Of Particular Significance

Category: Physics

So Much News, So Little Time

[No AI was used in composing this blog post.]

I’ve been trying to get back to the blog recently. But every time I plan to write a blog post, something happens that requires my attention and adds to the list of items I should be writing about.

I’ve decided that the best I can do, for now, is to summarize some of the key stories that have been on my radar. The overarching news, aside from the 2026 physics Nobel Prize, is what you’ve heard: artificial intelligence (AI) is transforming mathematics and high-energy theoretical physics, no question. That said, what is reported in the media about this is usually wrong in key details, and almost always wildly overstates what’s been accomplished. Nevertheless, the advances in AI models in the last couple of months are historic and transformative, and there is every reason to expect this to accelerate. For people like me, 2027 will surely be very different from autumn 2026, which in turn barely resembles spring 2026.

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POSTED BY Matt Strassler

ON October 30, 2026

Answers to Two Cosmic Questions From A Reader

Recently a reader, having read my post about why the speed of light seems so fast, sent me two questions that highlight important cosmic issues.

Is there in fact anything within physics as it’s presently understood that indeed prevents […] there existing something other than atoms as some basic “unit”?
I’ve long wondered why it is that despite the seeming brilliance of humans at building such complex understanding, we are still pushing at such limits as the time it would take to fly a space ship to another galaxy. Is it really true that nothing could ever exceed ‘c’ and thus we are indeed doomed to take lifetimes to travel beyond our solar system? Or is it because we have not yet discovered something much more fundamental about the universe, such as an ‘alternative to’ the atom?

These deep questions are examples of an even broader pair of questions about reality.

Which aspects of the cosmos are contingent?—in that one could easily imagine a similar universe in which these details are thoroughly altered.
Which aspects of the cosmos appear rock solid?—in that they are so deeply integrated into the universe that it is difficult to imagine changing them without ruining everything.

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POSTED BY Matt Strassler

ON October 28, 2024

Why is the Speed of Light So Fast? (Part 1)

I’m often asked two very natural and related questions.

Why is the speed of light, usually denoted c, so astonishingly fast?
Why, in Einstein’s famous equation relating energy and mass — E=mc² — does c², a gargantuan number, appear?

It’s true that the speed of light does seem fast — light can travel from your cell phone to your eyes in a billionth of a second, and in a full second and a half it can travel from the Earth to the Moon.

And indeed the energy stored in your body is comparable to the Earth’s most explosive volcanic eruptions and to the most violent nuclear bombs ever tested — enormously greater than the energy you use to walk across the room or even to lift a heavy suitcase.

What in the name of physics — and chemistry and biology — is responsible for these bewildering features of reality? The answer is fascinating, and originates in particle physics and the resulting structure of matter. It is surprisingly intricate, though, so I’m going to approach this step-by-step over three blog posts. Here’s the first.

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POSTED BY Matt Strassler

ON October 1, 2024

How To Make A Standing Wave Without Edges

I recently pointed out that there are unfamiliar types of standing waves that violate the rules of the standing waves that we most often encounter in life (typically through musical instruments, or when playing with ropes and Slinkys) and in school (typically in a first-year physics class.) I’ve given you some animations here and here, along with some verbal explanation, that show how the two types of standing waves behave.

Today I’ll show you what lies “under the hood” — and how you yourself could make these unfamiliar standing waves with a perfectly ordinary physical system. (Another example, along with the relevance of this whole subject to the Higgs field, is discussed in chapter 20 of the book.)

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POSTED BY Matt Strassler

ON March 25, 2024

A Relatively Important Question from a Reader

Recently, a reader raised a couple of central questions about speed and relativity. Since the answers are crucial to an understanding of Einstein’s relativity in particular and of the cosmos in general, I thought I’d bring them to your attention, in case you’ve had similar questions.

The Questions

I understand that the vacuum speed of light [“c“] is constant throughout the Universe, and I’m familiar with the math that shows that the energy required to accelerate a particle becomes infinite as the speed approaches c. But what physical effect enforces this behavior? If a proton, for example, gets ejected in a supernova explosion, how does it “know” that it’s getting close to c and can’t go any faster?

And as a corollary to this question, what is the reference frame for measuring these relativistic velocities? For example, when a particle beam at CERN is said to be moving at 99.99% the speed of light, is that speed relative to the infrastructure at CERN? Or does it somehow account for the velocity components that arise from the rotation of the Earth, the orbital motion of the Earth around the Sun, the galactic motion of the Sun in the Milky Way, and so on?…

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POSTED BY Matt Strassler

ON March 6, 2024

Dismantling Common Sense, Twice

In my last post I raised a question about the pros and cons of common sense. I left it as a wide-open question, as I was curious to see how readers would react.

Many aspects of common sense affect how we relate to other people, and it’s clear they have considerable value. But the intuitions we have for nature, though sometimes useful, are mostly wrong. These conceptual errors pose obstacles for students who are learning science for the first time.

It’s also interesting that once these students learn first chemistry and then Newtonian-era physics, they gain new intuitions for the natural world, a sort of classical-physics common sense. Much of this newfound common sense also turns out to be wrong: it badly misrepresents how the cosmos really works. This is a difficulty not only for students but also for many adults. If you’ve read about or even taken a class in basic astronomy or physics, it can then be challenging to make sense of twentieth-century physics, where Newtonian intuition can fail badly.

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POSTED BY Matt Strassler

ON June 20, 2023

Relatively Confused: Is It True That Nothing Can Exceed Light Speed?

A post for general readers:

Einstein’s relativity. Everybody’s heard of it, many have read about it, a few have learned some of it. Journalists love to write about it. It’s part of our culture; it’s always in the air, and has been for over a century.

Most of what’s in the air, though, is in the form of sound bites, partly true but often misleading. Since Einstein’s view of relativity (even more than Galileo’s earlier one) is inherently confusing, the sound bites turn a maze into a muddled morass.

For example, take the famous quip: “Nothing can go faster than the speed of light.” (The speed of light is denoted “c“, and is better described as the “cosmic speed limit”.) This quip is true, and it is false, because the word “nothing” is ambiguous, and so is the phrase “go faster”.

What essential truth lies behind this sound bite?

Faster Than Light? An Example.

Let’s first see how it can lead us astray.

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POSTED BY Matt Strassler

ON September 1, 2022

E = m c-Squared: The Simple Dimensions of a Discovery

In my last post I introduced you to dimensional analysis, an essential trick for theoretical physicists, and showed you how you could address and sometimes solve interesting and important problems with it while hardly doing any work. Today we’ll look at it differently, to see its historical role in Einstein’s relativity.

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POSTED BY Matt Strassler

ON June 23, 2022

Dimensional Analysis: A Secret Weapon in Physics

It’s not widely appreciated how often physicists can guess the answer to a problem before they even start calculating. By combining a basic consistency requirement with scientific reasoning, they can often use a heuristic approach to solving problems that allows them to derive most of a formula without doing any work at all. This week I want to introduce this to you, and show you some of its power.

The trick, called “dimensional analysis” or “unit analysis” or “dimensional reasoning”, involves requiring consistency among units, sometimes called “dimensions.” For instance, the distance from the Earth to the Sun is, obviously, a length. We can state the length in kilometers, or in miles, or in inches; each is a unit of length. But for today’s purposes, it’s irrelevant which one we use. What’s important is this: the Earth-Sun distance has to be expressed in some unit of length, because, well, it’s a length! Or in physics-speak, it has the “dimensions of length.”

For any equation in physics of the form X = Y, the two sides of the equation have to be consistent with one another. If X has dimensions of length, then Y must also have dimensions of length. If X has dimensions of mass, then Y must also. Just as you can’t meaningfully say “I weigh twelve meters” or “I am seventy kilograms old”, physics equations have to make sense, relating weights to weights, or lengths to lengths, or energies to energies. If you see an equation X=Y where X is in meters and Y is in Joules (a measure of energy), then you know there’s a typo or a conceptual mistake in the equation.

In fact, looking for this type of inconsistency is a powerful tool, used by students and professionals alike, in checking calculations for errors. I use it both in my own research and when trying to figure out, when grading, where a student went wrong.

That’s nice, but why is it useful beyond checking for mistakes?

Sometimes, when you have a problem to solve involving a few physical quantities, there might be only one consistent equation relating them — only one way to set an X equal to a Y. And you can guess that equation without doing any work.

Well, that’s pretty abstract; let’s see how it works in a couple of examples.

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POSTED BY Matt Strassler

ON June 21, 2022

Physics is Broken!!!

Last Thursday, an experiment reported that the magnetic properties of the muon, the electron’s middleweight cousin, are a tiny bit different from what particle physics equations say they should be. All around the world, the headlines screamed: PHYSICS IS BROKEN!!! And indeed, it’s been pretty shocking to physicists everywhere. For instance, my equations are working erratically; many of the calculations I tried this weekend came out upside-down or backwards. Even worse, my stove froze my coffee instead of heating it, I just barely prevented my car from floating out of my garage into the trees, and my desk clock broke and spilled time all over the floor. What a mess!

—

Broken, eh? When we say a coffee machine or a computer is broken, it means it doesn’t work. It’s unavailable until it’s fixed. When a glass is broken, it’s shattered into pieces. We need a new one. I know it’s cute to say that so-and-so’s video “broke the internet.” But aren’t we going a little too far now? Nothing’s broken about physics; it works just as well today as it did a month ago.

More reasonable headlines have suggested that “the laws of physics have been broken”. That’s better; I know what it means to break a law. (Though the metaphor is imperfect, since if I were to break a state law, I’d be punished, whereas if an object were to break a fundamental law of physics, that law would have to be revised!) But as is true in the legal system, not all physics laws, and not all violations of law, are equally significant.

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POSTED BY Matt Strassler

ON April 12, 2021

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Category: Physics

POSTED BY Matt Strassler

POSTED BY Matt Strassler

POSTED BY Matt Strassler

POSTED BY Matt Strassler

The Questions

POSTED BY Matt Strassler

POSTED BY Matt Strassler

Faster Than Light? An Example.

POSTED BY Matt Strassler

POSTED BY Matt Strassler

POSTED BY Matt Strassler

POSTED BY Matt Strassler

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