What If Dark Matter Really Doesn't Exist?

sonar67 writes "According to The Economist: 'It was beautiful, complex and wrong. In 150AD, Ptolemy of Alexandria published his theory of epicycles--the idea that the moon, the sun and the planets moved in circles which were moving in circles which were moving in circles around the Earth. This theory explained the motion of celestial objects to an astonishing degree of precision. It was, however, what computer programmers call a kludge: a dirty, inelegant solution. Some 1,500 years later, Johannes Kepler, a German astronomer, replaced the whole complex edifice with three simple laws. Some people think modern astronomy is based on a kludge similar to Ptolemy's. At the moment, the received wisdom is that the obvious stuff in the universe--stars, planets, gas clouds and so on--is actually only 4% of its total content. About another quarter is so-called cold, dark matter, which is made of different particles from the familiar sort of matter, and can interact with the latter only via gravity. The remaining 70% is even stranger. It is known as dark energy, and acts to push the universe apart. However, the existence of cold, dark matter and dark energy has to be inferred from their effects on the visible, familiar stuff. If something else is actually causing those effects, the whole theoretical edifice would come crashing down.'"

Comments

what if theory didn't exist?

[garcia]

So what if it doesn't really exist? We know very little about anything anyway. Trying to find a unified explanation via "String Theory" is spotty at best but at least it "helps".

What's the difference if dark-matter is really just another false theory? In the long run it's not going to make a whole heck of a lot of difference.

Re:what if theory didn't exist?

[Daniel_Staal]

Sure, in the long run it doesn't matter.

That is, of course, if we keep testing it and trying to see if it is true. (Or the closest approximation of 'true' we have been able to come up with.)

It matters now if it is not true because then we know we need a better theory. And that means we either didn't understand something we thought we understood, or that we hadn't explored our understanding fully. Either way, there is likely something else that will be affected...

Re:what if theory didn't exist?

[egomaniac]

I always thought this was an interesting an odd part of modern science and cosmology. Why should we assume occam's razor, that simpler explanations are better? Why should the universe be simple and elegant?

You have misunderstood Occam's razor. It doesn't say that at all.

Occam's razor, in its original form, translates to "Do not multiply entities unnecessarily". That has been modernized to "The simplest explanation is usually correct", which is close, but not exactly the same.

What Occam's razor really means is: given two (or more) possible explanations of a phenomenon, with no evidence favoring one over the other, assume that the simplest one is correct.

For instance, if I find a pinecone lying on the ground under a pine tree, the simplest explanation is that it fell off of the pine tree. Sure, it might have been planted there by invisible space aliens in conjunction with the Illuminati acting in strict accordance with the Masonic doctrine of the Coming of the Pine Cone King, but since there is no evidence to favor one explanation over the other, I should assume that it fell off of the pine tree.

That doesn't mean that it did fall off the pine tree, and it doesn't mean that I might not change my mind as more evidence is found. It also doesn't mean that I shouldn't look for more evidence and try to determine the origin of the pine cone with greater accuracy. That isn't what it says at all. It just means that until such evidence arises which would cause me to revise my view of things, I should assume the simplest explanation that fits the facts. The explanation should only change when the known facts do, or a better explanation is found.

Relativity

[mozumder]

Actually, with Einstein's relativity, doesn't Ptolemy's theories hold true? Everything is relative to a point of view?

Sorry I didn't ask this question in Modern Physics's class. It was a morning class, and I was sleeping.

Correct me if I'm wrong...

[AKAImBatman]

...but doesn't String Theory tend to suggest that "dark matter" isn't actually dark matter, but instead is gravitation bleeding from other universes? The same theory also explains why gravity in this universe is so weak. Because most of it bleeds of into other universes via the higher dimensions, it's weak enough for you and I to move our limbs.

Re:Correct me if I'm wrong...

[bob the Martian]

There are current astrophysical models which postulate that the Universe is a hyperplane embedded in higher dimensional space, called Randall-Sundrum models. In which case gravity can propagate trasverse to this plane, hence there can be matter outside the Universe which can still interact with it. There is also the idea that this 'brane' (as it is called - nothing to do with zombies) has a small extra dimension (less than 1mm in size) so the current gravitational law needs to be changed to r^{-4} or so at very short distances.

String theory as such tends not to comment on dark matter (could be D0-particles, could be fish) as no-one knows how to compactify it down from 10D and break supersymmetry in a useful way.

What does it matter?

[MrPCsGhost]

Are planes going to drop from the sky? Will we be thrown out of orbit? This sounds like the Bugs Bunny cartoon where Bugs floats on air because he never studied the laws of gravity (I know I've probably got the reference wrong, but you get the idea).

Your experiment fits the model, or it doesn't. If it doesn't then one or both need to be tweaked, or scrapped.

Something odd with gravity

[Tablizer]

There seem to be growing "hints" that something is wrong with current theories about the very nature and behavior of gravity. This includes alleged dark matter that cannot be identitied, planetary space probes with slight deviations from expected sun "pull" [1], and the fact that there is no identifiable "negative" gravity while the other forces do have negative values or particles.

[1] It was originally thought that heat generated from nuclear fuel cells was "pushing" the probes, but this was mostly ruled out because the heat lessens over time, but the pull was constant.

I hope its a kludge

[mnmn]

Science has been progressing on the basis of constantly proving theories as kludges and bringing about something newer and more real. Imagine if our currently held view was true (before Standard Model), we will never be able to travel faster than light, we'll never harness energy bigger than a hydrogen bomb, we'll never really travel far beyond the Solar system, travel back in time etc.

Before the cannon was invented everyone thought the arrow was the greatest weapon, and few could really predict the power of "Little Boy" on Hiroshima. Quantum Mechanics has given us so much hope, of unknown and unexplainable realities, and that far more is possible than we first thought. It means the road before us is much longer, but far more interesting. I'd prefer it that way.

Re:No dark matter ?

[Daniel_Staal]

Hey, all the better!

If the end of the universe is a heat death it might be possible to live forever, in smaller increments of time/energy. If the universe crunches, everyone and everything dies...

dark matter evidence

[dpa]

There is some intriguing evidence of the existence of strange quark matter, a dark matter candidate, which we've recently published in the Bulletine of the Seismological Society of America. as previously discussed on /.

SIGGRAPH keynote: geometry instead of dark energy

[peter303]

The keynote speaker at the 2003 SIGGRAPH conference in San Diego was the British astrophysicist Anthony Lasenby. He claimed that a new kind of unified Euclidean and hyperbolic geometry could explain acceleration and deceleration in the Big Bang. He was talking at SIGGRAPH because his new unification of geometry is supposed to be more elegant for computer graphics modeling than the current homogeneous coordinates now used. He wrote a book about the geometry. But I have been unable to find a paper relating to the cosmological application on the web.

This is not the first time geometry has been used to unify and simplify physics. Previous examples are Galilean coordinates, special relativity, and general relativity.

M.O.N.D.

[bokmann]

Bringing this up without mentioning M.O.N.D. is irresponsible journalism. MOND (Modification of Newtonian Dymanics) is a theory that simply says that gravity 'decays' at a slightly different rate than expected over astronomical distances. The effects predicted by this theory are spot on to the observed effects that dark energy and matter try to explain.

I googled about found this link, but I first read about it in New Scientist about a year ago.

Re:Theory.

[nacturation]

Just like the Theory of Evolution.

Yes, exactly. That evolution occurs is a fact which can be demonstrated. On the other hand, the theory, which tries to explain how evolution works, could be inaccurate/wrong. The theory itself may change many times and might be completely overhauled for some new radical explanation. However, regardless of whether or not we understand the mechanisms behind it, nothing can change the fact that evolution exists.

See: Evolution is a Fact and a Theory

physics overturned a couple times in my lifetime

[peter303]

I may be showing a few gray hairs here, but revolutions in the sciences have occurred in my lifetime with scientists adapting fairly well. The first was the acceptance of Big bang in the late 1950s. Between 1927 and 1955 the Big Bang was just one of several "equally attractive alternative theories" which included the eternal-infinite universe and continuous creation of matter. The microwave background and the abundance of helium brought the big bang into the fore front.

In the 1960s the quark unification of subatomic particle became the predominate theory. Plus quantum electrodyanamics was verfied in high energy experiments to extremely high precision.

Also in the 1960s plate tectonics replaced an up-and-down explanation of geologic forces.

If the evidence suggests a more powerful theory, then physicists will revise their theories again. Science does not stay attached to incorrect theories (though block-headed individuals do).

Pardon my naivete

[El]

I may be incredibly naive, but it has always bothered me that we insist on believing there are only 4 types of force in the Universe, each operating on widely different scales. Why can't there be other forces that operate on too large a scale or too small a scale for us to observe? Is the postulate of "dark force" effectively a theory about a fifth type of force?

Re:Brief History...

[Brandybuck]

From your article: "60% responded...", "half replied...". In other words, a self-selecting survey. Demonstrates nothing.

Re:The stuff doesn't exist.

[tgibbs]

But kludge's are the black eye of science, and even really bright people can make them (remember Einstein and his cosmological constant?).

To be fair, the cosmological constant was a constant that emerged naturally from the derivation of General Relativity, with no indication of what its value should be. To apply it to reality, some value had to be assumed or determined. The simplest thing to do would have been to arbitrarily give it a value of zero, but that would have implied an expanding universe. In the absence of evidence for expansion, Einstein chose to give it a value that made the universe static.

steady as she goes...

[sdedeo]

It is doubtful that the entire theoretical edifice of dark matter and dark energy will collapse all at once (in the way it might more reasonably have been said to have happened for the electromagnetic aether.)

In particular, dark matter, though incredibly mysterious, is probably on firm enough ground that it will withstand a series of challenges. Galactic rotation curves and measurements of cluster temperatures both give very strong evidence for dark matter on vastly different scales; in addition, it is difficult (OK, fine: downright impossible in standard Einsteinian gravity) to get any kind of structure to form *at all* in the universe if one is only allowed to use the visible matter. The precise ratio of dark to visible is definitely up in the air; and, of course, there are competing models that modify gravity -- if these matured enough (they may already have -- I haven't kept up) to make predictions on a wider range of scales, they might work as well.

Indeed, a lot of gravity modifications (extra dimensions, etc.) behave *phenomenologically* as if there was dark matter -- so all the effort we've put into simulating dark matter may not be in vain after all, even if Einsteinian four dimensional spacetime is not the name of the game.

In contrast, indeed, is the exact count of the "baryons" (ordinary matter.) I would be very surprised if we were off by a factor of (lets be ultra-conservative here) five in the baryon number, which is constrained very well by big bang nucleosynthesis, whose predictions remain in the "ordinary" realm of nuclear explosions. Something we know a little about.

The real mystery is "dark energy." There, the evidence is a lot shakier. It rests on a few pillars. There is a theoretical bias that wants the universe to be flat (so that the missing mass-energy is made up for by some dark energy component that doesn't cluster and affect our galactic rotation curves.) There are some really excellent (but difficult) measurements of universe acceleration, a signature of dark energy, from people who observe distant supernovae (these provide "standard candles" that allow you to measure distance given an apparent brightness.)

Finally, there are the CMB measurements, which provide a similar kind of distance measurement, but are open to alternative interpretations (instead of measuring apparent brightness, they measure apparent angular size -- but it is perhaps possible, if you squeezed around, to construct a different model where the apparent angular size is squished in odd ways.)

And then there are a host of other measurements that one might call more "marginal" (without prejudice to the people who work very hard to do them -- I aspire to be one of them.) They rely on a few more astrophysical assumptions, and perhaps would not convince the slashdot skeptic. (My profound apologies if I've missed out someone's awesome measurement.)

One big "trouble" is that we haven't seen good evidence for a very particular signal that one would associate with the simplest model of dark energy. (This is the "low quadrupole" -- the news stories you read about finite universes are from people who, in part, are motivated by the desire to explain this low quadrupole signal by other means.) Of course, it is entirely possible to make more exotic dark energy models that don't show this signal (I've coauthored a paper on one such model), but that missing signal, gosh, damn.

The Economist is usually good with science articles, but it really kind of missed the point on this one. Shanks et al. are not "bringing down the whole edifice"; they are pointing out what they see as a possibly problematic signal in the CMB data. This may inspire in some a little additional -- and very healthy -- skepticism about the dominant models. But it is important to mention that there really is no "dark energy mafia"; nearly any astrophysicist worth his or her salt would drop dark energy like a stone if the evidence started piling up, and many, many astrophysicists keep a hand in alternate models that don't rely on dark energy because, hey, what a scoop that would be.

Re:Theory.

[EvilTwinSkippy]

What do you mean absence. Look at dogs. We took wolves and turned them into a wide variety of shapes and colors from Great Danes to Chiwawa's all within the last 40,000 years.

The same is true with almost any domesticated animal. For pete's sake the entire science of animal husbandry is application of Evolution, just under our control.

Of course, our efforts in domesticating animals show that one force seems to be required to really make evolution work properly: a regulator. Someone who reviews what's good, what's bad, and what is really cool, though unexpected.

Next time some god-boy goes on a rant about how evolution doesn't exist, quote the parable of the Wheat and the Tares. In it Jesus talks about how God can't really tell what is useful and what is not until it has had a chance to develop. Once it is clear what is good, and what is not, someone comes by and clears the crap out.

Evolution by any other name to me.

Re:The stuff doesn't exist.

[rknop]

Entire careers in physics are going straight down the shitter because of dark matter, because it doesn't exist. From the very first time I read about it, I thought "Geez, this sounds like a 3 year old trying to cover up the fact that he doesn't KNOW the reason why".

Uh.

The primary evidence for dark matter is that if you look at how galaxies move and how clusters of galaxies move, they should all be flying apart. They are moving too fast for the amount of gravity we calculate by adding up all the mass of the stars and the gas that we can see. Since galaxies and clusters are around all over the place, we know they're not falling apart. Ergo, there must be more gravity than can be accounted for from the material we can see.

The simplest, easiest, and most direct explanation is that there is more there than we can see. Matter not emitting light, thus called dark matter. There's nothing kludgy or ad-hoc about this, it's the most natural conclusion to make. The alternative is that Newtonian Gravity (or General Relativity, which has Newtonian Gravity as a limit in the relevant case)-- that theory which perfectly predicts the motions of planets, spacecraft, apples, and other things that we have lots of experience with-- must be wrong. There are people who believe this over Dark Matter, in fact, but to me, "stuff there that we haven't found yet" seems to be a much more likely and plausible explanation.

The evidence for why the dark matter can't all be baryonic (i.e. made up of "normal" stuff) is more indirect, but it comes out of other theories for the construction of the elements in the hot early Universe-- and this other theory itself has made predictions that match well what was observed.

-Rob

Re:Ladies and Gentlemen: The Scientific Method

[Barlo_Mung_42]

"Do you really have to prove God exists before you'll believe?"

As a matter of fact, yes. ;)
Some people get by fine on faith and that works for them. I've known many happy faithful people and I sometimes even envy that quality in them.
But that just isn't how I work. I look at the world with an innate need to figure it out. This makes it impossible for me to take any religion literally.
I suspect this is common with many geeks.

Re:Theory.

[Noren]

In Britain, there are two types of gull which appear to be different species, a white herring gull and a lesser black-backed gull. They are quite different in appearance and do not (directly) interbreed. They are currently considered one species, though, because they share genetic material indirectly. The white gulls breed with the North American gulls and the black-backed breed with the northern European gulls... which, as you go around the world's northern edge, gradually change characteristics to become the other. Each local population occasionally breeds with its adjacent areas' slightly different gulls, and these small changes add up, until around the Alaska/Siberia area the gulls are roughly intermediate between the two types of gulls as found in Britain. There's no clear place to draw the line separating the spectrum between the two ends of the ring to separate those ends into two species.

If all the herring gulls in North America and/or Asia were to die due to some natural disaster (or to human interference), the white herring gull and lesser black-backed gull in Britain would become different species. In a sense this is a situation where the gulls have in most ways already evolved into two species, and could readily become two species given particular natural events. This type of species is called a ring species.

Re:Natural selection has been shown, not evolution

[Black Parrot]

> Evolution, OTOH, has never been demonstrated or shown in an experiment. To demonstrate evolution would require watching a planet from start to finish, which we have not yet done.

Sorry to inform you, but science allows indirect evidence as well.

> Something not taught in school that should be is that evolution is dependent upon natural selection, but not the other way around. The earth could have been populated by God/Aliens/someone creating species in a test tube somewhere and populating the earth. Natural selection would just as easily occur with this hypothesis.

You seem to be confused about the subject matter. It is correct to say that it doesn't matter whether gods/aliens/naturalforces/blindchance created life, because evolution could operate on the result regardless of the origin. All evolution requires is imperfect self-replicators.

> BTW, I'm a scientist

You certainly don't talk like a scientist. What is your field, and where can we find a list of your publications?

> WRONG. There is no such thing as proving a theory right (i.e. as truth).

And a real scientist would know that scientists don't spend their time trying to "prove" theories right. Rather, scientists look for explanations for observed phenomena, and theories are the product of that endeavor.

> Evolution is so mathematically improbable that I'm surprised that most scientists just accept it.

Can you show us the math on that?

> It's a great theory to explain things right now (which is why we use it), but there's a good chance it will probably be proven false someday.

Can you show us the math on that, too? (I'll gladly accept "it may be proven false someday", but you are asserting more than that, even with your double qualification. What are the chances that the theory of evolution will be proven to be false some day?)

Pascal's Wager is a fraud...

[Dr. Zowie]

If you convert to (say) Christianity to maximize your "expected return" from life, you're being a hypocrite -- unless you're very different than I am. I don't have a lot of conscious choice about what I believe -- it either happens or not. I do have a conscious choice about how I behave, but to act in contrast to my beliefs is, as they say, to be a hypocrite. No good: hypocrites don't get in to Heaven. In short, for me (and people like me), Pascal's Wager is a canard -- I don't get to choose what I believe, so the dichotomy isn't a real one.

It seems to me that a central tenet of Christianity is the Good News itself -- that an actual guy actually taught a bunch of people how to be good to each other, and actually came back from the dead. That is (at least in principle) a physical, provable proposition, and finding things like the shroud of Turin is a big part of that. Other religions work the same way -- there're a core set of beliefs that hold in the physical world, and that are thought to be supporting evidence for some metaphysical beliefs.

It also seems that this thread is pretty far afield from the topic of cosmology. Religion and physical cosmology are somewhat orthogonal.

I have to disagree

[cagle_.25]

I have trouble with your post. Not an "I'm offended" kind of trouble, but an "I really disagree" kind of trouble. Here it is:

I think AC, your post comes from one who does not get it, and by rushing to the defense of religion where no assault is being perpetrated, you miss the mark completely.

Well, it turns out that parent was responding to this:

Excellent response. It's too bad religion isn't as honest in their theories.

which is certainly an attack -- it's a charge of dishonesty. Mild by /. standards, but also typical fare for this site. So, yes, there was an attack.

It is human nature to "know" how or why things are the way they are. You choose your explanation to be God. It is a nice and easy way to go about life, believing that everything has a purpose, but you do not need know what that is because you have God. Scientists, on the other hand, have a driving desire to learn. This has nothing to do with "anti-religion" or a desire to prove there is no God. In fact, you may find that quite a few scientists do believe in God or a "creator" or what have you. They just don't try to use this "God" concept to explain away the unexplainable.

I think this severely misunderstands the state of Christian thought. If you look at the work of, for example, J.P. Moreland or Alvin Plantinga, you will see that they do not appeal to God as an explanation for the inexplicable. Instead, they believe in God because they believe that the evidence points firmly in that direction.

I teach science: H.S. Chem and Physics. I have a driving desire to learn, and I try to spark in my students a driving desire to learn and to analyze carefully, critically, and honestly. I also am an evangelical Christian (to use a loaded, ill-defined term) with an (additional) academic background in theology. I guess I would fit your description of the scientist who does believe in a God. So I have no problem with your suggestion that science and Scripture might converge on "God" as the "final answer to the Theory of Everything", and I heartily endorse your suggestion that science can give us a greater understanding of God. Indeed, I teach my students to think that way.
The problem I have is that you portray scientists as neutral pursuers and purveyers of knowledge. They aren't. It turns out (speaking philosophically here) that everyone has a prior notion of the answer to the "does God exist?" question. This is why the question has been and continues to be unresolved philosophically. Our prior judgment on that question entirely colors our judgment as to what "counts" as proof of God's existence. It's a vicious circle, and philosophers have been unable to untangle it.

Scientists are no exception to the rule, and it comes out in all sorts of ways. For instance, take Richard Dawkins, chair of the "Public Understanding of Science" at Oxford. He has written extensively promoting evolutionary thought. So far, a seemingly neutral scientific question, right? But his books contain not only an scientific defense of evolution, but also several defamatory comments about Christianity. It turns out that he integrates his scientific worldview with his atheistic worldview, and uses his position to promote both simultaneously. And so it goes in the world at large. No man is a neutral player on the "God question"; no evidence is ever evaluated without a priori judgments as to how much proof is enough proof. That is where "faith" comes in. For careful thinkers, Faith is not a substitute for evidence. Instead, it is a willingness to evaluate a certain amount of evidence in favor of God's existence, over agains

Re:I have to disagree

[Red Pointy Tail]

IMHO, the only way the idea of God can stand up to any rational scrutiny is to have it pared down to first principles, like a prime-mover of God or a necessary being, that is basically unprovable. Even science relies on the basis of first principles that we take for granted but are not provable (like induction, verifiability, falsifiability...). Consider Dawkins argument on why science is not a religion and you see him lapsing rather unscientifically on his conviction and intuition. The existence of God rests on a similar insight, something you either accept or you don't, based on your intuition. It is not that philosophers have not untangled it. It is fundamentally untangleable.

I am an atheist, but that does not mean I would not be able to appreciate the position of other point of views. So why don't I accept science, but not religion? My reason is simply Occam's razor: do not make unnecessary assumptions. Given all these transcendental insights, I must draw the line on what I will believe (induction) and what I will not believe (unicorns, God). Induction and science further my knowledge of the world and is required for the world to function. As for God, to quote Laplace, 'I have no need for that assumption'. The world can get by merrily without assuming Him or Her. But not gravity. And as for the retort that God created gravity, I've no need for that assumption either. :)

[ To cover bases: argument that God is the simplest assumption you can make about the world, is a misunderstanding of Occam's razor - which does not argue on simplicity, but on neccesity. Positing a God will still require the laws of gravity to be laid out. Is God a necessary being? The jury is out there! ]

Re:Ladies and Gentlemen: The Scientific Method

[Barlo_Mung_42]

I always like this question and I think Descartes' answer is a cop out.
In truth I can't. He said "I think therefore I am" but when you read his whole argument you see that it goes in a circle.
The best I can do is say that it doesn't matter. I do think. The fact that I think may not mean that I exist (it could be your caffeine addled mind thinking I'm thinking). But it doesn't matter from my perspective. My only option is to go about my life assuming that I exist until I'm proven wrong. What is the alternative?

Re:I Wish I Was a Scientist

[Mt._Honkey]

Note: I am a physics undergrad with some galactic dynamics / astronomy / cosmology education.

What if this is only a *very* good approximation for all normal purposes, and even for things as large as the solar system (in the same way that Newtonian mechanics is good enough for all earthly based stuff).

What if gravity doesn't quite work this way at galactic scales?

This is a possibility that is NOT being ignored by the astrophysics community. There have been several attempts (presumably like the one you reference, though I haven't checked it out) to modify gravity theories much like you say. Up close they predict the orbits of planets and such very well, but over longer distances they change the behavior of gravity as to match some of the observations. The problem with them thus far is that they fail to explain every observed system, such as galaxy interactions and clustering. They can only get some parts to work, not all. This doesn't imply, however, that there is no such theory, it is entierly possible that we haven't thought of it yet.

Several decades ago, the Big Bang theory wasn't universaly accepted by the cosmology community. Another thoery, the Steady State Theory had about as big of a following. Over time though, holes and failed predictions started showing up, and they kept mounting and mounting, while the Big Bang theory kept matching new observational discoveries. It has been modified now and then (like by adding inflation), but the basic concept is still the same, and now it is thought to be true (or at least the general idea) by the vast majority of cosmologists. The mountain of observational evidence is impossible to ignore. The weaker theory has been weeded out, and the consistent one has thrived.

Maybe a new theory of gravity or some other theory will come forth that explains the same thing that Dark Matter does, and maybe it will have correct predictions where dark matter fails. If that is the case then Dark Matter will be all but cast aside. It seems extremely unlikely though, since several entierly different sources have had the same predictions for dark matter / dark energy breakdowns. Observations of type Ia supernovae in distant galaxies gave the first major hints that the universe expansion is accelerating. It gave values for the relative amounts of dark matter and dark energy. A totaly unrelated observation (WMAP) of something with no relationship to type Ia supernovae gave effectivly the same results. Big Bang Nucleosynthesis theory starts with very few premises and derives a the same ratios of various mass particles that WMAP and other more conventional observations show. It would take something truly extrodanry to overthrow this theory.

But who knows? It can still happen. The community really is open to it, if a good theory comes forth, though they have gotten comfortable where they are.

One Word:

[Betelgeuse]

Or, an acronym, actually.

MOND = Modified Newtonian Dynamics

It's one of those theories that sounds totally crackpot when you first hear it (and, admittedly, has some problems), but many would argue that it's no weirder than a bunch of dark stuff that we know nothing about. The destain with which astronomers and physicists view MOND is quite surprising, since they are asking us to be believe that (something like) 95% of the matter in the universe is composed of some sort of weird, non-Baryonic particle (most people favor WIMPs over MaCHOs now-a-days).

Anyway, just food for thought.