Time According to Muons and Mayflies

By Frank and Clare Gouldstone

We were talking this morning about universal constants and speculating on whether they could be a function of how Humans sense the world. For example, suppose that (and we believe this is not the case, but let’s imagine) the speed of light was a function of how the Human eye sees. So then time, for an adult Mayfly, might be very different indeed.  This got us talking about decaying muons having an apparently much longer half-life to a Human observer than they themselves experience.

This opened up a whole new wonderful world of discovery. Let us share it with you!

The adult Mayfly, famously, lives for just a single day. A lifetime is from dawn til dusk. Prior to that, they will have spent 3 years as a larva in the near-dark River, made darker by the skin covering their eye, which filters out UV light from the Sun. How a Mayfly larva experiences time is still a mystery, but we know at least a little about the adult stage thanks to this paper by Egri et al https://www.nature.com/articles/s41598-025-14294-4

Certain species, like the Common Housefly, are known to have eyes that see things happening at an apparently slower rate than we do. What is actually happening is that they are less “blurred” – the insects may be able to process motion at a much higher rate than we do. In other words, their eyes may be faster-processing than ours. Paradoxically, this means that things appear to happen more slowly than they do for Humans. This is due to a phenomenon known as the Flicker Fusion Frequency (FFF). This is essentially like the number of frames per second of a movie. For Humans, the FFF is about 60 Hz. For the Common Housefly, it is about 250 Hz (or frames per second). With the adult Mayfly, things get really interesting: Male and female Mayflies have key differences in the structure of their eyes. It turns out that the male Mayfly has a compound eye and, while the rest of the eye has the same FFF as the female, the upper part of the eye sees things at this faster frame rate than the rest of their eye (and the whole of the female’s eye). It seems they have eyes that have evolved purely to find females amongst an emerging swarm of Mayfly in the late afternoon from Spring to Summer. Their eyes have evolved to make the most of just a few hours as a flying adult, seeking a female. Against the backdrop of a dusk sky, they see in UV, making the females appear dark and stand out from the crowd. This is a physiology they may share with Hoverflies, who have a love spot, which processes what it sees faster so appears to slow time down for this part of their eye even more than the rest of the eye. Of course, regardless of what current science tells us about eye anatomy, it’s not the whole picture – we simply don’t know what the Mayfly makes of what he sees. Even so, have Mayflies evolved eyes to ensure that time and tide wait for the females?

As the Mayfly looks upwards, elementary particles known as muons are hurtling towards them at close to the speed of light and arriving at a rate of about 1 muon per square centimetre per minute. The thing is, the muons are only supposed to exist for about 0.0000022 seconds before decaying into an electron and 2 types of neutrino. So they should never reach the Mayfly. In fact, they would only be expected to travel about 660 metres of the 15 km journey through our Earth’s atmosphere. But time, according to the muon, also looks rather different to what our Human eyes detect. Muons are created in the upper atmosphere by cosmic ray (proton) interactions. Because they are moving very fast, they experience time dilation – the time taken to decay happens at 2.2 microseconds on average on the muon’s clock but the clock appears to slow down for our Human (or Mayfly) observer, which means that the decay happens further along the muon’s journey, meaning that more of them reach the Mayfly.

Time, according to muons and Mayflies, is all relative. Maybe physics, like love, is in the eye of the beholder. Do the Mayfly’s few adult hours feel like eons? Perhaps to a Human it would feel very strange after 3 years underwater to emerge with a completely different view of the world! The muon tells us that time is just one part of the picture, a measure of change. And that measure depends upon the observer. We started this as a conversation between two people, speculating on how the Universe may work, and, as so often happens with these conversations, we may have only more questions, but we learned a little about the wonder of the world of the Mayfly and of the muon and how we are all quite literally impacted by our connection to the wider Universe. That we all arrive at the same place, but apparently along different routes seems remarkable. Somehow the Universe all fits together even when our clocks are apparently telling us different times.

 

Frank adds: “Or is all this just myopic spec-ulation?” 😂

Photo by Antonio Vivace on Unsplash