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

[Curunir_wolf]

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?

The neutrino hypothesis included some very specific property values for the particle, and possible ways it could be detected. Dark matter, not so much.

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

[Xyrus]

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.

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

[Applehu Akbar]

The best argument against wormholes is that if they existed, the aliens would already be here.

On second thought, that might explain the Kardashians.

Re:Handwavium

[MTEK]

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

Re: Handwavium

[JoeMerchant]

And then the whole concept is rendered irrelevant, like streaming.

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.

Re:Handwavium

[EvilSS]

Thank you. I can't believe GGP is at +4. I really don't understand what the fucking problem is for the /. crowd when it comes to dark matter.

Might as well argue that time dilation is handwavium and not being able to accelerate to the speed of light is a liberal conspiracy.

Fucking scientists. What do they know?

You must be new here. Everyone on /. is a Nobel laureate in waiting and knows more about physics from reading /. summaries and making quick, 30 second snap judgements than the people who write the papers the summaries are based on.

Re: Handwavium

[Dragonslicer]

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?

So were Uranus, Neptune, and Pluto, which were all known (or at least strongly supposed) to exist because the orbits of the outer planets weren't quite what they should be if there wasn't another massive body out there.

Re: Handwavium

[tnk1]

This is true. No matter how many times I see spooky action at a distance explained to not be FTL communication method, someone still thinks it can be a FTL communication method.

That said, FTL is not only movement of information at FTL speeds, it is movement of information at speeds which are FTL relative to other points. So yes, if there was a way to warp space-time so that a normal light speed EM wave simply had a shorter distance to go, that's still FTL communication.

Of course, since no one has demonstrated that warping space time is possible in that manner, and wormholes (while still not ruled out) appear to require a sort of exotic matter that is unlikely to exist, FTL is very much a goal with fiction wrapped around it, rather than science.

Re: Handwavium

[tnk1]

Realistically, wormholes or not, even a civilization limited to light speed travel should have been able to colonize or visit most of the galaxy in just a few million years with robotic exploration. So, it is looking like there is either no one else out there, or just as likely, there is some sort of barrier to intelligent civilizations being able to launch such an effort like colonization or robotic exploration.

Obviously, this all assumes that someone would have done all of this first. We might be either the first civilization at this point, or at the very least, a member of the "first wave" of civilizations where the other civilizations do exist, but their evidence has not yet arrived here. That scenario is just as likely as any other solution, but it is less useful because then we have nothing yet to look for in order to confirm our theory, so we tend to assume that we're not a member of "the First Ones".

There is also the idea that there may be a "Great Filter", which is some sort of event or situation that all intelligent species run into before they can do interstellar exploration. It could be something like nuclear holocaust or self-destruction being inevitable, or as simple as running out of available energy to be able to maintain high technology before they could start the program. Or some combination.

Nuclear war, unfortunately, is probably inevitable. It is a more distant threat than it used to be, but the weapons are all still there, and even pariah states like North Korea have working weapons. While those states remain somewhat rational, we're probably fine, but the stakes are pretty high.

Another possibility is simple overheating. Here I'm not exactly talking about Global Warming as caused by carbon emissions, but actual generation of heat by releasing it through energy production as waste heat. Solar energy doesn't help us with this because increased capture of solar radiation will increase waste heat on Earth. Eventually, carbon dioxide or not, we might simply add more waste heat to the planet than the Earth can actually radiate out into space. In that sense, I am very much a believer in AGW, although that scenario is probably more remote in time than a CO2 based greenhouse effect. Eventually, the Earth will need a giant heat sink if we want modern civilization for ever increasing numbers of people.

Re:Gravity leak from other dimensions?

[nightcats]

That actually makes some intuitive sense. My only problem with "dark matter" is the term itself: I saw recently in Nature (the science mag) that one astronomer had proposed the term "transparent matter," which I like a lot better.

Why so negative?

[wonkey_monkey]

New Hubble Release Puts Another Nail In the Coffin of Dark Matter's Competitors

Well that's a gloomy spin on it. What about "New Hubble data advances scientific understanding of the universe. Go science!"?

Re:Gravity leak from other dimensions?

[Sique]

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.

Re:Or it could be, you know, measurement errors

[mrsquid0]

> 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.