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'More than a hint' that dark energy isn't what astronomers thought
- pineaux 2y agohttps://archive.is/H23dH https://archive.is/H23dH
- menschen 2y ago[dead]
- mr_mitm 2y agoI 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.org/abs/1606.00180 https://arxiv.org/abs/1606.00180
- sigmoid10 2y agoDon'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.
- mr_mitm 2y agoI'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.
- sigmoid10 2y ago>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 mathematics of relativity if it is changing. Motivating that alone will we hard, not to speak of the consequences down the line.
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- deleted 2y ago[deleted]
- pdonis 2y ago> 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.
- sigmoid10 2y agoYou can do all sorts of stuff with the Einstein field equations (or any differential equation for that matter). People do this all the time because it's an easy paper. Many people for example make the Ricci scalar into a function. Aka "what happens if I magically introduce this." That way you can sometimes explain some stuff on one end while breaking stuff at other ends. But whenever you introduce such new degrees of freedom, you need to accommodate them somewhere in the overall picture. f(R) gravity in that sense would be better motivated, because in the infrared it boils down to a dumb extra scalar field. And you could get tons of those easily from string theory. But if you want to use local field theories of gravity to explain horizons, then you need something like holography to provide a consistent picture. Even if you go for metastable degenerate vacua, it will be really hard to explain how this leads to an apparently continuously varying cosmological constant. Is it possible? Maybe. Is it more likely that we misunderstood stellar evolution? Absolutely.
- pdonis 2y agoThank 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.
- thowawatp302 2y ago> Dark energy, the new measurement suggests, may not resign our universe to a fate of being ripped apart across every scale, from galaxy clusters down to atomic nuclei. Wasn’t ‘the universe won’t end in a “big rip” the widely held idea?
- mr_mitm 2y agoYes, big rip was clearly disfavored by available data, and heat death ("big freeze") the most likely scenario. I haven't kept up in the past few years, abut AFAIK nothing so far has changed that.
- timewizard 2y ago> 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?
- Cthulhu_ 2y agoSure, but this may be news to the target audience of the article.
- TheSpiceIsLife 2y agoStill, we’ve got a little while to go before star formation can no longer occur. 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.
- nkrisc 2y agoLike two gas clouds colliding, not like two cars colliding.
- s1artibartfast 2y agolike two flammable gas clouds colliding perhaps. Literally one of the most energetic processes in the known universe, with 100x the rate of star formation.
- nkrisc 2y agoTrue, but what I meant is it’s not like all the existing stars are going to collide and be blasted to bits.
- beeforpork 2y agoWhy 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?
- mellosouls 2y agoLots of non-paywalled coverage out there in the mainstream press, eg: https://www.theguardian.com/science/2025/mar/19/dark-energy-mysterious-cosmic-force-weakening-universe-expansion https://www.theguardian.com/science/2025/mar/19/dark-energy-...
- mr_mitm 2y agoI think this is also the better article. The other one is all over the place.
- araes 2y agoAgree 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 https://en.wikipedia.org/wiki/Dark_energy [2] https://en.wikipedia.org/wiki/Type_Ia_supernova#Light_curve 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"
- creer 2y agoThe Guardian is now paywalled. ... Hmmm not exactly - there's a page overlay which can be clicked past or something.
- fedeb95 2y agoAn 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-mysterious-cosmic-force-weakening-universe-expansion https://www.theguardian.com/science/2025/mar/19/dark-energy-...
- sigmoid10 2y agoIf 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.
- fedeb95 2y agoyes, that was my point! Interesting that's "on the rise"
- mr_mitm 2y agoI 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.
- rcxdude 2y agoThat's basically a particle physics threshold, because in particle physics you tend to do many, many experiments (usually you're doing thousands a second). It's hard to get something that certain in astronomy, where you've only got one universe to observe.
- gpderetta 2y agoIt is also an informed threshold. FTL neutrinos where, IIRC, above 6 sigma and nobody believed it was true, while there were strong rumors that Higs had been found well before it hit 5 sigmas.
- nanna 2y agoSide note: NYT have the best illustrators in the business.
- mikkom 2y agoAnd worst web developers it seems, I can't scroll the page.
- guerrilla 2y agoHillarious that we've come to the point where that's even difficult to get right. Full circle.
- sega_sai 2y agoAll the images there have been prepared by the collaboration, not NYT. I know, since I've made one of those images.
- thom 2y agoWere 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 insert new nodes in the linked list of spacetime, pushing galaxies apart and ensuring the complex timelines of intelligent species never have to snap together and run on a single instance. The work is constant and unrewarding, but I am thankful to Colin for his work, however mysterious it might seem to us.
- petargyurov 2y ago[BUG #3451249] 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
- stodor89 2y agoI reckon we're just a bug and Colin doesn't even know about our existence.
- cmsj 2y agoWe might even just be a heisenbug in a bug reproducer.
- doodlebugging 2y agoGood thing too. Once Colin finds out, we'll be features that he has to document so that everyone else involved will know to use us or to bypass us.
- tetris11 2y agoOh. I have a [PR#4519842] that implements a biased value system of labour which should reduce the time available for such patterns to occur, and limit the recursion to a brief few who can embed/summarise such artefacts in written record as a form of memoization. Should I rebase on your workaround?
- brador 2y agoEvery detection capability humans have uses EM. From eyeballs to x rays to red shift. Step 1 is making a new detector, then we talk about unknown unknowns.
- mr_mitm 2y agoWe measure neutrinos and gravitational waves as well. It's much more difficult though.
- Sharlin 2y agoIn 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).
- drpossum 2y ago[flagged]
- AnimalMuppet 2y agoOK, 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.
- Sharlin 2y agoA 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 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. [1] https://en.wikipedia.org/wiki/Strain_gauge https://en.wikipedia.org/wiki/Strain_gauge
- Sapere_Aude 2y agoWhy 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 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.
- MrBuddyCasino 2y agoRelated: "Dark matter is a symptom of the grant system" https://twitter.com/martianwyrdlord/status/1902004864630108388 https://twitter.com/martianwyrdlord/status/19020048646301083...
- jandrese 2y agoPeople 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.
- misja111 2y agoAnother observed phenomenon is that the universe expansion (so also dark energy) is not the same in every direction. https://www.nasa.gov/universe/universes-expansion-may-not-be-the-same-in-all-directions/ https://www.nasa.gov/universe/universes-expansion-may-not-be...
- Isamu 2y agoThey should have asked the internet community about dark matter, only highly confident answers there.
- deleted 2y ago[deleted]
- qrios 2y ago> Armed with the coolest business card in journalism, identifying me as the "cosmic affairs correspondent" of The New York Times … The author Dennis Overbye about his retirement in December 2024 [1] [1] https://archive.is/26oDb#selection-835.102-835.228 https://archive.is/26oDb#selection-835.102-835.228
- amai 2y agoNot so fast: The DESI 2024 hint for dynamical dark energy is biased by low-redshift supernovae https://arxiv.org/abs/2502.04212 https://arxiv.org/abs/2502.04212