New weight unit!
A re-analysis of radio telescope observations from three countries has yielded a surprising result: nearby galaxies harbour one-third more hydrogen than had previously been estimated. While nothing like enough matter to solve physics’ “dark matter” problem, the work by CSIRO astronomer Dr Robert Braun (chief scientist at the …
I think we need some new icons here - a brown pint for when a comment really deserves a beer to complement the yellow largery (fosters?) one when a comment is good enough for you to get one for yourself.
Or we could ask all foreign articles like this to be passed through Google Unit Converter before printing. Though a lot of countries don’t have real words for real pints poor sods.
See, the author was using Aussie Units of Measure, because the article really speaks to the fantastic science that is being done here in Australia (I'm writing this from Melbourne today). Now, IF the US was doing really cool things, then the units would be either robins to deer, or bibles to obese children. You know, things that are common in that country. However, as the majority of the US seems bent on thinking that the world is only 600,000 years old, and that evolution didn't really occur, and that you didn't _need_ a Superconducting Supercollider, and that most public schools should have their budgets slashed for teaching science (expensive subject compared to Home Economics or Gang Looting)...well then, I guess we should get used to more stories with weird, non-American units of comparison. Up next, El Reg will use the silkworm to panda ratio when they discuss just how badly China is out-researching the US...
And what about relative absorption of other, heavier free elements? While there are less of them around, they're heavier. Again, it may not solve the dark matter problem in the calcualtions, but it could provide another echidna or three'2 worth of those 30 echidnas in the Large Kangaroo-sized hole in the equations.
Dr Braun notes that “Although there’s more atomic hydrogen than we thought, it’s not big enough to solve the Dark Matter problem. If what we are missing had the weight of a large kangaroo, what we have found would have the weight of a small echidna.”
/Sign this is getting older than "I for one welcome or weigth of kangaroo overlords"
Is that the way it reduces the dark matter problem. Ok it only reduces it by 2-5% (or whatever the kangaroo/echidna mass ratio is) but is shows that there are still opportunities for visible matter explanations instead of dark matter - that are within an order of magnitude of the dark matter estimate itself.
Put it another way 19 more echidna sized breakthroughs and the need for dark matter goes away.
(and the need for dark matter goes away.)
About bloody time too, the sooner we get rid of this magical dark matter, that can't be detected what soever, the better.
Except to balance our accepted theory of the universe, nothing else in astronomy or sub atomic theory, supports it's existence. Either the missing mass is out there in good old fashioned mass somewhere, or our theory of the universe is wrong!
"nothing else in astronomy or sub atomic theory, supports it's existence."
No: Nothing in theory. Only our actual empirical evidence and observations.
Of course we could happily pretend to ignore visible evidence just to have a nice tidy theory as you suggest...
Dont forget empirical evidence also supported "bad humours" supporting the spread of disease. ie Bad Smell = cause not symptom of illness. Until the microscope was invented it was a perfectly good theory that matched established facts.
Im sure Dark Matter and Dark energy were only created as terms because some stuffy old physicists voted down "Stuff", "Magic" and the "Reversible Sedgewick particle"
There was empirical evidence for phlogiston too. There was also empirical evidence for another planet existing inside the orbit of Mercury to cause its orbit to behave non-Newtonianly. The former was explained by better experiments and a better understanding of the reaction of elements; the latter was explained by Einstein's General Theory of Relativity.
So the step from "we have observed this happening" to "some strange stuff must exist which has these properties" is bogus. Dark matter (and its even less explained counterpart, dark energy) may exist, but equally the fact that observations don't match theory may just need a different theory.
"If they can't detect dark matter, how do they make those 'dark matter maps' that look like the honeycombe understructure of the Universe?"
Simplistically, by measuring where the visible (non-dark) matter is.
The existence of "Dark Matter" was deduced from measuring the speed of rotation of galaxies and their mass.
Speed of rotation is measured by looking at the shift in the spectrum of the visible light emitted from a galaxy. Assuming a galaxy is 'edge on' relative to us, one side will be moving towards us, and thus the spectrum is shifted towards the blue end, and the opposite side moving away from us, and shifted towards the red. By measuring the relative difference in shift between the two sides, it is possible to work out how fast the galaxy is rotating.
Mass is estimated from observations of what we can see - visible light for the stars, comparing visible and infrared observations to identify the dust (blocks the former but not the latter), radio observations for hydrogen, etc.
Turns out that galaxies rotate too fast compared to the gravitational force generated by the matter we can observe. If the only matter they contain is what we can see, they would fly apart, flinging their starts, dust and gas off in all directions.
The fact that they don't leads to one of two conclusions:
1. Our current theories of gravity are incorrect. Serious consideration has been given to the idea that gravity may act differently over long distances than short ones. This is not currently a theory that holds much sway.
2. That the universe contains a whole lot more mass than we have been able to observe, i.e. "Dark Matter". The trouble is that weird/exotic types of unknown particle or other bogeyman make better headlines than forgetting to look under the bed for the missing mass.
To be fair, lots of 'boring' things like undetected gas or shedloads of brown dwarfs or similar objects that are to dim to detect have and are being pursued, as this story proves. The problem is that the discrepancy between what we can observe and the missing mass is so large that it seems entirely reasonable that there is a whole class of 'stuff' out there that we simply have no idea about and thus no (current) means of detecting.
Anyway, back to the original question. The large scale structure of the universe has been mapped (in a few directions) by measuring the distribution of galaxies. These do form a sort of 'honeycomb' structure with filaments and walls and great gulfs of empty space between them. The Dark Matter that holds galaxies together is also thought to be responsible for the formation of these larger scale structures.
Basically, current theories suggest that the dark matter is in the same places as the stuff we can already see because the latter is held together by the gravitational force generated by the former. As with all scientific theories, something may come up in the future that proves we were barking up completely the wrong tree all along.
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