Exploring Time as a Testable Dimension

[mangaroosh]

Just a quick question.

I know that it is pretty much taken to be axiomatic, but is time a testable dimension?

 

[jtbell]

What is a "testable dimension?"

 

[mangaroosh]

What is a "testable dimension?"

you'll have to forgive my lack of scientific understanding and therefore terms.

would measurable be a better way of stating it?

 

[A.T.]

would measurable be a better way of stating it?

Time is measurable.

 

[mangaroosh]

Time is measurable.

how is it measured?

 

[A.T.]

how is it measured?

With a clock.

 

[mangaroosh]

With a clock.

is that not circular reasoning though?

 

[Fredrik]

These old posts should be useful:
https://www.physicsforums.com/showthread.php?p=1944107
https://www.physicsforums.com/showthread.php?p=1925822

 

[A.T.]

is that not circular reasoning though?

Why?

 

[mangaroosh]

Why?

is it not using time to prove that time exists?

 

[EvilTesla]

Not really.

Becouse IF you are correct, and we are using time to prove that time exists. Then if time DIDN'T exist, then we wouldn't have it to prove that it exists.

If you see what I am saying.

Time undeniably exists. We measure it ever day. We experience it every day.

Take velocity, distence devided by time. If there is no time, there is no velocity.


Why time is so differnt from space, and what its underlying properties are is anouther matter.

 

[mangaroosh]

Not really.

Becouse IF you are correct, and we are using time to prove that time exists. Then if time DIDN'T exist, then we wouldn't have it to prove that it exists.

If you see what I am saying.

Time undeniably exists. We measure it ever day. We experience it every day.

Take velocity, distence devided by time. If there is no time, there is no velocity.


Why time is so differnt from space, and what its underlying properties are is anouther matter.

I'm not saying time doesn't exist, rather trying to investigate certain claims or ideas that I have heard, in a manner that assumes very little.

the above however that if time didn't exist then we wouldn't measure it, just seems to be further circular reasoning, the opposite side of the same coin if you will. It could be that we misinterpret certain things in nature, attribute certain characteristics to it, and devise a measurement for it, based on a limited perspective, and then apply that en masse to everything.

the fact that we measure time could be more based on a subjective interpretation of reality, as opposed to an objective one. How though can we get beyond this subjectivity, if we consider that consensu isn't satisfactory.

 

[mangaroosh]

These old posts should be useful:
https://www.physicsforums.com/showthread.php?p=1944107
https://www.physicsforums.com/showthread.php?p=1925822

cheers for that, just going through it too

 

[A.T.]

is it not using time to prove that time exists?

No, it is using a clock measure time.

You asked if time is a measureble dimension, not to prove that time exists (whatever "exists" might mean). Physics is not about proving that something exists, but about defining how to measure and predicting what you will measure.

 

[mangaroosh]

No, it is using a clock measure time.

You asked if time is a measureble dimension, not to prove that time exists (whatever "exists" might mean). Physics is not about proving that something exists, but about defining how to measure and predicting what you will measure.

Ok, but before something can be measured does it not have to be shown to exist first?

with regard to existing, I would say that it is part of what goes to making up reality. Would physics then be about defining how to measure and predict reality, or those things that actually exist?

a clock essentially isn't really a measurement of time though is it? It is more a measurement of the Earth's rotation, with a year being a measurement of the Earth's orbit around the sun. Does this mean that time is an intrinsic function of these two things?

 

[James Leighe]

No, a clock just measures time... and has nothing to do with the Earth's rotation.

As a matter of fact, a second (as an example) is defined as '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.'. So we can define time using periodic events in elementary particles.

 

[Fredrik]

The concept of time (and any other measurable quantity really) has to be defined twice. You need to define it operationally, i.e. by describing the equipment you intend to use to measure it, and you need to define it mathematically so that you have something in your mathematical model that represents the real-world concept. By using the same word for both things, you're implicitly saying that theoretical results about "mathematical" time should be interpreted as statements about "actual" time in the real world.

So operational definitions should be thought of as axioms of the theory. They are the statements that tell you how to interpret the mathematics as predictions about the results of experiments.

However, I think this is a pretty awkward way to state the axioms of the theory. I prefer to be more explicit. For example, I would take one of the axioms of special relativity to be "A clock measures the proper time of the curve in Minkowski space that represents its motion". This is more explicit than just using the same word for two different things.

 

[A.T.]

Ok, but before something can be measured does it not have to be shown to exist first?

No, how would you show that anyway? In physics, if something can be measured it "exists", just like numbers "exists" in math.

a clock essentially isn't really a measurement of time though is it?

Yes it is, per definition. A clock is defined as something that measures time.

It is more a measurement of the Earth's rotation, with a year being a measurement of the Earth's orbit around the sun. Does this mean that time is an intrinsic function of these two things?

You can use any process where measurable quantities change as a clock. Just a matter of conventions and practical considerations.

 

[mangaroosh]

No, a clock just measures time... and has nothing to do with the Earth's rotation.

As a matter of fact, a second (as an example) is defined as '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.'. So we can define time using periodic events in elementary particles.

has that happened with the transition to the atomic clock?

It is still used to measure, perhaps more accurately, what was origianlly the length of "time" of the Earth to revolve around its axis, no?

 

[mangaroosh]

The concept of time (and any other measurable quantity really) has to be defined twice. You need to define it operationally, i.e. by describing the equipment you intend to use to measure it, and you need to define it mathematically so that you have something in your mathematical model that represents the real-world concept. By using the same word for both things, you're implicitly saying that theoretical results about "mathematical" time should be interpreted as statements about "actual" time in the real world.

So operational definitions should be thought of as axioms of the theory. They are the statements that tell you how to interpret the mathematics as predictions about the results of experiments.

However, I think this is a pretty awkward way to state the axioms of the theory. I prefer to be more explicit. For example, I would take one of the axioms of special relativity to be "A clock measures the proper time of the curve in Minkowski space that represents its motion". This is more explicit than just using the same word for two different things.

Ok, just with regard to stating the equipment that you are going to use. What equipment would be used to measure time? If we assume that it is to be a scientific test for the existence of time.

 

[mangaroosh]

No, how would you show that anyway? In physics, if something can be measured it "exists", just like numbers "exists" in math.

Yes it is, per definition. A clock is defined as something that measures time.

You can use any process where measurable quantities change as a clock. Just a matter of conventions and practical considerations.

saying that something "exists" (in inverted commas), suggests one of two things, either that it really does exist and there is an emphasis on the word exist, or that it doesn't really exist.

If time exists in the same sense that numbers exist in maths, then that suggests that it is purely in the human mind, as opposed to in reality.

Indeed a clock is, per definition, something that measures time, however it is the nature of the "thing" that it measure. What is time defined as?

 

[mangaroosh]

I read through a lot of the thread you posted Frederic, so I'll do my best to avoid a similar progression in the discussion, as I understand how frustrating that can be. One aspect of my inquiry could be phrased as such:

in what way can time can be said to make up the "fabric of reality", does it actually make up the fabric of reality or is the notion that it does, based purely on an assumption, that is inherent in mankind, based on a misperception of reality.

Also, is it possible that this notion is borne out in the extrememly logical mathematics that have as a starting point, this potentially erroneous "axiom".

Where:

reality
• noun (pl. realities) 1 the state of things as they actually exist, as opposed to an idealistic or notional idea of them. 2 a thing that is actually experienced or seen. 3 the quality of being lifelike. 4 the state or quality of having existence or substance.

 

[Dale]

What equipment would be used to measure time? If we assume that it is to be a scientific test for the existence of time.

There is nothing different about time than about anything else in science. You propose a theory which contains some concept, you design an experiment to test the theory, you carry out the experiment, and you see if the results match the theory. So far all experimental results can be explained by theories which include time.

If you wish to do away with time then you are free to propose a theory of physics that does not use time, show that it correctly predicts the outcome of all experiments performed to date, and makes some new testable predictions.

 

[trini]

I think the question you are trying to ask is, is time a physical thing, and the answer is no. Someone cannot collect a jar of time can they? time is not a thing, it is a relationship between the progression of a fairly constant event with the progression of another.

Let's look at defining a day in terms of lunar orbit. We shall define 1 day as the time taken for the moon to orbit the Earth once. That's all, we do not consider at all the other possible definitions of the day, in this case, we consider only the definition in terms of lunar orbit. in this case, the understanding of the day is this:

"1 day defines the progression of an event during the course of the moon orbiting the Earth once"

Now the orbit of the moon can be defined in terms of its angle or the distance travelled, however whichever method is used does not change the fact that the relation in question is the amount of cycles of the moon to the progression of the event in question. so you cannot use one object's time to describe itself, that, as you say, is self conflicting. time describes the relationship between two separate events, with at least one of these events being periodic(that is, one event displays a constant progression, thus providing a stable base of observation.)

please realize, that in the absence of a third gauging system, if the periodic motion of the reference frame is accelerated, but the periods shape is the same, then it becomes impossible to tell that the reference frame has accelerated without having some artifact of the reference frame before it was accelerated to compare it with.

So for example, if all the clocks in the world suddenly stopped working, and then after that, the moon began to rotate faster, and the definition of the day remained unchanged, then after that all the clocks began to work, but still somehow divided up orbits into the same 24 hours(in other words you couldn't tell that its actually taking "less time" than it should to complete a day) you would no longer have an artifact of the old reference frame to realize how much "faster" this time moved. If however one clock magically remained untouched, you could now describe the rate of your 'present' time against the rate of 'past time'.

 

[Fredrik]

Ok, just with regard to stating the equipment that you are going to use. What equipment would be used to measure time?

A clock. I don't agree with AT's definition of a clock as something that measures time. That would make the definitions circular. When I say "clock" it refers to what we all think of as a "clock". We can be a bit more precise by describing how to build one of these clocks, but the definition can never be as exact and unambiguous as the definitions in mathematics.

If we assume that it is to be a scientific test for the existence of time.

That doesn't really make sense. The term "existence" is surprisingly useless in physics. The only thing experiments can tell us is how accurate a theory's predictions are, so the only meaningful definition of what it means for something to "exist" is that it's a concept that's used in a theory that makes good predictions. So the only way to interpret the claim that time exists is that it has a mathematical definition in a few theories (Newtonian mechanics, special relativity, general relativity) that make good predictions. Clocks are of course absolutely essential when we test the accuracy of those predictions.

in what way can time can be said to make up the "fabric of reality",

Science doesn't really answer questions like that. Theories make predictions. Experiments test how accurate those predictions are. The more accurate they are, the stronger we feel that we can understand something about how the universe works by understanding the theory. That's all. Science can't ever answer a question like "What is time really?".

does it actually make up the fabric of reality or is the notion that it does, based purely on an assumption, that is inherent in mankind, based on a misperception of reality.

I'd say that your question is based on a (very common and understandable) misconception of science. But you're on to something. All the theories that define the concept of time are making predictions that are less than perfect. So it clearly isn't the case that any of those models includes a perfect representation of time. This problem isn't unique for the concept of time. The same can be said about any observable.

 

[A.T.]

saying that something "exists" (in inverted commas), suggests one of two things, either that it really does exist and there is an emphasis on the word exist, or that it doesn't really exist.

My point was that "existence" is not clearly defined in physics, and not really part of physics but rather philosophy.

If time exists in the same sense that numbers exist in maths, then that suggests that it is purely in the human mind, as opposed to in reality.

This is true for all physical quantities: forces, energy... they all are abstract concepts invented by humans.

Indeed a clock is, per definition, something that measures time, however it is the nature of the "thing" that it measure.

"The nature of the thing" is not a physical quantity that I know of. Why invent so complicated names, if we have a simple on already: "time".

What is time defined as?

In physics quantities are defined by defining how you measure them.

 

[mangaroosh]

cheers for all the explanations, it has definitely helped with my understanding, of what time is with regard to the physical sciences.

Obviously as a lay person my overall understanding is limited, which is why I am undertaking to try and understand better. The media that are more accessible to me would be the likes of documentaries and message boards like these - as the option of studying the various sciences and indeed mathematics are not really a viable option, at this stage in my life.

Part of what leads me to question the nature of time is stuff that I have read - not necessarily scientific - that has made intuitive sense, and other things that I have come across. In most documentaries that I have come across, time, in particular spacetime, is portrayed as the fabric of reality, which could, potentiall be manipulated. I suppose in a sense, it is portrayed almost as though we, the planets etc. are almost like particles in a suspension tank, that work based on the laws of nature (of which we have a certain, developing understanding), but that that "material" that we are suspended in, can potentially be warped and manipulated. I would also wonder if this dimension of time is an intrinsic part of who we are.

Further caues for questioning is something else that I have read, with regard to "the Problem of time" in Physics, in particular with regard to the incompatibality of Quantum Mechanics and General Relativity, that both are based on quite different conceptualisations of time. It was posited that the two theories would actually be reconcilable if the concept of time was dropped.

I also came across the Lee Smolin lecture online, about "the problem of time", but unfortunately the second lecture was well beyond my level of comprehension, so I didn't persist with it. Is anyone familiar with that lecture and the conclusions or outcomes?

 

[Fredrik]

In most documentaries that I have come across, time, in particular spacetime, is portrayed as the fabric of reality, which could, potentiall be manipulated. I suppose in a sense, it is portrayed almost as though we, the planets etc. are almost like particles in a suspension tank, that work based on the laws of nature (of which we have a certain, developing understanding), but that that "material" that we are suspended in, can potentially be warped and manipulated.

Claims like that are fine, because they describe the mathematical spacetime that's used in general relativity, which is by far the best theory of time (and space, motion and gravity) that we have. I think people should understand that the mathematical concept isn't the same as the real-world concept, and that the relationship between the two is specified by an axiom of the theory, but I don't think we can change the way we talk to reflect that fact every time we say something about time. That would make any statement about physics really awkward. So we'll just continue to say things that seem to confuse the model with the real world, and some of us will try to spread the word about what statements like that really mean.

Is anyone familiar with that lecture and the conclusions or outcomes?

I am not.

 

[mangaroosh]

Claims like that are fine, because they describe the mathematical spacetime that's used in general relativity, which is by far the best theory of time (and space, motion and gravity) that we have. I think people should understand that the mathematical concept isn't the same as the real-world concept, and that the relationship between the two is specified by an axiom of the theory, but I don't think we can change the way we talk to reflect that fact every time we say something about time. That would make any statement about physics really awkward. So we'll just continue to say things that seem to confuse the model with the real world, and some of us will try to spread the word about what statements like that really mean.

yeah, that's fair enough. I suppose part of where the "conflict" arises is that to a relatively large extent, Physics (or more generally science) is considered to be somewhat an authority on what is and is not the reality of the world around us. This could perhaps be attributable to a select few peopel within the field who make certain claims, or indeed discuss certain topics with a certain air for authority and finality.

To a certain extent the claims that are made by many in the field of science, does in fact have an impact on the "reality" of those outside the field of science, as facts are reported about the world and indeed universe we live in, with certain assertions being made on the back of those facts. This inevitably has an impact on the collective psyche, and over time will have a material affect on the way in which society conducts itself, more so on a subconscious level.

This of course can be both positive and negative as certain myths that may hold back the development of mankind, but it can also give rise to certain other myths, that appear to have the backing of scientific evidence, or as appears to increasingly be the case, mathematical evidence. For example, the notion of parallell universes is one that appears to be gathering momentum, yet there appears to be little more than speculation based on complex mathematics, to support this idea. While this may not be a mainstream idea at present, it is certainly one that appears to be gathering momentum, especially as the search is on to unify the two widely accepted, and dominant theories in physics.

If, as has been postulated, that this discrepancy can be resolved more easily by resorting to Occams Razor and the conclusion that instead of resorting to, as of yet (and possibly for quite some time) unobservable vibrating strings and floating "branes", that something previously thought to make up "the fabric of reality", but is, upon careful consideration, perhaps less an actual dimension of the universe and more a misinterpretation of mankind, based on a limited perspective of the universe, in much the same way as the concept of the planets and the sun orbiting the Earth was based on a limited perspective, or rather limited analysis of evidence.

This of course is based on the potential that the incompatabiliy of the two most fundamental scientific theories can indeed be resolved by the removal of "time" as an actual, almost physical dimension.


here is that Problem of time lectures if you're interested. Like I said, it was beyond my level of comprehension, but it may be more intelligible for yourself.

 

[mangaroosh]

The following articles probably explain the issue in a more scientific sense.
http://discovermagazine.com/2007/jun/in-no-time
http://qd.typepad.com/17/2005/10/the_problem_of_.html

any comments on the validity of these is welcome