[freeone3000]

This doesn't really mesh with how we perceive time. It appears to be a product of accumulated experiences in short-term memory. People with attention deficit disorders experience time differently and are unable to gauge even short periods accurately, but even for neurotypical people, time seems to "pass quickly" if nothing takes place, or if you're distracted. It's a function of attention, instead of our other senses (smell, hunger, hearing), which happen whether we pay attention to them or not.

[Engineering-MD]

Actually time perception prospectively and retrospectively is completely different. They react to emotional content differently and seem to rely on different mechanisms. What you describe is only true for retrospective time perception.

[erinaceousjones]

Should be noted that our _perception of time_ is subtly different to _sensing of time_; consider our circadian rhythm, relating to the latter [1]:

> The daily light-dark cycle governs rhythmic changes in the behavior and/or physiology of most species. Studies have found that these changes are governed by a biological clock, which in mammals is located in two brain areas called the suprachiasmatic nuclei. The circadian cycles established by this clock occur throughout nature and have a period of approximately 24 hours. In addition, these circadian cycles can be synchronized to external time signals but also can persist in the absence of such signals.

> Circadian rhythms are self-sustaining (i.e., free running), meaning that they will persist when the organism is placed in an environment devoid of time cues, such as constant light or constant darkness. For comparison, see diurnal, infradian, and ultradian.

It's been noted that our "approximately 24 hours" sleep/wake cycle _does_ use external environmental cues (light, hunger) to keep it in check, but in absence of light cues we still generally tend to experience the cyclical 24-hour need to sleep followed by wakefulness. Without the external cues though sleep studies have shown it drifting - more like a 24.5 hour cycle. Can't find a citation for that one, but I remember it from the book "Why We Sleep" [2]

That being said! I just looked it up, and found studies suggesting that ADHD could either be a cause of, or consequence of, sleep disturbances [3]

But tl;dr of my comment is basically that we (mammals) do have a kind of internal clock ("suprachiasmatic nuclei"), which can operate in lieu of external cues -- but maybe we just haven't yet discovered another one of its' cue, which may be magnetic oscillations in the Earth's field..? Maybe this is something we'll have to consider as our astronauts venture further into space, away from Earth's influence [4] - maybe there's more to it than light cues!

[1] https://pubs.niaaa.nih.gov/publications/arh25-2/85-93.htm

[2] https://www.grahammann.net/book-notes/why-we-sleep-matthew-w...

[3] https://pubmed.ncbi.nlm.nih.gov/30927228/

[4] https://www.nasa.gov/feature/ames/nasa-research-reveals-biol...