If you put a human in a sealed room, with a light switch, and no way to tell the time, would they be able to do it?
What if you controlled the light and turned it on and off at random intervals? Do you think that would help or hinder this persons efforts at keeping time? Or perhaps the light is set at a dim level for the entire time?
It turns out, whilst light is the primary driver of our circadian rhythm, it is not strictly essential. Humans have an internal clock, an endogenous way of keeping time that cycles between 24-25 hours, with or without external interference.
Humans have a circadian pacemaker. It’s called the suprachiasmatic nuclei (SCN) and it sits in the hypothalamus. Through a pathway connected to the retina, it controls the release of melatonin and other chemicals into our body in response to light. These chemicals drive our wake up and sleep times.
But in the absence of light, or in consistent light, the body still maintains this roughly 24 hour cycle.
In 1966 two scientists, Jurgen Aschoff and Rutger Wever designed what has become known as the Bunker experiment. They built two bunkers, both (almost) identical, and funneled hundreds of volunteers into them for periods ranging from weeks to days.
What they found revolutionised the study of chronobiology.
The majority of participants held their sleep schedules within 24-25 hours and only wrongly guessed about what the local clock time was (thinking they were waking up at 6am when they were in fact waking up at 3pm, etc.). But others didn’t fair so well.
People lost track of their day. They reported days that in reality lasted well over 24 hours, in one case a participant stayed active for 50 hours, before thinking it was night and time for bed. These participants had one thing in common, they all stayed in one of the bunkers, and not the others, and these bunkers had a key difference.
This may read like a contradiction of the previous statement, that an endogenous system controls our clocks, however, it isn’t. All of the participants bodies still moved through a 24-25 hours cycle; core temperature and bodily functions pulsated within this time limit but some had their sleep schedule desynchronise with the rest.
Now, it’s time to reveal the difference between the bunkers, a difference that was swept under the rug by Aschoff as the results didn’t agree with his personal beliefs about how the human body measured time.
One bunker was just that, a bunker. But the other had walls filled with electromagnetic dampening materials. No magnetic field could penetrate this second bunker and it was only in this bunker that participants suffered desynchronisation, where their sleep schedule fell out of step with the rest of their bodily processes.
Let’s jump back in time to the 1950s. In a dark room, submerged in containers of brine, sealed from light and temperature controlled, held at a steady pressure, a bunch of oysters opened their shells as the moon reached its highest point in the sky.
Again, about 12 hours later at what would be the second high tide, they did it again.
There was no movement in the water, no change within the room. And they were a few hundred kilometers away from where they were natively found.
For the first two weeks they opened and closed with the high tide they were used to; if it was high tide on the shore where they were from, the oysters would open.
But after two weeks something happened. The oysters opening time shifted by fifty minutes. It now matched the time of the local high tide. These oysters had followed the moon, somehow, they knew that they were no longer at their local shore and had adjusted to their new conditions.
This confounded the scientist, Frank Brown, and it lead him down a life long path of trying to prove that animals and humans had some link to the cosmos, some way to sense fields that permeated everything.
He was discredited all the way up to his death.
But he was right, in a sense.
The oysters were sensing the geomagnetic field of the Earth, the same thing that the humans in the EM-sealed bunker couldn’t sense when they desynchronised from their internal rhythm. Does this mean that the participants in the normal bunker were in someway sensing the geomagnetic field of their Earth and it was, in turn, helping them keep their sleep pattern aligned with their internal clock?
Maybe. There isn’t enough evidence to say one way or the other at the moment but in recent years more study has been done.
In all sorts of animals, birds, whales, butterflies, a group of proteins can form called cryptochromes. In humans (yes, we have them too) these cryptochromes form in the retina but in us they don’t seem to help with navigation in the way that they help birds migrate or sea turtles find their home beach to lay eggs.
In 2011, a group of scientists took some fruit flies who usually use the magnetic field of the Earth to help them navigate. They bred a line of these flies with no ability to create their own cryptochromes; for all intents and purposes, these flies were now blind to the geomagnetic field of the Earth.
That is until the scientists took the human version of the cryptochrome and place it within the eyes of the fruit flies.
Suddenly, they could see magnetic fields again. They tested this by presenting the flies with a maze, one side magnetised, the other not. The group of flies that couldn’t sense the magnetic field showed no preference for direction, but the group of flies with the human genome overwhelmingly chose the magnetised side.
Does this means humans have some ability to sense the geomagnetic field?
The evidence is leaning that way, but as usual, more study needs to be done.
Further Reading/References:
Effects of light on human circadian rhythms, sleep and mood (nih.gov)
Living Without Temporal Cues: A Case Study (nih.gov)
We have the right stuff to sense magnetic fields | New Scientist
Physics and Fiction 
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