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Posts Tagged ‘dark energy

“Everything we know and love about the universe and all the laws of physics as they apply, apply to four percent of the universe”*…

 

dark matter

 

In 1969, the American astronomer Vera Rubin puzzled over her observations of the sprawling Andromeda Galaxy, the Milky Way’s biggest neighbour. As she mapped out the rotating spiral arms of stars through spectra carefully measured at the Kitt Peak National Observatory and the Lowell Observatory, both in Arizona, she noticed something strange: the stars in the galaxy’s outskirts seemed to be orbiting far too fast. So fast that she’d expect them to escape Andromeda and fling out into the heavens beyond. Yet the whirling stars stayed in place.

Rubin’s research, which she expanded to dozens of other spiral galaxies, led to a dramatic dilemma: either there was much more matter out there, dark and hidden from sight but holding the galaxies together with its gravitational pull, or gravity somehow works very differently on the vast scale of a galaxy than scientists previously thought.

Her influential discovery never earned Rubin a Nobel Prize, but scientists began looking for signs of dark matter everywhere, around stars and gas clouds and among the largest structures in the galaxies in the Universe. By the 1970s, the astrophysicist Simon White at the University of Cambridge argued that he could explain the conglomerations of galaxies with a model in which most of the Universe’s matter is dark, far outnumbering all the atoms in all the stars in the sky. In the following decade, White and others built on that research by simulating the dynamics of hypothetical dark matter particles on the not-so-userfriendly computers of the day.

But despite those advances, over the past half century, no one has ever directly detected a single particle of dark matter. Over and over again, dark matter has resisted being pinned down, like a fleeting shadow in the woods. Every time physicists have searched for dark matter particles with powerful and sensitive experiments in abandoned mines and in Antarctica, and whenever they’ve tried to produce them in particle accelerators, they’ve come back empty-handed. For a while, physicists hoped to find a theoretical type of matter called weakly interacting massive particles (WIMPs), but searches for them have repeatedly turned up nothing…

Dark matter is the most ubiquitous thing physicists have never found. Is it time to consider alternative explanations? “Does dark matter exist?

[image above: source]

* Neil deGrasse Tyson

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As we interrogate the invisible, we might recall that it was on this date in 1944 that one of the worst fire disasters in U.S. history occurred; the blaze broke out during an afternoon performance of the Ringling Bros. and Barnum & Bailey Circus that was attended by an estimated 7,000 people.  It killed 167 people; more than 700 were injured.

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Because of the paraffin wax waterproofing of the tent, the flames spread rapidly

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Emmett Kelly holding a water bucket on what became known as “the day the clowns cried

 

Written by LW

July 6, 2020 at 1:01 am

“I used to think information was destroyed in black holes. This was my biggest blunder, or at least my biggest blunder in science”*…

 

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Gravitational waves sent out from a pair of colliding black holes have been converted to sound waves, as heard in this animation. On September 14, 2015, LIGO [the Laser Interferometer Gravitational-wave Observatory] observed gravitational waves from the merger of two black holes, each about 30 times the mass of our sun. The incredibly powerful event, which released 50 times more energy than all the stars in the observable universe, lasted only fractions of a second.

In the first two runs of the animation, the sound-wave frequencies exactly match the frequencies of the gravitational waves. The second two runs of the animation play the sounds again at higher frequencies that better fit the human hearing range. The animation ends by playing the original frequencies again twice.

As the black holes spiral closer and closer in together, the frequency of the gravitational waves increases. Scientists call these sounds “chirps,” because some events that generate gravitation waves would sound like a bird’s chirp.

More background from LIGO:

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* Stephen Hawking

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As we scan the event horizon, we might send difficult-to-detect birthday greetings to Lawrence Maxwell Krauss; he was born on this date in 1954.  A theoretical physicist and cosmologist, Dr. Krauss was among the first to propose the existence of the enigmatic dark energy that makes up most of the mass and energy in the universe.  He directs the Origins Project, and has written several books on science for the general public, including Fear of Physics (1993), The Physics of Star Trek (1995), Quantum Man: Richard Feynman’s Life in Science (2011), and A Universe from Nothing (2012).

 source

 

Written by LW

May 27, 2016 at 1:01 am

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