Anders Sandberg

@anderssandberg

Academic jack-of-all-trades.

Vrijeme pridruživanja: rujan 2009.

Medijski sadržaj

  1. prije 3 sata

    The vial contains strontium aluminate. It starts the same, but then the electron gets trapped in a "triplet state" where the drop back down is harder (a "forbidden transition") and it remains there for a long time (up to hours) until it drops, releasing light.

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  2. prije 3 sata

    The test tube has pieces of uranium glass, containing some U2O3. When hit by a UV photon, electrons jump up to a high energy state, lose some energy through a few small jumps, and then drop back down, releasing a longer wavelength (=visible) photon.

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  3. prije 3 sata

    Friday physics fun: here are two yellowish solids. I shine UV light on them, they respond by shining green back. Afterwards one of the keeps on shining. What is going on? Fluorescence and phosphorescence.

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  4. 2. velj
    Odgovor korisniku/ci

    Neat animation! But what constitutes a "a sufficiently symmetric tiling"? When I try it on random graphs near percolation the result is very uneven. The heat kernel depends on the graph Laplacian, sensitive to local anisotropy

  5. 31. sij

    Here is a cute idea: MRI tends to be noisy and many patients get nervous from the weird sounds. So manipulate the field gradients to play music. Turn the superconductor into a cello!

  6. 31. sij

    If one uses a disordered graph one does get lines, velocities and circles that look like they should once the scale is big enough:

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  7. 31. sij

    Weyl pointed out that if you have a lattice with a shortest length the Pythagorean theorem does not work. Spheres will not be spheres but cubes, shortest paths follow taxi-cab geometry, space is not isotropic. This generalizes to any regular graph:

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  8. 31. sij

    Many dislike the idea that stuff could be truly continuous (you need infinite information to specify a point) and suggest some discrete structure like a lattice or a graph. Others think continuous symmetry is so important (conservation laws) it implies continuous spacetime.

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  9. 31. sij

    Friday (theoretical) physics fun: is spacetime discrete or not? Normally we assume space is infinitely divisible just like the real numbers: between two points there will always be at least one more point. It is not obvious this has to be true. Matter turned out to be atoms.

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  10. 29. sij
    Odgovor korisniku/ci
  11. 24. sij

    Friday physics fun: the crystallogens, alias the tetragens alias Group 14 alias Group IV alias the Carbon group in the periodic table. The name comes from the nice crystals C, Si and Ge make because they have 4 valence electrons, allowing diamondoid crystal structures.

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  12. 17. sij

    Friday physics fun: Of all the elements in my office these two came about in the weirdest way: cosmic rays whittling down atomic nuclei.

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  13. 14. sij

    Santa gives naughty kids a lump of coal. In my case, I got a cube of beryllium! Thank you santa!

  14. 14. sij
    Odgovor korisnicima

    I Feel Fantastic, Moderaterna styr Stockholms läns landsting. (Oväntat passande)

  15. 10. sij

    Friday physics fun: vanadium crystals. Nicely dendritic, and you can see hints of color from a passivating oxide layer on some crystals.

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  16. 10. sij

    I was interviewed by Francesca Ferrando on "The Near Future and the Transhuman" and "Far Futures and the Transhuman" for eps. 20 and 21 of the Vlog "Posthumans"

  17. 8. sij

    Lower middle: improper priors for change of natural laws.

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  18. 8. sij

    Lower right: some blackbody radiation for Jupiter brains

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  19. 8. sij

    Middle: overfitting is not a problem?!

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  20. 8. sij

    Middle: forecasting metrics with Ozzie Gooen

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