[HN Gopher] 'More than a hint' that dark energy isn't what astro...
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'More than a hint' that dark energy isn't what astronomers thought
Author : Hooke
Score : 116 points
Date : 2025-03-20 04:57 UTC (18 hours ago)
(HTM) web link (www.nytimes.com)
(TXT) w3m dump (www.nytimes.com)
| pineaux wrote:
| https://archive.is/H23dH
| mr_mitm wrote:
| 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.org/abs/1606.00180
| sigmoid10 wrote:
| 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.
| mr_mitm wrote:
| 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.
| sigmoid10 wrote:
| >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.
| pdonis wrote:
| _> 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.
| gadders wrote:
| This is nearly as good a comment as cperciva winning the
| Putnam.
| mr_mitm wrote:
| I wouldn't want to overstate it either, since I was just
| a lowly and IMHO mediocre PhD student at the time and my
| contribution to the paper was minor. Nevertheless, I
| believe I understand the relationship between the
| cosmological constant and dark energy just fine.
| pdonis wrote:
| 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.
| thowawatp302 wrote:
| > 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 wrote:
| Yes, 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 wrote:
| > 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_ wrote:
| Sure, but this may be news to the target audience of the
| article.
| TheSpiceIsLife wrote:
| Still, 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.
| beeforpork wrote:
| 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?
| Timwi wrote:
| > 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 let's not get distracted. We need to tackle climate
| change first. That's our first self-made extinction
| challenge.
| beeforpork wrote:
| > How do you know?
|
| 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.
| ben_w wrote:
| > 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_hu
| sbandry
| NoMoreNicksLeft wrote:
| I don't think climate change, even if it lives up to the
| most alarmist of predictions will make humanity extinct.
| We'll all be gone regardless of that. A functioning
| civilization is composed of humans (at least in our
| case), and every generation of humans must have as its
| first priority the task of making more humans to replace
| the oldest (dying) generation. The fertility rate is sub-
| replacement, the effects of a demographic implosion cause
| _more_ fertility rate issues, not less, and so that will
| accelerate. Too neurotic to have sex and make babies.
| Climate change wasn 't what you needed to tackle after
| all.
|
| We don't even survive for centuries.
| Sharlin wrote:
| The collision probably won't do much more than trigger a
| period of star formation - although that will be accompanied
| by an increase in supernova frequency as the most massive of
| the newly-born stars quickly burn out in mere millions of
| years.
| nkrisc wrote:
| Like two gas clouds colliding, not like two cars colliding.
| mr_mitm wrote:
| No, it could also end in a big crunch or big rip scenario.
| They'd have a finite lifetime of the universe.
| flowerthoughts wrote:
| 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?
| adrianN wrote:
| To harness energy you need a gradient. Once everything will
| be in equilibrium there is no gradient.
| ben_w wrote:
| 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.
| mr_mitm wrote:
| In the standard model, the temperature of the CMBR evolves
| reciprocally with the scale factor, so it will go to zero.
| wantoncl wrote:
| > The laws of thermodynamics pretty much guarantees this
| anyways does it not?
|
| Yes, but:
|
| http://www.thelastquestion.net/
| cryptonector wrote:
| One of my favorite sci-fi stories!
| mellosouls wrote:
| Lots of non-paywalled coverage out there in the mainstream press,
| eg:
|
| https://www.theguardian.com/science/2025/mar/19/dark-energy-...
| mr_mitm wrote:
| I think this is also the better article. The other one is all
| over the place.
| araes wrote:
| 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"
| creer wrote:
| The Guardian is now paywalled. ... Hmmm not exactly - there's a
| page overlay which can be clicked past or something.
| fedeb95 wrote:
| 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-...
| sigmoid10 wrote:
| 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.
| fedeb95 wrote:
| yes, that was my point! Interesting that's "on the rise"
| mr_mitm wrote:
| 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.
| rcxdude wrote:
| That'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 wrote:
| It 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.
| rcxdude wrote:
| Yeah, statistical significance can tell you nothing about
| systematic errors you're unaware of or errors in the
| statistics itself
| antognini wrote:
| As a former astronomer, one thing to highlight here is that
| statistical uncertainties aren't usually all that important in
| assessing how likely a result in astronomy is to be true. The
| main issue you grapple with in the field are your systematic
| uncertainties. When you report your uncertainty, it always is
| an uncertainty in the context of some model. However, if
| certain assumptions that your models have made are wrong, you
| will have underestimated your true uncertainty. Unfortunately,
| systematic uncertainties can't be reduced just by getting more
| data --- you have to somehow verify that the different
| assumptions your model has made are correct.
|
| 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.
| nanna wrote:
| Side note: NYT have the best illustrators in the business.
| mikkom wrote:
| And worst web developers it seems, I can't scroll the page.
| guerrilla wrote:
| Hillarious that we've come to the point where that's even
| difficult to get right. Full circle.
| sega_sai wrote:
| All the images there have been prepared by the collaboration,
| not NYT. I know, since I've made one of those images.
| thom wrote:
| 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 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 wrote:
| [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 wrote:
| I reckon we're just a bug and Colin doesn't even know about
| our existence.
| cmsj wrote:
| We might even just be a heisenbug in a bug reproducer.
| doodlebugging wrote:
| Good 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 wrote:
| Oh. 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?
| flopunctro wrote:
| This comment reminded me, with a smile, of Scott Alexander's
| Unsong: https://www.astralcodexten.com/p/unsong-available-in-
| paperba...
| thom wrote:
| I too enjoyed Unsong, but I've never gone back and reread it
| because I found the chapter about The Broadcast so haunting.
| IanCal wrote:
| It is a very well written, truly horrible chapter.
|
| It doesn't have a huge bearing on the story, so can be
| skipped - and I think a lot of people probably should.
| IanCal wrote:
| A very heavy recommendation from me for this.
|
| Hn has no spoiler tags but one of the really big things to me
| is this https://gist.github.com/IanCal/d9667ae9c6ce15315191a3
| 6c6b3af...
| indigoabstract wrote:
| Call it professional bias, but I like to think about it as a
| big VM. If for some reason, things go awry, the (said)
| programmer will hit the pause button, then diligently go to the
| last valid snapshot, fix the bug and then get things going
| again. If this isn't desired, fixing the current mess is also
| an option.
|
| The time required for fixing bugs isn't really an issue in this
| case, he can take as long as he likes.
| function_seven wrote:
| VMs are too resource hungry.
|
| No, the many-worlds interpretation shows that our universes
| are merely containers with copy-on-write behavior :)
| indigoabstract wrote:
| Yeah, could be a giant LMDB, but that's implementation
| detail :)
|
| I imagine there's some serious optimization involved to
| make it all fit in memory.
| jcarrano wrote:
| They say the deadline was quite literally 6 days. Some of the
| employees rage-quit and started their own business (they are
| doing fantastic but work conditions are reportedly hellish). As
| far as we know, they were still tweaking the physical constants
| until not long ago.
| DebtDeflation wrote:
| I once saw the Heisenberg Uncertainty Principle described as
| the result of the simulation creators using an 8 bit variable
| to store position and momentum combinations which were each
| themselves 8 bit values.
| atemerev wrote:
| This is the best of possible worlds. You may not like it, but
| this is what peak performance looks like.
| padangitik wrote:
| I love this comment but I don't understand the "linked list"
| reference. What aspect of physics/the universe is that
| referring to? Also why does the maximum speed enable sharding?
| Struggling with that part too haha.
| HappySweeney wrote:
| It's so space can expand without increasing the Planck length
| padangitik wrote:
| Ohh I think I understand. Thank you!
| api wrote:
| So the first lead coder was this Lucifer guy. Wrote the whole
| code for the physical universe layer in like days on Red Bull
| and maybe speed.
|
| 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.
| doodlebugging wrote:
| And then there's the kid Jesus who promises us relief from
| all the skullduggery coded into our existence if we will only
| agree to subscribe to his Salvation as a Service (SaaS)
| subscription model.
| karmakaze wrote:
| > a maximum speed
|
| It's even hackier than that. Everything moves at c always, if
| not through space then through time or some combination.
| cryptonector wrote:
| 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.
| russdill wrote:
| Ok, well then he went and screwed the pooch with non-locality.
| brador wrote:
| Every 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 wrote:
| We measure neutrinos and gravitational waves as well. It's much
| more difficult though.
| Sharlin wrote:
| 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).
| AnimalMuppet wrote:
| 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.
| Sharlin wrote:
| 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 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
| cryptonector wrote:
| 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.
| NwpierratorR wrote:
| For gravitational waves we still rely on EM radiation as it's
| measured by comparing perpendicular lasers through
| interferometer.
| mr_mitm wrote:
| I don't that's the kind of gotcha you imply it is. Of
| course radiation is somehow involved in everything, it's
| what keeps matter together. We also read off the
| measurements with our eyeballs, and even if you used some
| sort of braille system, touching things boils down to EM
| interaction. The primary probe here is gravitational, any
| musings beyond that are of little value. I challenge you to
| even conceive an experiment where your own objection
| wouldn't apply.
| somat wrote:
| No, it is worse than that, every detection capability humans
| have is only how em interacts with the electron shell around
| atoms.
|
| We have done some amazing things in spite of what appears a
| crippling limitation.
| Sapere_Aude wrote:
| 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 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 wrote:
| Related: "Dark matter is a symptom of the grant system"
| https://twitter.com/martianwyrdlord/status/19020048646301083...
| jandrese wrote:
| 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.
| misja111 wrote:
| Another 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...
| Isamu wrote:
| They should have asked the internet community about dark matter,
| only highly confident answers there.
| qrios wrote:
| > 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
| amai wrote:
| Not so fast:
|
| The DESI 2024 hint for dynamical dark energy is biased by low-
| redshift supernovae
|
| https://arxiv.org/abs/2502.04212
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