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what is time?


woodsong
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Where do you get the idea that black holes have no mass? Mass is one of the defining characteristics of a black hole (along with charge and angular momentum).

 

 

Obviously any answer can only be based on what we know now. That may change in future (but what we currently know will have to remain valid) but there is no way to give an answer based on that.

 

 

It would certainly be useful. But that doesn't mean that we will ever be able to.

how do we know it has mass when we can't see past the event horizon to know if there is anything there to have mass. All the data we have is what we can see before event horizon. OK just a what if question what if the black hole doesn't really have any mass and what we see in our readings in an echo wouldn't that mean you can have gravity without any type of mass.

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how do we know it has mass when we can't see past the event horizon to know if there is anything there to have mass. All the data we have is what we can see before event horizon. OK just a what if question what if the black hole doesn't really have any mass and what we see in our readings in an echo wouldn't that mean you can have gravity without any type of mass.

 

Well, for one thing, everything we know about black holes is from theory. And that theory is based on them having mass.

 

Also, mass is (in this context) defined by its gravitational effect.

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I define the length of my leg as a new unit called the elfleg. Tell me where that's circular and I'll buy you a doughnut.

 

That is not a definition of the concept of length: it is defining a unit of length.

 

Sorry to be the one to break it to you, but physics has advanced since Newton. Lagrangian mechanics for example, an alternative formulation of Newtonian mechanics, makes defining force extremely simple: the spatial derivative of the Lagrangian. No reference to mass whatsoever.

 

Wow, yes, I did not notice. Therefore I said Newtonian physics, and not classical mechanics. So first: you do see that Newtonian physics is circular in in the definition of its fundamental concepts of mass and force, don't you? Why do you think Newton came with such a clumsy definition of mass as 'volume times density'? Could you help him out? And besides this circularity of definitions, does Newtonian physics work? I shall answer it for you: yes.

 

You reference to Lagrangian mechanics is empty: the Lagrangian is defined in terms of energy. Can you define energy for me? (No, not a definition of its unit, a definition of the concept).

 

Darwinian evolution does not say that "the fittest survive." All it says is those that did survive could pass on their genes, whereas those that didn't survive couldn't.

 

Except that Darwin had no idea of genes, you just replaced a circular definition with another one, on microlevel.

 

I don't see how you can go from "all words are in the dictionary" to "all definitions are circular." How are you making that jump?

 

I would suggest you start thinking.

 

Regardless, the problem is not necessarily recursion. There are perfectly sensible recursive definitions. For example [math]\phi = \sqrt{ \phi +1}[/math] is a definition of the Golden Ratio. It is a useful definition because information can be extracted from it. We can figure out the numerical value of [math]\phi[/math] because despite its definition being recursive, it is still well-defined.

 

What has the recursive definition of a number to do with the circularity of definitions?

 

What you've essentially done with your "time is change" nonsense is say, "hey guys, I figured out that [math]x[/math] is actually [math]y[/math]." So then I ask, "well then, what is [math]y[/math]?" And you respond with "[math]y[/math] is [math]x[/math]." That tells me nothing. All it says is that if [math]x=y[/math] then [math]y=x[/math]: a tautology. It gives me no useful information. You've accomplished a change in variable, presumably for aesthetic purposes. That's why I earlier called it "a pedantic shift in vocabulary."

 

First: every definition is a tautology.

 

Then, if I say that 'x = y', and add to it: but only 'y' is observable, where is your problem? Every time I want to measure 'time' I do in fact compare some change with another, standardised, change. As there are many kinds of changes, but only one concept of time, I think I am fully justified to say that time is an abstraction of change, and nothing more.

 

 

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That is not a definition of the concept of length: it is defining a unit of length.

 

Yes, good, you can read. You claimed every definition is somehow circular. I just gave you a definition. Tell me where it's circular.

 

Wow, yes, I did not notice. Therefore I said Newtonian physics, and not classical mechanics. So first: you do see that Newtonian physics is circular in in the definition of its fundamental concepts of mass and force, don't you? Why do you think Newton came with such a clumsy definition of mass as 'volume times density'? Could you help him out? And besides this circularity of definitions, does Newtonian physics work? I shall answer it for you: yes.

 

That doesn't change the fact that there is a definition of force which makes no reference to mass. The definition [math]F_i = \partial_i L[/math] still works in Newtonian mechanics.

 

You reference to Lagrangian mechanics is empty: the Lagrangian is defined in terms of energy. Can you define energy for me? (No, not a definition of its unit, a definition of the concept).

 

Energy is the conserved Noether current generated by time-translation symmetry.

 

Except that Darwin had no idea of genes, you just replaced a circular definition with another one, on microlevel.

 

Nobody cares what Darwin did or did not know. The subject of Darwinian evolution is not restricted to the life and beliefs of Charles Darwin. If I have introduced a circular definition, please explain where. It does me no good if you don't tell me how my logic is flawed.

 

What has the recursive definition of a number to do with the circularity of definitions?

 

I was demonstrating that circular (i.e. making reference to itself) definitions can still contain useful information. I then contrasted the useful example against the nonsense sophistry you've been spouting.

 

First: every definition is a tautology.

 

I already gave you a definition: the length of my leg is one elfleg. Please tell me where that tautological.

 

Then, if I say that 'x = y', and add to it: but only 'y' is observable, where is your problem?

 

That's self-contradictory. You can't say that they're the same, except one is different. Then they're not the same.

 

Every time I want to measure 'time' I do in fact compare some change with another, standardised, change. As there are many kinds of changes, but only one concept of time, I think I am fully justified to say that time is an abstraction of change, and nothing more.

 

Since we've been doing this for ages now and you still haven't given me a useful definition of the word "change," what's to stop me from claiming "change is an abstraction of time"? That's just as meaningful as what you wrote: as in, it's not.

Edited by elfmotat
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Please explain the circularity of this famous definition to me as I can't see it.

 

"The Extremities of a Line are Points"

The way I understood it was that if you went to the extremities of every line of thought and looked closely enough you'd only see dots. Every word would need defining and within that definition every word would also need defining, ad infinitum.

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In what way does that make the definition circular?

Well the word "circular" was used but there maybe a better word, but at least I gave you my impression of the statement. It was more like one of those fractal patterns where you can delve in further and further, rather than going around circles, and I'd agree that is a bit different than circular.

Edited by Robittybob1
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Well, for one thing, everything we know about black holes is from theory. And that theory is based on them having mass.

 

Also, mass is (in this context) defined by its gravitational effect.

with all that mass being pulled into the black hole that fast under so much gravity being place into a confined space when it turns into a quasar would be like the big bang. For all that matter can only be compressed so much. So if there is mass in the black hole the mass might be from what is falling into it.

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with all that mass being pulled into the black hole that fast under so much gravity being place into a confined space when it turns into a quasar would be like the big bang.

 

Nothing like a big bang. A quasar is powered by material in the accretion disk being pulled into the black hole. The big bang was an expansion of space uniformly filled with hot dense matter. So they have nothing in common.

 

For all that matter can only be compressed so much.

 

Citation needed.

 

So if there is mass in the black hole the mass might be from what is falling into it

 

That is, of course, true.

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I count three different topics being discussed here, including Woodsong's mixed-up ideas about black holes.

Its getting rather confusing.

Maybe time to start splitting-off topics ?

 

Agreed

 

Time coordinates and light cones here

http://www.scienceforums.net/topic/86774-michels-qs-about-time-co-ords-split-from-what-is-time/

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Yes, good, you can read. You claimed every definition is somehow circular. I just gave you a definition. Tell me where it's circular.

OK, if you want it the hard way: every definition of a concept is circular. The length of specifically your leg is not a concept, but an empirical fact.

 

That doesn't change the fact that there is a definition of force which makes no reference to mass. The definition [math]F_i = \partial_i L[/math] still works in Newtonian mechanics.

It also does not change the fact that Newtonian physics is circular in the definitions of its basis concepts, and is just as well a perfect useful theory. Circularity is not a death verdict of a scientific theory! It is on one side proof of its consistency, and if some of the concepts can be connected to observations, in such a way that we can attach values to all elements in our theory (or at least to all other observable facts), it is a good scientific theory.

 

If I have introduced a circular definition, please explain where. It does me no good if you don't tell me how my logic is flawed.

 

This was your definition:

 

All it says is those that did survive could pass on their genes, whereas those that didn't survive couldn't.

 

Which organisms survive: those that pass on their genes.

Which genes are passed on: of those organisms that survive.

 

I already gave you a definition: the length of my leg is one elfleg. Please tell me where that tautological.

 

Well, tell me how long your leg is. In every logically possible world, in which the unit is of length is the length of your leg (whatever the length of your leg), the length of your leg is 1 elfleg. So your definition is tautological.

 

That's self-contradictory. You can't say that they're the same, except one is different. Then they're not the same.

 

Yes, you are right. I was a bit imprecise there. Let's say that [math]y=A(x)[/math], where [math]A[/math] means 'is abstraction of'. [math]x[/math] is an observable, so [math]y[/math] is the abstraction. Now for every individual change there is a projection on the time axis. But the opposite is not true: you cannot take the projection of a change on the time-axis, and find what the change was. The reason is that time has no independent existence.

Edited by Eise
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Eise

OK, if you want it the hard way: every definition of a concept is circular.

 

 

Eise, perhaps you missed my post#155 in all the chaff?

 

 

 

 

Posted Yesterday, 08:31 PM

StudioT

 

 

Eise

Don't you realise that every definition is somehow circular?

 

 

Please explain the circularity of this famous definition to me as I can't see it.

 

"The Extremities of a Line are Points"

 

Edited by studiot
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OK, if you want it the hard way: every definition of a concept is circular. The length of specifically your leg is not a concept, but an empirical fact.

 

That isn't what you originally said. You said "every definition is circular." Regardless, I still don't buy it. You haven't justified this claim.

 

It also does not change the fact that Newtonian physics is circular in the definitions of its basis concepts, and is just as well a perfect useful theory. Circularity is not a death verdict of a scientific theory! It is on one side proof of its consistency, and if some of the concepts can be connected to observations, in such a way that we can attach values to all elements in our theory (or at least to all other observable facts), it is a good scientific theory.

 

I completely agree with everything you say here, except for the notion that force and mass are circular. I gave you a mass-independent definition of force. Why isn't that good enough? You don't get to artificially restrict the bounds of my answer just because good ol' Newton didn't think of it himself back in the day. We can go deeper and talk about mass: how it comes from the masses of individual particles, that those particles are actually quantum field excitations, and mass is the coefficient on the quadratic term in the field Lagrangian. Then we could talk about mass renormalization, and even the Higgs mechanism. Or we could go the other route: we could talk about how all forces come down to four fundamental different types of interaction (really just two at macroscopic scales), their descriptions in terms of field theory, etc. All to convince you that mass and force are not circular.

 

You can't just say, "Newton didn't think of it, therefore it's not Newtonian, therefore I win." Well, I mean you can say it, but it's pretty silly.

 

Which organisms survive: those that pass on their genes.

Which genes are passed on: of those organisms that survive.

 

I don't see how that's circular. It seems the definition of "survivor" you're using is "organism that lived long enough to pass on its genes." So you just wrote the definition of "survive" tautologically. The definition itself isn't circular.

 

Well, tell me how long your leg is. In every logically possible world, in which the unit is of length is the length of your leg (whatever the length of your leg), the length of your leg is 1 elfleg. So your definition is tautological.

 

1 elfleg = 0.89 m = 2.92 ft. = 35 in.

 

Yes, the length of my leg is 1 elfleg by the definition of an elfleg. How is that tautological?

 

Yes, you are right. I was a bit imprecise there. Let's say that [math]y=A(x)[/math], where [math]A[/math] means 'is abstraction of'. [math]x[/math] is an observable, so [math]y[/math] is the abstraction. Now for every individual change there is a projection on the time axis. But the opposite is not true: you cannot take the projection of a change on the time-axis, and find what the change was. The reason is that time has no independent existence.

 

Let's say a man walks 10 m at constant velocity. How long did it take? Why do you think it is that you can't tell me?

 

Now break that 10 m into two halves. Since he traveled at constant velocity, the time for him to cross each half is also halved. Now break it into quarters, then eighths, etc. Eventually you'll get down to extremely tiny changes in position, yet the time for those changes to occur is still completely undefined. Why do you think this is? If time were "an abstraction of change" then why can't you tell me anything about the time intervals in the above example system, given that you know literally everything there is to know about all the changes that occur within the system? Are you so clever that you can invent information I haven't given you? If not, then I don't see how you can claim "time is an abstraction of change," given that it's impossible reconstruct information about time by using only information about changes.

Edited by elfmotat
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That isn't what you originally said. You said "every definition is circular." Regardless, I still don't buy it. You haven't justified this claim.

Yes, I have. With the dictionary. You just did not notice it.

 

Just one note of possible misunderstanding: the circle might be composed of more than 2 elements.

 

I completely agree with everything you say here, except for the notion that force and mass are circular. I gave you a mass-independent definition of force. Why isn't that good enough? You don't get to artificially restrict the bounds of my answer just because good ol' Newton didn't think of it himself back in the day.

No, that is not the reason. The reason I stick to Newton is that it is an example of a (simple) theory that perfectly works. So it shows that circularity of concepts does not mean that the theory is wrong, or incomplete or something like that. I am not deep enough in Lagrangian physics (and even less in formal quantum mechanics) to argue in detail about the circularity of their concepts, but you can easily try it yourself: ask for every new concept you introduce what its definition is. You will see that at some place you end where you began, or get at a simple direct circularity as with Newtonian physics.

 

I don't see how that's circular. It seems the definition of "survivor" you're using is "organism that lived long enough to pass on its genes." So you just wrote the definition of "survive" tautologically. The definition itself isn't circular.

 

Yes, of course I did! Otherwise it doesn't work! It is absolute essential for Darwinian evolution that organisms live long enough to pass on their genes. If they don't their genes will not be passed on.

 

Yes, the length of my leg is 1 elfleg by the definition of an elfleg. How is that tautological?

It seems to me you do not know what a tautology is. Whatever the length iof your leg, your leg would always have a length of 1 elfleg. So in every possible world 'the leg of elfmotat is 1 elfleg long' is true. So it is a tautology. Or taking it the other way round, it is impossible for the length of your leg not to be 1 elfleg.

 

Let's say a man walks 10 m at constant velocity. How long did it take? Why do you think it is that you can't tell me?

Because you have not compared it to a regular process, like a periodic series of events.

 

I have no idea what you want to say with the rest of your exposé. I see no problem by taking another regular process in which several events fit in one event of the other periodical series of events, and so dived my observing the walking man in finer parts.

Eise, perhaps you missed my post#155 in all the chaff?

 

No, I did not. But I choose not to answer it, because it has more of a bonmot than of a serious definition. How would you mathematically define a line and a point?

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No, I did not. But I choose not to answer it, because it has more of a bonmot than of a serious definition. How would you mathematically define a line and a point?

 

It's from Euclid - the father of geometry. A point is a defined and indivisible position with zero extension. A line is group of defined positions such that taken together one and only one dimension has extension; ie that has length but no breadth or height

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Yes, I have. With the dictionary. You just did not notice it.

 

Just one note of possible misunderstanding: the circle might be composed of more than 2 elements.

 

I asked you to explain how you can logically jump from "most words are in the dictionary" to "all definitions are circular." You didn't.

 

No, that is not the reason. The reason I stick to Newton is that it is an example of a (simple) theory that perfectly works. So it shows that circularity of concepts does not mean that the theory is wrong, or incomplete or something like that.

 

I agree with you.

 

but you can easily try it yourself: ask for every new concept you introduce what its definition is. You will see that at some place you end where you began, or get at a simple direct circularity as with Newtonian physics.

 

More unfounded claims.

 

Yes, of course I did! Otherwise it doesn't work! It is absolute essential for Darwinian evolution that organisms live long enough to pass on their genes. If they don't their genes will not be passed on.

 

Okay...

 

It seems to me you do not know what a tautology is. Whatever the length iof your leg, your leg would always have a length of 1 elfleg. So in every possible world 'the leg of elfmotat is 1 elfleg long' is true. So it is a tautology. Or taking it the other way round, it is impossible for the length of your leg not to be 1 elfleg.

 

I don't think you know what a tautology is. By your standard any definition is tautological. That's clearly a bad standard.

 

Because you have not compared it to a regular process, like a periodic series of events.

 

It doesn't matter. I gave you a contained system (if the complexity of "man walking" is confusing you, substitute "particle moving"), and all of the information about all of the changes in that system. If time is an abstraction of change, like you say, you should be able to work out the man's velocity without me having to tell you. That makes no sense, so your definition of time is clearly flawed.

 

I have no idea what you want to say with the rest of your exposé. I see no problem by taking another regular process in which several events fit in one event of the other periodical series of events, and so dived my observing the walking man in finer parts.

 

This is incomprehensible to me. Please explain more clearly.

 

No, I did not. But I choose not to answer it, because it has more of a bonmot than of a serious definition. How would you mathematically define a line and a point?

 

Are you serious? http://en.wikipedia.org/wiki/Euclid%27s_Elements

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I count three different topics being discussed here, including Woodsong's mixed-up ideas about black holes.

Its getting rather confusing.

Maybe time to start splitting-off topics ?

nothing is wrong until it is proven fact. A theory is not a fact. I don't care if my ideas or even thoughts might come along a mixed, but black holes do have to deal with gravity as time is effected by gravity so talking about black holes inside a question about time really still deals with time. so it might seem like more than one question but it is all the same question.

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I asked you to explain how you can logically jump from "most words are in the dictionary" to "all definitions are circular." You didn't.

 

Right, I did not. I challenged to find out yourself. But again: circularity can be via more than 2 concepts. Remember, I said the dictionary is complete.

 

More unfounded claims.

 

No it isn't. The problem is that I can't show it just for you. So do it: give a complete definition of all concepts of Lagrangian mechanics. You will see that at some moment you drive in circles.

 

I don't think you know what a tautology is. By your standard any definition is tautological. That's clearly a bad standard.

Of course I know what a tautology is: it is a proposition that is true in all possible worlds. Definitions always are tautological. That is a fact that every logician can confirm for you.

 

It doesn't matter. I gave you a contained system (if the complexity of "man walking" is confusing you, substitute "particle moving"), and all of the information about all of the changes in that system. If time is an abstraction of change, like you say, you should be able to work out the man's velocity without me having to tell you. That makes no sense, so your definition of time is clearly flawed.

Yes, and I said how you should do it. With a clock. Say the clock ticks exactly at the beginning of the trajectory, and at the end. Now I take a second clock that ticks one time more, i.e. it ticks together with the ticks of the first clock, but also one tick in the middle. Then I notice that the man in the box is exactly at the half of the trajectory. Etc. Where is your problem?

 

OK, then it is the unusual language that brought me on wrong track.

 

But if I look up the Elements, I do not find this as definition of a line, nor of a point. This is what I find.

 

A line is breadthless length.

A point is that which has no part.

 

Now do you see the problem? Now you must define 'breadthless', 'length', and 'part'.

 

So let's try this with 'part'.

 

If something can be divided, it has parts.

A point has no parts (per defintion).

So a point cannot be divided.

Now what is the definition of divided?

If something exists of parts, it can be divided.

A point cannot be divided.

So a point has no parts.

 

How do I get out of this?

 

You must not confuse 'defining' with 'immediate clarity'. If you define a concept, you do it with other concepts. You cannot get out of this circle, except by pointing to something observable. But 'pointing to something observable' is not a definition. If one defines the length of a meter, one compares it with the length of something else. But that is not defining what a length is, it is defining what a meter is (same with the elfleg).

Edited by Eise
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nothing is wrong until it is proven fact. A theory is not a fact. I don't care if my ideas or even thoughts might come along a mixed, but black holes do have to deal with gravity as time is effected by gravity so talking about black holes inside a question about time really still deals with time. so it might seem like more than one question but it is all the same question.

 

I thought we were discussing science?

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It's from Euclid - the father of geometry. A point is a defined and indivisible position with zero extension. A line is group of defined positions such that taken together one and only one dimension has extension; ie that has length but no breadth or height

 

 

Well someone recognised it

 

:)

 

Actually Imatfaal is too modern for my liking.

 

The phraseology I used is the 1908 translation to English of the third definition ever in human (scientifc) history.

 

Edit

 

I see more posts whilst I was composing the above.

 

Eise you offer a chain of definitions required not a circle (or other closed loop).

 

It is often the case that something rests on something else.

 

So what?

 

That still does not make it circular.

 

Euclid is the prime model for later thought system construct.

 

It has all the main ingredients.

 

Axioms, definitions and what he called 'common notions'

 

But the construct is not circular, it is not one chain but several, ie it is branching.

 

It rests on certain unproven propositions, again so what?

 

The whole point is that it is not self reflexive, despite literally millenia of attempts to prove it so.

Edited by studiot
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Eise you offer a chain of definitions required not a circle (or other closed loop).

 

Oh yes, if you decide to stick to defining you will run in a circle, how many links your definitional chain might have. Of course you can stop defining at some point ( :wacko:) and say 'this is immediately clear, what do I have to define further', but then it is still exactly that: you stopped defining.

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Right, I did not. I challenged to find out yourself. But again: circularity can be via more than 2 concepts. Remember, I said the dictionary is complete.

 

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.

 

No it isn't. The problem is that I can't show it just for you. So do it: give a complete definition of all concepts of Lagrangian mechanics. You will see that at some moment you drive in circles.

 

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.)

 

Of course I know what a tautology is: it is a proposition that is true in all possible worlds. Definitions always are tautological. That is a fact that every logician can confirm for you.

 

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

 

Yes, and I said how you should do it. With a clock. Say the clock ticks exactly at the beginning of the trajectory, and at the end. Now I take a second clock that ticks one time more, i.e. it ticks together with the ticks of the first clock, but also one tick in the middle. Then I notice that the man in the box is exactly at the half of the trajectory. Etc. Where is your problem?

 

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?

Edited by elfmotat
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