what is time?

[Strange]

Looks like Eise will need a hand moving those goalposts again...

[MigL]

Nonetheless he does make some valid points, as does the opposition.

A very interesting discussion so far, it has certainly made me think.

 

And civil too, a refreshing change.

[woodsong]

 

I thought we were discussing science?

We are sorry for my rant.

[AndresKiani]

One thing we do know is that time is a very "real" property of our universe and existence. However what it exactly is.. is a mystery at least to me. Perhaps there is some people who understand and have a sense for multi-dimensions and their properties.

 

I think for non physicists it's hard to imagine how complicated such a concept gets, specially in quantum gravity.. in which it get's extremely abstract. Even more so time near the big bang or in the early universe or even more so time before the big bang.

Edited December 9, 2014 by AndresKiani

[studiot]

 

One thing we do know is that time is a very "real" property of our universe and existence. However what it exactly is.. is a mystery at least to me. Perhaps there is some people who understand and have a sense for multi-dimensions and their properties.

 

I think for non physicists it's hard to imagine how complicated such a concept gets, specially in quantum gravity.. in which it get's extremely abstract. Even more so time near the big bang or in the early universe or even more so time before the big bang.

 

 

I find it refreshing for someone to acknowledge their limitations. +1

 

[Eise]

Except dictionaries aren't really complete, so this makes for a poor comparison with reality. If you can explain how you're getting from "most words are in the dictionary" to "all definitions are circular," then do it. If not then I don't accept this as a valid argument.

 

Ok. All definitions are expressed in words. Let's assume that a definition is not circular. This means I get at a concept for which there is no word in the dictionary, so which is not defined. But this contradicts the assumption that the dictionary is complete.

 

Applied on physics this means that one of the following must be true:

• Physics uses concepts that cannot be expressed, because they cannot be defined (btw, this would include a mathematical dictionary of physics).
• Definitions of concepts are circular.

See e.g. here:

 

Definitions can be broadly or narrowly circular. Narrowly circular definitions simply define one word in terms of another. A broadly circular definition has a larger circle of words. For example, the definition of the primary word is defined using two other words, which are defined with two other words, etc., creating a definitional chain. This can continue until the primary word is used to define one of the words used in the chain, closing the wide circle of terms. If all definitions rely on the definitions of other words in a very large, but finite chain, then all text-based definitions are ultimately circular. Extension (semantics) to the actual things that referring terms like nouns stand for, provided that agreement on reference is accomplished, is one method of breaking this circularity, but this is outside the capacity of a text-based definition.

 

(Italics by me).

The gist of the argument is that normally you stop defining when you use words that are unproblematic in the context.But in fundamental questions you are problematising, you want exact definitions: but then you will inevitably run in circles from some point.

 

The point I am making is that change is more fundamental as reference than time, because we can observe change, but we cannot see time, except through changes.

 

I don't see how I'd drive in circles. A particle is equipped with a Lagrangian, L(x(t),v(t)). The particle will always travel along paths x(t) such that ∫Ldt is stationary. In classical mechanics the Lagrangian is the particle's kinetic energy plus potential terms. (The Lagrangian is defined, then its consequences are worked out. Building physical models then comes down to merely finding Lagrangians which agree with observation.)

Really? That is just because you stopped. please define: kinetic energy and potential energy to begin with. For the moment I leave you path, the integral over time, and stationary.

 

You're confusing the formal logic definition of a tautology with rhetorical tautologies, the latter of which I have been accusing you of using.

No, I am confusing nothing. Definitions are logical tautologies. If not, then there would be a possible world in which the definition does not apply. Say I define a bachelor as an unmarried man. Now, is the sentence "a bachelor is an unmarried man" a tautology or not? Given the definition of the concept 'bachelor': is it possible to imagine a world where you meet a married bachelor?

 

The problem is that you've introduced additional objects into what was supposed to be a closed system. I'm giving you a scenario where I've defined all changes in space. You're claiming time is an abstraction of change. I'm giving you everything you need to know as far as changes are concerned. Why can't you tell me anything about the time?

If it really is a closed system, then I can say nothing about it. If I can say something about it, then I am, as observer, part of the system. The example you gave does not follow the rules. I have said that the only way we can determine time is by comparing with another process. So I introduced my clocks.

 

Edit: typo

Edited December 9, 2014 by Eise

[between3and26characterslon]

IF (and its a big if) you could be absolutely stationary how fast would time pass by. The faster you go the slower time passes therefore the slower you go the faster time passes, if you were stationary would time pass infinitely quickly so is time inextricably linked to motion?

[imatfaal]

IF (and its a big if) you could be absolutely stationary how fast would time pass by. The faster you go the slower time passes therefore the slower you go the faster time passes, if you were stationary would time pass infinitely quickly so is time inextricably linked to motion?

 

With respect to yourself you are always stationary. Others can observe you as moving relative to their frame of reference and would consider your time dilated - but in your own frame of reference you are always stationary and time is not changed.

[studiot]

 

Eise

No, I am confusing nothing. Definitions are logical tautologies. If not, then there would be a possible world in which the definition does not apply. Say I define a bachelor as an unmarried man. Now, is the sentence "a bachelor as an unmarried man" a tautology or not? Given the definition of the concept 'bachelor': is it possible to imagine a world where you meet a married bachelor?

 

 

If you must construct examples please at least make sure that your use of the terms is correct.

 

All (male in modern parlance) bachelors are men, true

 

but

 

Not all unmarried men are bachelors.

 

So where is the tautology?

[Eise]

Studiot,

I did not say 'all unmarried men are bachelors'. I gave a definition of the concept bachelor. Given that definition, is there a possible world where I can meet a married bachelor? So if something is true in all possible worlds, then it is a tautology:

 

 

Definition. A statement is logically true (or a tautology) if and only if it's impossible for it to be false.

In the language of possible-world semantics, a statement is logically true (or a tautology) if and only if it's true in all possible worlds.

Edited December 9, 2014 by Eise

[studiot]

You said

 

 

Definitions are logical tautologies

 

Which means they are reflexive or work both ways.

 

Your gave a definition of a bachelor

 

 

an unmarried man

 

If I can find an unmarried man who is not a bachelor your definition is not a tautology since it is not reflexive.

 

Since I can find an unmarried man (a widower) who is not a bachelor, the relationship is not reflexive and therefore not a tautology.

 

Therefore your definition is not a definition, or it is defective, or your claim that a definition is a tautology is untrue.

 

Suprisingly this refutation of an off-topic example, invokes time (on topic) since time is necessary for a man who was once a bachelor to become married and then widowed.

Edited December 9, 2014 by studiot

[Eise]

OK, I will change it specially for you:

 

A bachelor is a man who never has been married.

 

OK?

 

Can we go on, please?

[studiot]

 

Can we go on, please?

 

 

Only if we return to the topic?

[Eise]

Yes, please. What is time.

[between3and26characterslon]

Yes, please. What is time.

 

It's the stuff that stops everything happening all at once (Déjà vu anyone?)

[elfmotat]

Ok. All definitions are expressed in words.

 

I don't believe this is true either.

 

Let's assume that a definition is not circular. This means I get at a concept for which there is no word in the dictionary, so which is not defined. But this contradicts the assumption that the dictionary is complete.

 

And I'm telling you that this makes for a poor comparison with reality, because dictionaries aren't complete. Did you ignore that part last time?

 

Applied on physics this means that one of the following must be true:

• Physics uses concepts that cannot be expressed, because they cannot be defined (btw, this would include a mathematical dictionary of physics).
• Definitions of concepts are circular.

See e.g. here:

 

Wrong. You can't use a hypothetical complete dictionary to draw conclusions about reality. Also this is a false dichotomy. Why only those choices?

The gist of the argument is that normally you stop defining when you use words that are unproblematic in the context.But in fundamental questions you are problematising, you want exact definitions: but then you will inevitably run in circles from some point.

 

I simply don't agree that exact definitions need to be text-based.

 

The point I am making is that change is more fundamental as reference than time, because we can observe change, but we cannot see time, except through changes.

And we cannot see changes except through time. So congratulations, we're back to square one.

Really? That is just because you stopped. please define: kinetic energy and potential energy to begin with.

 

I don't need to. As I said, you start by defining a Lagrangian - as in you include whatever terms you want. After you've defined it, you work out what the physical consequences would be and compare the predictions with experiment. As it happens, some useful Lagrangians include terms which people have decided to call the "kinetic" and "potential" terms. They got those names because they happen to be useful for modeling the real world, so it's nice to have names to call things. You can certainly construct Lagrangians without them.

 

For the moment I leave you path, the integral over time, and stationary.

 

These are all well-defined math words that you should be able to look up yourself.

 

No, I am confusing nothing. Definitions are logical tautologies. If not, then there would be a possible world in which the definition does not apply. Say I define a bachelor as an unmarried man. Now, is the sentence "a bachelor is an unmarried man" a tautology or not? Given the definition of the concept 'bachelor': is it possible to imagine a world where you meet a married bachelor?

 

"In rhetoric, a tautology (from Greek το αυτο, "the same" and λόγος, "word/idea") is a logical argument constructed in such a way, generally by repeating the same concept or assertion using different phrasing or terminology, that the proposition as stated is logically irrefutable, while obscuring the lack of evidence or valid reasoning supporting the stated conclusion. (A rhetorical tautology should not be confused with a tautology in propositional logic.)^[a]"

 

http://en.wikipedia.org/wiki/Tautology_%28rhetoric%29

 

Please do me a favor and actually read my posts before you respond to them. It's frustrating having to say the same things over and over. I accused you of using rhetorical tautologies. Somehow you got it in your head that we were actually discussing logical tautologies (which makes no sense given the context of the conversation).

 

If it really is a closed system, then I can say nothing about it. If I can say something about it, then I am, as observer, part of the system. The example you gave does not follow the rules. I have said that the only way we can determine time is by comparing with another process. So I introduced my clocks.

 

Except for the fact that I TOLD YOU EVERYTHING ABOUT IT!

 

What I want to know is this: if time is an abstraction of change, then why can't we use information about change to figure out information about time? If time is the abstraction of change, surely knowledge of change would imply knowledge of time. If you say this is false then you must at least admit that "time is the abstraction of change" is a very misleading and probably useless definition. Which has been my point from the beginning.

Edited December 9, 2014 by elfmotat

[MigL]

I'm not going to present any arguments relating to definitions, dictionaries, or bachelors ( ? ).

I am gonna throw this out there again, though, Eise, as I don't think you gave it enough attention previously...

 

In post #181 you say

"change is more fundamental, as a reference, than time, because we can observe change, but we cannot see time, except through changes"

which is absurd, because without the passing of time NOTHING CHANGES !

So you cannot observe any changes without passing of time. Ever !

 

On the other hand, you can make the argument that time can pass without any change occurring ( numerous members have presented examples which won't be repeated ).

 

So which is the more fundamental ?

Or do you wanna argue the definition of fundamental ( kidding ) ?

[Robittybob1]

I'm not going to present any arguments relating to definitions, dictionaries, or bachelors ( ? ).

I am gonna throw this out there again, though, Eise, as I don't think you gave it enough attention previously...

 

In post #181 you say

"change is more fundamental, as a reference, than time, because we can observe change, but we cannot see time, except through changes"

which is absurd, because without the passing of time NOTHING CHANGES !

So you cannot observe any changes without passing of time. Ever !

 

On the other hand, you can make the argument that time can pass without any change occurring ( numerous members have presented examples which won't be repeated ).

 

So which is the more fundamental ?

Or do you wanna argue the definition of fundamental ( kidding ) ?

Given time it will change. You learn this as a human you have to wait. Time before change but then if the change is regular we use that change to measure time e.g the hourglass.

[Eise]

It's the stuff that stops everything happening all at once (Déjà vu anyone?)

 

Stuff? Can we detect it? How?

 

I don't believe this is true either.

 

Your belief without any argument doesn't bother me.

 

And I'm telling you that this makes for a poor comparison with reality, because dictionaries aren't complete. Did you ignore that part last time?

 

Yes, I did. Physicists also work with all kind of idealisations, like black bodies and isolated systems. So why shouldn't I? But more to the point is: would you accept a definition which contains words you do not know?

 

Wrong. You can't use a hypothetical complete dictionary to draw conclusions about reality. Also this is a false dichotomy. Why only those choices?

 

Give another one, that does not fit the above.

 

I simply don't agree that exact definitions need to be text-based.

 

Yes, I noted that. I also noted that you give no arguments for it. There are two possibilities: a (real) definition in words, which is logically necessary circular (even if it is over a long chain of other words). Or you give an operational definition, e.g. you point to something ('this here, this is red'). That is methodologically fully OK, but it is exactly what you cannot do directly with time. You cannot point to time: but you can point to change, e.g. a clock.

 

And we cannot see changes except through time. So congratulations, we're back to square one.

 

But it hardly makes for a description or definition of 'change'. Of course you can say 'Change is change in time', but then you have used the word change itself.

 

I'll give it another try: time is the most general abstraction of all changes. Now I am also not completely satisfied with this, but at least it shows that you cannot turn it around. How can individual changes be abstractions of something that is more general?

 

I don't need to. As I said, you start by defining a Lagrangian - as in you include whatever terms you want. After you've defined it, you work out what the physical consequences would be and compare the predictions with experiment. As it happens, some useful Lagrangians include terms which people have decided to call the "kinetic" and "potential" terms. They got those names because they happen to be useful for modeling the real world, so it's nice to have names to call things. You can certainly construct Lagrangians without them.

Right. You show how physicists use the Lagrangian to solve problems of mechanics. But I asked for a definition, first of the Lagrangian, and then of kinetic energy and potential energy. Obviously you immediately refrain from defining. 'Defining' is something else than knowing how to follow a recipe.

 

Let me help you, with the dimension of energy:

 

[J] = [kg . m²/s²]

 

What does the kg stand for?

 

Please do me a favor and actually read my posts before you respond to them. It's frustrating having to say the same things over and over. I accused you of using rhetorical tautologies. Somehow you got it in your head that we were actually discussing logical tautologies (which makes no sense given the context of the conversation).

Sorry, you are just wrong. Take the definition 'a bachelor is a man who never married'. Now I substitute the meaning of 'bachelor' in the definition. I get 'a man who never married is a man who never married'. Isn't that a tautology? (Maybe you are confusing tautology with one of its subclasses, the propositional tautology (A or not A).)

 

Except for the fact that I TOLD YOU EVERYTHING ABOUT IT!

 

Except that you did not follow the rules.

 

What I want to know is this: if time is an abstraction of change, then why can't we use information about change to figure out information about time?

 

Because it is an abstraction. You are like the middle age philosophers that discussed if 'whiteness', or 'horseness' existed, or even may be more real then a white plate or the horse standing in front of me.

 

If time is the abstraction of change, surely knowledge of change would imply knowledge of time. If you say this is false then you must at least admit that "time is the abstraction of change" is a very misleading and probably useless definition. Which has been my point from the beginning.

There is nothing to know about time except as a comparison between different processes. And of course the definition is pretty useless for a physicist. But the question of the thread is 'What is time?'. It is not 'Why all physics is completely wrong because they do not understand what time really is'.

"change is more fundamental, as a reference, than time, because we can observe change, but we cannot see time, except through changes"

which is absurd, because without the passing of time NOTHING CHANGES !

So you cannot observe any changes without passing of time. Ever !

 

How do you know time is passing? Without you being there, breathing, your heart beating, and if you want to be precise, without a clock?

[studiot]

 

Eise

 

Take the definition 'a bachelor is a man who never married'. Now I substitute the meaning of 'bachelor' in the definition. I get 'a man who never married is a man who never married'. Isn't that a tautology? (Maybe you are confusing tautology with one of its subclasses, the propositional tautology (A or not A).)

 

 

Do you understand the mathematical concept and application of equivalence relations?

[Eise]

 

Do you understand the mathematical concept and application of equivalence relations?

 

I assume you want to say I don't. Feel free to say what is wrong.

Wikipedia on logical tautologies:

 

The word tautology was used by the ancient Greeks to describe a statement that was true merely by virtue of saying the same thing twice, a pejorative meaning that is still used for rhetorical tautologies. Between 1800 and 1940, the word gained new meaning in logic, and is currently used in mathematical logic to denote a certain type of propositional formula, without the pejorative connotations it originally possessed.

 

In 1800, Immanuel Kant wrote in his book Logic:

 

"The identity of concepts in analytical judgments can be either explicit (explicita) or non-explicit (implicita). In the former case analytic propositions are tautological."

 

Here analytic proposition refers to an analytic truth, a statement in natural language that is true solely because of the terms involved.

 

Wikipedia on Definitions:

 

Given that a natural language such as English contains, at any given time, a finite number of words, any comprehensive list of definitions must either be circular or rely upon primitive notions. If every term of every definiens must itself be defined, "where at last should we stop?" A dictionary, for instance, insofar as it is a comprehensive list of lexical definitions, must resort to circularity.

 

 

[studiot]

 

I assume you want to say I don't. Feel free to say what is wrong.

 

 

 

Not at all, why do people always assume the worst of others?

 

 

Being old fashioned I asked because I wanted to know the answer.

 

 

I think equivalence relations has relevence to the subject of tautologies, but need go no further if you already understand this.

[david345]

I am just trying to figure out what is changing? Obviously not time. Time does not exist. You say a clock changes. How did it change? Did it change it's color? You say a clock measures change. What change? A change in the weather? The change of a curve's slope? A change in hairstyle? You could say it measures a certain type of change. This type of change is ∆t. t being the fourth dimension. Einstein's time has been tested and it has lead to accurate predictions. Defining ∆t as ∆decay does not explain dilation. Yes it takes a ∆t to measure a ∆t. You can not replace t with ∆. ∆slope has nothing to do with time. You could say a particle is at x at t. This is an instant in time and not a ∆t. In quantum mechanics the wave collapse is instant. You could question our ability to measure an instant in time. This has to do with the uncertainty principle. It is not a result of time being change.

Edited December 12, 2014 by david345

[Eise]

david345,

Colour of course. When I want to know the time, I look at the color of my clock, and I know what time it is. Don't you?

 

This is the most sensible answer I can give to your questions.

Edited December 13, 2014 by Eise

[studiot]

Time and change are closely associated, but they are not the same.

 

You can have one without the other.

 

But to only be prepared to discuss or condiser time in relation to change is blinkered thinking.

 

We use time (and) for other purposes.

 

Take, fo instance, the Rodistochrone problem.

 

Two hungry mice stand in their cages at 10m and 30m distance from the cheese.

 

At the starter pistol the cages are opened.

 

Which mouse eats the cheese?

 

Time is being used here for comparison, not change.

 

Now let me make a change; I remove a leg from one mouse.

 

Which mouse gets the cheese?

 

Temperature (with a large T) is another quantity we introduce to make comparisons like time (with a small t).