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# SI base units

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Hi,

It seems to me that time measurement with a clock is nothing else than counting how often a non-accelerating/decelerating object in a circular (or some other) trajectory passes through the same point. It only gives a frame of reference, it is a unit of constant motion. If I ask how fast someone runs, I get an answer back which tells me how many times some other event has occurred concurrently with the traversal of some distance by the runner.

But time is included in the SI base units: http://en.wikipedia.org/wiki/SI_base_unit

This seems wrong to me, (intricism?), I would include time in this list: http://en.wikipedia.org/wiki/SI_derived_unit

Maybe someone with more advanced knowledge of physics can change my perspective...

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SI is a system of units. The base units are defined, and all other units are derived from the base units. The base units must be independent of each other. To use a good word from Rand, the base units must be incommensurate. You can't measure length in seconds or time in meters. If the meter [m] and the second are base units, then meters-per-second [m/s] cannot be a base unit, nor can feet [ft] be a base unit (feet and meters are commensurate).

The base units do not have to be what they are. For example, you can build a system of units using Planck's constant [h], the Gravitational constant [G], and the speed of light in a vacuum [c]. These three units are independent of each other, and can be combined to give you units of length, area, volume, force, energy, power, etc. SI does this with kilograms [kg], meters [m], and seconds .

In Mathematics/Physics, neither approach is right or wrong in all contexts, but one approach may be more useful for a given problem. I believe the SI base units are what they are, because they are the most directly perceivable independent units of measure. In some cases, I think the base units are such because they were the first unit discovered. I think that electric charge [C] is a more appropriate base unit than electric current [A], since current is a measure of charge per unit time [A=C/s], but I suspect current was discovered and/or defined first (I haven't studied the history).

On a side note, did you notice (from your Wiki link) that SI defines the meter in terms of the second, and the second in terms of an atomic state change:

The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.

The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.

If your question is more along the lines of "can we measure time without change". I would say no, but that doesn't make time any less fundamental. How does one measure "change" as such? The Earth makes 365.2422 full rotations every time it makes 1 full revolution around the Sun, but rotations and revolutions as such are incommensurate. The concept of "time" allows us to relate the two.

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Lagroht,

The passing of that body through a given point may be repetitive, but how do you know that it is periodic (and thus a standard)?

To know that it is periodic, you must relate it to other repetitive events. Now you will observe that some of them repeat a fixed no. of times for a given repetitions of this event. This is based on the concept of simultaneity, which is based on the concept of time. Thus, the concept of motion is derivative of the concept of time, and not the other way around.

The unit of time has to be defined in terms of motion. This is because you cannot observe time directly. What you observe are entities and change in their spatial relationships. But to relate that change to motion, you must have the concept of time.

The argument is similar to that for the concept mole. Moles are measured in terms of mass and number (of atoms). In the same way, time is measured in terms of length and number (of repetitions). But units of both mole and time are base units.

edit: removed typos.

Edited by Rockefeller
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To use a good word from Rand, the base units must be incommensurate.

Ahh, I love that word; it is so precise.

The base units do not have to be what they are. For example, you can build a system of units using Planck's constant [h], the Gravitational constant [G], and the speed of light in a vacuum [c].

That reminds me one of the problems in my textbook (8 years ago) was how to express [L M T] in terms of [h G c]. :nostalgia:

In Mathematics/Physics, neither approach is right or wrong in all contexts, but one approach may be more useful for a given problem. I believe the SI base units are what they are, because they are the most directly perceivable independent units of measure.

Although the choice of units is contextual based on a given problem, but defining universal standards may only depend on the hierarchical level of concepts. For example to grasp velocity, one must first grasp length and time.

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The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.

Did you notice how this makes dimensionless counting the fundamental measurement? This puts math before physics in the hierarchy of knowledge.

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Thanks Jake, you cured me of wanting to change the SI system . I guess incommensurable is indeed the right criteria for the base units.

On a side note, did you notice (from your Wiki link) that SI defines the meter in terms of the second, and the second in terms of an atomic state change:

If your question is more along the lines of "can we measure time without change". I would say no, but that doesn't make time any less fundamental. How does one measure "change" as such? The Earth makes 365.2422 full rotations every time it makes 1 full revolution around the Sun, but rotations and revolutions as such are incommensurate. The concept of "time" allows us to relate the two.

Well actually I guess this is what makes me feel uncomfortable with the second, or time as a 'measurable' quantity for that matter. If you ask 'how does one measure 'change' as such?, I am tempted to answer; by inventing 'time' as a concept to refer to that. Do you agree that time is an human 'invention' that enables us to relate changes among the relative positions of matter more accurately than our unaided memories would allow us. I don't know for a fact what the mainstream opinion in science is on that, but I get the impression that time seems to be treated as more fundamental than that, something more implicit in reality as a given, not as a derivative.

Lagroht,

The passing of that body through a given point may be repetitive, but how do you know that it is periodic (and thus a standard)?

To know that it is periodic, you must relate it to other repetitive events. Now you will observe that some of them repeat a fixed no. of times for a given repetitions of this event. This is based on the concept of simultaneity, which is based on the concept of time. Thus, the concept of motion is derivative of the concept of time, and not the other way around.

Your observation that you need to relate a repetitive event to another repetitive event in order to know that it is periodic is very true (and useful for me), but i don't agree that the concept of simultaneity is based on the concept of time. In order for me to know that 2 events occur simultaneous I only have to be able to observe them, to know that this simultaneous events repeat I only have to remember the previous occurrences (and maybe count).

The unit of time has to be defined in terms of motion. This is because you cannot observe time directly. What you observe are entities and change in their spatial relationships. But to relate that change to motion, you must have the concept of time.

The argument is similar to that for the concept mole. Moles are measured in terms of mass and number (of atoms). In the same way, time is measured in terms of length and number (of repetitions). But units of both mole and time are base units.

edit: removed typos.

I do not exactly follow how you seem to require time before you can relate the change of the relative positions of entities with motion. I start my thinking about it with the perceptually given. When I see to 2 entities and their relative positions are changing I know this because I remember their previous positions. I call this motion. I only see time come in implicitly because of course a human has some capability to quantify the rate of position change (otherwise nobody could ever run into a field to catch a thrown ball).

Now I think of it....maybe the first implicit unit of time is actually determined by something like the speed at which human neuron can discharge and reload or something like that :-)

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i don't agree that the concept of simultaneity is based on the concept of time. In order for me to know that 2 events occur simultaneous I only have to be able to observe them, to know that this simultaneous events repeat I only have to remember the previous occurrences (and maybe count).

You are confusing two separate questions: 1. What is the hierarchical order of the concepts "simultaneity" and "time"?, and 2. What do I need in order to know that 2 events are simultaneous?

To answer 1, first notice that the concept of simultaneous-events is a narrower category of a wider concept: multiple-events. The commensurate characteristic (or the Conceptual Common Denominator) which is used to differentiate it from other multiple-events is duration. Simultaneous-events are multiple-events with duration equal to zero. It is a case of narrowing the range of a measurable characteristic to subdivide a concept.

Above means that hierarchically simultaneity is above "duration" (which is above "time"). Incidentally, in this particular case the logical order of these concepts also turns out to be the chronological order in which a child grasps them. When a child observes "button pushed + bulb glows" or "clock striking 12 + cuckoo coming out", he grasps the concept of simultaneity only by differentiating them from other multiple-events. To do that he needs (implicit) grasp of duration (and thus time), which serves as the differentiating characteristic.

I think I should have been more clear when I used the phrase "is based on".

To answer 2, notice that you already need a concept of simultaneity in order to judge whether two events are simultaneous. Then you "only have to ... observe them".

I do not exactly follow how you seem to require time before you can relate the change of the relative positions of entities with motion. I start my thinking about it with the perceptually given. When I see to 2 entities and their relative positions are changing I know this because I remember their previous positions. I call this motion. I only see time come in implicitly because of course a human has some capability to quantify the rate of position change (otherwise nobody could ever run into a field to catch a thrown ball).

Man is born tabula rasa; all his concepts including time are grasped by the effort of his mind. The concept of time is grasped (implicitly) as soon as an infant makes the first integration of his sensations. He realizes that a particular sensation persists! But time is an axiomatic concept. It is not formed by differentiating one group of existents from others. But it is formed by an integration of all existents. Actions, entities, attributes persist for some time, but they may persist for any time.

Now I think of it....maybe the first implicit unit of time is actually determined by something like the speed at which human neuron can discharge and reload or something like that :-)

I just discharged 2,000,001 neurons in writing this response. An infant doesn't need to measure anything; he grasps concepts by measurement omission.

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Do you agree that time is an human 'invention' that enables us to relate changes among the relative positions of matter more accurately than our unaided memories would allow us. I don't know for a fact what the mainstream opinion in science is on that, but I get the impression that time seems to be treated as more fundamental than that, something more implicit in reality as a given, not as a derivative.

As a concept, 'time' is a human invention, but so is 'length' - neither is arbitrary. Every known fact of physics implies a relationship. The way we know something is red is that it emits photons which strike the cones in our eyes, which send electrical signals to our brain, etc. While you can't point to the specific atom or photon and call either 'red', the 'redness' of the object (in our perception) is more epistemologically fundamental than knowledge of wavelengths, because it is perceived. For example, I don't believe 'space' as such exists alone without matter; it is just the set of all distance relationships between particles. A particle doesn't literally move through space. It's distance relationship with every other particle changes, but space is a convenient way to describe it at some scales. I would agree that some people reify concepts as having some implicit, metaphysical fundamentality disconnected from the perceptual-conceptual chain.

Here's something I just though of while contemplating your post...

Humans experience time on the perceptual level (i.e. without need of the concept), and not just as a direction (before/after). I am not a physchologist or neurologist, but I think we experience rhythm without having to conceive of time. It's difficult for me to determine if I sense rhythm without concepts, because I have automatized so much at my age. However, my 10-month old will sway or bounce to music or rhythmic beating, but not to random tappings. This would mean time is more fundamental a measurement than energy or power, because it is directly available through perception.

Any bio/neuro/psych types on the forum who can corrobate?

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Here's something I just though of while contemplating your post...

Humans experience time on the perceptual level (i.e. without need of the concept), and not just as a direction (before/after). I am not a physchologist or neurologist, but I think we experience rhythm without having to conceive of time. It's difficult for me to determine if I sense rhythm without concepts, because I have automatized so much at my age. However, my 10-month old will sway or bounce to music or rhythmic beating, but not to random tappings. This would mean time is more fundamental a measurement than energy or power, because it is directly available through perception.

I have a different hypothesis, which is solely based on perception of entities and their spatial relationships. But I think the forum rules prohibit posting such "musings". (Mods?)

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But I think the forum rules prohibit posting such "musings". (Mods?)

I don't see how that breaks Forum Rules, unless you claim it's an Objectivist position or maybe if the idea explicitly contradicts Objectivism.

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I tried to look up time in OPAR and IOE but I couldn´t find an explicit treating of the subject. OPAR doesn't even have an index entry called 'time'!

I however found this entry in the Ayn Rand lexicon:

http://aynrandlexicon.com/lexicon/time.html (also a little bit limited )

'Time is a measurement of motion', 'The universe is eternal'. My training in physics is strictly limited to Newtonian physics and this seems to fit right in with it with it. But maybe I will run into trouble with it if I try to use it as a starting point for trying to understand Einstein's relativity theory

You are confusing two separate questions: 1. What is the hierarchical order of the concepts "simultaneity" and "time"?, and 2. What do I need in order to know that 2 events are simultaneous?

I am not sure I am confusing, but I think you have correctly identified the difference in what we hold to be true ;-)

To answer 1, first notice that the concept of simultaneous-events is a narrower category of a wider concept: multiple-events. The commensurate characteristic (or the Conceptual Common Denominator) which is used to differentiate it from other multiple-events is duration. Simultaneous-events are multiple-events with duration equal to zero. It is a case of narrowing the range of a measurable characteristic to subdivide a concept.

You have me thinking here, because I think what you are saying is true!...I don't yet quite know how to unify this with my own starting point of reasoning about this. I start with for instance a snap-shot picture in my head of what a tabular rasa man would see when he would open his eyes for the first time on for instance a carnival where a roundabout is placed. The first image on his retina will be his starting point, a collection of entities; he has discovered simultaneity , in the next image his brain can identify entities will have changed position. He will have discovered motion. If he waits he will notice the roundabout having rotated a number of times, which he could count. When then some girl buys and eats an ice cream he can say; it took her 15 roundabout rotations to eat that ice cream. He will have discovered the quantification of motion; time.

Above means that hierarchically simultaneity is above "duration" (which is above "time"). Incidentally, in this particular case the logical order of these concepts also turns out to be the chronological order in which a child grasps them. When a child observes "button pushed + bulb glows" or "clock striking 12 + cuckoo coming out", he grasps the concept of simultaneity only by differentiating them from other multiple-events. To do that he needs (implicit) grasp of duration (and thus time), which serves as the differentiating characteristic.

I think I should have been more clear when I used the phrase "is based on".

To answer 2, notice that you already need a concept of simultaneity in order to judge whether two events are simultaneous. Then you "only have to ... observe them".

My concept of 'simultaneous' is derived from vision, not from a linguistic definition, when I look into my room I can concurrently, simultaneously see multiple objects, even when they are not moving. This makes the concept of simultaneity for me to be prior to both motion and time.

I just discharged 2,000,001 neurons in writing this response.

well, just make sure you have fun doing it

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My concept of 'simultaneous' is derived from vision, not from a linguistic definition, when I look into my room I can concurrently, simultaneously see multiple objects, even when they are not moving. This makes the concept of simultaneity for me to be prior to both motion and time.

This gets my vote.

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My concept of 'simultaneous' is derived from vision, not from a linguistic definition, when I look into my room I can concurrently, simultaneously see multiple objects, even when they are not moving. This makes the concept of simultaneity for me to be prior to both motion and time.

Theoretically, you are right that the concept of simultaneity can be formed just by looking around in a room. But I see two problems here.

1. Simultaneity pertains only to actions, not to entities. When you look around a room and form the concept of simultaneity, an abstraction is drawn not from actions of entities, but from actions of consciousness. However, the CCD is the still the same - duration. You focus together, or you focus one after another.

2. Conceptualization of actions of consciousness require a certain stage in child's development (ITOE, 2nd ed., p30). Therefore, I still think that actions of entities, such as "clock striking 12 + cuckoo coming out" are chronologically important in forming the concept of simultaneity.

By the way, pointing out the hierarchical or chronological order of concepts does not amount to deriving a concept "from a linguistic definition".

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1. Simultaneity pertains only to actions, not to entities. When you look around a room and form the concept of simultaneity, an abstraction is drawn not from actions of entities, but from actions of consciousness. However, the CCD is the still the same - duration. You focus together, or you focus one after another.

Entities can exist simultaneously while taking no other particular action.

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Entities can exist simultaneously while taking no other particular action.

In this sentence, "simultaneously" pertains to the action "exist" (a verb). 'Exist' serves the same role 'focus' serves in the example Lagroht provided.

True, entities can exist simultaneously. But to form the concept of simultaneity, you must distinguish this possibility from the case of them existing non-simultaneously. In Lagroht's example, distinction was focus together vs. focus one-after-another, in this case it would be exist together vs. exist one-after-another.

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Theoretically, you are right that the concept of simultaneity can be formed just by looking around in a room. But I see two problems here.

1. Simultaneity pertains only to actions, not to entities. When you look around a room and form the concept of simultaneity, an abstraction is drawn not from actions of entities, but from actions of consciousness. However, the CCD is the still the same - duration. You focus together, or you focus one after another.

2. Conceptualization of actions of consciousness require a certain stage in child's development (ITOE, 2nd ed., p30). Therefore, I still think that actions of entities, such as "clock striking 12 + cuckoo coming out" are chronologically important in forming the concept of simultaneity.

On some level you have me convinced; in order to grasp 'simultaneity' you need to grasp 'non-simultaneity', which requires a grasp of sequential and parallel events. While a grasp of the concept of 'event' presupposes recollection of multiple occurrences of matter displacements. Those matter displacements are based on some criteria hold to be separate from from the rest of the matter displacements (because otherwise the whole of the universe would constitute one big event and the concept would be meaningless )

As a side note: the Dutch word for 'Simultaneous' is 'Gelijktijdig'. 'Gelijk' literally means 'Equal'. 'Tijdig' literally means 'Timely'.

I now get the suspicion that I might be in the difficult position that I am trying to reason about development of awareness on the pre-conceptual level of awareness while I am forced to do this using concepts, which are obviously not yet acquired by a consciousness which doesn´t (yet) function on that level of awareness. But I do think it is relevant, an eagle for instance can perfectly deal with motion, when it falls out of the sky to the spot it predicted a moving mouse to be within the few second. Obviously an eagle has no concept of time. How can time be conceptual prior to motion if an eagle doesn't need a watch to kill a mouse?

You can ignore that eagle stuff if you want, I am not fully serious there.

At the moment I am content with the definition from the lexicon: 'Time is a measurement of motion; as such, it is a type of relationship'. I was sort of hang up on the notion that somehow time should be listed as a derived SI entry because I felt that it was a derivate of space and matter, since to my understanding relative motion of matter is what's gives rise to the concept of time. But it is the realization that this is irrelevant to commensurability that made me drop that idea. The units of time and matter are incommensurate and this justifies a separate entry in the SI base units list.

By the way, pointing out the hierarchical or chronological order of concepts does not amount to deriving a concept "from a linguistic definition".

I can imagine how you could choke reading that remark, I should have said 'higher level concepts'.

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I will stop posting in this topic now. I found this wikipedia page about the philosophy of time (http://en.wikipedia.org/wiki/Philosophy_of_space_and_time) and I realize this isn't a trivial subject and actually is a much more fundamental topic to physics than I realized. Expanding my insights on the topic enough to be able to see how Newton, Einstein and their buddies relate to my current understanding of time would require serious time consuming study. I probably won't get to that anytime soon.

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