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New Hubble Release Puts Another Nail In the Coffin of Dark Matter's Competitors (spacetelescope.org)
StartsWithABang writes: When it comes to the structure of the Universe — forming the galaxies, clusters, and Universe as we see it — the normal matter we know of simply isn't enough. Given our best-understood laws of physics, including Einstein's general relativity, what we see of galaxies and the Universe in general simply doesn't match up to our predictions. The simplest solution, arguably, is to just add a new ingredient: a new form of matter, a dark matter if you will. But a counterargument is that we've got the laws of gravity wrong, and that no new matter is necessary. There's only one way to settle an argument like this: with data, evidence and the full suite of observations at our disposal. The newest Hubble release, along with four other independent lines of evidence, rule out modifications of gravity and leave dark matter as the only option standing.
If it does not interact electromagnetically it must be transparent.
Actually no. All baryonic matter we know of, transparent and intransparent, interacts with electromagnetic waves. All transparent baryonic matter for instance comes with a specific refractive index describing how it reduces the speed of light crossing it. The refractive index of dark matter is 1, e.g. it has no influence on the speed of light. For light, dark matter just isn't there, quite different than transparent baryonic matter.
Dark matter is still handwavium. The best proof we have for it so far is that if it isn't there the model we use doesn't work.
No, it isn't.
If you're hunting for a bear and you find bear tracks, bear shit, bear claw marks on trees, and everything except for directly observing the bear itself, you don't say the bear is "handwavium" and all of the evidence was really caused by a mutant chicken just because you didn't "see" the bear itself.
Dark matter is exactly the same. We've measured. We've observed. The evidence points to some sort of weakly interacting/non-interacting form of matter. We can't "see" it, but we see the effects it has on everything else. It's the best and simplest explanation we have at the moment.
Now you may not like it. You may think there's a better explanation. But until you put forth your theory with evidence to the contrary that not only explains the current observations but also doesn't break current physics it's simply your unsubstantiated opinion.
~X~
> Frankly, "dark matter" is like "magnetic monopoles". It works in mathematical models, but hasn't shown up in experiments and is not a *necessary* to explain how things work. Simpler models are powerful and elegant enough to cover the existing structure.
I am breaking my usual rule of not responding to anonymous cowards, but the quoted statement is wrong at several levels and I am feeling masochistic this morning.
The idea of dark matter does not come from mathematical models, it comes from observations. The standard model of particle physics does not predict dark matter. Dark matter was detected in experiments (or observations if one wants to be pedantic). There is no theoretical basis for dark matter, but there is a large body of evidence, from many different types of observations, supporting the idea that dark matter is a real part of the Universe. At present there are no theoretical alternatives to dark matter than can reproduce what we observe in the sky. Unless the past 80 years of observations are wrong then dark matter is necessary to explain what we see. There are no simpler models. Many have been tried, including small- and large-scale changes to gravity, and none have been able to reproduce what we actually observe.
Dark matter is not simply a measurement error. There are too many independent observations that all point to the existence of dark matter. Not only that, they all point to the same amount of dark matter and require that similar properties for dark matter. Measurement errors do not always work in the same direction across vastly different types of measurements. Bib Bang nucleosynthesis and the COBE/WMAP/Planck observations are completely different from galactic rotation curve and cluster velocity dispersion measurements, and yet they all predict consistent amounts of missing mass. Stray planets and low density clouds of cold gas are not enough to close the gap. Even if they did work for galactic rotation curves they would not be able to explain the results of the cosmic background radiation observations.
Just because you are paranoid does not mean that no-one is out to get you.
What.
No.
We have several empirical results that point to a decoupling of the majority of the mass in a galaxy from it's light emitting matter. The bullet cluster shows us two galaxies colliding, we can see the light from both galaxies coalescing around each other. By measuring gravitational lensing, we can also see that the majority of the mass of those galaxies passing right through each other without interacting.
We know beyond any reasonable doubt that the majority of the mass in the universe does not interact with regular matter, does not produce light, does not interact with light beyond gravitational lensing. That is literally the definition of what dark matter is. There are a handful of viable theories (probably only 2 or 3 likely ones) as to what form that matter takes, but that hardly means we don't have evidence of dark matter existing.
The best proof we have for it so far is that if it isn't there the model [which we have created based on our observations of the universe] we use doesn't work.
So... that'd be like... science, then?
THIS.
Not only that, but the entire concept of modern science is predicated on mathematical models of phenomena that can't be observed directly or explained in detail (at least at first).
Our classic history story of the Scientific Revolution often misses this point. We have this vision of people like Copernicus and Kepler and Galileo standing up against ignorant buffoons who refuse to recognize empiricism. But that wasn't it. Scientists had been doing empirical observation for thousands of years. Scientists after Copernicus rapidly (late 1500s) started looking for evidence of the earth's motion -- like stellar parallax and coriolis "forces." They couldn't measure any, and they ultimately weren't measured until the 1800s. That was a major impediment to the heliocentric theory.
But another one was Aristotle's theory of physics, which was wrapped up in detailed explanations of "causes" for everything. And everything in the universe had its "natural place" -- terrestrial matter was assumed to always come to rest, because that's what empirical observation shows us.
If the earth was in some sort of perpetual motion, what caused it? What maintained it? Why didn't the earth fly out of its orbit? Why couldn't we seem to measure it?
The first three questions were answered when Newton's theory of universal gravitation came along. There was this magical unseen force called "gravity," which kept the universe in order.
Many scientists, who believed solidly in empiricism, were highly skeptical of Newton's "occult" forces. (The word "occult" comes from the Latin meaning "hidden" or "unseen," and "occult" phenomena such as unseen forces like magnetism and gravity were associated with "magic" in the 1600s -- not "science" as we understand it.)
Newton responded to his critics by publishing an addendum to later editions of his Principia (usually known as the "General Scholium") which basically said, "Yeah -- those weird invisible 'forces'? I admit they might not be real. But the point is that the math works out, and thus this can be a model for scholarly investigation, even if we can't observe these forces directly or attribute an Aristotelean 'cause' to them."
THAT was really the crux of the Scientific Revolution. Many scientists came to accept Newton's theory, even before the first empirical evidence of heliocentrism (stellar aberration) was measured in the mid-1700s. The math worked, and thus the "model" worked. Even if we couldn't explain all the details, that was now "science."
The history of science after Newton is filled with stories of theories about stuff we couldn't observe directly (electrical charges, atom models, etc.), but which we assumed to exist because they were consistent with the math and the empirical observation. It's also filled with apparent "failures" of invisible things like phlogiston and luminiferous ether.
But those weren't really "failures" of science. They were theories based on rational empirical observation -- they may have lasted a little longer than they should have, but when they were first posited, they were reasonable explanations of what might be going on.
We STILL don't have a complete explanation for how the invisible force of gravity works. But it's well-accepted part of science. Dark matter is no different. Maybe someday it will go the way of phlogiston, but right now it's one of the best explanations around. The fact that dark matter was invented to serve a place in a mathematical explanatory model is the very definition of modern science.
Reference to whether or not "FTL" is possible in physics almost always means communication of information and movement of mass/energy at faster than light speeds. There are all sorts of ways of thinking you have something moving faster than light that fails to do move information or mass & energy (marques, or the crossing point of a astronomical sized pair of scissors). Quantum entanglement provides no means of moving energy or information at faster than light speeds, even though though there appears to be something happening fast than light between an entangled pair.