'More than a hint' that dark energy isn't what astronomers thought
nytimes.com
nytimes.com
> 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.
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 mathematics of relativity if it is changing. Motivating that alone will we hard, not to speak of the consequences down the line.
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.
It shows up in the Einstein Field Equation as part of the stress-energy tensor. That is not a problem at all.
> and basically be something that enters alongside a cosmological constant.
The "cosmological constant" can just as easily be moved to the RHS of the Einstein Field Equation and also considered part of the stress-energy tensor, yes. There is no issue with that at all.
> Making dark energy or Λ itself vary
Is something nobody has claimed to be doing, as the GP said, so you are attacking a straw man.
"Varying dark energy density" does not mean trying to make the cosmological constant vary. It just means adding some other component of stress-energy whose density does not have to be constant, but which still produces accelerated expansion. Anything with pressure less than minus 1/3 of its energy density will do that. A scalar field is the simplest such thing, but not the only possibility. None of this poses the slightest problem for the Einstein Field Equation.
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-...
Astronomers spend a lot of time arguing with each other about whether they have properly incorporated all their systematic uncertainties. For measurements of dark energy this very quickly gets you into the weeds of Type Ia supernova physics (which is made more difficult because we don't know for certain what Type Ia supernovae are), stellar physics in Cepheids, the effect of metallicity, selection bias effects, and on and on.
The author Dennis Overbye about his retirement in December 2024 [1]
https://www.theguardian.com/science/2025/mar/19/dark-energy-...
[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"
The DESI 2024 hint for dynamical dark energy is biased by low-redshift supernovae
Wasn’t ‘the universe won’t end in a “big rip” the widely held idea?
The laws of thermodynamics pretty much guarantees this anyways does it not?
Some estimates put the star formation period from 1 to 100 trillion years.
I’d be more concerned about our collision course with the Andromeda Galaxy in four to five billion years.
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 let's not get distracted. We need to tackle climate change first. That's our first self-made extinction challenge.
Hmm, yes, I don't. I just honestly don't get why that galaxy collision is concerning. What's the concern? For whom? Four billion years is very, very long compared to humankind's evolutional history. Homo may be 2 My old, that's 1% of the time it takes the sun to rotate a single time around the center of the galaxy. Sol completed already ~20 rotations since it exists. Homo's whole history is 1/2000th the time ntil Andromeda will arrive. So, what's the concern? Humankind will not exist for many, many hundreds of millions of years.
> It's not far fetched to think that, they will continue to find ways to shape the world according to their needs.
Humans fixing Earth's and Humanity's problems is totally out of character. I did not even consider it.
Earth's death is certain. Sun's death is certain. Galaxy collision might even go unnoticed for quite a while -- it's not like millions of stars would crash into each other -- very unlikely. It's more like a reshaping, but what's concerning about that? More supernovas around us? Yeah, maybe.
But why is it more concerning that any other demise? It is an interesting question, I think, about perceived danger.
They said more concerning than the end of star formation. That doesn't mean they are losing sleep over it.
Existence, universe, galactic processes and time scales are very fascinating. I do loose sleep over it, but because it is impossible to grasp, so marvellous and unlikely. And it is treated like shit by too many of my fellow earthlings. My worries are much closer and much more concrete than a galaxy collision, and I think much more urgent.
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
We don't even survive for centuries.
What about the CMBR, I've never heard anyone say that's decaying, but surely it's not an infinite source of energy?
Yes, but:
Unlimited resource drain caused by conscious blobs of particles (a.k.a humans) invoking recursive thought patterns over their own existence.
Workaround: ponder function can return a feeling of existential dread accompanied by increased weights for headache "sensation", causing blob to terminate process.
Estimate: M
Label: Backend
Should I rebase on your workaround?
It doesn't have a huge bearing on the story, so can be skipped - and I think a lot of people probably should.
To Amazon!
Hn has no spoiler tags but one of the really big things to me is this https://gist.github.com/IanCal/d9667ae9c6ce15315191a36c6b3af...
The time required for fixing bugs isn't really an issue in this case, he can take as long as he likes.
No, the many-worlds interpretation shows that our universes are merely containers with copy-on-write behavior :)
I imagine there's some serious optimization involved to make it all fit in memory.
Unfortunately he was shady and found to be embezzling from the company so he was fired. Only then did the team actually look at that code. Absolutely incomprehensible mess, and it looked like he left back doors in so he and his pals could manifest weird stuff in the universe and fuck with the inhabitants.
Like get this... a human draws a five pointed star on the ground and says some weird stuff and it trips some code that looks like obfuscated malware that calls out to a dodgy server, but we can't remove it because the whole thing is a giant spaghetti monolith.
The Lord put together a proper team of angelic hosts to rewrite the whole thing using solid software engineering practices, but of course that was aeons ago. But when it finally does ship we will get a new heaven and a new Earth with a whole list of promised features.
Archangel Michael, who is in charge of the project, keeps moving the deadline back, but he says they're making progress. It's a microservice architecture.
It's even hackier than that. Everything moves at c always, if not through space then through time or some combination.
There will always be at least one turtle.
Step 1 is making a new detector, then we talk about unknown unknowns.
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 photons aren't interesting in themselves, it's what we can infer about them by following the causal chain backwards. In that sense, it doesn't matter whether the photons are produced on Earth or a billion parsecs away.
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.
We have done some amazing things in spite of what appears a crippling limitation.
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 supported by any independent experimental confirmation.
Oh,there are presents under the Christmas tree, it must've been Santa Claus!
They are patchwork "solutions" at best and by far not the only explanation for what's happening.
It's the aether rehashed.
This is a lingering sense that we have missed something big.