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.

Comments

Handwavium

[Anonymous Coward]

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.

Re: Handwavium

[Anonymous Coward]

So was the hypothesis of the neutrino before it was actually detected. You see, there was this anomaly in the beta decay spectrum and it was hypothesized that the missing energy was carried away by this particle called a neutrino. Decades later the neutrino was actually detected. In what way is dark matter different?

Re:Handwavium

[wonkey_monkey]

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?

Re: Handwavium

[Theovon]

As someone else said, dark matter is an ad hoc solution. We don’t have direct measurement of it. We just have a phenomenon, and we’re trying to come up with different possible explanations and then rule some out.

Currently, dark matter is the leading theory because it explains all the data and it’s also the SIMPLEST explanation.

This doesn’t mean that dark matter theory is TRUE. But as explanatory models, it is RELIABLE. Keep in mind that science can never prove any theory to be 100% incontrovertible, but it can show a theory to be very LIKELY to be true.

And as with any other successful human endeavor, the science here is a competition among competing theories. So far, dark matter theory is the winner, like VHS. (Betamax had better image quality, but VHS was “better” and won because it was an open format. Don’t get too distracted by the imperfect analogy!) Some day, someone will come along with something that explains more evidence and is more concise, like Blueray.

Re:Handwavium

[Black Parrot]

The best proof we have for it so far is that if it isn't there the model we use doesn't work.

That's kind of how science works: you notice an effect, assume there is a cause, generate some guesses about what that cause might be, and then start weeding them out.

Re:Handwavium

[MozeeToby]

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.

Re:Handwavium

[MTEK]

I'm not saying it's science... but it's science.

Re:Handwavium

[AthanasiusKircher]

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.