You can use epistemology to reduce any physical concept of the universe to "a concept of the mind, like numbers" by simply stating that we are all humans with minds, therefore anything we conceive or think of is simply a concept in the mind.

Outside of our minds, however, change does occur. Stars spend their fuel, galaxies spawn and migrate, rocks orbit stars in a periodic nature. The English word "time" is obviously a concept, and no matter which human word we use for "time", it's simply one way of measuring these changes we see around us. How can we measure the elapsing period over which we observe all natural phenomenon? That is the second, that is the unit of time.

There's also physics here: space-time. If we think of time as a concept of the mind purely, as you propose, then we also must consider space purely a concept as well, since Einstein proved space-time is a correct notion.

Biochemical circadian clocks are all over the place. Organisms generally do better if their behaviour is regulated in sync with the day-night cycle.

Are those clocks based on actual time or something else like reactions to lighting or number of heartbeats (which probably averages out to the same amount per day)?

There is a base circadian period which is roughly the length of a day, but it varies between individuals. If you put people in caves with no light at all, they'll still naturally fall into a sleep/wake cycle around 24 hours (it tends to be slightly longer).

Specifically it comes from your SCN https://en.m.wikipedia.org/wiki/Suprachiasmatic_nucleus

The answer is it's evolved and some kind of complex cellular feedback mechanism, but Wikipedia is a bit light on details. Apparently this clock is also fanned out in some way to other parts of the brain/body which also follow a daily cycle.

https://www.sciencedirect.com/science/article/pii/B978044459...

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2735866/

Light isn't mandatory, but the SCN will synchronise to daily light patterns (eg when you travel). The SCN is also physically located close to the optic nerve. I think this is why the underlying rhythm is a slightly longer than a day, because it allows the body to reset it to 24 hours. If the period was shorter, even slightly less than 24 hours, maybe you'd have problems when the clock restarted before the day finished and the error would propagate over time (you'd keep shifting the cycle).

Measuring regular changes in lighting (the day/night cycle) is actual time. (So would be heartbeats, although heartrates vary so much that measuring them would be very inaccurate on a daily scale.)

All definitions and measurements of time rely on counting events that are believed to happen at regular intervals. A second was defined for most of history as 1/246060 of a solar day, in other words, measuring changes in lighting.

I agree but I don't know if that explains how humans can tell time. If you put a human in a completely isolated room with no lighting changes then I doubt they'd be able to count the number of days.

Humans can't tell time accurately without external cues about the day and night cycle. We also can't tell time accurately to the minute if we can see outside but don't know how long the day is, i.e. latitude and time of year.

We can tell time inaccurately by timing somewhat regular internal biological events. That pretty much follows from the definition of time as the interval between regular events (which are assumed for physical reasons to be equally spaced). The only question is which underlying events we use and how.

https://en.wikipedia.org/wiki/Time_perception

I think the base circadian day time is about 25 hours, or 24 hours 11 minutes, or similar [1].

I've always wondered what would happen to the sleep cycles of astronauts on long space journeys. They may not have "daylight" to regulate their rhythms.

[1] https://news.harvard.edu/gazette/story/1999/07/human-biologi...

You don't need to go on space journeys to observe people's rhythm shift.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1330995/

It's supposedly regulated by light and by magnetic fields: https://www.nature.com/articles/458948f

> There is no notion of time at the level of molecular biology, organs, systems, etc.

Explain apoptosis without change over time.

Explain radioactive decay without change over time.

I am not sure I follow. Time is certainly an extremely important dimension in any complex biological system. The cells do not think about time, but the timing there is very precise too.

Couldn't agree more. The whole system is based on oscillations. It's more robust than literal clockwork, but the balance of systems is dependent upon interconnected oscillators. E.g., a neuron's timing is dependent upon rhythms of vescicle production, which is dependent upon rhythms of mitochondrial transport, which is based on rhythms of kinesin movement...

Please show any timing at cellular level. Thank you.

I'm not often this blunt, but you have no idea what you're talking about here. There are explicit clocking systems both within and across cells and they are very important for regulating many biological processes. Please read this article about how they literally use an analog clock synchronization algorithm (something that has been discussed in the literature for computers, too!) to make sure their internal clocks roughly match the macroscopic clock:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6585513/

This is a conceptual mess.

Synchronization does not imply time. It implies synchrony, which is a mechanical notion. Electric signals are used everywhere in life for that purpose.

What they called clocks are not clocks. No more than a frequency generator is a clock.

To an electronic engineer a frequency generator in fact is a clock.

A frequency generator is the essence of a clock. Why do you think we talk about clock speed in computer science? I'm honestly not sure what other definition you would even use in this context. And certainly, given that these "frequency generators" synchronize, divide time into repeating windows of roughly the same length, and are used to schedule and regulate biological processes, it is a bit bizarre for you to say that they somehow have nothing to do with timing.

What are you on dude? In what universe does synchronization not involve time? Synchronization is defined as "Occur at the same time or rate".

Even if you're so pedantic that you're going to say something like "it could mean rate and not time". Rate also means "the number occurrences in a specific time interval". So how exactly are you contorting your logic to come to this conclusion?

Not saying I agree with GP but there are 2 distinct notions of time. One is related to durations, and the other is absolute time (aka wall time). Clocks measure wall time, not durations. Cellular processes probably don’t care about wall time.

Wall clock time is pretty much only measured in practice as some offset relative to some repeating process, though (e.g. hours since start of day). Cells certainly have processes that repeat on a daily basis, at different offsets from the beginning of the day; they may not actually be measured by counting ticks (the jury's still out on exactly how they do it, I think?), but the effect is similar.

If things happened out of order, the cell wouldn't work at all. There are a lot of different signal pathways that ensure timing is correct. You can take a look at even the most basic functionalities like DNA replication, or energy exchange. And the cell is not timed only in regards to itself, but based on the system it lives in, too - and that system is timed too, repeat x1000000.

Humans (and other living beings) can work with such low amount of waste heat and intake energy only thanks to atomically precise clocking.

Perhaps the above commenter is talking about the perceived scale or speed of time? Order of events certainly seems to matter.

At the same time, order of events is also a certain way of modelling something. There may be alternative models which can be meaningful without the order of time. But most (probably all) models are designed with the way we perceive time in mind.

DNA replication is a structural pattern matching and has nothing to do with time.

Moreover, it is so stable exactly because it has neither the notion of time nor counting.

Maybe watch a video about the process on Youtube? What you're saying is correct in a very abstract sense, but does not really convey what is actually happening inside the cell. Timing is extremely important because if the proteins worked out of order (which is often different based on signals), wrong DNA would come out. Also, other systems inside and outside the cell have influence on the replication (you don't always replicate the whole DNA, sometimes it's necessary to not finish the whole process and do something else as the last step, etc). And replication is not stable at all, btw, but there is very good error handling. And don't get me started on DNA activation.

Cells literally have a clock pathway.

> Maybe watch a video about the process on Youtube?

Any recommendations?

I like this one: https://youtu.be/7Hk9jct2ozY

This one is about 'garbage collection' of cells: https://youtu.be/DR80Huxp4y8

That’s awesome. I learned more about DNA in 5 mins than all my biology classes.

One more time. DNA replication relies only on particular structures and enzimes to transform these. There is no notion of time whatsoever. Only availability of structural elements, and concentration. Everything is decoupled and feedback loops based.

And sequences of actions are maintained by pipelining of physical molecular structures - each enzime recognizes it's own unique patterns. That is it.

In old times this was called principle-guided science.

Understanding of principles spares one from knowing all the details.

The problem here is that what everyone recognizes as clocks, you don't. The scientific consensus is elsewhere though. There is no reason to call a clocking pathway anything else if its purpose is to determine after how much time should something happen.

I mean, it sounds cool to claim, but if you want to explain to me how a match goes from being a match to being embers without a change over time, I'm all ears.