But honestly: my money would have to go on this one. Black holes are by far the most boring and conventional of the existing theories, and the easiest to refute. aLIGO will tell us if it's right or not within years.
I was ready to start arguing, but then I realized you were speaking in the context of dark matter theories. :)
I feel there's gonna be a few interesting years or couple decades ahead. Maybe not as big as the early 1900s. Maybe as big. Maybe even bigger.
But it does seem to be a more or less realistic simulation of light ray distortion in the gravitational field of a black hole.
If you watch Interstellar, the imagery in the movie (the giant black hole, and even the wormhole the characters use to travel far away) is actually a physically-realistic simulation of the behavior of light in black-hole-like gravity fields. Kip Thorne, one of the top scientists in the field of general relativity, has collaborated with the movie makers to ensure the special effects were as close as possible to what science tells us right now about these objects.
When imaging outside of the visible spectrum, you have no choice. You must translate it into visible light, or else you could not see it. So, yes, there are many false-color images out there, and for a good reason - they show us the invisible part of the EM spectrum.
Of those taken with visible light, there are several categories.
Some of them are indeed false color. Examples: imaging the Sun with a narrow monochromatic filter such as hydrogen alpha, or some "magic" wavelengths like 540 nm. These should be displayed in their respective colors (red for hydrogen alpha, green for 540 nm, etc), but often arbitrary color choices are made, because the original image is monochromatic anyway, so it should not matter what color is displayed in as long as its nature is understood by the viewer.
And then there's a very broad slice of the pie where the colors are basically real, they're just not perceived that way by the human eye, or even by the camera - and yet they do represent the original spectral content of the incoming EM radiation.
For example, when observing a galaxy or a nebula, all the human eye can see is a black-and-white smudge. Even in a telescope, you almost never see color with your own eyes when looking at these objects. Why is that? Because we have two kinds of light receptors in our eyes, and the ones that actually see color do not work in low light conditions - we are all colorblind there.
But attach a camera to a telescope, have the instrument track the nebula for a long time, open the shutter and let the sensor collect photons for a while. Then look at the result. Suddenly, you see colors. Why is that? Because with long exposure, the camera can actually see colors. That's something that our eyes cannot do.
But are those images "enhanced" somehow in post-processing in ways that make those colors unnatural? It depends. For objects like the Orion nebula, or the Horsehead, the colors are strong enough to not need much post-processing. In other cases, you may have to apply fairly strong contrast and saturation boosts.
So there's a whole continuum of images taken in visible light, where the amount of post-processing varies from quite lightweight to pretty heavy. With some experience, you can tell which is which. I've taken images of the Moon in high resolution and I've left it alone in post - you can tell because the colors are drab, it looks like the surface of an asphalt road. I've also taken moonshots where I've applied very heavy saturation boosting - you can tell because you can start seeing colors in an otherwise gray landscape. This allows you to detect surface, terrain, and mineral features that would not be apparent otherwise, things like ejecta from impacts and so on.
And finally there are many, many images of planets such as Jupiter or Saturn, where the colors basically match the imagery taken by space probes hovering nearby, and would match what people would see with their own eyes if they were in actual orbit there.
TLDR: The real answer is "it depends". Some colors are totally fake. Some are real, but boosted. Some are real, it's just that the human eye could not see them due to our scotopic vision characteristics. And others are actually quite realistic in every way. It's a broad continuum. You learn to tell them apart by being involved in actually making them.
how about the event horizon then
Currently, there is a project underway (http://eventhorizontelescope.org/) coordinating the efforts of many different researchers with the goal of resolving the event horizon of a black hole. This project would only produce an image that most people would still call extremely blurry. But it would be the first legitimate image of the characteristic visual features of a black hole.
Even when Andromeda and the Milky way collide, almost nothing will hit each other, because there is no much empty space.
Stephen Hawking notes in his book "A Brief History of Time" that we know that there aren't infinite stars because otherwise the night sky would have no patches of darkness since an infinite number of stars would imply that you could shoot out an arbitrary ray from earth and it would always reach a star.
However, black holes (lots of them!) could trap light and obscure line-of-sight stars.
Black holes sans accretion disk clearly satisfy these criteria.
But if it turns out it's black holes, I'm guessing it would have physical interaction with other matter but still be hard to detect and not interact in the usual way we expect of normal matter.
All this is speculation though, and I don't really know what I'm talking about.
Could it be large transparent gas clouds? No, it turns out that gas clouds aren't completely transparent, and can be measured in various ways. We looked, we checked, such clouds don't contribute enough mass.
Could it be dust clouds? Dust clouds are not luminous but they do block visible light, so they'd be obvious. We looked, we checked. It wasn't dust clouds.
Could it be rogue planets or brown dwarfs? No, such objects would cause gravitational micro-lensing effects, which can be observed in dedicated campaigns. We looked, we checked. It wasn't planets or brown dwarfs.
The only theory that has withstood the last several decades of experimental observation and simulation has been the dark matter theory (weakly interacting massive particles at sub-relativistic speeds). It's the only thing that explains all the evidence across the board.
It seems most astronomy theoreticians will rather not rock the boat, they will rather keep believing in invisible stuff permeating space everywhere with variable but exactly right density so it is consistent with star motions and images observed. I guess it's because stuff with infinity of degrees of freedom is traditionally much more secure paradigm to base a career on than to question the established beliefs in applicability of Newtonian mechanics/General relativity.
> "The only theory that has withstood the last several decades of experimental observation and simulation"
Which competing theories were put to stand the test of observation? What made them not stand well in light of observations?
> "It's the only thing that explains all the evidence"
There is little example to such a thing as scientific theory explaining all the evidence. But even if dark matter paradigm did do such a feat, it would not be a good sign for the truthfulness of it. Theories that explain everything are suspicious - they may be exercises in fitting and may not be so scientific or useful as competing theories that explain less, but better.
As such there's no value in actually debating you on these points.
Please read my post again and if you can, address the points made there.
EDIT: those points, slightly expanded, are:
1) Could it be that Newtonian/Einsteinian models of motion in extremely distant, never visited places are extrapolations in error? If not, how do we know that, since we cannot experiment there, with massive objects on astronomical scales?
2) Is working in line of a popular paradigm much more preferable to most researchers than proposing a radical new theory that is inconsistent with it?
3) Searching for different model / theory is hard work but if it successfuly explains something and provides directions to continue, is preferable to fitting massive quanta of data to a model with infinity degrees of freedom (density of dark matter in space).
4) It is hard to find an example of scientific theory fitting all the evidence. Fitting all the evidence suggests we are doing a fitting exercise, not a scientific theory.
It's your job to not be wrong about knowable things. Read a summary of the literature if you are actually interested instead of just proposing that a well accepted theory is wrong because "theoreticians" are biased.
I was requesting the parent to point out which of my points and why they are wrong. I think reply of such kind would be far more useful to many people here sharing similar views to mine on the idea of dark matter or usefulness of academic work in this direction.
> 'Read a summary of the literature if you are actually interested'
I am actually interested in what people here, including you, think of my points; I was hoping for substantive replies to them. Your suggestion to 'read up and shut up' comes out as arrogant and uncalled for.
Or whoever programmed our reality couldn't build a consistent macro-physics engine so they hacked something together while hoping biological evolution wouldn't lead to anything that would notice it. Everything was going smoothly with the natural-selection add-on until the platypus and hominids showed up.
Dark matter seems to interact weekly even with itself, contrary to regular matter. So it really is completely different stuff, not just matter that's hidden from us.
There are four fundamental forces that govern the universe: gravity, electromagnetism, and strong and weak nuclear forces.
Dark matter interacts with gravity, but not electromagnetism. Electromagnetism is the force that we are acting upon when we touch things, or things bump into or collide with one another. Also, it's what makes light and magnetism.
So dark matter would never hit or bump into anything, but it can, say, orbit something.
Then recanted when we improved our knowledge of gravitation.
I have always been a bit skeptical about it being some elusive magical new particle or somesuch though.
we're pretty sure our theories are right
They didn't say "Well, the geocentric model is probably wrong but we'll use it for now" either.
I'm certainly not a physicist.
But instead, you could regard the observations as "experiments proving our theories wrong".
We already have weakly interacting particles like the neutrino, which don't interact with matter outside of the weak force, making them rather difficult to detect, it's not really that far out of the realm of possibility to have other particles that only interact via the gravitational force.
This is often mentioned as a reason not to spend time with alternative models. However, breaking stuff is sometimes necessary if we are to get out of the local maximum of theory usefulness. The Kopernik model was much worse fit for the observations of planet motion that the Ptolemy's model, but it did have other virtues, like simplicity. The broken parts got fixed later with development of mechanics and perturbation theory.
It does have some properties that we've managed to figure out, and they do look matter-ish.
Conjecting that the earth is round did not just explain why ships disappear behind the horizon. It also predicted that you can get back to point A by always moving away from it and many other phenomena.
And these not only are consistent with the existence of dark matter, but roughly indicate the same amount of it as a fraction of mass in the universe.
So I disagree strongly that the existence of dark matter hasn't led to other predictions. Indeed, the number of different phenomena that lead to it is one of those things that have made alternative theories so difficult. There are a ton of alternative gravitational theories that can explain one or two of the above phenomena, but trying to match them all (and not contradict other observations), seems to be somewhere between difficult and impossible.
The fact is that dark matter isn't just some half-baked theory that astrophysicists pulled out of their ass. Nor does it represent some lame attempt to just sweep complexity under the rug as if astronomers said "I dunno, probably magic", shrugged, and moved on.
Dark matter is a very specific and constrained theory that has withstood the test of decades of observational tests where all other theories have fallen by the wayside. Astrophysicists and cosmologists did not set out trying to force the theory of dark matter on the world, they have tried repeatedly to prove that other explanations could account for observational evidence, but none did. Instead they've had the reality of dark matter thrust upon them.
And it's not such a crazy theory either. We know that there are other kinds of weakly interacting massive particles such as neutrinos that exist in the Universe. And we know that our understanding of particle physics, the standard model, is incomplete. It is not a great leap to posit that potentially there are other types of weakly interacting massive particles that we have yet to discover. We know that neutrinos and "hot dark matter" does not make up the majority of the mass of dark matter in our Universe through several lines of observations. We know that baryonic (atomic) matter is also not dark matter as well. Only "cold" (sub-relativistic speeds) WIMPs fit the evidence for dark matter. The evidence gathered from galactic motion studies, gravitational lensing observations, simulations of the evolution of the large scale structure of the Universe, measurements of the cosmic microwave background, and many other experiments. Nothing fits all the data except the cold dark matter theory. That's why scientists believe it.
The fact that you are skeptical about it is irrelevant. Educate yourself on the evidence and science of it first, and then you can talk.
Scientists: Listen people! We have created models that explain why stuff does what it does! They are so complicated almost nobody can understand them. They involve 4 dimensions, a zoo of particles, randomness in everything and no reality independent of the observer. And they conflict. But at least they explain why stuff does what it does!
World: But they make the wrong predictions. Stuff does not behave like that.
Scientist: Oh, no problem. Just imagine there is an invisible force out there that moves stuff around. Imagine most of our universe is made of that invisible stuff. Now back to our awesome models!
We have well understood mathematical models which correctly and accurately predict all physical behavior relevant to our everyday lives, and, further, correctly and accurately predict the majority of our observations of the universe around us, period. As tools for understanding our world, they are incredible achievements.
In spite of us knowing these models to be fundamentally incomplete, we have yet (to my understanding) to perform an experiment on Earth which contradicts them. More to the point, the theory which supersedes them will, by virtue of needing to replicate all experimental results so far, will likely be even more esoteric, complicated, wild, baffling, and impenetrable (and--with any luck--elegant, inspiring, and beautiful).
accurately predict all physical behavior
It's still fairly immature, so still needs work - it violates the equivalence principle and relies on Unruh radiation which hasn't conclusively been observed.
There are the arxiv papers and some other reports (that all tend to link back to either the blog or arxiv) as well. Like you, I don't have a strong physics background, so find the published papers a challenging read.
-- then black holes would, in effect, be (our) universe's GC mechanism. Or at least, its "janitors" in some form.
Whether that's ’cool’ or not is a matter of persona preference.