nhaliday + waves   29

Why do stars twinkle?
According to many astronomers and educators, twinkle (stellar scintillation) is caused by atmospheric structure that works like ordinary lenses and prisms. Pockets of variable temperature - and hence index of refraction - randomly shift and focus starlight, perceived by eye as changes in brightness. Pockets also disperse colors like prisms, explaining the flashes of color often seen in bright stars. Stars appear to twinkle more than planets because they are points of light, whereas the twinkling points on planetary disks are averaged to a uniform appearance. Below, figure 1 is a simulation in glass of the kind of turbulence structure posited in the lens-and-prism theory of stellar scintillation, shown over the Penrose tile floor to demonstrate the random lensing effects.

However appealing and ubiquitous on the internet, this popular explanation is wrong, and my aim is to debunk the myth. This research is mostly about showing that the lens-and-prism theory just doesn't work, but I also have a stellar list of references that explain the actual cause of scintillation, starting with two classic papers by C.G. Little and S. Chandrasekhar.
nibble  org:junk  space  sky  visuo  illusion  explanans  physics  electromag  trivia  cocktail  critique  contrarianism  explanation  waves  simulation  experiment  hmm  magnitude  atmosphere  roots  idk 
december 2017 by nhaliday
Resonance in a Pendulum - YouTube
The vibration of any given washer is able to transmit its energy only to another washer with exactly the same frequency. Since the length of a pendulum determines its frequency of vibration, each pendulum can only set another pendulum vibrating if it has the same length.
nibble  video  social  physics  mechanics  waves  oscillation  synchrony  flux-stasis  increase-decrease  concrete  ground-up  dirty-hands  phys-energy  frequency  spreading 
september 2017 by nhaliday
Resonance - Wikipedia
Resonance occurs when a system is able to store and easily transfer energy between two or more different storage modes (such as kinetic energy and potential energy in the case of a simple pendulum). However, there are some losses from cycle to cycle, called damping. When damping is small, the resonant frequency is approximately equal to the natural frequency of the system, which is a frequency of unforced vibrations. Some systems have multiple, distinct, resonant frequencies.
nibble  physics  mechanics  waves  oscillation  synchrony  wiki  reference  article  flux-stasis  increase-decrease  frequency  spreading 
september 2017 by nhaliday
- the genetic book of the dead [Dawkins]
- complementarity [Frank Wilczek]
- relative information
- effective theory [Lisa Randall]
- affordances [Dennett]
- spontaneous symmetry breaking
- relatedly, equipoise [Nicholas Christakis]
- case-based reasoning
- population reasoning (eg, common law)
- criticality [Cesar Hidalgo]
- Haldan's law of the right size (!SCALE!)
- polygenic scores
- non-ergodic
- ansatz
- state [Aaronson]: http://www.scottaaronson.com/blog/?p=3075
- transfer learning
- effect size
- satisficing
- scaling
- the breeder's equation [Greg Cochran]
- impedance matching

- reciprocal altruism
- life history [Plomin]
- intellectual honesty [Sam Harris]
- coalitional instinct (interesting claim: building coalitions around "rationality" actually makes it more difficult to update on new evidence as it makes you look like a bad person, eg, the Cathedral)
basically same: https://twitter.com/ortoiseortoise/status/903682354367143936

more: https://www.edge.org/conversation/john_tooby-coalitional-instincts

interesting timing. how woke is this dude?
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may 2017 by nhaliday
Orthogonal — Greg Egan
In Yalda’s universe, light has no universal speed and its creation generates energy.

On Yalda’s world, plants make food by emitting their own light into the dark night sky.
greg-egan  fiction  gedanken  physics  electromag  differential  geometry  thermo  space  cool  curiosity  reading  exposition  init  stat-mech  waves  relativity  positivity  unit  wild-ideas  speed  gravity  big-picture  🔬  xenobio  ideas  scifi-fantasy  signum 
february 2017 by nhaliday
Building momentum | West Hunter
When people started farming, at first they were not biologically different from their immediate hunter-gatherer ancestors. Eventually they would be different: better adapted to the new diet, the increased crowding, the psychological demands of a very different way of life – but that took at least some time. After they were adapted to farming, the tendency towards farmers expanding, rather than the idea of farming being transmitted, would increase: the biological edge shows up. But at first, before much adaptation, idea transmission might have more competitive with demography. I throw this out as a possible partial explanation of the pattern we are seeing: first the idea of farming spreading through core populations in the Middle East (possibly combined with independent invention or stimulus diffusion), while a little later those core populations themselves begin spreading outward. In fact, on the ball really got rolling, those populations should have been adapting to expansion itself, just like cane toads.

Surfing the Wave: https://westhunt.wordpress.com/2011/11/05/surfing-the-wave/
Cane toads, to general dismay, have been spreading rapidly in Australia. And in the course of that spread, they have evolved. This is particularly true at the front of the wave of toads. Those leading-edge toads have longer legs, are more active at night, and have higher reproductive rates.

Something similar has happened in Quebec, where a few thousand French colonists grew more than a thousandfold over three centuries. A research team led by Damian Labuda, Helene Vezina, and Laurent Excoffier (lead author, Claudia Moreau) found that people living near the wavefront contributed significantly more ancestry to the modern Quebec population than those from the central regions. Moreover, fitness was heritable on that wavefront – so life-history traits measurably evolved during the Quebec expansion. Just as they have in cane toads.


The paper is also notable in that we see Laurent Excoffier saying that there has been noticeable recent evolutionary change in a human population – a change that has not occurred in all human populations. I had gotten the impression that he really did not like that kind of conclusion, which is too bad for him, because such change is ubiquitous. Maybe we’ll hear more such results from him: once you accept it, the dark side is with you forever.
west-hunter  agriculture  farmers-and-foragers  sapiens  antiquity  frontier  evolution  migration  competition  gene-flow  scitariat  spreading  cultural-dynamics  multi  nature  canada  anglo  recent-selection  natural-experiment  archaeology  similarity  life-history  fertility  waves  agri-mindset  eden 
november 2016 by nhaliday
Faster than Fisher | West Hunter
There’s a simple model of the spread of an advantageous allele:  You take σ, the typical  distance people move in one generation, and s,  the selective advantage: the advantageous allele spreads as a nonlinear wave at speed  σ * √(2s).  The problem is, that’s slow.   Suppose that s = 0.10 (a large advantage), σ = 10 kilometers, and a generation time of 30 years: the allele would take almost 7,000 years to expand out 1000 kilometers.


This big expansion didn’t just happen from peasants marrying the girl next door: it required migrations and conquests. This one looks as if it rode with the Indo-European expansion: I’ll bet it started out in a group that had domesticated only horses.

The same processes, migration and conquest, must explain the wide distribution of many geographically widespread selective sweeps and partial sweeps. They were adaptive, all right, but expanded much faster than possible from purely local diffusion. We already have reason to think that SLC24A5 was carried to Europe by Middle Eastern farmers; the same is probably true for the haplotype that carries the high-activity ergothioniene transporter and the 35delG connexin-26/GJB2 deafness mutation. The Indo-Europeans probably introduced the T-13910 LCT mutation and the delta-F508 cystic fibrosis mutation, so we should see delta-F508 in northwest India and Pakistan – and we do !

To entertain a (possibly mistaken) physical analogy, it sounds like you’re suggested a sort genetic convection through space, as opposed to conduction. I.e. Entire masses of folks, carrying a new selected variant, are displacing others – as opposed to the slow gene flow process of “girl-next-door.” Is that about right? (Hopefully I haven’t revealed my ignorance of basic thermodynamics here…)

Has there been any attempt to estimate sigma from these time periods?

Genetic Convection: https://westhunt.wordpress.com/2015/02/22/genetic-convection/
People are sometimes interested in estimating the point of origin of a sweeping allele: this is probably effectively impossible even if diffusion were the only spread mechanism, since the selective advantage might well vary in both time and space. But that’s ok, since population movements – genetic convection – are real and very important. This means that the difficulties in estimating the origin of a Fisher wave are totally insignificant, compared to the difficulties of estimating the effects of past colonizations, conquests and Völkerwanderungs. So when Yuval Itan and Mark Thomas estimated that 13,910 T LCT allele originated in central Europe, in the early Neolithic, they didn’t just go wrong because of failing to notice that the same allele is fairly common in northern India: no, their whole notion was unsound in the first place. We’re talking turbulence on steroids. Hari Seldon couldn’t figure this one out from the existing geographic distribution.
west-hunter  genetics  population-genetics  street-fighting  levers  evolution  gavisti  🌞  selection  giants  nibble  fisher  speed  gene-flow  scitariat  stylized-facts  methodology  archaeology  waves  frontier  agri-mindset  analogy  visual-understanding  physics  thermo  interdisciplinary  spreading  spatial  geography  poast  multi  volo-avolo  accuracy  estimate  order-disorder  time  homo-hetero  branches  trees  distribution  data  hari-seldon  aphorism  cliometrics  aDNA  mutation  lexical 
november 2016 by nhaliday

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