Basic understanding of time

[studiot]

 

Units might help. Spatial dimensions are measure in units of length. What are temporal dimensions measured in units of?

 

 

+1 a very perceptive statement.

 

Especially when you consider the metric involved.

[Schneibster]

Forgive me for not understanding how a transformation of something is used to define that something.

 

I always understood a transformation involved changing something into something else.

 

So for instance how would the transformation

[math]x \to {x^2}[/math]

help me define x?

 

It's all the definition we have; it's a postulate of relativity: the spacetime continuum.

 

[math]x \to {x^2}[/math]

BTW does not require or define a spacetime continuum. Surely you didn't intend to claim it does.

 

http://casa.colorado.edu/~ajsh/sr/postulate.html

 

Not only that but you do realize that you just substituted x for x, y, z, and t, right? Geometry no workie like that.

 

Units might help. Spatial dimensions are measure in units of length. What are temporal dimensions measured in units of?

 

Light seconds.

 

And that's amusing, but it's not a joke. We are hurtling through time at an unstoppable rate of the speed of light, and we can't ever stop it, we can only slow it down relative to the rest of the universe at best. And that's only by going as fast as we can.

Edited February 23, 2014 by Schneibster

[Strange]

Units might help. Spatial dimensions are measure in units of length. What are temporal dimensions measured in units of?

 

Units are irrelevant.

 

But obviously the temporal dimension is measured in units of time. What does that tell you? Nothing.

Edited February 23, 2014 by Strange

[Schneibster]

 

Units are irrelevant.

 

But obviously the temporal dimension is measured in units of time. What does that tell you? Nothing.

 

Actually, since you can convert time and space into each other, it's obvious that when a second of time is converted into space, it's a light-second long. There's a mirror assertion that goes the other way, too, that a light-second must be equivalent to a second of time.

[Strange]

 

Actually, since you can convert time and space into each other, it's obvious that when a second of time is converted into space, it's a light-second long. There's a mirror assertion that goes the other way, too, that a light-second must be equivalent to a second of time.

 

Quite. But I really didn't think the question deserved serious consideration.

 

Although, on second thoughts, your explanation makes it clearer that they are equivalent as dimensions.

Edited February 23, 2014 by Strange

[Schneibster]

To be precise 2.997925x10⁸ m. (Unless someone did a better measurement of c since my admittedly old reference.)

 

Quite. But I really didn't think the question deserved serious consideration.

 

Mmmm, maybe- but that appears to be a matter of taste.

 

Actually it seems quite important in defining how a function works to push it around with extreme values and see what it does, to me.

[Lizzie L]

 

Units are irrelevant.

 

Irrelevant to what?

 

But obviously the temporal dimension is measured in units of time. What does that tell you? Nothing.

 

 

Well, that's my question. I'm suggesting that units time are units of change. And that units of length are units of how many changes will happen between light leaving one place and arriving at the next

[Strange]

To be precise 2.997925x10⁸ m. (Unless someone did a better measurement of c since my admittedly old reference.)

 

The meter is now defined as the distance travelled by light in 1/299,792,458 second.

 

Well, that's my question. I'm suggesting that units time are units of change. And that units of length are units of how many changes will happen between light leaving one place and arriving at the next

 

So we are back to begging the question: "I am going to say that units of time are units of change and therefore time is defined as change".

 

That isn't how dimensions are defined, nor the units used to measure those dimensions.

Edited February 23, 2014 by Strange

[Lizzie L]

Well, how are they defined? You've defined length in terms of time, but how do you define a second? The only way I know is by a clock of some kind - i.e. something that changes.

[studiot]

 

It's all the definition we have; it's a postulate of relativity: the spacetime continuum.

 

BTW does not require or define a spacetime continuum. Surely you didn't intend to claim it does.

 

What did I say that in any way suggested I intended the above function to require or define a spacetime continuum?

 

x is a general variable and x squared was an example function.

 

If you prefer I can rewrite it as

[math]\xi [/math][math] \to [/math][math]f(\xi )[/math]

 

You are still missing the point that you cannot legitmately use time in the definition of time so properties like 'faster' are excluded because they require a definition of time to be able to make a speed comparison

.

As regards to spacetime, I did not ever refer to spacetime since the OP asked specifically about time.

 

Your link offers the fundamental postulate of the existance of a spacetime continuum and then goes on to develop a number of properties.

 

But

 

It uses a further number of hidden assumptions (as does Euclid) and it is drawn in Euclidian geometry.

Do you know what those assumptions are?

Edited February 23, 2014 by studiot

[Endercreeper01]

Well, how are they defined? You've defined length in terms of time, but how do you define a second? The only way I know is by a clock of some kind - i.e. something that changes.

A second is defined as 9,192,631,770 periods of radiation between the hyperfine levels of cesium 133.

Edited February 23, 2014 by Endercreeper01

[Strange]

Well, how are they defined? You've defined length in terms of time, but how do you define a second? The only way I know is by a clock of some kind - i.e. something that changes.

 

And now you are back to man made units to prop up your belief.

 

In GR, time and space are dimensions of a four dimensional pseudo-Riemannian manifold. Change is not involved.

[Schneibster]

 

In GR, time and space are dimensions of a four dimensional pseudo-Riemannian manifold.

 

Yep. That's the derivation of the Lorentz transform.

 

It's a postulate of relativity. This is one of the Four Big Assumptions relativity is based on. "Space and time form a four dimensional continuum." It's called "The Continuum Postulate."

Edited February 23, 2014 by Schneibster

[Strange]

It's a postulate of relativity. This is one of the Four Big Assumptions relativity is based on. "Space and time form a four dimensional continuum." It's called "The Continuum Postulate."

 

I was only aware of two postulates: the principle of relativity, and the invariance of c.

[Schneibster]

http://casa.colorado.edu/~ajsh/sr/postulate.html

 

This is not the first time I have posted this here. It's also in post 102.

 

There are four:

 

1. The spacetime continuum.

2. The existence of globally inertial frames.

3. The measured constancy of the speed of light.

4. The principle of special relativity, "The results of physics experiments are the same in all inertial frames."

Edited February 23, 2014 by Schneibster

[Schneibster]

So as you can see, it's not an aspect of the "temporal dimensions"; instead, the "hyperbola" comes (in some sense) from the interaction between the temporal and spatial dimensions. Between two temporal dimensions, you would still get a "circle".

 

I missed this cool fact and would like to go back and highlight it because it's cool. It's the relation between a dimension and space dimensions that makes it a time dimension, not the character of the dimension itself. A dimension is just a dimension. It's its relations to the space dimensions that make it temporal or spatial (and if string theory is right there are some other states too).

[studiot]

 

uncool, on 22 Feb 2014 - 11:57 PM, said:

So as you can see, it's not an aspect of the "temporal dimensions"; instead, the "hyperbola" comes (in some sense) from the interaction between the temporal and spatial dimensions. Between two temporal dimensions, you would still get a "circle".

 

I missed this cool fact and would like to go back and highlight it because it's cool. It's the relation between a dimension and space dimensions that makes it a time dimension, not the character of the dimension itself. A dimension is just a dimension. It's its relations to the space dimensions that make it temporal or spatial (and if string theory is right there are some other states too).

 

 

+1 for actually listening to someone else. It makes for a better quality discussion.

[michel123456]

 

I missed this cool fact and would like to go back and highlight it because it's cool. It's the relation between a dimension and space dimensions that makes it a time dimension, not the character of the dimension itself. A dimension is just a dimension. It's its relations to the space dimensions that make it temporal or spatial (and if string theory is right there are some other states too).

 

 

Relativity tells us that Space & Time form a continuuum, IOW that Space & Time are 2 sides of a same thing.

If Space can be rotated in time, and reversely, and if as you say "It's its relations to the space dimensions that make it temporal or spatial",

doesn't that mean that, in the end, Time and Space are exactly the same thing.

 

IOW it means that when I look at an object at a specific distance, I look at an object at a specific time. Which is exactly what happens.

[Lizzie L]

 

And now you are back to man made units to prop up your belief.

 

In GR, time and space are dimensions of a four dimensional pseudo-Riemannian manifold. Change is not involved.

 

Well, I'm not trying to prop up any "belief" - and I don't doubt that in GR time and space are dimensions of a four dimension pseudo-Riemannian manifold. Or at least I don't have the expertise with which to doubt it. But GR is a model of reality, and I'd like to know what is being plotted on the time axis. Once I know that, I also know what is being plotted on the spatial axes, because I can define it in terms of how far light can travel in some time unit.

 

And my more philosophical point, I guess, is that our models are, obviously "man made", we exist in a world that changes, and we have clocks based on changing things, whether it is a rotating planet, a swinging pendulum or periods of radiation between the hyperfine levels of cesium 133.

 

So, so far, I remain unpersuaded that the OP is wrong, except that I would substitute the more general world "change".

 

But it's not a "belief"! It's just something that I shall continue to regard provisionally as true until someone persuades me otherwise

[Strange]

 

But it's not a "belief"! It's just something that I shall continue to regard provisionally as true until someone persuades me otherwise

 

And like all who hold this belief you will continue to dismiss all evidence that contradicts it. (Which is all you have done up to know.)

 

This is why it is quasi-religious: no evidence for it; dismiss all evidence against it. Why are you posting on a science forum.

[michel123456]

No need to be harsh, Strange.

 

Permutating the word "change" with "time" does not shed light on the understanding of Time IMHO.

 

And you should admit that the 4 dimensional spacetime that drives to the concept of a static universe is not clearly understandable when comparing with everyday experience.

[Lizzie L]

 

And like all who hold this belief you will continue to dismiss all evidence that contradicts it. (Which is all you have done up to know.)

 

 

I haven't seen any evidence presented on this forum that contradicts it. Can you cite where you think there was some?

 

 

This is why it is quasi-religious: no evidence for it; dismiss all evidence against it. Why are you posting on a science forum.

 

 

Well, I don't think that characterises my position - and I think your evidence to support the hypothesis that it does is weak

 

As for your last - because I like science. I'm even a scientist.

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.

[studiot]

 

Lizzie L

and I'd like to know what is being plotted on the time axis.

 

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.

 

 

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.

 

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.

 

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.

 

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.

Edited February 23, 2014 by studiot

[swansont]

I'm suggesting that units time are units of change.

 

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.

[PeterJ]

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. .