Posted on 01/15/2002 7:02:17 AM PST by PatrickHenry
Once upon a time -- a bit more than 100 years ago -- many scientists believed that seemingly empty space wasn't empty at all, but was filled with a substance called luminous ether. This mysterious stuff, never seen in any laboratory on Earth, was thought to explain how gravity from one celestial body could affect another.
By the end of the 19th century, though, luminous ether had gone the way of countless other scientific misconceptions. Today, another mysterious substance beguiles astronomers, and this one isn't going away. In fact, it's been at the forefront of cosmological theories for decades. It's called dark matter, and it is now widely accepted by astronomers as the stuff most of the universe is made of.
"We've known that it exists for more than 25 years," says astronomer Virginia Trimble of the University of California Irvine. "But we don't know what the hell it is."
How can astronomers be so certain of something they have never seen? The answer comes from observations of how stars and galaxies move, studies that have been going on for more than 50 years. Within spiral galaxies, individual stars and clouds of gas are orbiting faster than they should if they were only being affected by the gravity of the galaxy's visible matter. The same is true for clusters of galaxies: The motions of individual galaxies can't be explained by the gravity of what astronomers can see.
To explain these observations, astronomers have deduced that galaxies are surrounded by vast halos of a different, unseen kind of matter.
This so-called dark matter is invisible to us because it does not radiate energy. But it does have mass, and that means it can supply the extra gravity necessary to hold galaxies, and clusters of galaxies, together. Even in the bizarre world of cosmology, it's a strange proposition.
But is dark matter the only explanation?
Perhaps scientists don't entirely understand the way gravity works; perhaps Isaac Newton's famous law of gravitation needs some revising. But that idea, says the University of Arizona's Chris Impey, is not very popular.
"Definitely most astronomers are extremely unwilling to give up Newton's law," he says. "So it's essentially a choice of two evils: You either hypothesize that Newton's law is wrong, and that our knowledge of the gravity theory is incomplete. Or, you hypothesize a fundamental microscopic particle that has never been detected in any physics lab, whose properties are only constrained by these astronomical observations. Which is a pretty uncomfortable position for physicists to be in."
Still, as Trimble explains, dark matter is the lesser of the two evils, simply because it requires fewer departures from accepted physics.
To explain the observations by revising the theory of gravity, astronomers would have to identify a few different effects, each of which would operate at a different distance scale. But with dark matter as the explanation, Trimble says, "You only need one Tooth Fairy."
[The rest is omitted, but you can visit the source and read it all.]
But the relatively new discovery of the annihilation fountain and clouds seems to be - from my layman's eyes - a possible indirect clue for analyzing black hole, dark matter, or whatever is going on at the center of the Milky Way.
I also apologize for the bad link. This is the correct link:
OSSE Annihilation Fountain Images
Reminds me of when I used to get into debates on the Bible with other people. One day I decided it might be better to read it from beginning to end if I was going to continue trying to think I knew what it was about.
Before I read it, I thought I knew a lot about the Bible. After reading the entire thing, cover to cover, I realized I knew absolutely nothing!
So Now I know how Einstein felt..when he said something like "The more I know, the more I realize how little I know".
I won't even go so far as to say "it's just crazy enough to be true" but just want to know if anyone else recalls the article. (If not I solemnly swear I will never read another Science Fiction novel based on Velikovsky's work again)
Seems to me though that if it is true it might partly explain galaxies spinning too slowly, (since we measure their rotation by redshift)
A small spherical universe after all?
The implication was this weakening was caused by expansion so accepted reasons for red shifting would still be true, if less so than thought.
Previous caveats still apply.
IS THE FINE STRUCTURE CONSTANT CHANGING? The inherent strength of the electromagnetic force is characterized by a parameter called the fine structure constant (denoted by the Greek letter alpha), defined as the charge of the electron squared divided by the product of Planck's constant and the speed of light. The size of alpha determines how well atoms hold together and what types of light atoms will emit when heated up. And just as the elastic band keeping a swimsuit snug will gradually relax with time, so it is reasonable to ask whether an atoms' elasticity (or alpha) might also vary with time, an idea broached by Paul Dirac in 1937. A group of scientists at the University of New South Wales in Australia (John Webb, jkw@edwin.phys.unsw.edu.au) test this proposition by sampling ancient light emitted by ancient atoms, and comparing them to modern light from modern atoms. In particular they looked at the relative spacing of doublets of absorption lines in the spectra of several types of atoms in distant gas clouds lying in front of still more distant quasars. The spacings, not easy to tease out from the faint spectra, are proportional to alpha squared. After taking into account Doppler effects owing to the expansion of the universe, the Australian scientists find that there is a consistent change in alpha with increasing redshift (z), especially above a z of one. Owing to the caution needed in claiming a "measurement" of alpha change, the researchers prefer to think of their result as constituting a new upper limit on the fractional alpha change for z>1 of about 2 parts in 10,000. (Webb et al., Physical Review Letters, tent. 25 Jan. 1999.)
Thanks!
v.
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