what is time?

[swansont]

 

Hmmm. That is a good point.

 

But we must be careful: length is the comparison with other objects. So there is a parallel with time, which is a comparison with one change with another, standardised change.

 

So, no. Length in itself is not a physical object. It also causes nothing. It are objects with certain lengths that causes something.

 

The reason that time bothers so more seems to me is the fact that where we can freely move in 3 dimensions, time seems to have one single direction.

 

Length as a comparison is like time measurement. But why can't I pick a point in space and describe the distance to it, even though there is nothing there? I think I can. We do this with rockets all the time — we send them to intercept a target at some future time and where nothing currently resides. So how is it that length can exist as an abstract but time can't?

[Eise]

Length as a comparison is like time measurement. But why can't I pick a point in space and describe the distance to it, even though there is nothing there? I think I can.

 

Yes, we can. I can also make an appointment for a time in the future that is not there. But they are always related to an arbitrary origin (arbitrary in the physical sense, not in the practical sense), and a clock (i.e. a standard-changer). For time we have our calendar and clocks, for space flight I assume we take some fixed coordinate system attached to the sun. So there is something there, to which I must relate: the sun, the position of the earth and e.g. the position of a comet. There is no space in itself.

 

So how is it that length can exist as an abstract but time can't?

 

I thought we agreed that time is an abstraction? Of what, according to you? I say it is an abstraction of change. Length is an abstraction of objects: their sizes or distances. So if you ask this way: yes, space and time exist, but as abstractions, not as physical objects: not as field, force, potential, mass, energy, or whatever.

 

I'll try another comparison: the laws of physics. Do they exist? I think we have here exactly the same situation: they do not exist in the same way as physical objects do, they are descriptions of how physical objects develop. Laws of physics cause nothing: they describe how certain classes of events lead to others, i.e. they describe how the causal relationship between certain classes of events is. They are abstract in the same way as space and time are. maybe we should not be wondered by that, because space and time play a major role in most laws of physics.

[elfmotat]

I'll try another comparison: the laws of physics. Do they exist?

 

And this is the root of the problem. Vague, ill-defined philosophical questions.

[swansont]

Yes, we can. I can also make an appointment for a time in the future that is not there. But they are always related to an arbitrary origin (arbitrary in the physical sense, not in the practical sense), and a clock (i.e. a standard-changer). For time we have our calendar and clocks, for space flight I assume we take some fixed coordinate system attached to the sun. So there is something there, to which I must relate: the sun, the position of the earth and e.g. the position of a comet. There is no space in itself.

 

An arbitrary origin, not a physical one. I say the length between two points exists, even if there is nothing there to measure, and I think that's consistent with physics, which does not insist on the physical existence of anything. As opposed to time only existing if something is physically there to change, allowing for a measurement; I don't see that requirement in any equations.

 

I thought we agreed that time is an abstraction? Of what, according to you? I say it is an abstraction of change. Length is an abstraction of objects: their sizes or distances. So if you ask this way: yes, space and time exist, but as abstractions, not as physical objects: not as field, force, potential, mass, energy, or whatever.

 

I'll try another comparison: the laws of physics. Do they exist? I think we have here exactly the same situation: they do not exist in the same way as physical objects do, they are descriptions of how physical objects develop. Laws of physics cause nothing: they describe how certain classes of events lead to others, i.e. they describe how the causal relationship between certain classes of events is. They are abstract in the same way as space and time are. maybe we should not be wondered by that, because space and time play a major role in most laws of physics.

It depends. Are you insisting that the laws of physics only exist when something is happening?

[Eise]

As opposed to time only existing if something is physically there to change, allowing for a measurement; I don't see that requirement in any equations.

 

No, you will never see that. So in the end it is a metaphysical topic.

But you forgot one of my questions: you said, many postings before, that time is an abstraction. Of what?

 

It depends. Are you insisting that the laws of physics only exist when something is happening?

 

That is even for me nearly a question too far... At least it is difficult to derive any law of physics from observation when there exists nothing that behaves like these law. One could say that the elementary entities that physics knows of, are defined by the way they interact with other entities (of the same or of another kind). When nothing happens, i.e. there is no interaction, then, yeah, maybe one should say that there are no laws of physics. Just be aware: of course I am not talking about some empty space in our universe where accidentally just nothing is happening.

 

So the whole discussion is pretty abstract.

Edited December 2, 2014 by Eise

[swansont]

No, you will never see that. So in the end it is a metaphysical topic.

But you forgot one of my questions: you said, many postings before, that time is an abstraction. Of what?

 

I don't know how to answer that. What is length an abstraction of?

 

That is even for me nearly a question too far... At least it is difficult to derive any law of physics from observation when there exists nothing that behaves like these law. One could say that the elementary entities that physics knows of, are defined by the way they interact with other entities (of the same or of another kind). When nothing happens, i.e. there is no interaction, then, yeah, maybe one should say that there are no laws of physics. Just be aware: of course I am not talking about some empty space in our universe where accidentally just nothing is happening.

 

So the whole discussion is pretty abstract.

I think the argument for physical laws is pretty easy, since they typically include the case where terms go to zero. Newton's laws of motion, for example, includes the case for being at rest. Ohm's law includes the case for zero current. Maxwell's equations can be solved for zero charge and current.

[Eise]

I don't know how to answer that.

 

Then you were bluffing when you said this? An abstraction is always an abstraction of something.

 

Time can't exert a force or impart momentum or transfer energy. It's an abstraction.

 

In fact, you are saying the same as I did, except that I said what time is an abstraction of.

What is length an abstraction of?

Space, not length: Space is an abstraction of objects and distances between objects.

It creates even some nice symmetry between space and time:

• Space is an abstraction of objects
• Time is an abstraction of processes.

Some philosophers think that the universe is made of processes (Whitehead). In the end objects only reveal themselves in processes, e.g. in the process of observation. Isn't there a similar discussion in QM? That particles are the locations and the moments of interaction between fields?

In relativity theory we see that space and time are not so strictly separated as we once thought. So that points in a similar direction.

But this is highly speculative.

I think the argument for physical laws is pretty easy, since they typically include the case where terms go to zero. Newton's laws of motion, for example, includes the case for being at rest. Ohm's law includes the case for zero current. Maxwell's equations can be solved for zero charge and current.

Would you like a cheese sandwich without cheese, or do you prefer a meat sandwich without meat?

[swansont]

 

Then you were bluffing when you said this? An abstraction is always an abstraction of something.

 

 

In fact, you are saying the same as I did, except that I said what time is an abstraction of.

Space, not length: Space is an abstraction of objects and distances between objects.

It creates even some nice symmetry between space and time:

• Space is an abstraction of objects
• Time is an abstraction of processes.

 

 

OK, then, let's say time is an abstraction of an ideal clock. If a clock were present, the time would read some value. That means a clock doesn't physically need to be somewhere, just as a test charge doesn't need to be at a point to say that a field exists there.

[Eise]

OK, then, let's say time is an abstraction of an ideal clock. If a clock were present, the time would read some value. That means a clock doesn't physically need to be somewhere, just as a test charge doesn't need to be at a point to say that a field exists there.

 

Hmm... An abstraction of something ideal... That sounds nearly as an abstraction of an abstraction. I just want to remind you again of what you said earlier:

 

Time can't exert a force or impart momentum or transfer energy.

And that is of course exactly the difference with a test charge in an electrical field. The test charge 'measures' the electrical field, because the field has a causal influence on the test charge. But time does not cause the clock to tick, so there is nothing that the clock measures.

[StringJunky]

 

... But time does not cause the clock to tick, so there is nothing that the clock measures.

It might not* cause it to tick but it does determine the rate at which the clock ticks either via gravitational field strength or relative velocity.or both together.

 

*On the other hand if there was no time there would be no 'tick'.

Edited December 4, 2014 by StringJunky

[Eise]

It might not* cause it to tick but it does determine the rate at which the clock ticks either via gravitational field strength or relative velocity.or both together.

 

I have learned that to change a movement, a force is needed. In the end, in relativity, time does not really slow down. We, in another inertial system, or in a weaker gravitational field, see the clock slowing down. But there is no force doing this. In order to have empirical proof of one event causing another, you must be able to observe them independently. But you can't observe time. You can only observe clock-ticks, or more general, change.

Edited December 4, 2014 by Eise

[Strange]

In order to have empirical proof of one event causing another, you must be able to observe them independently.

 

There are many cases where it is not possible to isolate causes and effects and study each independently. In such cases, other approaches are used.

 

Also, time is not an "event", and there is no "force" slowing the clock down, so this feels somewhat irrelevant. And, as always, any objection you raise to the temporal dimension applies equally to the spatial dimensions (which also change in the example you give).

 

But you can't observe length. You can only observe marks on a stick, or more general, distance.

[pears]

What's the difference between observing length and distance?

[Strange]

What's the difference between observing length and distance?

Length, distance, time, ...

[pears]

Huh??

[Strange]

It was just a hurried and not very accurate/useful rewording (reweirding?) of Eise's sentence. In an attempt to show that any meaningless "time doesn't exist" statements apply equally to the spatial dimensions.

[elfmotat]

What's the difference between observing length and distance?

 

 

dis·tance

ˈdistəns/

noun

1. an amount of space between two things or people.

   "I bicycled the short distance home"

   synonyms: interval, space, span, gap, extent;
2. the full length of a race.

   "he claimed the 10,000 meter title in only his second race over the distance"

 

length

leNG(k)TH,lenth/

noun

1. the measurement or extent of something from end to end; the greater of two or the greatest of three dimensions of a body.

   "it can reach over two feet in length"

   synonyms: extent, distance, linear measure, span, reach;
2. the extent of something, especially as a unit of measurement, in particular.

Edited December 4, 2014 by elfmotat

[StringJunky]

Huh??

 

It was just a hurried and not very accurate/useful rewording (reweirding?) of Eise's sentence. In an attempt to show that any meaningless "time doesn't exist" statements apply equally to the spatial dimensions.

I think she's confused about you using length and distance apparently as two different things.

[Strange]

Maybe I should have used "change [of position]" instead of distance....

[pears]

 

I think she's confused about you using length and distance apparently as two different things.

yes

 

Maybe I should have used "change [of position]" instead of distance....

Oh OK - that makes more sense now. Thanks.

[MigL]

This discussion between you, Eise, and swansont, has been extremely interesting, if a little philosophical recently.

 

You insist time is an abstraction of change, and cannot be independently defined.

In effect, there is no time without change.

Yet how can you define change without using the concept of time ?

You cannot have change without the passage of time.

By your standards, change is also an abstraction as it doesn't exist without time.

 

So what are you saying, time is an abstraction of another abstraction ?

[elfmotat]

This discussion between you, Eise, and swansont, has been extremely interesting, if a little philosophical recently.

 

You insist time is an abstraction of change, and cannot be independently defined.

In effect, there is no time without change.

Yet how can you define change without using the concept of time ?

You cannot have change without the passage of time.

By your standards, change is also an abstraction as it doesn't exist without time.

 

So what are you saying, time is an abstraction of another abstraction ?

 

Indeed, he's yet to respond to this point. All he said was "time is not physical" the last time I brought this up.

[davidivad]

what was the question?

what is time.

we have failed to come to an agreement on the meaning of time.

yet this is exactly what is needed.

agreement by the community to the terms by which to use a word.

step one...

i vote that time is at least the sequence of events.

Edited December 5, 2014 by davidivad

[woodsong]

I love reading everything that people have to say about time. I asked this question, because felt we should have an answer to what it truly is for how can be understand space time without understanding time its self. Seeing what people had to say about it makes me love science even more for this is what the world needs is people coming together to answer more of these questions. To many people don't want to step into that light just out of fear of being wrong, you can't learn anything if your not wrong first.

[david345]

It appears that relativity says we have block time. A 3d moving point is a 4d "motionless" world line. The universe is a 4d fixed "block". We think we are moving but we are just a 4d space-time worm. We are a picture fooled into thinking we are a motion picture. The past is still there and it is next to us in the direction of time. Karl Popper once called Einstein "Parmenides" after Einstein admitted this was his view of the universe. Quantum mechanics has raised doubt's about relativity. The block universe may not be set in stone.