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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.
"I don't think you appreciate the gravity of the situation."
I've abandoned my search for truth; now I'm just looking for some useful delusions.
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.
Does dark matter have anything to do with string theory? I thought those were more or less independent ideas.
The Quirkz Handbook of Self-Improvement for People Who Are Already Pretty Okay
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.
The Michelson-Morley experiment was experiment that turned up nothing, and lead to the development of general relativity. Perhaps this experiment will also turn nothing into something.
When all you have is a hammer, every problem starts to look like a thumb.
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".
Um, you do realize that scientists do have experimental evidence that dark matter exists indirectly, right? Not just one way but at least two different ways, scientists have been able to estimate the total mass of energy and mass. The problem is that the estimate of the known mass and energy that they have been able to detect is about 5% of the universe. That means 95% of the mass and energy is unaccounted. This experiment was a way to detect dark matter directly.
Well, there's spam egg sausage and spam, that's not got much spam in it.
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.
And also the huge affect it has on gravitational lensing -- or rather, there being far too much gravity within the galaxies producing the gravitational lensing for the amount of visible matter we know the given galaxy to hold.
Funny how ACs who are entirely ignorant of a subject imagine themselves to be experts with great insights.
Second class citizen of the New Gilded Age
The mass distribution in the galaxy can be determined by measuring the orbital velocity of stars at different distances and positions, which includes not only stars in the galactic disk but a spherical halo that surrounds the entire disk. It turns out that most of the mass of the galaxy is in that apparently nearly empty halo. We can rule out invisible gas, black holes, and any form of solid matter or known particles as the source of this mass, because we could detect them with other means at our disposal. Whatever is contributing all that mass hardly interacts with anything at all, except by gravity. It is not normal matter or anything we currently understand in physics.
Second class citizen of the New Gilded Age
We'll find so much dark matter if I am elected, you may get bored with dark matter! Believe me, I agree, you'll never get bored with matter. We never get bored. We are going to turn this matter around.
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.
The mass of the EM is accounted for in the 5% referred to above. All the "stuff" we can detect (mass and energy combined) only add up to 5% of the apparent total mass required to explain the effects we see.
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.
The observations are not wrong. Measuring the velocity dispersion of stars in a globular clusters is not a much harder, or more conceptually difficult, than measuring the colour of a fluorescent light. Determining a galactic rotation curve is a bit more complex, but not much so. These observations have been done tens of thousands of times using many different techniques, sometimes by groups of astrophysicists who hate each other and would like nothing more than to discredit the person who got to speak instead of them at last January's AAS meeting. The observational evidence for dark matter is overwhelming. The modeling, on the other hand, has more assumptions built in. The key assumption is that gravity, in the weak limit, follows Newton's law of gravity, and there is a 400 years of evidence to support that.
Just because you are paranoid does not mean that no-one is out to get you.
Right, a theory. But if you can't count it, can't measure it, does it really exist?
You're not listening: There is experimental data. DATA says that dark matter exists indirectly. Measuring directly is the hard part. It's not theory. Again please read what I wrote above. Measuring the total amount of mass and energy in the universe, physicists are about 95% short of the amount for which they can directly account. So either every instrument and measurement they have is wrong; or you just don't understand science.
Secondly, string theory has nothing to do with dark matter. String theory is an attempt to resolve gravity with quantum mechanics. If String Theory never existed, there would still be the dark matter/dark energy problem. Please read up on some science before commenting further.
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But we just proved it doesn't exist.
No, that's not what TFA says at all. You can't even blame a misleading Slashdot headline here: you just made that up. A detector was built to find a very specific kind of matter. It didn't find anything. No real surprise, as there was never any reason to think it would - it was just the sort of detector we already knew how to build.
Hence, my theory is just as valid, that EM has both mass and is a wave
Yes, that's called "Quantum Field Theory", and it's what nearly everyone believes. Doesn't explain anything that dark matter explains, though, so no.
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.
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But we just proved it doesn't exist. The missing mass exists.
Um no. They haven't detected it yet does not mean it doesn't exist. it was an experiment failure. It's hard to prove a negative. That's like saying the Higgs Boson particle was proven not to exist until they detected it. See how silly that sounds?
Hence, my theory is just as valid, that EM has both mass and is a wave, and we're just confused little podlings who will have to go back and adjust our theories again, as we did over and over and over.
You don't have a theory. That's conjecture.
Remember, at first we didn't think light bent due to gravity.
Yes but that doesn't mean neither light nor gravity existed. We didn't know about the interaction between them could produce such results.
Well, there's spam egg sausage and spam, that's not got much spam in it.
LoL. That may be an apt comparison, but we definitely know something is going on, and dark matter seems the most likely explanation. All this failure to detect really means is that several of the suspected types of dark matter are definitely not there, so now that have to look for the others. Either they'll find those, or fail to find them and someone will have to figure what less likely thing is causing those effects we've definitely seen that we thought was caused by dark matter.
It's kind of like the ball and cup game, except we get to keep looking without reshuffling the cups. Eventually we'll find it, even if it's in somebodies pocket.