Biophysics applies physics tools and concepts to living systems in three main ways: using physics instruments to measure biology more precisely, using biological systems to study fundamental physics phenomena that are otherwise hard to realize experimentally, and applying physics training to biomedical engineering problems. Medical physics, covering imaging and radiation therapy, is a related but…
Paper and context Paper discussion: Solar system expansion and strong equivalence principle as seen by the NASA MESSENGER mission. Antonio Genova, Erwan Mazarico, Sander Goossens, Frank G. Lemoine, Gregory A. Neumann, David E. Smith & Maria T. Zuber. Nature Communications volume 9, Article number: 289. Background: Sun and mass loss Students of physics learn many…
Macromolecules Paper overview A joint computational-experimental paper that I worked on was just published in MacroLetters, a journal that covers all topics relating to macromolecules (polymers and the like). In it, we looked at simulations of knotted polymer chains being stretched by an external flow field and studied how the knot affected the response of…
Twirling DNA Around a Rotating Wire A new paper from a group of Canadian physicists has demonstrated how simply twirling a wire through a solution of DNA molecules can align the molecules around the wire, similar to the way that twirling a fork can align noodles around it. The paper was published in Physical Review…
Introduction This article won’t contain much about physics that typical readers of this site don’t already know. However, deconstructing improper physics in literature and film can be a good exercise for physics teachers to share with their students. I’ll focus on one story, in particular, Edmond Hamilton’s The Second Satellite. How I came to this…
Overview In this Insight, I’m going to talk about two of the first science experiments in recorded history. One was allegedly performed by the Prophet Elijah in Israel in the 800s BC [1], and the other by the Pharaoh Psammetichus in Egypt in the 600s BC [2]. In each case, we only have one primary…
Introduction A single DNA molecule snaking its way through an array of cavities. This movie is from one of my later Ph.D. experiments. Why DNA is a good polymer model My main research focuses on using DNA molecules to study polymer physics. Theoretical polymer physics is based on the thermodynamic behavior of microscopic chains, but…
Introduction I recently wrote a post on my blog about a fairly esoteric idea regarding sound propagating through light. This inspired me to write an article about the more down-to-earth interactions between light and sound. Light is a transverse electromagnetic wave and sound is a longitudinal density wave through a medium, and it’s generally taught…
Roger Babson and His War on Gravity In the early 20th century, an eccentric businessman named Roger Babson declared gravity to be mankind’s greatest threat. He devoted part of his fortune to defeating it, creating the Gravity Research Foundation which sponsors a yearly essay contest focused on the understanding of gravity. This contest has been…
Practical applications of fundamental theoretical physics Positron Emission Tomography (PET) Less often, people ask about potential applications of anti-matter. Both of those questions can be answered with a common medical diagnostic technology, Positron Emission Tomography, or PET. Brief history of positrons Positrons were first theorized by Paul Dirac in 1928 when he realized that his…
Many are familiar with the “fundamental forces” of nature: gravity, electromagnetism, and the strong and weak nuclear forces. Three of these tend to bind things together in stable ways: as orbits, as atoms, or as nucleons. Once these systems are stable, there are still “residual” effects that the objects can have on one another through…
Introduction Earth’s gravitational field at the surface is approximately 9.8 Newtons/kilogram or 9.8 meters/second/second. But how does that change due to its shape, rotation, composition, and various locations along its surface and interior? This article will answer those questions. Latitude dependence due to Earth’s shape and rotation Centripetal acceleration at the equator One can simply…
Introduction In this article, I will discuss some experiments in the 19th and early 20th centuries that looked at how the velocity of a light source affects the speed of the light emitted from it. In particular, the Fizeau water experiment, the de Sitter double star experiment, and the Michelson-Morley experiment, which is the most…
I was perusing the Nature Nanotechnology website today when I came across an interesting article by Funke and Dietz, called “Placing molecules with Bohr radius resolution using DNA origami.” The authors created a hinge out of DNA which they selectively open or close by varying the length of one of the DNA molecules, which allows…
This post is about some simulations I did of self-avoiding random walks. These are what they sound like with each step, the position of the walk moves randomly, with the constraint that it can’t visit the same spot more than once. These are mathematically somewhat interesting and crop up in a few areas of physics;…
Introduction In this article I discuss how images of atoms are made, what exactly we are looking at, and what it means to “see” an atom. Over the decades there have been many attempts, claims, and misconceptions about what atoms look like and how we can photograph them. Below I set the record straight. Common…
Experiment overview In a recent paper published in Physical Review Letters (PRL), one of the top physics journals, Jérôme Duplat and Emmanuel Villermaux developed a method to generate centimeter-sized vacuum bubbles in water with miniature laser-driven explosions and observed the flash of light produced as the bubble collapsed, a not-fully-understood phenomenon known as sonoluminescence. They measured…
The Planck length is an extremely small distance constructed from physical constants. Many misconceptions overstate its physical significance, claiming it is the inherent “pixel size” of the universe. The Planck length does have physical significance in certain contexts; below I explain what it is and what it is not. What is the Planck length? Planck…
Introduction In a recent American Journal of Physics issue, I read an interesting paper by Nicole Meyer-Vernet and Jean-Pierre Rospars examining the top speeds of organisms across a huge range of sizes, from bacteria to blue whales. They found that the time it takes an animal to traverse its own body length is, to zeroth…