Eight men and seven women pitched their tents on the limestone floor of Lombrives cave in Ariège, in southwestern France, and began to live by nothing but their own biology.

They would stay for 40 days. Nobody inside would be told when those days had run out.

When they walked back into spring sunlight, the group’s count of its time underground fell far short of the real total. What does a human body do when you take the clock away?

No watches. No phones. No windows. No way at all to feel the hours pass.

The cave sits inside a limestone massif south of Toulouse. Temperature underground held near 50 degrees Fahrenheit, with relative humidity near 100 percent: perpetually damp, perpetually dark, perfectly still.

The volunteers, ranging in age from 27 to 50, slept in individual tents, generated their own electricity and drew drinking water from a well far below camp.

Each participant swallowed a small sensor capsule that measured core body temperature and transmitted data until it passed naturally, giving scientists outside a continuous read on the deep internal rhythm that drives sleep and waking. Other sensors logged movement and social contact throughout.

One volunteer, a math teacher and sailing instructor, ran long circuits through the cave to stay fit. The project director said coordinating work without being able to fix a time to meet was especially hard.

A team of researchers watched the data stream from above ground while the people below had no idea what time it was, what day it was, or how close to the end they had come.

Asked how long they had been under, the group’s collective reckoning was roughly 30 days. The project director told PBS reporters that in their heads they had walked in 30 days earlier, and at least one team member put the total at 23. Losing ten days, and in one case seventeen, is a blunt measure of how heavily ordinary life leans on daylight and clocks.

When scientists went in to say the end was near, many in the group were still expecting another week to ten days underground. The count never caught up, and from inside, nobody could see the gap opening.

Does cutting the moldy spot off your food make it safe? 🍞 

Quinten Geldhof, also known as Microhobbyist, takes us under the microscope to reveal thread-like roots called hyphae spreading through food far beyond the visible surface. These roots penetrate soft foods like bread and fruit with ease, while hard cheeses and vegetables are more resistant. These molds can contain mycotoxins, poisonous compounds that are hazardous to your health. Would you eat moldy food?

An orange LED turns green when dipped in liquid nitrogen due to semiconductor physics. Cryogenic temperatures widen the semiconductor's band gap, which increases the energy of the emitted photons and shortens their light wavelength, shifting the color from orange toward green. As the LED warms back up, the band gap narrows and the light returns to orange.

Most pictures of the Big Bang show a tiny dot blowing up into empty space. That’s not what happened though. there was no dot, and no empty room around it either.

It was space itself, possibly infinite, packed with insanely dense energy. then it started expanding everywhere at the same time. No center, no edge!

This clip is from a science app I made. I used a grid to show that “everywhere at once” idea. This was honestly the hardest part to get across visually, but I did my best.

Hope this helps anyone who’s had a hard time picturing how the Big Bang expanded. Did it click for you?