[Martin Taylor 2006.08.31.10.43]
[From Bill Powers (2006.08.30.1115 MDT)]
Jim Dundon 08.30.06.12:20pmedst --
That is why I brought up dark matter.
So called empirical science says that space consists mostly of dark matter. I think they say this because they were running out of things to do.I think that's unfair, because you don't really know why dark matter was proposed. In observing the orbits of stars in other galaxies (which is possible to do in an approximate way using doppler-shift measurements of radial velocity) it is found that the orbital velocities are too high (by a large margin) for the amount of matter (producing gravitational attraction) that can be seen in the form of stars and dust in the galaxies. The stars should have gone flying off into space long ago, but they didn't. So there must be more matter there than we can see as radiating stars and obscuring dust clouds, and it must be dark because we can't see it. That seems not unreasonable to me.
To reinforce what Bill says here, the most recent issue of Science (25 Aug 2006, p1033) discusses what they call "clinching evidence" for the existence of dark matter. The evidence refutes the idea that the kinds of observation Bill mentions could be due to the failure of the law of gravity to follow an inverse square law at long distances. In a collision of two galaxies observed by the Chandra X-ray observatory, gravitational lensing shows that the mass concentrations are not where the concentrations of normal matter (atoms and molecules etc.) are. Most of the mass is not normal matter.
Don't forget that 100 years ago, many scientists thought atoms were only a convenient mathematical fiction that accounted for quite a few empirical observations. In my high school in the late 1940's, the physics teacher taught that nobody would ever, in principle, see a picture that showed individual atoms. Now it is possible to spell out "IBM" in lines one atom wide by pushing individual atoms around until the letters look right. Who can guess what we will think of as being "real and solid" in another hundred years?
Same with string theory. I don't argue with the concept because if the brain can handle it OK.
Not mine. The mathematics is, I am told, pretty hairy and certainly beyond me. Do you understand it?
As with those involved in atomic theory after Einstein's 1905 revolutionary approach to the quantum (and I don't mean relativity), and even more after the further revolution of the 1920's, we have to assume that those who do understand are in a position to find and to publicise each other's mathematical errors. Whether the mathematics lead to empirically observable consequences is the issue, and now, 80 years later, it is clear that they do. We can even make a computer (a small one) in a coffee cup that works because somebody understood the mathematics of quantum entanglement. Maybe that concept will some day be superseded, but it has led to innumerable effects, predicted and observed, that lots of people think of as "spooky" because they don't work like most of our experience with objects of human scale.
The issue that many physicists have with string theory isn't that the mathematics is unintelligible -- probably more people understand it than understood quantum mechanics in 1935 -- but that nobody has derived unambiguous predictions of observable phenomena that aren't easily explained by other, generally accepted, theories. Einstein's prediction of the bending of light that passed near the sun is an example of that happening with a "spooky" theory.
If a version of string theory some day produces such "spooky" predictions and they pan out, I expect that a century later the theory will be taken to be self-evident, and the observations as evidence of the solidity and reaonableness of the universe. As today are atoms, which we can now manipulate one by one.
But it creates some problems when I try to blend or map it to the molecules and atoms in the nervous system in your model of behavior. Does it exist in those atoms? Probably not.
Neutrinos probably do, don't they? At least in the "Deduced Reality" of the generally accepted physical models. Trillions of them go right through you evey day. Who's to say what dark matter is, other than that it interacts with "atoms and molecules" even less than do neutrinos.
"Dark energy" is even more mysterious than "dark matter", but all the observational evidence seems to show that it's there, at least if we trust the wwhole interlocking network of physical theory and other observations. But then that's what models are all about, isn't it? Without the model, we wouldn't even know there was a mystery.
Martin