What is a particle?

Natalie Wolchover for Quanta Magazine asked several physicists what a particle is. She came away with several points of view. For example, the particle as a “irreducible representation of a group”:

It’s the standard deep answer of people in the know: Particles are “representations” of “symmetry groups,” which are sets of transformations that can be done to objects.

Take, for example, an equilateral triangle. Rotating it by 120 or 240 degrees, or reflecting it across the line from each corner to the midpoint of the opposite side, or doing nothing, all leave the triangle looking the same as before. These six symmetries form a group. The group can be expressed as a set of mathematical matrices — arrays of numbers that, when multiplied by coordinates of an equilateral triangle, return the same coordinates. Such a set of matrices is a “representation” of the symmetry group.

Oh boy. A lot of this was over my head, as I nearly failed physics in college, but the various explanations with basic diagrams taught me a few new things.

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How gears work

Bartosz Ciechanowski took a deep dive into how gears work and the physics behind the movement with a series of graphics and interactives:

I’ve always been fascinated by mechanical gears. There is something captivating about the way their teeth come together to create a fluid, unified motion.

In this blog post I’d like to look at these simple machines up close. I’ll explain how gears affect the properties of rotational motion and how the shape of their teeth is way more sophisticated than it may initially seem.

[Thanks, @mtoconnor3]

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The Physics & Astronomy Category Recipient of the PLOS ONE Early Career Travel Award in the Physical Sciences Is…

  The Physics & Astronomy Category Recipient of the PLOS ONE Early Career Travel Award in the Physical Sciences Is…   post-info Thank you to all community members who submitted applications! We are delighted to

The PLOS ONE Early Career Researcher Travel Awards in the Physical Sciences

By PLOS ONE Editors post-info Early career researchers (ECRs) are very much at the heart of what we do at PLOS. Last year alone, PLOS ONE published more than 20,000 research papers, undoubtedly with tens

ECRs Reflect on Stephen Hawking

0000-0002-8715-2896 “The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge.”  –Stephen Hawking 1942-2018   This week the world lost one of the most impressive scientists in history, the one and

My non supportive response to "All Biology is Computational Biology"

Nobel-worthy gravitational waves; Supreme Court legalities for climate change, abortion

GRAVITATIONAL WAVES MAKE WAVES Here it is only February, but the long-sought detection of gravitational waves announced last week is likely to be the biggest science news of 2016. The ability to see/hear gravitational waves

Gravity visualized in physics demo

Dan Burns explains some properties of time and space using marbles and two large pieces of spandex sewn together in a classroom demonstration.


Physics and me never got along in high school and college, but I did always enjoy the low-budget demonstrations. It's one thing to see calculations on paper. It's another when the professor sets up a stuffed monkey on one side of the room and then shoots a sock out of a pressurized cannon angled at the trajectory you just calculated to make sure the sock hits the monkey on its way down from ceiling height.

Of course you can look it up on YouTube:


In retrospect, shooting a monkey falling out of a tree seems kind of wrong.

And while we're at it, I always liked this demo too. A bicycle wheel gyroscope hangs from a rope, and when it spins its axis stays horizontal like magic.


MIT has a 43-demo playlist if you need something to watch during your lunch hour.

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A century of Einstein’s general #relativity, life on a Saturn moon, sugar industry influences dental research

Everything’s relative Einstein’s paper on general relativity was published in 1915. The paper didn’t appear until December of that year, but there’s already been some celebratory centennial doings. Science published a special issue last week, and it looks as if … Continue reading »

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Tortoise vs Hare, but in a vacuum this time

We all know how gravity is supposed to work. Without air resistance, a feather and a bowling ball (the standardized materials for all gravitational tests) should accelerate toward the center of the Earth at the same rate, thus striking the ground at the same time. Humans have tested this. It works.

Although we know this thing, it is so far removed from our daily experience that it is still stunning to watch it happen. This fundamental principle is nicely illustrated in this video from the BBC. The video also nicely shows how amazed a roomful of individuals who know how the experiment will work can be when the experiment works exactly as expected.

That is why we need the scientific method to rigorously test hypotheses and incrementally build our knowledge of how the universe works. Our day-to-day experience of and intuition about the world is extremely valuable, but also extremely deceptive.

For the record, the tortoise vs hare in a vacuum race I alluded to in the title would be incredibly inhumane and disappointing, in addition to having no winner – unless, UNLESS we had the tortoise and hare race in spacesuits. Why aren’t we racing animals in spacesuits?

HT: Jared Heidinger

Filed under: Curiosities of Nature Tagged: BBC, Brian Cox, gravity, Jared Heidinger, Physics, scientific method