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Posts Tagged ‘Cosmology

“Bohr was inconsistent, unclear, willfully obscure, and right. Einstein was consistent, clear, down-to-earth, and wrong.”*…

The founders of quantum mechanics understood it to be deeply, profoundly weird. Albert Einstein, for one, went to his grave convinced that the theory had to be just a steppingstone to a more complete description of nature, one that would do away with the disturbing quirks of the quantum.

Then in 1964, John Stewart Bell proved a theorem that would test whether quantum theory was obscuring a full description of reality, as Einstein claimed. Experimenters have since used Bell’s theorem to rule out the possibility that beneath all the apparent quantum craziness — the randomness and the spooky action at a distance — is a hidden deterministic reality that obeys the laws of relativity.

Now a new theorem has taken Bell’s work a step further. The theorem makes some reasonable-sounding assumptions about physical reality. It then shows that if a certain experiment were carried out — one that is, to be fair, extravagantly complicated — the expected results according to the rules of quantum theory would force us to reject one of those assumptions.

According to Matthew Leifer, a quantum physicist at Chapman University who did not participate in the research, the new work focuses attention on a class of interpretations of quantum mechanics that until now have managed to escape serious scrutiny from similar “no-go” theorems.

Broadly speaking, these interpretations argue that quantum states reflect our own knowledge of physical reality, rather than being faithful representations of something that exists out in the world. The exemplar of this group of ideas is the Copenhagen interpretation, the textbook version of quantum theory, which is most popularly understood to suggest that particles don’t have definite properties until those properties are measured. Other Copenhagen-like quantum interpretations go even further, characterizing quantum states as subjective to each observer…

… which has, as you will see as you read on in the piece excerpted above, some pretty profoundly weird implications. Either the rules of quantum mechanics don’t always apply, or at least one basic assumption about reality must be wrong: “A New Theorem Maps Out the Limits of Quantum Physics.”

See also “Reality is that which, when you stop believing in it, doesn’t go away.”

* John Stewart Bell

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As we pity Schrödinger’s cat, we might we might send penetrating birthday greetings to Henry Way Kendall; he was born on this date in 1926. A particle physicist, he shared the Nobel Prize in Physics in 1990 (with Jerome Isaac Friedman and Richard E. Taylor) “for their pioneering investigations concerning deep inelastic scattering of electrons on protons and bound neutrons, which have been of essential importance for the development of the quark model in particle physics.”

In 1969, Kendall helped found the Union of Concerned Scientists. In 1997, in connection with the Kyoto Climate Summit, he helped produce a statement signed by 2,000 scientists calling for action on global warming.

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“The distinction between past, present and future is only a stubbornly persistent illusion”*…

A dog dressed as Marty McFly from Back to the Future attends the 25th Annual Tompkins Square Halloween Dog Parade in New York October 24, 2015.
AFP PHOTO / TIMOTHY A. CLARY via Getty Images

“The past is obdurate,” Stephen King wrote in his book about a man who goes back in time to prevent the Kennedy assassination. “It doesn’t want to be changed.”

Turns out, King might have been onto something.

Countless science fiction tales have explored the paradox of what would happen if you do something in the past that endangers the future. Perhaps one of the most famous pop culture examples is Back to the Future, when Marty McFly went back in time and accidentally stopped his parents from meeting, putting his own existence in jeopardy.

But maybe McFly wasn’t in much danger after all. According a new paper from researchers at the University of Queensland, even if time travel were possible, the paradox couldn’t actually exist…

Find out why: “Paradox-Free Time Travel Is Theoretically Possible, Researchers Say.

* Albert Einstein

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As we ponder predestination, we might send cosmological birthday greetings to Enrico Fermi; he was born on this date in 1901.  A physicist who is best remembered for (literally) presiding over the birth of the Atomic Age, he was also remarkable as the last “double-threat” in his field:  a genius at creating both important theories and elegant experiments.  As recently observed, the division of labor between theorists and experimentalists has since been pretty complete.

The novelist and historian of science C. P. Snow wrote that “if Fermi had been born a few years earlier, one could well imagine him discovering Rutherford’s atomic nucleus, and then developing Bohr’s theory of the hydrogen atom. If this sounds like hyperbole, anything about Fermi is likely to sound like hyperbole.”

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Written by LW

September 29, 2020 at 1:01 am

“Evidently, the fundamental laws of nature do not pin down a single and unique universe”*…

For the World Is Hollow and I Have Touched the Sky Original printing of the Flammarion engraving, from 1888.
Artist unknown; from Camille Flammarion, L’Atmosphère: Météorologie Populaire

The name of the image—the “Flammarion engraving”—may not ring a bell, but you’ve seen it many times. It depicts a traveler wearing a cloak and clutching a walking-stick; behind him is a varied landscape of towns and trees; surrounding all is a crystalline shell fretted with countless stars. Reaching the edge of his world, the traveler pushes through to the other side and is dazzled by a whole new world of light and rainbows and fire.

The image was first published in 1888 in a book by French astronomer Camille Flammarion. (The original engraving was black and white, although colorized versions now abound.) He notes that the sky does look like a dome on which the celestial bodies are attached, but impressions deceive. “Our ancestors,” Flammarion writes, “imagined that this blue vault was really what the eye would lead them to believe it to be; but, as Voltaire remarks, this is about as reasonable as if a silk-worm took his web for the limits of the universe.”

The engraving has come to be seen as a symbol of humanity’s quest for knowledge, but I prefer a more literal reading, in keeping with Flammarion’s intent. Time and again in the history of science, we have found an opening in the edge of the known world and poked through. The universe does not end at the orbit of Saturn, nor at the outermost stars of the Milky Way, nor at the most distant galaxy in our field of view. Today cosmologists think whole other universes may be out there.

But that is almost quotidian compared to what quantum mechanics reveals. It is not just a new opening in the dome, but a new kind of opening. Physicists and philosophers have long argued over what quantum theory means, but, in some way or other, they agree that it reveals a vast realm lying beyond the range of our senses. Perhaps the purest incarnation of this principle—the most straightforward reading of the equations of quantum theory—is the many-worlds interpretation, put forward by Hugh Everett in the 1950s. In this view, everything that can happen does in fact happen, somewhere in a vast array of universes, and the probabilities of quantum theory represent the relative numbers of universes experiencing one outcome or another. As David Wallace, a philosopher of physics at the University of Southern California, put it in his 2012 book, The Emergent Multiverse, when we take quantum mechanics literally, “the world turns out to be rather larger than we had anticipated: Indeed, it turns out our classical ‘world’ is only a small part of a much larger reality.”…

If multiverses seem weird, it’s because we need to revamp our notions of time and space: “The Multiple Multiverses May Be One and the Same.”

* Alan Lightman, The Accidental Universe: The World You Thought You Knew

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As we find one in many, we might send relativistic birthday greetings to Victor Frederick “Viki” Weisskopf; he was born on this date in 1908. A theoretical physicist who contributed mightily to the golden age of quantum mechanics, Weisskopf did postdoctoral work with Werner Heisenberg, Erwin Schrödinger, Wolfgang Pauli and Niels Bohr. He emigrated from Austria to the U.S. in 1937 to escape Nazi persecution. During World War II he was Group Leader of the Theoretical Division of the Manhattan Project at Los Alamos, and later campaigned against the proliferation of nuclear weapons.

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Written by LW

September 20, 2020 at 1:01 am

“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

“Deep in the fundamental heart of mind and Universe there is a reason”*…

 

darkenergy

 

Why does the Universe exist? There are two questions here. First, why is there a Universe at all? It might have been true that nothing ever existed: no living beings, no stars, no atoms, not even space or time. When we think about this possibility, it can seem astonishing that anything exists. Second, why does this Universe exist? Things might have been, in countless ways, different. So why is the Universe as it is?…

Derek Parfit explores the most fundamental questions of all: “Why anything? Why this?”  Part 2 here.

For a 3-D tour of the subject in question– the universe– see here (the source of the image above).

* Douglas Adams, Life, the Universe and Everything

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As we explore existence, we might recall that today– and every June 16– is Bloomsday, a commemoration and celebration of the life of Irish writer James Joyce, during which the events of his novel Ulysses (which is set on 16 June 1904) are relived: Leopold Bloom goes about Dublin, James Joyce’s immortalization of his first outing with Nora Barnacle, the woman who would eventually become his wife.

The first Bloomsday was observed on the 50th anniversary of the events in the novel, in 1954, when John Ryan (artist, critic, publican and founder of Envoy magazine) and the novelist Brian O’Nolan organized what was to be a daylong pilgrimage along the Ulysses route. They were joined by Patrick Kavanagh, Anthony Cronin, Tom Joyce (a dentist who, as Joyce’s cousin, represented the family interest), and AJ Leventhal (a lecturer in French at Trinity College, Dublin).

The crew for the first Bloomsday excursion

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Written by LW

June 16, 2020 at 1:01 am

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