I make calming, satisfying simulations from real physics, maths and astronomy, plus short stories told with real physics
Joined April 2009
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Run The Sim retweeted
Do you understand what a light-year is? Here's a simple explanation.
Light is the fastest thing there is. It goes 300,000 km every second, and in one year it covers about 9.46 trillion km. We call that distance a light-year. So a light-year is not an amount of time. It's a way of measuring distances that are too big for kilometres.
Sirius, the brightest star you can see at night, is 8.6 light-years away. That means its light needs 8.6 years to reach you. Any time you look at Sirius, the light hitting your eyes left the star 8.6 years ago. You're not seeing the star as it is now. You're seeing it as it was back then.
The kidney stone breaker
You've probably seen this ellipse trick before: everything that leaves one focus bounces off the curve and arrives at the other focus at the same instant.
Since 1980, doctors have used it to break kidney stones without a single cut.
The patient lies on a dish of water shaped like half an ellipse. A spark at one focus sends out a shock wave, the dish bounces it back, and every part of it arrives at the other focus at once, right where the stone is. For a millionth of a second the stone feels about 300 times the pressure of the air.
After about 2,000 pulses, around half an hour, the stone is gravel and sand, and pieces under 2 mm can pass out of the body naturally.
Run The Sim retweeted
You've probably seen this ellipse trick before: everything that leaves one focus bounces off the curve and arrives at the other focus at the same instant.
Since 1980, doctors have used it to break kidney stones without a single cut.
The patient lies on a dish of water shaped like half an ellipse. A spark at one focus sends out a shock wave, the dish bounces it back, and every part of it arrives at the other focus at once, right where the stone is. For a millionth of a second the stone feels about 300 times the pressure of the air.
After about 2,000 pulses, around half an hour, the stone is gravel and sand, and pieces under 2 mm can pass out of the body naturally.
Run The Sim retweeted
Go outside before dawn this week and you may see a shooting star. It's a speck of dust from Halley's Comet. Every 76 years it sheds dust as it passes the Sun, and over thousands of years that dust has become a river around the Sun. Every October, Earth flies through it.
Run The Sim retweeted
You can't fold an ordinary sheet of paper in half more than about 7 or 8 times, however hard you try. Every fold doubles its thickness and halves its size, so after a few folds you're trying to bend a tiny block that's thicker than it is wide.
But what if you could keep going? If you could fold that same sheet 42 times, how thick do you think it would be? Make your guess, then watch to the end.
For 4.6 billion years, our Sun has been carrying us around the Milky Way at more than 800,000 km an hour. One lap takes about 220 million years, and so far it has gone around about 20 times.
This one makes me feel so small. Everything that has ever happened, every moment in history, every great person who ever lived, even the dinosaurs, all of it happened on that one tiny speck.
And it makes me wonder: where is heaven in all of this? 🤔
Run The Sim retweeted
A sheet of paper is about 0.1 mm thick, and each fold doubles it. After 7 folds it's 1.3 cm. After 20 folds it would be 105 m tall, higher than the Statue of Liberty. After 27 it would be higher than Everest, and after 42 it would be 439,805 km thick, further away than the Moon.
The real record is 13 folds, set by students in Massachusetts in 2011 using 16 km of toilet paper. To fold a single sheet 42 times, it would have to be about 100,000 light-years long, as long as our galaxy is wide.
Music: Grieg's "In the Hall of the Mountain King" (public domain), played on the Salamander Grand Piano by Alexander Holm (CC BY 3.0). Earth and Moon images: NASA. Milky Way: ESO/S. Brunier (CC BY 4.0).
You can't fold an ordinary sheet of paper in half more than about 7 or 8 times, however hard you try. Every fold doubles its thickness and halves its size, so after a few folds you're trying to bend a tiny block that's thicker than it is wide.
But what if you could keep going? If you could fold that same sheet 42 times, how thick do you think it would be? Make your guess, then watch to the end.
A sheet of paper is about 0.1 mm thick, and each fold doubles it. After 7 folds it's 1.3 cm. After 20 folds it would be 105 m tall, higher than the Statue of Liberty. After 27 it would be higher than Everest, and after 42 it would be 439,805 km thick, further away than the Moon.
The real record is 13 folds, set by students in Massachusetts in 2011 using 16 km of toilet paper. To fold a single sheet 42 times, it would have to be about 100,000 light-years long, as long as our galaxy is wide.
Music: Grieg's "In the Hall of the Mountain King" (public domain), played on the Salamander Grand Piano by Alexander Holm (CC BY 3.0). Earth and Moon images: NASA. Milky Way: ESO/S. Brunier (CC BY 4.0).
Run The Sim retweeted
I put 640 metronomes on one platform, each playing its own note, and started them all at once in total chaos. Watch what happens when they all sync in this physics simulation. 🔊
Run The Sim retweeted
This is the path Mars draws in our sky over 32 years. Every couple of years it slows down, loops backwards and carries on, and all those loops add up to this.
I put 640 metronomes on one platform, each playing its own note, and started them all at once in total chaos. Watch what happens when they all sync in this physics simulation. 🔊
This is the path Mars draws in our sky over 32 years. Every couple of years it slows down, loops backwards and carries on, and all those loops add up to this.