Clocks and rulers

[swansont]

Only the observed object is in the now isn't it? All observers see it in the past, whatever the distance.

 

 

"Now" isn't all that well defined. Which is why we typically use time-tagged measurements in such discussions. Everyone in a single frame has a solid grasp on the when of something, because you can synchronize your clocks. Between frames, of course, all bets are off.

[StringJunky]

 

 

"Now" isn't all that well defined. Which is why we typically use time-tagged measurements in such discussions. Everyone in a single frame has a solid grasp on the when of something, because you can synchronize your clocks. Between frames, of course, all bets are off.

Right. I was thinking in that post of the finite time it takes for light from an an event or object o reach an observer, so based on that, they can never be in the now of that event regardless of the distance.

[Delta1212]

(Hijacking again)

So. The situation is: we have a ruler, we send it to space and while traveling we are measuring it changing length, then upon coming back in our frame we are measuring that miraculously it has recovered its dimensions.

And if there were an astronaut with the ruler at hand all the time, we could even get a signed testimony that the ruler didn't change during the travel.

What makes us believe that the ruler did change at all and that it was not simply a kind of observational paramorphosis?

The ruler didn't change. It is always 1 foot in its rest frame and always 10 inches in a frame in which it is length contracted to 10 inches and 6 inches in a frame in which it is length contracted to 6 inches.

 

You can shift which frame it is each of these corresponding lengths in by changing its velocity, but it is always all of those lengths. The length of the ruler never changes. Only the relative speed at which you will measure a given length changes.

[michel123456]

The ruler didn't change. It is always 1 foot in its rest frame and always 10 inches in a frame in which it is length contracted to 10 inches and 6 inches in a frame in which it is length contracted to 6 inches.

 

You can shift which frame it is each of these corresponding lengths in by changing its velocity, but it is always all of those lengths. The length of the ruler never changes. Only the relative speed at which you will measure a given length changes.

Then i must have misunderstood Swansont post

 

 

We can do the same thing with a clock. And have done it under slightly different circumstances. Even though the clock didn't change according to the persons traveling with it, it comes back with a different amount of accumulated time. That's why we're confident it would happen with length, too, if we could measure length and distance as precisely.

What does that mean? That the ruler has changed after returning?

[swansont]

What does that mean? That the ruler has changed after returning?

The length of the ruler depends on who is doing the measuring.

 

There is no "change", as such. There is no inherent length; it's not an invariant quantity.

[StringJunky]

The length of the ruler depends on who is doing the measuring.

 

There is no "change", as such. There is no inherent length; it's not an invariant quantity.

But does the ruler negatively or positively accumulate length, like a clock, after it's travelled? Even a teeny, tiny bit; it's just that the instruments aren't accurate enough? This was the essence of my question.

Edited July 30, 2016 by StringJunky

[swansont]

But does the ruler negatively or positively accumulate length, like a clock, after it's travelled? Even a teeny, tiny bit; it's just that the instruments aren't accurate enough? This was the essence of my question.

A ruler doesn't accumulate length. As Endy noted, an odometer would be the proper instrument for comparison. The length of a ruler, like the frequency of a clock, depends on the observer. The value will be the same when it returns to the original frame

[studiot]

Space and time are different.

They behave differently classically, so why should you expect them to behave the same relativistically?

 

I gave an example of time accumulation following dilation, but not space accumulation following dilatation by classical means in my post 19, but no one has thought to comment.

[J.C.MacSwell]

Space and time are different.

They behave differently classically, so why should you expect them to behave the same relativistically?

 

I gave an example of time accumulation following dilation, but not space accumulation following dilatation by classical means in my post 19, but no one has thought to comment.

It wasn't time accumulation. It was instrument error.

 

Edit: OK you could debatably have a relativistic effect.

Edited July 30, 2016 by J.C.MacSwell

[studiot]

It wasn't time accumulation. It was instrument error.

 

Edit: OK you could debatably have a relativistic effect.

 

 

Please explain

 

An uncompensated clock runs more slowly in the presence of a gravitational field. (relativity)

 

An uncompensated clock runs more slowly in the presence of a thermal 'field' (classic)

 

Is there a difference?

[swansont]

Space and time are different.

They behave differently classically, so why should you expect them to behave the same relativistically?

 

I gave an example of time accumulation following dilation, but not space accumulation following dilatation by classical means in my post 19, but no one has thought to comment.

Heating a ruler or pendulum and causing it to expand is not an example of relativity. Physical changes in the instrument

Please explain

 

An uncompensated clock runs more slowly in the presence of a gravitational field. (relativity)

 

An uncompensated clock runs more slowly in the presence of a thermal 'field' (classic)

 

Is there a difference?

Yes. As above. Time doesn't run faster or slower because you physically alter a clock.

[Endy0816]

I think people confuse how many times the clock has ticked with the tick itself. See similar confusion trying to explain its role in circuits.

Edited July 31, 2016 by Endy0816

[michel123456]

The length of the ruler depends on who is doing the measuring.

 

There is no "change", as such. There is no inherent length; it's not an invariant quantity.

This is outrageous wrong.

Again you are putting the observer above reality. It cannot be that way. just because you are measuring something does not say that the thing IS that way.

As I said before, the observer has no power to change reality.

Except when he does, in a lab.

[Strange]

Again you are putting the observer above reality. It cannot be that way. just because you are measuring something does not say that the thing IS that way.

 

 

How can you know what reality is other than what you measure?

 

Are you planning to hijack every thread with your inability to understand?

[studiot]

 

Heating a ruler or pendulum and causing it to expand is not an example of relativity.

 

Disappointing.

 

You are completely missing my point.

 

 

I did not say that is was an example of relativity.

 

In fact I definitely stated and repeated that it was not.

 

So why contest?

 

Chemical wear and degradation is not an example of mechanical wear , but the effect is very similar.

 

This is the point I was making.

 

This is following in the footsteps of Bertrand Russell's delightful book on relativity in which he is fond positing that we should not be so surprised/frightened about the effects of einstinian relativity as other, more familiar, mechanisms can have similar effects.

 

 

michel12345

Again you are putting the observer above reality. It cannot be that way. just because you are measuring something does not say that the thing IS that way.

Strange

Are you planning to hijack every thread with your inability to understand?

 

Instead of attacking, why not try to help another understand?

 

Michel,

 

Following my theme to swansont here is another example of non relativistic observer dependence.

 

An observer has a field of vision, say x by y units or xy square units.

 

Let us suppose he wishes to place a fig leaf to cover the bottom half of his field.

 

We both know that the required minimum size of the fig leaf depends upon its distance from the observer.

This is because distant objects appear smaller to an observer.

 

This example is a bit artificial, but computer programmers do exactly this when constructing onscreen CGI.

 

PS I've got your six,

you get it back when you respond.

Edited July 31, 2016 by studiot

[michel123456]

 

 

How can you know what reality is other than what you measure?

 

Are you planning to hijack every thread with your inability to understand?

You cannot know what reality is.

Saying that reality IS what you measure is wrong.

The best way to know what reality is about is the get closer to it the much possible. The farther you are, the more elusive it gets.

but putting measurement ABOVE reality is wrong. the observer is constating (I'd like to translate this more properly) phenomenas. the observer has no power on reality (except when he makes an experiment in a lab).

 

 

 

 

----------

And you still believe that I don't understand.

Edited July 31, 2016 by michel123456

[blue89]

Good question!

 

 

 

 

not so much good question in my mind.

be sure ,intimately I had thought just this question many many years ago. and now I think that this question will not provide us so much information. (as exepcted)

but of course ,it is not bad question according to scientific reseraches/perspectives. I only mean it contains too many defficiciencies if the author make its consistency of information only as the content of the theread.

Edited July 31, 2016 by blue89

[swansont]

This is outrageous wrong.

Again you are putting the observer above reality. It cannot be that way. just because you are measuring something does not say that the thing IS that way.

As I said before, the observer has no power to change reality.

Except when he does, in a lab.

 

 

No, it's relativity, which has been shown to be correct to a fairly precise level. Insisting on something and then ignoring the evidence that contradicts your view is not a very persuasive argument.

You cannot know what reality is.

Saying that reality IS what you measure is wrong.

 

 

That's not what Strange said, though. The bit you quoted asked how you can determine reality, other than by what you measure. Because you can't know what reality is. So we go with the next best thing, which is observation. That's something we can know. So we treat that as reality, since it's pointless (from a physics standpoint) to do otherwise.

 

Disappointing.

 

You are completely missing my point.

 

 

I did not say that is was an example of relativity.

 

In fact I definitely stated and repeated that it was not.

 

So why contest?

 

Chemical wear and degradation is not an example of mechanical wear , but the effect is very similar.

 

This is the point I was making.

 

This is following in the footsteps of Bertrand Russell's delightful book on relativity in which he is fond positing that we should not be so surprised/frightened about the effects of einstinian relativity as other, more familiar, mechanisms can have similar effects.

 

 

IMHO that view is misguided; I don't see the relevance. It feeds the common misconception that relativity is a mechanical effect.

[michel123456]

 

 

No, it's relativity, which has been shown to be correct to a fairly precise level. Insisting on something and then ignoring the evidence that contradicts your view is not a very persuasive argument.

 

 

That's not what Strange said, though. The bit you quoted asked how you can determine reality, other than by what you measure. Because you can't know what reality is. So we go with the next best thing, which is observation. That's something we can know. So we treat that as reality, since it's pointless (from a physics standpoint) to do otherwise.

 

 

IMHO that view is misguided; I don't see the relevance. It feeds the common misconception that relativity is a mechanical effect.

Yes Relativity has been shown to be correct to a fairly precise level. There is no discussion about that.

 

But No, this is not what Relativity says.

Relativity says that what is observed in a frame can be translated in what is observed in another frame. That is all.

What more than that you believe it says, for example that what one observer IS "truly" happening, is not part of the equations of Relativity.

[StringJunky]

The best way to know what reality is about is the get closer to it the much possible. The farther you are, the more elusive it gets.

If you get too close you may not see the wood for the trees, which might be your problem.

[J.C.MacSwell]

 

 

Please explain

 

An uncompensated clock runs more slowly in the presence of a gravitational field. (relativity)

 

An uncompensated clock runs more slowly in the presence of a thermal 'field' (classic)

 

Is there a difference?

The difference is that time itself runs more slowly in the first case. The clock is working fine and is in no need of compensation. This is accepted and in accordance with GR. The other is an instrument error, a lack of accuracy due to a mechanical effect. This clock needs adjustment.

Edited July 31, 2016 by J.C.MacSwell

[studiot]

The difference is that time itself runs more slowly in the first case. The clock is working fine and is in no need of compensation. This is accepted and in accordance with GR. The other is an instrument error, a lack of accuracy due to a mechanical effect. This clock needs adjustment.

 

Thank you for your reply, that is pretty much what I thought you would say.

 

Now suppose the observer with the watch and standard rule slept whilst the changes occurred.

 

When he awoke he would have an unsynchronised watch and clock and a displaced ruler that still matched his standard.

 

How would he be able to tell whether the effect was due to relativity or heating and cooling?

 

In other words, the result or product of the process is the same, at least for the clocks.

 

 

IMHO there is too much attention paid to process and not enough to product these days.

 

Note my other examples in post40 about chemical v mechanical degradation and points of view v relativity.

[J.C.MacSwell]

 

 

Thank you for your reply, that is pretty much what I thought you would say.

 

Now suppose the observer with the watch and standard rule slept whilst the changes occurred.

 

When he awoke he would have an unsynchronised watch and clock and a displaced ruler that still matched his standard.

 

How would he be able to tell whether the effect was due to relativity or heating and cooling?

 

In other words, the result or product of the process is the same, at least for the clocks.

 

 

IMHO there is too much attention paid to process and not enough to product these days.

 

Note my other examples in post40 about chemical v mechanical degradation and points of view v relativity.

 

Without significant relativistic effects. and adequately precise measurements of them, you cannot tell.

[Delta1212]

You cannot know what reality is.

Saying that reality IS what you measure is wrong.

 

And yet you are insisting that one specific measurement really represents reality over all others.

[StringJunky]

You cannot know what reality is.

No we can't know, completely.

 

Saying that reality IS what you measure is wrong.

With measurements, it's the closest scientists can get to describing reality.