Slashdot Mirror
Scientists' Biggest Search For Dark Matter To Date Just Turned Up Nothing (sciencealert.com)
Peter Dockrill, reporting for ScienceAlert: For something that's hypothesised to make up more than 80 percent of the mass of the entire universe, it's no easy thing to detect the existence of dark matter. That's the conclusion the world is coming to today, after scientists announced that a massive $10 million experiment to find traces of elusive dark matter particles had failed after an exhaustive 20-month search. "We've probed previously unexplored regions of parameter space with the aim of making the first definitive discovery of dark matter," said physicist Cham Ghag from University College London in the UK, one of the scientists who took part in the Large Underground Xenon (LUX) project based in South Dakota. "Though a positive signal would have been welcome, nature was not so kind! Nonetheless, a null result is significant as it changes the landscape of the field by constraining models for what dark matter could be beyond anything that existed previously."Ars Technica has more details.
A null result is actually more valuable than an inconclusive result would have been.
From Ars:
The LUX detector (Large Underground Xenon) is designed to pick up signs of weakly interacting massive particles, or WIMPs, when they engage in one of their rare interactions with normal matter.
There are indeed other candidates for dark matter, WIMPs being only one of those. This experiment searched specifically for WIMPs, which only rules them out, while of course the other remaining candidates remain to be explored.
nothing to do with string theory, it's the search for why the stars in even our own galaxy have the orbits they do, and why the cosmic microwave background has certain imprints in it
The orbital period of a star in a galaxy depends, to first order, on the amount of mass that is closer to the centre of the galaxy than the star. (That's a consequence of gravity being an inverse-square force.)
The distribution of stellar orbital velocities in a galaxy indicates that there is additional mass, not at the centre, but distributed amongst the stars in a galaxy. An inventory of the visible mass shows there is nowhere near enough to account for the velocity distributions. Therefore, it is inferred that there is invisible, or dark matter, that accounts for the discrepancy. It has nothing to do with mismeasuring the mass at the centre of the galaxy, whether it's a black hole or not.
A null result is only a "fail" if you're not actually interested in science.
>the dark matter explanation feels a bit hacky anyway.
Dark matter isn't the explanation, it's the question.
We observe things like: https://en.wikipedia.org/wiki/...
but we don't know what is causing them. "Dark matter" is just a short way of saying "whatever it is that is responsible for these things we are observing".
If you can come up with some way to modify gravity in such a way match more than one or two of the dozen plus lines of evidence supporting dark matter, you've got a guaranteed PRL publication. Of course every attempt so far has failed pretty miserably.
Right, a theory. But if you can't count it, can't measure it, does it really exist?
But we can measure it. Its gravity reveals its existence, its quantity, and its location. So yes it exists. We just don't know what it is, and the detector experiments are testing theories about what it may be.
We also have pretty good estimates of the density of dark matter in the solar neighborhood. It amounts to 0.49 ± 0.13 GeV cm3. This means, if you weight 70 kg, your body contains about 34 trillion electron-volts of dark matter (or 6*10^-20 grams).
Second class citizen of the New Gilded Age
They do not entertain the idea that maybe their laws are wrong, or that some other phenomenon might be affecting gravity.
Sure, MOND never happened.
Many people have spent a lot of time looking for ways to explain single like galaxy rotation curves, stellar velocities in globular clusters and elliptical galaxies, the structure of galaxy clustering and what-not without success. The simplest explanation has always turned out to be that there is some sort of extra matter that we cannot see. Dark matter requires the smallest number of assumptions out of all explanations that people have proposed so far. By Ocham's Razor it is probably the right solution. And by Grabthar's Hammer you shall be avenged.
Just because you are paranoid does not mean that no-one is out to get you.
No, it is more than that. Astrophysicists give the attribute of "gravity" to dark matter. In fact, that was the reason they promulgated the idea, i.e., galaxies would fly apart otherwise so there must be something we cannot see which supplies the extra gravity.
They do not entertain the idea that maybe their laws are wrong, or that some other phenomenon might be affecting gravity.
That was true quite a few years ago, when there were many theories for galactic rotation rates, including MOND (precisely "the idea that maybe their laws are wrong"), hot dark matter, and cold dark matter which might be WIMPs or MACHOs.
Then we got more data.
WIMPs won out because they also explain gravitational lensing and the early universe. The cosmic microwave background radiation observations were decisive. The predictions made WIMPs were right on the money - turns out the early universe had just the predicted amount of (a) matter, that (b) wasn't moving near the speed of light, and (c) before block holes, brown dwarfs, etc could have formed.
That's how science works. Scientists do not lack creativity - there was a whole forest of ideas to explain galactic rotation rates. But as more observations of unrelated phenomena come it, only "some sort of particle" was left standing. Falsifiable theories were falsified.
This experiment was a bit silly IMO - it was just a detector much like the detectors we built for neutrinos, which had never shown any signs of dark matter before. It was very much a case of "well, we know how to build this sort of detector already, so let just build a big one and hope for the best".
Socialism: a lie told by totalitarians and believed by fools.
So, um...indirect experimental evidence is not actually empirical. It is absolutely, completely un-the-same as experimental evidence.,
Um, no you don't understand. There is direct evidence that we can measure the total amount of mass and energy in the universe. However, 95% is unaccounted for if we count all the stars and planets scientists think exist. Therefore indirectly, dark matter is the placeholder for the matter that should exist but can't detect. They could have called it Zoidberg matter and it would be the same.
It's like looking at the ocean. With the naked eye we can only see the top layers of the ocean. Historically, sonar allows us to determine the depths of the ocean to be miles deep; however, until the existence of deep underwater vehicles, scientists didn't know what the bottom was like. They could only guess. They could not imagine that life exists near the Marianas Trench for example.
The case for dark matter is more inductive or abductive reasoning. Given certain premises based on our current understanding of gravity and our observations of the universe, dark matter makes sense. However, our observations could be wrong, or our models could be incorrect.
Yes everything in science could be wrong; however, you must prove that every one of their observations is incorrect rather than assume that because someone doesn't have all the answers, they don't have any answers.
Well, there's spam egg sausage and spam, that's not got much spam in it.