Basic understanding of time

[Lizzie L]

 

Good morning, Lizzie,L.

I understand and support your point of view with the following proviso about change or movement.

It is comparison, not change or movement, that is the key. Without comparison we cannot demonstrate change or lack of it.

And it also follows that we must be considering at least two identifiable entities to compare.

 

 

Yes, that's an excellent point. I am happy to accept your emendation

 

I have been trying to prompt those here who feel that they can offer an insight into time through relativity, the spactime continuum and sundry mathematics to explain why they are doing the manipulations they offer.

 

I thought someone has posted about a light cone but I can't find it now so it must have been in another thread.

Never mind.

 

 

I think Schneibster's point about hyperbolic time is essentially about light cones.

 

 

The point about light cones, Lorenz transformations, etc etc is not change or movement but comparison in mathematical terms.

 

The equations diagrams etc follow a well worn scientific path that has served well for many purposes.

That path is to consider relevent properties of a 'point particle' and scale up to many particles.

 

 

 

Sure, but the equations have c in them, so any diagram of any of the equations is going to have time and space units, isn't it? And while we can express space in terms of light and time, we still need some kind of time unit. So aren't we back to clocks?

 

Now for most purposes we can simple sum the effects of all individual particles so to obtain for instance the mass of a body as the sum of the masses of all the individual particles that make it up.

 

There are, however, observable properties in this universe that do not sum in this way.

They are different.

 

When we write equations to link the connection between these particles, time is the parameter we use.

 

Hence the why of the transformations.

 

If we wish to compare physical properties of two or more particles, each with their own light cone, we need a mathematical connection that applies to both.

 

 

Yes, I think I get that.

 

I

also tried to discuss the physical reality of, past, present and future but no one took this up.

 

It is a simple exercise in logical observation to show that because we can "see into the past", given the present, that the past has as much physical reality as the present.

 

Moving into your realm, it is a short stride to realise that I can remember a past time when my present was in my future so I can offer nearly as strong evidence for the existence of the future, although I cannot "see" it in the present.

 

 

Indeed. And it's a short further stride to imagine an existence when all a person knows is the future, and it's the past that has to be guessed at. People with bilateral hippocampal lesions effectively live in such a world.

 

I think it's interesting that few people have a problem with the question of "what is length" but want to know what time is. There's a similarity in the difficulty in defining each without using some sort of circular reference, but as we have a visceral notion of length — we can see it — it rarely comes up.

 

Well, isn't that just because we have an easy translation from time into space via the speed of light? So we can define length in terms of time, but then we are stuck with a definition of time. Although I suppose we could reframe the question as: a unit of time is how long it takes for light to travel some unit of length, but what is length? I'm not sure that the reason we don't ask that one more often is because we can "see" length. It might simply because at scales at which it matters (astronomical scales) the tradition is to talk of length in light-years, rather than time in light-lengths.

 

The problem with equating time with movement or change is that it assumes a relation but doesn't show it. Does time pass because things change or do things change because time passes? The former is certainly false. We can look at systems that change more or less and measure time passage for each; the amount of change has no effect on the passage of time. One need go no further than time measurement for this. A grandfather clock with a 1m pendulum ticks every other second, and yet time passes at the same rate for it as the atomic clock next to it, "ticking" at 9192631770 times a second. More change, same amount of time. Similar arguments can be made for motion. So, no, the units of time and units of change are not the same.

 

Yes, I agree that time doesn't pass because things change. My original claim was that time only made sense in relation to change. I still think that's more or less true - for a universe in which nothing changed (as I understand you can get from some solutions to Einstein's field equations - I can't remember who said that, and I'm not in a position to argue it! ETA it was Strange) time wouldn't actually make a lot of sense within that universe, just for us, outside that universe, with clocks that do depend on change. As a toy example, if we plot the location of a stationary object over time, we get a horizontal line, while for a moving object we get a nice curve. From outside the world in which the object is stationary, time is meaningful - and we can compare its non-moving trajectory with the trajectory of something moving. But if All That Is is stationary and unmoving, then time ceases to have any meaning, I'm saying, within that universe - only for us, contemplating it from a changing one.

 

 

Perhaps the mere existence of change or motion somehow is what permits time to exist. The argument suffers from not being scientific, because you can't remove change or motion from a system in order to test the hypothesis. What we can do is reduce it as much as possible, and we see no effect whatsoever. Time does not pass more slowly for cold things; many modern clocks use exceedingly cold atoms for their measurement, and are state of the art, measuring time even more precisely than devices whose atoms are moving more quickly.

 

 

Well, I think it's what permits us to exist, and therefore for beings capable of modeling time as a dimension to exist! Even of systems in which time, within that system, would not.

Lighten up, Strange. You have no evidence that time is not just as religion says it is. You just have your opinion, same as Lizzie. Except that she seems to be less dogmatic. .

 

Heh. I try.

Edited February 23, 2014 by Lizzie L

[Strange]

I haven't seen any evidence presented on this forum that contradicts it.

 

Thanks for reinforcing my point.

 

 

Can you cite where you think there was some?

 

All of the posts that mention time as a dimension in GR (which does not involve change). Except that you insist it must involve change because (a) you don't understand the concept of a dimension and (b) you believe time involves change.

 

 

Just to disclose where I'm coming from on this - I'm a cognitive psychologist/neuroscientist, not a physicist, and I did my PhD on the subject of disordered time-perception (actually temporal-order perception). So I'm interested in how we perceive time and indeed the direction of causality - but that is not a million miles from the issue as to how we conceive time, I suggest.

 

That is really interesting. I'm sure that can give us some fascinating insights. But into perception not physics.

No need to be harsh, Strange.

 

I apologise if I have come across as abrupt or harsh. Not my intention....

[studiot]

 

Sure, but the equations have c in them, so any diagram of any of the equations is going to have time and space units, isn't it? And while we can express space in terms of light and time, we still need some kind of time unit. So aren't we back to clocks?

 

Yes indeed, which is why I objected to the use of the word 'faster' in some earlier posts.

 

There are quite a few instance of physical quantities that have been introduced to satisfy an observed need, Entropy is another.

 

Unlike entropy for which the need is only apparent in sophisticated systems, the need for time is pretty immediately obvious in very simple ones.

As you say we even have an innate 'sense' of time.

 

However our perceptions also lead us astray when dealing with subtleties.

 

Your description of drawing curves is a description of the parametric equations of a curve and in many maths books you will find the parameter called t, justified by the addended phrase "since t is often time".

[Lizzie L]

 

Thanks for reinforcing my point.

 

Well, no, it doesn't really.

 

All of the posts that mention time as a dimension in GR (which does not involve change). Except that you insist it must involve change because (a) you don't understand the concept of a dimension and (b) you believe time involves change.

 

 

Well, I'm disputing the assertion that because time is a dimension in GR (which I do not dispute) it cannot be is related to the concept of change (which I do). And as far as I am aware, I do understand the concept of a dimension, and I didn't say that time involved change. I said that that it is my position (not my "belief") that only makes sense in relation to change.

 

 

That is really interesting. I'm sure that can give us some fascinating insights. But into perception not physics.

 

Perception and conception. Both are ways in which we model the world. Physics is about modeling the world.

 

 

I apologise if I have come across as abrupt or harsh. Not my intention....

 

 

No problem I have a hide like the proverbial rhino. Or duck maybe.

Edited February 23, 2014 by Lizzie L

[Strange]

 

I said that that it is my position (not my "belief") that only makes sense in relation to change.

 

The thing is, it only makes sense to you in relation to change. That has nothing to do with physics.

 

Perception and conception. Both are ways in which we model the world. Physics is about modeling the world.

 

But these two sorts of models are very different. Your mental model of time requires change. A physical (mathematical) model of time doesn't.

[Lizzie L]

 

The thing is, it only makes sense to you in relation to change. That has nothing to do with physics.

 

Well, I'm not so sure it doesn't. It may not have anything to do with the math, but it has something, I suggest, to do with what the math models.

 

 

But these two sorts of models are very different. Your mental model of time requires change. A physical (mathematical) model of time doesn't.

 

 

I'm saying (or at least suggesting) that the mathematical model of time assumes uses units of time, and that those units of time are defined in terms of something changing.

Edited February 23, 2014 by Lizzie L

[Strange]

 

Well, I'm not so sure it doesn't. It may not have anything to do with the math, but it has something, I suggest, to do with what the math models.

 

The difference is that one's mental model is a purely qualitative thing based on instincts and ideas we have developed through evolution and exposure to the macroscopic, low energy world around us. These mental models are often inadequate for, and bear little relation to, the practical, quantitative models developed by science.

 

 

I'm saying (or at least suggesting) that the mathematical model of time assumes uses units of time, and that those units of time are defined in terms of something changing.

 

They aren't. (But I doubt you will ever accept that because you seem to think your mental model takes precedence over scientific models.

Edited February 23, 2014 by Strange

[Lizzie L]

 

The difference is that one's mental model is a purely qualitative thing based on instincts and ideas we have developed through evolution and exposure to the macroscopic, low energy world around us. These mental models are often inadequate for, and bear little relation to, the practical, quantitative models developed by science.

 

 

"Science" doesn't develop "practical quantitative models", people do. And they are mental models. What else would they be? They are the output of human minds. The cool thing about scientific models is that they can be communicated very precisely, and thus shared.

 

I'm saying (or at least suggesting) that the mathematical model of time assumes uses units of time, and that those units of time are defined in terms of something changing.

 

It doesn't. They aren't.

Well, can you give me an example of a mathematical model of time that doesn't use units of time?

 

They aren't. (But I doubt you will ever accept that because you seem to think your mental model takes precedence over scientific models.

In response to your edit: I don't say that "my" mental model "takes precedence over scientific models". I say that scientific models are the output of minds, and are as much mental models as any model. The special thing about scientific models is that they can be communicated accurately, and shared - and tested against data by independent observers.

I should also just say, as I am new here, that I am not proposing some effete post-modern view of science whereby everything's subjective and one woman's truth is as good as another woman's, even when they are directly contradictory. As I said, I'm a scientist, and having come to science from the humanities, I love the fact that in science what matters is not whether your idea is original or brilliant but whether it's a good fit for the data. Its objectivity, in other words.

 

And the fact that my branch of science is psychology/neuroscience doesn't mean that I'm sloppy about math, nor even mathematically ignorant (although I'm no mathematician!) It doesn't mean I'm sloppy about physics either - I collaborate with physicists all the time, and it's the output from their models that go into mine.

 

Just thought I'd mention that, in case anyone had the idea that psychology was all about potty training and how you feel

Edited February 23, 2014 by Lizzie L

[mooeypoo]

 

I think it's interesting that few people have a problem with the question of "what is length" but want to know what time is. There's a similarity in the difficulty in defining each without using some sort of circular reference, but as we have a visceral notion of length — we can see it — it rarely comes up.

 

The problem with equating time with movement or change is that it assumes a relation but doesn't show it. Does time pass because things change or do things change because time passes? The former is certainly false. We can look at systems that change more or less and measure time passage for each; the amount of change has no effect on the passage of time. One need go no further than time measurement for this. A grandfather clock with a 1m pendulum ticks every other second, and yet time passes at the same rate for it as the atomic clock next to it, "ticking" at 9192631770 times a second. More change, same amount of time. Similar arguments can be made for motion. So, no, the units of time and units of change are not the same.

 

Perhaps the mere existence of change or motion somehow is what permits time to exist. The argument suffers from not being scientific, because you can't remove change or motion from a system in order to test the hypothesis. What we can do is reduce it as much as possible, and we see no effect whatsoever. Time does not pass more slowly for cold things; many modern clocks use exceedingly cold atoms for their measurement, and are state of the art, measuring time even more precisely than devices whose atoms are moving more quickly.

 

This is probably the best explanation to why these sort of discussions about the definition of time (and length) are difficult.

 

 

 

That did remind me, however, of a book I read when I was little, about relativity. The book was meant for kids (I think I was like 9 years old) and so it clearly has its own problems in representing physics properly *but* there's one thing that stuck with me there, and that was a sort of an analogy to the idea that our brains might limit our understanding of reality.

 

So, the book gave an analogy of us looking at this huge rubber sheet that has heavy spheres on it and somewhere in the middle there's a colony of ants who can only see in 2D. We see spheres, and we also see that each sphere makes a little dent in the rubber sheet, so when an ant walks closeby, it "falls" in and has a harder time to climb out. We see why -- but the ants don't, because they don't understand three dimensions. They just notice that there's something "pulling" them towards the circles, and they even make up equations that describe it.

 

Now, I understand this is oversimplified, and I don't by any means intend to present this as an explanation of either relativity or the meaning of time -- *but* this does raise an interesting question. Could it be that time and distance are merely some "reflection" of the actual behavior of the universe, reflections that are created by the way our brains intercepts reality?

 

This would explain how space and time are (strongly) related, and how our entire physical understanding makes sense in mathematical and physical terms -- but also how we might not be able to properly define each of those terms independently.

 

 

 

Does this make any sort of sense?

[Lizzie L]

Does to me

[mooeypoo]

Oh, my, a blast from the past.. here's the book if anyone's interested: http://www.amazon.com/The-Time-Space-Uncle-Albert/dp/0571226159/ (it's a series of books, the one about 2D discussions, if I remember correctly, is book #2 http://www.amazon.com/Black-Holes-Albert-Russell-Stannard/dp/0571226140/ref=pd_bxgy_b_text_y )

 

It's a series, if I remember correctly, and while it's very much watered-down physics, it truly impacted my curiosity to know more as a little girl.

[Lizzie L]

My son loved those!

[mooeypoo]

These books and Star Trek were probably the biggest reason why I have a bachelor's in physics now. Awesome awesome books.

 

(And yes, I'm exposing my deeply ingrained nerdtasticness, but it led to a future in science, so I accept it... )

[michel123456]

 

I think it's interesting that few people have a problem with the question of "what is length" but want to know what time is. There's a similarity in the difficulty in defining each without using some sort of circular reference, but as we have a visceral notion of length — we can see it — it rarely comes up.

(...)

True.

I believe we are mystified by space. We have understood nothing. None of us.

(...) and that was a sort of an analogy to the idea that our brains might limit our understanding of reality.

(...)

I don't think so. We haven't reach the edge of human understanding.

 

(...)

I also tried to discuss the physical reality of, past, present and future but no one took this up.

 

It is a simple exercise in logical observation to show that because we can "see into the past", given the present, that the past has as much physical reality as the present.

(...)

Past, present & future. I need a diagram.

 

All information coming from a distance need time to reach the observer.

So if I put myself (the observer) in the centre of the diagram, all information (radiations, forces, wathever physical) comes from the Past. No information at a distance can reach the observer in zero time: no outside information from the present.

The only thing I can observe in the Present is the thing at zero distance: that's me.

 

So,

_in the Present is me, the observer, and nothing else.

_in the past is everything I can observe at a distance.

_in the future I can observe nothing.

Edited February 23, 2014 by michel123456

[Lizzie L]

OK, so what are the units on the axes

[michel123456]

OK, so what are the units on the axes

So far different units for Time & Space.

Time on the vertical axis in seconds.

Space on the horizontal hyperplane has units of meters.

Scaled so that Speed Of Light can be represented as a line 45 degrees between space & time axis.

[mooeypoo]

 

I don't think so. We haven't reach the edge of human understanding.

Oh, I am not at all talking about human understanding. I'm talking about limitations of our perception. We have a lot of those, even merely on a physical level. That's where things like Paraedolia and optical illusions come from. It's not that we can't understand them, but they are an indication of how our brain is hardwired.

 

The fact is that since we know that our brain is hardwired to "trick" us sometimes (again, optical illusions are an example) we take an extra step to understand how to analyze, interpret and explain those in light of objective reality.

 

My point is that perhaps we need to do the same about the concept of time and space.

[michel123456]

What we have for sure is this:

 

What we call "physical reality" is inside the past light cone.

All the rest, especially the so-called "Present" is knowable through duration. As time passes by, the observer translates higher on the time axis (he moves up) and operates a "scanning" of the world around him.

Edited February 23, 2014 by michel123456

[mooeypoo]

That's an interpretation, though, isn't it? It is a working valid interpretation, but if you ask for a definitive definition of time, it's a bit problematic.

[Lizzie L]

So far different units for Time & Space.

Time on the vertical axis in seconds.

Space on the horizontal hyperplane has units of meters.

Scaled so that Speed Of Light can be represented as a line 45 degrees between space & time axis.

 

OK, cool. So if we have time in seconds on the vertical axis we have space in light-seconds on the horizontal axes, right?

 

So how are we defining "seconds"?

 

9,192,631,770 periods of radiation between the hyperfine levels of cesium 133?

[michel123456]

That's an interpretation, though, isn't it? It is a working valid interpretation, but if you ask for a definitive definition of time, it's a bit problematic.

It is not a definition of time, that part has been abandonned. It is "working" with time as we (don't) know it

[mooeypoo]

Well, in that aspect, that's the point of all sciences -- find a way to describe objective reality as objectively and functionally as we can.

Which is also why these explanations tend to continuously evolve.

[michel123456]

 

OK, cool. So if we have time in seconds on the vertical axis we have space in light-seconds on the horizontal axes, right?

 

So how are we defining "seconds"?

 

9,192,631,770 periods of radiation between the hyperfine levels of cesium 133?

If you wish. The diagram is not intended to provide a definition of time. It is intended to get a grasp on the concepts of Past present Future.

The weird thing on this graph is the following:

if the Past light Cone is observable, why am I not able to directly observe myself in my own past?

Edited February 23, 2014 by michel123456

[mooeypoo]

If you wish. The diagram is not intended to provide a definition of time. It is intended to get a grasp on the concepts of Past present Future.

The weird thing on this graph is the following:

if the Past light Cone is observable, why am I not able to directly observe myself in my own past?

 

You absolutely are. When you look at your feet, you see them the way they were a split-split-split second before, because of the time it takes light to travel from your feet and to your eyes.

 

Which raises yet another interesting question: The way we observe time clearly depends on what we're looking at (which is the point of relativity) -- but it "changes" the rules of the game of observation:

 

When we look at the world close to us, we technically see the present but not the future or past

When we look at the sky, we see the past and are unable to see the present or future.

When we look at rotating galaxies, we see some starts more farther into the past as some others, which means we have a distorted view not only of space, but of time as well.

 

That cone is a way to make sense of something I don't quite think we are hardwired to make complete sense of.

[Lizzie L]

If you wish. The diagram is not intended to provide a definition of time. It is intended to get a grasp on the concepts of Past present Future.

 

Fair enough. But it does, doesn't it? I mean it shows quite clearly, I'd say, that "the math" isn't unit-free - it's based on an intrinsic definition of time that relates to some kind of clock.

 

 

The weird thing on this graph is the following:

if the Past light Cone is observable, why am I not able to directly observe myself in my own past?

 

 

Because you are standing in your own shadow