10 ms·

Dark matter appears, to a layman with some historical knowledge, as nothing more than modern day epicycles. When we can't explain something with the models we h

by douche 9y ago

Dark matter appears, to a layman with some historical knowledge, as nothing more than modern day epicycles. When we can't explain something with the models we have, and have to invent magic terms to balance the equations, that indicates that we really don't know what the fuck is going on.

douche 9y ago
Whoo, boy, the astrophysics fanboys that come out of the woodwork to suppress the notion that the emperor has no clothes
- jcranmer 9y ago
  Even as someone who would rather MOND be true than dark matter, I have to admit that dark matter is internally consistent in ways that MOND is not. By comparison to the theories of planetary movement (since you seem to love comparing dark matter to them so much), MOND is rather like the Copernican model and dark matter rather like Kepler's model. It's well-known that the traditional equations are off. MOND provides a fix that starts off looking better, but the more precise you do the measurements, the more you need to add the fudge factors in to make the numbers come out right, and it ends up being just as bad as the original--which is a reasonable description of the evolution of the Copernican model. By contrast, both Kepler's model and dark matter provide a much more accurate picture with a somewhat more complex addendum to the original non-fudged equations. But they also both lack mechanistic explanations for their origin: Kepler's model ruined the traditional explanation of how planets moved and inherited the stellar parallax death-knell from Copernicus's theory. In the case of planetary motion, it took the development of Newton's Law of Gravitation and the derivation of Kepler's laws of planetary motion from said theory to provide a sound mechanistic basis. We lack that mechanistic basis for dark matter, but that doesn't really mean that dark matter is inherently wrong.
  - nilson 9y ago
    Why do physicists believe that formulas should be elegant, beautiful etc.? Maybe that is not how universe works.
wayn3 9y ago
And that's exactly what dark matter is. Journalism misleads people very hard about physics research. Physicists dont run around claiming they've observed dark matter. That's the wrong direction. Physics has a problem with gravity because some things don't behave in such a way that makes theory agree with observation. Since we are talking about gravity here, we call the thing we are observing "matter". Simply because things that interact with gravity have historically been called matter. Because its "dark" in the sense that we can't see (observe) it, its called dark matter. As a placeholder for something that has not yet been explained. Then journalists come around and spin this tale about how physicists have found this super magical stuff called "dark" "matter" and its so exotic if you dropped it onto des moines it'd turn the place into honolulu. Dark Matter is just the placeholder name for an observation that disagrees with conventional theory.
- roywiggins 9y ago
  But dark matter is theorized to he a particle that we haven't observed yet, which sounds like "matter" to me. The specific idea to fix up the discrepancies is, there are huge clouds of invisible particles. There are competing theories on what sort of particle they might be, but dark matter theories predict that these particles are out there.
  - wayn3 9y ago
    again, thats what theoretical physicists do. Someone makes a weird observation and your theory is left with a hole. You try to plug it. They don't preach these things. Physicists don't run around preaching unprovable holy grail theories. They just make something up. Out of nothing. Because its their job. They need to come up with falsifiable theories that can be verified in lab experiments. In order to do so, they HAVE TO hypothesize something. They can't just say "err dark matter right?". They have to say "there could be a particle with these properties, a mass of roughly X, producing a cross-section of Y when bombarded with tau-leptons etc.". That's just the scientific method. Any physicist who postulates particles does that from a position of "it probably doesn't exist". The same way when you measure something to be faster than the speed of light, you assume that a cable is broken. Then some journalist comes around saying "lol paper says weird particle exists, scientists are whack". That's annoying. But it happens. If journalists wrote about CS the way they write about physics, the next time someone loses 2 BTC from their wallet, they'd claim that thats hard evidence of quantum computers being invented by north korea. Hypothetically plausible but as outlandish as permissible by reality.
hwillis 9y ago
You have a misunderstanding of the problems and evidence of dark matter: https://www.reddit.com/r/space/comments/6488wb/i_dont_want_to_be_anti_science_but_i_am_doubtful/dg05wx4/ https://www.reddit.com/r/space/comments/6488wb/i_dont_want_t...
- douche 9y ago
  I'm not seeing anything there that isn't a handwavey explanation for "reality doesn't match the models, so DARK MATTER!"
  - laretluval 9y ago
    It's still a nontrivial observation that the equations can be corrected to account for reality most simply by adding a term for unseen matter (rather than some factor or some other mathematical operation). Maybe the term doesn't have a straightforward physical explanation but there's a long history of introducing math without any corresponding mechanistic explanation---this is what gravity itself was until general relativity, nothing more than an inexplicable inverse-square attractive force.
    - electrograv 9y ago
      If a Newtonian model of gravity doesn't "explain" gravity, then neither does general relativity. These are all different models of reality with different levels of model complexity and predictive accuracy, but there's no fundamentally binary difference between them in their power of "explanation" etc. So new models like "dark matter" or "MOND" are all just different models that model observations better than prior theories but currently have the problem of being difficult to unify with the rest of theoretical physics.
  - hwillis 9y ago
    >One of the recent most convincing things was the bullet cluster as described here.[1] We saw two galaxies collide where the "observed" matter actually underwent a collision but the gravitational lensing kept moving un-impeded which matches the belief that the majority of mass in a galaxy is collisionless dark matter that felt no colliding interaction and passed right on through bringing the bulk of the gravitational lensing with it. How can you possibly even begin to explain that without dark matter? [1] http://www.preposterousuniverse.com/blog/2006/08/21/dark-matter-exists/ http://www.preposterousuniverse.com/blog/2006/08/21/dark-mat...
laretluval 9y ago
https://xkcd.com/1758/ https://xkcd.com/1758/
olavk 9y ago
There was/is nothing magic about epicycles. Epicycles was part of a model which described the movement of the planets. Now we have better and more precise model, but that does not mean epicycles was "magic". There is nothing magic about the the word "dark matter" either. Yes indeed it describe a phenomen we don't understand, this does not mean it is magic.
- TillE 9y ago
  Epicycles were wrong. They were an incorrect theory attempting to fit the math.
  - yorwba 9y ago
    Using epicycles just means to decompose the motion into its Fourier series. It may not be the most elegant description, but its not wrong per se, either.
    - JadeNB 9y ago
      > Using epicycles just means to decompose the motion into its Fourier series. It may not be the most elegant description, but its not wrong per se, either. One issue here is that (as I understand the history) epicycles were not originally proposed in the context of "just add them until you've got something that looks right"; it was proposed that, occasionally, one needed to add one epicycle. After a while it was found that even this didn't work, and we needed sometimes to add another. I forget whether the theory collapsed before instances were found where we'd need a third. This, I think, is 'wrong' in the sense of physics: if your model is constantly scrambling to catch up with newly acquired data, then it has no predictive, and hence little scientific, value. Further, the very ability of epicycles constantly to scramble to catch up—the ability of trigonometric polynomials to approximate continuous functions arbitrarily well over arbitrary bounded intervals, as you mention—is also a mark against them: a scientific theory that is so general that it could be tuned to predict anything can, in fact, for that reason actually predict nothing.
      - 9y ago
jrvidal 9y ago
On the other hand: https://en.wikipedia.org/wiki/Neutrino https://en.wikipedia.org/wiki/Neutrino

by douche 9y ago

douche 9y ago

Whoo, boy, the astrophysics fanboys that come out of the woodwork to suppress the notion that the emperor has no clothes

jcranmer 9y ago
Even as someone who would rather MOND be true than dark matter, I have to admit that dark matter is internally consistent in ways that MOND is not. By comparison to the theories of planetary movement (since you seem to love comparing dark matter to them so much), MOND is rather like the Copernican model and dark matter rather like Kepler's model. It's well-known that the traditional equations are off. MOND provides a fix that starts off looking better, but the more precise you do the measurements, the more you need to add the fudge factors in to make the numbers come out right, and it ends up being just as bad as the original--which is a reasonable description of the evolution of the Copernican model. By contrast, both Kepler's model and dark matter provide a much more accurate picture with a somewhat more complex addendum to the original non-fudged equations. But they also both lack mechanistic explanations for their origin: Kepler's model ruined the traditional explanation of how planets moved and inherited the stellar parallax death-knell from Copernicus's theory. In the case of planetary motion, it took the development of Newton's Law of Gravitation and the derivation of Kepler's laws of planetary motion from said theory to provide a sound mechanistic basis. We lack that mechanistic basis for dark matter, but that doesn't really mean that dark matter is inherently wrong.
- nilson 9y ago
  Why do physicists believe that formulas should be elegant, beautiful etc.? Maybe that is not how universe works.

wayn3 9y ago

And that's exactly what dark matter is. Journalism misleads people very hard about physics research. Physicists dont run around claiming they've observed dark matter. That's the wrong direction. Physics has a problem with gravity because some things don't behave in such a way that makes theory agree with observation. Since we are talking about gravity here, we call the thing we are observing "matter". Simply because things that interact with gravity have historically been called matter. Because its "dark" in the sense that we can't see (observe) it, its called dark matter. As a placeholder for something that has not yet been explained. Then journalists come around and spin this tale about how physicists have found this super magical stuff called "dark" "matter" and its so exotic if you dropped it onto des moines it'd turn the place into honolulu. Dark Matter is just the placeholder name for an observation that disagrees with conventional theory.

roywiggins 9y ago
But dark matter is theorized to he a particle that we haven't observed yet, which sounds like "matter" to me. The specific idea to fix up the discrepancies is, there are huge clouds of invisible particles. There are competing theories on what sort of particle they might be, but dark matter theories predict that these particles are out there.
- wayn3 9y ago
  again, thats what theoretical physicists do. Someone makes a weird observation and your theory is left with a hole. You try to plug it. They don't preach these things. Physicists don't run around preaching unprovable holy grail theories. They just make something up. Out of nothing. Because its their job. They need to come up with falsifiable theories that can be verified in lab experiments. In order to do so, they HAVE TO hypothesize something. They can't just say "err dark matter right?". They have to say "there could be a particle with these properties, a mass of roughly X, producing a cross-section of Y when bombarded with tau-leptons etc.". That's just the scientific method. Any physicist who postulates particles does that from a position of "it probably doesn't exist". The same way when you measure something to be faster than the speed of light, you assume that a cable is broken. Then some journalist comes around saying "lol paper says weird particle exists, scientists are whack". That's annoying. But it happens. If journalists wrote about CS the way they write about physics, the next time someone loses 2 BTC from their wallet, they'd claim that thats hard evidence of quantum computers being invented by north korea. Hypothetically plausible but as outlandish as permissible by reality.

hwillis 9y ago

You have a misunderstanding of the problems and evidence of dark matter: https://www.reddit.com/r/space/comments/6488wb/i_dont_want_to_be_anti_science_but_i_am_doubtful/dg05wx4/ https://www.reddit.com/r/space/comments/6488wb/i_dont_want_t...

douche 9y ago
I'm not seeing anything there that isn't a handwavey explanation for "reality doesn't match the models, so DARK MATTER!"
- laretluval 9y ago
  It's still a nontrivial observation that the equations can be corrected to account for reality most simply by adding a term for unseen matter (rather than some factor or some other mathematical operation). Maybe the term doesn't have a straightforward physical explanation but there's a long history of introducing math without any corresponding mechanistic explanation---this is what gravity itself was until general relativity, nothing more than an inexplicable inverse-square attractive force.
  - electrograv 9y ago
    If a Newtonian model of gravity doesn't "explain" gravity, then neither does general relativity. These are all different models of reality with different levels of model complexity and predictive accuracy, but there's no fundamentally binary difference between them in their power of "explanation" etc. So new models like "dark matter" or "MOND" are all just different models that model observations better than prior theories but currently have the problem of being difficult to unify with the rest of theoretical physics.
- hwillis 9y ago
  >One of the recent most convincing things was the bullet cluster as described here.[1] We saw two galaxies collide where the "observed" matter actually underwent a collision but the gravitational lensing kept moving un-impeded which matches the belief that the majority of mass in a galaxy is collisionless dark matter that felt no colliding interaction and passed right on through bringing the bulk of the gravitational lensing with it. How can you possibly even begin to explain that without dark matter? [1] http://www.preposterousuniverse.com/blog/2006/08/21/dark-matter-exists/ http://www.preposterousuniverse.com/blog/2006/08/21/dark-mat...

laretluval 9y ago

https://xkcd.com/1758/ https://xkcd.com/1758/

olavk 9y ago

There was/is nothing magic about epicycles. Epicycles was part of a model which described the movement of the planets. Now we have better and more precise model, but that does not mean epicycles was "magic". There is nothing magic about the the word "dark matter" either. Yes indeed it describe a phenomen we don't understand, this does not mean it is magic.

TillE 9y ago
Epicycles were wrong. They were an incorrect theory attempting to fit the math.
- yorwba 9y ago
  Using epicycles just means to decompose the motion into its Fourier series. It may not be the most elegant description, but its not wrong per se, either.
  - JadeNB 9y ago
    > Using epicycles just means to decompose the motion into its Fourier series. It may not be the most elegant description, but its not wrong per se, either. One issue here is that (as I understand the history) epicycles were not originally proposed in the context of "just add them until you've got something that looks right"; it was proposed that, occasionally, one needed to add one epicycle. After a while it was found that even this didn't work, and we needed sometimes to add another. I forget whether the theory collapsed before instances were found where we'd need a third. This, I think, is 'wrong' in the sense of physics: if your model is constantly scrambling to catch up with newly acquired data, then it has no predictive, and hence little scientific, value. Further, the very ability of epicycles constantly to scramble to catch up—the ability of trigonometric polynomials to approximate continuous functions arbitrarily well over arbitrary bounded intervals, as you mention—is also a mark against them: a scientific theory that is so general that it could be tuned to predict anything can, in fact, for that reason actually predict nothing.
    - 9y ago

jrvidal 9y ago

On the other hand: https://en.wikipedia.org/wiki/Neutrino https://en.wikipedia.org/wiki/Neutrino