- 2187 - Confusion is not unusual for astronomers. It started when they questioned why do stars shine? In the 1930’s more confusion came with the concept of dark matter, that is providing gravity but not providing light. In the 1990’s more confusion was added with the concept of dark energy. That unknown force that is expanding the Universe at an ever accelerating rate.
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----------------------------- 2187 - Dark Matter is confusing astronomers
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- Confusion is not unusual for astronomers. It started when they questioned why do stars shine? In the 1930’s more confusion came with the concept of dark matter. That unseen matter that is providing gravity but not providing light.
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- In the 1990’s more confusion was added with the concept of dark energy. That unknown force that is expanding the Universe at an ever accelerating rate. The two dark discoveries add up to 95% the total content of the Universe. Nice to have a job with lots of work to do.
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- Dark energy is a mysterious force that does not manifest itself locally. Astronomers have to go beyond multimillion lightyear’s range to yield the first traces of dark energy.
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- Dark matter is another matter. Astronomer Fritz Zwicky recognized it 80 years ago as an invisible substance exerting enough gravitational force to keep our local group of galaxies from flying apart and off into space.
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- Our galaxy rotates differently due to the presence of this dark matter. This unseen matter appears to be diffuse and scattered in an immense halo surrounding our galaxy. The immense spiral we are so familiar with is like a ship inside a bottle. Without this dark gravity stars near the center of the galaxy would orbit faster than we do 26,000 lightyears away. Dark matter is causing us to rotating like a solid structure, our galaxy is like a vinyl record. Does anyone remember what a vinyl record looks like?
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- This presence of dark matter is what is holding our total Local Group of galaxies together. There are some 48 galaxies that are held inside the Group while the galaxies outside are flying apart due to dark energy. It pays to live in the neighborhood.
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- Our Milky Way Galaxy is spinning at 143 miles per second. . (514,800 mile per hour). We will get to the other side of the galaxy in 100 million years.
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- Dark matter discoveries are unsettling. Astronomers are unnerved when they first noticed that galaxies don’t rotate by the same physics as a spinning plate, or a vinyl record. The stars at a galaxy’s edge rotate faster than expected. And their motion can only be explained by a lot of invisible matter that we can’t see.
Astronomers came up with two possibilities to explain the unknown dark matter. MACHOs (Massive Compact Halo Objects) and WIMPs (Weakly Interacting Massive Particles).
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- MACHOS aren’t the Answer. Brown dwarfs are an example of a MACHO, but they don’t exist in large enough numbers to solve the dark matter problem. MACHOs are the less exotic possibility, and, there is just are not enough of them to make the galaxy rotation math work.
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- The same problem pops up if we imagine a universe littered with black holes. We would need to see these light-bending gravitational lenses everywhere and we don’t, even though we are looking very hard.
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- So the astronomers mostly moved on to WIMPs. Rather than big objects, maybe the universe is full of little things we can’t see. These would be swarms of objects like atoms that just don’t reflect or absorb light or any other kind of electromagnetic energy, unlike all the ordinary matter.
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- This concept is even more unsettling. We do know that neutrinos exist: tiny, mostly mass-less particles that barely interact with the universe around them. The problem here is that they’re mostly mass-less. We can’t figure out how there are enough of them to make up the 84 percent of the universe’s matter that we can’t see.
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- So maybe dark matter is a different object we haven’t observed at all yet, something called a “neutralino“. Researchers have come up with a plausible description of such a particle, how the Big Bang might have created them, and how they would fit into the standard model of particle physics without breaking any rules we know about.. Emphasis on the later.
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- Researchers hope the XENON experiment will directly detect dark matter particles. But we have been looking for them for a while. We’ve built incredibly sensitive, bizarre instruments to look for them. These include vats of liquid xenon stored miles underground, and telescopes looking for dark matter particles that are decaying into gamma rays.
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- It includes the Large Hadron Collider, one of the most expensive science experiments ever built. And we haven’t found them. We haven’t found the WIMPs or convincing evidence that they even exist.
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- The universe the way we measure it is heavier than what we can see. Decades ago, scientists were confident about the existence of the “aluminiferous ether” as a medium to carry light. Now, that’s looked back on as a clumsy belief that should have been dropped far earlier than it was finally discredited.. Scientists persisted because they were sure that light, like sound, required a medium to move through in spite of the evidence piling up against that concept. Having been fooled once, scientists have to ask: Is dark matter the new ether?
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- For decades, a few rogue scientists have the theory called Modified Newtonian Dynamics, or MOND. Essentially, it says that physics doesn’t work as we know it at the largest scales. The laws of gravity change with large galactic dimensions. No one has managed to develop a theory of MOND that adequately explains the universe around us, but it occasionally gains converts simply because the competing theory of dark matter has a glaring flaw: we can’t find it.
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- Perhaps we’re wrong about something in the standard model of physics that defines how the tiniest particles in the universe behave and interact, and dark matter exists, but in a very different form than we’re expecting. Or perhaps we are wrong about the laws of gravity.
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- Or perhaps, an experiment will turn up a neutralino exactly where researchers say it should be. A new particle will strike a tank of super cooled xenon. The LHC team will discover a new particle. Science is hard. Until something changes, we’ll have to rest uneasy with the unsettling possibility that physics as we know it might be very wrong.
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- Darn, maybe I have taken all those physics courses for nothing?
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- November 23, 2018
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-------------------------- Friday, November 30, 2018 --------------------------
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