1. UW
Update 1/26/14
a. Woke
bright and early and headed out to physics. We discussed the strange phenomenon
of magnetism, which is related to electric force but not really the same thing
(after learning about electric force, I confused magnets with electric dipoles,
but magnetism is fundamentally distinct).
b. Planned
to study outside, but realized I’d left my computer in the dorm. Ran back and
researched for cow paper for a while—for a one-page paper, this was occasioning
a lot of work. I was realizing how bad the Wikipedia articles on Hinduism were
(a. Hinduism is fragmented, since India was never politically or culturally
unified, and b. there may not be that many expert English writers who are also
expert Hindus), and how multiple sources were often contradictory.
c. Returned
to physics complex for Lunchbox seminar with lunch from Motosurf. This one was
really accessible and interesting. The professor, a theorist from Caltech, was
interested in how to model supernova explosions. The reason that supernovas
explode is really not well understood.
d. Supernovas,
play by play:
i. When
the star can no longer generate enough nuclear energy to stop itself from
falling in under its own weight, or the star core of heavier elements gets
large enough,
ii. The
iron core at the center of the star starts to collapse. Why iron? Iron has the
stablest and most densely packed nucleus of all the elements, and fusing two
iron nuclei into larger elements takes more energy than it releases.
iii. The
iron core gets so dense that electrons and protons fuse to become neutrons.
This inner “neutron star” has a density of about 10^14 g/cm^2(!).
iv. At
some point, the strong nuclear force, which is usually attractive, becomes
repulsive, and the neutrons stop compacting. This sudden reversal in the effect
of the nuclear force generates a shock wave that ripples back outward towards
the infalling material. Now you have a neutron star, surrounded by a zone where
the shock from the strong force is holding up the infalling material.
v. Now
the neutrinos, obscenely tiny, massless particles generated in e- + p+ -> n
reaction, come into play. Because when you have ~10^57 tiny, massless
particles, they’re not negligible anymore.
vi. Normally,
neutrinos pass through ordinary matter as though it weren’t there. But the
neutron star is so dense that the neutrinos bounce around in the star before
escaping.
vii. These
neutrinos have two effects. First, they interact with matter in a part of the
shock zone (the “gain” region because this is where the star is gaining energy
from the neutrinos) and heat the matter. Second, if they get past the shock
zone, they pull massive amounts of energy out of the star as the star’s gravity
(yes, gravity works on massless particles if they’re moving fast enough) slows
them down.
viii.
There’s a one-second window before the escaping
neutrinos pull too much energy from the star for the star to explode (I think
this is how it works, my memory is not perfectly clear on this). In this time,
the inner neutrinos must heat the region inside the star sufficiently to blow
the star up. The problem is that calculations indicate that the neutrino
heating is not sufficient, and that based on this alone supernova-sizes stars
would not explode but collapse into black holes.
ix. This
researcher’s idea is that turbulence in the gain region is supplying the
additional energy, pressure against infalling material, required to blow the
star up. I don’t understand how this works, but the fluid dynamics of the gain
region cause the neutrinos to supply more energy in the gain region when
turbulence is taken into account.
x. He’s
running lots of simulations to try to understand how this works, since the math
is almost impossible. Although computers don’t yet have enough computing power
to model the supernova in high fidelity, they can model small regions in high
fidelity and capture the complexities of turbulence effects.
xi. Crazy
fascinating, right?!
e. From
the seminar, I went straight to my teaching class. We talked about the midterm
paper (due shortly L)
and brainstormed ideas.
f. The
sky was cloudless so I took a run to the arboretum across the Montlake Cut. It
was very pretty.
g. Returned
to the dorm, studied for a bit, ate dinner at the 8, then went to Judo class. I’ll
spare you the details of getting my locker combination, then having to
re-figure out how the locks work. I can’t remember simple manual instructions.
h. Learned
some more falls, the initial fighting stance, basic footwork, and started to
lead into throws.
i. Returned
to dorm listening to Serial, ate banana w/ peanut butter and gorp, and spent a
long time finishing cow paper. Did laundry and email.
j.
Went to bed.
