# Gravitational waves playground

An interactive iPad visualization I created in 2018 with Swift and the Swift Playgrounds App.

In this Swift playground book you can make gravitational waves visible and control the visualization of this elusive radiation emitted by two inspiraling and merging black holes.

From README.md in the nilsleiffischer/gravitational-waves-playground GitHub repository:

# Gravitational waves playground

In this Swift playground book you can make gravitational waves visible and control the visualization of this elusive radiation emitted by two inspiraling and merging black holes. It continues my series of interactive iPad simulations that started with my playground book on black holes.

• Adjust the black hole masses:

• Control visualization parameters, such as wave polarization and colors:

• Explore the visualization in three dimensions:

## Installation

2. Add the Play with Gravity feed to the Swift Playgrounds App and load the Gravitational waves playground.

Alternatively, this is the URL you can manually add to the Swift Playgrounds App to subscribe to the Play with Gravity feed:

• Play with Gravity feed URL: https://nilsleiffischer.de/relativity-playgrounds-feed/feed.json

## Simulated physics

• The rendered field is the lowest-order metric perturbation in TT-gauge (or gravitational wave strain) $h_+$ or $h_\times$, with their $\frac{1}{r}$ distance scaling removed.
• Selecting the option showFrequencyScaling is equivalent to visualizing the real or imaginary part of the Weyl scalar $\Psi_4$, depending on the chosen polarization.
• The six colors are chosen from the normalized field values discretized into bins with edges $\left\{\pm 1, \pm 0.7, \pm 0.5, \pm 0.3\right\}$.
• The rotating spheres depict the relative Schwarzschild radius of the black holes, with an arbitary rescaling for visualization.
• Orbital separation, time and wave propagation speed are also arbitrarily rescaled. Relative quantities are correct, however.
• The ringdown is modeled as a simple quadrupolar oscillation with an exponential decay in amplitude for visualization purposes only.