[Flipside]

http://news.bbc.co.uk/today/hi/today/newsid_9715000/9715092.stm

Audio clip talking about the suspected volume of Dark Matter being much lower than anticipated in the local area around Sol, and of strange behaviour with regards to Cosmic Rays and the lack of any Neutrinos that would point to their source.

Just thought some people might find this interesting

[Bobboau]

clearly the only explanation is Cthulhu, his coming nears.

[watsisname]

Paper regarding the Dark Matter Survey

Hungh, that's interesting, indeed.  :|a  So apparently there is very little DM in our solar neighborhood, which if correct would mean that any of the planned missions to detect DM particles directly in our solar system would be doomed to fail.  It would also mean that either DM in our galaxy is much more non-uniformly distributed than we thought, or it takes the shape of a very Prolate Spheroid (as opposed to spherical as is usually assumed).  Prolate structures are difficult to explain though, and the ΛCDM models don't produce them very well.

The authors caution that there's no simple explanation for their results, and await further study such as the planned GAIA survey.

[Cyborg17]

Reflects what I've suspected to be true for a long time: dark matter is a poor explanation for the state of the universe.  It just doesn't fit well with other parts of how we know the universe works.  Sure brown dwarf stars and such dark matter *objects* exist, but mysterious stuff we fly through without interacting with which is inferred only by its gravity seems like a solution that was suggested simply because it was a perfect solution to a problem.  Solutions like that don't usually bear out to being true.

I'm not saying that such particles are necessarily non-existent, and I can't give you an alternative, but I find their existence very unlikely.

[watsisname]

Reflects what I've suspected to be true for a long time: dark matter is a poor explanation for the state of the universe.  It just doesn't fit well with other parts of how we know the universe works.  Sure brown dwarf stars and such dark matter *objects* exist, but mysterious stuff we fly through without interacting with which is inferred only by its gravity seems like a solution that was suggested simply because it was a perfect solution to a problem.  Solutions like that don't usually bear out to being true.

I'm not saying that such particles are necessarily non-existent, and I can't give you an alternative, but I find their existence very unlikely.

There is a great deal of observational evidence for the existence of dark matter, and none of the alternative explanations, like modified gravity, have worked out very well thus far.


Also, check this out.

It is clear that the local surface density measured in our work, extrapolated to the rest of the
Galaxy, cannot retain the Sun in a circular orbit at a speed of ∼220 km s−1. A deep missing mass
problem is therefore evidenced by our observations.

[CommanderDJ]

Reapers.

[Cyborg17]

There is a great deal of observational evidence for the existence of dark matter, and none of the alternative explanations, like modified gravity, have worked out very well thus far.


Also, check this out.

It is clear that the local surface density measured in our work, extrapolated to the rest of the
Galaxy, cannot retain the Sun in a circular orbit at a speed of ∼220 km s−1. A deep missing mass
problem is therefore evidenced by our observations.

I already know what you're talking about. All we've observed are problems which are solved by this abstract solution.  And now, this article shows that this theory is now running into problems.

And how exactly is the speed of the Sun's revolution measured?  It's probably been inferred by the rotation of other galaxies rather than directly observed.  Which means that we're not even sure exactly how much dark matter would be needed to keep us in the Galaxy.

The problem with Astronomy is the one observer problem.  You have one eye, the solar system, to study the entire cosmos, and you cannot move that eye.  Therefore we are prey to optical illusions, error, and geometric limitations.  We may make many telescopes on the earth and even launch them into space, but such differences of distance are nearly meaningless when observing other galaxies.

My point is that there will be many things which we believe are true about the universe now which will not hold up as we thought they would in fifty years, and dark matter is probably one of them.

[watsisname]

When a discrepancy between theory and observations is found, scientists devise possible explanations for it.  These explanations are then tested via observation to see what holds up and what does not.  The theory is thus improved, and science progresses.  Dark matter has been the most successful explanation so far.  Modified gravity is the leading contender, but thus far hasn't been able to make predictions that would confirm it over GR/DM that have been verified observationally.

But let's assume that dark matter is incorrect, what then do you propose as the solution to the problem?  Do you think a modification of our understanding of gravity is necessary (an even more contrived solution by your reasoning)?  Or do you think there is not a problem in the first place -- galactic rotation curves are wrong, velocity dispersion data is wrong, gravitational lensing data is wrong, Bullet Cluster observations are wrong, CMB observations are wrong, ΛCDM model of cosmology is wrong?  That's a lot of evidence to go against.

But hey, if it's the latter, help demonstrate it to the scientific community.  You might get a prize for your work!

And how exactly is the speed of the Sun's revolution measured?  It's probably been inferred by the rotation of other galaxies rather than directly observed.  Which means that we're not even sure exactly how much dark matter would be needed to keep us in the Galaxy.

Instead of assuming that you know how astronomers figure things out, try reading up on it for yourself.  A quick search on google scholar or ApJ might have helped you there.  I think this excerpt from one of those papers is quite noteworthy:

Positions of Sgr A relative to the background source J1745-283 for epochs spanning 2 yr are plotted in Figure 1 with open circles.  They indicate a clear apparent motion for Sgr A* relative to J1745-283, consistent in magnitude and direction with the reflex motion of the Sun around the Galactic center.  The positions in the east-west direction have typical uncertainties of about 0.1 mas, as estimated from the scatter of the postfit position residuals about a straight-line motion.  It is interesting to note that, while it takes ~220 Myr for the Sun to complete an orbit around the Galactic center, the east-west component of the parallax from only 10 days motion can be detected with the VLBA!

Yep, we can actually see the parallax effect from the sun's orbital motion over a period of just 10 days.

The problem with Astronomy is the one observer problem.  You have one eye, the solar system, to study the entire cosmos, and you cannot move that eye.  Therefore we are prey to optical illusions, error, and geometric limitations.  We may make many telescopes on the earth and even launch them into space, but such differences of distance are nearly meaningless when observing other galaxies.

We can't trust the results of astronomical observations because we're stuck in one place?  So what?  The light from the whole Hubble Volume constantly falls on us, and we are constantly studying it, making theories, and testing those theories against that evidence.  Maybe the whole universe is lying to us, but I think that would be a pretty ridiculous philosophy to hold.

As for errors and whatnot, astronomers can and do account for this just as any other scientist does.  Optical Illusions?  You mean like gravitational lensing?  Geometric limitations?  Sure, we can't see galaxies blocked by the dust of our own galactic disk.  Differences of distance?  So what?  There is the cosmic distance ladder.

edit for typos

[Cyborg17]

My point is this: chances are that the phenomena we are observing are caused by things we don't understand yet.  Dark matter if it exists, probably doesn't behave the way we think it does and may not exist for the reasons we could think it does.  There also could be a more complex solution than just dark matter.  It could include dark matter *and* modified gravity.  It could be something we've never thought of.  (Though, I admit, it's probably impossible not to come up with an exotic solution to this problem.)

Assuming that the leading theory is always right can work against us as we try to understand the universe.  That's all I want to say.

[watsisname]

Right, we are not saying that DM is the correct explanation, just that it's the most successful one thus far, and the ΛCDM model is one of its greatest achievements.  That said, we have not given up on alternatives and likely will not for as long as there are any that agree with observations.  In the end, one will get enough support to be accepted above the rest, or a new one will be proposed that overrides everything.

That's part of the reason why this paper is so interesting and helpful; it puts more constraints on DM and other theories.

[redsniper]

Assuming that the leading theory is always right...

We're not and neither are any good scientists. It's just the best explanation to fit our observations for the time being. It would be good to find stuff that supports it, and it would be good to find stuff that debunks it. More knowledge is good either way, whether it confirms what we already think or leads us to new ways of thinking.

[Ghostavo]

"Yo momma is so fat, leading physicists are having trouble including her in the standard model..."

[Astronomiya]

So this paper got discussed at department Coffee today.  Suffice it to say, the postdoc who presented it was not very impressed with it.  Apparently the authors fail at error analysis (and seeing their quoted errors in a related paper which provided the data for this one, I'm inclined to agree), and also make a couple of very weird assumptions about local galactic dynamics.  They also assumed no flaring of the galactic disk, but if you introduce even a small amount of it, there's a plot in the paper which shows that their model goes to ****.  I'm not buying this result.

[Mika]

Yeah, I confess I have been thinking for several years that maybe the problem is not in the exotic particles or unknown matter or in unknown energy, but possibly just on the distances and in the measurements themselves. The thing is, Science works with the current evidence at hand, and this is the best we have. No-one has figured out yet what could possibly be wrong with the data, so I accept their results - yeah I have an inkling it might be that there is a systematic error somewhere, but since I can't find it then they know better. I'm not educated as an astrophysicist, only as a physicist, and lack the knowledge of a historical observation line leading to the current theory. And to be honest, I don't care enough to learn it, so I just let it pass. Not my cup of tea.

[z64555]

Wouldn't it be a huge downer if the Dark Matter phenomenon was the unfortunate effect of floating point round off errors?

[Nuke]

i doubt it. im sure some academic has done it all the math by hand just for the hell of it. im also sure that scientists would probibly be using some kind of high precision fixed point structure for accuracy's sake. a fixed point number of 128.149 bits can represent all floating point numbers. say a 512.512 bit fixed point number would do the trick nicely. math can be done with an integer unit, without any float wonkyness. not single cycle operations though.

[The E]

The discrepancies between the observed reality and the standard models is waaaayyyy too large to be explained by float inaccuracies.

[Dragon]

And yet, it works perfectly fine in other places (like predicting the mass of the Higgs boson). That's why I hoped they won't find this boson where they did. Then, I could write a new model after I finished studying quantum physics. Anyway, this entire "dark matter" seems fishy to me. There has to be some better explanation and I'm going to look for it.

[The E]

You're an idiot. There is no grand unified theory of everything yet; Dark matter is needed to explain the observations we can make with telescopes; there is no known link between it and what is happening in quantum physics at the moment.

[General Battuta]

If there's anything fishy in the physics that will let us remove dark matter from our models, it's the way gravity behaves at long distances.