# What really is the "rate" of time? and what is the "rate" of perception

It has bothered me for quite a while. What exactly is the rate of time, and the rate of perception? Any snapshot of reality is distinct from any other, as in a photograph is an instant of time that is different than the instant of time directly after it. But, when we look at the clock we internally know exactly when the next second will pass, we can count seconds in our head and they're always consistent, any second is as long as any other second. But what exactly is that rate? In any media that includes simulation we use steps, discrete steps between one state and the other and the place between them is discarded. We can say it's running at 60 frames per second; but reality on the other hand does not have a framerate, it's continuous. there is no next moment, and any moment which is not exactly the same moment will be different, even if on a minute scale.

Perhaps this was a bit hard to follow but this question really addresses continuity, how can there be a consistent rate of something which cannot be quantified? I guess it's a bit of a broad question but I hope the general point of my question is understandable.

Also, an argument that could arise is "how is space any different? no position is the same as any other but there's not an atomic unit for space" and that's true, though it's not the same. In space there's speed, the rate of traversal through space, which can change, but if we treat time as just another dimension, then we'll see that it's as if every single thing in the universe is traveling through that dimension at the same rate (well, not at the same rate if you think about relativity, but anything in any medium would feel by itself as if seconds pass just the same) and that rate cannot be changed, differently from how you may change the velocity of any object by applying a force.

• The last paragraph is denying relativity, but provides no reason for this belief. The universe doesn't "travel through" space or time, it is spacetime. Commented Aug 6 at 11:40
• Interesting. Time is only memory (according to QM, there are multiple futures, you know zero, there are multiples pasts, you know only one, and there is no present, present is just short-term memory). In such context, the rate of time would be the speed your mind processes facts. If you are fast, you live more than the rest of mortals. If you are slow, time passes fast. That's why being productive gives more earnings. Commented Aug 6 at 13:11
• I reckon it's clock against clock. If clock A is moving with respect to clock B, 1 second by one clock could be 2 seconds by the other clock. That's what relativity claims, oui? Time dilation, it's called, cogito. Commented Aug 7 at 7:24
• my answer here might be related Commented Aug 7 at 17:42
• @RodolfoAP - I agree the rate of time is subjective. I think physical models for time, other than counting resonant periods of a clock or cycles of earth's rotation, are mostly speculation. Psychological time is day and night in repetition and observing self and others age and die. While riding my motorcycle on the street I have felt time slow way down and my mind speed up its activity particularly when my life was under threat from collision with large fast moving vehicles. More earnings do not only flow from better productivity. Social institutions cause windfall profits and reward prestige. Commented Aug 7 at 19:03

Here is a condensed version of the physics answer.

Your rate of perception is established by the speed with which nerve impulses flow from your eyes into that portion of your brain that processes visual inputs, plus the amount of time it takes for those processed signals to get associated with image memory storage in the brain so you can then "identify" what your eyes are seeing.

The flow rate of time is more complex, as follows:

Our universe is embedded in what is called 3+1-dimensional space: 3 dimensions in space and one in time. Even when you are standing perfectly still, the passage of time is pulling you through that 3+1 space at the speed of light (called c) but all that speed is pointed in the time direction.

If you are instead moving with some velocity v then the arrow that represents your velocity through 3+1 space gets tipped a little off the time axis and a little bit into the space axies- representing the fact that you are moving at something like ~(c-v) through time and (v) through space.

Anything moving through space at c is then not moving at all through time anymore because that arrow is tipped completely off the time axis. So for a photon zooming through space at the speed of light, time has stopped.

This means the flow rate of time depends on your speed through space.

• Relativity is not synonymous with physics and, more importantly, it cannot be true because it cannot be applied universallly, at the very least, such a scientific theory should not inform metaphysics, rather, philosophy should guide science. Without philosophical assumptions no scientific experiment can be interpreted, ergo, philosophy is prior to science. Commented Aug 6 at 20:39
• @Glorius, as a philosopher you are free to believe anything you wish. Things are different In the world of physics, The two types of relativity are the foundational basis of all physical models of the universe- that is, if a putative model of the universe does not comport with special and general relativity, it cannot correctly describe the universe we inhabit and is rejected. Commented Aug 6 at 22:30
• @Hudjefa, yes- for the photon. Commented Aug 7 at 16:23
• @JD, anything that supercedes GR must mathematically contain it and also push into new territory. this is a way of expressing the fact that the requirement to comport with SR and GR places very severe restrictions on the mathematical form that any new model of the universe can possibly take. Commented Aug 8 at 17:05
• IN accelerator experiments, the scientists are often looking for two kinds of evidence: data that proves the existence of something, or data that proves its nonexistence. Given the tremendous costs of running an accelerator, every minute of beam time is applied for months in advance and thoroughly vetted from every angle- a paradigm that simply did not exist in semmelweiss's time. Physicists know that an anomalous result may represent a nobel prize in disguise and something strange in the data does not get excluded unless it cause is known already. Commented Aug 9 at 15:59

Like many questions, the definitions of the terms used are central.

What is a 'rate'? I would normally define a 'rate' of something as the number of repetitions of that thing per unit time - e.g. frames per second, as you said. I might sometimes define it as the number of repetitions of the thing per something else - e.g. the rate at which my car burns diesel can be expressed as X miles per gallon. So then your question becomes 'by what units can I define the rate of seconds passing,' and the answer is 'whatever units you like' - you could say that on average years pass at somewhere between 70 and 80 years per lifetime, and that is essentially another way of saying that time passing is purely a matter of perception; the change in the universe can be defined by how it affects you, the observer.

In your second paragraph, though, you say the core of your question is about time being continuous; you say that time cannot be quantised. That is far from a settled issue! You should read up on Zeno's paradoxes for an intuitive starting place (modern philosophical work will often be contrasted with them for ease of understanding), and quantum spacetime for scientific models of the question.

• Could we not see it as what is the rate of refreshment of the units of time/perception? I think that's what OP was aiming at. This assumes an objective and stable unit of time. It is a very good question Commented Aug 6 at 16:28
• @Sismetic You mean determining some basic unit of perception and considering how many (nano?)seconds that takes to complete? I agree that whether that is a useful model is an interesting question, but I understood the OP to be assuming that rate was a fixed constant. Commented Aug 7 at 7:50
• I think the OP does want a rate that is fixed. That's why it's interesting: is time unfolding in a constant plane or a relative one? Absent perception(which I think it's impossible, as an idealist) how would time unfold and what would it be a stable rate of unfolding, or whether there could even be? I think it's most likely relative, but then the question would be: what drives the change of the change? Some relative rates of change would be faster than others, how come(in a non-trivial sense)? Commented Aug 7 at 15:03
• I think we're getting back into the issue of defining the term 'rate' - I've spent the last 20 minutes writing replies and then re-interpreting what you and the OP wrote! I interpret 'rates' as, by definition, relative to something. E.g. acceleration is the rate of change of speed relative to time. You could say that perceived time passes at a rate of change of measurable time over some basic unit of perception (please excuse my very unclear definitions here!). I wouldn't say you could have a rate of, say, seconds without the seconds occurring at a rate relative to something else. Commented Aug 7 at 15:30

Time does not have a "rate." One uses the passage of time to determine or express rates of other occurrences. The basic unit of measurement has been defined variously over the years in relation to a fixed number of occurrences of some other regular event such as the orbit of the Earth around the sun, or the energy transitions of an atom.

Rate of perception is not a canonical term of art. But it could be used to refer to the shortest-duration change within one's field of view that would be perceptible. This depends on the structure of our eye as a sensor as well as related neurology. The value would depend on the stimulus: how large the change is, whether it is in the central or peripheral vision, whether color is involved, whether motion is involved, etc.

• Nice. This nails it without jargon.
– J D
Commented Aug 8 at 4:34

The notion of a rate necessarily involves a relationship between two quantities. We typically use a rate to express or reason about how one of the quantities changes in terms of the way the other quantity changes. Thus an interest rate expresses (1) the amount of interest (owed or earned) in terms of (2) the amount of principle. Often—but not always—when only one quantity is mentioned explicitly, we can infer that the second (and unmentioned) quantity is time.

So the notion of “rate of time” is undefined, since it involves only a single quantity: time. It’s sorta kinda analogous to the notion of “the sum of 7,” which invites reactions like, “The sum of 7 and what?” It’s also not too different from the class of errors common in introductory calculus classes where a student writes down an integral symbol followed by an expression, but forgets to include a dx, a ds, a dt, or a d-anything-else. Without one, the scrap of text has no meaning.

I doubt that time itself has a "rate", but change is not identical to the perception of it, though see Berkley for alternatives

There's also the idea that our perception of time slows down and speeds up as we age etc.; we might think the flow of time is actually changing, but I doubt that there is a "real" rate of flow subtending these facts. It just sounds wrong to say that we could experience temporal flow at the rate it really occurs.

I'm a little unsure whether that means there is no precise present

The answer depends on the definition of time.

Your question seems to assume time can be thought of as a dimension, like a spatial dimension. However, since that is absurd (because it implies the possibility of a cause being after its effect, among other things), I'll answer assuming the historically accepted definition of time which views it not as a concrete thing, like some kind of universal clock, but rather, as the measure of change, an abstraction of the relations before and after.

To elaborate, if only a rock existed and remained inert, no time would be passing. You could say time does not exist since no change is happening.

That is the way God is defined to be timeless, since there is no change in Him and He knows, in a sense, all of being from the first moment up to the last. You can imagine it as viewing each frame of a movie at the same time and immediately understanding the whole of the film.

To answer the question directly, time in se does not have a rate of passage.

The rate of the perception of time could be said to depend on the frequency of change, bottlenecked, of course, by the observer's capacity to take in information.

• "if only a rock existed and remained inert, no time would be passing." This is nonsense. No matter how "inert" a rock may seem physically and chemically, time is still relevant to the changing positions of its electrons etc. Commented Aug 6 at 12:28
• @BrianZ My statement is not nonsensical by any stretch of the imagination: Aristotle, Augustine and Aquinas would agree with it. Replace "rock" with "inert particle" or "dark matter", if you believe in that nonsense, and the sentence should make sense to you. Commented Aug 6 at 12:47
• I understand 'if only a rock existed and remained inert' to be equivalent to 'if the universe was entirely static and unchanging'. Just for clarification, is that how you intended it? Commented Aug 6 at 15:06
• @Glorius :D I certainly agree with your claims the answer is physics with metaphysical presumptions effaced. I find it a particularly common view among physicists that their metaphysics is the only metaphysics (apparently out of a lack of philosophical knowledge at that). Bully! You are willing to develop a metaphysical framework of your own to challenge the easier option of just accepting the modern consensus. I salute you. ; )
– J D
Commented Aug 8 at 16:45
• @JD Always nice to hear a fellow address the elephant in the room :D We need more independent thought o7 Commented Aug 8 at 19:37

The Science of Timekeeping

Hewlett Packard Application Note 1289

https://www.cnssys.com/files/PTTI/hpan1289.pdf

Clocks and Timekeeping on page 14

Figure 1. Almost any clock is a two part device. The first part provides equally-spaced periodic events as derived from and defined by some oscillating device. The second part adds up these events (an accumulation of these time intervals) to provide time from the clock.

In principle, if a clock were set perfectly and if its frequency or rate remained perfect, it would keep the correct time indefinitely. In practice, this is impossible for several reasons: the clock cannot be set perfectly; random and systematic variations are intrinsic to any oscilla tor, and when these random variations are averaged, the result is often not well-behaved; time is a function of position and motion (relativistic effects); and lastly and invariably, environmental changes cause the clock’s frequency to vary from ideal. So, if a clock is measured with sufficient precision, its reading will not agree with UTC, except at the instant when it momentarily passes through the correct time which, of course, is only correct by definition or convention.

Galileo normalized time because there were no standard units of time. Galileo used discrete-time mathematical models to describe average continuous motion because there were no methods of Calculus. Newton developed methods of Calculus where the derivative is defined geometrically as the slope of a line tangent to a curve at a point. The Calculus enables rate of change calculations in the context of integral and differential equations. The ancient philosophical problems of points that have no extension in space are not eliminated in the description of modern math we just accept and apply the definitions, and we get good results in practical applications, which seems to be independent of our philosophical concerns.

Our universe is not continuous, Or: All rates and flows are subjective

The rate of perception is subjective to humans (and other beings). It depends highly on the sensory information you can process in a given time. For example, our eyes "refresh" about 20 times a second (therefore 24 fps in a cinema is considered to be "smooth" for a human). The common housefly is assumed to have a visual refresh rate of about 400 times a second. Effectively, a housefly sees everything in ultra-slow-motion (chickens, by the way, also have a high refresh rate of about 250 Hz).

Actually, humane eyes are capable of distinguishing up to 150Hz, according this post on Quora (makes a lot of sense to me).

The flow of time is also subjective to any being. It is highly dependent on the metabolism. This determines (among other factors) the rate at which a body wears down while "aging".

There are animals which are said to live infinitely long (see biological immortality). One example is a jellyfish which can produce cells in a high rate, so it rejuvenates constantly. Another example are Tardigrades, small beings about 1mm in size, which can even survive in space (although maybe in hibernation).

Going down to a physical level, the "rate of time" is dependent on all kinds of oscillations. Like the electrons "flying" around its atom core. Or lightwaves oscillating up and down. Or planets revolving around their sun. Or quantum particles describing a standing wave on an orbital path.

In Quantum-mechanics as a simplification, and often referred to in popular-science in media (*See comments), there is even the notion, that our universe is by no means "continuous". It is rather build up of small blocks which have a definitive, minimal size/amount. You could (simplified) imagine this like our universe being build up of "pixels" in 3D (minimal lengths), having matter made of minimal tiny weights, temperature only changing in tiny tiny steps and time also increasing in steps, not as an infinite continuum.

The relevant units here are the so called Planck-Units - minimal deltas for any time, length, weight or temperature change existing/happening in our universe. But mostly used in formulas for simplification. They might have not a "real" physical component to them.

On a philosophical level I would argue, that even if we have time measuring all around us (in watches, smartphones, time schedules for the metro, sunrise, sunset, etc. etc.), there is no inert law or flow of time in the universe. A clock does not measure something like a real time, it measures oscillation events of a quartz crystal or Caesium atoms in beta-decay. The universe does not "age" - but we can ascribe an age to it. What we can measure are only movements of objects, distances of all kinds, etc. The "time inbetween" two events is just a perceived duration we can measure as "time" because of all the atoms moving around us - like the train moving from one stop to the next, - taking either its "time" - or its "distance to cover" - until it arrives at the next stop.

• Please stop regurgitating pop science about QM, such as planck units being the smallest possible changes. They are not, and you should learn QM properly to know what exactly those planck quantities mean. In fact, even Simple Wikipedia can tell you that. Commented Aug 7 at 13:44
• @user21820: True, my text simplifies to an extreme level. I incorporated your remarks. Thanks for the feedback! Commented Aug 7 at 14:35
• As for "Effectively, a housefly sees everything in ultra-slow-motion": I cannot imagine how evidence of this conclusion can possibly be collected (by humans, in 2024). Commented yesterday