-
Redefining SI
Today the SI (Système international d’unités) base units are redefined. The following are now exact. Memorize these numbers! Cs-133 transition frequency constant defines the second. Then light speed constant defines the meter. Then Planck’s constant defines the kilogram. Then electron charge constant defines the Ampere. Then Boltzmann’s constant defines the Kelvin. And Avogadro’s constant defines the mole. And luminous efficacy constant defines…
-
Black Hole Radii
I set the alarm for 8:55 AM. Brutal, but I wanted to watch live the National Science Foundation Event Horizon Telescope news conference. I was expecting the first image of a black hole, and the EHT team did not disappoint. But the black hole was not the Milky Way’s Sgr A*, but M87*, a thousand…
-
The Longest Day
The December solstice is the longest day of the year, despite being the northern hemisphere’s shortest daylight. Earth’s sidereal day is the time to rotate 360° with respect to distant stars, about 23 hours and 56 minutes, and its solar day is the time between successive noons, about 24 hours. Earth’s obliquity (tilt) and revolution (orbit) require…
-
Relativistic Colors
Metallium, Inc. is attempting to manufacture coins made from as many different metals (and elements) as possible, typically 99 to 99.9% pure. My Metallium coin collection currently includes aluminum, titanium, iron, nickel, copper, zinc, silver, tin, and gold coins. Most metals are silvery gray because they absorb ultraviolet light and reflect visible light. However, relativistic…
-
720° untangles 360° tangles
Despite growing up in three dimensions, as a kid I did not recognize one of 3D’s deep and subtle properties: full rotations tangle, but double rotations untangle! Following physicist Paul Dirac, twist a belt one full turn about its length. The 360° single twist cannot be undone without changing the belt buckles’ orientations, although the twist…
-
Luna’s Convex Orbit
Luna orbits Earth and Earth orbits Sol (where Luna is Earth’s moon and Sol is Earth’s star, the sun). As a kid, I thought Luna’s solar orbit formed a loopy spirograph pattern. Instead, Luna’s orbit is convex! Neglecting the eccentricity and tilts of the orbits and the incommensurability of the periods, Luna’s counterclockwise path around…
-
1+2+3+… = -1/12?
In quantum electrodynamics, the bare charge of an electron is infinite, but the renormalized dressed charge is finite. The bare electron shields itself by polarizing the virtual electron-positron pairs of the nearby quantum vacuum to reduce its coupling at large distances to in natural units, where the “I” decorating the equals sign denotes an informal relationship. Renormalization techniques help…
-
A Better Table
The periodic table of the elements is almost as old as The College of Wooster, and I am a big fan. As we approach next year’s sesquicentennial of Dmitri Mendeleev‘s 1869 periodic table, I present a modest addition to the over 600 known periodic tables, which include , , and even designs! I wanted the…
-
Math Grenade
I just bought a new calculator. New to me, that is, but older than me. Inspired by the 1600s Gottfried Leibniz stepped cylinder and the 1800s Thomas de Colmar arithmometer, the Curta mechanical calculator design was developed by Curt Herzstark while imprisoned in the Buchenwald concentration camp during World War II. Curta calculators were manufactured between…
-
Optical Tweezers
A focused light beam can trap a small particle, such as a micron-sized latex sphere (or biological cell). If the sphere is much larger than the light’s wavelength, ray optics suffices to explain the trapping. Light bends as it passes through the sphere, as in Fig. A. The piconewton forces (red and blue arrows) on…
Author: John F. Lindner
Recent Comments
Nice post, John! Thanks for writing these. I always enjoy them.
David Smith’s ein stein is an awesome shape!
Recent Posts
Categories
- Adventure (23)
- Architecture (6)
- Astronomy (27)
- Exploration (2)
- Fun (9)
- Mathematics (24)
- Miscellaneous (2)
- Outreach (5)
- Physics (120)
- Space Exploration (52)
- Students (45)
- Travel (34)
- Uncategorized (17)
- Wooster (35)
Thanks, Mark! I enjoy reading your posts as well.