Lurking in my recent research readings, this is a problem at the intersection of middle school geometry and quantum chaos …
This week’s post was delayed such that certain subscribers taking final exams won’t be disturbed. Hope you all had fun.
(more…)Will I have some theme for these posts?
(more…)I guess you know the drill by now. Round earth with a moon whizzing around, and the pair occasionally block sunlight from each other. Neat stuff.
Do you want to see an actual ray diagram of that?
Putting the iPad to the same good use, but publicly.
Summer is beginning, and my first three years of formal college education has come to an end. During this period, I have perfected the skills of Googling for good questions and solutions on a variety of subjects, *rarely* for homework, and for self-study.
It’s time to contribute too. New physics / maths blog posts in handwritten formats coming weekly. If there’s time to spare LaTeX things are possible as well.
Question #0
Q0. Show that the shortest path between two points on a sphere is the big circle.
a familiar exercise.
What’s left is long buried:
Roots in the dark,
stories dissolving—
pressure in every vesicle,
between the soil
and all the sky reachable.
They were the stage,
the actor,
the playwright.
A barren terrace
slowly grows its cover;
shuffling sunshine
weaves the shape.
What’s left is long buried:
lumber from the hill—
to build,
for fuel,
material ideal.
I pray
to the storm,
to the fire.
I pray
to the axe,
to the hand,
to the eyes.
Be kind
to the souls of a giant,
to the bones of time.
Berkeley,
March 2018
A few days back on Zhihu.com at home, there was an astronomy question that made it onto the “Trending Q&A” list (quite impressive for my homeland), “What is the most frightening celestial object known to science?”
Not surprisingly, in the scientifically literate answers — many of which I might be interested in covering in the near future — there were neutron stars, so dense that a star is compressed is a giant pulsating nucleus capable of destroying your credit card from across the solar system; there was Kepler-1 b, the darkest planet known to modern astronomy, absorbing upwards of 98% of its received radiation; there was Eta Carina et al, gamma ray canons aimed at us that is waiting to burn to a crisp anything crossing their light-cones*; there were also black holes and quasars, of course, I suppose that I follow the keyword “black hole” was why this question made it into my recommendation list.
By the time this is posted here, I have already written an answer, actually.
(CH: https://www.zhihu.com/question/268873123/answer/345000237)
I thought that it was quite ironic that the list did not include the one I always pictured as frightening, one that not everyone recognized as “Celestial object”, even.
— Planet earth.
Just for now, perhaps, picture this, shall we?
The earth is a speck of dust weighing less than 10^-30 of all matter in the observable universe, and occupies a volume lower than 10^-60 of it. Earth weighs a millionth the mass of the sun, who have already consumed many earth masses in its lifetime work of taking advantage of E=mc^2. This mass and scale, we round off in even the most precise computations. On paper, we might mean nothing to this great and empty place.
However, it is from earth that we measured the distance to the fuzziest dot of primordial galaxy; it is on earth that we heard the birthcry of space and time; it is on earth that we weighed stars and clusters; it is on earth that we, with all our history, confusion, suffering and terror, emerged onto a galactic stage, and left acts of greatness behind on the scrolls of time.
It’s fair to say this is rather a slightly non-traditional call to protect the environment ⋯ I love it, and am often frightened by it.
The planet’s sheer mass, resources, their finesse also: climate, tectonics, geomagnetism, ores… At the same time, our insignificance to the planet, and the planet’s obscurity to our cosmos.
It’s dark out there, and no one knows if there’s any audience, but we can bring our own light to the show.
//
Taking GR at Berkeley is really a good choice.
Featured Image: Ringed Earth, Me, 2015
I am committing this moment to memory.
(more…)
Yourong Frank Wang 