Barely Radioactive Elements

“What is the heaviest stable element?” This question, easily posed, is not so easy to answer. In fact, nobody knows. This document explores the stability of heavy elements, the difficulty of experimentally confirming theoretical predictions of very rare events, and elements whose half-lives are longer than the lives of all stars in the universe.


Cellular Automata Laboratory invites you to explore the world of cellular automata with the aid of a high-speed programmable simulator which runs within your Web browser. Cellular automata rules are defined by short programs written in JavaScript or Java. Rule definitions in JavaScript are compiled directly inside the browser and do not require installing a programming environment on your machine. The accompanying on-line laboratory manual explains the theory of cellular automata, how to use the simulator programs, documents the many ready-to-run rules included, describes how to create your own original experiments, and contains a comprehensive bibliography. A development kit supplies source code for all of the rule definitions and the files they use, providing a starting point for your own explorations. New: 2017 update includes browser-based simulation and JavaScript rule definition.


The only reason Einstein's special theory of relativity seems weird to those learning it is that the velocities we're familiar with are such a tiny fraction of the speed of light we've never had a chance to gain an intuitive sense of relativistic effects. If the speed of light were 100 kilometres per hour, footballers would have no trouble dealing with relativistic goal shots. C-ship uses computer image synthesis to put you aboard a starship entirely consistent with the laws of physics and lets you look out the window to experience special relativity with your own eyes.

Bending Spacetime in the Basement

This “basement science” experiment demonstrates the universality of gravitation, showing the gravitational attraction between masses of less than a kilogram. Could Archimedes have discovered universal gravitation nineteen centuries before Newton? Well, let's see….

Orbits in Strongly Curved Spacetime

An interactive animation illustrates how orbits around compact objects such as neutron stars and black holes depart drastically from Kepler's laws, and explains why.

Update: January 2017 update uses HTML5/JavaScript animation, eliminating the need for Java, and improves graphics rendering. The original Java version remains available.


Quantum mechanics teaches us that, at the deepest level, uncertainty rules the universe: there are things we cannot predict, even in principle. HotBits harnesses this fundamental uncertainty of nature to generate truly random bits, unlike the pseudorandom sequences created by an algorithm on a computer. Along the way, you'll find a discussion of the hardware and software used to generate the random bytes comprehensive enough to build your own, and peek under the hood of quantum mechanics to see why the data are genuinely random, and some of the implications of all this.

The Oh-My-God Particle

On October 15th, 1991 a proton with an energy of 31020 electron volts slammed into in the Earth's atmosphere. Let's crunch some numbers…. A performance comparison with 24th century Galaxy Class starship technology is presented.

On the Electrodynamics of Moving Bodies

An English language translation of Albert Einstein's 1905 paper which introduced Special Relativity, as published in the 1923 book The Principle of Relativity. This document is is both a monument of twentieth century physics and a masterpiece of scientific communication. In addition to the Web edition, a ready-to-print PostScript file and LaTeX source code of this document may be downloaded. Stefano Taschini has produced a beautiful Adobe Acrobat PDF edition of this document--thank you!

Does the Inertia of a Body Depend upon its Energy-Content?

An English language translation of Albert Einstein's 1905 paper which first derived the equivalence of mass and energy, as published in the 1923 book The Principle of Relativity. Starting solely from the principle of relativity for observers in uniform motion and the constancy of the speed of light, Einstein employs an elegant kinematical argument to deduce the most famous equation of twentieth century physics: the equivalence of mass and energy. In addition to the Web edition, ready-to-print PostScript and Adobe Acrobat PDF files as well as LaTeX source code of this document are available.

My Trip to CERN

In April 2013 I had the privilege of visiting CERN: the premier particle physics laboratory in the world. This photo essay shows some of the underground wonders of the largest and most complicated machine ever built by our species.

Potassium-40 and the Evolution of Higher Life

Why did such a long interval elapse between the appearance of life on Earth and the emergence of complex, multicellular organisms? Perhaps it had little to do with biology and everything to do with the half-life of a radionuclide forged in the supernova whose debris gave rise to us all.

What Gives Gold that Mellow Glow?

It's sometimes said that special relativity has no consequences in everyday life. Yet there's an effect of special relativity which is immediately apparent at the glance of an eye and observed (if not understood) since antiquity—the yellow gleam of gold.

From 1963: Nuclear Batteries Now!

In 1963, Analog was a large format monthly magazine, part slick and part pulp, with a cover price of 50 cents. Its eclectic readership and contents attracted some curious advertisements, such as this one from Leesona Moos Laboratories for aerospace devices self-powered by Krypton 85 nuclear batteries. How many Analog readers in 1963 assumed that in a couple of years there'd be nuclear flashlight batteries for sale at the hardware store? This one certainly did.

Pitch Drop

The longest continuously-running scientific experiment demonstrates that even extremely viscous fluids will eventually flow as the liquids they are. Do it yourself instructions are included.

Plutonium Production

To understand the news about negotiations with aspiring nuclear powers, it's important to comprehend the technical fundamentals of both paths to nuclear weapons. Here are the physics, chemistry, and engineering behind the production of plutonium for nuclear weapons applications, described for non-specialists. A companion document discusses uranium enrichment.

Project Pluto

In the late 1950s and early '60s Project Pluto aimed at developing a nuclear powered cruise missile which could fly three times the speed of sound at low altitude with unlimited range and deliver nuclear devastation to multiple targets with pinpoint accuracy. It was one of the most bizarre concepts of the age of unlimited nuclear optimism, and got as far as ground testing a full scale flight weight propulsion system.

Relativistic Nutrition

The books gotta balance! The mass of the inputs and outputs of the human body, averaged over time, are equal. So where does the energy the body consumes come from?

The Relativity of Simultaneity

Due to the finite speed of light, observers in different locations or moving with respect to one another may see events as occurring in different orders—simultaneity depends upon your viewpoint. You've heard the mission control recording of Apollo 11 landing on the Moon, but what did it sound like on board the lunar module? This document demonstrates the relativity of simultaneity and lets you experience the Eagle's touchdown from a lunar perspective, providing an insight about Neil Armstrong's first radio transmission after the landing.

Rocket Science

Rocket engineering is complicated and demanding, but rocket science is pretty straightforward. Explore the rocket equation, which governs the operation of all rockets, and understand why it's so difficult to get to orbit from the surface of the Earth and why multistage rockets make sense.

Cosmic Background Radiation Space Drive

Thermodynamics confronts special relativity in this physics puzzle which explains why intergalactic spacecraft will be streamlined just like in the movies.

Tipler's Physics of Immortality

A review/rant about Frank Tipler's 1994 book, The Physics of Immortality.

The Effects of Nuclear Weapons

The 1977 third (and most recent) edition of this book, compiled by Samuel Glasstone and Philip J. Dolan and published by the United States Department of Defense and Energy Research and Development Administration (now Department of Energy) is the definitive work on nuclear weapons effects. It is presented in a hybrid form, with an XHTML table of contents which links to PDF file containing scans of the pages of the book. An interactive Web edition of the nuclear bomb effects computer circular slide rule which accompanied the 1962 edition of the book is also available.

Strangelove Slide Rule: Nuclear Bomb Effects Computer

Relive the chilling calculations of the Cold War with this interactive edition of the Nuclear Bomb Effects Computer published in 1962 by the United States Atomic Energy Commission. Enter the yield and range, and the full suite of weapons effects will be displayed just as on the original pocket slide rule. Nuclear weapons users who prefer a physical slide rule, either out of nostalgia or an appreciation for its ability to operate in post-apocalyptic conditions, will find instructions for making their own.

Atomic Test Effects in the Nevada Test Site Region

In 1955 the giant mushrooms sprouted in abundance at the Nevada Test Site north of Las Vegas. A total of fourteen fission devices were detonated, with yields as high as 43 kilotons. The “Desert Rock VI” exercise exposed 8000 troops to nuclear blasts to train them for combat operations on the nuclear battlefield. This document was distributed in January 1955 to those living near the Nevada Test Site to prepare them for the 1955 test series. Illustrated with delightful 1950s line art, it includes such sage advice as, “Your best action is not to be worried about fall-out.” and “We can expect many reports that ‘Geiger counters were going crazy here today.’ Reports like this may worry people unnecessarily. Don't let them bother you.”

Uranium Enrichment

To understand the news about negotiations with aspiring nuclear powers, it's important to grasp the technical fundamentals of both paths to nuclear weapons. This document describes the science and engineering behind enriching natural uranium for use in civil nuclear power reactors or weapons. A companion document discusses plutonium production.

Vacuum Propellers

Fast interstellar travel will never be possible with any kind of rocket, regardless of the energy source (be it chemical, nuclear, or antimatter), due to the need to carry the rocket's reaction mass on board. How can a person who coined the maxim “Never invest in something that violates a conservation law” seriously entertain the possibility of “propellantless propulsion”? This brief document speculates on how a “Vacuum Propeller” might be built which violates no law of physics.