6 ms·

Seems like just further confirmation that we actually don't know how gravity works. Inventing some magic modifier that makes our theories (and formulas based o

Seems like just further confirmation that we actually don't know how gravity works. Inventing some magic modifier that makes our theories (and formulas based on those theories) "work" (dark matter) was always rather absurd.

mark_edward 9y ago
Are you a physicist or cosmologist?
contravariant 9y ago
Well, we were right about induction currents, gravitational waves and anti-matter, so it's not as if filling in the gaps is always incorrect.
- noetic_techy 9y ago
  Right eventually. Before that the explanations were a lot wackier. I could easily see "dark matter" the same way I see "ether".
- semi-extrinsic 9y ago
  Don't forget neutrinos... or a million other things.
macintux 9y ago
Positing some mystery matter that doesn't behave like anything we've observed strikes me as more absurd than gravity working differently at galactic scales, so I guess it's all a matter of perspective.
- InclinedPlane 9y ago
  It is more absurd. Firstly, WIMPs do not "behave unlike anything we've observed". They behave similarly to neutrinos except are much more massive and instead of almost always having so much energy that they travel at relativistic speeds they travel at much slower speeds. No new fundamental forces are required to explain WIMPs, they are simply particles we haven't discovered yet. Given that in the 20th century alone we discovered photons, protons, neutrons, anti-particles, quarks (and their whole family of composite particles in the form of baryons and mesons), neutrinos, and weak bosons while in the 21st century we've discovered the Higgs it would be ridiculous to say that new particle discoveries are beyond the realm of possibility. Moreover, we know that the standard model of particle physics is incomplete due to the existence of neutrino oscillations (among other things). So we can be fairly confident there are new particles yet to be discovered, and we have a model of dark matter which fits a hugely diverse set of data fairly well that no other model fits. To deny that dark matter is the best model for the data at present is nothing more than superstition.
  - noetic_techy 9y ago
    I have a engineering-physics degree, and while I will admit my day job involves more down to earth physics software simulation rather than advanced cosmology and particle theory, I would categorize WIMPS more so as the model with the least amount of gotcha's when compared with alternative gravity theories. I for one lean towards alternative gravity theories. "They behave similarly to neutrinos except are much more massive..." And yet we can build neutrino detectors and "see" neutrinos. So far similar detectors for dark matters have failed to detect anything: https://en.wikipedia.org/wiki/Large_Underground_Xenon_experiment https://en.wikipedia.org/wiki/Large_Underground_Xenon_experi... Lack of detection, plus this sparse galaxy with no sign of dark matter, is starting to slowly rule out the simpler explanations by virtue of outliers that don't fit any model. You yourself mentioned it, but I always remind detractors that the standard model IS WRONG. The sparseness of this galaxy is what intrigues me. What if the lack singularity at the center is the key?
    - sampo 9y ago
      > The sparseness of this galaxy is what intrigues me. But none of the ultra-diffuse galaxies discovered so far have been found to be lacking in dark matter. So even among this unusual class of galaxy, NGC 1052-DF2 is an oddball. https://www.nasa.gov/feature/goddard/2018/dark-matter-goes-missing-in-oddball-galaxy https://www.nasa.gov/feature/goddard/2018/dark-matter-goes-m...
  - raattgift 9y ago
    > They behave similarly to neutrinos except are much more massive and instead of almost always having so much energy that they travel at relativistic speeds they travel at much slower speeds You've mixed this up a bit. Because neutrinos have such a low invariant mass, they have little inertia, so are readily accelerated to speeds comparable to the speed of light at production time or when scattering off an atomic nucleus. A heavy neutrino has a higher invariant mass by definition, and thus more inertia, and thus are likely to move less than a lower-inertia regular neutrino when encountering an an atomic nucleus. Since there is a lot of gas and dust around at the start of structure formation, you need some mechanism to keep energy-momentum localized around the matter that will become luminous matter like stars and hot gas. Adding inertia to a particle that is otherwise highly comparable to a neutrino would do the job. Normal neutrinos approaching close enough ("scattering") to an atomic nucleus would tend to get a large kick, which can be considered as a substantial Lorentz boost. Heavy neutrinos suffer a smaller kick. There are is an additionally point worth considering here: there are almost certainly cold regular neutrinos in a relic field called the cosmic neutrino background, which is analogous to the cosmic microwave background. These neutrinos rarely interact with atomic nuclei, but when they do they are liable to get a big kick. They also are so low-energy that there would have to be an enormous amount of them if they were a major component of Cold Dark Matter; enough that there would be visible nuclear-reaction signatures in our sky as they get heated up by collision with hot gas and the like in the galaxies around which the standard cosmology expects there to be lots of Cold Dark Matter. The heating up of such huge densities of cold standard neutrinos (by weak interactions with hot baryons) would also kick many of the neutrinos out of galaxies over time, which produces a smearing out of visible matter as an observable. Those galaxy-scale observables and the peaks in the CMB power spectrum (plotting the fluctuations in the CMB temperature spectrum at different angular scales) preclude primordial cold standard neutrinos as an important component of Cold Dark Matter operating since the formation of the earliest galaxies.
InclinedPlane 9y ago
It's not "magic" it's a model that fits the observations: otherwise known as science. Let's be clear here, every other model does not explain the observations, by a pretty significant margin. Moreover, the concept of weakly interacting massive particles is not outlandish, we already know of some particles that behave very similarly (neutrinos).
- tzahola 9y ago
  >It's not "magic" it's a model that fits the observations: otherwise known as science. Epicycles.
  - deleted 9y ago
    [deleted]
- StanislavPetrov 9y ago
  Except dark matter isn't an observation. Its an unobserved variable that's been inserted to make models that don't match observations add up.
  - InclinedPlane 9y ago
    Dark matter is a theory that fits the observations. Prior to the 1980s nobody had ever been able to image a single atom as well, atoms are just theories that fit the observations. Proton-proton fusion has never been observed directly experimentally, and yet we confidently say that it is the primary method of energy generation inside our own Sun and many other stars, because it's the only theory that fits the observations. This is how science works.
    - StanislavPetrov 9y ago
      >Dark matter is a theory that fits the observations. You are mistaking "theory" and "hypothesis". Dark matter is a hypothesis. It is unproven, it has not been observed. Describing this as a "galaxy devoid of dark matter" rather than "a galaxy where the dark matter hypothesis does not add up" is absurd. There is a difference between speculation about potential causes for observed phenomena and observed phenomena themselves.
hnaccy 9y ago
Wouldn't this observation do the opposite? If dark matter doesn't exist and gravity works differently at large scales how do you explain this galaxy? A rare galaxy having its dark matter blown away or something seems more reasonable.
- noetic_techy 9y ago
  Look at how sparse this galaxy is. What if its simply an unknown property of the black hole singularity at the center of the galaxy that acts as some sort of gravity modifier? What is galaxy scale has nothing to do with it? No one really knows for sure what the hell is going on and everyone wants to cling to the mystery particle theories because its the easier explanation.
- StanislavPetrov 9y ago
  >how do you explain this galaxy? I can't, and neither can anyone else - which is why people are struggling with invented variables like "dark matter". Its fine to speculate, its absurd to claim with certainty (as many so-called scientists do).
tzahola 9y ago
I too have this feeling that with dark matter we’re at the epicycles phase...
- noetic_techy 9y ago
  What is this epicycle phase you reference?
  - tzahola 9y ago
    https://en.m.wikipedia.org/wiki/Deferent_and_epicycle https://en.m.wikipedia.org/wiki/Deferent_and_epicycle The canonical example of how tweaking your model to fit observed data doesn’t necessarily results in a good theory.
- 8bitsrule 9y ago
  Yep. Occam's razor is just not -that- flexible.

mark_edward 9y ago

Are you a physicist or cosmologist?

contravariant 9y ago

Well, we were right about induction currents, gravitational waves and anti-matter, so it's not as if filling in the gaps is always incorrect.

noetic_techy 9y ago
Right eventually. Before that the explanations were a lot wackier. I could easily see "dark matter" the same way I see "ether".
semi-extrinsic 9y ago
Don't forget neutrinos... or a million other things.

macintux 9y ago

Positing some mystery matter that doesn't behave like anything we've observed strikes me as more absurd than gravity working differently at galactic scales, so I guess it's all a matter of perspective.

InclinedPlane 9y ago
It is more absurd. Firstly, WIMPs do not "behave unlike anything we've observed". They behave similarly to neutrinos except are much more massive and instead of almost always having so much energy that they travel at relativistic speeds they travel at much slower speeds. No new fundamental forces are required to explain WIMPs, they are simply particles we haven't discovered yet. Given that in the 20th century alone we discovered photons, protons, neutrons, anti-particles, quarks (and their whole family of composite particles in the form of baryons and mesons), neutrinos, and weak bosons while in the 21st century we've discovered the Higgs it would be ridiculous to say that new particle discoveries are beyond the realm of possibility. Moreover, we know that the standard model of particle physics is incomplete due to the existence of neutrino oscillations (among other things). So we can be fairly confident there are new particles yet to be discovered, and we have a model of dark matter which fits a hugely diverse set of data fairly well that no other model fits. To deny that dark matter is the best model for the data at present is nothing more than superstition.
- noetic_techy 9y ago
  I have a engineering-physics degree, and while I will admit my day job involves more down to earth physics software simulation rather than advanced cosmology and particle theory, I would categorize WIMPS more so as the model with the least amount of gotcha's when compared with alternative gravity theories. I for one lean towards alternative gravity theories. "They behave similarly to neutrinos except are much more massive..." And yet we can build neutrino detectors and "see" neutrinos. So far similar detectors for dark matters have failed to detect anything: https://en.wikipedia.org/wiki/Large_Underground_Xenon_experiment https://en.wikipedia.org/wiki/Large_Underground_Xenon_experi... Lack of detection, plus this sparse galaxy with no sign of dark matter, is starting to slowly rule out the simpler explanations by virtue of outliers that don't fit any model. You yourself mentioned it, but I always remind detractors that the standard model IS WRONG. The sparseness of this galaxy is what intrigues me. What if the lack singularity at the center is the key?
  - sampo 9y ago
    > The sparseness of this galaxy is what intrigues me. But none of the ultra-diffuse galaxies discovered so far have been found to be lacking in dark matter. So even among this unusual class of galaxy, NGC 1052-DF2 is an oddball. https://www.nasa.gov/feature/goddard/2018/dark-matter-goes-missing-in-oddball-galaxy https://www.nasa.gov/feature/goddard/2018/dark-matter-goes-m...
- raattgift 9y ago
  > They behave similarly to neutrinos except are much more massive and instead of almost always having so much energy that they travel at relativistic speeds they travel at much slower speeds You've mixed this up a bit. Because neutrinos have such a low invariant mass, they have little inertia, so are readily accelerated to speeds comparable to the speed of light at production time or when scattering off an atomic nucleus. A heavy neutrino has a higher invariant mass by definition, and thus more inertia, and thus are likely to move less than a lower-inertia regular neutrino when encountering an an atomic nucleus. Since there is a lot of gas and dust around at the start of structure formation, you need some mechanism to keep energy-momentum localized around the matter that will become luminous matter like stars and hot gas. Adding inertia to a particle that is otherwise highly comparable to a neutrino would do the job. Normal neutrinos approaching close enough ("scattering") to an atomic nucleus would tend to get a large kick, which can be considered as a substantial Lorentz boost. Heavy neutrinos suffer a smaller kick. There are is an additionally point worth considering here: there are almost certainly cold regular neutrinos in a relic field called the cosmic neutrino background, which is analogous to the cosmic microwave background. These neutrinos rarely interact with atomic nuclei, but when they do they are liable to get a big kick. They also are so low-energy that there would have to be an enormous amount of them if they were a major component of Cold Dark Matter; enough that there would be visible nuclear-reaction signatures in our sky as they get heated up by collision with hot gas and the like in the galaxies around which the standard cosmology expects there to be lots of Cold Dark Matter. The heating up of such huge densities of cold standard neutrinos (by weak interactions with hot baryons) would also kick many of the neutrinos out of galaxies over time, which produces a smearing out of visible matter as an observable. Those galaxy-scale observables and the peaks in the CMB power spectrum (plotting the fluctuations in the CMB temperature spectrum at different angular scales) preclude primordial cold standard neutrinos as an important component of Cold Dark Matter operating since the formation of the earliest galaxies.

InclinedPlane 9y ago

It's not "magic" it's a model that fits the observations: otherwise known as science. Let's be clear here, every other model does not explain the observations, by a pretty significant margin. Moreover, the concept of weakly interacting massive particles is not outlandish, we already know of some particles that behave very similarly (neutrinos).

tzahola 9y ago
>It's not "magic" it's a model that fits the observations: otherwise known as science. Epicycles.
- deleted 9y ago
  [deleted]
StanislavPetrov 9y ago
Except dark matter isn't an observation. Its an unobserved variable that's been inserted to make models that don't match observations add up.
- InclinedPlane 9y ago
  Dark matter is a theory that fits the observations. Prior to the 1980s nobody had ever been able to image a single atom as well, atoms are just theories that fit the observations. Proton-proton fusion has never been observed directly experimentally, and yet we confidently say that it is the primary method of energy generation inside our own Sun and many other stars, because it's the only theory that fits the observations. This is how science works.
  - StanislavPetrov 9y ago
    >Dark matter is a theory that fits the observations. You are mistaking "theory" and "hypothesis". Dark matter is a hypothesis. It is unproven, it has not been observed. Describing this as a "galaxy devoid of dark matter" rather than "a galaxy where the dark matter hypothesis does not add up" is absurd. There is a difference between speculation about potential causes for observed phenomena and observed phenomena themselves.

hnaccy 9y ago

Wouldn't this observation do the opposite? If dark matter doesn't exist and gravity works differently at large scales how do you explain this galaxy? A rare galaxy having its dark matter blown away or something seems more reasonable.

noetic_techy 9y ago
Look at how sparse this galaxy is. What if its simply an unknown property of the black hole singularity at the center of the galaxy that acts as some sort of gravity modifier? What is galaxy scale has nothing to do with it? No one really knows for sure what the hell is going on and everyone wants to cling to the mystery particle theories because its the easier explanation.
StanislavPetrov 9y ago
>how do you explain this galaxy? I can't, and neither can anyone else - which is why people are struggling with invented variables like "dark matter". Its fine to speculate, its absurd to claim with certainty (as many so-called scientists do).

tzahola 9y ago

I too have this feeling that with dark matter we’re at the epicycles phase...

noetic_techy 9y ago
What is this epicycle phase you reference?
- tzahola 9y ago
  https://en.m.wikipedia.org/wiki/Deferent_and_epicycle https://en.m.wikipedia.org/wiki/Deferent_and_epicycle The canonical example of how tweaking your model to fit observed data doesn’t necessarily results in a good theory.
8bitsrule 9y ago
Yep. Occam's razor is just not -that- flexible.