Serious Question on Clocks & Time

roosh wrote: »

This will probably seem like a really basic question, so my apologies if it does; I have asked it elsewhere, but as of yet, haven't really had an answer to it.

The question is: how does a clock measure the property [of the universe] called time?

I can see how a clock can be used as a standard unit of comparison, which forms the basis of a system of measurement, called time; but I can't see how a clock actually measures a universal property called time.

In a discussion elsewhere, someone mentioned that

How is it meassured, with a clock, or otherwise?

roosh wrote: »

OK, so it is a system of measurement, not actually a property of the universe?

one manifestation of the issue is the assertion that gravity and/or velocity has an effect on time i.e. that time can slow down or speed up depending on either; this suggests that "time" interacts with the physical world somehow.

roosh wrote: »

How does a clock measure the relation between events; or the metric? Is it not the case that events are related to a clock, e.g. the number of oscillations of caesium between events are measured, and represent the number of seconds between events.

That clocks run at different rates depending on gravity or velocity suggests that gravity and/or velocity affect the physical process of a clock, not time.

How is a gravitational field anything other than a gravitational field; where does time enter into it?

roosh wrote: »

Reconciliation
There are a number of things I have difficulty reconciling, so it might be helpful to try and set out what some of those are.

Firstly, "time is not a substance"; by this I understand that time has no physical properties, which I understand as meaning that it is not something which can be measured?

Secondly, if it is not a substance, how then, can it be said to "bend", "twist", "speed up", "slow down", "warp", etc.? Also if time isn't physical how can gravity and motion appear to have tangible effects on it.

I also have trouble reconciling the notions of past and future with the use of a clock to measure time - I'm not entirely sure how to formulate it at present, but hopefully I can be more clear.

I also have trouble with the notion that gravity is space and time, because if space and time are not physical then how can they be gravity or vice versa, because gravity has physical effects.

The excluded middle
To my mind there are two possible solutions for what the nature of time is; either it is a system of measurement which does not have any intrinsic existence, or it is a physically existing "entity". I am open to correction on that though.

If time is a system of measurement, with no intrinsic existence, then it cannot speed up or slow down, it cannot bend or warp, and it cannot itself be measured - being the measuring system. This is how I personally see time. A clock which ticks slower because it is under the influence of gravity doesn't suggest that time is moving slowly, and that events which have that clock as their timepiece aren't further in the past than events measured using a faster ticking clock. It suggests that gravity impacts the physical mechanics of the clock to make it tick slower or faster.

The alternative is that time is a physically existng entity, force, property, call it what you will, and can be measured. It is this notion which gives rise to the dilemma of showing how a clock measures the physical property called time.

Is there an alternative that I have missed?

The Caesium clock only counts the number of oscillations though, doesn't it? There is no "distance" between the events which is measured, the distance is only imagined. That's not to say that the oscillations happen at the same moment, but just that the idea that the "distance" between the oscillations as a unit of time appears to be a re-ification of a concept.

I don't have any trouble with the idea of clocks per se, and the idea that a standard unit can be used for the purpose of comparison or measurement, the trouble I have is with what is actually being measured.

As for the existence of space, I haven't given it the same consideration, but I would imagine a similar argument could be put forward; as I say though, I haven't tried considering it to the same extent.

Would you necessarily expect gravity to affect different physical properties differently? The classic example of the bowling ball and the feather falling at the same rate springs to mind.

The thing is, all clocks are acted upon by gravity uniformly and all clocks don't tick at the same rate; so a uniform change in gravity should affect all clocks the same no? But I wouldn't be sure to be honest.

In the example you give, is a second for the photon clock defined in terms of caesium oscillations or the ping of a photon?

roosh wrote: »

This extract might be helpful in outlining the issue.

"Time may not exist" [page2]


The system of measurement, or the clock, provides a quantity which we designate as "time", but the quanity that it provides is the number of caesium oscillations, not a quantity of "physical time".

If we caricature the operations of a caesium clock as: a man sitting on a chair counting the number of oscillations as they appear in front of him. One pops into view, he counts one, and it disappears again; then another one pops into view, he counts two, and it disappears again; and so on.

Here, the "relation" between events is only an imagined one. The man observes them in a sequence, but each one ceases to exist after he counts it. To say that one event exists in the past is simply to imagine that it does.

Alternatively, if we imagine that each event is on a conveyor belt such that, as it comes into view he counts it and it continues along the conveyor belt without disappearing, or ceasing to exist. Again, there is no past/present/future relationship, other than in the imagination of the counter. As an event occurs i.e. as he counts the object on the conveyor belt, it continues to exist in the present, but he retains the memory of it having passed him and designates is as being "in the past" - again, this is only imagined, because the object continues to exist in the present and the physical relationship between it and the other events is entirely spacial, not temporal. The temporal relationship is imagined, on the basis of his capacity for memory.

The notion of a universal rive of time may have been abandoned, but the vestiges of it appear to remain in what could be labeled as "tributary time"; such that there is a river of time for each observer, which can combine with the rivers of other observers and also split off from them.

The re-ification doesn't lie in the fact that time is defined as anything more, rather that the "relation" is.

How do you mean in different locations along the gradient; what does the gradient measure; do the time dilation calculations work for hour glasses also?

Also, just on a previous question, is the second for a [pinging] photon clock defined in terms of the ping of a photon or the oscillations of caesium?

krd wrote: »

Something that's been bothering me. What if you use a sound wave as a clock?

What if you took middle C, on a piano, as your measure of time. That 440 cycles would be your piano second.

If you were on a train, and it was travelling fast enough, a stationary observer in front of the train, might hear D (587.330 Hz). And you wouldn't need to be moving that fast.

This bothers me - because it creates huge time dilations.

roosh wrote: »

How am I using the term "physical" wrong? I'm using it in it's most simplistic form as being something which is measurable; are messers Lloyd and Rovelli also using it incorrectly?

The assertion is that time is the physical relation between events, but the physical relation between events [if it exists] is spatial, not temporal; not only that but if it exists, it only exists in the present. The error lies in the double definition of the physical relation between those events i.e. as being both spatial and temporal, when only the spatial can be demonstrated.

Time, which encompasses the notions of "past" and "future", "emerges" on the basis of an observers capacity for memory and projection i.e. it is imagined. There is no evidence to suggest that either the past or the future exist, unless they are assumed to exist a priori.

As was outlined above, with the caricature of the Caesium clock, only the spatial relationship between "events" can be demonstrated; the "temporal" relation i.e. between any two of the past, present, and future, is only imagined, or assumed.

The reason that space and time appear to be so intertwined is because we derive our idea of time from observing the change that physical objects undergo; because we can remember a "past state" and can imagine an object in a "future state", we get the impression of linear time; but both "past" and "future" are only imagined, as the impression of linear time.

Firstly, the notion of a worldline, extending from the past, through the present, and into the future, only arises when the past and the future are assumed to exist.

Secondly, if all observers were at rest relative to each other, their worldlines would converge and very closely resemble the [partially] abandoned idea of a universal river of time; where the worldlines diverge, due to the relative motion of the observers, they would resemble tributaries.

The "temporal relation" is reified off the back of the spatial relationship, when only the spatial relationship can be demonstrated.

That's assuming that there is a uniform gravitational force; if the scenario was exaggerated, with one of us atop a mountain, that wouldn't be the case would it?

I know the "official" second is defined in terms of Caesium oscillations, but I thought I read somewhere [wikipedia I think] that each other kind of atomic clock has it's own definition of a second - which would make sense seeing as a hydrogen maser won't "measure time" in terms of Caesium oscillations.

Given the likely difference between the measurement of a second according to different clocks, I'm just wondering if the gravitational time dilation is the exact same for each clock, in terms of Caesium oscillations, or is it merely proportional?

Clock stuff

roosh wrote: »

I fully accept that the experiments have given rise to a model which is at odds with "presentism", but incorporated in the experiments is the assumption that time is physical and that a clock measures time. The proposition that time is not physical will not, I would imagine, change the experimental results, bcos clocks would still be used as a method of comparison, but the model of the universe would change.

EDIT: More concisely, the experimental evidence itself is not add odds with "presentism", it's the interpretation of that evidence that is; an interpretation which is based on a questionable assumption.

What needs to be demonstrated is the physical, temporal relation between events i.e. between past and present, or present and future, and how a clock measures that relation.

It has been outlined above how a clock does not demonstrate this relationship.

<snip>

This is just incidental however, how a clock demonstrates the physical relationship between past and present, or future and present is the critical issue.

<snip>

Did he demonstrate how the clock issue raised here is resolved?

<snip>

I fully accept the points being made, but there is the issue of how a clock demonstrates a physical relation between past and present to be resolved.

Presumably the worldlines of all observers in the same universe cannot be completely divergent, as this would suggest that each observer occupies their own universe. I would imagine that space-time is the "glue that binds them together"; presumably space-time to must have a worldline, or else is the sum of all worldlines - the block universe itself can be likened to a body of water.

OK, but we wouldn't be under a uniform gravitational field would we i.e. we wouldn't experience the same "degree of gravity".

This may of course all be academic, and largely is, because it has never been tested to that extent; and it follows from the arguably unverified assumption that time is physical and that a clock measures it.

himnextdoor wrote: »

I'm pretty sure that an hour-glass will show a much larger degree of time-dilation than a caesium clock under either acceleration or gravity which could be regarded as the same thing.

Any clock can be described in terms of a device that is counting events. Physical events. Acceleration/gravity affect all physical events. For instance, a pendulum clock would probably stop altogether during free-fall whereas a digital-watch would remain comparatively accurate under the same conditions.

Really, accurate time-keeping has been a struggle against natural forces. Candle-clocks can be affected by the wind; water-clocks can be affected by atmospheric conditions; clockwork-clocks are affected by movement and pendulum-clocks even more so.

Even electronic-clocks based on counting oscillations of a crystal are limited by the fact that the crystal is actually, physically bending and flexing at a rate based on its physical parameters. This means that a crystal that has undergone 'contraction' due to acceleration will have changed its resonant frequency.

Now we have atomic clocks and so forth and they are not affected to the same extent by conditions that place serious limitaion the the types of clock mentioned above.

But they do operate within physical laws and acceleration/gravity cause physical effects.

When a rocket takes off, it is accelerated from the rear and becomes slightly shorter; the front of the rocket lags the rear as information cannot be instantaneously transmitted and received. Surely this is the same as saying that the density of the materials comprising the rocket (and everything on board) undergoes an increase in density; atomic nuclei become closer to each other? It seems obvious that time-keeping would be affected under such conditions.

Then consider the case where the force of acceleration is applied at the front due to gravity, say. (Or because the rocket motor is attached to the nose of the rocket which would be wholly impractical of course.) If the rocket was heading into a black-hole, for instance, then the rocket would undergo 'stretching'; the rear would lag the front and the density of the rocket would be slightly lowered.

So there are two scenarios; two rockets accelerating in the same direction but one is powered from the rear whereas the other is powered from the front. Same rate of acceleration, same direction but one is stretched and the other is compressed; in one the density is decreased and in the other it is increased.

What I'm having trouble understanding is, why should we think that there is an actual thing called time that is affected by acceleration/gravity rather than think that acceleration/gravity have a physical effect (which they do) on time-keeping instrumentation? I mean, couldn't a change in density have thermal implications that could influence the integrity of the clock?

Morbert wrote:

Good, robust, standardised clocks, whether they be photon clocks, or caesium clocks, or processes like muon decay, all equally register time dilation, exposing its underlying, geometrical (or chronometrical) origin.

Morbert wrote:

Time dilation is independent of any mechanical principle you base your watch on