4 ms·

One way to think of non-detection is as evidence that we're looking in the wrong place. Another way to think of non-detection is as evidence that it doesn't ex

One way to think of non-detection is as evidence that we're looking in the wrong place. Another way to think of non-detection is as evidence that it doesn't exist.

mr_mitm 2y ago
> One way to think of non-detection is as evidence that we're looking in the wrong place We aren't looking in only one place > Another way to think of non-detection is as evidence that it doesn't exist. Absence of evidence is not evidence of absence. Exhausting the parameter space until evidence is found is simply the normal scientific progress.
- zmgsabst 2y ago
  How many places do I need to look before I start to have evidence my lost wallet isn’t in my house? The normal spot on the shelf? …checking my pockets? …searching the bags I used to go shopping? At each step, another of my theories about where my wallet is gets disproven — but none are direct evidence it’s not in my house. We are playing the same game with dark matter: they keep checking spots and it keeps not being there. At what point does checking wrong theories start to suggest that the entire idea is flawed?
  - mr_mitm 2y ago
    When you exhausted the parameter space (assuming you can with our current technical abilities) or a competing idea with actual evidence comes along. It's not like people aren't trying.
    - zmgsabst 2y ago
      That’s not the statistical definition of “evidence” — which is an occurrence that makes something more (or less) likely. I’d argue that each failure in a strictly statistical sense makes it more likely the whole conception is flawed — if only a little. So every failure is statistical evidence that dark matter theories are wrong. Just like each place I look for my wallet and don’t find it makes it slightly more likely that it’s not in my house.
  - elashri 2y ago
    The parameter space is usually (not only) a two dimensional plot of mass and the coupling force parameter. Those can give you a space that you would want to explore. There will be no one experiment that would give you sensitivity in all the parameter space. So you design experiments and collect data. If you don't find in the region your experiment were sensitive too (and you did your analysis carefully) then you establish a limit that says basically it cannot be in this region, look in other regions, then repeat. The analogy with your wallet is misleading because we know your habits, we don't know about nature habits. As I explained, when we exhaust the parameter space regions and can't find anything then this would tell us to give a shot to something else. Not that people are not doing this now already anyways.
- drdeca 2y ago
  Remember the principle of conservation of expected probability. P[X] = P[X|Y] * P[Y] + P[X|!Y] * P[!Y] . If P[X|Y] > P[X] and P[Y] is strictly between 0 and 1, then P[X|!Y] < P[X] . So, if X is “dark matter is some kind of matter that can be detected directly” and Y is “Dark matter is/would-be detected directly by this experiment (when/if the experiment is/would-be done)” then, if we do the experiment and it does not directly detect dark matter, then, if we previously assigned some positive probability that it would, our probability that we can detect it in some way, should go down (though not necessarily by a non-negligible amount).
  - deleted 2y ago
    [deleted]
nkrisc 2y ago
Except you don’t know which it is until you’ve exhausted the search space.
elashri 2y ago
"Absence of evidence is not evidence of absence" William Wright [1] [1] https://quoteinvestigator.com/2019/09/17/absence/ https://quoteinvestigator.com/2019/09/17/absence/
- marcosdumay 2y ago
  That's only true if you don't look.

One way to think of non-detection is as evidence that we're looking in the wrong place. Another way to think of non-detection is as evidence that it doesn't exist.

mr_mitm 2y ago

> One way to think of non-detection is as evidence that we're looking in the wrong place We aren't looking in only one place > Another way to think of non-detection is as evidence that it doesn't exist. Absence of evidence is not evidence of absence. Exhausting the parameter space until evidence is found is simply the normal scientific progress.

zmgsabst 2y ago
How many places do I need to look before I start to have evidence my lost wallet isn’t in my house? The normal spot on the shelf? …checking my pockets? …searching the bags I used to go shopping? At each step, another of my theories about where my wallet is gets disproven — but none are direct evidence it’s not in my house. We are playing the same game with dark matter: they keep checking spots and it keeps not being there. At what point does checking wrong theories start to suggest that the entire idea is flawed?
- mr_mitm 2y ago
  When you exhausted the parameter space (assuming you can with our current technical abilities) or a competing idea with actual evidence comes along. It's not like people aren't trying.
  - zmgsabst 2y ago
    That’s not the statistical definition of “evidence” — which is an occurrence that makes something more (or less) likely. I’d argue that each failure in a strictly statistical sense makes it more likely the whole conception is flawed — if only a little. So every failure is statistical evidence that dark matter theories are wrong. Just like each place I look for my wallet and don’t find it makes it slightly more likely that it’s not in my house.
- elashri 2y ago
  The parameter space is usually (not only) a two dimensional plot of mass and the coupling force parameter. Those can give you a space that you would want to explore. There will be no one experiment that would give you sensitivity in all the parameter space. So you design experiments and collect data. If you don't find in the region your experiment were sensitive too (and you did your analysis carefully) then you establish a limit that says basically it cannot be in this region, look in other regions, then repeat. The analogy with your wallet is misleading because we know your habits, we don't know about nature habits. As I explained, when we exhaust the parameter space regions and can't find anything then this would tell us to give a shot to something else. Not that people are not doing this now already anyways.
drdeca 2y ago
Remember the principle of conservation of expected probability. P[X] = P[X|Y] * P[Y] + P[X|!Y] * P[!Y] . If P[X|Y] > P[X] and P[Y] is strictly between 0 and 1, then P[X|!Y] < P[X] . So, if X is “dark matter is some kind of matter that can be detected directly” and Y is “Dark matter is/would-be detected directly by this experiment (when/if the experiment is/would-be done)” then, if we do the experiment and it does not directly detect dark matter, then, if we previously assigned some positive probability that it would, our probability that we can detect it in some way, should go down (though not necessarily by a non-negligible amount).
- deleted 2y ago
  [deleted]

nkrisc 2y ago

Except you don’t know which it is until you’ve exhausted the search space.

elashri 2y ago

"Absence of evidence is not evidence of absence" William Wright [1] [1] https://quoteinvestigator.com/2019/09/17/absence/ https://quoteinvestigator.com/2019/09/17/absence/

marcosdumay 2y ago
That's only true if you don't look.