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Dark Matter Hinted at Again at Cresst Experiment
physburn writes "The BBC is reporting recent results from the Cresst dark matter search in Italy. Between 2009 and 2011, Cresst have seen 67 events, a 4 sigma detection of dark matter particles with a mass of either around 15 GeV or 25 GeV. The results are near those previous results from DAMA and Cogent. So has dark matter finally been found, and if so what is it?"
4 sigma detection != (officially) found. You need 5 sigma for "discovery" status. The BBC have a good explanatory piece: http://www.bbc.co.uk/news/science-environment-14811580
Dark matter always seemed like a convenient hand wave, but I'm thrilled if there's some concrete evidence of it. I do love being wrong!
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It's consistent with DAMA and Cogent in the sense that it's ruled out by those experiments at only a few sigma. It's "near" Cogent in the sense that 8 is "near" 25, and it's "near" DAMA in the sense that 35 is "near" 10; that is, it's not near at all. It's ruled out by Xenon by many orders of magnitude. My favorite theoretical model to explain these results is IDM (Italian Dark Matter), which consists of dark matter that only exists in Italy. Presumably similar particles are responsible for whatever makes Guinness taste better in Ireland.
All the way down.
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Starts with a Bang is an astrophysics professor's coverage of dark matter and what we know about it (including why we believe it makes up most of the matter in the universe.)
Lacking <sarcasm> tags,
(paraphrasing here, this was almost 20 years ago)
Friend: "Look at this! It's Guiness! Real. Live. Irish. Guiness! And I got it.... at the [insert early 90's supermarket chain here]."
Me: "Oh I've heard of that stuff. Is it really all that special?"
Friend: "What? Philistine! Look at this stuff. It's blacker than your soul. You could eat this for lunch. Many Irish do. It takes your girly American lager out back and beats it with a 2x4. Look, even the can has this automagical thingy inside it to reproduce the legendary foamy head of a real draft Guiness. This is as close as you're going to get to Ireland without a passport. Here, try some." (Friend pours small amount in a glass, jealously hoarding the rest of his six-pack)
Me: (taking a slow sip) "Hmm... yeah. That is different. Not as bitter. But... hmm... it kinda reminds me of soy sauce."
Friend: "WHAT?!?!?! You're crazy."
Me: "No. Seriously. Check it out."
Friend: (takes his own slow sip). "..."
(Former) Friend: "DAMN YOU!"
There are lots of experiments of this type running right now. This team, CRESST-II, has announced that they have more events than can be explained by their background. However, that's not really the most convincing evidence you could ask for, since the background could have been underestimated. A more convincing thing to see is that some of the experiments are reporting signals that are modulated by the expected amount on a yearly basis by the earth's motion relative to the frame of the cosmic microwave background. Here is a paper that includes a survey of the the results as of June. There are some apparent contradictions between some groups' positive results and others' negative results.
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Were there any real deniers of luminiferous aether or was everyone (who cared) shocked when a supposedly routine experiment cast doubt on its existence?
I hate to tell you, but modern physics has luminiferous aether deeply entrenched in it via BOTH relativity and quantum mechanics. Relativity calls it "the fabric of spacetime." QM calls it "vacuum."
The original concept of luminiferous aether was a medium requisite for the propagation of lightwaves. I hate to tell you, but Einstein completely debunked it via special relativity. Of course, Einstein allowed for a concept of "relativistic aether", but it is nothing like the original luminiferous aether theory claimed and only shares the concept the presence of physical properties of space. In that sense, "aether" was a regrettable choice of term on his part.
If you wish to mentally substitute "an invisible medium that suffuses the vacuum and is requisite for the propagation of light" for "luminiferous aether" in the comment above, then by all means go ahead.
I consistently see it every night after a drinking binge.
But what if light works something like this https://hekla.ipgp.fr/IMG/pdf/Couder-Fort_PRL_2006.pdf ?
The abstract talks about "730 kg days". Huh?
I hate to tell you, but modern physics does not have luminiferous aether in it whatsoever.
It's not even difficult to completely disprove aether by running an experiment to measure the speed of light and see if it various according to the direction of the earth's movement "through the aether". If light propagates using aether, then it's speed won't be constant.
I bet you think that phlogiston is still used in physics as well.
You're a temporary arrangement of matter sliding towards oblivion in a cold, uncaring universe
You are mistaken. Your parent is right. The concept of aether is indeed comming back as Gedankenexperiement or as an analogy. If you had read your parents post till the end you had seen "space time" or "fabric of space time" or "vacuum" as modern variations of the same aether concepts our for fathers had. Why don't you google? You should find many modern publications that "use" the word aether ... but not in the old classical sense.
Cost free eBook I read (by iBook/Kobo/Amazon/ObookO/Gutenberg etc.): "The Green Odyssey" by Philip Jose Farmer.
It's not even difficult to completely disprove aether by running an experiment to measure the speed of light and see if it various according to the direction of the earth's movement "through the aether". If light propagates using aether, then it's speed won't be constant.
Amusingly, the gravity wave detectors are basically the same as the Michelson Morley apparatus, and the opposite result is expected. But of course we won't call these "aether waves" when we find them- that's so 19th century!
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"I bet you think that phlogiston is still used in physics as well."
Sure. Phlogiston was believed to be a substance that was released when things burned or rusted (i.e. oxidized). The matter that was left afterward was believed to be in it's "base" state. If you extend the concept a little and postulate that phlogiston is released in any exothermic chemical reaction (oxidization being the most common and easily observable), you have... chemical energy. Extend it a little bit more to include all reactions and you have the general concept of energy.
Yes, we have different words for the concepts of phlogiston and aether, and our understanding of them is much more sophisticated, but the concepts are still there, and never really went away.
Aether for example, was postulated as an all pervading but unobserved substance through which electromagnetic waves propagated. It was HYPOTHESIZED that electromagnetic waves propagating through aether should show differences in velocity depending on whether they were propagating parallel or perpendicular to the Earth's movement through the aether. That turned out not to be the case.
Then Einstein came along and explained, with special relativity, that the speed of light is always constant to a non-accelerating observer and space and time distort to accommodate. Wait... space and time distort? Hm... interesting.
A little later came general relativity, with the concepts of distortions in the fabric of spacetime better fleshed out. And voila, you have aether, except now it's relativistic aether. Kind of like how you had Newton's laws, and then Newton's laws with relativistic terms added.
The hypothesis of CLASSICAL aether was disproven by the Michealson-Morely experiment, not the more general concept of aether.
By the way, note that the Micahelson-Morely experiment was conducted on planet Earth, in the fresh (basement) air (picture: http://e-ducation.net/scientists/Michelson_Morley_intf.gif). Wait, air? So the light was actually propagating through AIR? But if M-M proves there is no such thing as aether then shouldn't it have also proved there is no such thing as air?
Physics is mostly a story about refinements and ever more sophisticated understanding, not complete replacement of concepts. Aether and phlogiston are both examples of that. But, as the subject says, haters gonna hate. And Slashdot seems to have a lot of hate for aether for some reason.
I was referring to "luminiferous aether" which would be the medium that transmits light (if it were true). You seem to be referring to spacetime fabric as aether which would make light the equivalent of gravity waves (i.e. spacetime would be the gravitational aether that transmits gravity waves).
Aether is used as a concept, but unfortunately, too many people confuse it with the old useless theory of luminiferous aether - yourself included.
You're a temporary arrangement of matter sliding towards oblivion in a cold, uncaring universe
I replied to someone else who was confusing luminiferous aether with a concept of aether. Luminiferous aether is completely useless as a theory as you'd have to fit in so many workarounds to get it to work, whereas General Relativity fits the data so much more easily.
I don't see how you can equate phlogiston with energy as they had the entire concept of combustion the wrong way round. They believed that phlogiston was a substance inside objects that got released during combustion. This in no way explains how substances become more massive when they are oxidised, nor how oxygen is depleted from the air. I think you are playing with semantics to try to shoe-horn phlogiston into physics when it's simply incorrect.
You're a temporary arrangement of matter sliding towards oblivion in a cold, uncaring universe
If you mean specifically classical Lorentzian luminiferous aether, then yes, it doesn't work. But the basic idea of a universal, all pervading "substance" is consistent with both relativity and QM. Given special relativistic properties, the concept of a medium though which electromagnetic disturbances propagate is essentially the same as the EM field from EM field theory.
Yes, phlogiston is a little more of a stretch, but you issued a challenge. However, my interpretation of phlogiston is completely compatible with combustion, so long as you add in oxygen. Phlogiston (energy) IS a "substance" that is released from objects during oxidization, or any other exothermic reaction. Once you compensate for the masses of ALL the reactants, you can even measure it's mass! Does that mean the ancients' explanation of phlogiston was correct and based on some mystical/alien knowledge? Of course not. But it was a valid explanation of the observations they had and, beefed up a bit, is not that different than what we believe today. Ditto, and more so, with aether.
The general ideas of aether and phlogiston are not "simply incorrect" they are incorrect in some of their details. The general concepts, with appropriated extended details, are accepted as valid today. No, I'm not playing with semantics. Einstein himself hung onto the idea of aether until the 30s, probably because he liked the idea of a medium through which electromagnetism propagates, similar to the spacetime through which he saw gravity propagating. Einstein would probably have been very happy calling the the fields of electromagnetic field theory "aether."
I think you need to realize that the history of science isn't quite as black and white as you'd like to think, and pre-1930s scientists weren't quite the fools Slashdotters like to paint them as (except Tesla, Slashdot loves Tesla).
Amusingly, the gravity wave detectors are basically the same as the Michelson Morley apparatus, and the opposite result is expected. But of course we won't call these "aether waves" when we find them- that's so 19th century!
Well of course, because the phenomenon and thus expected experimental results are completely different. The gravitational potential of the detector relative to the earth will be constant, ergo there would be no distortion based on the earth's movement -- consistent with the Michelson/Morely experimental results -- whereas you would expect a difference if there was a light-propagation medium through which the earth was moving.
It's the same reason why when they detect minute changes due to seismic vibrations, they don't call those aether waves either. :P
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Let's try it another way. The idea of luminiferous aether suggested an experiment to try and find the "aether wind." If you work out the speed of light propagating in a medium through which Earth is also moving, using Newton's equations you find that you should observe a difference in speed depending on the direction the light is travelling. Michaelson and Morely (and others) looked for that difference and didn't find it.
However, if you calculate the speed of light using special relativity instead of Newtonian mechanics, you get no difference. Which is what the experiments showed. The Michaelson-Morely experiment is NOT a test of the existence of aether, it's a test of Newtonian mechanics. Note that special relativity is generally interpreted with the concept of space-time, which is a medium through which all things travel, including light, and the medium deforms and affects that movement, which is why light bends in gravitational fields (another famous test of relativity). So what you're left with at the end of the experiment is special relativity replacing Newtonian mechanics and an expanded concept of aether.
Perhaps you're the one playing semantic games and artificially restricting your definition of "luminiferous aether" to a particular formulation of the hypothesis that specifically involved Newtonian mechanics? If you read about the time you'll find that there were all sorts of different hypotheses about the aether, with different properties, and more continued to be proposed and tested after the Michaelson-Morely experiment. In fact, the scorn for aether seems to be mostly revisionist history, particularly here on Slashdot and among other armchair scientists, particularly those who ridicule the concept of dark matter. Remember, the context of this thread is dark matter. Your argument that luminiferous aether is analogous to claiming that the concept of dark matter is ridiculous because the MACHO hypothesis didn't work out.
Imagine if the 19th century test equipent had been accurate enough to find gravity waves - don't you think Michelson and Morley would have seen that as evidence of something aetheric going on? How confusing would that have been.
Ultimately, there is a light-propagating medium through which the Earth is moving - call it the vacuum, the "fabric of space time", or whatever - which can be distorted by the passage of objects, and which does act like a series of potential wells.
The nature of this medium is IMO one of the big remaining mysteries - what is actually happening down there at Plank-length scales? Is the medium continous, or a scattering of allowed loci? Does it change over time (i.e., is the medium something, or just some place)? It is observer-invariant? If we knew, we might have a workable theory of quantum gravity.
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Myself certainly not included, insult to injustice, sigh.
Cost free eBook I read (by iBook/Kobo/Amazon/ObookO/Gutenberg etc.): "The Green Odyssey" by Philip Jose Farmer.
Imagine if the 19th century test equipent had been accurate enough to find gravity waves - don't you think Michelson and Morley would have seen that as evidence of something aetheric going on? How confusing would that have been.
Maybe, but they would have realised that it was very different than the theorised medium of the luminiferous aether. They expected a consistent difference between the arm of their device parallel to the motion of the earth versus the one perpendicular, showing the effect of the earth's motion through the medium. Transient effects not aligned with or related to the earth's motion would have indicated that their theory needed to be entirely re-worked.
Saying ultimate light propagates through the medium of space-time is true in one sense, but only metaphorically similar to the type of 'medium' that the aether theory was intended to supply. The same sense in which matter is the medium for sound waves -- some kind of stuff that exists in space so that the wave can travel through space. Space is what everything including the medium travels through, but the aether was light's medium, not everything's.
These two senses of 'medium' produce different experimental predictions. So "the medium for light is space-time" is the answer equivalent to what they would have called "light doesn't require a medium of its own, it can exist in empty space itself just like matter". Luminiferous aether is what you get if you believe that isn't the case.
The ultimate nature of space-time is a huge mystery, to be sure.
I'm just saying, whatever it is, it's nothing like the aether -- we know this much from experiment. Yes, they are in some ways analogous. That's not a reason to call it "luminiferous aether" when the whole point of how we got to here is that it isn't. And so the snark was unwarranted. "So 19th century" is no problem for the things from the 19th century that weren't wrong.
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, but the aether was light's medium, not everything's.
But that's just it - that's the underpinning of modern physics right there - it's no that there's not an aether, it's that as goes light so goes the universe.
Amd this is /. - all snark is warrented, elsewise what would we read?
Socialism: a lie told by totalitarians and believed by fools.
But that's just it - that's the underpinning of modern physics right there - it's no that there's not an aether, it's that as goes light so goes the universe.
Not, that's not just it. The underpinning of modern physics is that there is no privileged reference frame, when the whole point of the aether was that it was such a frame. That frame -- the aether -- does not exist. That's the first major distinction between "modern" and the prior physics in which the aether was hypothesised. It is inherently contradictory to talk about modern physics and then say "it's not that there's not an aether" because it is an inherent consequence of the true underpinning of modern physics that there isn't.
So calling space-time the luminiferous aether is completely stupid and and categorically wrong.
That's why nobody does. Hard to believe, I know.
Amd this is /. - all snark is warrented, elsewise what would we read?
You're so right; what would people do if they had to be snarky and make sense?
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