buy artwork

▲ 2025 π DAY | TTCAGT: A sequence of digits. 768 digits of `\pi` as a Sanger sequencing trace of 1,536 peaks. Decode the sequence (BUY ARTWORK)

`\pi` Day 2016 Art Posters

▲ 2024 π DAY | Explore the garden of digits.

▲ 2023 π DAY | Repeated sequence

▲ 2022 π DAY | three one four: a number of digits

▲ 2021 π DAY | Good things grow for those who wait.' edition.

▲ 2020 π DAY | The piku.

▲ 2019 π DAY | Hundreds of digits, hundreds of languages and a special kids' edition.

▲ 2018 π DAY | Street maps to new destinations.

▲ 2017 π DAY | Imagine the sky in a new way.

▲ 2016 π APPROXIMATION DAY | What would happen if about right was right.

▲ 2016 π DAY | These digits really fall for each other.

▲ 2015 π DAY | A transcendental experience.

▲ 2014 π APPROXIMATION DAY | Spirals into roughness.

▲ 2014 π DAY | Hypnotizes you into looking.

▲ 2014 π DAY | Come into the fold.

▲ 2013 π DAY | Where it started.

▲ CIRCULAR π ART | And other distractions.

On March 14th celebrate `\pi` Day. Hug `\pi`—find a way to do it.

For those who favour `\tau=2\pi` will have to postpone celebrations until July 26th. That's what you get for thinking that `\pi` is wrong. I sympathize with this position and have `\tau` day art too!

If you're not into details, you may opt to party on July 22nd, which is `\pi` approximation day (`\pi` ≈ 22/7). It's 20% more accurate that the official `\pi` day!

Finally, if you believe that `\pi = 3`, you should read why `\pi` is not equal to 3.

support my work ·

Most of the art is available for purchase as framed prints and, yes, even pillows. Sleep's never been more important — I take custom requests.

This year's `\pi` day art collection celebrates not only the digit but also one of the fundamental forces in nature: gravity.

In February of 2016, for the first time, gravitational waves were detected at the Laser Interferometer Gravitational-Wave Observatory (LIGO).

The signal in the detector was sonified—a process by which any data can be encoded into sound to provide hints at patterns and structure that we might otherwise miss—and we finally heard what two black holes sound like. A buzz and chirp.

The art is featured in the Gravity of Pi article on the Scientific American SA Visual blog.

this year's theme music

All the art was processed while listening to Roses by Coeur de Pirate, a brilliant female French-Canadian songwriter, who sounds like a mix of Patricia Kaas and Lhasa. The lyrics Oublie-moi (Forget me) are fitting with this year's theme of gravity.

Mais laisse-moi tomber, laisse-nous tomber
Laisse la nuit trembler en moi
Laisse-moi tomber, laisse nous tomber
Cette fois

But let me fall, let us fall
Let the night tremble in me
Let me fall, let us fall
This time

simulating gravity in 2d

The gravitational force between two masses `m_1` located at `(x_1,y_1)` and `m_2` located at `(x_2,y_2)` is given by

$$F = \frac{G m_1 m_2}{r^2} \tag{1} $$

where `r` is the distance between the masses given by

$$r = \sqrt{ \Delta x ^2 + \Delta y ^2 } = \sqrt{ (x_2-x_1)^2 + (y_2-y_1)^2 } \tag{2} $$

The force is directed along the vector formed by `r` and can be decomposed into `x` and `y` components using \begin{align} F_x &= F \frac{ \Delta x}{r} = F \frac{x_2-x_1}{r} \tag{3} \\ F_y &= F \frac{ \Delta y}{r} =F \frac{y_2-y_1}{r} \tag{4} \end{align}

The acceleration of each mass can be obtained using `F = ma` and similarly decomposed into `x` and `y` components \begin{align} a_{1x} &= \frac { F_{1x} }{ m_1} = \frac{G m_2 \Delta x}{r^3} \tag{5} \\ a_{1y} &= \frac { F_{1y} }{ m_1} = \frac{G m_2 \Delta y}{r^3} \tag{6} \\ a_{2x} &= \frac { F_{2x} }{ m_2} = -\frac{G m_1 \Delta x}{r^3} \tag{7} \\ a_{2y} &= \frac { F_{2y} }{ m_2} = -\frac{G m_1 \Delta y}{r^3} \tag{8} \end{align}

When there are `n` masses in the system, the acceleration of mass `i` is the sum of the accelerations due to all other masses \begin{align} a_{ix} &= \sum_{i \ne j} \frac{G m_j \Delta x_{ij}}{r_{ij}^3} \tag{9} \\ a_{iy} &= \sum_{i \ne j} \frac{G m_j \Delta y_{ij}}{r_{ij}^3} \tag{10} \end{align}

The equations of motion for the masses over a period of time `\Delta t` are

\begin{align} \Delta v_x &= \Delta t a_x \tag{11} \\ \Delta v_y &= \Delta t a_y \tag{12} \\ \Delta x &= \Delta t \left( v_x + a_x \frac{\Delta t}{2} \right) \tag{13} \\ \Delta y &= \Delta t \left( v_y + a_y \frac{\Delta t}{2} \right) \tag{14} \end{align}

numerical simulation

There are various ways in which the numerical simulation can be performed. The Euler, Verlet, Runge-Kutta methods are perhaps the most common. I use the Verlet approach.

Using the equations of motions above, the Verlet simulation goes as follows

1. calculate acceleration, `a_1` (eq 9,10)
2. update position (eq 13,14)
3. calculate new acceleration, `a_2` (eq 9,10)
4. update velocity using `(a_1+a_2)/2` (eq 7,8)

The masses are initially uniformly distributed on a circle and given a zero initial velocity or a normally distributed random velocity.

I ran about 10,000 individual simulations with different values of `n` and `k` and collected ones that stood out as pretty.

collisions

The size of a mass is taken to be `s = m^{1/3}`. When two masses, `m_1` and `m_2` come within a distance of `\left( s_1 + s_2 \right)(1-z)` of each other, they collide. Here `z` is a collision margin parameter that I set to either `z=0` or `z=0.25`.

During the collision, a new body is created with mass `M = m_1 + m_2` given a speed that conserves momentum in the collision. \begin{align} v_x &= \frac{m_1 v_{1x} + m_2 v_{2x} }{M} \\ v_y &= \frac{m_1 v_{1y} + m_2 v_{2y} }{M} \end{align}

values

For my simulation, the following values are used

• `G = 100`
• mass for each digit, `d` is `(1+d)^k`
• masses placed on circle with radius `216`
• when randomized, `(v_x,v_y) \sim N(0,1)`
• `\Delta t = 0.01`
• simulation runs for up to 100,000 steps
• canvas size is `1440 \times 1440`