The Search for Dark Matter and Dark Energy 212
mlimber writes "The New York Times Magazine has a lengthy article on dark matter and dark energy, discussing the past, present, and future. 'Astronomers now realize that dark matter probably involves matter that is nonbaryonic ["meaning that it doesn't consist of the protons and neutrons of 'normal' matter"]. And whatever it is that dark energy involves, we know it's not 'normal,' either. In that case, maybe this next round of evidence will have to be not only beyond anything we know but also beyond anything we know how to know.'"
Re:Can dark matter just be.. (Score:5, Informative)
The 'size' of the universe is an ill-defined question. We can only observe what's in our past light cone, and it is *that* universe which suffers from a budget shortfall of matter/energy.
Re:Telescopes invented 400 years ago? (Score:5, Informative)
I didn't know telecopes were that old. Is this a typo, and didn't they mean decades instead? If not, what did ancient telescopes do?
FooBarWidget, meet Galileo: Widely credited as the inventor of the modern telescope, in 1609.
Though, as with all major developments in human history, some accounts have him as merely improving on preexisting tech, whether copying the work of Lippershey from 40 years before, or even the possibly MUCH older designs of the ancient Persians.
So no, not a typo.
Re:Questions from a B- physics student (Score:4, Informative)
This could all be accounted for by dark matter save for the observations of Type 1A supernovae which indicate accelerating expansion, and this requires domination by a state of matter with negative pressure, and this is what's been coined dark energy.
Re:Can dark matter just be.. (Score:5, Informative)
Galactic dark matter, which is required to explain the rotation curves of spiral galaxies, can be completely explained by baryonic dark matter, which would be at least partially dust.
Extra-galactic dark matter cannot be primarily baryonic. The baryon density of the universe is known from big bang nucleo-synthesis and the primordial H/He ratio, and is too small to account for extra-galactic dark matter. Therefore extra-galactic dark matter has no relation at all to galactic dark matter, as it cannot be made of the same stuff as galactic dark matter.
So there are at least two completely different, totally unrelated dark matter problems. One can and probably is solved by baryons. The other requires exotic particles or possibly exotic physics.
Re:I'm all for it (Score:3, Informative)
http://en.wikipedia.org/wiki/Black_hole#Black_hol
Dark Matter Exists (Score:5, Informative)
Here [cosmicvariance.com] is an excellent article by Sean Carroll [preposterousuniverse.com] of the California institute of Technology that explains why all the suggestions of the parent post may not be correct.
Basically, what it says is that if two large clusters of galaxies went right through each other, and dark matter was really like the normal matter in the way the parent post suggests, we would get a different result from what would happen if dark matter was for real. Astronomers have discovered one such system and this provides conclusive evidence for the existence of dark matter.
Re:Can dark matter just be.. (Score:5, Informative)
GR does not work at Galactic Levels (Score:3, Informative)
The real problem is MOND. If it did not exist then Dark Matter would be free to exist wherever it wanted. But with MOND the picture becomes more complex, now DM must fit MOND. It is quite easily provable that DM cannot fit MOND, just apply it to small cluster of stars at the outer edge of Milky Way which show Dark Matter. The problem is that for DM to fit Milky Way, it cannot be present in the Clusters. But some clusters do require DM. Now MOND fits both reasonably.
If you talk about Bullet Cluster, then don't because it proves that DM should have a new type of interaction because the DM itself is experiencing higher gravity than relativity predicts. Now this can be due to MOND. MOND can be fit to the Cluster by using hot and massive neutrinos. See the following papers.
http://www.citebase.org/abstract?id=oai%3AarXiv.o
http://www.citebase.org/abstract?id=oai%3AarXiv.o
The additional benefit is that MOND supplies the higher than gravity force required to fit the velocity of DM in Bullet Cluster.