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> raises lots of interesting questions Exactly. What I liked about MOND was that it basically amounted to "we don't know." The populist notion that dark matter

> raises lots of interesting questions Exactly. What I liked about MOND was that it basically amounted to "we don't know." The populist notion that dark matter is conclusively matter, and dark energy is energy seems a bold claim for such a young species. Crazy theories like non-universal constants are probably crazy, but they do explore unconventional lines of thought. One of those, most likely an unknown unknown, may be answer. Focusing all our energy on one explanation (that has been falsified more than once) seems like a waste.

acqq 8y ago
“What’s most impressive is that the predictions of dark matter were first made in the 1970s and 1980s, and were observationally confirmed later. This is not a case of tweaking the model to fit the data; this is a case of the best kind of science you hope for: where you make predictions, make the observations, and what you see validates and confirms the predictions you had made. And yet, even 35 years later, there are no modifications of gravity that achieve the galaxy-scale successes of MOND that also explain these other observations. The best tests of dark matter vs. MOND, which are on large, cosmic scales, have a clear winner and a clear loser.” https://medium.com/starts-with-a-bang/theres-a-debate-raging-over-whether-dark-matter-is-real-but-one-side-is-cheating-d25f28319d70 https://medium.com/starts-with-a-bang/theres-a-debate-raging... In short: looking at everything we can observe and can model, we do know that the “dark matter” is matter. Because we first made predictions (“it should behave as matter”), then confirmed them, many times. And MOND can’t even explain that what’s already observed.
- guscost 8y ago
  "Every genuine test of a theory is an attempt to falsify it, or to refute it. Testability is falsifiability; but there are degrees of testability: some theories are more testable, more exposed to refutation, than others; they take, as it were, greater risks." - Karl Popper
- zamalek 8y ago
  That's putting the effect before the cause. The dark matter map can also be a map of "how wrong we are," not only "how much invisible mass is there." An incomplete periodic table of physics, if you will. We need to produce a WIMP here, on Earth, and watch it decay. That's a "thruthifiable" experiment, but it'd be enough to convince me that we've found the correct line of thinking (which the popular opinion could very well be, don't get me wrong - I simply believe that we're overconfident).
  - acqq 8y ago
    > We need to produce a WIMP here, on Earth, and watch it decay. No. You can't "need" something if that is simply unreachable. There’s reasonable chance that to produce the particles (which still don’t have to be the WIMPs as we imagined them, and still would be „matter“) the energies needed are simply beyond those that will ever be available to humanity. It wold not mean more than that: that we, humans, just can't repeat with our technology the extreme conditions that the Universe had/has. The WIMPs in the form discoverable by the energies that are available to us at the moment would have been nice luck, but the existence of dark matter is not anything less certain when the dark matter is simply different from that. It would still be "matter" and not something else.
antidesitter 8y ago
> that has been falsified more than once What has been falsified more than once?
- zamalek 8y ago
  We haven't observed any of the predicted WIMPs at the LHC, as one example. They were subsequently relegated to a higher energy level.
  - acqq 8y ago
    That doesn’t disprove the “matter-like” observed behavior, it just shows that the particular assumptions under which exactly these non-found WIMPs were imagined were false.
    - dnautics 8y ago
      If you have an infinite space of particle parameters and a series of tests keeps eliminating large swaths of this space, at some point it feels like you're playing a god of inbetweens game a la creationists arguing using gaps in the fossil record. There is a categorical difference, of course, but as a practical matter the parallels are useful, at what point do we table (for now) the search for the populist position and break for alternatives?
      - acqq 8y ago
        It's not "populist" anything. It's the best science that can be done: https://medium.com/starts-with-a-bang/five-reasons-we-think-dark-matter-exists-a122bd606ba8 https://medium.com/starts-with-a-bang/five-reasons-we-think-... "Five Reasons We Think Dark Matter Exists: No other idea explains even two of these." "1.) Galaxy Clusters" "2.) Galactic Rotation Curves" "3.) The Cosmic Microwave Background" "4.) The Bullet Cluster" "5.) Large-Scale Structure Formation" From these 5, only dark matter matches all. Whereas MOND theories match only one, the "item number 2" and only as an attempt to after-the-fact-explanation of what's anyway observed, not as any prediction of anything new. As I've quoted in my another message here: "the predictions of dark matter were first made in the 1970s and 1980s, and were observationally confirmed later. This is not a case of tweaking the model to fit the data; this is a case of the best kind of science you hope for: where you make predictions, make the observations, and what you see validates and confirms the predictions you had made." Moreover, there's nothing "large" of the possible space that is now excluded. The possible space includes everything that "behaves like matter". What's (still just "probably") eliminated is just what were for us, humans, in this particular moment of our history very convenient to happen: that the energies needed are exactly such that WIMPs that were conveniently postulated to be such can be generated by the device which design and maintenance costs less than 2% of the total cost of the F-35 fighter planes (the money invested and planned to be invested in F-35 is 75 times bigger than the international investment in LHC). It would have been luck if it had happened, but the possibilities are much bigger and include such which are going to remain physically unreachable to be produced by our technologies. That we, humans, can't produce some particles doesn't disprove that dark matter exists when we have precise observations that can only be explained by dark matter and effectively by nothing else.
bmh100 8y ago
The Bullet Cluster seems pretty conclusive though.

acqq 8y ago

“What’s most impressive is that the predictions of dark matter were first made in the 1970s and 1980s, and were observationally confirmed later. This is not a case of tweaking the model to fit the data; this is a case of the best kind of science you hope for: where you make predictions, make the observations, and what you see validates and confirms the predictions you had made. And yet, even 35 years later, there are no modifications of gravity that achieve the galaxy-scale successes of MOND that also explain these other observations. The best tests of dark matter vs. MOND, which are on large, cosmic scales, have a clear winner and a clear loser.” https://medium.com/starts-with-a-bang/theres-a-debate-raging-over-whether-dark-matter-is-real-but-one-side-is-cheating-d25f28319d70 https://medium.com/starts-with-a-bang/theres-a-debate-raging... In short: looking at everything we can observe and can model, we do know that the “dark matter” is matter. Because we first made predictions (“it should behave as matter”), then confirmed them, many times. And MOND can’t even explain that what’s already observed.

guscost 8y ago
"Every genuine test of a theory is an attempt to falsify it, or to refute it. Testability is falsifiability; but there are degrees of testability: some theories are more testable, more exposed to refutation, than others; they take, as it were, greater risks." - Karl Popper
zamalek 8y ago
That's putting the effect before the cause. The dark matter map can also be a map of "how wrong we are," not only "how much invisible mass is there." An incomplete periodic table of physics, if you will. We need to produce a WIMP here, on Earth, and watch it decay. That's a "thruthifiable" experiment, but it'd be enough to convince me that we've found the correct line of thinking (which the popular opinion could very well be, don't get me wrong - I simply believe that we're overconfident).
- acqq 8y ago
  > We need to produce a WIMP here, on Earth, and watch it decay. No. You can't "need" something if that is simply unreachable. There’s reasonable chance that to produce the particles (which still don’t have to be the WIMPs as we imagined them, and still would be „matter“) the energies needed are simply beyond those that will ever be available to humanity. It wold not mean more than that: that we, humans, just can't repeat with our technology the extreme conditions that the Universe had/has. The WIMPs in the form discoverable by the energies that are available to us at the moment would have been nice luck, but the existence of dark matter is not anything less certain when the dark matter is simply different from that. It would still be "matter" and not something else.

antidesitter 8y ago

> that has been falsified more than once What has been falsified more than once?

zamalek 8y ago
We haven't observed any of the predicted WIMPs at the LHC, as one example. They were subsequently relegated to a higher energy level.
- acqq 8y ago
  That doesn’t disprove the “matter-like” observed behavior, it just shows that the particular assumptions under which exactly these non-found WIMPs were imagined were false.
  - dnautics 8y ago
    If you have an infinite space of particle parameters and a series of tests keeps eliminating large swaths of this space, at some point it feels like you're playing a god of inbetweens game a la creationists arguing using gaps in the fossil record. There is a categorical difference, of course, but as a practical matter the parallels are useful, at what point do we table (for now) the search for the populist position and break for alternatives?
    - acqq 8y ago
      It's not "populist" anything. It's the best science that can be done: https://medium.com/starts-with-a-bang/five-reasons-we-think-dark-matter-exists-a122bd606ba8 https://medium.com/starts-with-a-bang/five-reasons-we-think-... "Five Reasons We Think Dark Matter Exists: No other idea explains even two of these." "1.) Galaxy Clusters" "2.) Galactic Rotation Curves" "3.) The Cosmic Microwave Background" "4.) The Bullet Cluster" "5.) Large-Scale Structure Formation" From these 5, only dark matter matches all. Whereas MOND theories match only one, the "item number 2" and only as an attempt to after-the-fact-explanation of what's anyway observed, not as any prediction of anything new. As I've quoted in my another message here: "the predictions of dark matter were first made in the 1970s and 1980s, and were observationally confirmed later. This is not a case of tweaking the model to fit the data; this is a case of the best kind of science you hope for: where you make predictions, make the observations, and what you see validates and confirms the predictions you had made." Moreover, there's nothing "large" of the possible space that is now excluded. The possible space includes everything that "behaves like matter". What's (still just "probably") eliminated is just what were for us, humans, in this particular moment of our history very convenient to happen: that the energies needed are exactly such that WIMPs that were conveniently postulated to be such can be generated by the device which design and maintenance costs less than 2% of the total cost of the F-35 fighter planes (the money invested and planned to be invested in F-35 is 75 times bigger than the international investment in LHC). It would have been luck if it had happened, but the possibilities are much bigger and include such which are going to remain physically unreachable to be produced by our technologies. That we, humans, can't produce some particles doesn't disprove that dark matter exists when we have precise observations that can only be explained by dark matter and effectively by nothing else.

bmh100 8y ago

The Bullet Cluster seems pretty conclusive though.