7 ms·

Hypothesis That Universe Has No Dark Matter and Is 27B Years Old

85 points by passwordoops 3y ago

yawpitch 3y ago
[flagged]
deleted 3y ago
[deleted]
austin-cheney 3y ago
Frequently, at least in the past, when people raise speculation about dark matter/energy that somehow becomes deeply controversial. The controversy is a very non-scientific position to take in the science of astronomy, which is both confusing and troubling. Science is meant to be challenged.
- boxed 3y ago
  Does it? I think it's more that we collectively try to tamp down on the breathless reporting of revolutions in media when there isn't any. As you say science should be challenged, but popular science reporting doesn't really do that...
- proaralyst 3y ago
  I tend to understand 'controversial' here as a shorthand for new theories not explaining some observations. There's lots of good evidence for the models that require dark matter and dark energy (which I also understand to be very different), so if you want to propose an alternative model it must do at least as well as those. My second belief is that popular science articles are not good at explaining nuance, and tend to focus on human factors. Both of these are fine for lay audiences but should probably not be used to judge the health of the scientific process itself
  - candiodari 3y ago
    It's just that people just can't deal with existence proofs. In Math people seriously tried for ~180 years to prove that you don't need a single existence proof (which notably means you can't have real numbers, or calculus) For Dark Matter we have existence proofs. It MUST exist, in some form, we just don't know what it is. It will take another century before we're at 180 years ...
- 3abiton 3y ago
  But in real life, there is a spillover of cultural norm into science communities, thus controversies in the sciences are born. In my university there used to be these 2 competing professor (and their respective teams) working on Dark Energy vs Modified Gravity, and their rivalry was very known on the campus. Whenever an external speaker invited by either one, you'd expect a presence from the other with very sharp round of questioning. It made physics fun for us.
- chongli 3y ago
  That’s because dark matter is frequently referred to as a theory. It’s not. Dark matter is a set of observations which we try to account for in our theories. New theories which account for some observations of dark matter but ignore others are rightfully considered suspect.
  - willis936 3y ago
    This assumes that dark matter exists when there has been no direct evidence of it. The observations demand that the models change to fit the data. Some argue a light touch (dark matter).
    - chongli 3y ago
      Entirely on the contrary. Dark matter is the label given to a set of anomalous observations. The entire problem is that we called it “dark matter” when we should have called it “missing mass”, because that’s what it is. There would be no controversy with the latter name.
      - queuebert 3y ago
        Technically, "missing gravity". The mass is inferred, but not absolutely required. (Though it is by far the simplest explanation.)
  - rcxdude 3y ago
    I'm not really sure that's a useful way of putting it. There are a set of observations which don't match expectations, one idea which explains most of them is that there is some matter present that we can't directly observe (and then there's a wide variety of more specific ideas of what the nature of this matter may be, some of which fit observations better than others). That's in contrast to the idea that our theory of gravity may be incorrect, which also explains some of the observations (including ones which dark matter does not), but less of them overall, and there's a wide variety of specific ideas of how we might modify gravity to fit the observations (and generally I think the difficulty is you can come up with modifications that explain one obversation well but it's hard to explain a lot of them at once). DM and MOND are referring to different ideas of matching the anomolous observations, not the observations themselves. And each is really a family of different theories, as opposed to one singular theory each.
- ordu 3y ago
  When I see people being yelled at for their non-standard theories in internet it mostly boils down to them ignoring (let's call it) the structure of a scientific knowledge, when they just pick from a textbooks statements they like, reject other statements they do not like, and then try to build something on top of a resulting mess. Scientific knowledge has a structure, similar to a structure of a math theory where axioms and definitions are used to prove theorems which in their turn are used to prove even more statements and so on. You can trace a path from any statement to axioms and definitions. But empirical sciences have structure more complex than that of math. They rely on empirical evidence which is limited by abilities of instruments, and they are subject to change when instruments become better. Sometimes they reject some hypotheses not due to contradicting evidence, but because there were several competing hypotheses and one of them had more supporting evidence. If you start asking questions why physics thinks that X is true, and ask a lot of them not accepting any statement without asking such question then you'll get a lot of answers (conditionally on a benevolent physicist willing to answer them all), and you'll get eventually the structure of physics. But then comes some freak and claims he proved Einstein wrong, while it is clear to physicists that he doesn't understand the structure of the theory. To get a simple example I can resort to a calculus and... Imagine a student that when asked to prove that sin(x)/x -> 1 when x->0, "proved" it with a help of L'Hôpital's rule by taking derivatives of nominator and denominator. L'Hôpital's rule doesn't forbid it explicitly, and it may seem to be ok, but the trouble is the derivative of sin is proved with reference to a limit of sin(x)/x when x->0. So it becomes a circular reasoning and if you see how student does it you know that the student doesn't understand a thing about calculus, his attempts to pretend to know calculus are pathetic. Similar mistakes one can make in any discipline, though in them the structure or reasoning behind the theory is more complex, in math you can rely on pure logic, you need no Occam's Razor or something like. In social sciences you need to know all the history of your chosen domain of knowledge, how it evolved and why so. In physics it is simpler but still you need to understand at least some decisions made in the past (or maybe all of them, I'm not a physicist, so I'm just speculating). One can propose any insane theory contradicting to Einstein, Newton or anyone else and not to be yelled at, but you need to state your starting position carefully with regard to a structure of a scientific knowledge. Like if you want to derive statement sin(x)/x->1 when x->0 by resorting to L'Hôpital's rule then you need first to build your own calculus with blackjack and hookers from scratch in a way that make it to be a non-circular reasoning. And probably you will need to explain your motivation why are you doing that, because people will be asking about it a lot.
- mr_mitm 3y ago
  The controversy is really only present in laymen circles. In scientific circles, DM proponents vastly outnumber MOND proponents. I agree that science is meant to be challenged, but a worthy challenger must produce a better theory. The consensus is that DM fits the available evidence best. The case about dark energy is way less settled and way less clear due to lack of evidence. The standard model (i.e. a cosmological constant) fits best while having the least number of parameters, but I'd say that most cosmologists agree that it is not the final answer. It is expected that another theory with more free parameters will prevail, but current observations are not precise enough to decide which ones can be ruled out.
- yieldcrv 3y ago
  faithful die with their beliefs, scientists let their beliefs die its a pretty easy rubric to tell what you're currently doing on any topic ask yourself what information would alter your belief, is reproducibility a factor in your belief at all, does your belief conveniently exempt itself from reproducibility in some way, such as a reward for maintaining your belief ... perhaps after you die?
- Sysreq2 3y ago
  I don’t know anything about physics at that level. Really just the pop science stuff. But I know how people work pretty damn well. I will tell you, right now, with 100% certainty: dark matter is modern witch craft. Bunch of nerds got together and convinced themselves of magical forces that can’t be seen, heard, felt, or touched because their models of the universe don’t work without it. Might be 200 years until we figure it out, but there is an error somewhere and scientists are too proud to admit that they ain’t got a clue. How’d the moon get in the sky? Well I guess someone had to put it up there. How do birds fly? I guess God made them float on account of their lack of sin. Why don’t our models of gravity work? I guess the universe is made up of weird, invisible stuff. Humans don’t like not knowing. So they make wild theories about stuff no one can explain. Someone will come along and figure it out eventually.
  - exe34 3y ago
    The whole point of "dark" in the dark matter and energy cases is to indicate "we don't know." It looks like there needs to be something there for everything to make sense, but we can't see it. Let's try to work out what the properties of the stuff is based on what we can measure and see if anything starts to make sense.
  - andrewflnr 3y ago
    If you know anything about physics at that level, you would know that cosmologists don't like dark matter either. They'd love an alternative but the evidence keeps beating the candidates to death.
    - Sysreq2 3y ago
      Aristotle believed that all objects desire to be in their natural state. Throw a rock and it aims to return to the earth. Burn some twigs and the fire eventually stops. And the natural state of any object is at rest. Every piece of evidence for hundreds of years proved this point. Every scientist knew it to be true. And yet I ask you today, does an object in motion desire to rest OR does it stay in motion until acted upon by an outside force? It wasn’t until later that people had the tools to say, hey, wait a minute, this isn’t right. There is more here than we understand. Which of these scenarios seems more likely: 85% of the matter and 95% of the universe is made up of stuff that we can’t detect, doesn’t interact with anything and doesn’t follow the rules of everything else OR there is something going on that we don’t yet understand?
- dotnet00 3y ago
  The deeper you get into scientific communities, the less controversial it is to speculate since the more likely you are to care about knowing enough about the topic before saying anything (or otherwise have a better read on how much you don't know of what you're talking about). The controversy comes up because it has become pop science to discuss alternative proposals to DM/DE without properly conveying why DM/DE are the leading candidates for their associated measurement abnormalities. So you get a lot of people who functionally know nothing about the topic arguing that DM/DE are illogical because according to them scientists are just fudging the data. This is a thing even with the more informed/STEM-minded crowd of HN.
- rcxdude 3y ago
  The thing is, MOND was for a long time the preferred option, for basically all the same reasons a scientifically-literate layman would prefer it. The only reason DM is generally the more popular option amongst physicists is because it's beaten out the other theories at explaining the data (and it's not like it's universal: as can be seen by this paper there are many credible scientists still exploring and advocating for the idea, even if they are the minority). What I think gets tiring is people looking at it without that much depth (and pop-sci articles are a puddle) and then jumping to the conclusion that the majority of scientists are wrong because obviously MOND-type theories are a more appealing option. They would be, if they worked well enough. DM itself still has problems with some observations. It's not settled, but it's not going to get settled by a bunch of internet comments.
boxed 3y ago
Just a few days ago there was an alternative gravity theory linked here that proposed no dark matter. I have to ask the same question about this linked article: can this model handle the found galaxies that are missing dark matter? Because if not, that's basically game over directly no?
- magicalhippo 3y ago
  There's also the Bullet Cluster[1]. I'm just a layman, but at this point it seems to me there's a strong chance there's two things going on, not just one. As in, we likely have actual dark matter, say sterile neutrinos, but we also have something else like quantum corrections to gravity. [1]: https://en.wikipedia.org/wiki/Bullet_Cluster https://en.wikipedia.org/wiki/Bullet_Cluster
danbruc 3y ago
Not an expert but the major issue to me seems that the proposed model CCC+TL makes use of tired light (TL) which is an almost 100 year old idea with no supporting evidence or theoretical underpinning, at least according to Wikipedia [1]. The paper assumes TL but does not otherwise address it. [1] https://en.wikipedia.org/wiki/Tired_light https://en.wikipedia.org/wiki/Tired_light
- jvanderbot 3y ago
  I'm also not an expert, but the article states "It’s been tested and has been shown to match up with several observations, such as about how galaxies are spread out and how light from the early universe has evolved."
  - danbruc 3y ago
    Sure, it matches some observations, it would be pretty useless if it did not, but it has to match all of them. But my point with the use of tired light is that there seems to not even be a workable theory how this could work. The idea is that light loses energy as it travels through space and therefore shifts towards red, but nobody can say how this would work. An early but immediately discarded idea was that light bumps into matter on its way and loses energy in those interactions, but that does not work because it would make everything look blurry as light scatters in all directions due to those interactions. As far as I can tell from a few minutes of reading, nothing was ever proposed that could work and matches with observations. But the CCC+TL paper ignores that, assumes that TL is true, and works from there.
- perihelions 3y ago
  That article reads to me as if that theory is outright incompatible with the experimental evidence. Like: tired light predicts the wavelength of light from distant sources gets increased. Expanding universe predicts that—and additionally, that distant objects will be appear to be undergoing time dilation, by the same factor as their redshift. Astronomical observations of distant supernovas' light curves shows the latter. Here's a page focused on explaining this stuff: https://www.astro.ucla.edu/~wright/tiredlit.htm https://www.astro.ucla.edu/~wright/tiredlit.htm - "The tired light model does not predict the observed time dilation of high redshift supernova light curves. This time dilation is a consequence of the standard interpretation of the redshift: a supernova that takes 20 days to decay will appear to take 40 days to decay when observed at redshift z=1."
badcppdev 3y ago
I wish that they were clear about whether they were talking about dark energy or dark matter. Quotes from the author of the paper seem to use both terms which is confusing. All I know is that dark energy != dark matter "Despite the name, dark energy isn’t like dark matter, except that they’re both invisible. Dark matter pulls galaxies together, while dark energy pushes them apart." - 0 [0] - https://www.cfa.harvard.edu/research/topic/dark-energy-and-dark-matter#:~:text=Despite%20the%20name%2C%20dark%20energy,dark%20energy%20pushes%20them%20apart https://www.cfa.harvard.edu/research/topic/dark-energy-and-d....
frumiousirc 3y ago
> While his analysis concludes his hybrid tired light theory can play nicely with certain features of the Universe's residual echoes of light and sound, it does so only if we also ditch the idea that dark matter is also a thing. Is it the journal or the researcher (or me) being obtuse here? A new theory can not just ignore observations of localized structure such as galaxy rotation speeds (and be taken seriously). If dark matter is removed, the theory must account for why galaxies rotate faster than merely their visible matter allows.
zettabomb 3y ago
The original source from the University of Ottowa would probably be a better link: https://www.uottawa.ca/about-us/media/news/new-research-suggests-our-universe-has-no-dark-matter https://www.uottawa.ca/about-us/media/news/new-research-sugg...
perlgeek 3y ago
There are now several good lines of evidence for dark matter, at least: * rotation curves of galaxies * cosmic microwave background fluctuations * gravitational lensing of galaxies which would otherwise have far too little mass Whenever a "no dark matter" proposal comes along, I do a quick ctrl+f if it even tries to address all three lines of evidence. This doesn't seem to be the case here. Don't get me wrong, this could still be an interesting approach to cosmology, but IMHO it's not ready for widespread coverage to a possibly-not-so-informed audience until it tackles all three.
- deleted 3y ago
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- throw1234651234 3y ago
  Appreciate people "going back to the fundamentals" - without sarcasm, I lived for ages without even ever understanding where the idea of dark matter comes from. To be honest, I still don't understand how "cosmic microwave background fluctuations" is an argument for dark matter, but #1 and #2 at least help me intuitively understand where the theory comes from.
  - sigmoid10 3y ago
    Cosmic microwave background fluctuations are actually some of the strongest, most precisely measured evidence we have today for DM. The CMB was measured with incredibly high resolution thanks to the Planck satellite [1], and when you look at the distribution of angular sizes of the density fluctuations, you get a very peculiar plot [2]. Through some rather complicated math, the position and height of the peaks in this plot directly correspond (among other things) to "normal" matter that interacts electromagnetically and "dark matter" which does not interact electromagnetically. Since at the time of the CMB the whole universe was still very hot and therefore ionized, the data tells us there was a large amount of matter that only interacted gravitationally, but not electromagnetically. Ex post facto, the amount of "dark" matter calculated this way directly corresponds to the amount you would need to also explain galaxy rotation curves and gravitational lensing observations in today's universe. [1] https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2013/03/planck_wmap_comparison/12584155-7-eng-GB/Planck_WMAP_comparison_pillars.jpg https://www.esa.int/var/esa/storage/images/esa_multimedia/im... [2] https://ned.ipac.caltech.edu/level5/Sept17/Freese/Figures/figure5.jpg https://ned.ipac.caltech.edu/level5/Sept17/Freese/Figures/fi...
CuriousCosmic 3y ago
The actual paper for those interested: Abstract: https://dx.doi.org/10.3847/1538-4357/ad1bc6 https://dx.doi.org/10.3847/1538-4357/ad1bc6 Direct PDF Link: https://iopscience.iop.org/article/10.3847/1538-4357/ad1bc6/pdf https://iopscience.iop.org/article/10.3847/1538-4357/ad1bc6/...
PaulHoule 3y ago
I don't accept the idea that there is really a problem between quantum mechanics and gravity. When it comes to making calculations, string theory works, loop quantum gravity works, and numerous other theories work. Had Steven Hawking been able-bodied we might even have been spared that whole ridiculous thing over the information loss "paradox". The difficulties of quantum gravity today are mainly experimental and not theoretical.
- dotnet00 3y ago
  If any of those theories worked, there indeed wouldn't be an issue. But none of them fully reconcile the massive discrepancies in predictions without adding glaring discrepancies of their own. If by "the difficulties of quantum gravity today are mainly experimental" you mean that if we could go and study the behavior of quantum mechanics near the event horizon of a black hole we might have solved the problem already, you'd be right, but that's kind of tautological.
  - PaulHoule 3y ago
    My guess is that you don't see anything that isn't semiclassical at the outside of any reasonably sized black hole (say greater than 1 Earth mass) My guess is that the classical picture of the black hole interior is completely wrong but of course you can't know because you can't look inside and then tell us what you saw.
- queuebert 3y ago
  Most of us physicists would probably prefer a theory without a mathematical singularity in the middle of it. ¯\_(ツ)_/¯
  - PaulHoule 3y ago
    It is the theory telling you it is wrong and it is gentle in doing so because it seems those singularities are always on the other side of an apparent (as opposed to event) horizon. The following paradox is never taken seriously: if I watch an object fall into a classical black hole I will never see it actually cross the horizon. That makes sense for a classical black hole because it lasts forever, but a semi classical black hole does not last forever so the viewer on the outside probably sees the object that fell in get destroyed when the black hole explodes at end, not to mention destroyed by the extreme tidal forces that will exist around the hole at the end of its life. If the classical picture of what falling in looks like from the outside makes no sense than I think the idea that you fall through the horizon in a finite proper time and then hit the singularity in the future of that really makes no sense. I think the outside observer who sees you torn apart by tidal forces near the apparent horizon and turned into radiation is probably right. That to me is a much more important “paradox” than the silly bet about information loss because if you throw out unitarity you throw out quantum mechanics. That people can pooh-pooh firewalls but believe in the no-unitarity fairy is just beyond me. (e.g. my PhD thesis was about an alternate way to compute quantum mechanical density of states and unitarity turned out to be the most important guiding principle in that)
ChrisArchitect 3y ago
[dupe] Some more discussion: https://news.ycombinator.com/item?id=39726388 https://news.ycombinator.com/item?id=39726388
deleted 3y ago
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85 points by passwordoops 3y ago

yawpitch 3y ago

[flagged]

deleted 3y ago

[deleted]

austin-cheney 3y ago

Frequently, at least in the past, when people raise speculation about dark matter/energy that somehow becomes deeply controversial. The controversy is a very non-scientific position to take in the science of astronomy, which is both confusing and troubling. Science is meant to be challenged.

boxed 3y ago
Does it? I think it's more that we collectively try to tamp down on the breathless reporting of revolutions in media when there isn't any. As you say science should be challenged, but popular science reporting doesn't really do that...
proaralyst 3y ago
I tend to understand 'controversial' here as a shorthand for new theories not explaining some observations. There's lots of good evidence for the models that require dark matter and dark energy (which I also understand to be very different), so if you want to propose an alternative model it must do at least as well as those. My second belief is that popular science articles are not good at explaining nuance, and tend to focus on human factors. Both of these are fine for lay audiences but should probably not be used to judge the health of the scientific process itself
- candiodari 3y ago
  It's just that people just can't deal with existence proofs. In Math people seriously tried for ~180 years to prove that you don't need a single existence proof (which notably means you can't have real numbers, or calculus) For Dark Matter we have existence proofs. It MUST exist, in some form, we just don't know what it is. It will take another century before we're at 180 years ...
3abiton 3y ago
But in real life, there is a spillover of cultural norm into science communities, thus controversies in the sciences are born. In my university there used to be these 2 competing professor (and their respective teams) working on Dark Energy vs Modified Gravity, and their rivalry was very known on the campus. Whenever an external speaker invited by either one, you'd expect a presence from the other with very sharp round of questioning. It made physics fun for us.
chongli 3y ago
That’s because dark matter is frequently referred to as a theory. It’s not. Dark matter is a set of observations which we try to account for in our theories. New theories which account for some observations of dark matter but ignore others are rightfully considered suspect.
- willis936 3y ago
  This assumes that dark matter exists when there has been no direct evidence of it. The observations demand that the models change to fit the data. Some argue a light touch (dark matter).
  - chongli 3y ago
    Entirely on the contrary. Dark matter is the label given to a set of anomalous observations. The entire problem is that we called it “dark matter” when we should have called it “missing mass”, because that’s what it is. There would be no controversy with the latter name.
    - queuebert 3y ago
      Technically, "missing gravity". The mass is inferred, but not absolutely required. (Though it is by far the simplest explanation.)
- rcxdude 3y ago
  I'm not really sure that's a useful way of putting it. There are a set of observations which don't match expectations, one idea which explains most of them is that there is some matter present that we can't directly observe (and then there's a wide variety of more specific ideas of what the nature of this matter may be, some of which fit observations better than others). That's in contrast to the idea that our theory of gravity may be incorrect, which also explains some of the observations (including ones which dark matter does not), but less of them overall, and there's a wide variety of specific ideas of how we might modify gravity to fit the observations (and generally I think the difficulty is you can come up with modifications that explain one obversation well but it's hard to explain a lot of them at once). DM and MOND are referring to different ideas of matching the anomolous observations, not the observations themselves. And each is really a family of different theories, as opposed to one singular theory each.
ordu 3y ago
When I see people being yelled at for their non-standard theories in internet it mostly boils down to them ignoring (let's call it) the structure of a scientific knowledge, when they just pick from a textbooks statements they like, reject other statements they do not like, and then try to build something on top of a resulting mess. Scientific knowledge has a structure, similar to a structure of a math theory where axioms and definitions are used to prove theorems which in their turn are used to prove even more statements and so on. You can trace a path from any statement to axioms and definitions. But empirical sciences have structure more complex than that of math. They rely on empirical evidence which is limited by abilities of instruments, and they are subject to change when instruments become better. Sometimes they reject some hypotheses not due to contradicting evidence, but because there were several competing hypotheses and one of them had more supporting evidence. If you start asking questions why physics thinks that X is true, and ask a lot of them not accepting any statement without asking such question then you'll get a lot of answers (conditionally on a benevolent physicist willing to answer them all), and you'll get eventually the structure of physics. But then comes some freak and claims he proved Einstein wrong, while it is clear to physicists that he doesn't understand the structure of the theory. To get a simple example I can resort to a calculus and... Imagine a student that when asked to prove that sin(x)/x -> 1 when x->0, "proved" it with a help of L'Hôpital's rule by taking derivatives of nominator and denominator. L'Hôpital's rule doesn't forbid it explicitly, and it may seem to be ok, but the trouble is the derivative of sin is proved with reference to a limit of sin(x)/x when x->0. So it becomes a circular reasoning and if you see how student does it you know that the student doesn't understand a thing about calculus, his attempts to pretend to know calculus are pathetic. Similar mistakes one can make in any discipline, though in them the structure or reasoning behind the theory is more complex, in math you can rely on pure logic, you need no Occam's Razor or something like. In social sciences you need to know all the history of your chosen domain of knowledge, how it evolved and why so. In physics it is simpler but still you need to understand at least some decisions made in the past (or maybe all of them, I'm not a physicist, so I'm just speculating). One can propose any insane theory contradicting to Einstein, Newton or anyone else and not to be yelled at, but you need to state your starting position carefully with regard to a structure of a scientific knowledge. Like if you want to derive statement sin(x)/x->1 when x->0 by resorting to L'Hôpital's rule then you need first to build your own calculus with blackjack and hookers from scratch in a way that make it to be a non-circular reasoning. And probably you will need to explain your motivation why are you doing that, because people will be asking about it a lot.
mr_mitm 3y ago
The controversy is really only present in laymen circles. In scientific circles, DM proponents vastly outnumber MOND proponents. I agree that science is meant to be challenged, but a worthy challenger must produce a better theory. The consensus is that DM fits the available evidence best. The case about dark energy is way less settled and way less clear due to lack of evidence. The standard model (i.e. a cosmological constant) fits best while having the least number of parameters, but I'd say that most cosmologists agree that it is not the final answer. It is expected that another theory with more free parameters will prevail, but current observations are not precise enough to decide which ones can be ruled out.
yieldcrv 3y ago
faithful die with their beliefs, scientists let their beliefs die its a pretty easy rubric to tell what you're currently doing on any topic ask yourself what information would alter your belief, is reproducibility a factor in your belief at all, does your belief conveniently exempt itself from reproducibility in some way, such as a reward for maintaining your belief ... perhaps after you die?
Sysreq2 3y ago
I don’t know anything about physics at that level. Really just the pop science stuff. But I know how people work pretty damn well. I will tell you, right now, with 100% certainty: dark matter is modern witch craft. Bunch of nerds got together and convinced themselves of magical forces that can’t be seen, heard, felt, or touched because their models of the universe don’t work without it. Might be 200 years until we figure it out, but there is an error somewhere and scientists are too proud to admit that they ain’t got a clue. How’d the moon get in the sky? Well I guess someone had to put it up there. How do birds fly? I guess God made them float on account of their lack of sin. Why don’t our models of gravity work? I guess the universe is made up of weird, invisible stuff. Humans don’t like not knowing. So they make wild theories about stuff no one can explain. Someone will come along and figure it out eventually.
- exe34 3y ago
  The whole point of "dark" in the dark matter and energy cases is to indicate "we don't know." It looks like there needs to be something there for everything to make sense, but we can't see it. Let's try to work out what the properties of the stuff is based on what we can measure and see if anything starts to make sense.
- andrewflnr 3y ago
  If you know anything about physics at that level, you would know that cosmologists don't like dark matter either. They'd love an alternative but the evidence keeps beating the candidates to death.
  - Sysreq2 3y ago
    Aristotle believed that all objects desire to be in their natural state. Throw a rock and it aims to return to the earth. Burn some twigs and the fire eventually stops. And the natural state of any object is at rest. Every piece of evidence for hundreds of years proved this point. Every scientist knew it to be true. And yet I ask you today, does an object in motion desire to rest OR does it stay in motion until acted upon by an outside force? It wasn’t until later that people had the tools to say, hey, wait a minute, this isn’t right. There is more here than we understand. Which of these scenarios seems more likely: 85% of the matter and 95% of the universe is made up of stuff that we can’t detect, doesn’t interact with anything and doesn’t follow the rules of everything else OR there is something going on that we don’t yet understand?
dotnet00 3y ago
The deeper you get into scientific communities, the less controversial it is to speculate since the more likely you are to care about knowing enough about the topic before saying anything (or otherwise have a better read on how much you don't know of what you're talking about). The controversy comes up because it has become pop science to discuss alternative proposals to DM/DE without properly conveying why DM/DE are the leading candidates for their associated measurement abnormalities. So you get a lot of people who functionally know nothing about the topic arguing that DM/DE are illogical because according to them scientists are just fudging the data. This is a thing even with the more informed/STEM-minded crowd of HN.
rcxdude 3y ago
The thing is, MOND was for a long time the preferred option, for basically all the same reasons a scientifically-literate layman would prefer it. The only reason DM is generally the more popular option amongst physicists is because it's beaten out the other theories at explaining the data (and it's not like it's universal: as can be seen by this paper there are many credible scientists still exploring and advocating for the idea, even if they are the minority). What I think gets tiring is people looking at it without that much depth (and pop-sci articles are a puddle) and then jumping to the conclusion that the majority of scientists are wrong because obviously MOND-type theories are a more appealing option. They would be, if they worked well enough. DM itself still has problems with some observations. It's not settled, but it's not going to get settled by a bunch of internet comments.

boxed 3y ago

Just a few days ago there was an alternative gravity theory linked here that proposed no dark matter. I have to ask the same question about this linked article: can this model handle the found galaxies that are missing dark matter? Because if not, that's basically game over directly no?

magicalhippo 3y ago
There's also the Bullet Cluster[1]. I'm just a layman, but at this point it seems to me there's a strong chance there's two things going on, not just one. As in, we likely have actual dark matter, say sterile neutrinos, but we also have something else like quantum corrections to gravity. [1]: https://en.wikipedia.org/wiki/Bullet_Cluster https://en.wikipedia.org/wiki/Bullet_Cluster

danbruc 3y ago

Not an expert but the major issue to me seems that the proposed model CCC+TL makes use of tired light (TL) which is an almost 100 year old idea with no supporting evidence or theoretical underpinning, at least according to Wikipedia [1]. The paper assumes TL but does not otherwise address it. [1] https://en.wikipedia.org/wiki/Tired_light https://en.wikipedia.org/wiki/Tired_light

jvanderbot 3y ago
I'm also not an expert, but the article states "It’s been tested and has been shown to match up with several observations, such as about how galaxies are spread out and how light from the early universe has evolved."
- danbruc 3y ago
  Sure, it matches some observations, it would be pretty useless if it did not, but it has to match all of them. But my point with the use of tired light is that there seems to not even be a workable theory how this could work. The idea is that light loses energy as it travels through space and therefore shifts towards red, but nobody can say how this would work. An early but immediately discarded idea was that light bumps into matter on its way and loses energy in those interactions, but that does not work because it would make everything look blurry as light scatters in all directions due to those interactions. As far as I can tell from a few minutes of reading, nothing was ever proposed that could work and matches with observations. But the CCC+TL paper ignores that, assumes that TL is true, and works from there.
perihelions 3y ago
That article reads to me as if that theory is outright incompatible with the experimental evidence. Like: tired light predicts the wavelength of light from distant sources gets increased. Expanding universe predicts that—and additionally, that distant objects will be appear to be undergoing time dilation, by the same factor as their redshift. Astronomical observations of distant supernovas' light curves shows the latter. Here's a page focused on explaining this stuff: https://www.astro.ucla.edu/~wright/tiredlit.htm https://www.astro.ucla.edu/~wright/tiredlit.htm - "The tired light model does not predict the observed time dilation of high redshift supernova light curves. This time dilation is a consequence of the standard interpretation of the redshift: a supernova that takes 20 days to decay will appear to take 40 days to decay when observed at redshift z=1."

badcppdev 3y ago

I wish that they were clear about whether they were talking about dark energy or dark matter. Quotes from the author of the paper seem to use both terms which is confusing. All I know is that dark energy != dark matter "Despite the name, dark energy isn’t like dark matter, except that they’re both invisible. Dark matter pulls galaxies together, while dark energy pushes them apart." - 0 [0] - https://www.cfa.harvard.edu/research/topic/dark-energy-and-dark-matter#:~:text=Despite%20the%20name%2C%20dark%20energy,dark%20energy%20pushes%20them%20apart https://www.cfa.harvard.edu/research/topic/dark-energy-and-d....

frumiousirc 3y ago

> While his analysis concludes his hybrid tired light theory can play nicely with certain features of the Universe's residual echoes of light and sound, it does so only if we also ditch the idea that dark matter is also a thing. Is it the journal or the researcher (or me) being obtuse here? A new theory can not just ignore observations of localized structure such as galaxy rotation speeds (and be taken seriously). If dark matter is removed, the theory must account for why galaxies rotate faster than merely their visible matter allows.

zettabomb 3y ago

The original source from the University of Ottowa would probably be a better link: https://www.uottawa.ca/about-us/media/news/new-research-suggests-our-universe-has-no-dark-matter https://www.uottawa.ca/about-us/media/news/new-research-sugg...

perlgeek 3y ago

There are now several good lines of evidence for dark matter, at least: * rotation curves of galaxies * cosmic microwave background fluctuations * gravitational lensing of galaxies which would otherwise have far too little mass Whenever a "no dark matter" proposal comes along, I do a quick ctrl+f if it even tries to address all three lines of evidence. This doesn't seem to be the case here. Don't get me wrong, this could still be an interesting approach to cosmology, but IMHO it's not ready for widespread coverage to a possibly-not-so-informed audience until it tackles all three.

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throw1234651234 3y ago
Appreciate people "going back to the fundamentals" - without sarcasm, I lived for ages without even ever understanding where the idea of dark matter comes from. To be honest, I still don't understand how "cosmic microwave background fluctuations" is an argument for dark matter, but #1 and #2 at least help me intuitively understand where the theory comes from.
- sigmoid10 3y ago
  Cosmic microwave background fluctuations are actually some of the strongest, most precisely measured evidence we have today for DM. The CMB was measured with incredibly high resolution thanks to the Planck satellite [1], and when you look at the distribution of angular sizes of the density fluctuations, you get a very peculiar plot [2]. Through some rather complicated math, the position and height of the peaks in this plot directly correspond (among other things) to "normal" matter that interacts electromagnetically and "dark matter" which does not interact electromagnetically. Since at the time of the CMB the whole universe was still very hot and therefore ionized, the data tells us there was a large amount of matter that only interacted gravitationally, but not electromagnetically. Ex post facto, the amount of "dark" matter calculated this way directly corresponds to the amount you would need to also explain galaxy rotation curves and gravitational lensing observations in today's universe. [1] https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2013/03/planck_wmap_comparison/12584155-7-eng-GB/Planck_WMAP_comparison_pillars.jpg https://www.esa.int/var/esa/storage/images/esa_multimedia/im... [2] https://ned.ipac.caltech.edu/level5/Sept17/Freese/Figures/figure5.jpg https://ned.ipac.caltech.edu/level5/Sept17/Freese/Figures/fi...

CuriousCosmic 3y ago

The actual paper for those interested: Abstract: https://dx.doi.org/10.3847/1538-4357/ad1bc6 https://dx.doi.org/10.3847/1538-4357/ad1bc6 Direct PDF Link: https://iopscience.iop.org/article/10.3847/1538-4357/ad1bc6/pdf https://iopscience.iop.org/article/10.3847/1538-4357/ad1bc6/...

PaulHoule 3y ago

I don't accept the idea that there is really a problem between quantum mechanics and gravity. When it comes to making calculations, string theory works, loop quantum gravity works, and numerous other theories work. Had Steven Hawking been able-bodied we might even have been spared that whole ridiculous thing over the information loss "paradox". The difficulties of quantum gravity today are mainly experimental and not theoretical.

dotnet00 3y ago
If any of those theories worked, there indeed wouldn't be an issue. But none of them fully reconcile the massive discrepancies in predictions without adding glaring discrepancies of their own. If by "the difficulties of quantum gravity today are mainly experimental" you mean that if we could go and study the behavior of quantum mechanics near the event horizon of a black hole we might have solved the problem already, you'd be right, but that's kind of tautological.
- PaulHoule 3y ago
  My guess is that you don't see anything that isn't semiclassical at the outside of any reasonably sized black hole (say greater than 1 Earth mass) My guess is that the classical picture of the black hole interior is completely wrong but of course you can't know because you can't look inside and then tell us what you saw.
queuebert 3y ago
Most of us physicists would probably prefer a theory without a mathematical singularity in the middle of it. ¯\_(ツ)_/¯
- PaulHoule 3y ago
  It is the theory telling you it is wrong and it is gentle in doing so because it seems those singularities are always on the other side of an apparent (as opposed to event) horizon. The following paradox is never taken seriously: if I watch an object fall into a classical black hole I will never see it actually cross the horizon. That makes sense for a classical black hole because it lasts forever, but a semi classical black hole does not last forever so the viewer on the outside probably sees the object that fell in get destroyed when the black hole explodes at end, not to mention destroyed by the extreme tidal forces that will exist around the hole at the end of its life. If the classical picture of what falling in looks like from the outside makes no sense than I think the idea that you fall through the horizon in a finite proper time and then hit the singularity in the future of that really makes no sense. I think the outside observer who sees you torn apart by tidal forces near the apparent horizon and turned into radiation is probably right. That to me is a much more important “paradox” than the silly bet about information loss because if you throw out unitarity you throw out quantum mechanics. That people can pooh-pooh firewalls but believe in the no-unitarity fairy is just beyond me. (e.g. my PhD thesis was about an alternate way to compute quantum mechanical density of states and unitarity turned out to be the most important guiding principle in that)

ChrisArchitect 3y ago

[dupe] Some more discussion: https://news.ycombinator.com/item?id=39726388 https://news.ycombinator.com/item?id=39726388

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