22 ms·

What's surprising about that if I may ask? We have observations that match quite well what would be expected if there was additional matter in the universe. We

What's surprising about that if I may ask? We have observations that match quite well what would be expected if there was additional matter in the universe. We cannot detect this matter though, so the conjecture is that there must be something that interacts gravitationally with the rest of the universe but not in other ways. We call it dark matter for now. We do not yet know what it consists of, there are even competing theories but mapping the effects of it? That we can do. This approach is not at all unusual. If you want to know about another example from a different field, look no further than genetics. Gregor Mendel observed rules for inheritance of certain traits in plants and was able to make predictions from that. He discovered genetics. In the 1850-60ies. This was a long time before Crick, Watson and Franklin discovered the structure of the underlying mechanism for inheritance (DNA).

galaxyLogic 5y ago
What if Dark Matter is just that? Dark matter. If there were lots and lots of something like planets out there, which for one reason or another don't reflect light, that would be something dark right? Or what if Dark Matter was lots of Black Holes? We (more or less) know what Black Holes are so why don't we assume there could be lots of them having a gravitational effect but no visibility? In other words why do we need to assume that Dark Matter is made of some kind of exotic unknown matter?
- _Microft 5y ago
  That’s indeed a possible explanation. See also: https://en.m.wikipedia.org/wiki/Massive_compact_halo_object https://en.m.wikipedia.org/wiki/Massive_compact_halo_object
- kl4m 5y ago
  Here's an expanded explanation of the "lots of black holes" hypothesis, posted this week by PBS Space Time. "What If (Tiny) Black Holes Are Everywhere?" https://www.youtube.com/watch?v=srVKjWn26AQ https://www.youtube.com/watch?v=srVKjWn26AQ Dark Matter is just a placeholder name, don't read too much into the "Matter" part. There are no assumptions there and plenty of alternate explanations are proposed, like Modified Gravity (MOND)
- javier2 5y ago
  They have actually looked for black holes of many sizes and have ruled out most of the range. It might still be possible, though improbable because they looked very hard for black holes.
- magicalhippo 5y ago
  > Or what if Dark Matter was lots of Black Holes? Black holes are indeed[1] a dark matter contender! Just because the best explanation[2] we have right now is cold dark matter (CDM), doesn't mean physicists are content. They're looking for new ways[3] to probe not just CDM but other dark matter models as well, like primordial black holes[4]. Dark matter is by no means a settled topic. [1]: https://en.wikipedia.org/wiki/Primordial_black_hole https://en.wikipedia.org/wiki/Primordial_black_hole [2]: http://pirsa.org/20040087/ http://pirsa.org/20040087/ "Dark Matter: A Cosmological Perspective", nice colloquium talk giving overview of what we know about dark matter. [3]: http://pirsa.org/20100052/ http://pirsa.org/20100052/ "Strong gravitational lensing as a cosmological probe: new ways of constraining dark", random technical talk about new way of probing CDM. [4]: https://arxiv.org/abs/2002.12778 https://arxiv.org/abs/2002.12778 "Constraints on Primordial Black Holes".

galaxyLogic 5y ago

What if Dark Matter is just that? Dark matter. If there were lots and lots of something like planets out there, which for one reason or another don't reflect light, that would be something dark right? Or what if Dark Matter was lots of Black Holes? We (more or less) know what Black Holes are so why don't we assume there could be lots of them having a gravitational effect but no visibility? In other words why do we need to assume that Dark Matter is made of some kind of exotic unknown matter?

_Microft 5y ago
That’s indeed a possible explanation. See also: https://en.m.wikipedia.org/wiki/Massive_compact_halo_object https://en.m.wikipedia.org/wiki/Massive_compact_halo_object
kl4m 5y ago
Here's an expanded explanation of the "lots of black holes" hypothesis, posted this week by PBS Space Time. "What If (Tiny) Black Holes Are Everywhere?" https://www.youtube.com/watch?v=srVKjWn26AQ https://www.youtube.com/watch?v=srVKjWn26AQ Dark Matter is just a placeholder name, don't read too much into the "Matter" part. There are no assumptions there and plenty of alternate explanations are proposed, like Modified Gravity (MOND)
javier2 5y ago
They have actually looked for black holes of many sizes and have ruled out most of the range. It might still be possible, though improbable because they looked very hard for black holes.
magicalhippo 5y ago
> Or what if Dark Matter was lots of Black Holes? Black holes are indeed[1] a dark matter contender! Just because the best explanation[2] we have right now is cold dark matter (CDM), doesn't mean physicists are content. They're looking for new ways[3] to probe not just CDM but other dark matter models as well, like primordial black holes[4]. Dark matter is by no means a settled topic. [1]: https://en.wikipedia.org/wiki/Primordial_black_hole https://en.wikipedia.org/wiki/Primordial_black_hole [2]: http://pirsa.org/20040087/ http://pirsa.org/20040087/ "Dark Matter: A Cosmological Perspective", nice colloquium talk giving overview of what we know about dark matter. [3]: http://pirsa.org/20100052/ http://pirsa.org/20100052/ "Strong gravitational lensing as a cosmological probe: new ways of constraining dark", random technical talk about new way of probing CDM. [4]: https://arxiv.org/abs/2002.12778 https://arxiv.org/abs/2002.12778 "Constraints on Primordial Black Holes".