Evidence Points to the Detection of Dark Matter

[trish]

http://www.guardian.co.uk/science/20...atter-detected

[BrendaQG]

Right now the media is over hyping this.

Dan Bauer, head of the Cryogenic Dark Matter Search (CDMS), said the group had spotted two particles with all the expected characteristics of dark matter. There is a one in four chance that the result is due to some other effect in the underground detectors, Bauer told a seminar at the Fermi National Accelerator Laboratory, near Chicago.

A 1/4 chance that this is some other random effect is as good as not having a discovery at all. At Fermilab the scientist will not say they have detected the particle until they have eliminated all the uncertainty out to 6 standard deviations. In plain language, a lot less than a 1/4 chance of random error. This is as good as no detection at all.

In short I agree with the comments in the comment thread. This is a statistically insignificant measurement.

In terms appropriate for Hung Angels. It's like saying that a tranny who's non-functional 1/4 of the time is 100% guaranteed functional.

[El Nino]

Cool article, Trish. Thanks for posting. If it does turn out a positive result, this is an epic scientific discovery. I wonder what "it" is exactly?? Can it even be explained using current vocabulary? I also am curious as to why the detection experiments were carried out at the bottom of a mine? Is it because there are fewer molecular compounds present in the air? And if Dark Matter is down there, does it also pervade everywhere on this planet? Hmmm, all so very interesting.

[hippifried]

For 80 years, it has eluded the finest minds in science. But tonight it appeared that the hunt may be over for dark matter, the mysterious and invisible substance that accounts for three-quarters of the mass of the universe.

So... If nobody's ever actually found any of this stuff before, how do they know it makes up 3/4 of the mass of the universe? Sounds more like hubris than science.

[BrendaQG]

Cool article, Trish. Thanks for posting. If it does turn out a positive result, this is an epic scientific discovery. I wonder what "it" is exactly?? Can it even be expained using current vocabulary? I also am curious as to why the detection experiments were carried out at the botom of a mine? Is it because there are fewer molecular compounds present in the air? And if Dark Matter is down there, does it also pervade everywhere on this planet? Hmmm, all so very interesting.

We don't really know. The type of search that was being done was looking for so called "weakly interacting massive particles" or WIMPS. These WIMPS were supposed to only interact by gravity, and by the weak atomic force. Essentially the only way they could interact with normal matter is by directly hitting it, dead bang on the nucleus.

The detectors were large tanks filled with fluid and lined with very sensitive light sensors. When a WIMP hits a atom in the fluid it would release a flash of light. Until now these flashes could not be attributed to WIMPS.

Supposedly there is much more dark matter in the universe than there is normal matter. In turn there is more dark energy than either normal matter, or dark matter. It must pervade everywhere and be all around us.

It has taken decades of operating these experiments to get even a marginal signal, if it takes decades to detect two more possible particles; then I think scientist should reconsider how much dark matter there is, if any. This observation needs to be replicated by another group of scientist in order to be validated.

It was originally proposed to balance our observations of the universe with Einstein's theory of general relativity.

[El Nino]

Mathematics, Hippi.

[BrendaQG]

For 80 years, it has eluded the finest minds in science. But tonight it appeared that the hunt may be over for dark matter, the mysterious and invisible substance that accounts for three-quarters of the mass of the universe.

So... If nobody's ever actually found any of this stuff before, how do they know it makes up 3/4 of the mass of the universe? Sounds more like hubris than science.

Exactly!

I said in a colloquium I spoke at a while back that , if there were as much dark matter as they say we could just about flap our arms and fly through it.

The longer the interval between supposed detections is the less of it there must be.

As for the timing of this kind of thing. Follow the money. Cuts mark 'sad day for British science' "Researchers criticise government U-turn as major projects are closed down and studentships slashed"

This is the inevitable result of a bad economy. Displaying results which can justify sitting in a hole and collecting a paycheck is good business.

[El Nino]

Thanks for the reply, Brenda. I was aware of the popular theory of D energy and D matter being present in the known universe but have not studied a whole lot about it as I am a cell biologist. Maybe it is kind of like an inter-dimensional entity or energy, it's source of which is undetectable. Anything is possible at this rate...

So you said that this was originally proposed to establish some equillibrium to "holes" Einstein's Theory of Relativity?

[BrendaQG]

So you said that this was originally proposed to establish some equillibrium to "holes" Einstein's Theory of Relativity?

Yep. General Relativity, the modern theory of gravity, by itself predicts the wrong distribution of velocities for stars in a galaxy. If the universe is filled with only normal matter and energy it gets the wrong results for a number of other observed cosmological facts.

The alternatives are much more complex theories of gravity. GR is already so complex that most physicist give up trying to understand it. In a class of 20 students only four finished the course in general relativity I took. There is a real desire to not have to create a more complex theory. If dark matter exist it makes life relatively simple.

The real straight talk on this is in Scientific American. "Dark Matter Researchers Still in the Dark as Underground Search Returns Uncertain Results"

Even so, Cooley and her colleagues calculated that the detectors could be expected to pick up approximately 0.5 WIMP-mimicking background events in the course of acquiring the newly unveiled CDMS-2 data set, a run that spanned 2007 and 2008. Even with a more cautious look at background sources, the CDMS team came to an estimated background contribution of 0.8 event.

I am not a particle physicist per se, I specialize in cosmology. But as I understand this a new detector being built will have an 80% chance of detecting a random event that will be indistinguishable from dark matter.

How the heck does such a mess get funded? While I must struggle just to get a student loan.

[trish]

While I was composing this Brenda already made most of the points I wanted to make. But I'll post it anyway.

So... If nobody's ever actually found any of this stuff before, how do they know it makes up 3/4 of the mass of the universe? Sounds more like hubris than science.

Brenda’s right to say we don’t know. Dark matter was hypothesized as a possible for a problem that arose in attempting to understand how galaxies “spin” around their centers. The velocity of a star’s orbit around galactic center depends on its distance to that center, but not in the way Newtonian gravity or general relativity predict … unless there was a significant amount of undetected matter yet to be found in each galaxy. Dark matter isn’t the only way around the observation/theory discrepancy. Another possibility is that general relativity is wrong on galactic scales. There have been a number of people promoting various “modified theories of gravity” in opposition to the dark matter hypothesis. Fewer scientists were willing to take this route because general relativity seems to be very well tested on the large scale. The dark matter hypothesis gained ground as observations of colliding galaxies seems to exhibit dynamical features that confirmed the DM hypothesis, and also as particle theorists were quick to provide possible candidates for what dark matter could be.

Newspaper articles that state scientific advances as facts (especially advances as speculative as this one) do in fact make the endeavor seem like an act of hubris. Most of my colleagues are in fact quite humble and quite willing to hedge their claims like I did with the title of this post, “Evidence Points to …”