Dark matter and dark energy.

We don't even know what we don't know.

It's amazing how clueless we are about all things around us, under us, and in us. Let alone space and all that entails.

It's pretty cool to speculate though. And we'll never run out of things to speculate on, that's for sure.

Obviously I have no idea what it's is, but I wouldn't be shocked if the ultimate explanation is our models and/or observations were a bit off, and dark matter is as real as the ether was.

racist

This is almost certainly the case. Our equations don't match reality, so we propose a form of matter that cannot be interacted with in any way and whose only effect on the universe is to neatly and exactly fill in the gap in said equations? Yeah... ok. That sounds awfully convenient to me.

There will eventually be another paradigm shift which will explain away dark matter the way relativity explained away the ether and "light tiredness."

I thought Dark matter was Niblonian poop

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Yes, I'm aware of the "evidence" for dark matter, which is that currently accepted models for how gravity work show that, for galaxies and other supermassive objects to behave the way that they do, they should contain orders of magnitude more mass than what we observe them to have.

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Yes, evidence in science is only that which is observable.

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The examples that you included in your post are just variations on that theme.

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These examples are the only evidence, indirect as they are, that an unknown entity scientists are labeling dark matter is exerting gravitational influence upon known matter. They seem to be quite strong, however, since they occur everywhere we look in the Universe.

It should be said at this point that the term "dark matter" is being used by scientists merely to designate an unknown entity. It does not imply that any properties other than the exertion of gravity is known or, god forbid, assumed.

A scientist doesn't use the word "assumed" because it implies a lack of evidence. Rather, he can hypothesize from observations. However, he must be ready to defend his proposal or face humiliation. The scientific community can be vicious and doesn't take kindly to anyone who seeks notoriety or self gain, especially at the expense of the scientific method. Religion and politics may tolerate grandiose personalities but science doesn't. Even the great Stephen Hawking is eroding his stature within the scientific community with some of the bullshite he's feeding the lay public regarding the perils of alien contact, for example. It's difficult to blame him for using his stature to make money, but that's the nature of the standards for scientists.

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Now, since the models don't match with observed reality, there are only two possible conclusions that can be drawn: either a) the models are wrong or b) we aren't observing reality properly. Astrophysicists have chosen to go with answer "b" and have assumed the existence of an invisible, undetectable, undefinable substance called "dark matter" whose supposed properties are revealed solely by the amount of error in the models. The way we know how much "dark matter" a given galaxy supposedly contains is by solving the relevant equations of motion for it and then seeing how much they don't match with the galaxy's actual behavior. If that isn't the very definition of a "solution of the gaps," then I don't know what is

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Science is eternally malleable. Every discovery causes more questions to be asked. Words such as "reality" and "conclusions" evoke a sense of absolutism. They can only be subjective and aren't useful in describing observations or principles.

Also, when you say, "Astrophysicists have chosen to go with answer 'b'and have assumed the existence of an invisible, undetectable, undefinable substance called 'dark matter' whose supposed properties are revealed solely by the amount of error in the models," you are implying that a majority of scientists are endorsing aspects of dark matter. This just isn't so.

First, no assumptions are being made. That's unscientific. Also, the only property that is proposed and supported by observation is a gravitational exertion by the unknown entity.

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The other conclusion - that current gravitational models are wrong - is obviously scary for astrophysicists and so no one wants to propose it, especially because no one has yet come up with a better model that continues to work at supermassive scales (you don't make a name for yourself as a scientist by saying, "I just don't know.").

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The mark of a great scientist is his ability to say, "I don't know." I can't imagine why you would think otherwise. Furthermore, anyone who wants to make a name for himself in science knows that he must first impress his peers with his knowledge and discoveries. That isn't easy, to say the least.

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Since the two men who have done the most to shape humanity's current understanding of gravity (Newton and Einstein) are considered two of the greatest geniuses that ever lived, this is not particularly surprising. Men like that don't come along in every generation, or even every century. So, while we wait for the next paradigm-shifter, some very smart people will sit and play with their pet theories about how to fill the gaps in the models. The true genius, however, will be the man who doesn't fill the gaps, but eliminates them.

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I have only two words as a response, Edward Witten. The world's leading string theorist, he makes Stephen Hawking seem like a high schooler by comparison.

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Translation of that last image: our data might well be misleading = the outer galaxies from our perspective might well NOT be rotating at the same rate as the inner galaxies.

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There's no evidence that physics is different in other parts of the Universe. Actually, all observations indicate that physical laws are uniform, at least in this Universe. They are likely different in other Universes, though.

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Also, our isolated perspective doesn't even come close to representing reality. It's analogous to taking a single sample of ocean water at some shoreline and assuming it is representative of all the ocean water on earth.

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Reality is subjective while observations are objective. From our vantage point we can see the Universe very well. While there may be parts of the Universe that we will never be able to observe because of expansion, we can project our observations upon them based on the laws of physics.

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Is it not more probable that we have, once again, run up against the boundaries of our current understanding of how things work and need to improve our models, than it is that this incredibly convenient substance actually exists?

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Well, I can only add this: The scientific method is sacrosanct and infallible. It is beyond anthropomorphic influence. Current observational evidence indicates that dark matter and dark energy exist.

Certainly something is strongly influencing the orbits of stars and other matter within galaxies. Also, something is bending light in areas where we can't detect anything via observation. For lack of a better term that might describe this entity, "dark matter" is used as a kind of placeholder. More knowledge will describe what we're observing.

Mathematical models are useful in guiding our explorations. There is no substitute for observation, however. As you've suggested, models must acquiesce to observations. This happens continuously in physics.

You seem to be saying that scientists are being misguided by the lure of dark matter and dark energy. Here again I invoke the scientific method as insurance that, no matter what dark matter and dark energy ultimately turn out to be, scientists will not be drawn away from the course of knowledge that reveals what is causing the gravitational anomalies we are seeing.

You're right. We don't have a clue as to what dark matter is. We can only see its effects. That's why I mentioned that the term "dark matter" is only a placeholder name. No one should think that scientists are assigning any other properties to it, whatever it is.

The reason dark matter and dark energy are being used comes from basic physics. Einstein's equation, e=mc2, tells us that everything is either matter or energy depending upon its current state. Matter in motion is energy so energy not in motion is matter. Both exert gravity. Matter tends to be stationary so the term dark matter is used to designate a possible entity that's affecting galaxies and light.

Of course, the common term that's involved in any of this speculation is gravity. Despite hundreds of years of research, thought experiments and math by humanity's greatest minds, we still don't know what gravity is. We are extremely familiar with its effects and can predict it with great accuracy, all without knowing it's composition or cause.

Is it a force or an effect? Is it truly one of four or five basic forces that originated when the Universe was born? Or is it the effect of space upon mass?

Is it a pull or a push? Are there really gravitons that carry a force that binds mass together or does space actually push mass together? We just don't know.

Quantum physics may answer this and other mesmerizing questions. It's fun following our human progress towards solutions.