We can't directly see it, but we can see the gravitational lensing it causes. Dark matter isn't as invisible as believed.
Then there are cases of galaxies which don't contain any dark matter, and therefore act the way we were expecting them to from simple gravitational mechanics on visible matter. That rules out any solution involving changes to the laws of gravity, since such a change would be universal. The fact that galaxies can exist which contain none means it must be a substance of some kind which can exist more in one spot than another.
Dark matter doesn't interact with anything else (or even itself) so they pass right through each other.
Edit: well there are galaxies without dark matter (maybe) [1] and there are dark matter galaxies [2]
[1] https://www.space.com/19-galaxies-missing-dark-matter.html
[2] https://www.space.com/33850-weird-galaxy-is-mostly-dark-matt...
Most of the mass of galaxies isn't in their stars (which, for the most part, keep moving with the dark matter) it's in gas clouds and dust formations. When two galaxies collide, the gas and dust effectively halts.
What we see when galaxies collide is that most of the mass of the galaxies move straight through each other without appreciably decelerating. And most of the matter, the gas clouds and star forming regions, halt in the middle.
MOND was taken seriously as a theory from its inception in the '70s through the end of the 20th century, but because of the bullet cluster, it is effectively dead. MOND is falsified by observational evidence.
For this article to discuss MOND so thoroughly, but not mention the bullet cluster once... It doesn't pass the smell test. This is pseudo-scientific trash.
There's other evidence against MOND and various alternative-gravity models (there are several of them, it's a large umbrella) but most of them do a very poor job at explaining the edge cases, such as the bullet cluster and ultra diffuse galaxies. Some ultra diffuse galaxies have a conspicuous absence of gravitational lensing and stars which orbit extraordinarily slowly; ie, they have very little dark matter. If the explanation for dark matter was that we had the laws of physics wrong, the newly revised gravitational theories should apply equally well to these galaxies- which they don't.
The argument the article makes is that just because emergent gravity or many alternative candidates potentially cannot explain all of evidence that dark matter can , does not mean it should be thrown out completely and rejected, it could be still funded and studied to see if it can explain some of it.
The real issue is given the way modern academic funding works we have been tending more and more towards narrower research with main line theories and lesser riskier proposals perhaps being incentivised. This is not just limited not dark matter , this phenomenon is evident in string theory research and many other fields as well.
This is the equivalent of someone reading some nasty things about C and claiming we need to investigate python for kernel development.
cosmology was convinced that the universe is homogeneous and isotropic (the universe is about the same everywhere). they we learn that the rotation of galaxies is not random...
the universe is flat, and then its not.
the expansion of the universe is the same everywhere... and then it might not be...
we had one way of measuring the age of the universe with method a, and another with method b, and they use to have overlap. and now they dont... https://youtu.be/cnn_5YMpo3Q?t=876
Honestly, if we agreed that we know 10% of what the heck is going on out there, that is probably being way too optimistic. so to blindly parroting "that's pseudoscience' to cast doubt on something that hasn't been observed in 60 years despite supposed to be representing the majority of the universe... that feels like religion, not science
What specific circular assumptions are you suggesting?
And the theories themselves can't be proven as true, since this isn't math but empirical science, but we can get an idea about how well they predict natural phenomena and we can disprove them by empirical evidence, observations that show these theories don't predict the universe well.
Scientific theories are a dime a dozen and in the presence of empirical evidence that falsifies them, we should consider such theories as falsified and move on.
When people continue believing in theories that are non-falsifiable or that have been falsified, that's pseudo-science.
> And the theories themselves can't be proven as true, since this isn't math but empirical science
This distinction is meaningful and extends to logic, metaphysics, etc.
> When people continue believing in theories that are non-falsifiable or that have been falsified, that's pseudo-science.
Popper distinguished between rationally justified claims and "scientific", i.e., empirically testable claims. He only claimed that falsifiability was a feature of empirically testable claims. That he should do so should be obvious because the claim that all claims must be empirically falsifiable is not itself empirically falsifiable and large swathes of human knowledge lay beyond the empirically testable, hence the restriction. That they are not empirically falsifiable does not make them pseudoscience. Indeed, the viability of empirical science hinges utterly on unfalsifiable assumptions.
> Scientific theories are a dime a dozen and in the presence of empirical evidence that falsifies them, we should consider such theories as falsified and move on.
Not so fast. Even within the domain of the empirical sciences, falsification is not simply a matter of performing a tidy critical experiment. As Duhem (and Quine) observed, the theory under scrutiny hinges on many other hypotheses, theories and assumptions. Even something as simple as observing something under a microscope hinges on the soundness of optics as well as many other assumptions that are not falsifiable.
There is most certainly an economy, a parsimony, an order to how science and common sense proceed when met with conflicting evidence. We tend to doubt the the outer layer of the epistemic onion where there is less certainty before asking questions about our assumptions.
And of course, science occurs in a social context such that it is subject to practical and cultural forces that influence what is given priority. In any case, the point is that falsification is not simply a matter of demonstrating that an expected outcome does not occur.
> but we can get an idea about how well they predict natural phenomena and we can disprove them by empirical evidence, observations that show these theories don't predict the universe well.
Predictability is only part of the story. If we reduce science to predictability, then we're back to a purely instrumental view of science. But as Hillary Putnam notes, science aspires to describe reality as it is. It does not merely want to produce a model that "works" which is to say one that allows physical phenomena to be predicated. In any case, that predictability should be a feature of empirically testable claims is not falsifiable, and predictability itself presumes that the universe is a certain way that affords predictability which is, again, not falsifiable.
But -correct me if wrong - today there is one known kind of fusion that -cause-(crossed out) leaves us with "Anti-Materie" as reaction (remembering the 1st art law, saying 'Energy is a Sum') ? (-;
Can you elaborate with more details (my "reading comprehension" is such that I enjoy/comprehend academic papers more than watered down (and sometimes wrong) "pop-science" simplifications) about the counter-evidence against MOND?
You've given me some great topics to google search for, and it's much appreciated! (somehow I missed hearing about the bullet cluster. reading about it now... including the rebuttal: https://web.archive.org/web/20160721044735/http://www.astro....)
Can you perhaps drop a few more links to things I can dig into that provide counter evidence for MOND? MOND has been sort of a ... romantic crush ... of mine since I first learned of it 20 years ago. :)
The dark matter doesn't stop; it keeps going.
> Don't colliding galaxies stop due to gravity
Not really. As others have noted, they stop due to non-gravitational interactions between the ordinary matter (mainly gas and dust clouds).
You mean zero at ALL, or with little measurable effects?
We can see that some galaxies rotate as if they had no dark matter, but we don’t know why their dark matter isn’t there.The prevalent, but still speculative, hypothesis is that it was “stolen” by a bigger galaxy in a close pass-by.
>So does dark matter interact with itself outside of gravity? There are different ideas about what dark matter could be. Some have it interacting through other forces (WIMPs interacted through the weak force, for example), some are purely gravitational. There's always talk of 'dark matter candidates', theoretical or otherwise particles that could plausibly be dark matter.
- velocities in galaxy clusters
- getting the fine details of the complicated, wiggly cosmic microwave background spectrum right to extreme precision
- getting the fine details of cosmological structure formation (as measured from matter density fluctuations on very large scales) right
- galaxy collisions, like the Bullet cluster (hard to explain with modified gravity)
- the fact that some galaxies have much less dark matter than others (very hard to explain with modified gravity)