EDIT: Let’s cool it with the downvotes, dudes. We’re not out to cut funding to your black hole detection chamber or revoke the degrees of chiropractors just because a couple of us don’t believe in it, okay? Chill out, participate with the prompt and continue with having a nice day. I’m sure almost everybody has something to add.
We observe patterns of behavior – orbits, movement, gravitational lensing – that are exactly what we would see if, for example, there were great clouds of matter or other galaxies in those places. But we don’t see the hydrogen gas. We see non-uniform distributions of dark matter mass that imply there is not simply some consistent calculation error, but rather that there is dark matter that is not uniformly distributed. Again, read up on the Bullet Cluster because it shows a VERY clear example of what I am talking about, where the regular, electromagnetically-interacting matter behaves one way but the apparent shadow of dark matter behaves in a different way that is consistent with lack of electromagnetic interactions.
We’ve also discovered things like ultradiffiuse galaxies – likely remnants from ancient collisions – that have apparently been stripped of their dark matter. MOND cannot explain these observations because these galaxies essentially behave in a Newtonian manner that would be impossible in a MOND framework.
Why does stuff clump together? For all non-dark matter, the answer is electromagnetism. Outside of the extreme cases of neutron stars and black holes, where gravity overwhelms and defeats electromagnetism and the nuclear forces theoretically take over to create degeneracy pressure, electromagnetism is the reason things clump. Absent electromagnetism, what would cause clumping? Essentially nothing, stuff would whizz straight through other stuff and go into orbits. Potentially HUGE orbits, which is why there’s so many theories around dark matter “halos”. Maybe if there were DIRECT collisions of theoretical DM particles, that might cause an energy-releasing event – this is one of the things current dark matter detectors are looking for and may yet find within the upcoming years.
Yep, and more than a handful Many that make specific predictions we can test for and so are testing for. For example, you could look at axions, which are a theoretical particle predicted by an entirely different theory that may be a good fit for the dark matter particle.
Which would still not rule out anything else…
That non-uniformity though, yes, this is a good point for a “dark matter exists” hypothesis. Although I would still word it differently: Not “We see non-uniform distributions of dark matter mass” but “We see a non-uniform mass-like effect”. I’ve learned that keeping the terms as neutral as possible, or it might exert too much pressure on the thought process to go in just one direction.
Which is basically an extreme case on “not uniformly distributed”.
That is acceptable. I was not “selling” MOND here (or any other theory), btw, I’m just wondering what kind of possibilities are there to explain all those observations. “An invisible mass nobody has observed except for it’s gravity effect” sounded a bit thin of a leg to stand on there, while incomplete models are a rather widespread phenomenon.
Gravity? I mean, we are talking about something that has gravity. Did planets form because of electromagnetism?
Indeed. Try that with the wannabe-sciences like economics…
Well, at least they share the common trait of not being found yet… ;-)
For myriad reasons, the answer to this is an emphatic yes.
Gravity may attract particles towards each other, but the force that actually causes them to interact with each other is almost entirely electromagnetism. The collisions of grains of cosmic dust are caused by electromagnetic fields interacting with each other. As is the gradual loss of kinetic energy – the friction – that allows some amount of potential energy to get converted to heat, allowing the particles to slow down and, as you described it, clump.
Absent electromagnetism, the actual particle nuclei would need to directly hit each other to cause an interaction via the nuclear forces, which is VERY improbable in the vastness of space. Improbable doesn’t mean it wouldn’t happen, but in this case it does mean the universe is way too big and young. Without electromagnetic interactions, particles just form orbits. Which again, that’s what a “dark matter halo” is. It’s all the dark matter stuff orbitting around a galaxy’s center of mass because it doesn’t get easily trapped in the center. It’s all the dark matter in a gravitational system constantly whizzing back and forth across the center of mass since there’s no electromagnetic force to rob them of the potential or kinetic energy and stop them from heading back out.
And, conveniently, these halos are just what our observations seem to indicate dark matter is doing in a typical galaxy. The observations and theory align well
OK, I can accept that. Good luck hunting down whatever this dark matter is made of, then.
See, I think this is where you’re getting tripped up. You’ve got a strong instinctive bias against models that include new particles, and you probably need to examine why. New particles are no more of an update to an incomplete model then any other firm update, and is common in proposals for new science. We already know of atleast one extremely abundant, near undetected particle in the form of the neutrino, and one of the leading candidates for dark matter, the axion, comes from an unrelated model.
I don’t have a bias against new particles. For me as a non astrophysicist, just another theory having a big hole was simply more likely. And the theory of gravity breaks anyway when it approaches quantum theory, why shouldn’t it be broken elsewhere, too?
But I can easily accept the information given here, primarily the case with uneven distribution, which is a good case for something being there. Now you just have to nail the particle down.
Why? If you don’t have a bias against new particles. Why is a hole in one theory more likely than a hole in another?
Why should it?
Indeed, people think dark matter is motivated by observations disagreeing with theory in one consistent way, but it’s actually a case of observation showing a large distribution of invisible mass.
It’s tricky to do, as dark matter is non-interacting by nature. It will likely be a case of process of elimination.