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What Happens When Light Goes Boom? Part 2: The Crowd, the Molasses, and the Speed of Light (Sort Of)

(This is Part 2 of a series on Cherenkov radiation — the “light boom.” Read Part 1 first.)

Before we get to Brad Bradington sprinting down the red carpet, we need to talk about the crowd itself. Because the crowd is where all the magic happens, and the crowd has some very specific properties that make this whole story possible.

Specifically: the crowd slows down light.

In 1865, James Clerk Maxwell published four equations that unified electricity, magnetism, and light into a single framework. It’s one of the towering achievements of 19th century physics — the kind of result that makes you feel like the universe was trying to tell us something, and Maxwell was just the person paying close enough attention to hear it.

One of the things those equations tell you, if you work through the mathematics, is the speed of light. It falls out of two constants — properties of empty space itself — and gives you exactly 299,792,458 meters per second. Not approximately. Exactly. The universe just decided that’s what light does in a vacuum, and Maxwell’s equations are how we know.

But here’s the asterisk: those constants describe the vacuum. Empty space. Put a material in the way, and those effective constants change. The material has its own electric and magnetic properties — its own way of responding to oscillating fields — and those properties act as a drag on the wave. The speed that falls out of the math is now lower.

How much lower depends entirely on the material. Physicists capture this with a single number called the index of refraction — the ratio of the vacuum speed of light to the actual speed in the medium. In air, the index is about 1.0003 — so close to vacuum you’d never notice the difference. In water it’s 1.33, meaning light moves at about 75% of its maximum speed. In glass it’s around 1.5. In diamond it’s 2.4, meaning light is cut to less than half its vacuum speed passing through the stone. HALF. We’ve even engineered special laboratory materials that slow light to walking pace — literally the speed of a person strolling down a corridor, achieved inside ultracold atomic clouds.

This is, if you stop to think about it, genuinely strange. Light doesn’t have mass. It can’t be grabbed or pushed. And yet the mere presence of atoms and molecules — the way they respond to oscillating electric fields, creating their own little ripples that interfere with the original wave — is enough to drag it down from the cosmic speed limit to something a fast cyclist could beat.

Now, WHY this happens in detail is a whole episode on its own. You can picture it a few different ways. You can imagine the light waves interacting with the electrons in each atom or molecule, which then generate their own little electromagnetic waves, which then interfere with the original — slowing the whole thing down like trying to run through a room full of people who all want to stop and chat. You can picture it as individual photons bouncing around in an elaborate quantum pinball machine. Or you can invoke something called phonons, which is my favorite picture because it’s both the most accurate and the most fun to say out loud.

But the HOW doesn’t matter for our story. What matters is the FACT: light inside a material moves slower than c. Sometimes much, much slower.

Here’s where it gets interesting.

In empty space, nothing can outrun light. Einstein’s special relativity closes that door completely, with no exceptions and no loopholes. There is no shortcut, no workaround, no fine print. The cosmic speed limit is absolute.

But what if you filled the stadium with molasses?

Usain Bolt runs at about 10 meters per second. In open air, light outruns him by a factor of thirty million. The gap is not closeable by any conventional means.

But if you fill the stadium with molasses, Bolt slows down. More importantly, light slows down too — and inside certain materials, light slows down dramatically more than a charged particle does. A fast-moving electron barely notices there’s a medium there — it plows through atoms like they’re not its problem. But light gets caught up in all those interactions, all those tiny delays, all that electromagnetic interference.

The result: inside certain materials, a sufficiently energetic charged particle can move faster than light is moving in that same material. Not faster than c — the vacuum speed of light, the true cosmic limit. That’s still inviolable. But faster than the local, in-this-material, slowed-down speed of light. Which is a very different, and entirely permissible, thing.

You’re not breaking any laws of physics. You’re not violating relativity. You’ve just found a material where light has to slog through molasses, and you happen to be a particle that barely notices the molasses is there.

And when that happens — when a charged particle exceeds the local speed of light in its medium?

Brad Bradington has entered the building.

In Part 3, we watch Brad Bradington sprint — and find out exactly what a light boom looks like.

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Learning to fly from the ground up: Owl sighting in Redondo Beach sparks public service announcement

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A young great horned owl discovered at the base of a palm tree in Redondo Beach has prompted police to release a public service announcement video to educate residents on how to respond to such fledgling birds.

The owl was brought in by Redondo Beach Animal Services after it was found on the ground, a situation that may appear concerning but is often part of a normal development stage for young owls, according to Redondo Beach Police Det. Evelo, who did not provide her full name.

In the video, Evelo said the goal is to educate the public about what to do when encountering young owls.

“At this age where they have flight feathers or fledging feathers, they’re starting to branch out and learn how to fly and move around,” Evelo said.

She noted that Redondo Beach’s local geography can make this stage more difficult.

“Unfortunately in Redondo Beach we have a lot of palm trees and that’s not a great home for owls because there’s no branches for them to start learning how to fly,” she said. “You’ll find that at this age these owls will actually fall to the ground and that’s where they’ll do all their learning.”

According to the nonprofit Owl Research Institute, this stage is known as fledgling, when young birds leave the nest before they are fully capable of flight and begin exploring their surroundings. During this time, the owls are still under parental care. This period could last weeks.

“Don’t worry, their parents are still taking care of them. You’ll see mom and dad still coming down to feed them,” Evelo said.

The video also advises residents not to approach or touch owl fledgings and to keep pets and children away to avoid stressing the bird.

“Don’t be alarmed if you see them, just leave them where they are,” the detective said.

However, she said anyone who finds a young owl should not hesitate to call the Redondo Police Department Animal Control if it looks like a dog or another animal is going to get to them.

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A Century Later, the Flatiron’s Revolving Door Is Restored

The revolving door’s inventor built this one over 100 years ago. It was reinstalled this week.

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Public school enrollment decline is steepest in LAUSD and L.A. County

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Schools in Los Angeles County and especially those in the L.A. Unified School District are seeing the steepest decline in enrollment in California, based on new state data posted Thursday.

Across California, enrollment dropped by 1.3% — about 75,000 students — over the last year, a percentage decline that is about average compared with 39 states that have so far released enrollment figures for the current school year. All 39 have recorded enrollment decreases, based on an analysis by the California Department of Education. States with a larger percentage decline include Hawaii, New Hampshire and New York.

“Declining school enrollment in California reflects the national trend,” said Elizabeth Sanders, a spokesperson for the state Department of Education. In addition, “the data shows that some California families are relocating to less expensive suburban communities like Elk Grove and Vacaville.”

The statewide figures correlate to declining birth rates nationwide, although other factors are in play locally, including in Los Angeles County, such as housing costs, a decline in immigration and aggressive federal efforts to deport undocumented immigrants.

“There are some surprises in these data, but the decline itself shouldn’t be surprising,” said Thomas J. Kane, director of the Center for Education Policy Research at Harvard. “Declining birth rates inevitably mean declining enrollment. The size of the decline should be manageable — but only if schools adjust their plans now, rather than wait.”

Typical ways of coping with declining enrollment including closing schools and reducing the number of employees. Both are painful measures for school communities and have been resisted in the Los Angeles Unified School District and elsewhere.

This week, LAUSD officials just barely headed off a strike by agreeing to significant employee raises as well as by rescinding about 200 layoffs and agreeing to hundreds of new hires of counselors, school psychologists and other student support staff. The school system has not identified campuses that could be closed.

Los Angeles County, with 80 school districts, has far more students than any other California county, so its effect on statewide enrollment always will be significant. Over the last year enrollment drops were pronounced, pulling down statewide numbers.

Los Angeles County public school enrollment for the 2025-26 academic year decreased from the prior year by 32,953 students, or 2.6%, to 1,242,816. That drop would equate to the disappearance of the entire Moreno Valley Unified School District, which is one of the 25 largest school systems in the state.

The county decrease represents 44% of the statewide decline. By comparison, the county comprises about 22% of the state’s students.

For L.A. Unified, the decline was 16,765 students, or 4.5%. L.A. Unified’s share of the statewide decrease is 22.4%. The district has about 7% of the state’s public school students.

Per the state numbers, the L.A. Unified enrollment is 353,065 and was 369,830 last year.

L.A. Unified has a different and larger enrollment figure based on a different tabulation system, but the percentage decrease is similar to what the state calculated — and it was no surprise to district officials when asked for their reaction.

District officials also noted state figures showing that enrollment is lower, too, for homeschooling, private schools and charter schools. Charters are privately operated public schools.

“Los Angeles Unified’s enrollment trends reflect the same broader demographic shifts impacting school systems across California and the nation,” officials said in a statement. “Enrollment declined across all school types this year, driven largely by long-term factors such as declining birth rates and changes in migration patterns due to cost of living.”

“Like other large urban districts, Los Angeles Unified is also navigating additional local pressures, including housing affordability and the impact of federal immigration enforcement policies, which have contributed to a more pronounced decline in our communities.”

School district critics say the management of the school system itself must bear some blame, although demographic experts lend support to the district analysis.

It’s “quite possible that some of this decline is driven by the increased scale and intensity of immigration enforcement,” said Stanford University professor Thomas S. Dee. “I’ve found in prior research that immigration enforcement reduces enrollment by causing some to flee and deterring newcomers.”

In terms of raw numbers, Santa Ana Unified, which lost 2,291 students, follows L.A. Unified in declining enrollment. That’s a 6.4% drop since last year. Immigration enforcement also has fallen heavily on families in that school system.

School systems with higher enrollment include Elk Grove Unified, which gained 1,097 students, a 1.7% increase. Vacaville Unified enrolled 557 more students, a 4.9% increase. Counties with higher enrollment included San Joaquin, Placer and Sutter.

Mixed picture for private and home schooling

There was a year-over-year decline across all school types.

Schools operated by traditional school districts dropped 1.4%, almost exactly the same as the statewide numbers. This reflects that most students, about 5.73 million, are in public schools.

Charter schools dropped slightly statewide, about 0.3%.

The number of students being homeschooled dropped 3.7%. For data purposes, a home school is defined as a private school with fewer than six students. Before the COVID-19 pandemic, in the 2018-19 school year, there were just under 25,000 homeschoolers. The number peaked in 2020-21, at the height of the pandemic campus closures, at nearly 60,000. The current figure is 49,365.

Private school enrollment dropped 6.6% compared with last year; it’s now a little less than before the pandemic.

In 2018-19, private school enrollment approached 500,000. Enrollment dropped early in the pandemic, then peaked in 2022-23. The current enrollment is 461,650 students, a decrease of 32,814 from last year.

In the big picture, said Stanford’s Dee, “we see continued evidence that the families that left the public school system during the pandemic haven’t really returned.”

UC Berkeley education professor Bruce Fuller focused on the recent private school decline, noting that “fewer parents appear able to afford private schools.”

He also was drawn to another figure — an increase in the number of families taking advantage of transitional kindergarten, which became fully available across the state to 4-year-olds for the current school year.

That enrollment figure is 213,313, up 20.1% over last year.

“Free TK is growing in popularity, especially among middle-income Angelenos who earlier faced daunting child-care bills,” Fuller said. “The downside is that scores of nonprofit preschools have gone under after losing their 4-year-olds.”

Overall, the declining birth rate “continues to wreak havoc with the fragile vitality of public schools,” Fuller added. “The irony is that steadily rising education attainment, notably enjoyed by young Latina mothers, leads to bearing fewer children.”