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Dark Matter : supposedly makes up a big amount of the mass of the universe, but cant be seen, does not emit, absorb, or reflect light. Also it can 'pass throug

Dark Matter : supposedly makes up a big amount of the mass of the universe, but cant be seen, does not emit, absorb, or reflect light. Also it can 'pass through' other normal matter, and other dark matter. It's basically magic aka not actually real, just something in vogue to pretend is real at the present moment.

njarboe 5mo ago
Dark Unknown Matter would be a better name for lay people to understand what's going on. I'm no cosmologist but isn't it just a placeholder for something that gravity interacts with (and not much else) and we don't know what it currently is. When we discover what it is the name will change.
_ZeD_ 5mo ago
Or, you know, as aether. It's a scientific theory. It's the best that we have right now to model the real world and be able to do prediction on its behavior. Does it seems to be kept together by duct tape? Maybe. Is it yet useful? Yep. Will it be discarded if anything more fitting will came up? You can be sure of it.
- Joker_vD 5mo ago
  Yeah, pretty much, which is why this adherence to dark matter seems even more puzzling: we already had a mysterious substance with nonsensical mechanical properties (perfectly solid, but has zero collision) that turned out to be completely superfluous; the actual answer was the different shape of the physical laws. Now we again have a mysterious substance with nonsensical properties (has gravitational pull, doesn't interact with normal matter in any other way) — could it be that it simply doesn't exist? And it's not like the concept of aether itself was really all that useful for anything. The physicists wanted the light to have some mechanical medium to propagate through instead of being a thing of itself, that actual itself shaped mechanical media, not the other way around (mechanical properties arise from the E-M interaction, not the other way around), simply because all other known waves phenomena existed in mechanical media.
  - strogonoff 5mo ago
    Of course, it could be that dark matter does not exist. In a very real way, nothing in physics “exists” because like all natural sciences physics does not make statements of objective truth, it makes testable predictions. Dark matter, string theory, aether, etc., those are models that we, at some point in time, think may help us get better predictions and design further experiments. All models turn out to be wrong in the end, but they can be helpful until we come up with better ones. If you drop the dark matter model, then you would want to have some other model as for why we observe what we observe. Some people find that other available models are even worse than the dark matter one, but if you don’t think so you can take your pick.
  - tsimionescu 5mo ago
    Except that there is nothing nonsensical about a particle that has mass and doesn't participate in any SM interaction. It's inconvenient if such a particle exists, as it's very very hard to detect things precisely by their gravitational effects, but there is nothing nonsensical, or even particularly weird, about the idea. Plenty of particles only interact with a few of the SM forces - e.g. photons are not affected by the strong force, nor are electrons, neutrinos are affected by neither the strong force nor EM, only the weak force, gluons only interact with the strong force, not EM nor the weak force, etc
pixl97 5mo ago
I mean it's easy to say it's fake, but to counter this, why can a particle that only interacts with gravity not exist? The neutrino is a good example of a particle that almost doesn't exist. They are produced in solar reactions in spectacular amounts. Trillions of them are flitting through you right now as if you don't exist. You'd need a light year block of lead to ensure you could stop one. Mind-boggling amounts of them have to pass through our detectors to see even a single interaction. Simply put, the particle physics does not have to behave nice so you can sleep well at night.
- dnautics 5mo ago
  I mean sure nature has no obligation to not have a unfalsifable particle, but you wind up in weird places, like, there exists a distribution of dark matter that explains the poltergeist that knocked over your coffee cup last week.
  - davrosthedalek 5mo ago
    If there would be a distribution of dark matter that explains the poltergeist, we could measure that distribution of dark matter. We can measure the mass distribution on astronomical scales. We "see" the dark matter. Just not with light.
    - ShinyLeftPad 5mo ago
      We don't measure dark matter, we measure some anomaly and then we say "it must've been dark matter". It's not crazy different from saying the same about that poltergeist.
      - davrosthedalek 5mo ago
        We measure the matter distribution by its affect on light (strong/weak lensing). We also measure the matter distribution by the amount of light coming from it. The results are not the same. The simplest explanation is that there is matter which does not produce or reflect light via e/m, i.e. it is dark. Dark Matter. We know of particles which behave the same way. Neutrinos for example.
davrosthedalek 5mo ago
The "pass through matter" is a consequence of not interacting electromagnetically. That's not that uncommon. Think neutrinos. (Also, "not" might just mean "very much reduced")
- glitchc 5mo ago
  It's one thing to be electromagnetically inert, but if it is matter, it has mass, and if it has mass then it must be possible to collide with it. That we can't suggests it does not exist.
  - davrosthedalek 5mo ago
    Yes, and dark matter will interact with visible matter gravitationally. When we say "doesn't collide with normal matter", it is not exact. It just means "the interaction length is very very long". Same for neutrinos. Their interaction length is huge as well: 1 TeV Neutrinos have an interaction length of 2.5 million kilometers.
thiht 5mo ago
> cant be seen, does not emit, absorb, or reflect light. Also it can 'pass through' other normal matter, and other dark matter Why do you say that like it's obviously ridicule or impossible? Neutrinos do exist and they fit all these criteria. We just know they're not dark matter (or at least not all of it) because they're not heavy enough (and some other things). Don't try to rely on intuition when thinking about particles, there's no reason for evolution to make what happens at quantum scale or relativistic scale intuitive to us.
rcxdude 5mo ago
Dark matter doesn't necessarily have to be a new kind of particle (though there are enough constraints it's a bit hard to explain otherwise): it could be cold dust, gas, diffuse and tiny black holes, or large amounts of cold rocky planets.

njarboe 5mo ago

Dark Unknown Matter would be a better name for lay people to understand what's going on. I'm no cosmologist but isn't it just a placeholder for something that gravity interacts with (and not much else) and we don't know what it currently is. When we discover what it is the name will change.

_ZeD_ 5mo ago

Or, you know, as aether. It's a scientific theory. It's the best that we have right now to model the real world and be able to do prediction on its behavior. Does it seems to be kept together by duct tape? Maybe. Is it yet useful? Yep. Will it be discarded if anything more fitting will came up? You can be sure of it.

Joker_vD 5mo ago
Yeah, pretty much, which is why this adherence to dark matter seems even more puzzling: we already had a mysterious substance with nonsensical mechanical properties (perfectly solid, but has zero collision) that turned out to be completely superfluous; the actual answer was the different shape of the physical laws. Now we again have a mysterious substance with nonsensical properties (has gravitational pull, doesn't interact with normal matter in any other way) — could it be that it simply doesn't exist? And it's not like the concept of aether itself was really all that useful for anything. The physicists wanted the light to have some mechanical medium to propagate through instead of being a thing of itself, that actual itself shaped mechanical media, not the other way around (mechanical properties arise from the E-M interaction, not the other way around), simply because all other known waves phenomena existed in mechanical media.
- strogonoff 5mo ago
  Of course, it could be that dark matter does not exist. In a very real way, nothing in physics “exists” because like all natural sciences physics does not make statements of objective truth, it makes testable predictions. Dark matter, string theory, aether, etc., those are models that we, at some point in time, think may help us get better predictions and design further experiments. All models turn out to be wrong in the end, but they can be helpful until we come up with better ones. If you drop the dark matter model, then you would want to have some other model as for why we observe what we observe. Some people find that other available models are even worse than the dark matter one, but if you don’t think so you can take your pick.
- tsimionescu 5mo ago
  Except that there is nothing nonsensical about a particle that has mass and doesn't participate in any SM interaction. It's inconvenient if such a particle exists, as it's very very hard to detect things precisely by their gravitational effects, but there is nothing nonsensical, or even particularly weird, about the idea. Plenty of particles only interact with a few of the SM forces - e.g. photons are not affected by the strong force, nor are electrons, neutrinos are affected by neither the strong force nor EM, only the weak force, gluons only interact with the strong force, not EM nor the weak force, etc

pixl97 5mo ago

I mean it's easy to say it's fake, but to counter this, why can a particle that only interacts with gravity not exist? The neutrino is a good example of a particle that almost doesn't exist. They are produced in solar reactions in spectacular amounts. Trillions of them are flitting through you right now as if you don't exist. You'd need a light year block of lead to ensure you could stop one. Mind-boggling amounts of them have to pass through our detectors to see even a single interaction. Simply put, the particle physics does not have to behave nice so you can sleep well at night.

dnautics 5mo ago
I mean sure nature has no obligation to not have a unfalsifable particle, but you wind up in weird places, like, there exists a distribution of dark matter that explains the poltergeist that knocked over your coffee cup last week.
- davrosthedalek 5mo ago
  If there would be a distribution of dark matter that explains the poltergeist, we could measure that distribution of dark matter. We can measure the mass distribution on astronomical scales. We "see" the dark matter. Just not with light.
  - ShinyLeftPad 5mo ago
    We don't measure dark matter, we measure some anomaly and then we say "it must've been dark matter". It's not crazy different from saying the same about that poltergeist.
    - davrosthedalek 5mo ago
      We measure the matter distribution by its affect on light (strong/weak lensing). We also measure the matter distribution by the amount of light coming from it. The results are not the same. The simplest explanation is that there is matter which does not produce or reflect light via e/m, i.e. it is dark. Dark Matter. We know of particles which behave the same way. Neutrinos for example.

davrosthedalek 5mo ago

The "pass through matter" is a consequence of not interacting electromagnetically. That's not that uncommon. Think neutrinos. (Also, "not" might just mean "very much reduced")

glitchc 5mo ago
It's one thing to be electromagnetically inert, but if it is matter, it has mass, and if it has mass then it must be possible to collide with it. That we can't suggests it does not exist.
- davrosthedalek 5mo ago
  Yes, and dark matter will interact with visible matter gravitationally. When we say "doesn't collide with normal matter", it is not exact. It just means "the interaction length is very very long". Same for neutrinos. Their interaction length is huge as well: 1 TeV Neutrinos have an interaction length of 2.5 million kilometers.

thiht 5mo ago

> cant be seen, does not emit, absorb, or reflect light. Also it can 'pass through' other normal matter, and other dark matter Why do you say that like it's obviously ridicule or impossible? Neutrinos do exist and they fit all these criteria. We just know they're not dark matter (or at least not all of it) because they're not heavy enough (and some other things). Don't try to rely on intuition when thinking about particles, there's no reason for evolution to make what happens at quantum scale or relativistic scale intuitive to us.

rcxdude 5mo ago

Dark matter doesn't necessarily have to be a new kind of particle (though there are enough constraints it's a bit hard to explain otherwise): it could be cold dust, gas, diffuse and tiny black holes, or large amounts of cold rocky planets.