38 ms·

Evidence that the key assumption made in discovery of dark energy is in error

486 points by apsec112 7y ago

btilly 7y ago
https://xkcd.com/955/ https://xkcd.com/955/ comes to mind. I am going to wait to get excited about this until it is replicated by others.
- ncmncm 7y ago
  Ya, I should have placed bets that dark energy would turn out to be illusory.
- deleted 7y ago
  [deleted]
jshevek 7y ago
"...Prof. Young-Wook Lee (Yonsei Univ., Seoul), who led the project said, "Quoting Carl Sagan, extraordinary claims require extraordinary evidence, but I am not sure we have such extraordinary evidence for dark energy. Our result illustrates that dark energy from SN cosmology, which led to the 2011 Nobel Prize in Physics, might be an artifact of a fragile and false assumption."" Is he implying that other cosmologists have proceeded as if dark energy is well evidenced?
- AnimalMuppet 7y ago
  It is my impression that dark energy is generally accepted in cosmology. Whether that counts as "proceeding as if dark energy is well evidenced" is perhaps a different question. If everyone believes it's there, but nobody knows what it is, well... there was still something that convinced them that it was there. That something should be evidence. Is it enough to count as "well evidenced"? Perhaps not, especially if this new study is correct that one piece of the evidence does not actually support dark energy.
  - ncmncm 7y ago
    I don't know of any other evidence for dark energy, other than that mathematical physicists think the equations would be prettier with some, although they sort of wish there was more. It is quite embarrassing that the value was so close to zero without being zero, so that might be one embarrassment less. We already knew there was likely to be something fishy about the most distant supernovas, because we have two divergent values for the Hubble constant, one of them based on these same supernovas.
    - AnimalMuppet 7y ago
      Hmm. Is this new result in the right direction to solve the Hubble Constant problem?
      - ncmncm 7y ago
        Haha, it would be fun if we now have three Hubble constants.
        mindcrime 7y ago
        https://xkcd.com/927/ https://xkcd.com/927/
        trhway 7y ago
        my personal favorite value for the Hubble constant is the "c" divided by the age of Universe, it results in 70.8 km/s/Mpc, right in the middle of the other 2 established Hubble constant's values, a very nice coincidence that the objects at the Universe age distance are running away exactly with "c".
        AnimalMuppet 7y ago
        A coincidence? I think it might be an identity. But that would mean that disputes about the value of the Hubble Constant are also disputes about the age of the universe, and vice versa.
- carbocation 7y ago
  This doesn't really address your point, but the 2011 physics Nobel [1] said that "What is known is that dark energy constitutes about three quarters of the Universe." Not saying the Nobel write-ups constitute evidence, but dark energy has certainly been popular, at least. 1 = https://www.nobelprize.org/prizes/physics/2011/press-release/ https://www.nobelprize.org/prizes/physics/2011/press-release...
  - doodliego 7y ago
    The Luminiferous Aether was popular too.
    - stefantalpalaru 7y ago
      > The Luminiferous Aether was popular too. It still is: https://en.wikipedia.org/wiki/Quantum_field_theory https://en.wikipedia.org/wiki/Quantum_field_theory
- phkahler 7y ago
  >> Is he implying that other cosmologists have proceeded as if dark energy is well evidenced? As a non-cosmologist just reading HN I would say yes. Not quite as extensively as Dark matter though. I personally think that's a mistake too based on my limited research on the topic. If these are both overturned it will be a huge blow to "scientists" credibility in the eyes of the public. That's how invested they are.
  - coliveira 7y ago
    > If these are both overturned it will be a huge blow to "scientists" credibility This is nonsense. Scientists have been wrong in several occasions, it is just part of the profession. For example, in the years leading to the discovery of relativity, many physicists believed there was something called "ether" that worked to fix the speed of light that they had evidence to be the same in all directions.
    - deleted 7y ago
      [deleted]
    - ShorsHammer 7y ago
      Generally called aether, believe that ether is a misspelling which has lingered. https://en.wikipedia.org/wiki/Aether_theories https://en.wikipedia.org/wiki/Aether_theories
      - mishac 7y ago
        I believe it's just a regional spelling issue (like paediatriction/pediatriction or encylopaedia/encyclopedia)
      - ncmncm 7y ago
        If you care what sort of ether you're on about, you say "luminiferous ether".
    - chrisco255 7y ago
      Yeah but that was in an age before clickbait and "In this house, we believe science is real" yard signs. People are too bought into science as a source for truth instead of being a messy, difficult method of discovery.
- dfischer 7y ago
  As a frequent listener of cosmologists I'd say they regularly frame answers as dark energy were true.
- awb 7y ago
  > Is he implying that other cosmologists have proceeded as if dark energy is well evidenced? I thought dark matter and dark energy are simply placeholders for a discrepancy we see between our models of the universe and our observations. No?
  - unlinked_dll 7y ago
    it's my understanding that dark matter is another word for the indirect observation of matter that we can't otherwise detect, through gravity. I don't know if calling it a placeholder is the proper parlance. Dark energy is something predicted by general relativity and iirc it's what is behind the expansion of space (and acceleration of expansion).
    - pdonis 7y ago
      > Dark energy is something predicted by general relativity Not really. GR can accommodate it just fine, but GR did not predict it. In fact, Einstein, who originally introduced the cosmological constant (which was the term then for what we now call "dark energy") in order to allow a static solution to his equation, thereby missed the chance to predict that the universe was expanding, a decade before Hubble's observations showed that it was. Once it became clear that expanding models matched the data, and did not (then) require a cosmological constant to do so, Einstein dropped it, calling it "the biggest blunder of my life". Only in the 1990s, when evidence for accelerating expansion became available, was the cosmological constant (now called "dark energy") put back into the equations so they would match the data. > it's what is behind the expansion of space (and acceleration of expansion) The expansion itself, no. The acceleration, yes.
      - galangalalgol 7y ago
        How much would the fate of the universe page on Wikipedia change with linear expansion? Do we have a bit longer before the stretch?
        pdonis 7y ago
- K0SM0S 7y ago
  The question is moot: it's precisely because we have evidence of things not currently explained (observation does not fit theory) that we must postulate that our theory is wrong, or that there is more to discover, or both. "Dark energy" is a conventional term to describe some energy of unknown source that has the effect of accelerating space expansion with time. We call "dark energy" the thing that explains this observation, whatever that thing might be (we just assume it's some form of energy since it produces motion, acceleration, in a way seemingly opposed to, and stronger than gravity, but for all we knew it could be fluffy creatures from the 7th dimension, "energy" is just an educated guess). If you remove the observational discrepancy, then you remove the need for "dark energy" to exist in the first place. The article precisely suggests that: - there was no such observational discrepancy, rather errors in calculations following observation - reality is thus shown to conform to our current equations; it's our interpretation of the pretty pictures we took that was wrong all along; this is now corrected. If true, it's the end of dark energy as a cause because the consequence is gone. At no point (before or after it's proven or disproven) does "dark energy" imply a postulate on "what it actually is" — and chances are, when we explain previously unknown phenomena, the finders come up with a new theory and ad hoc terminology. Rarely the word sticks when it's just too good an intuition — e.g. the "atom". Note that "dark matter" is exactly the same, it's a conventional term to denote some matter-like unknown object that has the effect of giving galaxies their characteristic shapes and interactions forming much larger patterns (structure about as big to individual galaxies as galaxies are to individual stars).
sparker72678 7y ago
> Taken at face values, the luminosity evolution of SN is significant enough to question the very existence of dark energy. When the luminosity evolution of SN is properly taken into account, the team found that the evidence for the existence of dark energy simply goes away Cosmology is great because there's still so much in flux. There are so many fundamental things that are still in active research. I find it all very exciting.
- tomrod 7y ago
  My exact thought was "Yaye for science!" I love that science has self-correction built into its core.
layoutIfNeeded 7y ago
So... Big Rip is postponed indefinitely?
- gbrown 7y ago
  I thought there was little reason to expect a big rip, because it requires assumptions about an increasing cosmological constant, which there’s no evidence for.
  - 6nf 7y ago
    What do you mean? There's lots of evidence that the expansion of the universe is accelerating and that's the whole reason we believe that dark energy exists. Most cosmologists do believe we're heading for a big rip.
    - marcosdumay 7y ago
      The existence of a cosmological constant is different from it's ever increasing value. The evidences for the later are non-existent.
    - mirimir 7y ago
      According to TFA, it's the "most direct and strongest evidence for the accelerating universe" that's now possibly an artifact. As I understand it, "dark energy" is fundamentally just another way to say "accelerating expansion".
    - pdonis 7y ago
      No, "big rip" and "accelerating expansion" are not the same thing. A big rip would require that the density of dark energy in the universe is increasing with time. We have no evidence that it is, and most cosmologists do not believe we are heading for a big rip.
      - gbrown 7y ago
        Exactly.
zipotm 7y ago
Read more about the Primer Fields.
- AnimalMuppet 7y ago
  Why should we? No, really. Rather than tell us to go read something (just a term, not even a link) that has a name that might, just possibly, be relevant to the topic at hand (or might be some obscure abstract mathematical thing, or something about painting), maybe you could tell us why you think we should read more about them, and where you recommend we go to do so.
- civilian 7y ago
  seems like quackery https://www.quora.com/Has-anyone-considered-the-primer-fields-as-a-solid-theory https://www.quora.com/Has-anyone-considered-the-primer-field...
  - AnimalMuppet 7y ago
    After a bit of looking at it, I agree: It looks very much like a quack.
flick 7y ago
Not so fast. See [1] and [2] for an explanation. There are good reasons to suspect that there are errors made in this analysis. [1]: https://arxiv.org/abs/1912.02191 https://arxiv.org/abs/1912.02191 [2]: https://www.quantamagazine.org/no-dark-energy-no-chance-cosmologists-contend-20191217/ https://www.quantamagazine.org/no-dark-energy-no-chance-cosm...
- knzhou 7y ago
  Hold up, this is a different thing than what [1] and [2] are responding to.
  - crazygringo 7y ago
    Yes, I'm totally lost. Was there accidental confusion here? Or is the new paper (by completely different authors) somehow building on those other papers and flick is implying it suffers from the same criticisms? Would love to know if this is genuinely newsworthy or not.
- dannykwells 7y ago
  It would be pretty impressive indeed if [1] countered this article, since the Arxiv preprint came online 6 days later.
- ssivark 7y ago
  Thanks! It’s a little disingenuous/irresponsible on part of the phys.org article to not even mention the Rubin+Heitlauf rebuttal and the ensuing discussion, even though they’re from a month ago. EDIT: No wait, this OP is about a different paper from a week later... Hmm.... interesting times.
crazygringo 7y ago
Do I understand correctly that this is actually saying that accelerating expansion of the universe may be in error? That there is, instead, no accelerating at all, but merely constant expansion? Or can there still be acceleration without dark energy? I'm unclear if they are essentially the same hypothesis or if there are more complicated subtleties I'm missing.
- philipov 7y ago
  There are very few ways to modify Einstein's Equations and still have them make sense. An easy one is to add a constant term. Such a term is known as the Cosmological Constant, and a positive value for it would result in a constant repulsive force between masses regardless of distance. This results in an accelerating expansion of the entire universe, but, with a supremely small value it only becomes noticeable at large scales, where it starts to dominate attractive gravity. This appears to model what we're observed happening with galaxy clusters. Dark Energy is a hypothesis for explaining why such a very small cosmological constant might exist, suggesting that the universe is permeated with a constant negative energy field. However, the article refers to observational evidence measuring the expansion of the universe, not dark energy. There is no evidence for dark energy as such, and if you listen to colloquia on cosmology, you will hear about the cosmological constant, not dark energy. It is not necessary to hypothesize the existence of negative energy particles to model what we've observed, and you'll only really hear the term used in the popular press because it sounds sexy.
  - pdonis 7y ago
    > Dark Energy is a hypothesis for explaining why such a very small cosmological constant might exist, suggesting that the universe is permeated with a constant negative energy field. No, that's not what dark energy is. "Dark energy" is just a general term for "anything that acts like a cosmological constant in the Einstein Field Equation". It could be an actual physical constant, just an inherent property of spacetime, or it could be some kind of energy field. We don't know. (Btw, the energy associated with dark energy is positive, not negative; the pressure is what's negative.)
tus88 7y ago
"discovery"
ncmncm 7y ago
Haha, called it! Feynman warned about this specific phenomenon: basing new physics on the points at the extreme end of your graph, where the measurements are least reliable. In this case, these points correspond to demolition of the most distant and youngest stars in the sample, which could differ in many ways from the common, much more recent events. Low metallicity is a difference that is obvious to every AP, but there is no reason to assume it is the only one. We just don't get to study any young-universe stars that haven't blown up. Did anybody even discuss metallicity and possible effects on brightness of t1a sn's, when DE was first proclaimed? If not, why not?
- dmix 7y ago
  Does this have any affect on the search for dark matter? Are the two interconnected at all?
  - lanstin 7y ago
    No. Dark matter is assumed to exist from the excessively quick rotation of stars around the cores of galaxies. Dark energy is/was assumed to exist in anomalous expansion of the universe based on redshifts.
    - stan_rogers 7y ago
      >Dark matter is assumed to exist from the excessively quick rotation of stars around the cores of galaxies. That's what initiated Zwicky's notion in the '30s. It is far from being the only, or even the main, evidence for dark matter (which can be read as "mass effects we can detect not associated with matter we can currently detect").
      - ncmncm 7y ago
        More accurately: motion dynamics not compatible with both General Relativity and the mass we can see and reasonably infer. There is of course a stupendously huge amount of mostly invisible "interstellar medium", and even more "intergalactic medium", mostly ions of loose atoms and small molecules, and we use estimates of how much of that there must be. If its motion has anything to do with plasma fluid dynamics, all bets are off, because those equations are what mathematicians call intractable, and physicists would call career-limiting. They will happily declare 3x more unknowable Dark Matter than normal stuff before allowing plasma dynamics to have any effect on anything. Can hardly blame them.
flashman 7y ago
To know if the universe is expanding, we need to know the following: how far away things are, and whether they're moving away from us. In an accelerating universe, there's evidence that things were moving away from us slower in the past. The evidence that things are moving away from us is that as the universe expands, the wavelength of any light travelling through it also expands, shifting it towards the red end of the spectrum: redshift. (Think of the wavelength of a wavy line drawn on a piece of rubber that's then stretched out.) We've known for nearly 100 years that the universe is expanding. (Edit: not just that the objects in it are moving apart but that space itself is expanding.) The evidence of accelerating expansion is that based on the redshift of nearby objects, we would expect distant objects to have a higher redshift than they actually do. That means they were moving away from us slower in the past, so something must be accelerating them. We use the brightness of Type Ia supernovae to measure distance. Even though supernovae aren't identically bright, their brightness follows a curve which lets us calculate their peak brightness (they are standardizable). This paper argues that the calculations cosmologists use to standardize supernovae brightness fail to take into account the age of the progenitor stars, as far as I can tell. If true, this means our distance measurements are inaccurate and these stars are actually closer than we thought, enough to restore to linear relationship between distance and redshift that one would expect in a universe expanding at a constant rate. In other words, their redshift is lower not because the expansion rate of space was lower in the past, but because they're not as far away as we thought they were.
- mirimir 7y ago
  That's how I understand it. But maybe there are other standardizable objects. The sense I got from TFA is that there aren't.
  - kiliantics 7y ago
    There are actually. There is a class of star in the "tip of the red giant branch" (TRGB) which have also been used to calibrate luminosities of type Ia supernovae[0] to form a "cosmic distance ladder". I believe they have been used to confirm the accelerated expansion results (though less strongly). I am not super well versed in stellar evolution, but I believe that the TRGB should make this calibration method independent of progenitor age? Hopefully someone could chime in on this. I was formerly a cosmologist and would be very interested to know more about this result from any experts that might be reading this. [0] There is an explanation of this calibration here: https://aasnova.org/2019/07/26/tldr-the-trgb-gives-us-another-h0ttake/ https://aasnova.org/2019/07/26/tldr-the-trgb-gives-us-anothe...
fluxby 7y ago
Personally, I’m a fan of ideas of Quantized Inertia [1] [2] which proposes that Dark Energy does not exist at all. We’ve been on a wild goose chase after dark energy for 30 years, which so far has proven to be an untestable theory. [1] https://youtu.be/1itasiXNUPg https://youtu.be/1itasiXNUPg [2] https://youtu.be/VYdebV9YlnI https://youtu.be/VYdebV9YlnI
mathiasrw 7y ago
If you find things like this interesting I suggest you look on youtube for videos on the electric universe. The main take is that our current models having gravity as the main driving force shaping our universe is a misunderstanding - hence rejecting the idea of dark matter / dark energy that was "invented" to make for math for gravity work with the observations of expansion.
- Jweb_Guru 7y ago
  Despite the similar name, dark matter really has very little to do with dark energy, and the lines of evidence for them are totally different. AFAIK there is fairly overwhelming evidence for the existence of dark matter at this point, and it's mostly a question of what exactly it is rather than whether the effect is real.
  - briantakita 7y ago
    Dr. Anthony Perat, protege of Hannes Alfven, has a cosmological model based on plasma, which is observable & subject to physically reproducible experiments & replaces the need for both Dark Matter & Dark Energy as mathematical artifacts. https://www.amazon.com/Physics-Plasma-Universe-Anthony-Peratt/dp/1461478189 https://www.amazon.com/Physics-Plasma-Universe-Anthony-Perat...
- d2v 7y ago
  ... you mean this? https://www.vice.com/en_us/article/nz7neg/electric-universe-theory-thunderbolts-project-wallace-thornhill https://www.vice.com/en_us/article/nz7neg/electric-universe-...
- _bohm 7y ago
  It should be noted that among cosmologists, electric universe is widely considered to be bunk science.
  - briantakita 7y ago
    And Plasma Physicists think that "dark matter", "dark energy", & the assertion of gravity (ignoring plasma) being the dominant force in the Univese is mathematics without physical evidence. Thus "pathological science". Irving Langmuir, discoverer of the double layer effect in plasmas & coined the term "plasma" physics, came up with the definition of "Pathological Science". He was also around during the birth of the "Standard Model". https://en.m.wikipedia.org/wiki/Pathological_science https://en.m.wikipedia.org/wiki/Pathological_science
ltbarcly3 7y ago
I guess people are going to act like I'm a lunatic, but of course it's wrong. Dark Energy violates basic conservation of energy, and the evidence for it has never been strong or convincing. Lots of us have been saying this since forever.
- ncmncm 7y ago
  Conservation of energy has only ever been observed in local conditions. The universe is not obliged to respect our local expectations, and has always turned out to violate them in uncomfortable ways. The ground looks flat near you (at least in Nebraska). The Sun seems to go around Earth.
  - ltbarcly3 7y ago
    Which is more likely, that you can have infinite free energy or that the very careful measurements of the distances to supernova that happened billions of years ago on the other side of the universe, and for which we have virtually no standard yardstick to compare against are not accurate? You are just making an appeal to ignorance. All of physics and astronomy is based on the assumption that the rest of the universe follows the same basic laws that the part we can study follows. That the universe is isotropic and homogeneous is a necessary basic assumption to even begin to measure the distance to objects that are very far away. If you can't assume that the basic laws of physics operate the same everywhere, then you have no basis to make any claims about anything that isn't local.
    - ncmncm 7y ago
      That is the condition of cosmology. Not everyone envies it.
      - ltbarcly3 7y ago
        It's an assumption, and while you might make a reasonable argument to try to justify it, it's still an assumption. The real problem is when we cross from 'assuming these things, which we don't really have a strong reason to assume' to 'this is the way the universe is'. Without the qualifications it's extremely misleading and loses any basis it started with.
platz 7y ago
Sabine Hossenfelder comments on this paper: Dark Energy might not exist after all https://youtu.be/oqgKXQM8FpU https://youtu.be/oqgKXQM8FpU
- ncmncm 7y ago
  Amusingly, this video is about entirely different work that also calls into question the basis for claims about dark energy. Nobody seems to be saying how the two results interact. Taking away dark energy twice could give us negative dark energy, which would be fun. I don't know whether unexpected negative dark energy would be more embarrassing than unexpected zero dark energy.
  - platz 7y ago
    Ah, that is funny - I just assumed i didn't understand the different descriptions because I'm not an expert. That they are different explains my puzzlement. * indeed this is the same result as https://www.quantamagazine.org/no-dark-energy-no-chance-cosmologists-contend-20191217/ https://www.quantamagazine.org/no-dark-energy-no-chance-cosm... which is different from the OP paper
  - SubiculumCode 7y ago
    negative dark energy. sounds sexy.
  - Jweb_Guru 7y ago
    It sounds like the earlier article is pretty flawed and doesn't control for things like redshift associated with the motion of the solar system, so I very much doubt that the observations in that paper will end up "stacking" with those in this one. I'm no expert, but it seems like this more recent paper presents a much more serious challenge to the existence of dark energy.
rs23296008n1 7y ago
Good. Science is meant to be a honest search for facts: data, knowledge and wisdom. Being wrong is a feature. "I don't know" is an acceptable starting point with no shame attached. Being certain means a mountain of data to back it up. Being allowed to be wrong is a requirement. Anyone saying a scientist can't ever be wrong is likely placing oddball limits on progress that will only damage and limit the future[1]. How can you experiment if you can never be wrong? It would be good if people knew about the mountain-of-data aspect of science. Even with that mountain, subtleties creep in and plenty of surprises still remain. Even something like water probably has properties we are clueless about. Interesting aspects that might redefine science itself and create entirely new approaches to medicine or manufacture or whatever. Maybe if you change temperature and pressure enough in the right way you end up with exotic metallic / bonding properties. Or some new water-based ion structure having other properties. Who knows? Maybe not. Perhaps water is what it is and there is not much more to learn. Asserting we already know everything about water leads to dogma[2] and inflexibility. That's just one example. Dark matter/dark energy may be a rounding error for all I know. Good. Now we know about the error. We* likely asked a bunch of other questions as well and now we have new answers about to appear because now that error has been confirmed. * not me. [1] being wrong about bridge structure is unhelpful as you drive over it. That kind of wrong is related but I'm not directly addressing that. [2] dogma has expectations, rules and consequences. Science has plenty of people who forget this and turn their understanding into dogma. That too is a experience generating moment that will catch up with them later. Mountain-of-data + knowledge + wisdom.
- tiborsaas 7y ago
  Dark matter is definitely not a rounding error [0]. There are multiple evidence for strong gravity effects where we just don't see the required matter the explain the observed phenomenons [1][2] [0] https://www.forbes.com/sites/briankoberlein/2016/09/23/rotating-galaxies-could-prove-dark-matter-wrong/ https://www.forbes.com/sites/briankoberlein/2016/09/23/rotat... [1] https://en.wikipedia.org/wiki/Bullet_Cluster#Significance_to_dark_matter https://en.wikipedia.org/wiki/Bullet_Cluster#Significance_to... [2] http://cosmology.berkeley.edu/Education/CosmologyEssays/Gravitational_Lensing.html http://cosmology.berkeley.edu/Education/CosmologyEssays/Grav... Briefly, dark matter is very real, it's our knowledge that is dark.
yeahigotgoats 7y ago
the science is settled! the science is settled!
exabrial 7y ago
Can someone eli5 why if space itself is expanding, how can an observer detect that if they too are expanding at the same rate?
- osbertlancaster 7y ago
  As I understand it: We are not expanding. Size of e.g. a hydrogen atom is not changing.
  - magicalhippo 7y ago
    And we are not expanding because other forces are stronger at short range. Similar to how the electroweak force is preventing you from falling through your chair, even though the gravity of the entire earth is pulling you. Dark energy, as we thought before this paper at least, would overcome gravity only on the grandest scales, between galaxies.
- cygx 7y ago
  Spatial expansion is a great heuristic explanation, but it can be misleading: Locally, the cosmological constant will manifest as just another pseudo-force, easily overcome by nuclear and electromagnetic forces holding us together.
j-dr 7y ago
Even if this paper is correct, there is still overwhelming evidence for dark energy provided by other observations, in particular those of the Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillations (BAO). This article provides some details on why Dark Energy is in no danger of being called in question: https://www.quantamagazine.org/no-dark-energy-no-chance-cosmologists-contend-20191217/ https://www.quantamagazine.org/no-dark-energy-no-chance-cosm...
- ash 7y ago
  As far as I can tell, Quanta Magazine article does mention the original post findings. Additionally, the Quanta article and the findings preprint were published just a week apart. Not enough time to formulate a good response: * Quanta Magazine article: 17 Dec 2019 * Arxiv preprint: 10 Dec 2019 [1] CMB and BAO are mentioned in the original post too: > Other cosmological probes, such as the cosmic microwave background (CMB) and baryonic acoustic oscillations (BAO), are also known to provide some indirect and "circumstantial" evidence for dark energy, but it was recently suggested that CMB from Planck mission no longer supports the concordance cosmological model which may require new physics (Di Valentino, Melchiorri, & Silk 2019). Some investigators have also shown that BAO and other low-redshift cosmological probes can be consistent with a non-accelerating universe without dark energy (see, for example, Tutusaus et al. 2017). In this respect, the present result showing the luminosity evolution mimicking dark energy in SN cosmology is crucial and very timely. [1]: https://arxiv.org/abs/1912.04903 https://arxiv.org/abs/1912.04903
  - ash 7y ago
    Correction: "Quanta Magazine article does NOT mention the original post findings"
guygurari 7y ago
It is hard to overstate how important the resolution of this question is to physics, and in particular to theoretical physics. The “cosmological constant problem”, that is the problem explaining the cosmological acceleration (if it exists), is arguably the most important and hardest question in high energy theoretical physics. Many theoreticians have spent significant effort studying this question, working under the assumption that the empirical evidence is solid. If this is not the case, it changes the landscape of cutting edge physics research. There are several reasons why explaining the observed acceleration is so hard. The cosmological constant (the measure of how much dark energy there is) is a tiny positive number which seems to require a lot of “fine tuning” to explain theoretically. We can easily include it in general relativity, but our best understanding of quantum physics says that if it is there then it should be much larger. This means there probably is something we don’t understand about its microscopic origins. If we try to build a microscopic model that has this small constant using string theory (our best guest at a complete theory), we find that such models are hard to create. In fact, it is not clear that any model that includes dark energy is even valid in string theory! Any way we look at it, it seems more difficult to explain this number if it is tiny and positive than if it is strictly zero (no acceleration). Finally, theoreticians don’t have much to go on when explaining this phenomenon besides this one single number — there aren’t closely related experiments we can combine to come up with a coherent picture of what’s happening. Combine this with particle physics, where accelerators provide us with an abundance of data. It is a single tiny number that has puzzled theoreticians for decades.
- BoiledCabbage 7y ago
  What's more mind-boggling to me is all these thousands of scientists running around looking at the extreme oddity of multi-dimensional string theory, and nobody bothered to check if the cosmological constant is actually real. It seems like physics is really being held back by perverse incentives. And of course my pocket view that string theory will turn out to be the single largest waste of brilliant human minds in history.
  - eloff 7y ago
    I'm not a physicist, but I don't think string theory is a total waste. It agrees with our existing theories and predictions, so it can be viewed as just an alternative mathematical abstraction, and there is value in that. Whether or not tiny vibrating strings are really at the heart of things is neither here nor there. It's about as relevant to science as god.
mikorym 7y ago
As a mathematician, I will inherently be biased against dark matter and dark energy (if you're calculations don't fit, then your mathematics is not suitable, so change the math before you change the physical description). What is the relationship between dark matter and dark energy, and does this have any effect on the r^2 law assumptions and the introduction of dark matter? For example, does this mean that when we thought that r^2 was not strictly followed that in fact we had the positions of the bodies wrong?
- fsh 7y ago
  They are not related at all. Dark matter is visible on the scale of galaxies, dark energy on the scale of the universe. Dark matter is currently the best model that can describe the rotational curves of galaxies under the assumption that general relativity is correct. Since GR has so far stood all tests extremely well, this is a very compelling argument for the existence of dark matter. There are also some more direct observations, such as gravitational lensing caused by dark matter.
- has2k1 7y ago
  > if you're calculations don't fit, then your mathematics is not suitable, so change the math before you change the physical description Physics is littered with mathematical formulations predicting new phenomenon (forces and particles). > What is the relationship between dark matter and dark energy There is no known relationship between dark matter and dark energy. They could have been called unknown matter and unknown energy! The absence of a good account for each does not infer a relationship between the two.
  - mikorym 7y ago
    > Physics is littered with mathematical formulations predicting new phenomenon (forces and particles). Sorry, I should have clarified: I mean I would spend all my days doubting the mathematics, rather than doubting the physical universe. If that makes sense? Of course all of mathematics can be argued to have a physical sort of root.
    - 7y ago
scotty79 7y ago
Do you know any good source where I could follow through the whole argument that universe is expanding and the expansion accelerates? Without handweaving.
vectorEQ 7y ago
if you look at the magnetic soup we call matter, or maybe electromagnetism is a better term, is dark matter / dark energy / anti-matter (&anti energy??) just the same thing of a higher frequency say if matter / observables go from 0hz - 30+ Zhz.. is dark energy from 30+Zhz to ???Zhz and perhaps anti matter / energy from ???Zhz to ???????Zhz? (more question marks being higher ? :D ) or is this completely invalid and a dumb thought?
- _Microft 7y ago
  Electromagnetism is only one of a number of fundamental forces [1]. See [0] if you are curious about EM radiation at different frequencies. Radio and microwaves, infrared and visible light, ultraviolet light up to x-rays and gammarays are all part of the EM spectrum. [0] https://en.wikipedia.org/wiki/Electromagnetic_spectrum https://en.wikipedia.org/wiki/Electromagnetic_spectrum [1] https://en.wikipedia.org/wiki/Standard_Model https://en.wikipedia.org/wiki/Standard_Model
scotty79 7y ago
Are galaxies in old universe more densely packed than in our neighbourhood? Can expansion be seen not in redshift but in angular distances of galaxies? I'm asking in general not in relationship to the article. It wouldn't help for the problem raised by this article.
imvetri 7y ago
One less thing to worry about.
SiempreViernes 7y ago
Preprint is here: https://arxiv.org/abs/1912.04903 https://arxiv.org/abs/1912.04903
nxpnsv 7y ago
So these guys criticize SN-!a as standard candles, and then rely on other results criticizing BAO and CMB measurements also indicating accelerating expansions. However, why all these measurement would err in the wrong direction is not clear. I'm not convinced yet.
mannykannot 7y ago
When dark energy was first accepted, it seemed to me, as an outsider, that it happened very quickly, without, apparently, any time as a possibly-contentious, 'could this be so?' hypothesis in the way that, for example, dark matter did (and, to some extent, still is.) That surprised me because, up to that point, there seemed to be a problem with the cosmological distance ladder, with different methods getting different results, and with there being stars that seemed older than the universe supposedly was. In comparison, when superluminal neutrinos were tentatively announced a few years ago, there was a lot of justified skepticism about there being experimental error (admittedly, overthrowing special relativity is an even more extraordinary claim than dark energy.)
Hoagy 7y ago
Late to the party but does anybody know if this is connected to the findings a few weeks ago that this Quanta article is replying to? (https://www.quantamagazine.org/no-dark-energy-no-chance-cosmologists-contend-20191217/ https://www.quantamagazine.org/no-dark-energy-no-chance-cosm...) I know they are proposing different mechanisms for the error in calculation but it gives a sense of a 'moment' shifting against dark energy. Coincidence?
cerealbad 7y ago
radiation spreads and matter clumps. in this universe matter was allowed to form but radiation dominates. island chains swallowed up by a rising ocean.

486 points by apsec112 7y ago

https://xkcd.com/955/ https://xkcd.com/955/ comes to mind. I am going to wait to get excited about this until it is replicated by others.

ncmncm 7y ago
Ya, I should have placed bets that dark energy would turn out to be illusory.
deleted 7y ago
[deleted]

jshevek 7y ago

"...Prof. Young-Wook Lee (Yonsei Univ., Seoul), who led the project said, "Quoting Carl Sagan, extraordinary claims require extraordinary evidence, but I am not sure we have such extraordinary evidence for dark energy. Our result illustrates that dark energy from SN cosmology, which led to the 2011 Nobel Prize in Physics, might be an artifact of a fragile and false assumption."" Is he implying that other cosmologists have proceeded as if dark energy is well evidenced?

AnimalMuppet 7y ago
It is my impression that dark energy is generally accepted in cosmology. Whether that counts as "proceeding as if dark energy is well evidenced" is perhaps a different question. If everyone believes it's there, but nobody knows what it is, well... there was still something that convinced them that it was there. That something should be evidence. Is it enough to count as "well evidenced"? Perhaps not, especially if this new study is correct that one piece of the evidence does not actually support dark energy.
- ncmncm 7y ago
  I don't know of any other evidence for dark energy, other than that mathematical physicists think the equations would be prettier with some, although they sort of wish there was more. It is quite embarrassing that the value was so close to zero without being zero, so that might be one embarrassment less. We already knew there was likely to be something fishy about the most distant supernovas, because we have two divergent values for the Hubble constant, one of them based on these same supernovas.
  - AnimalMuppet 7y ago
    Hmm. Is this new result in the right direction to solve the Hubble Constant problem?
    - ncmncm 7y ago
      Haha, it would be fun if we now have three Hubble constants.
      - mindcrime 7y ago
        https://xkcd.com/927/ https://xkcd.com/927/
      - trhway 7y ago
        my personal favorite value for the Hubble constant is the "c" divided by the age of Universe, it results in 70.8 km/s/Mpc, right in the middle of the other 2 established Hubble constant's values, a very nice coincidence that the objects at the Universe age distance are running away exactly with "c".
        AnimalMuppet 7y ago
        A coincidence? I think it might be an identity. But that would mean that disputes about the value of the Hubble Constant are also disputes about the age of the universe, and vice versa.
carbocation 7y ago
This doesn't really address your point, but the 2011 physics Nobel [1] said that "What is known is that dark energy constitutes about three quarters of the Universe." Not saying the Nobel write-ups constitute evidence, but dark energy has certainly been popular, at least. 1 = https://www.nobelprize.org/prizes/physics/2011/press-release/ https://www.nobelprize.org/prizes/physics/2011/press-release...
- doodliego 7y ago
  The Luminiferous Aether was popular too.
  - stefantalpalaru 7y ago
    > The Luminiferous Aether was popular too. It still is: https://en.wikipedia.org/wiki/Quantum_field_theory https://en.wikipedia.org/wiki/Quantum_field_theory
phkahler 7y ago
>> Is he implying that other cosmologists have proceeded as if dark energy is well evidenced? As a non-cosmologist just reading HN I would say yes. Not quite as extensively as Dark matter though. I personally think that's a mistake too based on my limited research on the topic. If these are both overturned it will be a huge blow to "scientists" credibility in the eyes of the public. That's how invested they are.
- coliveira 7y ago
  > If these are both overturned it will be a huge blow to "scientists" credibility This is nonsense. Scientists have been wrong in several occasions, it is just part of the profession. For example, in the years leading to the discovery of relativity, many physicists believed there was something called "ether" that worked to fix the speed of light that they had evidence to be the same in all directions.
  - deleted 7y ago
    [deleted]
  - ShorsHammer 7y ago
    Generally called aether, believe that ether is a misspelling which has lingered. https://en.wikipedia.org/wiki/Aether_theories https://en.wikipedia.org/wiki/Aether_theories
    - mishac 7y ago
      I believe it's just a regional spelling issue (like paediatriction/pediatriction or encylopaedia/encyclopedia)
    - ncmncm 7y ago
      If you care what sort of ether you're on about, you say "luminiferous ether".
  - chrisco255 7y ago
    Yeah but that was in an age before clickbait and "In this house, we believe science is real" yard signs. People are too bought into science as a source for truth instead of being a messy, difficult method of discovery.
dfischer 7y ago
As a frequent listener of cosmologists I'd say they regularly frame answers as dark energy were true.
awb 7y ago
> Is he implying that other cosmologists have proceeded as if dark energy is well evidenced? I thought dark matter and dark energy are simply placeholders for a discrepancy we see between our models of the universe and our observations. No?
- unlinked_dll 7y ago
  it's my understanding that dark matter is another word for the indirect observation of matter that we can't otherwise detect, through gravity. I don't know if calling it a placeholder is the proper parlance. Dark energy is something predicted by general relativity and iirc it's what is behind the expansion of space (and acceleration of expansion).
  - pdonis 7y ago
    > Dark energy is something predicted by general relativity Not really. GR can accommodate it just fine, but GR did not predict it. In fact, Einstein, who originally introduced the cosmological constant (which was the term then for what we now call "dark energy") in order to allow a static solution to his equation, thereby missed the chance to predict that the universe was expanding, a decade before Hubble's observations showed that it was. Once it became clear that expanding models matched the data, and did not (then) require a cosmological constant to do so, Einstein dropped it, calling it "the biggest blunder of my life". Only in the 1990s, when evidence for accelerating expansion became available, was the cosmological constant (now called "dark energy") put back into the equations so they would match the data. > it's what is behind the expansion of space (and acceleration of expansion) The expansion itself, no. The acceleration, yes.
    - galangalalgol 7y ago
      How much would the fate of the universe page on Wikipedia change with linear expansion? Do we have a bit longer before the stretch?
      - pdonis 7y ago
K0SM0S 7y ago
The question is moot: it's precisely because we have evidence of things not currently explained (observation does not fit theory) that we must postulate that our theory is wrong, or that there is more to discover, or both. "Dark energy" is a conventional term to describe some energy of unknown source that has the effect of accelerating space expansion with time. We call "dark energy" the thing that explains this observation, whatever that thing might be (we just assume it's some form of energy since it produces motion, acceleration, in a way seemingly opposed to, and stronger than gravity, but for all we knew it could be fluffy creatures from the 7th dimension, "energy" is just an educated guess). If you remove the observational discrepancy, then you remove the need for "dark energy" to exist in the first place. The article precisely suggests that: - there was no such observational discrepancy, rather errors in calculations following observation - reality is thus shown to conform to our current equations; it's our interpretation of the pretty pictures we took that was wrong all along; this is now corrected. If true, it's the end of dark energy as a cause because the consequence is gone. At no point (before or after it's proven or disproven) does "dark energy" imply a postulate on "what it actually is" — and chances are, when we explain previously unknown phenomena, the finders come up with a new theory and ad hoc terminology. Rarely the word sticks when it's just too good an intuition — e.g. the "atom". Note that "dark matter" is exactly the same, it's a conventional term to denote some matter-like unknown object that has the effect of giving galaxies their characteristic shapes and interactions forming much larger patterns (structure about as big to individual galaxies as galaxies are to individual stars).

sparker72678 7y ago

> Taken at face values, the luminosity evolution of SN is significant enough to question the very existence of dark energy. When the luminosity evolution of SN is properly taken into account, the team found that the evidence for the existence of dark energy simply goes away Cosmology is great because there's still so much in flux. There are so many fundamental things that are still in active research. I find it all very exciting.

tomrod 7y ago
My exact thought was "Yaye for science!" I love that science has self-correction built into its core.

layoutIfNeeded 7y ago

So... Big Rip is postponed indefinitely?

gbrown 7y ago
I thought there was little reason to expect a big rip, because it requires assumptions about an increasing cosmological constant, which there’s no evidence for.
- 6nf 7y ago
  What do you mean? There's lots of evidence that the expansion of the universe is accelerating and that's the whole reason we believe that dark energy exists. Most cosmologists do believe we're heading for a big rip.
  - marcosdumay 7y ago
    The existence of a cosmological constant is different from it's ever increasing value. The evidences for the later are non-existent.
  - mirimir 7y ago
    According to TFA, it's the "most direct and strongest evidence for the accelerating universe" that's now possibly an artifact. As I understand it, "dark energy" is fundamentally just another way to say "accelerating expansion".
  - pdonis 7y ago
    No, "big rip" and "accelerating expansion" are not the same thing. A big rip would require that the density of dark energy in the universe is increasing with time. We have no evidence that it is, and most cosmologists do not believe we are heading for a big rip.
    - gbrown 7y ago
      Exactly.

zipotm 7y ago

Read more about the Primer Fields.

AnimalMuppet 7y ago
Why should we? No, really. Rather than tell us to go read something (just a term, not even a link) that has a name that might, just possibly, be relevant to the topic at hand (or might be some obscure abstract mathematical thing, or something about painting), maybe you could tell us why you think we should read more about them, and where you recommend we go to do so.
civilian 7y ago
seems like quackery https://www.quora.com/Has-anyone-considered-the-primer-fields-as-a-solid-theory https://www.quora.com/Has-anyone-considered-the-primer-field...
- AnimalMuppet 7y ago
  After a bit of looking at it, I agree: It looks very much like a quack.

flick 7y ago

Not so fast. See [1] and [2] for an explanation. There are good reasons to suspect that there are errors made in this analysis. [1]: https://arxiv.org/abs/1912.02191 https://arxiv.org/abs/1912.02191 [2]: https://www.quantamagazine.org/no-dark-energy-no-chance-cosmologists-contend-20191217/ https://www.quantamagazine.org/no-dark-energy-no-chance-cosm...

knzhou 7y ago
Hold up, this is a different thing than what [1] and [2] are responding to.
- crazygringo 7y ago
  Yes, I'm totally lost. Was there accidental confusion here? Or is the new paper (by completely different authors) somehow building on those other papers and flick is implying it suffers from the same criticisms? Would love to know if this is genuinely newsworthy or not.
dannykwells 7y ago
It would be pretty impressive indeed if [1] countered this article, since the Arxiv preprint came online 6 days later.
ssivark 7y ago
Thanks! It’s a little disingenuous/irresponsible on part of the phys.org article to not even mention the Rubin+Heitlauf rebuttal and the ensuing discussion, even though they’re from a month ago. EDIT: No wait, this OP is about a different paper from a week later... Hmm.... interesting times.

crazygringo 7y ago

Do I understand correctly that this is actually saying that accelerating expansion of the universe may be in error? That there is, instead, no accelerating at all, but merely constant expansion? Or can there still be acceleration without dark energy? I'm unclear if they are essentially the same hypothesis or if there are more complicated subtleties I'm missing.

philipov 7y ago
There are very few ways to modify Einstein's Equations and still have them make sense. An easy one is to add a constant term. Such a term is known as the Cosmological Constant, and a positive value for it would result in a constant repulsive force between masses regardless of distance. This results in an accelerating expansion of the entire universe, but, with a supremely small value it only becomes noticeable at large scales, where it starts to dominate attractive gravity. This appears to model what we're observed happening with galaxy clusters. Dark Energy is a hypothesis for explaining why such a very small cosmological constant might exist, suggesting that the universe is permeated with a constant negative energy field. However, the article refers to observational evidence measuring the expansion of the universe, not dark energy. There is no evidence for dark energy as such, and if you listen to colloquia on cosmology, you will hear about the cosmological constant, not dark energy. It is not necessary to hypothesize the existence of negative energy particles to model what we've observed, and you'll only really hear the term used in the popular press because it sounds sexy.
- pdonis 7y ago
  > Dark Energy is a hypothesis for explaining why such a very small cosmological constant might exist, suggesting that the universe is permeated with a constant negative energy field. No, that's not what dark energy is. "Dark energy" is just a general term for "anything that acts like a cosmological constant in the Einstein Field Equation". It could be an actual physical constant, just an inherent property of spacetime, or it could be some kind of energy field. We don't know. (Btw, the energy associated with dark energy is positive, not negative; the pressure is what's negative.)

tus88 7y ago

"discovery"

ncmncm 7y ago

Haha, called it! Feynman warned about this specific phenomenon: basing new physics on the points at the extreme end of your graph, where the measurements are least reliable. In this case, these points correspond to demolition of the most distant and youngest stars in the sample, which could differ in many ways from the common, much more recent events. Low metallicity is a difference that is obvious to every AP, but there is no reason to assume it is the only one. We just don't get to study any young-universe stars that haven't blown up. Did anybody even discuss metallicity and possible effects on brightness of t1a sn's, when DE was first proclaimed? If not, why not?

dmix 7y ago
Does this have any affect on the search for dark matter? Are the two interconnected at all?
- lanstin 7y ago
  No. Dark matter is assumed to exist from the excessively quick rotation of stars around the cores of galaxies. Dark energy is/was assumed to exist in anomalous expansion of the universe based on redshifts.
  - stan_rogers 7y ago
    >Dark matter is assumed to exist from the excessively quick rotation of stars around the cores of galaxies. That's what initiated Zwicky's notion in the '30s. It is far from being the only, or even the main, evidence for dark matter (which can be read as "mass effects we can detect not associated with matter we can currently detect").
    - ncmncm 7y ago
      More accurately: motion dynamics not compatible with both General Relativity and the mass we can see and reasonably infer. There is of course a stupendously huge amount of mostly invisible "interstellar medium", and even more "intergalactic medium", mostly ions of loose atoms and small molecules, and we use estimates of how much of that there must be. If its motion has anything to do with plasma fluid dynamics, all bets are off, because those equations are what mathematicians call intractable, and physicists would call career-limiting. They will happily declare 3x more unknowable Dark Matter than normal stuff before allowing plasma dynamics to have any effect on anything. Can hardly blame them.

flashman 7y ago

To know if the universe is expanding, we need to know the following: how far away things are, and whether they're moving away from us. In an accelerating universe, there's evidence that things were moving away from us slower in the past. The evidence that things are moving away from us is that as the universe expands, the wavelength of any light travelling through it also expands, shifting it towards the red end of the spectrum: redshift. (Think of the wavelength of a wavy line drawn on a piece of rubber that's then stretched out.) We've known for nearly 100 years that the universe is expanding. (Edit: not just that the objects in it are moving apart but that space itself is expanding.) The evidence of accelerating expansion is that based on the redshift of nearby objects, we would expect distant objects to have a higher redshift than they actually do. That means they were moving away from us slower in the past, so something must be accelerating them. We use the brightness of Type Ia supernovae to measure distance. Even though supernovae aren't identically bright, their brightness follows a curve which lets us calculate their peak brightness (they are standardizable). This paper argues that the calculations cosmologists use to standardize supernovae brightness fail to take into account the age of the progenitor stars, as far as I can tell. If true, this means our distance measurements are inaccurate and these stars are actually closer than we thought, enough to restore to linear relationship between distance and redshift that one would expect in a universe expanding at a constant rate. In other words, their redshift is lower not because the expansion rate of space was lower in the past, but because they're not as far away as we thought they were.

mirimir 7y ago
That's how I understand it. But maybe there are other standardizable objects. The sense I got from TFA is that there aren't.
- kiliantics 7y ago
  There are actually. There is a class of star in the "tip of the red giant branch" (TRGB) which have also been used to calibrate luminosities of type Ia supernovae[0] to form a "cosmic distance ladder". I believe they have been used to confirm the accelerated expansion results (though less strongly). I am not super well versed in stellar evolution, but I believe that the TRGB should make this calibration method independent of progenitor age? Hopefully someone could chime in on this. I was formerly a cosmologist and would be very interested to know more about this result from any experts that might be reading this. [0] There is an explanation of this calibration here: https://aasnova.org/2019/07/26/tldr-the-trgb-gives-us-another-h0ttake/ https://aasnova.org/2019/07/26/tldr-the-trgb-gives-us-anothe...

fluxby 7y ago

Personally, I’m a fan of ideas of Quantized Inertia [1] [2] which proposes that Dark Energy does not exist at all. We’ve been on a wild goose chase after dark energy for 30 years, which so far has proven to be an untestable theory. [1] https://youtu.be/1itasiXNUPg https://youtu.be/1itasiXNUPg [2] https://youtu.be/VYdebV9YlnI https://youtu.be/VYdebV9YlnI

mathiasrw 7y ago

If you find things like this interesting I suggest you look on youtube for videos on the electric universe. The main take is that our current models having gravity as the main driving force shaping our universe is a misunderstanding - hence rejecting the idea of dark matter / dark energy that was "invented" to make for math for gravity work with the observations of expansion.

Jweb_Guru 7y ago
Despite the similar name, dark matter really has very little to do with dark energy, and the lines of evidence for them are totally different. AFAIK there is fairly overwhelming evidence for the existence of dark matter at this point, and it's mostly a question of what exactly it is rather than whether the effect is real.
- briantakita 7y ago
  Dr. Anthony Perat, protege of Hannes Alfven, has a cosmological model based on plasma, which is observable & subject to physically reproducible experiments & replaces the need for both Dark Matter & Dark Energy as mathematical artifacts. https://www.amazon.com/Physics-Plasma-Universe-Anthony-Peratt/dp/1461478189 https://www.amazon.com/Physics-Plasma-Universe-Anthony-Perat...
d2v 7y ago
... you mean this? https://www.vice.com/en_us/article/nz7neg/electric-universe-theory-thunderbolts-project-wallace-thornhill https://www.vice.com/en_us/article/nz7neg/electric-universe-...
_bohm 7y ago
It should be noted that among cosmologists, electric universe is widely considered to be bunk science.
- briantakita 7y ago
  And Plasma Physicists think that "dark matter", "dark energy", & the assertion of gravity (ignoring plasma) being the dominant force in the Univese is mathematics without physical evidence. Thus "pathological science". Irving Langmuir, discoverer of the double layer effect in plasmas & coined the term "plasma" physics, came up with the definition of "Pathological Science". He was also around during the birth of the "Standard Model". https://en.m.wikipedia.org/wiki/Pathological_science https://en.m.wikipedia.org/wiki/Pathological_science

ltbarcly3 7y ago

I guess people are going to act like I'm a lunatic, but of course it's wrong. Dark Energy violates basic conservation of energy, and the evidence for it has never been strong or convincing. Lots of us have been saying this since forever.

ncmncm 7y ago
Conservation of energy has only ever been observed in local conditions. The universe is not obliged to respect our local expectations, and has always turned out to violate them in uncomfortable ways. The ground looks flat near you (at least in Nebraska). The Sun seems to go around Earth.
- ltbarcly3 7y ago
  Which is more likely, that you can have infinite free energy or that the very careful measurements of the distances to supernova that happened billions of years ago on the other side of the universe, and for which we have virtually no standard yardstick to compare against are not accurate? You are just making an appeal to ignorance. All of physics and astronomy is based on the assumption that the rest of the universe follows the same basic laws that the part we can study follows. That the universe is isotropic and homogeneous is a necessary basic assumption to even begin to measure the distance to objects that are very far away. If you can't assume that the basic laws of physics operate the same everywhere, then you have no basis to make any claims about anything that isn't local.
  - ncmncm 7y ago
    That is the condition of cosmology. Not everyone envies it.
    - ltbarcly3 7y ago
      It's an assumption, and while you might make a reasonable argument to try to justify it, it's still an assumption. The real problem is when we cross from 'assuming these things, which we don't really have a strong reason to assume' to 'this is the way the universe is'. Without the qualifications it's extremely misleading and loses any basis it started with.

platz 7y ago

Sabine Hossenfelder comments on this paper: Dark Energy might not exist after all https://youtu.be/oqgKXQM8FpU https://youtu.be/oqgKXQM8FpU

ncmncm 7y ago
Amusingly, this video is about entirely different work that also calls into question the basis for claims about dark energy. Nobody seems to be saying how the two results interact. Taking away dark energy twice could give us negative dark energy, which would be fun. I don't know whether unexpected negative dark energy would be more embarrassing than unexpected zero dark energy.
- platz 7y ago
  Ah, that is funny - I just assumed i didn't understand the different descriptions because I'm not an expert. That they are different explains my puzzlement. * indeed this is the same result as https://www.quantamagazine.org/no-dark-energy-no-chance-cosmologists-contend-20191217/ https://www.quantamagazine.org/no-dark-energy-no-chance-cosm... which is different from the OP paper
- SubiculumCode 7y ago
  negative dark energy. sounds sexy.
- Jweb_Guru 7y ago
  It sounds like the earlier article is pretty flawed and doesn't control for things like redshift associated with the motion of the solar system, so I very much doubt that the observations in that paper will end up "stacking" with those in this one. I'm no expert, but it seems like this more recent paper presents a much more serious challenge to the existence of dark energy.

rs23296008n1 7y ago

Good. Science is meant to be a honest search for facts: data, knowledge and wisdom. Being wrong is a feature. "I don't know" is an acceptable starting point with no shame attached. Being certain means a mountain of data to back it up. Being allowed to be wrong is a requirement. Anyone saying a scientist can't ever be wrong is likely placing oddball limits on progress that will only damage and limit the future[1]. How can you experiment if you can never be wrong? It would be good if people knew about the mountain-of-data aspect of science. Even with that mountain, subtleties creep in and plenty of surprises still remain. Even something like water probably has properties we are clueless about. Interesting aspects that might redefine science itself and create entirely new approaches to medicine or manufacture or whatever. Maybe if you change temperature and pressure enough in the right way you end up with exotic metallic / bonding properties. Or some new water-based ion structure having other properties. Who knows? Maybe not. Perhaps water is what it is and there is not much more to learn. Asserting we already know everything about water leads to dogma[2] and inflexibility. That's just one example. Dark matter/dark energy may be a rounding error for all I know. Good. Now we know about the error. We* likely asked a bunch of other questions as well and now we have new answers about to appear because now that error has been confirmed. * not me. [1] being wrong about bridge structure is unhelpful as you drive over it. That kind of wrong is related but I'm not directly addressing that. [2] dogma has expectations, rules and consequences. Science has plenty of people who forget this and turn their understanding into dogma. That too is a experience generating moment that will catch up with them later. Mountain-of-data + knowledge + wisdom.

tiborsaas 7y ago
Dark matter is definitely not a rounding error [0]. There are multiple evidence for strong gravity effects where we just don't see the required matter the explain the observed phenomenons [1][2] [0] https://www.forbes.com/sites/briankoberlein/2016/09/23/rotating-galaxies-could-prove-dark-matter-wrong/ https://www.forbes.com/sites/briankoberlein/2016/09/23/rotat... [1] https://en.wikipedia.org/wiki/Bullet_Cluster#Significance_to_dark_matter https://en.wikipedia.org/wiki/Bullet_Cluster#Significance_to... [2] http://cosmology.berkeley.edu/Education/CosmologyEssays/Gravitational_Lensing.html http://cosmology.berkeley.edu/Education/CosmologyEssays/Grav... Briefly, dark matter is very real, it's our knowledge that is dark.

yeahigotgoats 7y ago

the science is settled! the science is settled!

exabrial 7y ago

Can someone eli5 why if space itself is expanding, how can an observer detect that if they too are expanding at the same rate?

osbertlancaster 7y ago
As I understand it: We are not expanding. Size of e.g. a hydrogen atom is not changing.
- magicalhippo 7y ago
  And we are not expanding because other forces are stronger at short range. Similar to how the electroweak force is preventing you from falling through your chair, even though the gravity of the entire earth is pulling you. Dark energy, as we thought before this paper at least, would overcome gravity only on the grandest scales, between galaxies.
cygx 7y ago
Spatial expansion is a great heuristic explanation, but it can be misleading: Locally, the cosmological constant will manifest as just another pseudo-force, easily overcome by nuclear and electromagnetic forces holding us together.

j-dr 7y ago

Even if this paper is correct, there is still overwhelming evidence for dark energy provided by other observations, in particular those of the Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillations (BAO). This article provides some details on why Dark Energy is in no danger of being called in question: https://www.quantamagazine.org/no-dark-energy-no-chance-cosmologists-contend-20191217/ https://www.quantamagazine.org/no-dark-energy-no-chance-cosm...

ash 7y ago
As far as I can tell, Quanta Magazine article does mention the original post findings. Additionally, the Quanta article and the findings preprint were published just a week apart. Not enough time to formulate a good response: * Quanta Magazine article: 17 Dec 2019 * Arxiv preprint: 10 Dec 2019 [1] CMB and BAO are mentioned in the original post too: > Other cosmological probes, such as the cosmic microwave background (CMB) and baryonic acoustic oscillations (BAO), are also known to provide some indirect and "circumstantial" evidence for dark energy, but it was recently suggested that CMB from Planck mission no longer supports the concordance cosmological model which may require new physics (Di Valentino, Melchiorri, & Silk 2019). Some investigators have also shown that BAO and other low-redshift cosmological probes can be consistent with a non-accelerating universe without dark energy (see, for example, Tutusaus et al. 2017). In this respect, the present result showing the luminosity evolution mimicking dark energy in SN cosmology is crucial and very timely. [1]: https://arxiv.org/abs/1912.04903 https://arxiv.org/abs/1912.04903
- ash 7y ago
  Correction: "Quanta Magazine article does NOT mention the original post findings"

guygurari 7y ago

It is hard to overstate how important the resolution of this question is to physics, and in particular to theoretical physics. The “cosmological constant problem”, that is the problem explaining the cosmological acceleration (if it exists), is arguably the most important and hardest question in high energy theoretical physics. Many theoreticians have spent significant effort studying this question, working under the assumption that the empirical evidence is solid. If this is not the case, it changes the landscape of cutting edge physics research. There are several reasons why explaining the observed acceleration is so hard. The cosmological constant (the measure of how much dark energy there is) is a tiny positive number which seems to require a lot of “fine tuning” to explain theoretically. We can easily include it in general relativity, but our best understanding of quantum physics says that if it is there then it should be much larger. This means there probably is something we don’t understand about its microscopic origins. If we try to build a microscopic model that has this small constant using string theory (our best guest at a complete theory), we find that such models are hard to create. In fact, it is not clear that any model that includes dark energy is even valid in string theory! Any way we look at it, it seems more difficult to explain this number if it is tiny and positive than if it is strictly zero (no acceleration). Finally, theoreticians don’t have much to go on when explaining this phenomenon besides this one single number — there aren’t closely related experiments we can combine to come up with a coherent picture of what’s happening. Combine this with particle physics, where accelerators provide us with an abundance of data. It is a single tiny number that has puzzled theoreticians for decades.

BoiledCabbage 7y ago
What's more mind-boggling to me is all these thousands of scientists running around looking at the extreme oddity of multi-dimensional string theory, and nobody bothered to check if the cosmological constant is actually real. It seems like physics is really being held back by perverse incentives. And of course my pocket view that string theory will turn out to be the single largest waste of brilliant human minds in history.
- eloff 7y ago
  I'm not a physicist, but I don't think string theory is a total waste. It agrees with our existing theories and predictions, so it can be viewed as just an alternative mathematical abstraction, and there is value in that. Whether or not tiny vibrating strings are really at the heart of things is neither here nor there. It's about as relevant to science as god.

mikorym 7y ago

As a mathematician, I will inherently be biased against dark matter and dark energy (if you're calculations don't fit, then your mathematics is not suitable, so change the math before you change the physical description). What is the relationship between dark matter and dark energy, and does this have any effect on the r^2 law assumptions and the introduction of dark matter? For example, does this mean that when we thought that r^2 was not strictly followed that in fact we had the positions of the bodies wrong?

fsh 7y ago
They are not related at all. Dark matter is visible on the scale of galaxies, dark energy on the scale of the universe. Dark matter is currently the best model that can describe the rotational curves of galaxies under the assumption that general relativity is correct. Since GR has so far stood all tests extremely well, this is a very compelling argument for the existence of dark matter. There are also some more direct observations, such as gravitational lensing caused by dark matter.
has2k1 7y ago
> if you're calculations don't fit, then your mathematics is not suitable, so change the math before you change the physical description Physics is littered with mathematical formulations predicting new phenomenon (forces and particles). > What is the relationship between dark matter and dark energy There is no known relationship between dark matter and dark energy. They could have been called unknown matter and unknown energy! The absence of a good account for each does not infer a relationship between the two.
- mikorym 7y ago
  > Physics is littered with mathematical formulations predicting new phenomenon (forces and particles). Sorry, I should have clarified: I mean I would spend all my days doubting the mathematics, rather than doubting the physical universe. If that makes sense? Of course all of mathematics can be argued to have a physical sort of root.
  - 7y ago

scotty79 7y ago

Do you know any good source where I could follow through the whole argument that universe is expanding and the expansion accelerates? Without handweaving.

vectorEQ 7y ago

if you look at the magnetic soup we call matter, or maybe electromagnetism is a better term, is dark matter / dark energy / anti-matter (&anti energy??) just the same thing of a higher frequency say if matter / observables go from 0hz - 30+ Zhz.. is dark energy from 30+Zhz to ???Zhz and perhaps anti matter / energy from ???Zhz to ???????Zhz? (more question marks being higher ? :D ) or is this completely invalid and a dumb thought?

_Microft 7y ago
Electromagnetism is only one of a number of fundamental forces [1]. See [0] if you are curious about EM radiation at different frequencies. Radio and microwaves, infrared and visible light, ultraviolet light up to x-rays and gammarays are all part of the EM spectrum. [0] https://en.wikipedia.org/wiki/Electromagnetic_spectrum https://en.wikipedia.org/wiki/Electromagnetic_spectrum [1] https://en.wikipedia.org/wiki/Standard_Model https://en.wikipedia.org/wiki/Standard_Model

scotty79 7y ago

Are galaxies in old universe more densely packed than in our neighbourhood? Can expansion be seen not in redshift but in angular distances of galaxies? I'm asking in general not in relationship to the article. It wouldn't help for the problem raised by this article.

imvetri 7y ago

One less thing to worry about.

SiempreViernes 7y ago

Preprint is here: https://arxiv.org/abs/1912.04903 https://arxiv.org/abs/1912.04903

nxpnsv 7y ago

So these guys criticize SN-!a as standard candles, and then rely on other results criticizing BAO and CMB measurements also indicating accelerating expansions. However, why all these measurement would err in the wrong direction is not clear. I'm not convinced yet.

mannykannot 7y ago

When dark energy was first accepted, it seemed to me, as an outsider, that it happened very quickly, without, apparently, any time as a possibly-contentious, 'could this be so?' hypothesis in the way that, for example, dark matter did (and, to some extent, still is.) That surprised me because, up to that point, there seemed to be a problem with the cosmological distance ladder, with different methods getting different results, and with there being stars that seemed older than the universe supposedly was. In comparison, when superluminal neutrinos were tentatively announced a few years ago, there was a lot of justified skepticism about there being experimental error (admittedly, overthrowing special relativity is an even more extraordinary claim than dark energy.)

Hoagy 7y ago

Late to the party but does anybody know if this is connected to the findings a few weeks ago that this Quanta article is replying to? (https://www.quantamagazine.org/no-dark-energy-no-chance-cosmologists-contend-20191217/ https://www.quantamagazine.org/no-dark-energy-no-chance-cosm...) I know they are proposing different mechanisms for the error in calculation but it gives a sense of a 'moment' shifting against dark energy. Coincidence?

cerealbad 7y ago

radiation spreads and matter clumps. in this universe matter was allowed to form but radiation dominates. island chains swallowed up by a rising ocean.