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kottke.org posts about physics

Did The Future Already Happen?

posted by Jason Kottke   Jan 30, 2024

Kurzgesagt’s latest video on the paradox of time is a bit more of a brain-bender than their usual videos. From the accompanying sources document:

This video summarizes in a narrative format two well-known theories about time: the so-called “block universe” and the “growing block”.

The block universe is an old theory of time which appears to be an unavoidable consequence of Einstein’s theory of special relativity. In philosophical contexts, basically the same idea is known as “eternalism”. Simplified, this theory posits that, although not apparent to our human perception, both the past and the future exist in the same way as the present does, and are therefore as real as the present is: The past still exists and the future exists already. As a consequence, time doesn’t “flow” (even if it looks so to us) and things in the universe don’t “happen” - the universe just “is”, hence the name “block universe”.

But then: “Quantum stuff is ruining everything again.” And so we have the growing block theory:

The Evolving/Growing Block: A relatively new alternative to the classical block universe theory, which asserts that the past may still exist but the present doesn’t yet, and all that in a way that is still compatible with Einstein’s relativity.

And there are still other theories about how time works:

Some scientists think that the idea of “now” only makes sense near you, but not in the universe as a whole. Others think that time itself doesn’t even exist — that the whole concept is an illusion of our human mind. And others think that time does exist, but that it’s not a fundamental feature of the universe. Rather, time may be something that emerges from a deeper level of reality, just like heat emerges from the motion of individual molecules or life emerges from the interactions of lifeless proteins.

Like I said, a brain-bender.

The Science of Snowflakes

posted by Jason Kottke   Jan 11, 2024

In a video for the Royal Society, physicist Brian Cox explains the science of snowflakes, from how they form to where their shape and symmetry comes from. Plus this bombshell: “Snowflakes aren’t actually white.” (via aeon)

How Would Interstellar Weaponry Work?

posted by Jason Kottke   Nov 16, 2023

In their latest video, Kurzgesagt takes a break from their more serious topics to consider a scenario from the realm of science fiction: interstellar combat. Using technology that is theoretically available to us here on Earth, could a more advanced civilization some 42 light years away destroy our planet without any warning? They outline three potential weapons: the Star Laser, the Relativistic Missile, and the Ultra-Relativistic Electron Beam.

Here’s what I don’t understand though: how would the targeting work? In order for an alien civilization to hit the Earth with a laser from 42 light years away, it has to not only predict, within a margin of error of the Earth’s diameter, precisely where the Earth is going to be, but also have a system capable of aiming across 42 light years of distance with that precision. Is this even possible? How precisely do we know where the Earth is going to be in 42 years? And if you’re aiming at something 42 light years away, if you move the sights a nanometer, how much angular distance does that shift the the destination by? And how much does the gravity of matter along the way shift the trajectory and is it possible to accurately compensate for that? Maybe this should be their next video…

Why Some of the Rainbow Is Missing

posted by Jason Kottke   Nov 01, 2023

If you look closely at a rainbow made from sunlight (e.g. through a prism or an actual rainbow), you’ll notice that some of the colors are missing. It turns out that these absent colors (called Fraunhofer lines) have something to do with the types of elements that are present in the Sun (and the Earth’s atmosphere). Dr. Joe Hanson explains in the video above.

Over 200 years ago, scientists were looking at sunlight through a prism when they noticed that part of the rainbow was missing. There were dark lines where there should have been colors. Since then, scientists have unlocked the secrets encoded in these lines, using it to uncover mind-boggling facts about the fundamental nature of our universe and about worlds light-years away.

Science is fascinating…Fraunhofer lines can tell us something about objects and processes all along the Powers of Ten scale, from the inner workings of the atom to the composition of the Earth’s atmosphere to how quickly the universe is expanding or contracting.

If you’d like to check out the missing parts of the rainbow for yourself, you can make this DIY spectroscope using a CD or DVD and a few other items. (via the kid should see this)

How Do Black Holes Compare to Regular Holes?

posted by Jason Kottke   Oct 24, 2023

a humorous chart from XKCD about how black holes compare to regular holes

From XKCD, a comparison chart that shows how black holes and regular holes measure up to one another. Some of these are pretty clever: “some of them are the mouths of wormholes”.

One Revolution Per Minute

posted by Jason Kottke   Oct 04, 2023

Erik Wernquist made his short film One Revolution Per Minute to explore his “fascination with artificial gravity in space”. The film shows what it would be like to travel on a large, circular space station, 900 meters (0.56 miles) in diameter that rotates a 1 rpm. Even at that slow speed, which generates 0.5 g at the outermost shell, I was surprised to see how quickly the scenery (aka the Earth, Moon, etc.) was rotating and how disorienting it would be as a passenger.

Realistically - and admittedly somewhat reluctantly — I assume that while building a structure like this is very much possible, it would be quite impractical for human passengers.

Putting aside the perhaps most obvious problem with those wide windows being a security hazard, I believe that the perpetually spinning views would be extremely nauseating for most humans, even for short visits. Even worse, I suspect — when it comes to the comfort of the experience — would be the constantly moving light and shadows from the sun.

I calculated that the outer ring of the space station is moving at 105.4 mph with respect to the center. That’s motoring right along — no wonder everything outside is spinning so quickly.

The Plot of All Objects in the Universe

posted by Jason Kottke   Sep 26, 2023

a scientific plot of all of the objects in the universe

You just have to admire a chart that casually purports to show every single thing in the Universe in one simple 2D plot. The chart in question is from a piece in the most recent issue of the American Journal of Physics with the understated title of “All objects and some questions”.

In Fig. 2, we plot all the composite objects in the Universe: protons, atoms, life forms, asteroids, moons, planets, stars, galaxies, galaxy clusters, giant voids, and the Universe itself. Humans are represented by a mass of 70 kg and a radius of 50 cm (we assume sphericity), while whales are represented by a mass of 10^5 kg and a radius of 7 m.

The “sub-Planckian unknown” and “forbidden by gravity” sections of the chart makes the “quantum uncertainty” section seem downright normal — the paper collectively calls these “unphysical regions”. Lovely turns of phrase all.

But what does it all mean? My physics is too rusty to say, but I thought one of the authors’ conjectures was particularly intriguing: “Our plot of all objects also seems to suggest that the Universe is a black hole.” Huh, cool.

What Happens If You Destroy A Black Hole?

posted by Jason Kottke   Sep 21, 2023

Here’s a fun thought experiment: can you destroy a black hole? Nuclear weapons probably won’t work but what about antimatter? Or anti black holes? In this video, Kurzgesagt explores the possibilities and impossibilities. This part baked my noodle (in a good way):

Contrary to widespread belief, the singularity of a black hole is not really “at its center”. It’s in the future of whatever crosses the horizon. Black holes warp the universe so drastically that, at the event horizon, space and time switch their roles. Once you cross it, falling towards the center means going towards the future. That’s why you cannot escape: Stopping your fall and turning back would be just as impossible as stopping time and traveling to the past. So the singularity is actually in your future, not “in front of you”. And just like you can’t see your own future, you won’t see the singularity until you hit it.

🤯

The Science of the Perfect Second

posted by Jason Kottke   Sep 13, 2023

I really enjoyed this piece by Tom Vanderbilt on how time is kept, coordinated, calculated, and forecast. It’s full of interested tidbits throughout, like:

Care to gawk at one of the world’s last surviving original radium standards, a glass ampoule filled with 20.28 milligrams of radium chloride prepared by Marie Curie in 1913? NIST has it in the basement, encased in a steel bathtub, buried under lead bricks.

And:

For GPS to work, it needs ultra-exact timing: accuracy within fifteen meters requires precision on the order of fifty nanoseconds. The 5G networks powering our mobile phones demand ever more precise levels of cell-tower synchronization or calls get dropped.

And:

And as Mumford could have predicted, nowhere has time become so fetishized as in the financial sector, with the emergence over the past decade of algorithmic high-frequency trading. Donald MacKenzie, the author of Trading at the Speed of Light, estimated in 2019 that a trading program could receive market data and trigger an order in eighty-four nanoseconds, or eighty-four billionths of a second.

And:

All this makes F1 staggeringly accurate: it will gain or shed only one second every 100,000,000 years. Since the days when time was defined astronomically, the accuracy of the second is estimated to have increased by a magnitude of eight.

And:

“A clock accurate to a second over the age of the cosmos,” Patrick Gill, a physicist at the U.K.’s National Physical Laboratory, is quoted as saying in New Scientist, “would allow tests of whether physical laws and constants have varied over the universe’s history.”

And:

“If you were to lift this clock up a centimeter of elevation,” Hume told me, “you would be able to discern a difference in the ticking rate.” The reason is Einstein’s theory of relativity: Time differs depending on where you are experiencing it.

And I could go on and on. If any or all of those tidbits is interesting to you, you should go ahead and read the whole thing.

Oppenheimer: More Science and More Heist Please

posted by Jason Kottke   Aug 11, 2023

Craig Mod has my favorite take to date on Oppenheimer: that it should have been more like Richard Rhodes’ The Making of the Atomic Bomb:

My ideal version of this film would have begun in the 1900s or ’10s, with flashes of Relativity and then the steps of Quantum Mechanics with Planck, Bohr, and Heisenberg. Quantum tunneling with Gamow and Gurney. The nuclear shell model with Maria Goeppert Mayer and J. Hans D. Jensen. Chadwick’s discovery of the neutron. Anderson’s positron unveiling. Hold the camera longer on Lawrence and his cyclotron. What’s going on there? (I mean, ya got Josh Hartnett’s pretty head, plaster it up!) Shoot in high-grade mega-IMAX-bokeh the oddly simple experimental setups, the beakers, the blips, the radiation tick-tick-ticks, the iterations, the step-by-step expansion of understanding the fabric of everything around us. Give us an hour of this, this arguably greatest moment of human insight. You can still call the film Oppenheimer. Let the man loom, weave him between it all as he makes his way through Europe, sets up at Berkeley, is selected to lead Los Alamos. Ramp up the Nazi threat. Show the diaspora of brilliance more clearly. Believe the audience is willing to sit through more than just “Is it a wave … or is it particle?” Oh! There is so much excitement, so much incredible science to be mined, and Nolan mined so little.

Mod and I both share a love for that masterpiece of a book and I would watch the hell out of an 10-part HBO series (in the vein of Chernobyl) based on it, American Prometheus, and John Hersey’s Hiroshima.

How Big Are the Biggest Black Holes?

posted by Jason Kottke   May 12, 2023

This short animation from NASA shows the sizes of some of the supermassive black holes that feature at the center of galaxies. Some are relatively small:

First up is 1601+3113, a dwarf galaxy hosting a black hole packed with the mass of 100,000 Suns. The matter is so compressed that even the black hole’s shadow is smaller than our Sun.

While others are much larger than the solar system…and this isn’t even the biggest one:

At the animation’s larger scale lies M87’s black hole, now with a updated mass of 5.4 billion Suns. Its shadow is so big that even a beam of light — traveling at 670 million mph (1 billion kph) — would take about two and a half days to cross it.

Can Water Solve a Maze?

posted by Jason Kottke   Apr 13, 2023

I saw this video on the front page a YouTube a couple of weeks ago and ignored it. Like, of course water can solve a maze, next! But then it got the Kid Should See This seal of approval so I gave it a shot. It turns out: water can solve a maze…but specifics are super interesting in several respects. Steve Mould, who you may remember from the assassin’s teapot video not too long ago, built four mazes of different sizes and shapes, each of them useful for demonstrating a different wrinkle in how the water moves through a maze. Recommended viewing for all ages.

The Assassin’s Teapot

posted by Jason Kottke   Mar 23, 2023

The assassin’s teapot is certainly an eye-catching name for pottery, but there’s also an interesting bit of physics going on here. The teapot in question has two separate chambers for holding liquid, and the flow out of the pot from each chamber can be controlled by covering or uncovering small holes located on the handle. So, as the legend goes, a would-be assassin could pour themselves a perfectly fine drink from one chamber and then pour a poisoned drink to their prey from the other chamber, just by discreetly covering and uncovering the proper holes with their fingers. As the video explains, the mechanism here has to do with surface tension and air pressure.

You can get your own assassin’s teapot right here.

Leonardo da Vinci’s Surprisingly Accurate Experiments with Gravity

posted by Jason Kottke   Feb 16, 2023

notes and graphs from Leonardo da Vinci regarding his gravity experiments

This is super-interesting: in papers written by Leonardo da Vinci collected in the Codex Arundel, he documents experiments that show that gravity is a form of acceleration and also calculated the gravitational constant to within 97% accuracy, hundreds of years before Newton formalized gravity in theory.

In an article published in the journal Leonardo, the researchers draw upon a fresh look at one of da Vinci’s notebooks to show that the famed polymath had devised experiments to demonstrate that gravity is a form of acceleration — and that he further modeled the gravitational constant to around 97 percent accuracy.

Da Vinci, who lived from 1452 to 1519, was well ahead of the curve in exploring these concepts. It wasn’t until 1604 that Galileo Galilei would theorize that the distance covered by a falling object was proportional to the square of time elapsed and not until the late 17th century that Sir Isaac Newton would expand on that to develop a law of universal gravitation, describing how objects are attracted to one another. Da Vinci’s primary hurdle was being limited by the tools at his disposal. For example, he lacked a means of precisely measuring time as objects fell.

As the piece notes, Leonardo didn’t get things exactly right:

Da Vinci sought to mathematically describe that acceleration. It is here, according to the study’s authors, that he didn’t quite hit the mark. To explore da Vinci’s process, the team used computer modeling to run his water vase experiment. Doing so yielded da Vinci’s error.

“What we saw is that Leonardo wrestled with this, but he modeled it as the falling object’s distance was proportional to 2 to the t power [with t representing time] instead proportional to t squared,” Roh says. “It’s wrong, but we later found out that he used this sort of wrong equation in the correct way.” In his notes, da Vinci illustrated an object falling for up to four intervals of time-a period through which graphs of both types of equations line up closely.

But it’s still pretty impressive how far he did get. The piece also notes that this work was discovered because the codex was made available online to the general public, demonstrating the value of easy access of materials like this.

Supermassive Black Holes: A Possible Source of Dark Energy

posted by Jason Kottke   Feb 16, 2023

A group of astronomers say they have evidence that links supermassive black holes at galactic centers with dark energy, the mysterious force that accounts for roughly 68% of the energy in the universe. Here’s the news release and the paper. From the Guardian:

Instead of dark energy being smeared out across spacetime, as many physicists have assumed, the scientists suggest that it is created and remains inside black holes, which form in the crushing forces of collapsing stars.

“We propose that black holes are the source for dark energy,” said Duncan Farrah, an astronomer at the University of Hawaii. “This dark energy is produced when normal matter is compressed during the death and collapse of large stars.”

The claim was met with raised eyebrows from some independent experts, with one noting that while the idea deserved scrutiny, it was far too early to link black holes and dark energy. “There’s a number of counter-arguments and facts that need to be understood if this claim is going to live more than a few months,” said Vitor Cardoso, a professor of physics at the Niels Bohr Institute in Copenhagen.

And here’s a short video explainer:

It’s a radical claim to be sure — it’ll be interesting to see how it shakes out in the weeks and months to come as other scientists interpret the results.

Where the Elements Came From

posted by Jason Kottke   Feb 08, 2023

a color-coded periodic table of the elements that shows how each element was created

From Wikipedia contributor Cmglee and Astronomy Picture of the Day, a color-coded periodic table that displays which cosmic events — the Big Bang, exploding stars, merging neutron stars, etc. — was responsible for creating each element, according to our present understanding of the universe.

The hydrogen in your body, present in every molecule of water, came from the Big Bang. There are no other appreciable sources of hydrogen in the universe. The carbon in your body was made by nuclear fusion in the interior of stars, as was the oxygen. Much of the iron in your body was made during supernovas of stars that occurred long ago and far away. The gold in your jewelry was likely made from neutron stars during collisions that may have been visible as short-duration gamma-ray bursts or gravitational wave events.

The data for the table came from OSU’s Jennifer Johnson, who quotes Carl Sagan:

The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.

(thx, caroline)

Cars vs Giant Bulge and Other Outlandish Vehicular Simulations

posted by Jason Kottke   May 06, 2022

It is Friday and this is the perfect Friday sort of post. BeamNG is a video game of sorts that’s “a dynamic soft-body physics vehicle simulator capable of doing just about anything”. In the simulator, you can quickly devise all sorts of situations with a variety of cars and then press play to see what happens, with (mostly) realistic physics and collisions. For instance, here’s Cars vs Big Bulge:

Chained Cars vs Bollards:

Cars vs 100 Fallen Trees:

Trains vs Giant Pit:

And many many more. My god if this simulator had been around when I was 12 years old, I might not have done anything else. Hell, if I downloaded and installed this right now, I might not ever get anything done ever again. (via @tvaziri)

What If the Moon Crashes Into the Earth?

posted by Jason Kottke   Feb 08, 2022

No doubt motivated by this month’s release of Moonfall, the latest movie from disaster shlockmeister Roland Emmerich, Kurzgesagt has made a video that shows what would happen to civilization should the Moon somehow get knocked from its orbit and head straight for the Earth. Spoiler: the Moon doesn’t even need to reach us to kill almost all life on the planet.

See also A Scientific Simulation of Seveneves’ Moon Disaster.

How the James Webb Space Telescope Orbits Nothing

posted by Jason Kottke   Feb 07, 2022

The James Webb Space Telescope is designed to be positioned near one of the five Lagrange Points in the Sun/Earth system, special areas of gravitational equilibrium that keep objects stationary relative to both the Earth and the Sun. Here’s how Lagrange Points work and why they are so useful for spacecraft like the Webb.

See also What Makes Lagrange Points Special Locations In Space.

How Does The James Webb Space Telescope Work?

posted by Jason Kottke   Jan 19, 2022

The James Webb Space Telescope is still winging its way to its permanent home at the L2 point1 about 930,000 miles from Earth — it’s due to arrive in about 4 days. It’s a massive and fascinating project and for his YouTube series Smarter Every Day, Destin Sandlin talked to Nobel laureate John Mather, the senior project scientist for the JWST, about how the telescope works.

Also worth a watch is Real Engineering’s The Insane Engineering of James Webb Telescope:

It really is a marvel of modern science & engineering — I can’t wait to see what the telescope sees once it’s fully operational.

  1. You can read about Lagrange points here or here…they are interesting!

Randomly Bouncing Balls Arrange Themselves Into Satisfying Patterns

posted by Jason Kottke   Jan 12, 2022

In this clever simulation, bouncing balls obeying the laws of physics somehow arrange themselves, mid-chaos, into neat patterns. This is immensely satisfying.

Spoiler: the trick here is a pair of simulations stitched together, like a physics Texas Switch: “Each sequence is obtained by joining two simulations, both starting from the time in which the balls are arranged regularly. One simulates forward in time, one backwards.”

Powers of Ten, Updated With Current Science

posted by Jason Kottke   Jan 05, 2022

Charles and Ray Eames’ 1977 short film Powers of Ten is one of the best bits of science communication ever created…and a personal favorite of mine. Here’s a description of the original film:

Powers of Ten takes us on an adventure in magnitudes. Starting at a picnic by the lakeside in Chicago, this famous film transports us to the outer edges of the universe. Every ten seconds we view the starting point from ten times farther out until our own galaxy is visible only a s a speck of light among many others. Returning to Earth with breathtaking speed, we move inward — into the hand of the sleeping picnicker — with ten times more magnification every ten seconds. Our journey ends inside a proton of a carbon atom within a DNA molecule in a white blood cell.

As an homage, the BBC and particle physicist Brian Cox have created an updated version that reflects what we’ve learned about the universe in the 45 years since Powers of Ten was made. The new video zooms out to the limits of our current observational powers, to about 100 billion light years away, 1000X wider than in the original. (I wish they would have done the zoom in part of the video too, but maybe next year!)

And if you’d like to explore the scales of the universe for yourself, check out the Universe in a Nutshell app from Tim Urban and Kurzgesagt — you can zoom in and out as far as you want and interact with and learn about objects along the way.

Most People Don’t Know How Bikes Work

posted by Jason Kottke   Nov 30, 2021

How do you steer a bike? You turn the handlebars to the left to go left, correct? Actually, you don’t: you turn the handlebars to the right to go left…at least at first. And also? Bikes don’t even need riders to remain upright…they are designed to steer themselves.

If you’d like to play around with your own bicycle geometries, try this web app for analyzing bicycle dynamics.

How Bowling Balls Are Made

posted by Jason Kottke   Nov 16, 2021

I have been a fan of how things are made videos since my Mister Rogers and Sesame Street days, so I was not expecting to be so surprised watching the video above about how bowling balls are made. It’s a ball — how complicated could it be? Well, it turns out that modern bowling balls contain an asymmetric weight block in the middle that looks a little like a car’s starter. Weird, right?

As I started to wonder why it would be advantageous to include such a lopsided core in a ball you want to roll predictably down a lane, I noticed YouTube’s algorithm doing its job in recommending that I watch Veritasium’s recent video on How Hidden Technology Transformed Bowling, which totally explains the wonky weight block thing:

The weight blocks are wonky in a precise way. They’re designed to cause the ball to contact the lane over more of the surface of the ball, giving it more traction once it hits the unoiled part of the lane, which is desirable for expert bowlers looking for a wicked hook. So cool! (thx, mick)

Update: Brendan Koerner wrote a piece for Wired several months ago about Mo Pinel, who revolutionized bowling with the asymmetric cores described in the video above.

Pinel toured Faball’s factory and examined a freshly made core that the company used in its Hammer brand. It had a symmetrical and unexciting shape — the center looked like a lemon, and there were two convex caps of equal size on either side. In a moment that has now passed into ball-design legend, Pinel grabbed the core, which was still soft because the polyester had yet to cure, and sliced off the ends with a palette knife. Then he smooshed the caps back on into positions that were slightly askew, so that the contraption now looked like a Y-wing fighter from Star Wars.

The ball that contained this revamped core, the Hammer 3D Offset, would become Pinel’s signature achievement. “That ball sold like hotcakes for three years, where the average life span of a ball was about six months,” says Del Warren, a former ball designer who now works as a coach in Florida. “They literally couldn’t build enough of them.” In addition to flaring like few other balls on the market, the 3D Offset was idiot-proof: The core was designed in such a way that it would be hard for a pro shop to muck up its action by drilling a customer’s finger holes incorrectly, an innovation that made bowlers less nervous about plunking down $200 for a ball.

(via @danhwylie)

What Would Life on a Flat Earth Be Like?

posted by Jason Kottke   Oct 05, 2021

So let’s say, for the sake of argument and against all scientific evidence to the contrary, the Earth was flat instead of being an oblate spheroid. What would life on a flat Earth be like? Well for one thing, gravity would present some challenges. From a 2018 piece by Doug Main at the Columbia Climate School:

People who believe in a flat Earth assume that gravity would pull straight down, but there’s no evidence to suggest it would work that way. What we know about gravity suggests it would pull toward the center of the disk. That means it would only pull straight down at one point on the center of the disk. As you got increasingly far from the center, gravity would tug more and more horizontally. This would have some strange impacts, like sucking all the water toward the center of the world, and making trees and plants grow diagonally, since they develop in the opposite direction of gravity’s pull.

And even more than that, gravity would tend to pull a flat disc shape back into a spheroid, so absent an intense spinning force (for which there is zero evidence) or some other completely unknown effect, a flat Earth couldn’t even exist:

For Earth to take the shape of a flat disk in the first place, gravity — as we know it — must be having no effect. If it did, it would soon pull the planet back into a spheroid.

A flat Earth would also likely not have a magnetic field (or at least one that is scientifically possible), meaning no atmosphere:

Deep below ground, the solid core of the Earth generates the planet’s magnetic field. But in a flat planet, that would have to be replaced by something else. Perhaps a flat sheet of liquid metal. That, however, wouldn’t rotate in a way that creates a magnetic field. Without a magnetic field, charged particles from the sun would fry the planet. They could strip away the atmosphere, as they did after Mars lost its magnetic field, and the air and oceans would escape into space.

Oh and no tectonic plates, volcanos, mountains, etc. Or GPS. Or weather. Or satellites. Or different night skies in, say, South Africa and Denmark. Or the Sun behaving the way it does in respect to the Earth. Or air travel. Or plant and animal life as it exists presently. To suppose a flat Earth also supposes that physics doesn’t explain our observable universe the way in which it reliably and comprehensively does. The simplest, best evidence for a round Earth is that we’re here living on it in the manner in which we are living on it.

A million people can call the mountains a fiction, yet it need not trouble you as you stand atop them.

See also What If the Earth Suddenly Turned Flat?, Flat Earthers and the Double-Edged Sword of American Magical Thinking, and Flat Earthers Listening to Daft Punk.

The Simple Physics Trick That Helps Trains Stay on Their Tracks

posted by Jason Kottke   Oct 04, 2021

Train wheels do not sit completely flat on the tracks — they’re designed with a slight taper that increases the stability of the train and allows the train to go around curves without any of the wheels skidding. In this short video, Tadashi Tokieda explains how those conical wheels keep trains on track.

See also Richard Feynman’s explanation of this and this science project at Scientific American. (via the prepared)

Here’s Why You’ll Fail the Milk Crate Challenge

posted by Jason Kottke   Sep 10, 2021

Bored of dying from Covid-19, Americans have dreamed up a more entertaining way to mortally wound themselves: the milk crate challenge. Wired asked structural engineer Dr. Nehemiah Mabry (who explained the different types of bridges to us earlier in the year) to explain the physics behind the challenge and why you shouldn’t attempt it. (via @pomeranian99)

Size Comparison: The Largest Black Hole in the Universe

posted by Jason Kottke   Aug 04, 2021

Black holes are the largest single objects in the universe, many times larger than even the biggest stars, and have no upper limit to their size. But practically, how big is the biggest, heaviest black hole in the universe? (A: More massive than the entire Milky Way.)

The largest things in the universe are black holes. In contrast to things like planets or stars they have no physical size limit, and can literally grow endlessly. Although in reality specific things need to happen to create different kinds of black holes, from really tiny ones to the largest single things in the universe. So how do black holes grow and how large is the largest of them all?

Videos about space are where Kurzgesagt really shines. I’ve seen all their videos about black holes and related objects, and I always pick up something I never knew whenever a new one comes out. This time around, it was quasistars and the surprisingly small mass of supermassive black holes located at galactic centers compared to the galaxies themselves.

“If It Doesn’t Shine In Your Face, You Don’t See Anything”

posted by Jason Kottke   Jul 28, 2021

Jocelyn Bell Burnell as a graduate student

As I’ve written before, in the history of astronomy and astrophysics, women have made major discoveries and played a significant role in advancing our understanding of the universe but have often not gotten the recognition their male peers enjoy. In 1967, while she was working on her doctoral research with her advisor Antony Hewish, Jocelyn Bell Burnell (then Jocelyn Bell) discovered a new and unusual kind of object, the pulsar. In this short documentary, Bell Burnell shares her story — how she got interested in radio astronomy, the prejudice with which she was treated as the only woman in her university program, how she discovered the first pulsar and persisted (more than once) through Hewish’s assertions that the object was “interference”, and how she was passed over for the Nobel Prize for her discovery.

In 2018, Bell Burnell was awarded the Special Breakthrough Prize in Fundamental Physics “for fundamental contributions to the discovery of pulsars, and a lifetime of inspiring leadership in the scientific community”, joining past honorees like the LIGO team, Stephen Hawking, and the team that discovered the Higgs boson. She donated the entire $3 million prize to the Institute of Physics to help support “PhD physics students from under-represented groups” with their educations.

It’s not justice, but I will note that Bell Burnell’s Wikipedia page is longer and more substantial than Hewish’s, despite his Nobel.

Visualization of How Fast a Ball Drops on Various Solar System Bodies

posted by Jason Kottke   Jul 14, 2021

This is an animation of how quickly an object falls 1 km to the surfaces of solar system objects like the Earth, Sun, Ceres, Jupiter, the Moon, and Pluto. For instance, it takes 14.3 seconds to cover that distance on Earth and 13.8 seconds on Saturn.

It might be surprising to see large planets have a pull comparable to smaller ones at the surface, for example Uranus pulls the ball down slower than at Earth! Why? Because the low average density of Uranus puts the surface far away from the majority of the mass. Similarly, Mars is nearly twice the mass of Mercury, but you can see the surface gravity is actually the same… this indicates that Mercury is much denser than Mars.

(via @thekidshouldsee)