Tom Wong @thomaswong.net · 09/10/2026Yesterday in #PHY201 #GenPhys1: A box is moved some distance by several forces, including yours (F). The work you did is the component of your force along the direction of movement (Fcosθ), times the distance. Your perpendicular component (Fsinθ) didn't contribute to the work. 000
Tom Wong @thomaswong.net · 07/10/2026Last time in #PHY531 #QuantumMechanics: The scattering states of a delta function well have the same reflection and transmission coefficients as the delta function well. It has one bound state corresponding to decaying exponentials on each side. 000
Tom Wong @thomaswong.net · 02/10/2026Today in #PHY201 #GenPhys1: Static friction has strength up to the coefficient of static friction (μₛ) times the normal force (N). Beyond that, it slips, and kinetic friction is μₖN. Objects in circular motion have centripetal acceleration. 000
Tom Wong @thomaswong.net · 01/10/2026Today in #PHY131 #QuantumForEveryone: When atoms are near, their orbitals overlap, interfere constructively or destructively, and yield molecular orbitals and energy levels. With many atoms, the levels form bands. The bandgap yields conductors, insulators, and semiconductors. 000
Tom Wong @thomaswong.net · 30/09/2026Lately in #PHY201 #GenPhys1: Applications of Newton's 2nd Law involving the normal force, inclines, multiple objects, and tension. 000
Tom Wong @thomaswong.net · 29/09/2026Today in #PHY131 #QuantumForEveryone: A trapped wave has stable ways it can wiggle. A wave on a string or electron in a box has standing waves. An electron trapped by a nucleus (i.e., an atom) has orbitals. Molecular bonding is explained by the interference of orbitals. 000
Tom Wong @thomaswong.net · 28/09/2026Today in #PHY531 #QuantumMechanics: The initial wave function can be expressed as weighted sum of the eigenfuctions of the Hamiltonian, which for the free particle is an integral and inverse Fourier transform. So, the weights are the Fourier transform of the initial state. 010
Tom Wong @thomaswong.net · 25/09/2026Today in #PHY531 #QuantumMechanics: For the quantum harmonic oscillator, the raising and lower operators are Hermitian conjugates of each other. Using this, we can determine the normalization constant when finding eigenfunctions by raising and lowering, resulting in this ladder: 100
Tom Wong @thomaswong.net · 25/09/2026Today in #PHY131 #QuantumForEveryone: Wave-particle duality isn't just a curiosity, it's useful! Microscopes with smaller wavelengths have higher resolution, and microscopes using electrons can have resolutions five orders of magnitude greater than visible light. toutestquantique.fr/en/transmiss... 000
Tom Wong @thomaswong.net · 23/09/2026Today in #PHY531 #QuantumMechanics: The Hamiltonian for the quantum harmonic oscillator can be written in terms of raising and lower operators. Applying them to an eigenfunction yields a new eigenfunction with eigenenergy ℏω higher or lower. Lowering the ground state yields 0. 020
Tom Wong @thomaswong.net · 23/09/2026Today in #PHY201 #GenPhys1: Near the surface of the earth, the force of gravity is mg, which is weight. Objects resting on a surface experience a normal force perpendicular to the surface, and it could be equal to, greater than, or less than the weight depending on the situation. 000
Tom Wong @thomaswong.net · 23/09/2026Yesterday in #PHY131 #QuantumForEveryone: Precision timekeeping via atomic clocks enabled the first picture of a black hole by synchronizing radio telescopes across the earth. It also makes GPS possible using the time between GPS signals being sent and received. 000
Tom Wong @thomaswong.net · 22/09/2026Today in #PHY201 #GenPhys1: The first exam, covering units, 1D kinematics, vectors, and 2D kinematics. 000
Tom Wong @thomaswong.net · 22/09/2026Of course, having lived in Latvia for two years for a postdoc at the University of Latvia, I had to find and take a picture of the Latvian ambassador's contribution! 110
Tom Wong @thomaswong.net · 22/09/2026In celebration of the United States' 250th birthday, ambassadors from EU nations each gave a book to celebrate our friendship. See the list at www.eeas.europa.eu/delegations/.... 100
Tom Wong @thomaswong.net · 22/09/2026The European Union ambassador to the United States, Jovita Neliupšienė @euambus.bsky.social, is speaking at Creighton! 100
Tom Wong @thomaswong.net · 21/09/2026Today in #PHY531 #QuantumMechanics: The eigenfunctions of the quantum harmonic oscillator are Hermite polynomials times a Gaussian. Classically, a particle is confined to a spatial region, but quantumly, it has a nonzero probability of being found outside this region. 010
Tom Wong @thomaswong.net · 18/09/2026Today in #PHY531 #QuantumMechanics: For the quantum harmonic oscillator, energy eigenfunctions are only normalizable at certain discrete energies. Its power series is unnormalizable if the series is infinite, so it terminates as a polynomial, where the order n gives E = (n+½)ℏω. 000
Tom Wong @thomaswong.net · 17/09/2026Today in #PHY131 #QuantumForEveryone: The second used to be defined by the earth's motion. Now it's the time for 9,192,631,770 cycles of a microwave light that excites cesium atoms. Such atomic clocks also define the meter and enable the internet, stock trading, & power grid. 000
Tom Wong @thomaswong.net · 16/09/2026Yesterday in #PHY131 #QuantumForEveryone: Lasers are one of the most important inventions of the 20th century. It uses stimulated emission to create more and more coherent photons that are released as a collimated monochromatic beam. 000
Tom Wong @thomaswong.net · 14/09/2026Today in #PHY531 #QuantumMechanics: The first midterm, covering the statistical nature of the wave function through the particle in a box. Here's the first question: 000
Tom Wong @thomaswong.net · 12/09/2026The Fields Medal is often described as the "Nobel Prize of Mathematics." Twenty-five Fields Medalists have signed an joint statement about "A Severe Misalignment of AI in Mathematics." mathandai.org 030
Tom Wong @thomaswong.net · 11/09/2026Yesterday in #PHY131 #QuantumForEveryone: Each atom's spectra is like a barcode or fingerprint that uniquely identifies the element. They are why neon signs and fireworks are different colors. In spectroscopy, an object's spectrum determines what it is made of and how it moves. 000
Tom Wong @thomaswong.net · 10/09/2026My *third* paper with undergraduate student Jonas Duda is out! In "Faster Computation with the Generalized Laplacian Quantum Walk," we give a quantum walk that outperforms typical quantum walks at a search problem and solves it optimally. arxiv.org/abs/2609.10429 010
Tom Wong @thomaswong.net · 09/09/2026Today in #PHY531 #QuantumMechanics: A particle trapped in a box with initial wave function equal to an upside-down parabola has a probably density that evolves as shown in the animation. 000
Tom Wong @thomaswong.net · 09/09/2026Today in #PHY201 #GenPhys1: In projectile motion, there is constant velocity in the x-direction (with two equations) and constant acceleration in the y-direction (with four equations). 000
Tom Wong @thomaswong.net · 09/09/2026Today in #PHY131 #QuantumForEveryone: We made spectrometers and saw that only certain colors are emitted from each element. The Bohr model of the atom explains this by restricting electrons to discrete shells. Electrons absorb and emit photons to jump up and fall down. 000
Tom Wong @thomaswong.net · 05/09/2026Today in #PHY531 #QuantumMechanics: Say a particle in a box has an initial wave function that's an upside-down parabola. Expressing it as a linear combination of the eigenstates of the Hamiltonian, which are sines, is finding its Fourier series. 000
Tom Wong @thomaswong.net · 04/09/2026One of my students drew a picture on their homework. #PHY531 #QuantumMechanics 000
Tom Wong @thomaswong.net · 04/09/2026New paper with postdoc/mathematician Yujia Shi! By adjusting the strength of a nonlinear quantum walk, we can selectively trap and release a particle, which allows timing in state transfer or use as a quantum memory. doi.org/10.1088/1402... 000
Tom Wong @thomaswong.net · 03/09/2026Today in #PHY131 #QuantumForEveryone: Einstein explained the photoelectric effect, where light ejects electrons from a metal, by proposing that Planck's quantized energies correspond to particles, now called photons. The effect is the basis for image intensification night vision. 000
Tom Wong @thomaswong.net · 03/09/2026Yesterday in #PHY531 #QuantumMechanics: The stationary states of a particle in a box are sine functions, which go to zero at the ends of the box. Their various wavelengths give rise to different energies, which are spaced quadratically apart. 000
Tom Wong @thomaswong.net · 02/09/2026Today in #PHY201 #GenPhys1: Ignoring air resistance, objects near the surface of the earth feel an acceleration due to gravity of -9.8 m/s^2, regardless of the mass of the object. This is constant acceleration, so we can use the kinematic equations for such "free fall" problems. 010
Tom Wong @thomaswong.net · 01/09/2026Today in #PHY131 #QuantumForEveryone: Planck explained blackbody radiation by proposing a quantum of energy = hf. Applications: (1) Blackbody radiation explains why people emit infrared light, which thermal imaging picks up. (2) Planck's constant defines the kilogram. 010
Tom Wong @thomaswong.net · 31/08/2026Today in #PHY531 #QuantumMechanics: Schrödinger's equation is a PDE. If the potential is time independent, it separates into two ODEs. One yields a complex exponential in time. The other is the time-independent Schrödinger equation, an eigenvalue relation for the Hamiltonian. 010
Tom Wong @thomaswong.net · 31/08/2026Today in #PHY201 #GenPhys1: Acceleration is the rate of change of velocity. Assuming acceleration is constant, we derived four kinematic equations which have different combinations of variables. 000
Tom Wong @thomaswong.net · 28/08/2026Today in #PHY531 #QuantumMechanics: The expected value of a quantity Q(x,p) is found by replacing p with its operator, sandwiching Q between Ψ* and Ψ, and integrating. The spread of position and momentum measurements of identically prepared systems satisfy Heisenberg's uncertainty principle. 010
Tom Wong @thomaswong.net · 28/08/2026I've been using a refillable dry erase marker for #PHY531 #QuantumMechanics, which only last 1.75 lectures. I mentioned bringing a second marker, and a student said, "It's faster to switch to your secondary than refill your primary." That earned a laugh and a tweet. 010
Tom Wong @thomaswong.net · 27/08/2026Today in #PHY131 #QuantumForEveryone: Students shined lasers through two slits and saw bright and dark fringes, corresponding to constructive and destructive interference, so light is a wave. It's an electromagnetic wave, and different wavelengths have different names and uses. 010
Tom Wong @thomaswong.net · 27/08/2026Yesterday in #PHY531 #QuantumMechanics: For a plane wave to satisfy the Einstein and de Broglie relations, energy and momentum are differential operators. The Hamiltonian equals the total energy, and we get Schrödinger's equation. A normalized wave function stays normalized. 000
Tom Wong @thomaswong.net · 26/08/2026Today in #PHY201 #GenPhys1: If I walk 2 m right and 3 m left, how far did I travel? Two possible answers: (1) 5 m is distance, a scalar. (2) -1 m is displacement, a vector. Velocity is the slope of a position vs time graph, and speed its magnitude. 010
Tom Wong @thomaswong.net · 24/08/2026Today in #PHY531 #QuantumMechanics: A review of probability, including measures of central tendency and spread. Variance is the average of the squared deviation from the mean, but it can be found from the average of the square minus the average squared. 010
Tom Wong @thomaswong.net · 19/08/2026First day of #PHY531 #QuantumMechanics: Firing electrons through two slits, one at a time, results in a wave interference pattern, where the wave determines the likelihood of where the particle will be found. This is wave-particle duality. Relations include p = ħk and E = ħω. 020
Tom Wong @thomaswong.net · 18/08/2026Today in #PHY131 #QuantumForEveryone: 100% of my students had heard of "quantum" before, mostly from movies. A quantum is the smallest amount of something, so a sugar grain is a quantum of granulated sugar, and a water molecule is a quantum of water. Nearly everything has a quantum when you zoom in. 021
