A video from science YouTuber James Orgill, better known by the channel’s name The Action Lab, has demonstrated how you might be able to use a mug of hot drink as a particle detector.

If your aim is to detect and see the effect of particles that happen to be passing through your kitchen, that’s actually pretty easy. All you need to do is make a “cloud chamber“, and for that you only need a few cheap and readily available parts, including a plastic tub or cup, some felt or a sponge, some isopropyl alcohol, and the most difficult part to obtain: dry ice.

By soaking the felt or sponge in the alcohol and securing it to the top of the tub, then placing the tub on top of a surface above the dry ice, you create your cloud chamber. 

At the top of the chamber, the liquid slowly evaporates into a gas. But as it sinks to the bottom of the chamber, the cold ice makes it want to turn back into liquid form. In the bottom of the chamber, the air becomes supersaturated. When a particle travels through it, it can knock off some of the electrons of the molecules within the gas. As the molecules become charged, the alcohol gas becomes attracted to it and forms tiny droplets, resulting in streaks in the cloud chamber showing you the particle’s path. 

In this setup, you can see all sorts of particles, including radon atoms – the larger streaks you see – and muons – the small long streaks. It’s pretty cool.

But there may be an easier way to see the effects of cosmic rays using ingredients you are far more likely to have in your kitchen: a nice hot mug of cocoa.

Under the right lighting, you can see a layer of droplets form on top of a mug of cocoa, tea, or coffee – possibly held up by the steam rising from beneath, or due to a difference in the electric charge of the droplets compared with the bulk of the liquid. If you watch your mug for a while, you may notice that cracks form on the surface, which look an awful lot like particle streaks in a cloud chamber. 

The phenomenon has been known about since at least 1922, when Japanese physicist Torahiko Terada wrote an essay titled A Cup of Hot Tea. However, the mechanism is still not definitively known, and suggestions range from cosmic rays to convection forces in the liquid.

“Droplets individually and collectively vanish. In a collective event, the vanishing front propagates at approximately 1 m/s, which is close to the capillary surface wave speed of the water with a wave-length of 0.1 ~ 1 mm,” one team explained on the topic in a paper published in Scientific Reports. 

“Whether a vanishing event triggers a collective event or not, it is not clear what causes a droplet to vanish in the first place; the reason may be fluctuations in the evaporation flow or an electric disturbance that is caused by a cosmic ray if the droplets are levitated by the electrostatic force.”

It is possible that the disrupting event is cosmic rays, though that isn’t entirely clear. 

“The observed concurrent events are likely to be triggered by a common disturbance in the levitation force because it is highly improbable that more than one event occurs in less than 10 ms in a small area of the microscope field of view,” the team continued.

Orgill conducted his own informal experiments on hot drinks, and came to a similar conclusion. Key to this was that gamma radiation did not appear to have an effect on the drink. However, bringing an electrostatic charge close to the chamber did have a pronounced effect on the vapor, similar to inside a cloud chamber. As explained in the study above, this could indicate that cosmic rays are involved, as it suggests the droplets are levitated by the electrostatic force.

However, Orgill noticed that the patterns tended to appear along natural convection of the liquid, suggesting it could be down instead to convective forces within your drink.

“There must be enough turbulence that this causes the drops to touch and have a coalescing pattern,” Orgill said in the video. “So it seems that this isn’t very much cosmic rays causing it but a combination of electric charges interacting with the convection cells in the liquid. So what do you think? Why do you think the drops levitate and what causes these cascading patterns when they disappear?”

Either way, it’s a pretty interesting phenomenon, all taking place in your morning coffee.