Mysterious Dark Matter Mapped In Finest Detail Yet (bbc.com) 34
According to the BBC, the Atacama Cosmology Telescope (ACT) in Chile has traced the distribution of dark matter "on a quarter of the sky and across almost 14 billion years of time." From the report: In the image [here], the colored areas are the portions of the sky studied by the telescope. Orange regions show where there is more mass, or matter, along the line of sight; purple where there is less. Typical features are hundreds of millions of light-years across. The grey/white areas show where contaminating light from dust in our Milky Way galaxy has obscured a deeper view. The distribution of matter agrees very well with scientific predictions.
ACT observations indicate that the "lumpiness" of the Universe and the rate at which it has been expanding after 14 billion years of evolution are just what you'd expect from the standard model of cosmology, which has Einstein's theory of gravity (general relativity) at its foundation. Recent measurements that used an alternative background light, one emitted from stars in galaxies rather than the CMB, had suggested the Universe lacked sufficient lumpiness.
Another tension concerns the rate at which the Universe is expanding - a number called the Hubble constant. When [the European Space Agency's Planck observatory] looked at temperature fluctuations across the CMB, it determined the rate to be about 67 kilometres per second per megaparsec (A megaparsec is 3.26 million light-years). Or put another way - the expansion increases by 67km per second for every 3.26 million light-years we look further out into space. A tension arises because measurements of the expansion in the nearby Universe, made using the recession from us of variable stars, clocks in at about 73km/s per megaparsec. It's a difference that can't easily be explained. ACT, employing its lensing technique to nail down the expansion rate, outputs a number similar to Planck's. "It's very close - about 68km/s per megaparsec," said Dr Mathew Madhavacheril from the the University of Pennsylvania. ACT team-member Prof Blake Sherwin from Cambridge University, UK, added: "We and Planck and several other probes are coming in on the lower side. Obviously, you could have a scenario where both the measurements are right and there's some new physics that explains the discrepancy. But we're using independent techniques, and I think we're now starting to close the loophole where we could all be riding this new physics and one of the measurements has to be wrong."
Papers describing the new results have been submitted to The Astrophysical Journal and posted on the ACT website.
ACT observations indicate that the "lumpiness" of the Universe and the rate at which it has been expanding after 14 billion years of evolution are just what you'd expect from the standard model of cosmology, which has Einstein's theory of gravity (general relativity) at its foundation. Recent measurements that used an alternative background light, one emitted from stars in galaxies rather than the CMB, had suggested the Universe lacked sufficient lumpiness.
Another tension concerns the rate at which the Universe is expanding - a number called the Hubble constant. When [the European Space Agency's Planck observatory] looked at temperature fluctuations across the CMB, it determined the rate to be about 67 kilometres per second per megaparsec (A megaparsec is 3.26 million light-years). Or put another way - the expansion increases by 67km per second for every 3.26 million light-years we look further out into space. A tension arises because measurements of the expansion in the nearby Universe, made using the recession from us of variable stars, clocks in at about 73km/s per megaparsec. It's a difference that can't easily be explained. ACT, employing its lensing technique to nail down the expansion rate, outputs a number similar to Planck's. "It's very close - about 68km/s per megaparsec," said Dr Mathew Madhavacheril from the the University of Pennsylvania. ACT team-member Prof Blake Sherwin from Cambridge University, UK, added: "We and Planck and several other probes are coming in on the lower side. Obviously, you could have a scenario where both the measurements are right and there's some new physics that explains the discrepancy. But we're using independent techniques, and I think we're now starting to close the loophole where we could all be riding this new physics and one of the measurements has to be wrong."
Papers describing the new results have been submitted to The Astrophysical Journal and posted on the ACT website.
Post it already (Score:1, Funny)
This totally ought to go onto that "dark web" journos keep on yabbering about. Mysterious dark matter onto the mysterious dark web, already!
Re:Post it already (Score:5, Informative)
You don't have to trust the science. We get progress by proposing models. Sometimes the model is right, and sometimes it is wrong.
Luminiferous ether came from the evidence that light is a wave (Young's slits, etc.) and all known waves travel in a medium. But there is a vacuum! - Proposal: it travels on a medium ("ether") with interesting properties. - Long term outcome: after Michelson-Morley, etc., it's OK to have waves in a vacuum.
The Neutrino was proposed because energy didn't seem to be conserved in beta decay. - Proposal: a nearly undetectable particle carries away energy. - Long term outcome: neutrinos were eventually discovered after 20 years or so.
Dark matter aims to explain why rotating galaxies don't fly apart. - Proposal: nearly undetectable particles interact with normal matter gravitationally. - Long term outcome: We don't know yet.
Dark matter as proposed does not interact electromagnetically, so it shouldn't occlude views, or glow, as those both rely on interacting with EM waves.
Re:Post it already (Score:4, Informative)
If scientists propose new stuff it has to be consistent with what we observe. They couldn't propose a charged neutrino, as that would not have been consistent with charge conservation in beta decay. They had to propose the neutrino carrying away energy, as otherwise it doesn't solve the energy conservation problem. I don't see those as circular arguments, and if you think most of theoretical physics as being circular then you are missing huge triumphs of the standard model, like explaining an enormous zoo of hadrons in terms of a small number of quarks.
It's well known that the standard model can't be the full story. For example, the big scale stuff (general relativity) and the small scale stuff (quantum mechanics) will have to be included as limiting cases in some larger theory, just like Newtonian mechanics is true for v<<c. So it's great to fill in gaps (the Higgs), but the theory doesn't cover everything. Getting upset with the popularizers of science is not a good use of anyone's time.
Re:Post it already (Score:4, Informative)
Everyone is allowed to question the science and demand better explanations at need.
Demand politely of course! I'm sometimes surprised how little context the angry people have: they aren't aware that neutrinos weren't detected for long time, that Ceres and Pallas were once classified as planets, or that humans and animals have swapped diseases from the dawn of humanity. So good faith, humility, and politeness would be good starting points.
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"good faith, humility, and politeness would be good starting points."
Why are these emotional factors so important to science? What does tone have to do with anything but feelings?
If scientists are that sensitive, how afraid are they of going against the consensus because it's just not polite?
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I wasn't trying to imply that scientists are sensitive, but rather thinking of the Pluto hate directed at Neil DeGrasse Tyson (mentioned by the GP) by people who don't know much context. I think good faith, humility, and politeness would be good in a lot of situations, and we tend to overestimate the net benefit of rudeness.
Emotional factors are not in any way important to science. Conversations between peers can obviously get heated, of course!
It's funny you should talk about "feelings" as there is quite a
Re: (Score:3)
Neutrino: competing theories (energy non-conservation, magic particle)... see which one matches the data best over a range of observations
Dark matter: competing theories (many [wikipedia.org], including MOND, magic particle)... see which one matches the data best over a range of observations
It is science.
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Dark matter is the ultimate example of what's wrong with SCIENCE.
Problem: Our theory of gravity doesn't work at galactic scale or above. Is the theory wrong?
Answer: NO! There must be more matter around that explains the discrepancies.
Science is the very process of making theories that match observed facts.
That is the definition of science. That's why dark matter is a perfect example of science happening.
Science, all of us here, and reality, none give a shit that you personally believe the theory isn't wrong.
Our observations do not match the theory.
How can you even logically argue "Is the theory wrong? NO" ???
Your argument falls flat the second your pet theory doesn't match observation.
You can keep claiming it isn't wrong all you want,
Interesting (Score:2)
That would mean that "dark matter" is no longer a placeholder, and is just matter.
No matter, it doesn't matter, no matter what is the matter.
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Um no. It is dark matter because it has the properties that normal baryonic matter does not have. For example it does react with, absorb, or emit EM radiation.
Seems like it isn't matter then. No matter. Before we go too far, I'm just having a bit of light fun this morning.
The Dark Matter Nursery Rhyme, by Ol Olsoc
Oh dear, what can the matter be,
Oh dear, universe ain't right to me
Oh dear where can the matter be,
Dark matter's the answer for me.
It's 80 percent of all universe matter
We can't see it though it should be on a platter,
Enough to make physicists mad as a hatter,
Dark matter's the answer for me.
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Might want to google what matter is.
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Might want to google what matter is.
Ah, ya might want to get a sense of humor, homie. Then again nahh, Show that guy what wrote the children's rhymes with your known facts.
Anyhow, If you are going to be serious, let's have a line by line refutation of what I wrote, with peer reviewed citations showing the faults in a silly little joke. Then tell us exactly what the nature and composition of dark matter is. You know exactly what Dark matter is, amirite? So share it with the world.
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Seems like it isn't matter then.
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Seems like it isn't matter then.
Strange attributions, fo shizzle.
Then as Slashdot's ranking cosmologist, What exactly is it? Don't say dark matter. Seems like most of the world doesn't know, and uses "dark matter as a placeholder, and have a number of candidates for this dark matter, which is apparently 85 percent of all the "matter" in the universe. That is a pretty big amount of unseen and unknown matter. I don't care about what you think about my nursery rhymes either - I want you to inform us exactly what dark matter is.
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Re:Interesting (Score:4, Funny)
They've determined that "Dark Matter" is matter and know the mass of it?
About three seasons [wikipedia.org] :-)
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They've determined that "Dark Matter" is matter and know the mass of it?
About three seasons [wikipedia.org] :-)
This is the best reply yet. I mean that. At least it is unambiguous! 8^)
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They've determined that "Dark Matter" is matter and know the mass of it?
About three seasons [wikipedia.org] :-)
This is the best reply yet. I mean that. At least it is unambiguous! 8^)
I would have enjoyed the show continuing, but (apparently) SyFy was going to cut either Dark Matter or Killjoys [wikipedia.org], for cost reasons, and I enjoyed Killjoys more so was okay with that decision. I'm also not sure where the story line was going in Dark Matter...
Quartz (Score:2)
Interesting similarity to amorphous crystaline structures.