Saturday, January 14, 2012 9:07:44 AM
F6, that totally spaced me out, lol, even now i found myself wondering how dark matter was 'found' ..
Dark matter ..
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly seen with telescopes. Dark matter is believed to constitute 83% of the matter in the universe and 23% of the mass-energy.
Dark matter was postulated by Fritz Zwicky in 1933 to account for evidence of "missing mass" in the orbital velocities of galaxies in clusters. Subsequently, other observations have indicated the presence of dark matter in the universe; these observations include the rotational speeds of galaxies, gravitational lensing of background objects by galaxy clusters such as the Bullet Cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies. Dark matter is widely believed to be composed primarily of a new, not yet characterized, type of subatomic particle. The search for this particle, by a variety of means, is one of the major efforts in particle physics today.[5] Though the existence of dark matter is generally accepted by the mainstream scientific community, some alternative theories have been proposed to explain the anomalies that dark matter is intended to account for, without hypothesizing dark matter.
Dark matter's existence is inferred from gravitational effects on visible matter and gravitational lensing of background radiation, and was originally hypothesized to account for discrepancies between calculations of the mass of galaxies, clusters of galaxies and the entire universe made through dynamical and general relativistic means, and calculations based on the mass of the visible "luminous" matter these objects contain: stars and the gas and dust of the interstellar and intergalactic medium. The most widely accepted explanation for these phenomena is that dark matter exists and that it is most likely composed of heavy particles that interact only through gravity and possibly the weak force; however, alternate explanations have been proposed, and there is not yet sufficient experimental evidence to determine which is correct. Many experiments to detect proposed dark matter particles through non-gravitational means are underway. .. http://en.wikipedia.org/wiki/Dark_matter
Dark Energy
In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain observations since the 1990s that indicate that the universe is expanding at an increasing rate. In the standard model of cosmology, dark energy currently accounts for 73% of the total mass-energy of the universe.
Two proposed forms for dark energy are the cosmological constant, a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli, dynamic quantities whose energy density can vary in time and space. Contributions from scalar fields that are constant in space are usually also included in the cosmological constant. The cosmological constant is physically equivalent to vacuum energy. Scalar fields which do change in space can be difficult to distinguish from a cosmological constant because the change may be extremely slow. .. http://en.wikipedia.org/wiki/Dark_energy
starry eyed and spaced out .. what the heck is the difference between dark matter (some 83% of the
matter of the universe, above) and dark energy "73% of the total mass-energy of the universe."
===============
Dark matter vs dark energy
Hoosier (below) is a bit confused between Dark Matter and Dark Energy, and
unconvinced by the whole shebang. This is very common, so let’s have a post on it..
Dark matter .. http://en.wikipedia.org/wiki/Dark_matter .. is thought to account for 20% of all the matter/energy of the universe. Although we can’t see it, we’re pretty sure it exists, because its gravitational effect on visible matter can be seen. Put differently, we don’t insist that all existing matter must be ‘visible’ (i.e. emit or reflect electromagnetic radiation). Instead , we include the possibility that some matter may be seen only by its gravitational effect on neighbouring matter. The idea was first postulated by Fritz Zwicky .. http://en.wikipedia.org/wiki/Fritz_Zwicky .. in the 1930s – today, the known motion of certain spiral galaxies suggests that dark matter makes up 22% of all matter/energy, while ordinary (visible) matter makes up only 4% .
Of course, like the MOND .. http://en.wikipedia.org/wiki/Modified_Newtonian_dynamics .. crowd suggest, there is always the possibility is that our laws of gravity (both Newtonian and Einsteinian) are simply wrong. But most physicists consider this unlikely, as the predictions of our theory of gravity match observation in so many other instances…
Dark energy .. http://en.wikipedia.org/wiki/Dark_energy .. is a lot more speculative, and a lot more recent. It’s simply the name we give to whatever is causing the expansion of the universe to speed up (since 1998, it has been known that the expansion rate is currently increasing). The physical cause for dark energy is thought to be some sort of vacuum energy, but nobody’s sure yet. (From the point of view of theory, the phenomenon suggests that Einstein’s equations need an extra term, known technically as the ‘positive cosmological constant’.)
Putting the two together, cosmologists postulate that ordinary matter, dark matter and dark energy all add up to the critical density required for the geometry of the universe to be flat (which is what observation suggests). In other words, the current model of the universe can be summed up by
Density ord matter (4%) + Dens dark matter (22%) + Dens dark energy (74%) = 100%
More
The strongest evidence .. http://www.msnbc.msn.com/id/14453775/ .. yet for dark matter was reported last summer. In the passage of one galaxy through another, one might expect the dark matter of one galaxy to interact differently than its ordinary matter, and researchers at the University of Arizona are pretty sure this is exactly they saw.
Galaxy collision seen by the CHANDRA space telescope
It is also reported here .. http://apetrov.wordpress.com/2008/04/16/damalibra-claims-to-see-dark-matter/ .. and here .. http://www.symmetrymagazine.org/breaking/2008/04/12/dark-matter-discovered-aps-april-2008/ .. that another group, the DAMA-LIBRA collaboration, have observed separate evidence of dark matter, but this claim is more controversial.
17 Comments »
1. Thanks so much for taking time out of your day to help explain the mysteries of the universe Doctor C.
I really do appreciate it!
a couple more things..That’s a beeautiful picture..but what do the colors of red and blue mean? what does it represent? How does it show dark matter when it can’t be seen? Is that gasses of some sort? how does that prove dark matter?
Also..I read something somewhere about this guy that put forth the idea that dark energy doesn’t really exist.. the reason it appears to us the the universe is expanding faster and faster is because the speed of light over time is slowing down and makes the red shift skewed to us observers. Have you read that also? Maybe at the big bang light was twice as fast as today..Boy if that was true ole albert would be spinning in his grave! :)
but if true then e=mc squared would mean that the energy levels near the big bang would have been twice of what we would calculate and slowly everything would be degrading.
I’ll try to find that link for you to check out.
Again..thanks for answering my dumb questions..
I went to one web page and the guy bragged about how smart he was and how stupid i was..I don’t get that alot when speaking in person.. They don’t have the courage to insult you when they know I’d kick thier ass..But this is the beauty of the internet..people can call you stupid and get away with it. Some people are smart..some play sports well..Some know how to fix stuff..why the ego?
I dunno..thanks again Doc.
Comment by HoosierHoops | May 23, 2008 | Reply
and
4. btw, regarding the red and blue in the picture. If I recall that correctly, it’s an overlay of two data-sets (and both over the Hubble image with the stars). The red one shows the mass-distribution of visible matter (can’t recall which parts of the spectrum precisely), the blue one shows the mass-distribution as inferred from gravitational lensing data. What you see is that both are offset from each other. The interpretation is that the bulk of the matter which causes the gravitational lensing is not where the visible matter is. The reason why the visible matter is lagging behind is that it interacts more strongly than the dark matter (usually thought to consist of WIMPs – weakly interacting massive particles). Best,
B. .. http://coraifeartaigh.wordpress.com/2008/05/22/dark-matter-and-dark-energy/
Thanks for all your hard work F6. Even though it often leaves me galaxy eyed and universally out of touch. LOL
How can it be considered that our universe, starting from nothing and expanding in all directions, could be flat?
I feel about 6 years old.
Dark matter ..
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly seen with telescopes. Dark matter is believed to constitute 83% of the matter in the universe and 23% of the mass-energy.
Dark matter was postulated by Fritz Zwicky in 1933 to account for evidence of "missing mass" in the orbital velocities of galaxies in clusters. Subsequently, other observations have indicated the presence of dark matter in the universe; these observations include the rotational speeds of galaxies, gravitational lensing of background objects by galaxy clusters such as the Bullet Cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies. Dark matter is widely believed to be composed primarily of a new, not yet characterized, type of subatomic particle. The search for this particle, by a variety of means, is one of the major efforts in particle physics today.[5] Though the existence of dark matter is generally accepted by the mainstream scientific community, some alternative theories have been proposed to explain the anomalies that dark matter is intended to account for, without hypothesizing dark matter.
Dark matter's existence is inferred from gravitational effects on visible matter and gravitational lensing of background radiation, and was originally hypothesized to account for discrepancies between calculations of the mass of galaxies, clusters of galaxies and the entire universe made through dynamical and general relativistic means, and calculations based on the mass of the visible "luminous" matter these objects contain: stars and the gas and dust of the interstellar and intergalactic medium. The most widely accepted explanation for these phenomena is that dark matter exists and that it is most likely composed of heavy particles that interact only through gravity and possibly the weak force; however, alternate explanations have been proposed, and there is not yet sufficient experimental evidence to determine which is correct. Many experiments to detect proposed dark matter particles through non-gravitational means are underway. .. http://en.wikipedia.org/wiki/Dark_matter
Dark Energy
In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain observations since the 1990s that indicate that the universe is expanding at an increasing rate. In the standard model of cosmology, dark energy currently accounts for 73% of the total mass-energy of the universe.
Two proposed forms for dark energy are the cosmological constant, a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli, dynamic quantities whose energy density can vary in time and space. Contributions from scalar fields that are constant in space are usually also included in the cosmological constant. The cosmological constant is physically equivalent to vacuum energy. Scalar fields which do change in space can be difficult to distinguish from a cosmological constant because the change may be extremely slow. .. http://en.wikipedia.org/wiki/Dark_energy
starry eyed and spaced out .. what the heck is the difference between dark matter (some 83% of the
matter of the universe, above) and dark energy "73% of the total mass-energy of the universe."
===============
Dark matter vs dark energy
Hoosier (below) is a bit confused between Dark Matter and Dark Energy, and
unconvinced by the whole shebang. This is very common, so let’s have a post on it..
Dark matter .. http://en.wikipedia.org/wiki/Dark_matter .. is thought to account for 20% of all the matter/energy of the universe. Although we can’t see it, we’re pretty sure it exists, because its gravitational effect on visible matter can be seen. Put differently, we don’t insist that all existing matter must be ‘visible’ (i.e. emit or reflect electromagnetic radiation). Instead , we include the possibility that some matter may be seen only by its gravitational effect on neighbouring matter. The idea was first postulated by Fritz Zwicky .. http://en.wikipedia.org/wiki/Fritz_Zwicky .. in the 1930s – today, the known motion of certain spiral galaxies suggests that dark matter makes up 22% of all matter/energy, while ordinary (visible) matter makes up only 4% .
Of course, like the MOND .. http://en.wikipedia.org/wiki/Modified_Newtonian_dynamics .. crowd suggest, there is always the possibility is that our laws of gravity (both Newtonian and Einsteinian) are simply wrong. But most physicists consider this unlikely, as the predictions of our theory of gravity match observation in so many other instances…
Dark energy .. http://en.wikipedia.org/wiki/Dark_energy .. is a lot more speculative, and a lot more recent. It’s simply the name we give to whatever is causing the expansion of the universe to speed up (since 1998, it has been known that the expansion rate is currently increasing). The physical cause for dark energy is thought to be some sort of vacuum energy, but nobody’s sure yet. (From the point of view of theory, the phenomenon suggests that Einstein’s equations need an extra term, known technically as the ‘positive cosmological constant’.)
Putting the two together, cosmologists postulate that ordinary matter, dark matter and dark energy all add up to the critical density required for the geometry of the universe to be flat (which is what observation suggests). In other words, the current model of the universe can be summed up by
Density ord matter (4%) + Dens dark matter (22%) + Dens dark energy (74%) = 100%
More
The strongest evidence .. http://www.msnbc.msn.com/id/14453775/ .. yet for dark matter was reported last summer. In the passage of one galaxy through another, one might expect the dark matter of one galaxy to interact differently than its ordinary matter, and researchers at the University of Arizona are pretty sure this is exactly they saw.
Galaxy collision seen by the CHANDRA space telescope
It is also reported here .. http://apetrov.wordpress.com/2008/04/16/damalibra-claims-to-see-dark-matter/ .. and here .. http://www.symmetrymagazine.org/breaking/2008/04/12/dark-matter-discovered-aps-april-2008/ .. that another group, the DAMA-LIBRA collaboration, have observed separate evidence of dark matter, but this claim is more controversial.
17 Comments »
1. Thanks so much for taking time out of your day to help explain the mysteries of the universe Doctor C.
I really do appreciate it!
a couple more things..That’s a beeautiful picture..but what do the colors of red and blue mean? what does it represent? How does it show dark matter when it can’t be seen? Is that gasses of some sort? how does that prove dark matter?
Also..I read something somewhere about this guy that put forth the idea that dark energy doesn’t really exist.. the reason it appears to us the the universe is expanding faster and faster is because the speed of light over time is slowing down and makes the red shift skewed to us observers. Have you read that also? Maybe at the big bang light was twice as fast as today..Boy if that was true ole albert would be spinning in his grave! :)
but if true then e=mc squared would mean that the energy levels near the big bang would have been twice of what we would calculate and slowly everything would be degrading.
I’ll try to find that link for you to check out.
Again..thanks for answering my dumb questions..
I went to one web page and the guy bragged about how smart he was and how stupid i was..I don’t get that alot when speaking in person.. They don’t have the courage to insult you when they know I’d kick thier ass..But this is the beauty of the internet..people can call you stupid and get away with it. Some people are smart..some play sports well..Some know how to fix stuff..why the ego?
I dunno..thanks again Doc.
Comment by HoosierHoops | May 23, 2008 | Reply
and
4. btw, regarding the red and blue in the picture. If I recall that correctly, it’s an overlay of two data-sets (and both over the Hubble image with the stars). The red one shows the mass-distribution of visible matter (can’t recall which parts of the spectrum precisely), the blue one shows the mass-distribution as inferred from gravitational lensing data. What you see is that both are offset from each other. The interpretation is that the bulk of the matter which causes the gravitational lensing is not where the visible matter is. The reason why the visible matter is lagging behind is that it interacts more strongly than the dark matter (usually thought to consist of WIMPs – weakly interacting massive particles). Best,
B. .. http://coraifeartaigh.wordpress.com/2008/05/22/dark-matter-and-dark-energy/
Thanks for all your hard work F6. Even though it often leaves me galaxy eyed and universally out of touch. LOL
How can it be considered that our universe, starting from nothing and expanding in all directions, could be flat?
I feel about 6 years old.
It was Plato who said, “He, O men, is the wisest, who like Socrates, knows that his wisdom is in truth worth nothing”
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