7 ms·

Neutrino Particles May Be a Link to the Dark Sector

69 points by LinuxBender 6y ago

dschuetz 6y ago
"Dark Sector" - the next big thing in sciency stuff?
- qubex 6y ago
  It’s just shorthand for stuff that we cannot detect but ordinary (electromagnetic) means. In theory everything ‘feels’ gravity and anything with mass contributes to it. The left-handed neutrino is unusual in that it experiences only gravity and the extremely weak (though far stronger than gravity) “weak nuclear force” (and their right-handed brethren, if they even exist, might not exist en experience that). The “dark sector” is that 95% or so of the entire universe we infer must exist for either gravitational reasons (stronger gravity leads us to infer unseen mass, which we term “dark matter” though “transparent and apparently frictionless” would be a better term, or to infer unseen energy (dark energy that seems to be driving the accelerating rate of the universe).
  - contravariant 6y ago
    It's worth noting that there is an explanation for dark energy, namely quantum fluctuations of the vacuum. It's also worth noting that this explanation is off by over 100 orders of magnitude, which lead to it being called "the worst prediction in physics". Oddly enough we haven't come up with a better explanation as far as I know, the current assumption is just that the mass somehow almost cancels out.
    - evanb 6y ago
      It's not the fluctuations, but the zero-point energy. In a supersymmetric theory the number exactly cancels. If the Standard Model is some low-energy EFT of a supersymmetric theory, it could be almost-0.
  - throwaway_kufu 6y ago
    > 95% or so of the entire universe we infer must exist Isn’t the reason we infer dark matter exists, is our observations of the spin of galaxies? In other words there must be a lot more gravity produced by matter we aren’t observing (dark matter) to explain large scale observations? Aren’t there competing theories to dark matter, which haven’t been ruled out, from Einstein’s theories of gravity being wrong; or in the same way Einstein’s theory of gravity breaks down/is incomplete on the quantum scale his theories may breakdown at the scale of galaxies; and even more simply our observations not be accurate?
    - AnHonestComment 6y ago
      I believe there’s three sources: 1. Galaxy rotations require more mass than is visible to be gravitationally bound. 2. Clusters, super clusters, etc seem to lie on filaments and other large structures of something. 3. The map of gravitational lensing when we look past a cluster. I have my own personal pet theories — but that set of observations is thought to be explained by “dark matter”.
    - jasonwatkinspdx 6y ago
      There are many independent lines of evidence: https://en.wikipedia.org/wiki/Dark_matter#Observational_evidence https://en.wikipedia.org/wiki/Dark_matter#Observational_evid... Contrarian theories have outsized popularity here on hnews, and this tends to get fed by garbage articles from the usual sources (glances at quanta with mild disdain). Modified gravity theories are not some alternate path we just didn't explore. We explored them. They fail to explain the observational evidence. In particular the way stuff moves in galactic collisions makes very clear there's dark matter distinct from some modified version of gravity interacting with visible matter. It ends up that the consensus view of thousands of Phds that study this stuff is actually not trivially mistaken.
      - throwaway_kufu 6y ago
        I wasn’t implying mistaken by any means, I understand is the leading theory (not the only theory), I didn’t realize everything else had been ruled out or considered junk science (I just understood no one wants to be the person saying Einstein’s theories/equations for gravity need modification...even though that happens to be the consensus at the quantum level. But the galaxy collision observations is something I want to read more about (I’ve obviously seen simulations), thanks!
- evanb 6y ago
  A "sector" of the Standard Model---like the QCD sector, or the electroweak sector, or the Higgs sector---is just shorthand for a part of the the Standard Model that consists of particles and forces. It's possible that dark matter is just like Standard Model matter, in the sense that it only talks to a force that we already know in the Standard Model, like the weak force. But it's also possible that there are other forces. The "dark sector" is short hand for 'whatever stuff is making up the dark matter, and however they interact'.
dumbfoundded 6y ago
So it seems like this may have a link to dark matter but not energy. I have no expertise in physics but it seems like dark is a bad term as it only reflects our ignorance and inability to detect through normal electromagnetic means.
- thekingofh 6y ago
  Dark is just a placeholder until we find out exactly what's causing it.
- at_a_remove 6y ago
  Astronomers work through photons obtained and scientific inference on those photons. Lots and lots of inference. "Light" matter simply means "we can see it through a telescope because it gives off light," which means stars at a great distance, or closer up, light from a star reflected off of a surface. Dark, therefore, means "we know it is there but it isn't directly observable by gathering photons with a telescope."
  - raattgift 6y ago
    Crucially we can show it's there by examining how it affects the light from bright background sources passing through it: there is a spectral shift without the imposition of new emission or absorption lines, and there is Einstein lensing [ https://en.wikipedia.org/wiki/Gravitational_lens https://en.wikipedia.org/wiki/Gravitational_lens ]. We can see this in the large by observing the http://www.astro.ucla.edu/~wright/Lyman-alpha-forest.html http://www.astro.ucla.edu/~wright/Lyman-alpha-forest.html on lines of sight through and near galaxy clusters. For example, [presentation abstract] https://depts.washington.edu/astron/event/tba-liang-dai/ https://depts.washington.edu/astron/event/tba-liang-dai/ [related paper https://arxiv.org/abs/1804.03149v2 https://arxiv.org/abs/1804.03149v2 ] or https://arxiv.org/abs/1706.07870 https://arxiv.org/abs/1706.07870 The tl;dr is that distant light sources (distance obtained by among other things comparing the angular diameter and brightness on the sky of spiral galaxies containing common bright sources within them such as supernovae or molecular clouds lit by quasars) are redshifted in a way that is very hard to explain without an accelerating expansion of space (which in the equations of the Standard Cosmology we represent as dark energy), and are lensed by luminous galaxy clusters in such a way that is very hard to explain without mass that doesn't emit or absorb light. "Hard to explain" because (just as one example) the Lyman-alpha line and its relativistic behaviour is extremely well studied in controlled laboratory conditions in various places in our solar system (notably sensitive experiments carried in various spacecraft probing other bodies in our solar system). In a number of spacecraft, Lyman-alpha photometry testing is used to determine the Hydrogen-Deuterium ratio of planetary atmospheres, since cells of those two gasses form practically ideal narrow-band rejection filters, and over time a mixture of cells reveals the atomic ratio of those isotopes in the atmosphere. People who observe Mars have used this technique to study the rate at which Mars is outgassing water vapour, in particular. As it is useful to planetary scientists to look through varying depths of a given planetary atmosphere backlit by distant luminous objects, in practice the cosmological Lyman-alpha forest can be sampled by orbiting Ly-a photometers "for free". You can't really reject the resulting Ly-a data without also rejecting the Deuterium/Hydrogen ratio obtained from probes on the surface of Mars, which happen to match. And the data typically also encodes other spectral lines principally from the intergalactic medium, and those lines are similarly redshifted and amplified by relativistic -- including general relativistic -- effects. Both dark matter and dark energy induce matching general relativistic effects, and nobody has figured out how to produce the same spectral features without including dark matter and dark energy.
dilippkumar 6y ago
> The idea that our experiments might be detecting a fourth neutrino remains controversial, however, because the Standard Model of particle physics is one of the most tested and thoroughly confirmed theoretical frameworks in history—and it allows for only three neutrinos. I am frustrated with how the "Standard Model" has become a veil with which a priestly particle physicist class hides sacred knowledge of how the universe works from plebeians like myself. Why does the Standard Model only allow for three neutrinos? Is it because the math says so? Is it because some other maths only work if this number is three? Does it come from some fascinating group-theory or symmetry groups that nobody teaches at a highschool math level? I can't be the only one who wants to learn more about this stuff. I don't believe that the Particle Physicist or the broader Physics community is at fault here. I blame our approach to school education. If we accept that it's ok for a 14 year to be bewildered at quadratic equations and is expected to accept the "Don't worry, it'll all make sense later" line, it should also be possible for the same student to learn about Heisenberg's uncertainty principle, the basics of non-Euclidean geometry and symmetry groups. Our society today has several cohorts of adults who do not have the necessary foundations to understand the Standard Model. We don't plan to educate children in schools today to be able to understand this stuff. It will take a highly motivated adult several years of self study to reach a point where the Standard Model becomes approachable. Do we really want to live in the world where an attempt to understand fundamental truths about the universe can only be an extremely ambitious goal? History shows us how the world changed when the first translations of the Bible became widely available. We need to think hard about what lessons we can learn and how to apply it to the comprehension-inequality that plagues our world today. I wonder if the stagnation in Particle Physics after 2012 needs a second renaissance led by a generation who grew up never hearing the phrase "Nobody understands Quantum Mechanics".
- rimunroe 6y ago
  I get what you're saying. I studied physics in undergrad but decided not to go to grad school. I kept hearing stuff like that well into my junior and senior years. I ended up doing internships on two HEP experiments, one at Brookhaven National Lab and the other at Jefferson Lab. It was enormously frustrating to hear that something was allowed/not allowed because "the Great and Powerful Standard Model says so". If there's one thing I picked up from my program and being on experiment teams, it's that effectively communicating science is extremely hard. It's not fair to characterize it as malicious ("priestly particle physicist class hides sacred knowledge") when it's really just people not knowing how to simplify concepts accurately. I don't know a single physicist who wouldn't dearly have loved to be able to explain this stuff to laypeople more easily. People are scared to use metaphors or other rough answers. In the least bad case they can result in misunderstanding or confusion. In the worst case they can lead to perpetual motion machine people. This is extremely niche knowledge and there's a lot more stuff that should be explained first. I went to grade school in Virginia in the 90s and early 2000s. We were taught that the American Civil War was about states rights, and that it was the War of Northern Aggression. I'd much rather we focus broad educational efforts on making people understand their fellow humans and try to prevent repeating the atrocities of the past than get people to understand quantum flavordynamics or chromodynamics.
hanselot 6y ago
Breaking: Evidence of racism found in the fabric of the universe itself.

69 points by LinuxBender 6y ago

dschuetz 6y ago

"Dark Sector" - the next big thing in sciency stuff?

qubex 6y ago
It’s just shorthand for stuff that we cannot detect but ordinary (electromagnetic) means. In theory everything ‘feels’ gravity and anything with mass contributes to it. The left-handed neutrino is unusual in that it experiences only gravity and the extremely weak (though far stronger than gravity) “weak nuclear force” (and their right-handed brethren, if they even exist, might not exist en experience that). The “dark sector” is that 95% or so of the entire universe we infer must exist for either gravitational reasons (stronger gravity leads us to infer unseen mass, which we term “dark matter” though “transparent and apparently frictionless” would be a better term, or to infer unseen energy (dark energy that seems to be driving the accelerating rate of the universe).
- contravariant 6y ago
  It's worth noting that there is an explanation for dark energy, namely quantum fluctuations of the vacuum. It's also worth noting that this explanation is off by over 100 orders of magnitude, which lead to it being called "the worst prediction in physics". Oddly enough we haven't come up with a better explanation as far as I know, the current assumption is just that the mass somehow almost cancels out.
  - evanb 6y ago
    It's not the fluctuations, but the zero-point energy. In a supersymmetric theory the number exactly cancels. If the Standard Model is some low-energy EFT of a supersymmetric theory, it could be almost-0.
- throwaway_kufu 6y ago
  > 95% or so of the entire universe we infer must exist Isn’t the reason we infer dark matter exists, is our observations of the spin of galaxies? In other words there must be a lot more gravity produced by matter we aren’t observing (dark matter) to explain large scale observations? Aren’t there competing theories to dark matter, which haven’t been ruled out, from Einstein’s theories of gravity being wrong; or in the same way Einstein’s theory of gravity breaks down/is incomplete on the quantum scale his theories may breakdown at the scale of galaxies; and even more simply our observations not be accurate?
  - AnHonestComment 6y ago
    I believe there’s three sources: 1. Galaxy rotations require more mass than is visible to be gravitationally bound. 2. Clusters, super clusters, etc seem to lie on filaments and other large structures of something. 3. The map of gravitational lensing when we look past a cluster. I have my own personal pet theories — but that set of observations is thought to be explained by “dark matter”.
  - jasonwatkinspdx 6y ago
    There are many independent lines of evidence: https://en.wikipedia.org/wiki/Dark_matter#Observational_evidence https://en.wikipedia.org/wiki/Dark_matter#Observational_evid... Contrarian theories have outsized popularity here on hnews, and this tends to get fed by garbage articles from the usual sources (glances at quanta with mild disdain). Modified gravity theories are not some alternate path we just didn't explore. We explored them. They fail to explain the observational evidence. In particular the way stuff moves in galactic collisions makes very clear there's dark matter distinct from some modified version of gravity interacting with visible matter. It ends up that the consensus view of thousands of Phds that study this stuff is actually not trivially mistaken.
    - throwaway_kufu 6y ago
      I wasn’t implying mistaken by any means, I understand is the leading theory (not the only theory), I didn’t realize everything else had been ruled out or considered junk science (I just understood no one wants to be the person saying Einstein’s theories/equations for gravity need modification...even though that happens to be the consensus at the quantum level. But the galaxy collision observations is something I want to read more about (I’ve obviously seen simulations), thanks!
evanb 6y ago
A "sector" of the Standard Model---like the QCD sector, or the electroweak sector, or the Higgs sector---is just shorthand for a part of the the Standard Model that consists of particles and forces. It's possible that dark matter is just like Standard Model matter, in the sense that it only talks to a force that we already know in the Standard Model, like the weak force. But it's also possible that there are other forces. The "dark sector" is short hand for 'whatever stuff is making up the dark matter, and however they interact'.

dumbfoundded 6y ago

So it seems like this may have a link to dark matter but not energy. I have no expertise in physics but it seems like dark is a bad term as it only reflects our ignorance and inability to detect through normal electromagnetic means.

thekingofh 6y ago
Dark is just a placeholder until we find out exactly what's causing it.
at_a_remove 6y ago
Astronomers work through photons obtained and scientific inference on those photons. Lots and lots of inference. "Light" matter simply means "we can see it through a telescope because it gives off light," which means stars at a great distance, or closer up, light from a star reflected off of a surface. Dark, therefore, means "we know it is there but it isn't directly observable by gathering photons with a telescope."
- raattgift 6y ago
  Crucially we can show it's there by examining how it affects the light from bright background sources passing through it: there is a spectral shift without the imposition of new emission or absorption lines, and there is Einstein lensing [ https://en.wikipedia.org/wiki/Gravitational_lens https://en.wikipedia.org/wiki/Gravitational_lens ]. We can see this in the large by observing the http://www.astro.ucla.edu/~wright/Lyman-alpha-forest.html http://www.astro.ucla.edu/~wright/Lyman-alpha-forest.html on lines of sight through and near galaxy clusters. For example, [presentation abstract] https://depts.washington.edu/astron/event/tba-liang-dai/ https://depts.washington.edu/astron/event/tba-liang-dai/ [related paper https://arxiv.org/abs/1804.03149v2 https://arxiv.org/abs/1804.03149v2 ] or https://arxiv.org/abs/1706.07870 https://arxiv.org/abs/1706.07870 The tl;dr is that distant light sources (distance obtained by among other things comparing the angular diameter and brightness on the sky of spiral galaxies containing common bright sources within them such as supernovae or molecular clouds lit by quasars) are redshifted in a way that is very hard to explain without an accelerating expansion of space (which in the equations of the Standard Cosmology we represent as dark energy), and are lensed by luminous galaxy clusters in such a way that is very hard to explain without mass that doesn't emit or absorb light. "Hard to explain" because (just as one example) the Lyman-alpha line and its relativistic behaviour is extremely well studied in controlled laboratory conditions in various places in our solar system (notably sensitive experiments carried in various spacecraft probing other bodies in our solar system). In a number of spacecraft, Lyman-alpha photometry testing is used to determine the Hydrogen-Deuterium ratio of planetary atmospheres, since cells of those two gasses form practically ideal narrow-band rejection filters, and over time a mixture of cells reveals the atomic ratio of those isotopes in the atmosphere. People who observe Mars have used this technique to study the rate at which Mars is outgassing water vapour, in particular. As it is useful to planetary scientists to look through varying depths of a given planetary atmosphere backlit by distant luminous objects, in practice the cosmological Lyman-alpha forest can be sampled by orbiting Ly-a photometers "for free". You can't really reject the resulting Ly-a data without also rejecting the Deuterium/Hydrogen ratio obtained from probes on the surface of Mars, which happen to match. And the data typically also encodes other spectral lines principally from the intergalactic medium, and those lines are similarly redshifted and amplified by relativistic -- including general relativistic -- effects. Both dark matter and dark energy induce matching general relativistic effects, and nobody has figured out how to produce the same spectral features without including dark matter and dark energy.

dilippkumar 6y ago

> The idea that our experiments might be detecting a fourth neutrino remains controversial, however, because the Standard Model of particle physics is one of the most tested and thoroughly confirmed theoretical frameworks in history—and it allows for only three neutrinos. I am frustrated with how the "Standard Model" has become a veil with which a priestly particle physicist class hides sacred knowledge of how the universe works from plebeians like myself. Why does the Standard Model only allow for three neutrinos? Is it because the math says so? Is it because some other maths only work if this number is three? Does it come from some fascinating group-theory or symmetry groups that nobody teaches at a highschool math level? I can't be the only one who wants to learn more about this stuff. I don't believe that the Particle Physicist or the broader Physics community is at fault here. I blame our approach to school education. If we accept that it's ok for a 14 year to be bewildered at quadratic equations and is expected to accept the "Don't worry, it'll all make sense later" line, it should also be possible for the same student to learn about Heisenberg's uncertainty principle, the basics of non-Euclidean geometry and symmetry groups. Our society today has several cohorts of adults who do not have the necessary foundations to understand the Standard Model. We don't plan to educate children in schools today to be able to understand this stuff. It will take a highly motivated adult several years of self study to reach a point where the Standard Model becomes approachable. Do we really want to live in the world where an attempt to understand fundamental truths about the universe can only be an extremely ambitious goal? History shows us how the world changed when the first translations of the Bible became widely available. We need to think hard about what lessons we can learn and how to apply it to the comprehension-inequality that plagues our world today. I wonder if the stagnation in Particle Physics after 2012 needs a second renaissance led by a generation who grew up never hearing the phrase "Nobody understands Quantum Mechanics".

rimunroe 6y ago
I get what you're saying. I studied physics in undergrad but decided not to go to grad school. I kept hearing stuff like that well into my junior and senior years. I ended up doing internships on two HEP experiments, one at Brookhaven National Lab and the other at Jefferson Lab. It was enormously frustrating to hear that something was allowed/not allowed because "the Great and Powerful Standard Model says so". If there's one thing I picked up from my program and being on experiment teams, it's that effectively communicating science is extremely hard. It's not fair to characterize it as malicious ("priestly particle physicist class hides sacred knowledge") when it's really just people not knowing how to simplify concepts accurately. I don't know a single physicist who wouldn't dearly have loved to be able to explain this stuff to laypeople more easily. People are scared to use metaphors or other rough answers. In the least bad case they can result in misunderstanding or confusion. In the worst case they can lead to perpetual motion machine people. This is extremely niche knowledge and there's a lot more stuff that should be explained first. I went to grade school in Virginia in the 90s and early 2000s. We were taught that the American Civil War was about states rights, and that it was the War of Northern Aggression. I'd much rather we focus broad educational efforts on making people understand their fellow humans and try to prevent repeating the atrocities of the past than get people to understand quantum flavordynamics or chromodynamics.

hanselot 6y ago

Breaking: Evidence of racism found in the fabric of the universe itself.