John Carlos Baez

@johncarlosbaez

I do math, physics, network theory at U. C. Riverside and the Centre for Quantum Technologies in Singapore.

Riverside, CA
math.ucr.edu/home/baez/
Vrijeme pridruživanja: rujan 2016.

Medijski sadržaj

  1. prije 18 sati

    Planck's formula for momentum almost matches Newton's for speeds much slower than light. But it gives dramatically different answers at high speeds! (2/n)

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  2. prije 19 sati

    Max Planck was the first established physicist to embrace Einstein's work on special relativity. He worked out some important consequences! Later, in 1914, Planck helped Einstein get a research position in Berlin. (1/n)

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  3. 31. sij

    It's well-known that when the potential wells in a crystal get strong enough, its electrons "localize": instead of having spread-out wavefunctions, they get trapped in specific locations as shown here. This is called "Anderson localization". (3/n)

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  4. 31. sij

    As you increase the intensity of the lasers, the Bose-Einstein condensate (in blue) suddenly collapses from a quasicrystal to a "localized" state where all the atoms sit in the same place! Here the gray curve is the potential formed by the lasers. (2/n)

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  5. 31. sij

    Condensed matter physics is so cool! Bounce 4 laser beams off mirrors to make an interference pattern with 8-fold symmetry. Put a Bose-Einstein condensate of potassium atoms into this "optical lattice" and you get a SUPERFLUID CRYSTAL! But that's not all... (1/n)

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  6. 30. sij

    Computer science and category theory blend in the theory of "optics": different systems for viewing and interacting with data. As part of the ACT2019 school, Emily Pillmore and Mario Román have written a great overview of these: Lenses, prisms & more!

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  7. 29. sij

    Here's a corrected meme:

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  8. 29. sij

    One great thing about math is that you can still learn new things about the sphere - yes, the good old 2-sphere, S². There's more than one way to wrap an n-sphere around the S² except for n=1! More precisely: (1/n)

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  9. 28. sij

    As you keep zooming in, you think: it's a point! No, it's a line! No, it's a rectangle! No, it's a bunch of points! No... It's a subset of the plane invented by Simon Willerton, which shows that your estimate of the dimension can keep changing as you zoom in more and more.

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  10. 27. sij
    Odgovor korisnicima

    He was a bit of a joker, so this seems more believable than all the inspirational apocryphal Einstein quotes.

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  11. 27. sij
    Odgovor korisniku/ci

    My friend Michael Weiss gave me this picture. It's nice but it doesn't attempt to capture how an etale space is often non-Hausdorff. Drawing a non-Hausdorff space is tough, hence the poor quality of my own pictures.

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  12. 27. sij
    Odgovor korisniku/ci

    The analogue in 4d is also fun! From Thomas F. Banchoff:

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  13. 25. sij

    This is from "Excitations in strict 2-group higher gauge models of topological phases" by Bullivan and Delcamp. Physicists are starting to use 2-groups - categorified groups - to create mathematical models of new topological phases of matter.

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  14. 24. sij
    Odgovor korisnicima i sljedećem broju korisnika:

    Right. Does someone claim that Venus had Earth-like ocean at some time? For some reason I've never read about that! For Mars I've read a lot about things like the Noachian Period.

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  15. 24. sij

    But the entropy of black holes grows *quadratically* with mass! So black holes tend to merge and form bigger black holes. There are "supermassive" black holes at the centers of most galaxies. These dominate the entropy of the observable Universe: about 10^104 bits. (9/n)

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  16. 24. sij

    What's the total number of stars in the observable Universe? Estimates go up as telescopes improve. We think there are between 100 and 400 billion stars in the Milky Way. We think there are between 170 billion and 2 trillion galaxies in the Universe. (4/n)

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  17. 24. sij

    But as the Universe expands, the distant ancient stars and gas we see have moved even farther away, so they're no longer observable. The so-called "observable Universe" is really the "formerly observable Universe". Its edge is 46.5 billion light years away now! (3/n)

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  18. 24. sij

    What's the observable Universe? The further you look out into the Universe, the further you look back in time! You can't see through the hot gas from 380,000 years after the Big Bang. That "wall of fire" marks the limits of the observable Universe. (2/n)

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  19. 24. sij

    This zoomable image of the Milky Way shows 84 million stars: But stars contribute only a tiny fraction of the total entropy in the observable Universe. If it's random information you want, look elsewhere! (1/n)

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  20. 23. sij
    Odgovor korisnicima i sljedećem broju korisnika:

    Branding yourself:

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