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Giant Sheets Of Dark Matter Detected
Wandering Wombat writes "The largest structures in the universe have been, if not directly found, then at least detected and pounced upon by scientists. 'The most colossal structures in the universe have been detected by astronomers who tuned into how the structures subtly bend galactic light. The newfound filaments and sheets of dark matter form gigantic features stretching across more than 270 million light-years of space — three times larger than any other known structure and 2,000 times the size of our own galaxy. Because the dark matter, by definition, is invisible to telescopes, the only way to detect it on such grand scales is by surveying huge numbers of distant galaxies and working out how their images, as seen from telescopes, are being weakly tweaked and distorted by any dark matter structures in intervening space.' By figuring how to spot the gigantic masses of dark matter, hopefully we can get a better understanding of it and find smaller and smaller structures."
so the scientists are lol cats? Oh, hai drk mater! i pownse on u!
The whole rubber sheet of space time analogy is wrong, it is missing something.
Current analogy of space time:
Take a rubber sheet and stretch it out over a frame and drop a bowling ball and marble and drop them on it, they push down and those dents are gravitation fields in space-time.
New more correct analogy:
Take a swimming pool and fill it all the way to the top with water. THEN, stretch a rubber sheet over it and seal it so that no water leaks out. Then put your bolwing ball and marble on it. Draw a line running between the bowling ball and marble, and take that cross section, note that the bowling ball and marble behave the same way at close distance like they do above, but when they are a opposite sides of the pool there is a slight "repulsive" effect. We call that Dark Energy! This repulsive effect also can help stick objects together applying a "pressure" against all the other objects, hence "Dark Matter". This effect will also affect light waves moving past it, hence gravitational lensing.
I'll take my Nobel prize now!
Tsukasa: All I really want, is to be left alone...
First, remember that the distribution of dark matter and ordinary matter are, actually, pretty similar (we find galaxies accumulated along the dark matter filaments, and at smaller scales see dark matter concentrated into galaxies).
Second, my understanding is that dark matter (whatever it is) must be fairly weakly-interacting. The normal matter that we see aggregating into stars and galaxies interacts with itself (the particles bounce off each other, exchanging momentum, and also they repel each other at very short distances). This interaction, in addition to gravity, dictates the shapes we see for ordinary matter.
Dark matter doesn't interact strongly (with matter, and presumably with itself), so it aggregates differently. Imagine a cluster of dark matter that is being gravitationally collapsed: as the particles get closer to each other, instead of bouncing off each other (and thereby e.g. transforming their large-scale kinetic energy into heat), they 'pass through' each other (actually just pass by each other without scattering). This means that the matter will aggregate differently (the dark matter particles will mutually gravitate and orbit, but can't coalesce).
I'm painting a simplistic picture, but the point is that there are some fundamental differences about how dark matter interacts, versus ordinary matter. I believe the filamentary structure itself is an artifact of the universe's inflationary epoch, where massive expansion has amplified small-scale quantum fluctuations into the very large-scale distribution we now see.
It's a good philosophical question though. When is a collection of things (say atoms, bricks and mortar, etc.) a thing and when is it just lots of things? Deep down atoms don't come anywhere near touching each other to make molecules and larger structures. I myself am just a collection of tiny dots floating in space a long way from each other.
No. When we try to predict the large scale distribution of matter using simulations we get filaments.
Doesn't it make you feel good to know that our freedoms are protected by politicans, lawyers and journalists.
Or at least our current mathematical description of it is wrong. We cannot explain how disk galaxies spin. We cannot explain how the big bang happens without the magic fairy dust for inflation. Now we have a large wall of dark matter. Oh, and there is dark energy for galaxy acceleration. One more thing, we cannot quantize our approach to gravity.
These are the reasons I work on a rank 1 field theory for gravity. For the details, read as much of this thread as you like: http://physicsforums.com/showthread.php?t=87097 This is a LONG thread, more than 36k views, I make learn things along the way. Right now I am trying to find derive the Maxwell equations, and then the unified field theory, instead of using tensors. Quite a bit of fun. I have never had to write so many partial differential equations in my life.
Doug
Working on new views of old physics at http://VisualPhysics.org
You joke, but consider if the universe were a simulation -- quantum mechanics makes a lot more sense in term of a simulation. Things like spooky action at a distance become lazy evaluation. Quanta become memory locations, variables. And so on. Quantum mechanics is easy to simulate.
But how does one simulate gravity? It has to propagate in every direction at the something like speed of light or else -- god forbid -- information could travel faster than light. The whole concept of gravity, that every individual particle affects however slightly every other particle, is not possible to compute directly.
Now suppose the universe were simulated as a sparse matrix. Each cell could contain a gravity component that stored the aggregate gravity force from each of a certain number of directions (perhaps expressed as several point masses). Depending on the number of directions this would give highly accurate simulation at a small scale, where error is absorbed as noise, while being computable for the overall universe as a whole. However the error would magnify over great distances due to 'floating point' type errors accumulating.
What if what these people are seeing as dark matter is not matter at all, but simulation error. Perhaps even dark matter is related to a sparse simulation of the universe where intervening space is approximated by invisible masses that gravity affects but nothing else does. These mass would act to consolidate cells in the matrix to reduce the overall memory requirements.