Entries by Alex Klotz

Either the Sun Is Getting Smaller or Gravity Is Getting Weaker

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. Students of physics learn some interesting facts about the sun, spread over different lessons and…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

New Research on Untying Knots in Polymers

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 the polymer to…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

Using the Spaghetti-Twist to Align DNA

A new paper from a collaboration 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 X (PRX), an open-access journal that…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

Assessing the Physics in Edmond Hamilton’s “The Second Satellite”

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. Just for a bit of context, I’ll explain…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

History’s First Science Experiments

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], the other by the Pharaoh Psammetichus in Egypt in the 600s BC [2]. In each case, we only have one primary source from…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

Polymer Physics and Genetic Sequencing

Introduction My main research focuses on using DNA molecules to study polymer physics. Theoretical polymer physics is based on the thermodynamic behaviour of microscopic chains, but experiments examining single chain behaviour wasn’t possible until improvements in fluorescence microscopy in the 1990s allowed us to visualize the dynamics of DNA molecule in real time. DNA makes…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

The Interaction of Sound and Light

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 that they…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

Roger Babson’s Anti-Gravity Contest

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 won by the likes of Stephen Hawking…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

The Basics of Positron Emission Tomography (PET)

People often ask about the practical applications of fundamental theoretical physics. Less often, people ask about potential applications of anti-matter. Both of those questions can be answered with a common medical diagnostic technolo gy, Positron Emission Tomography, or PET. Positrons were first theorized by Paul Dirac in 1928 when he realized that his equation describing the…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

Secondary Forces Explored

Many are familiar with the “fundamental forces” of nature: gravity, electromagnetism, and the strong and weak nuclear forces. Three of these have a tendency 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…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

All about Earth’s Gravity

Earth’s gravitational field at the surface is approximately 9.8 Newtons/kilogram, or equivalently, 9.8 meters/second/second. But how does that change due to its shape, rotation, and composition and various locations along its surface and within its interior? This article will answer those questions. Latitude dependence due to Earth’s shape and rotation One can simply calculate the…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

The Speed of Light and Galilean Relativity

Introduction In this article I will discuss some experiments in the 19th and early 20th centuries that looked 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 well…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

Atomic Positioning with DNA Hinges

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…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

Fun with Self-Avoiding Walks

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;…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

Can We See an Atom?

If you look on the internet for pictures of atoms, you will see images like this: Or like this: Or like this: In this article I will discuss how these images are made, what exactly we are looking at, and what it really means to see an atom. See with your eyes. The answer to…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

Explosion-Generated Collapsing Vacuum Bubbles Reach 20,000 Kelvin

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 temperature inside the…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

A Hand-Wavy Discussion of the Planck Length

The Planck length is an extremely small distance constructed from physical constants. There are a lot of misconceptions that generally overstate its physical significance, for example, stating that it’s the inherent pixel size of the universe. The Planck length does have physical significance, and I’ll talk about what it is, and what it isn’t. What…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)

Scaling Laws and the Speed of Animals

In a recent issue of the American Journal of Physics, I read an interesting paper by Nicole Meyer-Vernet and Jean-Pierre Rospars examining the top speeds of organisms of varying sizes, from bacteria up to blue whales. They found that the time it takes for an animal to move its own body length is almost independent of…

Postdoctoral Research Associate at Massachusetts Institute of Technology (MIT)