This runs live on an Apple silicon GPU.

Every bird reacts only to the ones near it. Nothing choreographs the shape and nothing is keyframed, so what you are watching falls out of 137,500 of them following local rules at once.

It is a GPU flock on an atomic spatial hash, which keeps neighbour lookups linear instead of quadratic at that count. Each bird steers on a bounded turn rate and banks into its turns, and the banking is what makes the flock flicker as they roll.

Based this on starling literature rather than plain boids, mostly Cavagna's work on scale-free correlations in real flocks and Couzin on spatial sorting. Cool thins is that the same system with one flag flipped runs a bait ball instead: change the attractor from polarised streaming to milling and the sheet becomes a rotating sphere.

Built in Swift and Metal as part of TideGlass, a small Mac app I make where worlds like this run on a second monitor while you work. Happy to answer anything about the sim.

A while ago I posted a version of this on a circular track. Two things came up in the comments often enough that I decided to rebuild the whole thing.

The first was the loop itself. Several people said it was distracting, and that it was hard to tell whether a jam was really moving backwards or whether the track was just going round. The second was lane closures - a few of you asked what would happen if one lane were blocked. So this time the road is straight, it has four lanes and one of the cases is a closed lane with the merge that follows it.

In the phantom-jam case there is no accident and no obstacle at all. The density is simply high enough that one driver braking a little harder than necessary gets amplified by the cars behind, and the wave then travels backwards along the road while every individual car keeps moving forwards.

There is one comment from last time that I want to answer. Someone wrote that the narration read like AI slop. That is fair. English is not my first language, so I use AI assistance for the wording. The simulation, model and idea are my own work, the phrasing had help. I am trying to get better at that part.

I should also be clear that there is no income expectation in this. The channel is not monetised and I am not expecting it to be. I am doing it as a hobby, to learn how simulation and visualisation actually work, so that I can use them properly in my own field. Youtube is simply where the files are stored.

The full version, with the other cases and a proper explanation, is here:

https://www.youtube.com/watch?v=msX3kewLRIQ

What you see here is the short version. The full one works through the cases I had to leave out. It covers where the tipping point actually sits, which is the density above which the road stops recovering from a disturbance, why the lane next to you nearly always looks faster than the one you are in, what a small proportion of slow trucks does to the flow behind them, what tailgating costs you compared with keeping your distance, which was not the result I expected, and what changes when roughly one car in five drives itself. It ends with the few things a driver can actually do to avoid making a jam worse.

Along with other essential features for a proper muscle simulation tool. The good thing is that I’m using it as a character artist while developing it, which allows me to find the most artist-friendly workflows and implement them directly into th

An origami crane is flying in a mirror cube. The camera is a rear shot following the origami crane as it flies inside the cube.

The Gulf is pretty shallow, about 35 meters on average, and only 11.9 meters deep at the northwest end. During the last ice age the sea level was 120 meters lower, so the whole basin was completely dry. The exploration ship Meteor confirmed it: an entirely dry basin around 15,000 BC.The Tigris, the Euphrates and the Karun all met up and flowed the entire length of it as one single river, heading out through the Strait of Hormuz. That old channel is still there. You can see it clearly in the bathymetry.
it wasn’t empty. There was a floodplain down there with vegetation, wildlife, and Neolithic communities living on it.Then the ice melted. Sea level rose 150 meters between 12,000 and 7,000 BC, and at the fastest stretch the shoreline was advancing ten meters a year. They didn’t get washed away. They just got pushed out, one salty well at a time, over generations.Bahrain’s name is the dual form of the Arabic word for sea, meaning two seas. One reading of it is the salt water above and the fresh water below. Pearl divers have said for centuries that in certain spots you can flip a bucket on the seabed and bring it up full of fresh water. That’s the old river system still draining.The clip is that basin emptying, run in a planetary model I’ve been building. I used a different method. I closed the strait and let it evaporate instead of dropping global sea level, but the same floor comes back out and the river shows up right where it’s supposed to be.

1.5 years ago some friends and I were talking about global warming and got onto a question: if you could move any amount of dirt, how much could you lower global sea level?

I built a planet simulator to find out.

7 cm.

The move is to open the Caspian. It sits 28 m below sea level with a huge flat depression north of it. Cut a channel, the Atlantic pours in, the hole fills. About 25,000 km³ parked where it can't be ocean anymore. Stabilises in under a year, though that's really a function of how wide I cut the channel.

Then it stops. Evaporation off the new sea just rains back into the ocean. The only lasting change is the water sitting in the hole.

the mechanics:

Real bathymetry, 2048×1024 grid, about 20 km a cell. Every cell holds a water depth and the global total is conserved to 2 parts in 10,000 . Cut a channel and the solver just pours: fills each connected body from its deepest cell until volume and terrain balance, merges two bodies when they touch. The sea level drop isn't scripted anywhere. It falls out of the pour.Fill time is a weir calculation on the throat you dug such as cross-section and head.

Climate is energy-balance per latitude band with heat transport, so temperature comes out of the physics instead of a lookup table. Precipitation gets shaped by terrain and sea surface temperature, and that feeds evaporation minus precipitation per cell, plus river inflow weighted by catchment rainfall.

I have a casting simulation assignment to show reduction shrinkage defect in two weeks. Is there any way to do it fast and any software that help to do it faster this for assignment rights my three fourth of my entire semester mark

Super excited to share the latest update on my physics-based muscle simulation tool!
This test uses a relatively low-res simulation, as the main goal was to go through the full character pipeline and make sure everything works together.

I'm simulating a ball pit with 20,000 capsule balls in this game prototype. Trying to make it more satisfying and fun.
[OC]

No AI were used.

Based on feedback in the comments section, I re-recorded the video of blocking the Strait of Gibraltar (the third one), and also set up a simulation of the river drying up process in this simulator, as well as the main menu.

This project goal was large waterfalls in a real-time forest experience, developed in C++/Vulkan. Note: I am no expert in fluid simulation - and wanted to learn by creating every piece of the sim.

The following is the story of how I got to the current version in the video. With the simulator I developed for my forest project, I could already simulate half million particles at 30 FPS, but my implementation was not scaling to a large domain. I replaced mesh extraction (first most expensive component) with rendering directly the isosurface of water with raymarching + hardware ray tracing. This scaled rendering, giving more time for sim. Then I moved the simulation to active cells only, making the cost depend mostly on the amount of water rather than the size of the world. These two made large mountain streams practical, but a waterfall requires simulating also the mix of air and water.

Rapids could do with air entrainment, while waterfalls also needed airborne droplets interacting with the surrounding airflow. I ended up writing a different solver for air, coupled to the water: the cascade pushes air downward, the air domain is simulated, and the mist is advected by the air field. This gets closer to a dual phase simulation of water and air, with an engineering approach. The air solver is a eulerian grid solver, whereas the water solver is hybrid sph-grid.

I got a nice looking waterfall, though it lacks some of the "clustering" and filaments that large waterfalls produce - mostly due to surface tension (I guess! the project should "prove" it). This spawned the exploration of surface tension, and it appeared that a simpler more contained "water crown" experiment would be the right place to tune the physics for this; I was apparently wrong as the experiment showed.

I tested a single droplet, made of hundreds of thousands of particles, to try and reproduce the "crown" upon impact with a flat water surface. I could not get the crown, and I thought - yeah sure, I lack a simulation of surface tension. I implemented surface tension by "cohesion forces". Surface tension made droplets spherical, so it did its job apparently, but no crown.

I found out - and here I ask confirmation - that the main thing for this crown effect is actually incompressibility. If water is compressible, the droplets gets swallowed and energy is dissipated; if water is "stiff", then all sorts of more realistic impacts occur; high stiffness gave me nice crowns.

But stiffness makes impacts turn into chaos, as it generates local "high pressure" areas. Real-time water is usually somewhat compressible — and therefore slightly rubbery — because disturbances remain local and cheap to simulate, it seems. How to make it incompressible and "stable"? For my realtime scenario, I decided to add an iterative "fix" that corrects particle positions for getting closer to incompressiblity. THere are other ways, a full solver for all particles would be more correct I guess. In any case the "incompressibility fix" coupled with high stiffness gave me a nice crown as you see in the video.

All in all, a very nice adventure in simulation. By looking at the crown, and also at the waterfall, I am sure that a better model of surface tension is still missing here, and that will be the next step.

In general, I don’t want to tell water how to look realistic. I’d rather give it simple enough rules and let realism emerge: foam from entrained air, mist from airflow, a crown from pressure propagation. To me that's the beauty of simulation: when it looks right, we have understood enough of the physics.

This acts as the final CFX layer for creatures and characters.
Unlike systems that can feel too cloth-like, my goal is to achieve more skin-like sliding, compression, and deformation. Here’s an early test of the solution.

The Mediterranean runs at a loss: it evaporates about 0.5-1 m of water level per year more than rain and rivers put back, and the Atlantic covers the deficit through Gibraltar around the clock. My simulator derives a 0.7 m/yr deficit on its own from its climate model - right in the textbook range - so I felt entitled to do something irresponsible with it.

I sealed the strait (14 km wide at its narrowest) and let it run. No scripted animation - every cell tracks its own evaporation, precipitation and river inflow each year, and global water volume has to conserve to within 2 parts in 10,000.

Timeline:

- 25 years: level down 17 m. Venice's gondoliers are the first out of work.

- ~500 years: the Adriatic is gone (average depth only 250 m).

- ~700 years: the Sicily-Tunisia ridge surfaces and the Med splits into two shrinking lakes. When this actually happened 5.97 million years ago, hippos walked to Cyprus - their stranded descendants shrank into dwarf hippos. The fossils exist.

- ~2,100 years: the basin is effectively dead. 2.5 million km² of new land, nearly the size of Argentina, crusted with precipitating salt.

- ~4,300 years: the deepest pools bottom out. Except one - a bitter lake in the east kept on life support by the Nile. I never coded that; evaporation, rivers and terrain balanced it into existence on their own.

The Black Sea survives: once its level drops below the Bosporus sill it detaches and holds steady on the Danube and Dnieper. The Caspian was my control group - untouched, it drifts 17 m in 300 years and then stabilizes.

This genuinely happened. It's called the Messinian Salinity Crisis: 5.97 million years ago Gibraltar really did close. In 1970 the drillship Glomar Challenger pulled gypsum and rock salt out of the Mediterranean seafloor under 3,000 m of water. My simulator has never heard of the Messinian - it just agrees with the drill cores.

It's all from a game I'm building where you do this with a brush. Link in the comments to keep things tidy.

Started this to show my kids where the Moon came from, because "a Mars-sized planet hit the Earth" is a sentence that explains nothing. Turned out the fun part is letting them break it.

Proto-Earth and a Mars-sized Theia falling together under their own gravity: the splash, the tidal arm, the debris disk, and the moon that gathers out of it.

What's actually computed: self-gravity from the particles themselves (64³ particle mesh + pairwise correction for loose material), spring-dashpot contacts with no tension, frictional heating that conducts between grains and lights the scene, differentiated bodies with per-material density, and momentum/angular momentum/energy conserved to a fraction of a percent on screen.

What isn't: no SPH, so no pressure, no shock, no vaporization. No material strength or fracture. No cooling or latent heat. A grain is a couple hundred km across, so the Moon itself is scaling from the disk, not a run.

Different scenarios what if Thea was bigger or had more speed.

Live demo: https://gaploid.github.io/cosmic-collisions/

Open source code: https://github.com/Gaploid/cosmic-collisions

Celestial lets you explore star systems as a deformable gravity sheet instead of flat orbital diagrams.

The star moves. Planets sit on and ride the surface it bends. You can change the gravitational constant, push a planet, or drop a new body in and watch the whole system respond in real time.

Systems included:

* Our solar system (with a drifting barycentre)
* Alpha Centauri (two moving funnels)
* Kepler-16 (circumbinary planet)
* TRAPPIST-1 (seven worlds inside Mercury’s orbit)
* The classic three-body figure-eight

It’s a proper Newtonian n-body integrator running in the browser, not pre-scripted ellipses. The sheet itself is an exaggerated visual analogy, and the site is unusually honest about what is real and what is drawn that way on purpose.

[https://celestial.logicaleap.com\](https://celestial.logicaleap.com)

Free, no account, runs in the browser.

I’ve finally turned a project I’ve been coming back to for years into something I can actually release.

Makarov Physics Suite is a collection of around 120 interactive physics simulations. It covers everything from classical mechanics, waves and electromagnetism to optics, fluids, thermodynamics, relativity and quantum physics.

The project has a rather long history. Its earliest version goes all the way back to my university days, about 20 years ago. That version was basically a student project, and over the years I repeatedly returned to the idea, experimented with different approaches, rewrote things, added new simulations, and sometimes abandoned it again for long periods.

The current suite is essentially the result of all those years of accumulated ideas and experiments.

From the programming side, there’s quite a mix of things under the hood: numerical solvers, N-body simulations, SPH fluids, charged particle dynamics, GPU computing, ray tracing and path tracing, among others.

The main idea is simple: instead of explaining physics with static diagrams or prerecorded animations, I wanted the systems themselves to be interactive, so you can change parameters, disturb them, experiment with them and immediately see what happens.

It’s now on Steam, which still feels a little strange considering where the project started.

If you’re into physics, simulation, scientific computing or graphics programming, I’d be interested to hear what you think.

https://reddit.com/link/1vzgsrc/video/u0ozqxqdellh1/player