Modern Physics and Relativity

Blackbody Spectrum

How does the blackbody spectrum of the sun compare to visible light? Learn about the blackbody spectrum of the sun, a light bulb, an oven, and the earth. Adjust the temperature to see the wavelength and intensity of the spectrum change. View the color of the peak of the spectral curve.

Photoelectric Effect

See how light knocks electrons off a metal target, and recreate the experiment that spawned the field of quantum mechanics.

Rutherford Scattering

How did Rutherford figure out the structure of the atomic nucleus without looking at it? Simulate the famous experiment in which he disproved the Plum Pudding model of the atom by observing alpha particles bouncing off atoms and determining that they must have a small core.

Models of the Hydrogen Atom

How did scientists figure out the structure of atoms without looking at them? Try out different models by shooting photons and alpha particles at the atom. Check how the prediction of the model matches the experimental results.

Neon Lights and Discharge Lamps

Produce light by bombarding atoms with electrons. See how the characteristic spectra of different elements are produced, and configure your own element's energy states to produce light of different colors.


Create a laser by pumping the chamber with a photon beam. Manage the energy states of the laser's atoms to control its output.

Simplified MRI

Is it a tumor? Magnetic Resonance Imaging (MRI) can tell. Your head is full of tiny radio transmitters (the nuclear spins of the hydrogen nuclei of your water molecules). In an MRI unit, these little radios can be made to broadcast their positions, giving a detailed picture of the inside of your head.

Alpha Decay

Watch alpha particles escape from a Polonium nucleus, causing radioactive alpha decay. See how random decay times relate to the half life. (Previously part of the Nuclear Physics simulation - now there are separate Alpha Decay and Nuclear Fission sims.)

Beta Decay

Watch beta decay occur for a collection of nuclei or for an individual nucleus.

Radioactive Dating Game

Learn about different types of radiometric dating, such as carbon dating. Understand how decay and half life work to enable radiometric dating to work. Play a game that tests your ability to match the percentage of the dating element that remains to the age of the object.

Nuclear Fission

Start a chain reaction, or introduce non-radioactive isotopes to prevent one. Control energy production in a nuclear reactor! (Previously part of the Nuclear Physics simulation - now there are separate Alpha Decay and Nuclear Fission sims.)

Einstein's Train and Tunnel

The Einstein's Train and Tunnel model displays the famous thought experiment from special relativity where a train enters a tunnel as seen from two points of view.  In one case the train is seen in the reference frame of the tunnel, while in the other case the train is seen in its reference frame.


The Simultaneity model displays the effect of relative motion on the relative ordering of the detection of events.  The wave source and two equidistant detectors are at rest in reference frame S', which moves with constant velocity, v, in frame S.

Simultaneous Events

The Simultaneous Events program displays the effect of relative motion on the relative ordering of events in special relativity.   In the default scenario two simultaneous events are observed in a stationary reference frame (the Other Frame) and the spacetime diagram of the observation of these events is depicted in another reference frame (the Home Frame).

Twin Paradox

The Twin Paradox program displays the effect of time dilation on a moving twin as seen from a stationary twin.   In the default scenario the light signals sent from the moving twin are depicted using a spacetime diagram and are shown as seen in the stationary twin's reference frame (the Home Frame).

Proper Length

The GR Proper Length program simulates the distance between points using the Schwarzschild metric.  It displays the proper length between two points and the light-travel path.  It is distributed as a ready-to-run (compiled) Java archive. 

Blackbody Radiation Spectrum

The Blackbody Radiation Spectrum model shows six fixed-temperature curves between Tmin and Tmax and a red variable-temperature curve that can be adjusted using a slider.

Eigenstate Superposition

The Eigenstate Superposition model illustrates the fundamental building blocks of one-dimensional quantum mechanics, the energy eigenfunctions  ψn(x) and energy eigenvalues En.

Free Particle Energy Eigenstates

The Free Particle Energy Eigenstates model shows the time evolution of a superpostion of free particle energy eigenstates.  A table shows the energy, momentum, and amplitude of each eigenstate.

Quantum Mechanical Measurement

The QM Measurement program displays the time evolution of the position-space wave function and can be used to simulate the quantum-mechanical measurements of energy, position, and/or momentum.  The default wave function is an equal-mix four-state superposition in the infinite square well.

Barrier Scattering

The Barrier Scattering model shows a quantum mechanical experiment in which an incident wave (particle) traveling from the left is transmitted and reflected from a potential step at x=0.

Double Pendulum

The Double Pendulum model displays the motion of a double pendulum and its Poincare map. A double pendulum is a pendulum with another pendulum attached to its end and the state of this dynamical system is specified by two angles and two angular velocities.

Michelson Morley Experiment A simple analogy involving two swimmers that sets up the Michelson-Morley Experiment.
Simultaneity A tutorial that shows how the relative nature of the simultaneity of two events must follow from the existence of length contraction.
Time Dilation A demonstration that the phenomenon of time dilation from the special theory of relativity necessarily follows from the idea that the speed of light is the same value for all observers.
Twin Paradox There are many ways of approaching this classic "paradox". Here we discuss it as an example of the relativistic Doppler effect.
Length Contraction A tutorial that shows how relativistic length contraction must follow from the existence of time dilation.
Pair Production and Annihilation A simple illustration of electron-positron production and annihilation.
Interaction of X-Rays with Matter

Illustrating the 3 principle modes by which X-rays interact with matter.

Bohr Model of Hydrogen

The photon excitation and photon emission of the electron in a Hydrogen atom as described by the Bohr model.

Wave / Particle Duality Here we visualize a hydrogen atom, which consists of an electron in orbit around a proton. In one view the electron is a particle and in the other view it is a probability distribution.
Double Slit Experiment with Electrons The famous "Feynman Double Slit Experiment" for electrons. Here we fire one electron at a time from the electron gun, and observe the build-up of electron positions on the screen.
Bells Theorem Based on an analysis by Mermin, this animation explores correlation measurements of entangled pairs.
Nuclear Decay The decay of 500 atoms of the fictional element Balonium. Uses a proper Monte Carlo engine to simulate real decays

The Java Applets were taken either from PhET or Open Source Physics.

The Flash Animations were all taken from David M. Harrison from the University of Toronto.