9 ms·

Cosmology Has Some Big Problems

64 points by LinuxBender 8y ago

michaelsbradley 8y ago
https://www.nobelprize.org/uploads/2018/06/alfven-lecture.pdf https://www.nobelprize.org/uploads/2018/06/alfven-lecture.pd...
- eaim 8y ago
  Yes! Thanks for this
stcredzero 8y ago
It is of course entirely plausible that the validity of general relativity breaks down much closer to our own home than at the edge of the hypothetical end of the universe. Is it really? Have people formulated specific break downs, then gone to look for evidence?
- fhars 8y ago
  A more damning quote seems to be Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere. There is no reference given, but I have the suspicion that it refers to the discovery of galaxies with almost no dark matter (cf. https://news.ycombinator.com/item?id=16701248 https://news.ycombinator.com/item?id=16701248). That does indeed refute the assumpion that dark matter is everywhere, but that is not an assumption anyone makes and is not part of any relevant theory of dark matter. On the contrary, the existence of galaxies like that is generally seen as one of the strongest arguments for the existence of dark matter as an independent, if elusive physical entity.
  - nabnob 8y ago
    Couldn't it just as easily mean that our predictions based on general relativity are wrong? Either 1) the prediction for a particular galaxy is right, and there's no "dark energy" or "dark matter" or 2) the prediction is wrong, and you add a bunch of dark energy or dark matter to make the equations work out. It's not testable at all - no matter whether predictions for a particular galaxy are right or wrong, you're still allowing yourself to think that the theory is correct. How is this scientific?
    - darkmighty 8y ago
      It's not that simple. It's not like a) Some galaxies fit predictions, b) Some do not, and we add unknown dark matter. It's that when they do not fit predictions, there is a single parameter (the mass of dark matter) that does explain its behavior, whose model is that of a weakly interacting gas halo. So dark matter tries to fix things in a very precise way, it's not an arbitrary curve fitting exercise. Now whether there is really weakly interacting matter out there or some other explanation is valid is still an open question afaik; but the evidence is quite strong so far.
      - astrobe_ 8y ago
        > Now whether there is really weakly interacting matter out there Not "out there". It's supposed to be >80% of the matter of the universe. We supposedly are eating some every day.
        pdonis 8y ago
        > It's supposed to be >80% of the matter of the universe. We supposedly are eating some every day. It's >80% of the average density of the matter in the universe. But that's an average over all of the universe. On the scale of our planet, or of the solar system, that density is negligible--as in "30 orders of magnitude smaller than the density of the stuff you eat" negligible.
    - fhars 8y ago
      No, the only consistent explanation for both the overwhelming majority of galaxies as well as the few outliers is general relativity and independent dark mater. All other theories that make testable predictions (modified newtonian dynamics or MOND seems to be the only class that is not completely add odds with almost all observations) cannot explain the behaviour of those galacies that are as big as other galaxies but rotate wih a different speed. But the difference is easily explained with different amounts of dark matter in the galaxies, and the bullet cluster cited elsewhere in this thread give a plausible explanation of how these galaxies might form.
    - pdonis 8y ago
  - czbond 8y ago
    Not necessarily. This great video from PBS Spacetime is a fairly detailed, but good for a 'nearly' layman on the findings in depth. https://www.youtube.com/watch?v=5t0jaE--l0Y https://www.youtube.com/watch?v=5t0jaE--l0Y A discussion on how a galaxy could be missing dark matter - or how it could be separated from a galaxy
- AnimalMuppet 8y ago
  Well... assuming that the local rules are the same as the rules billions of light-years away is an assumption, based on a philosophical presupposition that the rules are uniform. What probability should we assign to that assumption? 100% in the absence of evidence to the contrary? Or should we reserve some skepticism, remembering that it is an assumption? Your question is reasonable: Have people formulated specific breakdowns, and gone looking? But it's also unreasonable. An assumption shouldn't necessarily be treated beyond plausible doubt until we can prove it wrong.
  - jerf 8y ago
    "Have people formulated specific breakdowns, and goon looking?" They have. Considerable effort has been expended trying to detect changes in various constants related to light, including speed but also some other things. It is expected that if constants were changing, spectra would change as well. So far as I know, all those results have been negative, but it's not for lack of trying. Similar arguments can be deployed for the nuclear forces as well w.r.t. spectrum, rates of fusion, various things you'd be able to observe in certain types of supernovae, etc. One of the things I don't like about this genre of articles is that it's typically quite mistaken, if not outright disingenuous, about the current state of cosmology. From what I could see, the idea that cosmologists are all stodgy old fogies brought up in a paradigm of the Big Bang and who won't entertain any other thoughts is diametrically opposed to the truth. To my eyes, the field is a bubbling cauldron of various exotic ideas and attempts to resolve all these issues. There's no lack of theories in cosmology and attempts to resolve these issues, including many quite radical ones (the holographic principle, changing constants over time, heck even "Dark Energy" is quite radical in many ways even if it is also the accepted theory at the moment). What we lack are theories that explain all the observations. Dark matter is favored not because it's the only idea that anyone has come up with, but because it's still the one that best fits the facts. (As PBS Space Time pointed out last week, ironically, the galaxies recently discovered to not contain dark matter are themselves quite strong evidence dark matter must exist: https://www.youtube.com/watch?v=5t0jaE--l0Y https://www.youtube.com/watch?v=5t0jaE--l0Y , because almost all other theories to explain galactic rotations are based on characteristics that can not vary by galaxy like matter distributions can. "MOND", for instance, is not "MOND, except in these two galaxies".) If you can solve all these problems, as near as I can tell, you'll be celebrated, not shut down by the old fogerati. But be prepared for your theory to need to cover a lot of existing observations; we're centuries past "Well, what if gravity just worked differently?" or "What if the constants aren't constant?" You're going to need a great deal more detail than that.
rgrieselhuber 8y ago
Biggest takeaway from this is how many underlying presuppositions appear to be assumptions.
- eaim 8y ago
  Yes.
shrimp_emoji 8y ago
>It's perhaps worth stopping to ask why astrophysicists hypothesize dark matter to be everywhere in the universe? >To explain observations of galaxies inconsistent with general relativity, the existence of dark matter was posited as an unknown and invisible form of matter calculated to make up more than a quarter of all mass-energy content in the universe Food for thought: the best current evidence of dark matter is the Bullet Cluster[0]. In particular, look at this picture: https://upload.wikimedia.org/wikipedia/commons/a/a8/1e0657_scale.jpg https://upload.wikimedia.org/wikipedia/commons/a/a8/1e0657_s... At first, these were two blobs of dark matter and gas. They collided. That resulted in what we see now: the dark matter portions (purple, measured by gravity lensing) magically went through each other (because dark matter is weird like that) while the gas portions (pink) actually collided and formed a shockwave (like normal matter behaves), with much of the gas remaining in the middle. The tone in the article quotes there makes it seem like dark matter is some esoteric rounding error, but that seems like pretty "solid" evidence for... the anomalous mass readings we call dark matter. 0: https://en.wikipedia.org/wiki/Bullet_Cluster https://en.wikipedia.org/wiki/Bullet_Cluster
- deleted 8y ago
  [deleted]
calebgilbert 8y ago
To be fair, I bet most, if not all, cosmologists would agree that they know far less than they don't know. The title of the article is a bit sensationalistic from that point of view, but then I guess "Cosmology has some big details to work on" isn't nearly as catchy.
hhs 8y ago
Interesting view. Near the end, it says: “The crux of today's cosmological paradigm is that in order to maintain a mathematically unified theory valid for the entire universe, we must accept that 95 percent of our cosmos is furnished by completely unknown elements and forces for which we have no empirical evidence whatsoever.” Empiricism is based on sense observations. And a lot of science has been confined to human senses. I’m curious if tapping into more basic science research by analyzing different types of senses, for instance, available to animals, may offer breakthroughs down the line. For instance, fish employ the lateral line system to detect pressure gradients in the environment.
- wilg 8y ago
  What kind of senses available to animals are there that we should be using for science? Also I'm not entirely sure what you mean that we're confined to "the 5 senses". First, humans have way more senses. Second, I don't think it's confining ourself to build technology that converts something we can't sense (like gravitational waves) into something we can (like a spreadsheet).
- dfischer 8y ago
  What aren’t we using from the animal kingdom? We create sensors that are extra human. Infrared etc... Maybe this is an unknown unknown problem. We can’t develop technology for senses we do not know about and so on.
  - hhs 8y ago
    Indeed, I agree with your point, “Maybe this is an unknown unknown problem.” I’m not sure why my comment is being downvoted, is there something I said that’s in bad taste?
    - dfischer 8y ago
      I think you’re fine. Sorry you’re getting downvoted.
- chongli 8y ago
jcroll 8y ago
Ethan Siegel write up on this problem: https://www.forbes.com/sites/startswithabang/2018/06/22/why-cosmologys-expanding-universe-controversy-is-an-even-bigger-problem-than-you-realize/#3587f0422381 https://www.forbes.com/sites/startswithabang/2018/06/22/why-...
- acqq 8y ago
  But also about other claims from the Ekeberg's article (who, as I see, is a "a philosopher of science"): https://www.forbes.com/sites/startswithabang/2018/07/26/theres-a-debate-raging-over-whether-dark-matter-is-real-but-one-side-is-cheating/ https://www.forbes.com/sites/startswithabang/2018/07/26/ther... "There's A Debate Raging Over Whether Dark Matter Is Real, But One Side Is Cheating" Careful reader of Ekeberg's article can both recognize that the article claims are inspired by the claims of the "cheating" side but also that where he writes his own he completely fails on physics. I.e. if one side is cheating, he'd be a third side, the one that's completely unscientific: even the physicists that develop theories that compete with dark matter would not write what Ekeberg wrote: "Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere. But according to the latest measurements, it is not, suggesting the theory needs to be reexamined." It's plain nonsense. The reason: https://www.forbes.com/sites/startswithabang/2019/01/16/mysterious-galaxy-measured-exquisitely-and-contains-no-dark-matter-at-all/ https://www.forbes.com/sites/startswithabang/2019/01/16/myst... "Ironically, the discovery of a galaxy without dark matter — amidst a sea of galaxies that require huge amounts of it — helps prove the validity of the dark matter-rich picture of the Universe. Only if normal matter can be separated out from the dark matter and left to form its own structures would such a galaxy be possible." We even have the pictures where the galaxies and dark matter aren't at the same place, totally the opposite of Ekeberg's "everywhere" strawman claim, and exactly that opposite was always treated as the biggest support for dark matter: https://www.forbes.com/sites/startswithabang/2017/11/09/the-bullet-cluster-proves-dark-matter-exists-but-not-for-the-reason-most-physicists-think/ https://www.forbes.com/sites/startswithabang/2017/11/09/the-... Once I've reached that strawman claim, I've checked what the profession of Ekeberg is. I openly admit his uncritical bias just confirmed my own bias about that profession.
astro123 8y ago
I'm a grad student working on cosmology, and while I agree there is a lot of work still to do (we don't know what 95% of the matter that makes up the universe is!), I disagree with a lot of what the author says. > Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere. We have found evidence of a few galaxies without DM. But most galaxies provide strong evidence for DM - https://en.wikipedia.org/wiki/Galaxy_rotation_curve https://en.wikipedia.org/wiki/Galaxy_rotation_curve > For a crucial function of theories such as dark matter, dark energy and inflation, which each in its own way is tied to the big bang paradigm Big bang was only the accepted paradigm from the 60s (post CMB observations). We have had DE since Einstein in 1917 and DM since Zwicky in the 30s. > Historically, Newton's physical laws made up a theoretical framework that worked for our own solar system with remarkable precision. Both Uranus and Neptune, for example, were discovered through predictions based on Newton's model. But as the scales grew larger, its validity proved limited. Actually some of the earliest evidence for GR came from the orbit of mercury https://en.wikipedia.org/wiki/Tests_of_general_relativity https://en.wikipedia.org/wiki/Tests_of_general_relativity > It is of course entirely plausible that the validity of general relativity breaks down much closer to our own home than at the edge of the hypothetical end of the universe. And if that were the case, today's multilayered theoretical edifice of the big bang paradigm would turn out to be a confusing mix of fictional beasts invented to uphold the model This is something that people are working on! This is a hypothesized source of DE. However, disproving GR does nothing to disprove the big bang. > Today's space telescopes provide no direct view of anything I have no idea what that means. They literally observe the sky... There is a ton of work to do: finding what DM is, finding what DE is, finding whether GR is correct. But I'm not sold that the author knows what he is talking about...
- scrozart 8y ago
  > > Today's space telescopes provide no direct view of anything > I have no idea what that means. They literally observe the sky... Seriously! At this point they're just spitballing.
  - astro123 8y ago
    I was maybe a bit too cavalier here. I think I understand what the author means - the data that they gather is understood in the context of the model that we think is best. But, it isn't as if cosmologists are rigidly holding to the model. Here's a paper looking at extensions to lambda CDM https://arxiv.org/abs/1512.05356 https://arxiv.org/abs/1512.05356. As I mentioned, changing GR is being looked at as an alternative to DE http://www.resceu.s.u-tokyo.ac.jp/workshops/resceu08s/presen/koyama-1.pdf http://www.resceu.s.u-tokyo.ac.jp/workshops/resceu08s/presen... People aren't challenging some things though - I don't think anyone is seriously working on cosmologies that don't include a big bang, because without one I can't imagine how you explain the CMB.
ccvannorman 8y ago
I've never been a fan of Dark Matter. Not all galaxies have dark matter, but only incredibly diffuse galaxies don't have it[0]. Doesn't that mean that the density of matter in a galaxy is what gives rise to "faster rotations/more gravity", and not just the total matter irrespective of its galactic density? Furthermore, the "Bullet Cluster" example is telling. Apparently, the extra mass stuck around the more dense part of the galaxy, and not in the less dense gas cloud that resulted from the collision. Again, only the dense parts of this cluster exhibit "faster rotations/more gravity". So to me, this is terribly un-compelling. So there's a magic invisible matter that just so happens to only coalesce around dense galaxies/galactic areas and never around sparse ones. [0] http://www.astronomy.com/news/2019/03/ghostly-galaxy-without-dark-matter-confirmed http://www.astronomy.com/news/2019/03/ghostly-galaxy-without... edit: s/no matter/irrespective of (poor use of the homonym "matter")
eaim 8y ago
@astro123 There’s a tautology in your critique. You’re attempting to suggest that there is evidence for dark matter. There isn’t. Dark matter is a theory, one that has not yet produced empirical evidence to support it (& perhaps cannot ever do so.)
- mkl 8y ago
  If you want to reply to a comment, please click the "reply" button below that comment, rather than starting a new comment thread. @<username> doesn't do anything here.
  - eaim 8y ago
    Ah, understood, thanks. Sorry about that.
eaim 8y ago
@astro123 Sorry my comment uploaded before I was done. It is an error to state that there is evidence for dark matter. There is no evidence for it other than that as a hypothesis it adds support to a larger cosmological theory; that of the so-called Big Bang. But that is basically a circle in the proof. A tautology.
- ephimetheus 8y ago
  What about the Bullet Cluster?
  - eaim 8y ago
    If the Bullet Cluster had offered not hypothetical but empirical, incontrovertible evidence for Dark Matter, at this juncture we wouldn’t even be calling it Dark Matter anymore.
eaim 8y ago
@astro123 The following excerpt is the crux of the author’s argument regarding DM, & it points to the dark elephant in the room that a lot of physicists are bothered by but don’t want to discuss: “It's perhaps worth stopping to ask why astrophysicists hypothesize dark matter to be everywhere in the universe? The answer lies in a peculiar feature of cosmological physics that is not often remarked. For a crucial function of theories such as dark matter, dark energy and inflation, which each in its own way is tied to the big bang paradigm, is not to describe known empirical phenomena but rather to maintain the mathematical coherence of the framework itself while accounting for discrepant observations. Fundamentally, they are names for something that must exist insofar as the framework is assumed to be universally valid.”
eaim 8y ago
All said and done, the current state of cosmology (whether one falls in with mainstream theories or not) is a mess. It has so many addendums, codicils & caveats that one has to be almost a type of lawyer of physics to be able to navigate it. We await our new Einstein. Our new Heisenberg. Our elegant theory of everything; or as one science writer put it: The universe on a T-shirt.
eaim 8y ago
Here’s an article from Rob Sheldon, who worked on ROSETTA. He is less timid than Ekeberg: https://uncommondescent.com/intelligent-design/rob-sheldon-the-real-reason-there-is-a-crisis-in-cosmology/ https://uncommondescent.com/intelligent-design/rob-sheldon-t...

64 points by LinuxBender 8y ago

https://www.nobelprize.org/uploads/2018/06/alfven-lecture.pdf https://www.nobelprize.org/uploads/2018/06/alfven-lecture.pd...

eaim 8y ago
Yes! Thanks for this

stcredzero 8y ago

It is of course entirely plausible that the validity of general relativity breaks down much closer to our own home than at the edge of the hypothetical end of the universe. Is it really? Have people formulated specific break downs, then gone to look for evidence?

fhars 8y ago
A more damning quote seems to be Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere. There is no reference given, but I have the suspicion that it refers to the discovery of galaxies with almost no dark matter (cf. https://news.ycombinator.com/item?id=16701248 https://news.ycombinator.com/item?id=16701248). That does indeed refute the assumpion that dark matter is everywhere, but that is not an assumption anyone makes and is not part of any relevant theory of dark matter. On the contrary, the existence of galaxies like that is generally seen as one of the strongest arguments for the existence of dark matter as an independent, if elusive physical entity.
- nabnob 8y ago
  Couldn't it just as easily mean that our predictions based on general relativity are wrong? Either 1) the prediction for a particular galaxy is right, and there's no "dark energy" or "dark matter" or 2) the prediction is wrong, and you add a bunch of dark energy or dark matter to make the equations work out. It's not testable at all - no matter whether predictions for a particular galaxy are right or wrong, you're still allowing yourself to think that the theory is correct. How is this scientific?
  - darkmighty 8y ago
    It's not that simple. It's not like a) Some galaxies fit predictions, b) Some do not, and we add unknown dark matter. It's that when they do not fit predictions, there is a single parameter (the mass of dark matter) that does explain its behavior, whose model is that of a weakly interacting gas halo. So dark matter tries to fix things in a very precise way, it's not an arbitrary curve fitting exercise. Now whether there is really weakly interacting matter out there or some other explanation is valid is still an open question afaik; but the evidence is quite strong so far.
    - astrobe_ 8y ago
      > Now whether there is really weakly interacting matter out there Not "out there". It's supposed to be >80% of the matter of the universe. We supposedly are eating some every day.
      - pdonis 8y ago
        > It's supposed to be >80% of the matter of the universe. We supposedly are eating some every day. It's >80% of the average density of the matter in the universe. But that's an average over all of the universe. On the scale of our planet, or of the solar system, that density is negligible--as in "30 orders of magnitude smaller than the density of the stuff you eat" negligible.
  - fhars 8y ago
    No, the only consistent explanation for both the overwhelming majority of galaxies as well as the few outliers is general relativity and independent dark mater. All other theories that make testable predictions (modified newtonian dynamics or MOND seems to be the only class that is not completely add odds with almost all observations) cannot explain the behaviour of those galacies that are as big as other galaxies but rotate wih a different speed. But the difference is easily explained with different amounts of dark matter in the galaxies, and the bullet cluster cited elsewhere in this thread give a plausible explanation of how these galaxies might form.
  - pdonis 8y ago
- czbond 8y ago
  Not necessarily. This great video from PBS Spacetime is a fairly detailed, but good for a 'nearly' layman on the findings in depth. https://www.youtube.com/watch?v=5t0jaE--l0Y https://www.youtube.com/watch?v=5t0jaE--l0Y A discussion on how a galaxy could be missing dark matter - or how it could be separated from a galaxy
AnimalMuppet 8y ago
Well... assuming that the local rules are the same as the rules billions of light-years away is an assumption, based on a philosophical presupposition that the rules are uniform. What probability should we assign to that assumption? 100% in the absence of evidence to the contrary? Or should we reserve some skepticism, remembering that it is an assumption? Your question is reasonable: Have people formulated specific breakdowns, and gone looking? But it's also unreasonable. An assumption shouldn't necessarily be treated beyond plausible doubt until we can prove it wrong.
- jerf 8y ago
  "Have people formulated specific breakdowns, and goon looking?" They have. Considerable effort has been expended trying to detect changes in various constants related to light, including speed but also some other things. It is expected that if constants were changing, spectra would change as well. So far as I know, all those results have been negative, but it's not for lack of trying. Similar arguments can be deployed for the nuclear forces as well w.r.t. spectrum, rates of fusion, various things you'd be able to observe in certain types of supernovae, etc. One of the things I don't like about this genre of articles is that it's typically quite mistaken, if not outright disingenuous, about the current state of cosmology. From what I could see, the idea that cosmologists are all stodgy old fogies brought up in a paradigm of the Big Bang and who won't entertain any other thoughts is diametrically opposed to the truth. To my eyes, the field is a bubbling cauldron of various exotic ideas and attempts to resolve all these issues. There's no lack of theories in cosmology and attempts to resolve these issues, including many quite radical ones (the holographic principle, changing constants over time, heck even "Dark Energy" is quite radical in many ways even if it is also the accepted theory at the moment). What we lack are theories that explain all the observations. Dark matter is favored not because it's the only idea that anyone has come up with, but because it's still the one that best fits the facts. (As PBS Space Time pointed out last week, ironically, the galaxies recently discovered to not contain dark matter are themselves quite strong evidence dark matter must exist: https://www.youtube.com/watch?v=5t0jaE--l0Y https://www.youtube.com/watch?v=5t0jaE--l0Y , because almost all other theories to explain galactic rotations are based on characteristics that can not vary by galaxy like matter distributions can. "MOND", for instance, is not "MOND, except in these two galaxies".) If you can solve all these problems, as near as I can tell, you'll be celebrated, not shut down by the old fogerati. But be prepared for your theory to need to cover a lot of existing observations; we're centuries past "Well, what if gravity just worked differently?" or "What if the constants aren't constant?" You're going to need a great deal more detail than that.

rgrieselhuber 8y ago

Biggest takeaway from this is how many underlying presuppositions appear to be assumptions.

eaim 8y ago
Yes.

shrimp_emoji 8y ago

>It's perhaps worth stopping to ask why astrophysicists hypothesize dark matter to be everywhere in the universe? >To explain observations of galaxies inconsistent with general relativity, the existence of dark matter was posited as an unknown and invisible form of matter calculated to make up more than a quarter of all mass-energy content in the universe Food for thought: the best current evidence of dark matter is the Bullet Cluster[0]. In particular, look at this picture: https://upload.wikimedia.org/wikipedia/commons/a/a8/1e0657_scale.jpg https://upload.wikimedia.org/wikipedia/commons/a/a8/1e0657_s... At first, these were two blobs of dark matter and gas. They collided. That resulted in what we see now: the dark matter portions (purple, measured by gravity lensing) magically went through each other (because dark matter is weird like that) while the gas portions (pink) actually collided and formed a shockwave (like normal matter behaves), with much of the gas remaining in the middle. The tone in the article quotes there makes it seem like dark matter is some esoteric rounding error, but that seems like pretty "solid" evidence for... the anomalous mass readings we call dark matter. 0: https://en.wikipedia.org/wiki/Bullet_Cluster https://en.wikipedia.org/wiki/Bullet_Cluster

deleted 8y ago
[deleted]

calebgilbert 8y ago

To be fair, I bet most, if not all, cosmologists would agree that they know far less than they don't know. The title of the article is a bit sensationalistic from that point of view, but then I guess "Cosmology has some big details to work on" isn't nearly as catchy.

hhs 8y ago

Interesting view. Near the end, it says: “The crux of today's cosmological paradigm is that in order to maintain a mathematically unified theory valid for the entire universe, we must accept that 95 percent of our cosmos is furnished by completely unknown elements and forces for which we have no empirical evidence whatsoever.” Empiricism is based on sense observations. And a lot of science has been confined to human senses. I’m curious if tapping into more basic science research by analyzing different types of senses, for instance, available to animals, may offer breakthroughs down the line. For instance, fish employ the lateral line system to detect pressure gradients in the environment.

wilg 8y ago
What kind of senses available to animals are there that we should be using for science? Also I'm not entirely sure what you mean that we're confined to "the 5 senses". First, humans have way more senses. Second, I don't think it's confining ourself to build technology that converts something we can't sense (like gravitational waves) into something we can (like a spreadsheet).
dfischer 8y ago
What aren’t we using from the animal kingdom? We create sensors that are extra human. Infrared etc... Maybe this is an unknown unknown problem. We can’t develop technology for senses we do not know about and so on.
- hhs 8y ago
  Indeed, I agree with your point, “Maybe this is an unknown unknown problem.” I’m not sure why my comment is being downvoted, is there something I said that’s in bad taste?
  - dfischer 8y ago
    I think you’re fine. Sorry you’re getting downvoted.
chongli 8y ago

jcroll 8y ago

Ethan Siegel write up on this problem: https://www.forbes.com/sites/startswithabang/2018/06/22/why-cosmologys-expanding-universe-controversy-is-an-even-bigger-problem-than-you-realize/#3587f0422381 https://www.forbes.com/sites/startswithabang/2018/06/22/why-...

acqq 8y ago
But also about other claims from the Ekeberg's article (who, as I see, is a "a philosopher of science"): https://www.forbes.com/sites/startswithabang/2018/07/26/theres-a-debate-raging-over-whether-dark-matter-is-real-but-one-side-is-cheating/ https://www.forbes.com/sites/startswithabang/2018/07/26/ther... "There's A Debate Raging Over Whether Dark Matter Is Real, But One Side Is Cheating" Careful reader of Ekeberg's article can both recognize that the article claims are inspired by the claims of the "cheating" side but also that where he writes his own he completely fails on physics. I.e. if one side is cheating, he'd be a third side, the one that's completely unscientific: even the physicists that develop theories that compete with dark matter would not write what Ekeberg wrote: "Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere. But according to the latest measurements, it is not, suggesting the theory needs to be reexamined." It's plain nonsense. The reason: https://www.forbes.com/sites/startswithabang/2019/01/16/mysterious-galaxy-measured-exquisitely-and-contains-no-dark-matter-at-all/ https://www.forbes.com/sites/startswithabang/2019/01/16/myst... "Ironically, the discovery of a galaxy without dark matter — amidst a sea of galaxies that require huge amounts of it — helps prove the validity of the dark matter-rich picture of the Universe. Only if normal matter can be separated out from the dark matter and left to form its own structures would such a galaxy be possible." We even have the pictures where the galaxies and dark matter aren't at the same place, totally the opposite of Ekeberg's "everywhere" strawman claim, and exactly that opposite was always treated as the biggest support for dark matter: https://www.forbes.com/sites/startswithabang/2017/11/09/the-bullet-cluster-proves-dark-matter-exists-but-not-for-the-reason-most-physicists-think/ https://www.forbes.com/sites/startswithabang/2017/11/09/the-... Once I've reached that strawman claim, I've checked what the profession of Ekeberg is. I openly admit his uncritical bias just confirmed my own bias about that profession.

astro123 8y ago

I'm a grad student working on cosmology, and while I agree there is a lot of work still to do (we don't know what 95% of the matter that makes up the universe is!), I disagree with a lot of what the author says. > Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere. We have found evidence of a few galaxies without DM. But most galaxies provide strong evidence for DM - https://en.wikipedia.org/wiki/Galaxy_rotation_curve https://en.wikipedia.org/wiki/Galaxy_rotation_curve > For a crucial function of theories such as dark matter, dark energy and inflation, which each in its own way is tied to the big bang paradigm Big bang was only the accepted paradigm from the 60s (post CMB observations). We have had DE since Einstein in 1917 and DM since Zwicky in the 30s. > Historically, Newton's physical laws made up a theoretical framework that worked for our own solar system with remarkable precision. Both Uranus and Neptune, for example, were discovered through predictions based on Newton's model. But as the scales grew larger, its validity proved limited. Actually some of the earliest evidence for GR came from the orbit of mercury https://en.wikipedia.org/wiki/Tests_of_general_relativity https://en.wikipedia.org/wiki/Tests_of_general_relativity > It is of course entirely plausible that the validity of general relativity breaks down much closer to our own home than at the edge of the hypothetical end of the universe. And if that were the case, today's multilayered theoretical edifice of the big bang paradigm would turn out to be a confusing mix of fictional beasts invented to uphold the model This is something that people are working on! This is a hypothesized source of DE. However, disproving GR does nothing to disprove the big bang. > Today's space telescopes provide no direct view of anything I have no idea what that means. They literally observe the sky... There is a ton of work to do: finding what DM is, finding what DE is, finding whether GR is correct. But I'm not sold that the author knows what he is talking about...

scrozart 8y ago
> > Today's space telescopes provide no direct view of anything > I have no idea what that means. They literally observe the sky... Seriously! At this point they're just spitballing.
- astro123 8y ago
  I was maybe a bit too cavalier here. I think I understand what the author means - the data that they gather is understood in the context of the model that we think is best. But, it isn't as if cosmologists are rigidly holding to the model. Here's a paper looking at extensions to lambda CDM https://arxiv.org/abs/1512.05356 https://arxiv.org/abs/1512.05356. As I mentioned, changing GR is being looked at as an alternative to DE http://www.resceu.s.u-tokyo.ac.jp/workshops/resceu08s/presen/koyama-1.pdf http://www.resceu.s.u-tokyo.ac.jp/workshops/resceu08s/presen... People aren't challenging some things though - I don't think anyone is seriously working on cosmologies that don't include a big bang, because without one I can't imagine how you explain the CMB.

ccvannorman 8y ago

I've never been a fan of Dark Matter. Not all galaxies have dark matter, but only incredibly diffuse galaxies don't have it[0]. Doesn't that mean that the density of matter in a galaxy is what gives rise to "faster rotations/more gravity", and not just the total matter irrespective of its galactic density? Furthermore, the "Bullet Cluster" example is telling. Apparently, the extra mass stuck around the more dense part of the galaxy, and not in the less dense gas cloud that resulted from the collision. Again, only the dense parts of this cluster exhibit "faster rotations/more gravity". So to me, this is terribly un-compelling. So there's a magic invisible matter that just so happens to only coalesce around dense galaxies/galactic areas and never around sparse ones. [0] http://www.astronomy.com/news/2019/03/ghostly-galaxy-without-dark-matter-confirmed http://www.astronomy.com/news/2019/03/ghostly-galaxy-without... edit: s/no matter/irrespective of (poor use of the homonym "matter")

eaim 8y ago

@astro123 There’s a tautology in your critique. You’re attempting to suggest that there is evidence for dark matter. There isn’t. Dark matter is a theory, one that has not yet produced empirical evidence to support it (& perhaps cannot ever do so.)

mkl 8y ago
If you want to reply to a comment, please click the "reply" button below that comment, rather than starting a new comment thread. @<username> doesn't do anything here.
- eaim 8y ago
  Ah, understood, thanks. Sorry about that.

eaim 8y ago

@astro123 Sorry my comment uploaded before I was done. It is an error to state that there is evidence for dark matter. There is no evidence for it other than that as a hypothesis it adds support to a larger cosmological theory; that of the so-called Big Bang. But that is basically a circle in the proof. A tautology.

ephimetheus 8y ago
What about the Bullet Cluster?
- eaim 8y ago
  If the Bullet Cluster had offered not hypothetical but empirical, incontrovertible evidence for Dark Matter, at this juncture we wouldn’t even be calling it Dark Matter anymore.

eaim 8y ago

@astro123 The following excerpt is the crux of the author’s argument regarding DM, & it points to the dark elephant in the room that a lot of physicists are bothered by but don’t want to discuss: “It's perhaps worth stopping to ask why astrophysicists hypothesize dark matter to be everywhere in the universe? The answer lies in a peculiar feature of cosmological physics that is not often remarked. For a crucial function of theories such as dark matter, dark energy and inflation, which each in its own way is tied to the big bang paradigm, is not to describe known empirical phenomena but rather to maintain the mathematical coherence of the framework itself while accounting for discrepant observations. Fundamentally, they are names for something that must exist insofar as the framework is assumed to be universally valid.”

eaim 8y ago

All said and done, the current state of cosmology (whether one falls in with mainstream theories or not) is a mess. It has so many addendums, codicils & caveats that one has to be almost a type of lawyer of physics to be able to navigate it. We await our new Einstein. Our new Heisenberg. Our elegant theory of everything; or as one science writer put it: The universe on a T-shirt.

eaim 8y ago

Here’s an article from Rob Sheldon, who worked on ROSETTA. He is less timid than Ekeberg: https://uncommondescent.com/intelligent-design/rob-sheldon-the-real-reason-there-is-a-crisis-in-cosmology/ https://uncommondescent.com/intelligent-design/rob-sheldon-t...