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When we're confronted with something we can't explain using our existing equations and theories, the conclusion is that there must be some mysterious thing ther

by maratd 9y ago

When we're confronted with something we can't explain using our existing equations and theories, the conclusion is that there must be some mysterious thing there that fixes our current equations and makes them work again? A thing we can't detect or see or have any other evidence of ... other than our equations and theories need that thing there for them to work? > In other words situations where we see twin images of a very distant galaxy It's entirely possible our equations do not function well on those scales.

joeberon 9y ago
Firstly, they function well enough to predict that gravitational waves exist, the ones which we measured being produced by an extreme gravitational event. Secondly, many other areas of physics have worked this out. The prime example of Quantum Field Theory and the Standard Model, which has been incredibly successful in predicting the existence of new types of particles from purely mathematical equations and theories (and trust me that stuff is pretty damn abstract, even compared to General Relativity) It is of course a possibility, although you make it sound somewhat obvious, as if physicists just haven't bothered to question that the widely-regarded theories might be wrong. I assure you this is not the case; there are no politics involved in this kind of research which is stopping people presenting questions such as "are we sure our current models are correct?" In cases like this, it is safe to assume that researchers have already explored any ideas you could come up with, especially the particularly simple ones...
- maratd 9y ago
  > Firstly, they function well enough to predict that gravitational waves exist, the ones which we measured being produced by an extreme gravitational event. I don't think that aspect of the theories is in dispute? Newtonian physics well enough at certain scales, but breaks down at others. The question is if there's something better out there and if we adopt something better, would it remove the need for all this "dark matter". > Secondly, many other areas of physics have worked this out. The prime example of Quantum Field Theory and the Standard Model Wait, what? Quantum Field Theory suggests the existence of dark matter?
  - joeberon 9y ago
    >The question is if there's something better out there and if we adopt something better, would it remove the need for all this "dark matter". I'm not sure about this, personally I don't know enough about quantum gravity to comment on that. Dark energy is a tricky question though because it is somewhat explainable within our current theories, and it is unobservable. > Secondly, many other areas of physics have worked this out. I don't know why I put this. I meant to put that QFT is an example of a theory which predicts many more phenomena than it was originally invented to describe.
- autokad 9y ago
  "there are no politics involved in this kind of research" While it might not be true in this case, you couldn't be further from the truth. there is an EXTREME amount of politics. people's careers are based on entire assumptions, thesis', papers, and work could be all for not if based on false assumptions.
  - joeberon 9y ago
    Yeah there's a huge amount of politics in research IN GENERAL, but not so much in physics. Like there are no big questions covered up because they're inconvenient or anything.
    - autokad 9y ago
      the big bang theory was dismissed for decades. Even Einstein said to someone suggesting it that his physics was "abominable".
      - JadeNB 9y ago
        > the big bang theory was dismissed for decades. Dismissing a theory that is (now known to be) right is not necessarily political; it can be just a mistake. There are certainly cliques that are invested in believing the orthodoxy, but there are ways in the hard sciences of absolutely disproving that orthodoxy; and, though they are subject to fierce scrutiny, as they should be, they can be, and have been, accepted after surviving that scrutiny.
        autokad 9y ago
        it can be but you offered no evidence contrary. the data WAS there, but it conflicted with their well established views, call them political or not - it doesn't matter. it would take a great deal of hubris to say 'yes, all other sciences and research suffer from the human condition, but not physics!'
    - dnautics 9y ago
      I think the commenter meant politics in the "office politics"/"playing politics" sense, not the "political party" sense
jrvidal 9y ago
FWIW, this approach is popular because it has worked pretty well in the past. https://en.wikipedia.org/wiki/Neutrino https://en.wikipedia.org/wiki/Neutrino
hwillis 9y ago
Dark matter is predicted at every level of astrophysics. It's not just "hey, galaxies look weird". The amount of visible matter only accounts for 4% of the cosmic microwave background. The CMB is extremely smooth, but visible matter is highly clumped up. This can only be explained by a huge amount of matter that doesn't clump up ie non-baryonic. The ratio of deuterium to hydrogen rises based on the density, since there's more pressure from gravity. There's way more deuterium than can be explained by visible matter, so there must be some extra compression happening. Galaxies have more kinetic energy than they can have given their visible matter and how fast it's moving. This implies a huge amount of invisible mass. Gravitational lensing around the edges of galaxy clusters indicates a halo of invisible mass. Colliding galactic clusters show their mass splits into two parts: one that clumps up into a bright, dense blob, and another that has much higher inertia and continues past the bright blob as if it didn't interact with it in any way besides gravity. We can map variations in empty space where there is more mass than is expected, in a way that can't be explained by a self-consistent theory of gravity but can be explained by invisible mass. Dark matter as a theory hasn't changed for 80 years and every single one of these discrepancies is solved exactly by using the measurements of dark matter that already existed. They all agree with each other perfectly. There is no theory that even competes with dark matter. Nobody has come up with another idea that explains all of those or even most of those problems.
- effie 9y ago
  > The amount of visible matter only accounts for 4% of the cosmic microwave background. Could you explain what do you mean by 'accounts for 4% of the cosmic microwave background'? How is one supposed to account for CMB by matter density, when its spectrum is almost equilibrium one (thus consistent with almost any value of matter density)?
  - hwillis 9y ago
    The CMB has a certain spectrum and temperature. The amount of energy in the universe correlates to the amount of mass in the universe. The more energy and mass was present in the big bang, the hotter the CMB will be. The amount of visible matter corresponds to a CMB temperature that is far lower than what we see.

by maratd 9y ago

joeberon 9y ago

Firstly, they function well enough to predict that gravitational waves exist, the ones which we measured being produced by an extreme gravitational event. Secondly, many other areas of physics have worked this out. The prime example of Quantum Field Theory and the Standard Model, which has been incredibly successful in predicting the existence of new types of particles from purely mathematical equations and theories (and trust me that stuff is pretty damn abstract, even compared to General Relativity) It is of course a possibility, although you make it sound somewhat obvious, as if physicists just haven't bothered to question that the widely-regarded theories might be wrong. I assure you this is not the case; there are no politics involved in this kind of research which is stopping people presenting questions such as "are we sure our current models are correct?" In cases like this, it is safe to assume that researchers have already explored any ideas you could come up with, especially the particularly simple ones...

maratd 9y ago
> Firstly, they function well enough to predict that gravitational waves exist, the ones which we measured being produced by an extreme gravitational event. I don't think that aspect of the theories is in dispute? Newtonian physics well enough at certain scales, but breaks down at others. The question is if there's something better out there and if we adopt something better, would it remove the need for all this "dark matter". > Secondly, many other areas of physics have worked this out. The prime example of Quantum Field Theory and the Standard Model Wait, what? Quantum Field Theory suggests the existence of dark matter?
- joeberon 9y ago
  >The question is if there's something better out there and if we adopt something better, would it remove the need for all this "dark matter". I'm not sure about this, personally I don't know enough about quantum gravity to comment on that. Dark energy is a tricky question though because it is somewhat explainable within our current theories, and it is unobservable. > Secondly, many other areas of physics have worked this out. I don't know why I put this. I meant to put that QFT is an example of a theory which predicts many more phenomena than it was originally invented to describe.
autokad 9y ago
"there are no politics involved in this kind of research" While it might not be true in this case, you couldn't be further from the truth. there is an EXTREME amount of politics. people's careers are based on entire assumptions, thesis', papers, and work could be all for not if based on false assumptions.
- joeberon 9y ago
  Yeah there's a huge amount of politics in research IN GENERAL, but not so much in physics. Like there are no big questions covered up because they're inconvenient or anything.
  - autokad 9y ago
    the big bang theory was dismissed for decades. Even Einstein said to someone suggesting it that his physics was "abominable".
    - JadeNB 9y ago
      > the big bang theory was dismissed for decades. Dismissing a theory that is (now known to be) right is not necessarily political; it can be just a mistake. There are certainly cliques that are invested in believing the orthodoxy, but there are ways in the hard sciences of absolutely disproving that orthodoxy; and, though they are subject to fierce scrutiny, as they should be, they can be, and have been, accepted after surviving that scrutiny.
      - autokad 9y ago
        it can be but you offered no evidence contrary. the data WAS there, but it conflicted with their well established views, call them political or not - it doesn't matter. it would take a great deal of hubris to say 'yes, all other sciences and research suffer from the human condition, but not physics!'
  - dnautics 9y ago
    I think the commenter meant politics in the "office politics"/"playing politics" sense, not the "political party" sense

jrvidal 9y ago

FWIW, this approach is popular because it has worked pretty well in the past. https://en.wikipedia.org/wiki/Neutrino https://en.wikipedia.org/wiki/Neutrino

hwillis 9y ago

Dark matter is predicted at every level of astrophysics. It's not just "hey, galaxies look weird". The amount of visible matter only accounts for 4% of the cosmic microwave background. The CMB is extremely smooth, but visible matter is highly clumped up. This can only be explained by a huge amount of matter that doesn't clump up ie non-baryonic. The ratio of deuterium to hydrogen rises based on the density, since there's more pressure from gravity. There's way more deuterium than can be explained by visible matter, so there must be some extra compression happening. Galaxies have more kinetic energy than they can have given their visible matter and how fast it's moving. This implies a huge amount of invisible mass. Gravitational lensing around the edges of galaxy clusters indicates a halo of invisible mass. Colliding galactic clusters show their mass splits into two parts: one that clumps up into a bright, dense blob, and another that has much higher inertia and continues past the bright blob as if it didn't interact with it in any way besides gravity. We can map variations in empty space where there is more mass than is expected, in a way that can't be explained by a self-consistent theory of gravity but can be explained by invisible mass. Dark matter as a theory hasn't changed for 80 years and every single one of these discrepancies is solved exactly by using the measurements of dark matter that already existed. They all agree with each other perfectly. There is no theory that even competes with dark matter. Nobody has come up with another idea that explains all of those or even most of those problems.

effie 9y ago
> The amount of visible matter only accounts for 4% of the cosmic microwave background. Could you explain what do you mean by 'accounts for 4% of the cosmic microwave background'? How is one supposed to account for CMB by matter density, when its spectrum is almost equilibrium one (thus consistent with almost any value of matter density)?
- hwillis 9y ago
  The CMB has a certain spectrum and temperature. The amount of energy in the universe correlates to the amount of mass in the universe. The more energy and mass was present in the big bang, the hotter the CMB will be. The amount of visible matter corresponds to a CMB temperature that is far lower than what we see.