Physics in a nutshell

In our culture, the phrase “big bang theory” is often used to mean the idea that the universe was created in one explosive moment (or it’s a TV sitcom or a Styx album). For cosmologists, however, “big bang” means the early expansion of the universe, which might or might not have begun in an instant. The late stages of this process are better understood than the beginning: It ended with a sky full of stars, but at the beginning, even…

Particle collisions can be achieved in two different modes: fixed-target and collider. As depicted here, shooting a beam into a non-moving target is much easier than shooting two moving beams at each other, as is done in the collider mode. The precision of LHC collider-type collisions is equivalent to that of shooting one sewing needle from Fermilab and another from Winfield (six miles away) and having them collide in the middle. The very large improvement in collision energy is the…

Rotating a picture frame mixes horizontal and vertical in much the same way that relativity mixes space and time. Special relativity is a well-established fact of nature. Although we rarely encounter relativistic effects in everyday life, they are routine in the world of subatomic particles and in the cosmos. Objects traveling close to the speed of light become spatially compressed and experience time at a slower rate. For example, lead nuclei in a stationary brick are roughly spherical, but when…

E = mc2

Einstein’s equation is the most famous one of modern physics; however, it never appeared in his first paper. Instead his paper included the unwieldy but equivalent, K0 – K1 = (L/c2) × (v2/2). Einstein’s equation is the most famous equation in history. Even people who have absolutely no interest in science recognize it. But what does it mean? Well, like all equations, it has a left side and a right side, separated by an equal sign. On the left-hand side…

Top-left: a low-entropy painting by Piet Mondrian. Bottom-right: a high-entropy painting by Jackson Pollock. Entropy is a fundamental concept, spanning chemistry, physics, mathematics and computer science, but it is widely misunderstood. It is often described as “the degree of disorder” of a system, but it has more to do with counting possibilities than messiness. Entropy is the number of configurations of a system that are consistent with some constraint. In thermodynamics, the study of heat, this constraint is the total…

While architects and artists have long known of the beauty of symmetry, as demonstrated in the breathtaking Taj Mahal, it was mathematician Emmy Noether who taught physicists to appreciate the beauty and power of symmetries in our equations. Symmetry has several ordinary meanings. It is often taken to mean aesthetic beauty in a pleasing and regular form. It also has a technical meaning. This meaning is often geometrical in nature, as in the five-way symmetry of a starfish or how…

In this series of Physics in a Nutshell articles, Don and I have talked about each of the four fundamental forces of nature: electromagnetism, the strong force, the weak force and gravity. However, these four forces are not truly distinct. Many physicists are motivated by the idea that they are really four manifestations of a single principle, yet to be discovered. It’s already clear that two of them, electromagnetism and the weak force, are related by a unifying principle, known…

Legends have made a whole menagerie of mythical creatures, from centaurs to hippogryphs. The graviton is a proposed subatomic particle that causes gravity. However, since there is no experimental evidence substantiating its existence, for the moment the graviton remains mythical. Without knowing a lot about a given topic, sometimes it’s hard to separate fact from fiction. We might think the mythology of Ancient Greece to be silly with its Pegasus, mermaids and centaurs. Creatures with such a mix of properties…

Of the four fundamental forces, the weak force is the most mysterious. It is the only one with no obvious role in the world we know: The strong force builds protons and nuclei, electromagnetism is responsible for nearly every macroscopic phenomenon, and gravity, though weaker than the rest, is noticeable because of our close proximity to a reasonably large planet. The only observable phenomenon due to the weak force is the radioactivity of certain substances (not all). I sometimes wonder…

The strong nuclear force holds together the protons and neutrons in the nucleus of an atom. This is actually a side effect of its function binding quarks together to make the protons and neutrons themselves. The particle of the strong force is called the gluon because of the strong force’s glue-like properties. The strongest of the subatomic forces is the aptly named strong nuclear force. In the realm in which it operates, it is about 100 times stronger than the…