4 ms·

But there’s been no detection of dark matter whatsoever, ever. The fact that people cling to this theory is strange because the most basic evidence, ie. viewing

But there’s been no detection of dark matter whatsoever, ever. The fact that people cling to this theory is strange because the most basic evidence, ie. viewing it, doesn’t exist.

mr_mitm 3y ago
You also cannot "view" neutrinos, yet no one doubts their existence. By the way, they too have been postulated because collision experiments were showing some missing kinetic energy and momentum. People said "maybe there is a new particle that does not interact electromagnetically carrying away the energy", and they turned out to be correct. It's a very fruitful way of thinking. Your perceived strangeness goes away as soon as you understand all the evidence, in particular BAO and lensing, as mentioned above.
- perihelions 3y ago
  Well, we do have the ability to detect individual neutrinos, through their interactions with ordinary matter. That's not currently the case for dark matter: it's sort of in the place neutrinos were in between 1930 (when neutrinos were postulated (as you describe) to explain missing momentum) and 1956 (when they were first observed [0] in nuclear fission reactors). https://en.wikipedia.org/wiki/Cowan–Reines_neutrino_experiment https://en.wikipedia.org/wiki/Cowan–Reines_neutrino_experime... /tangent I learned a fun fact! The original proposal for the neutrino experiment wanted to detonate a nuclear bomb. The reactor was a last-minute change. - "Eminent physicists enthused about the plan. It was approved by Reines’s employer, the government-funded Los Alamos laboratory in New Mexico. Work began on the detector, nicknamed El Monstro, and on the construction of the shaft. At the last minute, Reines and Cowan transferred the experiment to a nuclear reactor, but not because of environmental or safety concerns. They had worked out that although the reactor would deliver a flux of neutrinos three orders of magnitude lower than that from the bomb, it offered a better option for distinguishing signal from noise." https://www.physics.uci.edu/node/14126 https://www.physics.uci.edu/node/14126 ("The singing UCI Nobel Laureate who nearly bombed Nevada")
- adrian_b 3y ago
  That is not correct. While the probability that neutrinos will interact with other kinds of particles is very low, it is finite. Therefore we have neutrino detectors, even if they are very big and very expensive. So we can actually view neutrinos in the same way as we view anything else. We can imagine even building a video camera that would provide images of the spatial distribution of the neutrino flux, i.e. an image of the sky based on the incoming neutrino rays. Such a neutrino video camera would be made like a compound insect eye, in order to separate by angle the incoming neutrinos with shields. Unfortunately such a video camera for neutrinos would need to have a planetary size, because shields that could block a large fraction of the neutrinos coming from different directions than the one desired for reception would be humongous. For neutrino sources that are much more luminous (in neutrino flux) than their background, e.g. supernova explosions or the Sun, there is an alternative way to separate the neutrinos that come from a specified direction, besides shielding. One can use 2 neutrino detectors located at a great distance between them and count only the neutrino fluxes recorded in both detectors. Unfortunately the great distance needed for good angular resolution and the size of the individual neutrino detectors still make impossible the construction of a neutrino receiver that could be oriented in any direction, at will.
  - mr_mitm 3y ago
    It all depends on what you mean by "view". In my understanding it does not immediately follow that it must be "viewed" by making use of collision experiments. This picture in my opinion "views" dark matter just as much as you would "view" neutrinos: https://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/1e0657_scale.jpg/1200px-1e0657_scale.jpg https://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/1e... (the bullet cluster) Regardless, I find the discussion on the meaning of ill-defined laymen language tiring while we probably agree on the actual facts.
    - adrian_b 3y ago
      No, the current status of neutrinos and of dark matter are not at all comparable. Like another poster has already written, the status of dark matter is like that of the neutrinos when their existence had been postulated, but before means to detect them by alternative methods have been devised. In the beginning, the existence of neutrinos has been presumed because in certain reactions the conservation of the energy and of the linear momentum and of the angular momentum was not observed. So every time when there were missing energies and momenta, it was assumed that they had been carried away by neutrinos. In the same way, nowadays whenever there is an extra gravitational force, it is assumed that there exists some dark matter that is the source of the extra force. Until another means of determining the existence of dark matter is discovered, this does not constrain enough the properties of the dark matter. For any mathematical model of the gravitational forces, when we see that it does not match reality we can add a fictitious distribution of dark matter computed to match the observations. In fact, for the postulated neutrinos even before their first detection we had much more knowledge about them, because they had to satisfy many distinct conservation laws, so we knew that they must be fermions with null electric charge and h_bar/2 spin and that their mass must be much smaller than the mass of the electron. On the other hand, we are really in the dark about dark matter. We know nothing about any properties of any constituents of dark matter.
tuyiown 3y ago
> But there’s been no detection of dark matter whatsoever, ever. Well, dark matter got its name because we couldn't find direct observation. It's just a nickname for «unexplained gravitational effect from invisible source», the closest explanation we have is non-radiating matter. Next physics might explain this without any additional matter, but for now, that's all we have.

But there’s been no detection of dark matter whatsoever, ever. The fact that people cling to this theory is strange because the most basic evidence, ie. viewing it, doesn’t exist.

mr_mitm 3y ago

You also cannot "view" neutrinos, yet no one doubts their existence. By the way, they too have been postulated because collision experiments were showing some missing kinetic energy and momentum. People said "maybe there is a new particle that does not interact electromagnetically carrying away the energy", and they turned out to be correct. It's a very fruitful way of thinking. Your perceived strangeness goes away as soon as you understand all the evidence, in particular BAO and lensing, as mentioned above.

perihelions 3y ago
Well, we do have the ability to detect individual neutrinos, through their interactions with ordinary matter. That's not currently the case for dark matter: it's sort of in the place neutrinos were in between 1930 (when neutrinos were postulated (as you describe) to explain missing momentum) and 1956 (when they were first observed [0] in nuclear fission reactors). https://en.wikipedia.org/wiki/Cowan–Reines_neutrino_experiment https://en.wikipedia.org/wiki/Cowan–Reines_neutrino_experime... /tangent I learned a fun fact! The original proposal for the neutrino experiment wanted to detonate a nuclear bomb. The reactor was a last-minute change. - "Eminent physicists enthused about the plan. It was approved by Reines’s employer, the government-funded Los Alamos laboratory in New Mexico. Work began on the detector, nicknamed El Monstro, and on the construction of the shaft. At the last minute, Reines and Cowan transferred the experiment to a nuclear reactor, but not because of environmental or safety concerns. They had worked out that although the reactor would deliver a flux of neutrinos three orders of magnitude lower than that from the bomb, it offered a better option for distinguishing signal from noise." https://www.physics.uci.edu/node/14126 https://www.physics.uci.edu/node/14126 ("The singing UCI Nobel Laureate who nearly bombed Nevada")
adrian_b 3y ago
That is not correct. While the probability that neutrinos will interact with other kinds of particles is very low, it is finite. Therefore we have neutrino detectors, even if they are very big and very expensive. So we can actually view neutrinos in the same way as we view anything else. We can imagine even building a video camera that would provide images of the spatial distribution of the neutrino flux, i.e. an image of the sky based on the incoming neutrino rays. Such a neutrino video camera would be made like a compound insect eye, in order to separate by angle the incoming neutrinos with shields. Unfortunately such a video camera for neutrinos would need to have a planetary size, because shields that could block a large fraction of the neutrinos coming from different directions than the one desired for reception would be humongous. For neutrino sources that are much more luminous (in neutrino flux) than their background, e.g. supernova explosions or the Sun, there is an alternative way to separate the neutrinos that come from a specified direction, besides shielding. One can use 2 neutrino detectors located at a great distance between them and count only the neutrino fluxes recorded in both detectors. Unfortunately the great distance needed for good angular resolution and the size of the individual neutrino detectors still make impossible the construction of a neutrino receiver that could be oriented in any direction, at will.
- mr_mitm 3y ago
  It all depends on what you mean by "view". In my understanding it does not immediately follow that it must be "viewed" by making use of collision experiments. This picture in my opinion "views" dark matter just as much as you would "view" neutrinos: https://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/1e0657_scale.jpg/1200px-1e0657_scale.jpg https://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/1e... (the bullet cluster) Regardless, I find the discussion on the meaning of ill-defined laymen language tiring while we probably agree on the actual facts.
  - adrian_b 3y ago
    No, the current status of neutrinos and of dark matter are not at all comparable. Like another poster has already written, the status of dark matter is like that of the neutrinos when their existence had been postulated, but before means to detect them by alternative methods have been devised. In the beginning, the existence of neutrinos has been presumed because in certain reactions the conservation of the energy and of the linear momentum and of the angular momentum was not observed. So every time when there were missing energies and momenta, it was assumed that they had been carried away by neutrinos. In the same way, nowadays whenever there is an extra gravitational force, it is assumed that there exists some dark matter that is the source of the extra force. Until another means of determining the existence of dark matter is discovered, this does not constrain enough the properties of the dark matter. For any mathematical model of the gravitational forces, when we see that it does not match reality we can add a fictitious distribution of dark matter computed to match the observations. In fact, for the postulated neutrinos even before their first detection we had much more knowledge about them, because they had to satisfy many distinct conservation laws, so we knew that they must be fermions with null electric charge and h_bar/2 spin and that their mass must be much smaller than the mass of the electron. On the other hand, we are really in the dark about dark matter. We know nothing about any properties of any constituents of dark matter.

tuyiown 3y ago

> But there’s been no detection of dark matter whatsoever, ever. Well, dark matter got its name because we couldn't find direct observation. It's just a nickname for «unexplained gravitational effect from invisible source», the closest explanation we have is non-radiating matter. Next physics might explain this without any additional matter, but for now, that's all we have.