Of Particular Significance

Category: History of Science

Event with Professor Daniel Whiteson on Monday November 17 at 7pm

Next Monday, November 17th at 7pm, I’ll be at the Harvard Bookstore with particle physicist and author Daniel Whiteson. Professor Whiteson and his co-author Andy Warner have a nice new book, for the general science-aware reader, exploring an age-old and unanswered question: how universal is the knowledge and understanding that we call “physics”? How much of modern physics is actually telling us about the universe, and how much of it is created by, or an accident of, the humans who have helped bring it about?

For instance, if we started all over again and reran history from scratch, would the physics (and science more generally) of this re-run culture look much like our own, or might it turn out very differently? If another culture on Earth had had time to develop highly mature science (or something like it) in its own direction, independent of Western Europe’s influence, how different might that science be? (Indeed, would our word “science” even be translatable into their worldview?) Or if we encountered aliens with far greater understanding of the universe than we have, would we be able to recognize, parse, grok, appreciate, comprehend, and/or otherwise make sense of their notions of scientific knowledge?

Whiteson and his co-author, wanting to write a popular book rather than a scholarly one, and desiring nevertheless to take on these serious and challenging intellectual questions, have set their focus mostly on the aliens, accompanied by amusing cartoons and a generous helping of dad jokes (hey, some dad jokes are actually very funny.) They’re looking for a broad audience, and hopefully they will get it. But don’t let the light-hearted title (“Do Aliens Speak Physics?“) or the charmingly goofy cover fool you: this book might well make you laugh, but I guarantee it will make you think. Whether you’re just curious about science or you’ve been doing science yourself for years, I suspect that, within the vast array of problems and issues that are raised in this broad-minded book, there will be some you’ve never thought of.

Among scientists and philosophers, there are some who believe that any aliens with the capacity to reach the Earth will obviously “speak physics” — that math and physics float above contingencies of culture and species, and will easily be translated from any intelligent creature to any other. But are they perhaps flying too high? It’s clear that Whiteson and Warner are aiming to poke some holes — lots of holes —- in their hot-air balloon, and to do so in a way that a wide variety of readers can appreciate and enjoy.

I tend to agree with Whiteson on a lot of these issues, but that won’t stop me from asking him some tough questions. You can ask him some tough questions too, if you like — just come to the Harvard Bookstore at 7:00 on Monday and join the conversation!

POSTED BY Matt Strassler

ON November 14, 2025

Extreme and Dumb Cuts to US Science

As many of you are no doubt aware, in the past few days the US Congress voted to make major cuts to scientific research, and the president signed the bill. The government’s National Science Foundation has been cut by more than half, which means that its actual science budget has been cut by much more than that after you account for fixed costs. So vast, sudden and draconian are these cuts that it will take a long time for me and others in the field to figure out what has actually happened.

The reductions seem extreme, quite arbitrary and very poorly thought out. As an example, half of the LIGO observatory (the Laser Interferometer Gravitational-Wave Observatory, whose amazing discoveries, such as this one and this one, earned the United States a Nobel Prize in 2017) is being hit hard. There are currently two interferometers, one in Washington state and one in Lousiana, but one has been largely defunded in this bill, if I understand correctly.

I can see the logic: the scientists have two interferometers, but in tough times they ought to be able to get along with just one, right?

Well, that’s like cutting off one of a runner’s legs. Two were built because two were needed.

With just one, the signal from most gravitational wave events is so weak that you can’t distinguish it from noise. Other interferometers around the world just aren’t working well enough to make up for throwing away one of LIGOs. (And besides, you need three or four interferometers around the world to be able to know precisely in the sky where the waves are coming from, knowledge which can make other major discoveries possible.)

According to Science magazine, “In a two-sentence email to Science, an NSF spokesperson said the plan reflects `a strategic alignment of resources in a constrained fiscal environment.’ “

This is not strategic. This is stupid. The amount of money saved, less than 10 cents per year per US citizen, is very small compared to what we as a nation have already spent on this wonderful facility, and cutting LIGO in half makes it dramatically less than half as good — so this is actually a big waste of money both past and future. The decision to make this cut in this way is nothing short of ridiculous and incompetent.

[Not to mention that “constrained fiscal environment” is quite a phrase when you’re increasing the budget deficit rather than shrinking it.]

I fear there are many other similar examples to be found.

POSTED BY Matt Strassler

ON July 7, 2025

What is an Electron? How Times Have Changed

When the electron, the first subatomic particle to be identified, was discovered in 1897, it was thought to be a tiny speck with electric charge, moving around on a path governed by the forces of electricity, magnetism and gravity. This was just as one would expect for any small object, given the incredibly successful approach to physics that had been initiated by Galileo and Newton and carried onward into the 19th century.

But this view didn’t last long. Less than 15 years later, physicists learned that an atom has a tiny nucleus with positive electric charge and most of an atom’s mass. This made it clear that something was deeply wrong, because if Newton’s and Maxwell’s laws applied, then all the electrons in an atom should have spiraled into the nucleus in less than a second.

From 1913 to 1925, physicists struggled toward a new vision of the electron. They had great breakthroughs and initial successes in the late 1920s. But still, something was off. They did not really find what they were looking for until the end of the 1940s.

Most undergraduates in physics, philosophers who are interested in physics, and general readers mainly learn about quantum physics of the 1920s, that of Heisenberg, Born, Jordan and of Schrödinger. The methods developed at that time, often called “quantum mechanics” for historical reasons, represented the first attempt by physicists to make sense of the atomic, molecular, and subatomic world. Quantum mechanics is all you need to know if you just want to do chemistry, quantum computing, or most atomic physics. It forms the basis of many books about the applications of quantum physics, including those read by most non-experts. The strange puzzles of quantum physics, including the double-slit experiment that I reviewed recently, and many attempts to interpret or alter quantum physics, are often phrased using this 1920s-era approach.

What often seems to be forgotten is that 1920s quantum physics does not agree with data. It’s an approximation, and sometimes a very good one. But it is inconsistent with Einstein’s relativity principle, a cornerstone of the cosmos. This is in contrast to the math and concepts that replaced it, known as relativistic quantum field theory. Importantly, electrons in quantum field theory are very different from the electrons of the 1920s.

And so, when trying to make ultimate conceptual sense of the universe, we should always be careful to test our ideas using quantum field theory, not relying on the physics of the 1920s. Otherwise we risk developing an interpretation which is inconsistent with data, at a huge cost in wasted time. Meanwhile, when we do use the 1920s viewpoint, we should always remember its limitations, and question its implications.

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POSTED BY Matt Strassler

ON February 6, 2025

Double Trouble: The Quantum Two-Slit Experiment (1)

Happy New Year! 2025 is the centenary of some very important events in the development of quantum physics — the birth of new insights, of new mathematics, and of great misconceptions. For this reason, I’ve decided that this year I’ll devote more of this blog to quantum fundamentals, and take on some of the tricky issues that I carefully avoided in my recent book.

My focus will be on very basic questions, such as: How does quantum physics work, to the extent we humans understand it? Which of the widely-held and widely-promulgated ideas about quantum weirdness are true? And for those that aren’t, what is the right way to think about them?

I’ll frame some of this discussion in the context of the quantum two-slit experiment, because

it’s famous,
it’s often poorly explained
it’s often poorly understood,
it highlights (when properly understood) an extraordinarily strange aspect of quantum physics.

Not that I’ll cover this subject all in one post… far from it! It’s going to take quite some time.

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POSTED BY Matt Strassler

ON January 16, 2025

Celebrating the Standard Model: The Magic Angle

Particle physicists describe how elementary particles behave using a set of equations called their “Standard Model.” How did they become so confident that a set of math formulas, ones that can be compactly summarized on a coffee cup, can describe so much of nature?

My previous “Celebrations of the Standard Model” (you can find the full set here) have included the stories of how we know the strengths of the forces, the number of types (“flavors” and “colors”) and the electric charges of the quarks, and the structures of protons and neutrons, among others. Along the way I explained how W bosons, the electrically charged particles involved in the weak nuclear force, quickly decay (i.e. disintegrate into other particles). But I haven’t yet explained how their cousin, the electrically-neutral Z boson, decays. That story brings us to a central feature of the Standard Model.

Here’s the big picture. There’s a super-important number that plays a central role in the Standard Model. It’s a sort of angle (in a sense that will become clearer in Figs. 2 and 3 below), and is called θ_w or θ_weak. Through the action of the Higgs field on the particles, this one number determines many things, including

the relative masses of the W and Z bosons
the relative lifetimes of the W and Z bosons
the relative probabilities for Z bosons to decay to one type of particle versus another
the relative rates to produce different types of particles in scattering of electrons and positrons at very high energies
the relative rates for processes involving scattering neutrinos off atoms at very low energies
asymmetries in weak nuclear processes (ones that would be symmetric in corresponding electromagnetic processes)

and many others.

This is an enormously ambitious claim! When I began my graduate studies in 1988, we didn’t know if all these predictions would work out. But as the data from experiments came in during the 1990s and beyond, it became clear that every single one of them matched the data quite well. There were — and still are — no exceptions. And that’s why particle physicists became convinced that the Standard Model’s equations are by far the best they’ve ever found.

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POSTED BY Matt Strassler

ON November 20, 2024

Particles, Waves, and Wavicles

In my role as a teacher and explainer of physics, I have found that the ambiguities and subtleties of language can easily create confusion. This is especially true when well-known English words are reused in scientific contexts, where they may or may not be quite appropriate.

The word “particle”, as used to describe “elementary particles” such as electrons and quarks and photons, is arguably one such word. It risks giving the wrong impression as to what electrons etc. are really like. For this reason, I sometimes replace “particle” with the word “wavicle”, a word from the 1920s that has been getting some traction again in recent years. [I used it in my recent book, where I also emphasized the problems of language in communicating science.]

In today’s post I want to contrast the concepts of particle, wave and wavicle. What characterizes each of these notions? Understanding the answer is crucial for anyone who wants to grasp the workings of our universe.

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POSTED BY Matt Strassler

ON July 9, 2024

Celebrating the Standard Model: The Twins We’re Made Of

At the core of every atom lies its nucleus, where protons and neutrons are found. As their names suggest, these two subatomic particles are profoundly different.

Protons carry positive electric charge, and can attract negatively-charged electrons, making atoms possible.
Neutrons have no electric charge and are thus electrically neutral, hence their name; they have no impact on the electrons in atoms.

The distinctions extend to their magnetic effects. Both protons and neutrons have a “magnetic moment,” meaning that in a magnetic field, they will point like compasses. But neutrons point in the opposite direction from protons, and less agressively.

Nevertheless, the proton and neutron have almost identical masses, differing by less than two tenths of a percent! If we ignored their electric and magnetic effects, they’d almost be twins. Why are they so different in some ways and so similar in others? What does it reflect about nature?

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POSTED BY Matt Strassler

ON May 29, 2024

Peter Higgs versus the “God Particle”

The particle physics community is mourning the passing of Peter Higgs, the influential theoretical physicist and 2013 Nobel Prize laureate. Higgs actually wrote very few papers in his career, but he made them count.

It’s widely known that Higgs deeply disapproved of the term “God Particle”. That’s the nickname that has been given to the type of particle (the “Higgs boson”) whose existence he proposed. But what’s not as widely appreciated is why he disliked it, as do most other scientists I know.

It’s true that Higgs himself was an atheist. Still, no matter what your views on such subjects, it might bother you that the notion of a “God Particle” emerged neither from science nor from religion, and could easily be viewed as disrespectful to both of them. Instead, it arose out of marketing and advertising in the publishing industry, and it survives due to another industry: the news media.

But there’s something else more profound — something quite sad, really. The nickname puts the emphasis entirely in the wrong place. It largely obscures what Higgs (and his colleagues/competitors) actually accomplished, and why they are famous among scientists.

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POSTED BY Matt Strassler

ON April 12, 2024

How Far Could the Sun Possibly Be?

(This is the third post in a series, though it can be read independently; here are post #1 and post #2; and post #4 blows this one out of the water, so don’t miss it!)

Measuring the distance to the Sun is challenging, for reasons explained in my last post. Long ago, the Greek thinker Aristarchus proposed a geometric method, which involves estimating the Moon’s sunlit fraction on a certain date. Unfortunately, because the Sun is so far away, his approach isn’t powerful enough; Aristarchus himself underestimated the distance. [This last remained true for later astronomers before the 17th century, though they got closer to the truth, presumably by using more precise methods than you or I could easily apply. I doubt anyone truly found a maximum possible distance to the Sun just using geometry.] The best we can do, using Aristarchus’ method and our naked eyes, is determine a minimum possible distance to the Sun: a few million miles.

Figure 1: A simple application of Aristarchus’ method tells us that the minimum distance to the Sun is a few million miles (km), ruling out the red region. But the entire green region is still allowed.

Today we’ll see how to obtain a maximum distance to the Sun, using an approach suggested in the previous post: by measuring speeds. Specifically, we’ll make use of a speed that the ancient astronomers weren’t aware of: the speed of light, also known as the cosmic speed limit c. That’s 186,000 miles (300,000 km) per second, or 5.9 trillion miles (9.5 trillion km) per year. We’ll find the Sun’s distance is less than 12 billion miles… still much larger than its true distance, but a significant improvement on our starting point!

*Figure 2: By the end of this post, we’ll know a maximum possible distance for the Sun, too.*

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POSTED BY Matt Strassler

ON January 19, 2024

Why is it So Hard to Measure the Distance to the Sun?

(This is the second post in a series; here’s post #1.)

It’s not too hard to measure the distance to the Moon; the Greeks did it over two thousand years ago. First you measure the size of the Moon, which can be done in various ways; for instance, you can use the occultation (i.e. blocking) by the Moon of a star or planet, or the outer edges of a solar eclipse, as viewed in different locations on the Earth. These measurements do require multiple people at different locations to accurately report what they have witnessed, but they don’t require any fancy equipment or highly precise observations. Then you can quickly determine the distance to the Moon using the angular diameter of the Moon on the sky.

However, measuring the distance to the Sun, or to any other planet, is much more difficult. Today I’ll explain why… and this will help us envision a way around the problem.

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POSTED BY Matt Strassler

ON January 17, 2024

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Category: History of Science

POSTED BY Matt Strassler

POSTED BY Matt Strassler

POSTED BY Matt Strassler

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