7 ms·

Is this really such a definitive result, as the source suggests?

I_Am_Nous 3y ago
Good question, I've understood dark matter to be a kind of "we haven't proved its existence/discovered definitive examples yet but the existence of dark matter seems to explain many behaviors we see in the universe" thing, so it's possible the true mechanism would "suddenly" be discovered and the hypothesis of "dark matter drives space expansion" be abandoned just as quickly. I think this is a good example of the whiplash science seems to go through. If you have studied science (or even remember high school science) you know it's the scientific process working as intended. In the eyes of the public, though, science keeps "changing its mind" as though its a monolithic structure of truth which keeps lying to us. I'm not sure there's a solution to this issue short of science journalism adoption an addiction to qualifying statements -- the ones everyone hates in ChatGPT but from a liability standpoint are required so nobody tries a new home blood chelation therapy hallucinated by an LLM.
- Cacti 3y ago
  Dark matter is largely an instrumentation problem. The universe is very big, and direct observation of individual objects is largely limited by distance/luminosity, which is problematic when you are looking for lots of old dark stars very far away. The history of astronomy is largely a process of deriving estimates of new phenomena from what we can observe, and thus underestimating the significance until a better instrument comes along (as at first we only can see the larger objects, which often results in undercounting). Dark energy is partly instrumental, but largely a theoretical gap in understanding. God only knows what is going on there.
  - JumpCrisscross 3y ago
    > Dark matter is largely an instrumentation problem The bullet cluster refutes this hypothesis [1]. [1] https://en.m.wikipedia.org/wiki/Bullet_Cluster https://en.m.wikipedia.org/wiki/Bullet_Cluster
    - Cacti 3y ago
      No, the current most reasonable explanation for the dynamics of the bullet cluster are merely consistent with our current best dark matter theories. It is suggestive at best.
      - JumpCrisscross 3y ago
        I’m not claiming those observations prove dark matter. I’m saying they are problematic for the claim that this is an instrumentation issue.
  - Misdicorl 3y ago
    This is unlikely. There are many many theories of how dark matter could be accounted for with ordinary matter that we simply can't detect because our telescopes/etc aren't good enough. Not all of these theories are completely excluded yet but most have very very thin margins of phase space left to explore (even when combining multiple explanations together). Every time a new telescope comes online we see the phase space diminish rather than hints towards first observations. We are left with: A) new particles that don't (or very weakly) interact with electro magnetic fields. B) New theories of gravity. C) New theories of the early universe that open up phase space previously thought closed to existing matter contributions D) better instrumentation that sees actual contribution in the tiny phase space left to ordinary matter and ordinary physics D is by far the least interesting of these options and so gets very little press. But it gets plenty of academic attention and you can be assured it is not being ignored by scientists
  - jameshart 3y ago
    The problem of dark matter isn't best thought of as 'dark matter is theorized as an explanation for observations'. It's better thought of as 'observations of the mass of matter in the universe are inconsistent with observation of the amount of light coming from matter in the universe'. Matter generally does two things: interacts with other matter through gravity, because it has mass; and emits EM radiation, because it has temperature. When you look at galaxies and try to figure out how much matter they contain, if you look at the gravity, you get one number for mass that implies one quantity of matter; and if you look at the EM radiation, you get a smaller number that implies a lower quantity of matter. So the conclusion is, there must be some matter that's causing the gravitational effects, but that's not emitting any EM radiation. Matter that is dark. Dark matter. I blame George Lucas for a lot of this confusion. When people hear 'dark matter' they think it's dark in the sense of 'mysterious'. It's way more literal than that. It's just matter that's dark.
    - SoftTalker 3y ago
      So it's cold matter, basically? Matter that's at or close to absolute zero temp?
      - nyssos 3y ago
        "Cold" in this context means "a typical particle is moving slow enough that we can safely neglect relativistic effects". Hydrogen plasma on the surface of the sun is "cold", in this sense. Solar neutrinos are not.
      - jameshart 3y ago
        I mean, it could be - but you'd need to come up with an explanation for why it isn't warming up at all. Most matter reaches an equilibrium temperature where the outgoing EM radiation equals the incoming EM radiation. This matter isn't doing that.
        SoftTalker 3y ago
        There are areas of the universe that are "voids" where there's almost nothing, maybe that's where this cold/dark matter is? There's nothing nearby to warm it up? Though this article seems to be specifically about the Milky Way.
  - jacquesm 3y ago
    That's not what 'Dark' means in this context. It's not that it is too far away to be detected, it is non-luminous (as in: not emitting any electromagnetic radiation) and so it isn't detectable other than by its secondary effects on other objects. Black holes are another example of something that we can not directly observe using instruments, but that we can observe through their secondary effects. But black holes are part of the cosmic accounting book in an identified manner, dark matter is not.
- JumpCrisscross 3y ago
  > the hypothesis of "dark matter drives space expansion" This is dark energy [1]. [1] https://en.m.wikipedia.org/wiki/Dark_energy https://en.m.wikipedia.org/wiki/Dark_energy
- uoaei 3y ago
  Dark matter is just a theory hallucinated by computational models. It is and has always been defined as nothing but "where matter could be to explain the gap between model and data" but no good reason is ever given as to why it could be matter and not anything else. You can do the same thing with the solar system to "explain" a geocentric universe if you wanted.
  - JumpCrisscross 3y ago
    > no good reason is ever given as to why it could be matter and not anything else Man, astrophysics and finance are not this forum’s strong suit. See the bullet cluster observations [1]. Explain it simultaneously with most galaxy’s spins, but also NGC 1277’s [2], without using dark matter. [1] https://en.m.wikipedia.org/wiki/Bullet_Cluster https://en.m.wikipedia.org/wiki/Bullet_Cluster [2] https://en.m.wikipedia.org/wiki/NGC_1277 https://en.m.wikipedia.org/wiki/NGC_1277
    - uoaei 3y ago
      Far from settled: https://arxiv.org/abs/1003.0939 https://arxiv.org/abs/1003.0939 But armchair physicists love to shriek 'bullet cluster' every time because they aren't aware of the extent of their ignorance. Considering your HN bio I'd comfortably classify you as "knows just enough to be dangerous". Fair, given your generalization knowing nothing about me? More reading for your benefit, from a working astrophysics professor specializing in ultra-diffuse galaxies: https://tritonstation.com/2016/12/23/crater-2-the-bullet-cluster-of-lcdm/ https://tritonstation.com/2016/12/23/crater-2-the-bullet-clu... https://tritonstation.com/2017/03/06/lcdm-has-met-the-enemy-and-it-is-itself/ https://tritonstation.com/2017/03/06/lcdm-has-met-the-enemy-... https://tritonstation.com/2016/07/30/missing-baryons/ https://tritonstation.com/2016/07/30/missing-baryons/
      - deleted 3y ago
        [deleted]
      - JumpCrisscross 3y ago
        Lots of ground between settled science and “no good reason is ever given.” There are strong arguments for dark matter (broadly, not just Lambda CDM). They are inconclusive. The bullet cluster is less strong evidence for dark matter than good evidence against common armchair refutations. (I agree with your author that it doesn’t rule out MOND as is commonly claimed.)
- Swizec 3y ago
  As a complete lay person, I’ve always understood dark matter to be our generation’s aether. Obviously there’s an undetectable medium in space for light to propagate through, how else could it work? We know from all our best observations and models that everything propagates through a medium. Dark matter has a similar vibe, we need it for our best models measurements and understanding to work. But that doesn’t mean there isn’t a crucial detail we’ll discover later that makes dark matter sound as silly as aether. Or we could find a way to directly detect/measure it! That too would be cool
  - miramba 3y ago
    I never heard of aether before, so here is a reference for anyone else: https://en.m.wikipedia.org/wiki/Luminiferous_aether https://en.m.wikipedia.org/wiki/Luminiferous_aether
    - nobodyandproud 3y ago
      That’s surprising. Proving/disproving the existence of a medium was the whole point of the Michaelson-Morley experiment.
      - TheOtherHobbes 3y ago
        Disproving the existence of a medium with certain expected properties and behaviours - one of which was that light travelled through it like waves through water. The reality is that light travels through spacetime and has completely unexpected and non-intuitive properties, one of which is an absolutely constant velocity. This doesn't mean spacetime isn't a medium of some kind, it means spacetime isn't a medium of any familiar or intuitive kind, and the old waves-on-water metaphor is too simple to explain it. QFT suggests spacetime is filled with fields of all kinds and particles are excitations of these fields. But what these "fields" actually are, and what they're made of, and why there are certain kinds of fields and not others, and why they operate with relativistic geometry, is a complete mystery.
  - tekla 3y ago
    Are you trying to discount Aether as a pseudoscience versus a serious theory? You're italicizing "Obviously" which makes me think that.
- jacquesm 3y ago
  And some scientists aren't exactly helping by making it seem as if this inherent conflict between 'this' and 'better' isn't part and parcel of the whole but instead driven by personal conflict. The damage done like that is likely long term fairly massive, hopefully prospective scientists won't be discouraged by these vendetta like phenomenon.
ksherlock 3y ago
It's a better explanation than dark matter (aka cosmic fudge)
mannykannot 3y ago
As it shows the observations of positron flux are consistent with well-established physics, I would guess that it is pretty solid. To be clear, this result does not rule out some form of dark matter as the cause of the phenomena it was posited to explain in the first place.
forgotpwd16 3y ago
>If it’s pulsars that are truly generating the positrons that could be responsible for the signal that cosmic ray experiments are seeing [...] >Whenever there’s an unexplained phenomenon that we’ve measured or observed, it presents a tantalizing possibility to scientists: that perhaps there’s something new at play beyond what’s presently known. (Is it me or this paragraph that sentence is taken from has a strange flow in it?) >However, we cannot claim evidence for a new discovery until we first scrupulously and quantitatively account for everything that represents the physics and astrophysics of what’s already known. The source doesn't show it as definitive.

Good question, I've understood dark matter to be a kind of "we haven't proved its existence/discovered definitive examples yet but the existence of dark matter seems to explain many behaviors we see in the universe" thing, so it's possible the true mechanism would "suddenly" be discovered and the hypothesis of "dark matter drives space expansion" be abandoned just as quickly. I think this is a good example of the whiplash science seems to go through. If you have studied science (or even remember high school science) you know it's the scientific process working as intended. In the eyes of the public, though, science keeps "changing its mind" as though its a monolithic structure of truth which keeps lying to us. I'm not sure there's a solution to this issue short of science journalism adoption an addiction to qualifying statements -- the ones everyone hates in ChatGPT but from a liability standpoint are required so nobody tries a new home blood chelation therapy hallucinated by an LLM.

Cacti 3y ago
Dark matter is largely an instrumentation problem. The universe is very big, and direct observation of individual objects is largely limited by distance/luminosity, which is problematic when you are looking for lots of old dark stars very far away. The history of astronomy is largely a process of deriving estimates of new phenomena from what we can observe, and thus underestimating the significance until a better instrument comes along (as at first we only can see the larger objects, which often results in undercounting). Dark energy is partly instrumental, but largely a theoretical gap in understanding. God only knows what is going on there.
- JumpCrisscross 3y ago
  > Dark matter is largely an instrumentation problem The bullet cluster refutes this hypothesis [1]. [1] https://en.m.wikipedia.org/wiki/Bullet_Cluster https://en.m.wikipedia.org/wiki/Bullet_Cluster
  - Cacti 3y ago
    No, the current most reasonable explanation for the dynamics of the bullet cluster are merely consistent with our current best dark matter theories. It is suggestive at best.
    - JumpCrisscross 3y ago
      I’m not claiming those observations prove dark matter. I’m saying they are problematic for the claim that this is an instrumentation issue.
- Misdicorl 3y ago
  This is unlikely. There are many many theories of how dark matter could be accounted for with ordinary matter that we simply can't detect because our telescopes/etc aren't good enough. Not all of these theories are completely excluded yet but most have very very thin margins of phase space left to explore (even when combining multiple explanations together). Every time a new telescope comes online we see the phase space diminish rather than hints towards first observations. We are left with: A) new particles that don't (or very weakly) interact with electro magnetic fields. B) New theories of gravity. C) New theories of the early universe that open up phase space previously thought closed to existing matter contributions D) better instrumentation that sees actual contribution in the tiny phase space left to ordinary matter and ordinary physics D is by far the least interesting of these options and so gets very little press. But it gets plenty of academic attention and you can be assured it is not being ignored by scientists
- jameshart 3y ago
  The problem of dark matter isn't best thought of as 'dark matter is theorized as an explanation for observations'. It's better thought of as 'observations of the mass of matter in the universe are inconsistent with observation of the amount of light coming from matter in the universe'. Matter generally does two things: interacts with other matter through gravity, because it has mass; and emits EM radiation, because it has temperature. When you look at galaxies and try to figure out how much matter they contain, if you look at the gravity, you get one number for mass that implies one quantity of matter; and if you look at the EM radiation, you get a smaller number that implies a lower quantity of matter. So the conclusion is, there must be some matter that's causing the gravitational effects, but that's not emitting any EM radiation. Matter that is dark. Dark matter. I blame George Lucas for a lot of this confusion. When people hear 'dark matter' they think it's dark in the sense of 'mysterious'. It's way more literal than that. It's just matter that's dark.
  - SoftTalker 3y ago
    So it's cold matter, basically? Matter that's at or close to absolute zero temp?
    - nyssos 3y ago
      "Cold" in this context means "a typical particle is moving slow enough that we can safely neglect relativistic effects". Hydrogen plasma on the surface of the sun is "cold", in this sense. Solar neutrinos are not.
    - jameshart 3y ago
      I mean, it could be - but you'd need to come up with an explanation for why it isn't warming up at all. Most matter reaches an equilibrium temperature where the outgoing EM radiation equals the incoming EM radiation. This matter isn't doing that.
      - SoftTalker 3y ago
        There are areas of the universe that are "voids" where there's almost nothing, maybe that's where this cold/dark matter is? There's nothing nearby to warm it up? Though this article seems to be specifically about the Milky Way.
- jacquesm 3y ago
  That's not what 'Dark' means in this context. It's not that it is too far away to be detected, it is non-luminous (as in: not emitting any electromagnetic radiation) and so it isn't detectable other than by its secondary effects on other objects. Black holes are another example of something that we can not directly observe using instruments, but that we can observe through their secondary effects. But black holes are part of the cosmic accounting book in an identified manner, dark matter is not.
JumpCrisscross 3y ago
> the hypothesis of "dark matter drives space expansion" This is dark energy [1]. [1] https://en.m.wikipedia.org/wiki/Dark_energy https://en.m.wikipedia.org/wiki/Dark_energy
uoaei 3y ago
Dark matter is just a theory hallucinated by computational models. It is and has always been defined as nothing but "where matter could be to explain the gap between model and data" but no good reason is ever given as to why it could be matter and not anything else. You can do the same thing with the solar system to "explain" a geocentric universe if you wanted.
- JumpCrisscross 3y ago
  > no good reason is ever given as to why it could be matter and not anything else Man, astrophysics and finance are not this forum’s strong suit. See the bullet cluster observations [1]. Explain it simultaneously with most galaxy’s spins, but also NGC 1277’s [2], without using dark matter. [1] https://en.m.wikipedia.org/wiki/Bullet_Cluster https://en.m.wikipedia.org/wiki/Bullet_Cluster [2] https://en.m.wikipedia.org/wiki/NGC_1277 https://en.m.wikipedia.org/wiki/NGC_1277
  - uoaei 3y ago
    Far from settled: https://arxiv.org/abs/1003.0939 https://arxiv.org/abs/1003.0939 But armchair physicists love to shriek 'bullet cluster' every time because they aren't aware of the extent of their ignorance. Considering your HN bio I'd comfortably classify you as "knows just enough to be dangerous". Fair, given your generalization knowing nothing about me? More reading for your benefit, from a working astrophysics professor specializing in ultra-diffuse galaxies: https://tritonstation.com/2016/12/23/crater-2-the-bullet-cluster-of-lcdm/ https://tritonstation.com/2016/12/23/crater-2-the-bullet-clu... https://tritonstation.com/2017/03/06/lcdm-has-met-the-enemy-and-it-is-itself/ https://tritonstation.com/2017/03/06/lcdm-has-met-the-enemy-... https://tritonstation.com/2016/07/30/missing-baryons/ https://tritonstation.com/2016/07/30/missing-baryons/
    - deleted 3y ago
      [deleted]
    - JumpCrisscross 3y ago
      Lots of ground between settled science and “no good reason is ever given.” There are strong arguments for dark matter (broadly, not just Lambda CDM). They are inconclusive. The bullet cluster is less strong evidence for dark matter than good evidence against common armchair refutations. (I agree with your author that it doesn’t rule out MOND as is commonly claimed.)
Swizec 3y ago
As a complete lay person, I’ve always understood dark matter to be our generation’s aether. Obviously there’s an undetectable medium in space for light to propagate through, how else could it work? We know from all our best observations and models that everything propagates through a medium. Dark matter has a similar vibe, we need it for our best models measurements and understanding to work. But that doesn’t mean there isn’t a crucial detail we’ll discover later that makes dark matter sound as silly as aether. Or we could find a way to directly detect/measure it! That too would be cool
- miramba 3y ago
  I never heard of aether before, so here is a reference for anyone else: https://en.m.wikipedia.org/wiki/Luminiferous_aether https://en.m.wikipedia.org/wiki/Luminiferous_aether
  - nobodyandproud 3y ago
    That’s surprising. Proving/disproving the existence of a medium was the whole point of the Michaelson-Morley experiment.
    - TheOtherHobbes 3y ago
      Disproving the existence of a medium with certain expected properties and behaviours - one of which was that light travelled through it like waves through water. The reality is that light travels through spacetime and has completely unexpected and non-intuitive properties, one of which is an absolutely constant velocity. This doesn't mean spacetime isn't a medium of some kind, it means spacetime isn't a medium of any familiar or intuitive kind, and the old waves-on-water metaphor is too simple to explain it. QFT suggests spacetime is filled with fields of all kinds and particles are excitations of these fields. But what these "fields" actually are, and what they're made of, and why there are certain kinds of fields and not others, and why they operate with relativistic geometry, is a complete mystery.
- tekla 3y ago
  Are you trying to discount Aether as a pseudoscience versus a serious theory? You're italicizing "Obviously" which makes me think that.
jacquesm 3y ago
And some scientists aren't exactly helping by making it seem as if this inherent conflict between 'this' and 'better' isn't part and parcel of the whole but instead driven by personal conflict. The damage done like that is likely long term fairly massive, hopefully prospective scientists won't be discouraged by these vendetta like phenomenon.

ksherlock 3y ago

It's a better explanation than dark matter (aka cosmic fudge)

mannykannot 3y ago

As it shows the observations of positron flux are consistent with well-established physics, I would guess that it is pretty solid. To be clear, this result does not rule out some form of dark matter as the cause of the phenomena it was posited to explain in the first place.

forgotpwd16 3y ago

>If it’s pulsars that are truly generating the positrons that could be responsible for the signal that cosmic ray experiments are seeing [...] >Whenever there’s an unexplained phenomenon that we’ve measured or observed, it presents a tantalizing possibility to scientists: that perhaps there’s something new at play beyond what’s presently known. (Is it me or this paragraph that sentence is taken from has a strange flow in it?) >However, we cannot claim evidence for a new discovery until we first scrupulously and quantitatively account for everything that represents the physics and astrophysics of what’s already known. The source doesn't show it as definitive.