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Dark Matter Measurements
ksp0704 writes: "According to this article at space.com, scientists have finally measured the approximately 90% of the universe we can't see (the dark matter)." I'm sure it will continue to be a topic of debate for years, but two independent measurements agreeing is a good sign.
Figuring that Excite got /.'ed here:
"Astronomers Celebrate Reliable Measure of Dark Matter
By Heather Sparks
Staff Writer
posted: 12:48 pm ET
29 October 2001
Scientists are closer than ever to balancing the
checkbook of cosmic matter. This is because two recent independent measurements of normal matter in the universe are in agreement. The results further strengthen the case for the Big Bang theory and for the nature of the universe as astronomers understand it today.
The universe contains normal atomic matter, what makes you, your dog, the stars, and everything in between. Normal matter is what Carl Sagan was talking about when he said we are all star-stuff.
But in addition to star-stuff, there is invisible dark matter that is known only because the universe is denser than normal matter alone, as evidenced by how structures, like clusters of galaxies, are bound together by gravity. Even individual galaxies don't have enough normal matter in them -- that which can be directly detected -- to keep them from simply flying apart.
Now, through different measurements of conditions existing at the very start of time, astronomers are beginning to see the light.
"There is more than one way of measuring the total amount of matter in the universe," said astronomer Brian Fields from the Center for Theoretical Astrophysics at the University of Illinois, Urbana-Champaign. "And if you have an idea of how much normal stuff there is to all the universe, then you know how much other stuff there is, too." Creation of normal matter
All the "normal stuff" is thought to have been made in two steps, one occurring when the universe was roughly three minutes old, and the other some 300,000 years later.
According to the leading theory, an enormous nuclear explosion called the Big Bang happened 13 billion to 15 billion years ago. From it, the universe appeared in an instant, but as a billion-degree mess of neutrons, protons and electrons. The explosion was so energetic that nothing could come together close enough, for long enough, to form atoms. But the universe expanded and cooled so rapidly that within three minutes protons and neutrons bonded in twos and fours, and formed all the atomic nuclei in the universe. This Big Bang Nucleosynthesis determined how much normal matter would ever exist.
Just how much matter that was can be estimated from observing the most recently formed stars and galaxies, because they are fueled by the hydrogen atoms formed from those original nuclei of twos.
Fields explained that young stars, like our Sun, are just now fusing that original hydrogen into helium whereas older stars fuse helium into oxygen and iron. Because the hydrogen fuel has not been converted, scientists are able to measure the proportion of original normal matter to dark matter.
"Stars change the amount of hydrogen and helium in the universe," he said, "and we want to know what the Big Bang did. So we have to find places where pollution from stars is minimal" to estimate the original amounts of normal and dark matter.
But before any stars could form, hydrogen atoms had to exist. This took 300,000 years after the Big Bang Nucleosynthesis the universe had to cool down enough so that electrons could bind with the nuclei.
Once this happened, there was a curious side effect: the creation of light in the Universe. Unbound electrons scattered the UV radiation from the Big Bang, but once the electrons were bound, the radiation was allowed uniform movement, thus, light was finally released in the young cosmos.
This light has existed since then, travelling along the edge of the universe, stretching and weakening into a still measurable microwave radiation, called the Cosmic Microwave Background, or CMB as astronomers call it.
Weak attraction
At the time of the original release of light, dark matter had congregated in clumps, which created small fields of gravity that eventually pulled in normal matter as well. Images of the CMB are therefore mostly smooth, but have spots, or wiggles, of slight variation, a result of the dark and normal matter pooling together.
"The nature of these 'wiggles' is basically saying how the normal matter was responding to that crazy dark matter," explained Fields, "by amplifying the places where the extra density was."
The CMB, most recently measured by highly sensitive probes in Antarctica, therefore gives a detailed measure of the proportion of normal to dark matter.
Phenomenally, both the measurements of young galaxies and of the cosmic microwave background showed that normal matter makes up just one-tenth of the universe. The rest must be dark matter, researchers say. Fields, who wrote about this astronomical agreement in the Oct. 19 issue of the journal Science, explained why this is causing astronomers to "bring out the bubbly."
"It didn't have to be true," Fields explained, "because they're completely independent things. It's just gorgeous that they agree with each other."
Earlier studies had showed that dark matter made up anywhere from 85 to 95 percent of the universe. Only now do the two different measures of dark matter agree. Now, 90 percent of everything is known to be virtually nothing."
forget it.
Astronomers Celebrate Reliable Measure of Dark Matter
By Heather Sparks
Scientists are closer than ever to balancing the checkbook of cosmic matter. This is because two recent independent measurements of normal matter in the universe are in agreement. The results further strengthen the case for the Big Bang theory and for the nature of the universe as astronomers understand it today.
The universe contains normal atomic matter, what makes you, your dog, the stars, and everything in between. Normal matter is what Carl Sagan was talking about when he said we are all star-stuff.
But in addition to star-stuff, there is invisible dark matter that is known only because the universe is denser than normal matter alone, as evidenced by how structures, like clusters of galaxies, are bound together by gravity. Even individual galaxies don't have enough normal matter in them -- that which can be directly detected -- to keep them from simply flying apart.
Now, through different measurements of conditions existing at the very start of time, astronomers are beginning to see the light.
"There is more than one way of measuring the total amount of matter in the universe," said astronomer Brian Fields from the Center for Theoretical Astrophysics at the University of Illinois, Urbana-Champaign. "And if you have an idea of how much normal stuff there is to all the universe, then you know how much other stuff there is, too."
Creation of normal matter
All the "normal stuff" is thought to have been made in two steps, one occurring when the universe was roughly three minutes old, and the other some 300,000 years later.
According to the leading theory, an enormous nuclear explosion called the Big Bang happened 13 billion to 15 billion years ago. From it, the universe appeared in an instant, but as a billion-degree mess of neutrons, protons and electrons. The explosion was so energetic that nothing could come together close enough, for long enough, to form atoms. But the universe expanded and cooled so rapidly that within three minutes protons and neutrons bonded in twos and fours, and formed all the atomic nuclei in the universe. This Big Bang Nucleosynthesis determined how much normal matter would ever exist.
Just how much matter that was can be estimated from observing the most recently formed stars and galaxies, because they are fueled by the hydrogen atoms formed from those original nuclei of twos.
Fields explained that young stars, like our Sun, are just now fusing that original hydrogen into helium whereas older stars fuse helium into oxygen and iron. Because the hydrogen fuel has not been converted, scientists are able to measure the proportion of original normal matter to dark matter.
"Stars change the amount of hydrogen and helium in the universe," he said, "and we want to know what the Big Bang did. So we have to find places where pollution from stars is minimal" to estimate the original amounts of normal and dark matter.
But before any stars could form, hydrogen atoms had to exist. This took 300,000 years after the Big Bang Nucleosynthesis the universe had to cool down enough so that electrons could bind with the nuclei.
Once this happened, there was a curious side effect: the creation of light in the Universe. Unbound electrons scattered the UV radiation from the Big Bang, but once the electrons were bound, the radiation was allowed uniform movement, thus, light was finally released in the young cosmos.
This light has existed since then, travelling along the edge of the universe, stretching and weakening into a still measurable microwave radiation, called the Cosmic Microwave Background, or CMB as astronomers call it.
Weak attraction
At the time of the original release of light, dark matter had congregated in clumps, which created small fields of gravity that eventually pulled in normal matter as well. Images of the CMB are therefore mostly smooth, but have spots, or wiggles, of slight variation, a result of the dark and normal matter pooling together.
"The nature of these 'wiggles' is basically saying how the normal matter was responding to that crazy dark matter," explained Fields, "by amplifying the places where the extra density was."
The CMB, most recently measured by highly sensitive probes in Antarctica, therefore gives a detailed measure of the proportion of normal to dark matter.
Phenomenally, both the measurements of young galaxies and of the cosmic microwave background showed that normal matter makes up just one-tenth of the universe. The rest must be dark matter, researchers say. Fields, who wrote about this astronomical agreement in the Oct. 19 issue of the journal Science, explained why this is causing astronomers to "bring out the bubbly."
"It didn't have to be true," Fields explained, "because they're completely independent things. It's just gorgeous that they agree with each other."
Earlier studies had showed that dark matter made up anywhere from 85 to 95 percent of the universe. Only now do the two different measures of dark matter agree. Now, 90 percent of everything is known to be virtually nothing.
"If he thinks he can hide and run from the United States and our allies, he's sorely mistaken." Bush on bin Laden
rtfm
I mean, com'on, things are event-driven or object-oriented, and without objects, one must only assume that an event triggered what was to follow - the big bang. Something was there to explode, and something had to cause it. Did one of the tiny dark matter particles spark up the wrong way and set it off?
:)
Interesting statement. Things are either (A) event-driven or (B) object oriented. But objects have not always existed (that is, the big bang caused the objects to exist). Hence the objects are event-driven (i.e., they are the results of the big bang). Thus everything is event-driven. Thus object are really events. But everything in Java inherits from Object. Thus, Java sucks. quod erat demonstrandum.
Tastes like burning! - Ralph Wiggum