermodynamics pretty much guarantees this anyways does it not? Yes, but: http://www.thelastquestion.net/

One of my favorite sci-fi stories!

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

#87

Post by pdonis »

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…

Thank you for linking to this paper. It looks like a very comprehensive review of the "theory space", so to speak, that's currently being explored.

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

#88

Post by pdonis »

sigmoid10 wrote: post #22
mr_mitm wrote: post #21

Earlier quoted context omitted.

I'm not sure where you got that I'm confusing something. For what's it worth, my name is in the author list of that paper.

>where you got that I'm confusing something From the idea that the constant that equates to dark energy in the stress energy tensor is not commonly thought to be a constant. People didn't call it that way as some joke. This isn't even up to astronomers, this is something that mathematicians will tell you. And it could potentially cause some real trouble not just for our models of the universe but for the basic mathem…

> it could potentially cause some real trouble not just for our models of the universe but for the basic mathematics of relativity if it is changing.

The Einstein Field Equation can accommodate models in which the density of dark energy changes with time just fine. The paper mr_mitm linked to discusses such models. There is no "real trouble" for the basic math of relativity involved here at all.

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

#89

Post by russdill »

thom wrote: post #27

Were I to have a religion, it would be following the poor, stressed programmer tasked with creating (on some insane deadline) the universe we inhabit. To fix various performance bugs, he (I like to think he's called Colin) had to implement all sorts of hacky workarounds: lazy loading so some information is only calculated when it's observed, a maximum speed of information propagation to enable sharding, a system to i…

Ok, well then he went and screwed the pooch with non-locality.

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

#90

Post by araes »

mellosouls wrote: post #7

Lots of non-paywalled coverage out there in the mainstream press, eg: https://www.theguardian.com/science/2025/mar/19/dark-energy-...

Agree that this is a much better summary, and generally gets to the point much better with relatively clear summaries of the issues. Once you get down to the mid-section, the NYT notably has a somewhat clearer description of the initial issues with supernovas and using them as references. The Dark Energy article [1] and the "Light Curve" portion of the Type Ia Supernova article [2] on Wikipedia offer further reading.

[1] https://en.wikipedia.org/wiki/Dark_energy

[2] https://en.wikipedia.org/wiki/Type_Ia_supernova#Light_curve

- Human's believe that Type Ia supernovas are the best way of measuring distance, because of an implied standard brightness and light curve that helps to avoid issues with only measuring redshift.

- Human's initially believed supernovas were supposed to show reduced brightness, further away, with a predictable reduction based on distance.

- Observations showed that supernovas were actually dimmer than expected.

- Implies that the universe is actually expanding, because supernovas were receding faster than expected.

- New results appear to show that the acceleration is decreasing. "there is something pushing galaxies away from each other, but it is not constant. It is declining.” "gently lifting its foot off the pedal"

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