Author Archives: gmcdavid

About gmcdavid

Retired IT professional with a wide range of interests. Married. Three sons, two with autistic-spectrum disorders and the third being transgender with Ehlers-Danlos syndrome. From Chicago but now living in the Twin Cities metro, Minnesota. Episcopalian. Carleton College (BA 1972, physics) and Stanford University (MS 1974, Applied Physics; MS 1976 Statistics).

The Dark Side of Gaia

I was reminded tonight of the Gaia hypothesis. It was quite a thing in the 1970s.

The Gaia hypothesis, named after the ancient Greek goddess of Earth, posits that Earth and its biological systems behave as a huge single entity. This entity has closely controlled self-regulatory negative feedback loops that keep the conditions on the planet within boundaries that are favorable to life. Introduced in the early 1970s, the idea was conceived by chemist and inventor James E. Lovelock and biologist Lynn Margulis.

This had a natural appeal in the early days of the environmental movement. I was skeptical back then, thinking of it as new age wishful thinking, and impossible to test. I was wrong: Its origins are far darker. Here is the abstract of Gas Guzzling Gaia, or: A Prehistory of Climate Change Denialism:

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The mass of Dark Matter particles

An email from Cosmoquest led me to find Physicists Narrow Range of Potential Masses for Dark Matter Candidate articles. Technical details at Theoretical bounds on dark matter masses and on the Arxiv. The mass range is 10−3eV≲mφ≲107eV. Thus we have a range from neutrino masses (still very uncertain, but nonzero) up to about 1/10 the mass of a muon. This appears to exclude WIMPs, which were already in trouble. This also suggests that finding dark matter is not a justification for building a more powerful particle accelerator than the LHC; 107eV is well within the range of the LHC and other current devices.

We still do not have a complete theory of quantum gravity, but apparently enough is understood to make such calculations possible. I am looking forward to seeing what other theoretical physicists say about this.

Blinking Astronomical Photographs

Low-Cost Approach to Scanning Historic Glass Plates Yields an Astronomical Surprise. Technical details at Precise Photometric Measurements from a 1903 Photographic Plate Using a Commercial Scanner.

Professional astrophotography used to be done on emulsion-coasted glass places. That was how astromical discoveries were made for nearly a century.

More than an estimated 2.4 million glass plates are out there in collections in North America alone. These were taken starting in the 1890s right up until the 1970s, when CCD (Charged Couple Device) detectors started to come online for astronomy. Of these, only an estimated 400,000 plates have been digitized to research quality

The team in this article has found a much cheaper way to proceed with this process, using off-the-shelf hardware.

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Rang Gaeilge, 26ú lá mí Eanáir 2021

Duinnín agus an Bhean nár tugadh Nimh di (tuilleadh)

  • ‘Bhí sailéid[veriant] ag Miss Montague. Ubh beirithe a bhí agam féin.’
    ‘Cad a bhí sa sailéid?’
    ‘Bradán stánaithe, leitís, tráta agus prátaí beirithe.’
    D’ith an Duinníneach slaimice aráin agus d’ól sé muigín tae, gan focal as [3rd pers sing prep pronoun]. D’ól Minnie deora beaga tae ón mhuigín aici siúd go béasach agus chogain sí grabhóga aráin lena fiacla tosaigh mar dhéanfadh coinín.

    ‘Miss Montague had a salad. I myself had a boiled egg.’
    ‘What was in the salad?’
    ‘Canned salmon, lettuce, a tomato, and boiled potatoes.’
    Dineen ate a chunk of bread and drank a little mug of tea, without a word out of him. Minnie drank small drops of tea from her little mug there politely and she chewed bread crumbs with her front teeth like a rabbit would.

    sailéadsaladm gs npl sailéid
    Bradánsalmon
    stánaithecanned
    mugamugm
    deoirdropf npl deora
    béasachWell-behaved; mannerly, polite
    cogainchew
    grabhrógcrumbf npl grabhróga
    tosaighbegin, start
    tosachbeginning, frontm gs tosaigh

  • Léigh tuilleadh

The Eyes of Legolas

Tumblr User Explains Why Elves’ Eyes In Lord Of The Rings Shouldn’t Look The Way They Do, but in fact there is no problem.

In The Two Towers Legolas claims to clearly see the horsemen of Rohan at a distance of 5 leagues. How is this possible when you consider the curvature of the Earth? You can come up with some bizarre ideas about Elven anatomy which are not suggested in the books or seen in the movies. However, there is a an elegant answer based on the nature of Arda, Tolkien’s world. It was flat, not round, until the end of the second age. At that time the Valar made it round so that mortals could not access Valinor. But Elves could still go there. For them the Earth was still flat and they could sail the straight path to Valinor. Hence for Legolas the curvature of the Earth and the horizon did not exist and hence he could accurately see the horsemen 5 leagues away.

Another Hobbit

Exploring the People of Middle-earth: Lobelia Sackville-Baggins, an Unexpected Hero.

… Lobelia is one of only a few Hobbit women who are given more than a momentary glance in Middle-earth, and a compelling character in her own right. And what’s more, her narrative arc illustrates beautifully some of the more important lessons The Lord of the Rings has to teach, as she becomes an unlikely hero to those who had consistently refused to give her a chance.

This will only make sense if you have read the books. Peter Jackson did not include the Scouring of the Shire in the film version of The Return of the King.

Supernovae

I went (via Zoom) to a great lecture last night. Serafina Nance spoke to the The Calgary Centre of the Royal Astronomical Society of Canada on Tracing the Lives, Deaths, and Explosions of Massive Stars.

Supernovae are cosmic events of gigantic power. Their explosions can shine as bright as a galaxy, a pinprick of extraordinarily bright light in the night sky. What is less well-understood, however, is which stars reach the point of explosion and how they evolve to their deaths. Interestingly, their explosions provide astronomers with key tools to uncover fundamental aspects of our Universe. While we know that the Universe is expanding at an accelerated rate due to dark energy, the rate of the expansion of the Universe is not well-constrained. Supernovae provide us with independent ways to measure this expansion and work to resolve one of the most pivotal questions in astronomy: How fast is the Universe really expanding?
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