# DIY Pilot wave hydrodynamics

Approximately two years ago, I wrote a series of posts covering Pilot wave hydrodynamics with Nicole Sharp from FYFD. Since then I have always wanted to try this out at home and visualize the phenomenon. Following is an informal report on how I was able to get this to work from things I found at home:

#### Things needed

• A sub-woofer or a woofer
• Petri dish
• Dropper
• Cardboard
• Hot glue
• Vegetable/ Silicon/ Linseed oil

### Setup

One of the first things that I did was to grab a cardboard and cut it to the size of the sub-woofer.

I then hot-glued a white sheet of paper with grid lines on the cardboard and carefully placed the petridish on the center of this cutout and glued the petridish onto the cardboard.

(Since I was using my personal speaker for these experiments I did not glue the cardboard-petridish setup to the sub-woofer. But if you are dedicating an entire woofer/sub-woofer to these experiments you can glue the setup to the its edges so that it does not wobble when you vibrate it from below)

I finally made a striped color pattern with some strips of paper and placed it in the background such that the reflection of the striped pattern was seen on the petridish. This helps to visualize the perturbations on the surface of the fluid.

Connect the speaker to your computer and voila! you have a setup for visualizing pilot wave hydrodynamic phenomenon

### Making droplets bounce

I primarily used vegetable oil for most of my experiments. This has the disadvantage that the bouncing droplets do not last for long but it is more commonly available at home. Other oils that offer longer bouncing time are Silicon and Linseed oil.

Pour the vegetable oil on to the petridish*, tune the speaker to 23-33 Hz, and reduce the volume until you do not see any perturbations on the surface (i.e below the Faraday threshold).

Using the dropper take some vegetable oil and carefully drop it on the vibrating bath (see gif below). And you should be able to see a tiny droplet of oil bouncing happily on the surface.

With a bit of patience, it is also possible to make multiple droplets bounce together (known as a droplet lattice. see gif below )

Following are some interesting footage that I shot at 240/1000 fps using this setup on my Galaxy S9:

I strongly encourage the interested reader to try this out. It was a lot of fun to make it and you will not be disappointed at the results. If you have any questions, feel free to email me at 153armstrong@gmail.com, I would be happy to help you out.

### Known issues/ Ways to make it better

• Since I was using my personal speaker for these experiments I did not glue the cardboard-petridish to the sub-woofer. But doing this would be very optimal. I often had to ensure that petri dish was aligned to the center of the sub-woofer from time to time. This could have been easily resolved by gluing it to the sub-woofer surface
• As you can notice from some of the gifs, there were some tiny contaminants in the oil or some air bubbles that got trapped inside. Although I tried to maintain a clean environment it was hard to avoid such contamination entirely.

### Acknowledgements and references

A huge thanks to Dan Harris for helping me on this venture. This post is based on his paper (Harris, D.M., Quintela, J., Prost, V. et al. Visualization of hydrodynamic pilot-wave phenomena. J Vis20, 13–15 (2017) doi:10.1007/s12650-016-0383-5) which outlines this setup in more technical detail and I strongly recommend that you give that a read.

If you are looking for a general resource page on Pilot wave hydrodynamics, check this out.