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Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Harri on 07/12/2018 22:47:18

Title: What does the term 'time' relate to in time dilation?
Post by: Harri on 07/12/2018 22:47:18
In general, a clock runs slower on the surface of the earth than it does higher and further away from the earth. Is it accurate also to say that 'time' runs slower nearer the surface of the earth and faster further away? Doesn't this depend on an agreed definition of 'time' ?

If I said time is the measured rate of 'change' then does change happen much slower away from the force of gravity throughout the whole universe?
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Colin2B on 07/12/2018 22:59:48
For a person next to a clock on the surface of the earth time appears to run at the rate we all experience. This is also true of someone far away from the influence of earth’s gravitational field, time passes normally.
However, if the person on earth views the clock next to the person in deep space they would say it is running faster, whereas the person in deep space would say that the clock on earth is running slower. This is true for all clocks* including our body clock and aging processes, also chemical reactions and nuclear decay.

* note some clocks eg those with pendulums don’t work without a gravitational field so can’t be used for this.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: evan_au on 09/12/2018 10:32:59
In developing his theories, Einstein ran many thought experiments on relativity and time dilation.

After developing his theories, he used thought experiments to illustrate them.

Illustrations about time often referred to a clock which is next to an observer (ie stationary, in the observer's frame of reference, and at the same level in a gravitational field). This observer is then able to observe clocks that are moving relative to himself, or clocks that are at different levels in a gravitational field (or both).

Today, with accurate atomic clocks, we can do these experiments and measure the results.
- Every time you use GPS to find your destination or track your position on a map, this uses Einstein's equations to calculate the right rate of the atomic clocks in orbit (which is different from those same atomic clocks, sitting on the ground before they were launched).
- Some of the most accurate atomic clocks can detect a difference in elevation of 1 foot (30cm), due to the different time dilation.
- If we could put an atomic clock outside the Solar System (away from the Sun's gravitational well), the time difference would be more extreme
- If we could put an atomic clock outside our galaxy, the time difference would be even more extreme
- We have no way of traveling outside the galaxy (or communicating with a space probe outside the galaxy) with today's technology. But physicists expect that Einstein's predictions would hold to a high degree of accuracy.
- My observation is that it is a brave physicist who bets against Einstein (except when it comes close to a black hole - Einstein knew that he didn't have a solution there)

See: https://en.wikipedia.org/wiki/Einstein_synchronisation
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 09/12/2018 15:17:45
A “timely” thought experiment

“In a galaxy far away”, there exists a star identical to our sun, with an identical “solar system”.
Earth is planet A with physicist A (PA) and clock A (CA).
Earth’s twin is planet B with physicist B (PB) and clock B (CB).
Each physicist can see his own clock and the other’s with no time delay for information transfer.

Three assumptions:

1.  PA and PB each sees time passing at 1 sec per sec on his own clock.

2.  Each physicist sees the rate of time on the other’s clock as unaffected by gravity.

3.  Any difference between the perception of the rate of time between CA and CB, observed by either physicist, will be due to the degree of relative motion between the two galaxies; or relative motion resulting from differential motion within the individual galaxies.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 09/12/2018 17:43:30
A “timely” thought experiment

“In a galaxy far away”, there exists a star identical to our sun, with an identical “solar system”.
Earth is planet A with physicist A (PA) and clock A (CA).
Earth’s twin is planet B with physicist B (PB) and clock B (CB).
Each physicist can see his own clock and the other’s with no time delay for information transfer.
This last one is unrealistic unless both clocks are stationary relative to each other, in which case both clocks will run at the same pace in any frame.

If they're moving apart as distant things tend to do, then each clock will run slower in the frame of the other, but they will appear to run even slower than that due to Doppler effect.  That Doppler effect is why is it unrealistic to assume no delay in looking at each other's clocks.

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2.  Each physicist sees the rate of time on the other’s clock as unaffected by gravity.
No.  If there was another clock in the same frame as the distant clock but not as deep in a gravity-well such as these planet-bound physicists, the clocks on any planet would appear to run slower.  Hence they all appear to be affected by gravity, but equally since both CA and CB are in similar gravity wells.

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3.  Any difference between the perception of the rate of time between CA and CB, observed by either physicist, will be due to the degree of relative motion between the two galaxies; or relative motion resulting from differential motion within the individual galaxies.
Yes.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 10/12/2018 00:05:31
Thanks, Halc.  I put that post together in a hurry without due thought for the possibilities for misinterpretation.

Quote from: Bill
Each physicist can see his own clock and the other’s with no time delay for information transfer.

This was badly expressed and invited your response.  I was thinking of two clocks, in different galaxies, experiencing an identical gravitational situation, and thinking that, by reason of gravity alone, the clocks would be seen to tick at the same rate, were it possible for their rate to be compared without any influence other than gravity.  (I’m not sure that’s any better).   

Quote from: Halc
.  Hence they all appear to be affected by gravity, but equally since both CA and CB are in similar gravity. wells.

Rather than “unaffected by gravity”; I should have said “affected equally by gravity”.  Essentially, that’s what I was trying to get at.
Quote from: Halc
Yes

Sigh of relief!  :)
Title: Re: What does the term 'time' relate to in time dilation?
Post by: set fair on 10/12/2018 02:27:27
For the purposes of the OP's question we can say clocks measure rates of change. A quartz crystal on earth would appear to vibrate more slowly if an astronaut could observe it from the space station. And the astronaut would see a quartz clock on earth running slower than a quartz clock on the space station.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 10/12/2018 11:56:16
Hi, Set fair; it's always good to look back to the OP when thread drift has moved the discussion away. Mea culpa :)

Quote from: Harri
If I said time is the measured rate of 'change' then does change happen much slower away from the force of gravity throughout the whole universe?

My “layman” thought is that time is, as you suggest, a measure of rate of change. It becomes convenient to talk of changes in the rate of time’s flow, or of the rate of our passage through time, and to treat time as though it were an entity with existence that was independent of the things being measured and those doing the measuring; which may not be the case.  It certainly streamlines scientific thought and discussion. 

Thinking along those lines suggests that change does happen at different rates in different gravitational situations; however, reference frames and observer dependence must not be overlooked.

Title: Re: What does the term 'time' relate to in time dilation?
Post by: Colin2B on 10/12/2018 14:21:27
It becomes convenient to talk of changes in the rate of time’s flow, or of the rate of our passage through time, and to treat time as though it were an entity with existence that was independent of the things being measured and those doing the measuring; which may not be the case.  It certainly streamlines scientific thought and discussion. 
The problem with using ‘rate of change’ or ‘rate of time’s flow’, is that it implies measurement against time, or that there is another deeper time flow. That’s why the clock ticks are usually used; you count the clock ticks in your frame using your time standard.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 10/12/2018 14:47:55
Quote from: Colin
The problem with using ‘rate of change’ or ‘rate of time’s flow’, is that it implies measurement against time, or that there is another deeper time flow. That’s why the clock ticks are usually used; you count the clock ticks in your frame using your time standard.

Rate of change is measured using time; why does this involve a deeper time flow?
Wouldn’t a deeper time be necessary only if time is considered as a separate entity?
Title: Re: What does the term 'time' relate to in time dilation?
Post by: alancalverd on 10/12/2018 16:30:40
Time is what separates sequential events. If we build an atomic clock, we know that the separation between sequential events is absolutely fixed by the nature of the internal fields of the atoms.

Now we place the clocks in different gravitational potentials. Each appears to run at a different rate from the point of view of the other. The difference is calculable and experimentally verifiable.

Any further discussion rapidly becomes philosophical or metaphysical and therefore pointless intellectual vanity, by definiton.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Colin2B on 10/12/2018 17:53:31
Rate of change is measured using time;
Exactly, but what time?
Best to keep things simple as @alancalverd suggests. That's why counting the clock ticks in a different frame from your own timed against your own std clock avoids the philosophical discussion on whether 'rate of time' exists or whether the 'rate of passage through time' has meaning.. Relative to you their clock is either faster or slower, whether those clocks are atomic, chemical or biological.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 10/12/2018 18:11:07
Alan, as usual, a neat explanation, with which I have, essentially, no problem, but as a “certified and practicing” nit-picker, I have to ask about “Time is what separates sequential events.” If that is “pointless intellectual vanity”, so be it.  Julian Barbour would probably disagree.

If time separates sequential events, does this mean that something exists between events that is not, in itself an event, and that that something is time?  (Smolin)
Alternatively, does it mean that our perception of time allows us to distinguish as sequential events something that is essentially continuous? (Barbour)
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Colin2B on 10/12/2018 19:23:32
If time separates sequential events, does this mean that something exists between events that is not, in itself an event, and that that something is time?  (Smolin)
Alternatively, does it mean that our perception of time allows us to distinguish as sequential events something that is essentially continuous? (Barbour)
Sequential = following in a logical order or sequence

Let’s say you are born, then you die. Those are sequential events. Hopefully they are separated by as much time as possible.
Read the above quotes in the light of those 2 events.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Harri on 10/12/2018 20:28:42
And talking of death! If I die and no longer observe time passing and experience change no longer, does time still exist?
Title: Re: What does the term 'time' relate to in time dilation?
Post by: alancalverd on 10/12/2018 21:12:40
The bit between birth and death is called life. You can count  the clock ticks if you like, but generally the earth goes round the sun between 50 and 100 times. History suggests that this sequential and repetitive event is not affected by the death of anyone.


Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 10/12/2018 22:35:57
Quote from: Harri
And talking of death! If I die and no longer observe time passing and experience change no longer, does time still exist?

Yes, otherwise your body would not decompose.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Colin2B on 10/12/2018 23:24:16
You can count  the clock ticks if you like,
There is probably a meditation method somewhere that suggests this

And talking of death! If I die and no longer observe time passing and experience change no longer, does time still exist?
Well, you certainly won’t experience it (other religious theories are available), but there is no reason to believe that it doesn’t.
To suggest otherwise implies you are the only person in existence and everything is in your imagination.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Harri on 11/12/2018 16:46:16
I am the only person in existence and everything is in my imagination!? I'm not sure why, but I find that quite interesting.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: yor_on on 11/12/2018 17:18:06
Depends on definitions Ham.

Time dilation is a measure done from your local clock. That clock also contain your life expectancy. Relative other 'frames of reference' aka 'the universe' you might to seem aging 'slower' or 'faster', and actually you can do both of them 'simultaneously', just by changing reference frame, but relative your own wrist watch, you won't.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: yor_on on 11/12/2018 17:40:06
You first need to understand one thing. There is no standard for what is a 'universal time'. It doesn't exist. What you use is your wrist watch, that is what defines time dilation's when you compare it to other 'frames of reference'. It doesn't really matter where you are for this. Your clock will always be equivalent your life expectancy.

The rest of it is a question of how you look at the universe. From what I call a 'global view' it's 'oberver dependent' aka comparing your clock to others. From a local point of view, aka, your life expectancy relative your wrist watch, it never changes. This is loosely speaking though. From a scaling point of view there should be differences relative for example standing up relative laying down. aka the Nist experiments. But frames of reference is a abstract idea, as much as anything else you will meet in physics or for that sake 'real life'.

Just take 'money'
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 11/12/2018 21:18:29
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Read the above quotes in the light of those 2 events.

That’s about where I started.  These two events, in My case, are separated by a lot of years, each of which constitutes a sequence of events. So I looked at events that were closer together, and wondered if a point could be reached where there could be said to be nothing between two events.  Would they then have to become one event?  That didn’t make sense.  I felt it must be possible to have two events that were contiguous, but were still distinct, but in that case, what separated them?
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 11/12/2018 21:29:22
Quote from: Colin
There is probably a meditation method somewhere that suggests this
Perhaps Fred Alan Wolf could find us a yogi who could help.

Quote from: Harri
  I am the only person in existence and everything is in my imagination!? I'm not sure why, but I find that quite interesting.
Have you read Edwin Abbot’s “Flatland”?  His description of the occupant of “Pointland” might make you wonder how interesting it would be. :)
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Colin2B on 11/12/2018 22:50:30
So I looked at events that were closer together, and wondered if a point could be reached where there could be said to be nothing between two events.  Would they then have to become one event? 
Not if they are separated by distance.
Also you need to think what you mean by an event, what causes you to think of events as separate.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 12/12/2018 01:02:40
I am the only person in existence and everything is in my imagination!? I'm not sure why, but I find that quite interesting.
Wrong forum to go into it in detail, but the view is called philosophical idealism: the idea that what is experienced defines existence.  No experience, no existence, so the universe ceases to be if you do.  It leads to solipsism (only I exist).
The opposite is realism:  There is a reality independent of experence.
I'm a relativist myself, which is somewhere in between.  Things only exist only in relation to other things, but there is no relation-independent existence.  That's pretty non-standard, so I don't expect others to buy into it, but theory of relativity fits right into that, denying absolute time in favor of only relations:  A happens before B in relation to frame X, but not in relation to different frame Y.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Recher on 12/12/2018 03:43:07
Identical twins are separated at birth. One stays on Earth while the other is whisked away in a rocket traveling 2/3 the speed of light. After 60 Earth years, the rocket returns. The 60 year old earth  bound twin is there to greet his thirty year old twin astronaut. Time dilation. The faster an object of mass is moving relative to the sped of light ageing is slowed and time dilated. From the earth the rocket twin and his clock are moving at half speed while the astronaut views earthlings and their clocks moving at double time relative to his clock.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 12/12/2018 04:34:13
Identical twins are separated at birth. One stays on Earth while the other is whisked away in a rocket traveling 2/3 the speed of light.
Going to need at least 6/7 c to get the sort of age difference you describe.
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The faster an object of mass is moving relative to the sped of light ageing is slowed and time dilated.
One cannot move relative to a speed.  One moves relative to a frame, and speed of light is not a frame.
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From the earth the rocket twin and his clock are moving at half speed while the astronaut views earthlings and their clocks moving at double time relative to his clock.
No, from a given inertial reference frame (IRF) of the astronaut (either the outbound or the return one), the Earth clock runs at half speed.  In either of those frames, it is the Earth clock that has the speed.  The astronaut is always stationary in his own frame.

Everybody assumes Earth is stationary, but it is in fact moving relative to almost anything else, and in particular, any other IRF.  I cannot think of a single other object in whose frame Earth is stationary.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: yor_on on 12/12/2018 12:07:57
There is quite a problem in defining what you will measure your speed against as no stars, as far as relativity knows, are 'unmoving'. The best you can do there possibly is to place yourself as being 'at rest' with some star, then arbitrarily define that as a 'zero speed' and then accelerate. The other thing one might be able to do is to use what's called 'fixed stars', being so far away that they to us become 'unmoving'. Then again, all uniform motion is from a black box perspective equivalent. No way to measure a difference, So?

Relativity has only two modes, uniform motion and accelerations in where acceleration is a equivalence to gravity, and in where all uniform motions becomes a equivalence too. Defining it as standing still or moving doesn't matter from a black box perspective..
=

Presuming you to, at all times, accelerating you could use a lightbulb placed at some absolute center, inside your ship, and then check if it blue and red shift I think, but that will only tell you that you're accelerating, not your 'speed'. And as soon you're back in uniform motion that light bulb will be without red and blue shifts. Using stars outside the black box  (ship) though you should be able to tell a difference between the way they were before your acceleration relative after (blue and red shift)
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 12/12/2018 15:02:13
 
Quote from: Colin
…. what causes you to think of events as separate.
Oxford Dictionary: Event:  Physics: A single occurrence of a process.

Quote from: Bill
.  I felt it must be possible to have two events that were contiguous, but were still distinct, but in that case, what separated them?

I progressed from there to the idea that “reality” is made up of a “series of snapshots”.   Barbour and Deutsch use these concepts in different ways; in Barbour’s case, it is to argue against the “reality” of time. 

He says:  “….when we think we see motion at some instant, the underlying reality is that our brain at that instant contains data corresponding to several different positions of the object perceived to be in motion.  My brain contains, at any one instant, several ‘snapshots’ at once.  The brain, through the way in which it presents data to consciousness, somehow ‘plays the movie’ for me.”

I found much of Barbour’s book quite heavy going, and the idea of progressing from one “snapshot” to another, without the aid of time was an example of my inability to feel sure I grasped what he was saying.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 12/12/2018 15:13:51
Quote from: Colin
…. what causes you to think of events as separate.
Oxford Dictionary: Event:  Physics: A single occurrence of a process.
In the context of a topic like this one, an event is defined as a point in spacetime.

As points, you can discuss such geometric relations as their separation and such.

Quote from: Bill
.  I felt it must be possible to have two events that were contiguous, but were still distinct, but in that case, what separated them?
Not sure what contiguous events are.  Points are not usually described as being contiguous.

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He says:  “….when we think we see motion at some instant, the underlying reality is that our brain at that instant contains data corresponding to several different positions of the object perceived to be in motion.
OK, so you're talking about quanta of time, sort of like frames of a movie.  Somehow I suspect our brains don't process reality at the frame rate of the universe, if there is any such thing.
Yes, movies frames can be contiguous, meaning there's nothing between them that is meaningful to the process (brain perception say) in question.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: alancalverd on 12/12/2018 15:28:11
I progressed from there to the idea that “reality” is made up of a “series of snapshots”. 
This is not possible. If a rock were to roll in a series of discrete jumps you would need to apply an infinite force for an infinitesimal time, first forward and then backward, to make it do so.

The assertion is the basis of Zeno's paradox and as with every other paradox, it is founded on philosophy rather than physics. Unfortunately the adoption of digital information processing has led to many similar misconceptions, including the redefinition of a circle as 360 straight lines and the notion that the human eye has a consistent scan or frame rate.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 12/12/2018 19:47:34
Quote from: Halc
As points, you can discuss such geometric relations as their separation and such.

Separation in space is a related, but rather different, issue. It was “separation” in time I was trying to understand.

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Not sure what contiguous events are.  Points are not usually described as being contiguous.

I interpreted “contiguous” as having nothing by which they are separated.  We were talking earlier about the events of birth and death.  Obviously, these are not contiguous, in normal circumstances. Using the “snapshot” idea I was trying to imagine a situation in which it would be possible to have “snapshots” that didn’t exist in time, but could be “interpreted” sequentially by the brain; using “unreal” time.  It didn’t make sense to me, but Barbour is a professional and I an ill-informed amateur, so I was trying to follow his reasoning.

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OK, so you're talking about quanta of time, sort of like frames of a movie.  Somehow I suspect our brains don't process reality at the frame rate of the universe, if there is any such thing.

Another of my stumbling blocks.  How could the Universe have a frame rate if time didn’t exist?
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 12/12/2018 19:59:00
Quote from: Alan
This is not possible.

That was my initial reaction.  I’ve explained, above, why I didn’t leave it at that.

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If a rock were to roll in a series of discrete jumps you would need to apply an infinite force for an infinitesimal time, first forward and then backward, to make it do so.

I tried a few simpler “thought experiments”, but they all raised the same question as yours.  How could they work in a timeless Universe? 
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 12/12/2018 20:18:21
Separation in space is a related, but rather different, issue. It was “separation” in time I was trying to understand.
Two events separated by space but not time are termed 'simultaneous', not 'contiguous'.  It is a frame dependent relation.  Those events will be simultaneous in one frame but not another, and using the word 'contiguous' doesn't change that.

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I interpreted “contiguous” as having nothing by which they are separated.
That would be the same point then.
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Using the “snapshot” idea I was trying to imagine a situation in which it would be possible to have “snapshots” that didn’t exist in time
I don't see how there could be a 'snapshot' without there being a time to which the snapshot corresponds.  I have photos taken of me, but all of them were taken at some moment in time.
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but could be “interpreted” sequentially by the brain; using “unreal” time.
Sounds like a dualistic set of philosophical assumptions, having little to do with physics, including brains.  The usual term is 'mind', which is is not the 'brain', which is incapable of processing during a snapshot.

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OK, so you're talking about quanta of time, sort of like frames of a movie.  Somehow I suspect our brains don't process reality at the frame rate of the universe, if there is any such thing.

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Another of my stumbling blocks.  How could the Universe have a frame rate if time didn’t exist?
If time doesn't exist, then there would be no meaning to my age, or the velocity of this here rock.  Of course time exists.
A frame rate is another thing.  I have no reason to support a claim that spacetime is discreet and that there is such a thing as successive moments or adjacent locations in space.  Sure, there is Planck length and Planck time, but that's just the limits of measurability, not a model of how anything works.  Such a model would seem to violate all conservation laws.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 12/12/2018 23:06:05
Quote from: Halc
Two events separated by space but not time are termed 'simultaneous', not 'contiguous'.

Precisely. Remember that I was trying to grasp Barbour’s idea of “Platonia” as illustrated by the “snapshot” concept. I was trying to get away from the semantics to see if that would help. It didn’t.

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That would be the same point then.


Not necessarily. Two areas of land are said to be contiguous if they share a common boundary.  Two of Barbour’s snapshots would be contiguous if their borders were together, but none of this sheds any light on the “mechanism” by which a timeless array of snapshots can become sequential without time in which to make that change.

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  I don't see how there could be a 'snapshot' without there being a time to which the snapshot corresponds.

Exactly.  I felt there must also be a specific time in which each snapshot was observed. I couldn’t equate that with the timelessness of “Platonia”.

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I have photos taken of me, but all of them were taken at some moment in time.

I suspect the analogy was not intended to be taken that far.  :)

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The usual term is 'mind', which is is not the 'brain',

Barbour’s term, not mine.

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If time doesn't exist, then there would be no meaning to my age, or the velocity of this here rock.  Of course time exists.

It’s some years since I read “The End of Time”, but that was roughly the point I was at when I reached the end; with the proviso: Of course time exists, in our Universe.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 12/12/2018 23:11:07
Quote from: Alan
Unfortunately the adoption of digital information processing has led to many similar misconceptions, including the redefinition of a circle as 360 straight lines

I think Edwin Abbot beat them to that "definition" of a circle.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 12/12/2018 23:43:23
Quote from: Halc
That would be the same point then.

Not necessarily. Two areas of land are said to be contiguous if they share a common boundary.
Areas of land are not points.

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Two of Barbour’s snapshots would be contiguous if their borders were together
That would be two simultaneous snapshots if there were no temporal distance separating them.
I know, this is somehow a discreet model where there is a concept of successive instants.  I find that contradictory, but that's me.

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Exactly.  I felt there must also be a specific time in which each snapshot was observed.
How can a snapshot be observed at any other time than the time of the snapshot?  I can't observer yesterday.  At 5 PM I have no choice but to observe the 5PM snapshot.  Introducing a second sort of time (one of the snapshot, and another for when it is observed) is dualistic: The former being when the movie was shot with the camera, and the latter being when it is observed at the cinema.
Find and dandy to make a model like that, but it makes no predictions and thus isn't science.
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It’s some years since I read “The End of Time”, but that was roughly the point I was at when I reached the end; with the proviso: Of course time exists, in our Universe.
That is well put.  I agree with that more than you know.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 13/12/2018 11:28:24
Quote from: Halc
Areas of land are not points.

And analogies are not perfect representations of the things with which they are compared. I would rather not get into a discussion of the nature of points here.  I’m still waiting for clarifications elsewhere. I’m not going to suggest that continued waiting is “pointless”.

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I know, this is somehow a discreet model where there is a concept of successive instants.  I find that contradictory, but that's me.

It’s certainly not just you, but it’s another of those subjects that seem to be interminable.

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How can a snapshot be observed at any other time than the time of the snapshot?


I think the main thrust of Barbour’s reasoning was that there is no “time of the snapshot”.  The illusion of time is added by the observer.  I had (have) trouble with this because if there is no time before the observation is made, how can it be made?

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That is well put.  I agree with that more than you know.

Thanks. This is probably not the place for it, but I would love to hear more about your ideas on that. Possibly another thread.  What would be the best question to ask to evoke an appropriate response?
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 13/12/2018 12:43:39
I’m not going to suggest that continued waiting is “pointless”.
I would have.  I cannot resist such comments.

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I think the main thrust of Barbour’s reasoning was that there is no “time of the snapshot”.
???  Any snapshot of the universe contains the state of every clock, each of which nicely indicates the time of the snapshot.  So I find that pretty contradictory reasoning.

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The illusion of time is added by the observer.  I had (have) trouble with this because if there is no time before the observation is made, how can it be made?
He doesn't say time is created by the observer.  It is an illusion.  What is added is the perception of the flow of time, not the addition of time itself.  I don't think time flows.  It's just a dimension to me.  The 2011 version of me experiences 2011 and not any other moment, which is what I mean when I ask how any snapshot can be experienced at a different time.  The version of me making this post exists no more or less than that 2011 version.  A 'present' that has flowed from 2011 and is currently 'now' is the thing that Barbour probably says is added by the observer.  Not sure.   I've not actually read what was said, only what was posted in this topic.

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Thanks. This is probably not the place for it, but I would love to hear more about your ideas on that. Possibly another thread.  What would be the best question to ask to evoke an appropriate response?
Depends on what aspect of it you want to discuss.  The idea of time as part of the universe is opposed to the universe existing in time.  That might be mangled into a question.  A lot of the 'more than you know' part is philosophy, best posted in the 'Chat' section of this site since it isn't really science at all.  Sign up on a philosophy site and start a discussion there.
OK, it is a question of QM interpretations, something I don't see discussed hardly at all on this site.  I find that surprising.  So start one.  QM interpretation questions are technically philosophical since none of the valid interpretations have falsification tests.  But I think you can post QM questions in General or in Physics forums.
My preference is the relational interpretation (Rovelli, '94), which I like precisely because I find it to be a neat solution to the question of why the universe exists.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: phyti on 13/12/2018 17:31:29
One of my favorite forum subjects.
A few questionable lines.

#3
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Each physicist can see his own clock and the other’s with no time delay for information transfer.

If light speed is finite, there must be a time delay, which alters perception. Without a delay you can’t measure distance.

#6
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For the purposes of the OP's question we can say clocks measure rates of change

Clocks measure amount of activity in terms of a human defined standard event (clock cycle). Rate of change or time dilation, is calculated from observations.

#7
Quote
It becomes convenient to talk of changes in the rate of time’s flow, or of the rate of our passage through time, and to treat time as though it were an entity with existence that was independent of the things being measured and those doing the measuring; which may not be the case.

Not the case. Time flow is the mental sequential perception of the current event following the previous event in memory. Because perception is a real mental process, it is difficult to separate it from physical processes occurring outside the mind. It cannot be independent of those doing the measuring, since it's a human convention, and the reason for subjective time.

#12
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If time separates sequential events, does this mean that something exists between events that is not, in itself an event, and that that something is time?  (Smolin)
Alternatively, does it mean that our perception of time allows us to distinguish as sequential events something that is essentially continuous? (Barbour)

Time is not a causal factor. The time of an event is recorded after the event occurs, after awareness of the event. It's an historical account for a multitude of purposes.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 13/12/2018 23:40:33
Quote from: Phyti
A few questionable lines.

Possibly some lines become more "questionable" when taken out of context.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: yor_on on 14/12/2018 12:12:05
Halc

"  Any snapshot of the universe contains the state of every clock, each of which nicely indicates the time of the snapshot.  So I find that pretty contradictory reasoning. "

That would then be the perspective from someone 'outside' this universe of clocks. If it's a 'inside perspective' then it's not a privileged one, as no observer inside has a way of defining his clock to be the 'golden standard' from where this snapshot should be taken. And if that observer would happen to ask others what they though the observers clock rate to be, the answers would vary widely. That's from what I call a 'global view', which I think you're evoking here?

If we stop using that, and stay local then it doesn't matter where you are or how fast you go. your life expectancy will be the same relative your wrist watch, and that goes for all observers inside this universe. The 'global view' is filled with traps.
=

Thinking of it even the 'outside' observer should have the same problem, presuming he's using a clock. And actually, from a 'global view' the observers clockrate then will depend on what he compares it too, if he now would want to define it as a 'golden standard'. What physics offer in this case is Lorentz transformations, and they don't talk about a 'golden standard', they just prove that it's possible to translate that clock rate into another. And if that wasn't possible we would have to give up on logic and instead prepare ourselves for a 'magic universe'
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 14/12/2018 14:45:35
Halc

"  Any snapshot of the universe contains the state of every clock, each of which nicely indicates the time of the snapshot.  So I find that pretty contradictory reasoning. "

That would then be the perspective from someone 'outside' this universe of clocks.
What I said is simply true of the slice, and is independent of the perspective from which that slice might be considered.

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If it's a 'inside perspective' then it's not a privileged one, as no observer inside has a way of defining his clock to be the 'golden standard' from where this snapshot should be taken.
I don't think any snapshot is privileged in this way.  Again, this is independent of observers.  The snapshot is a 3D cross section of 4D spacetime, and that cross section can be taken at any particular angle.  There is seemingly no privileged way to orient it.

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And if that observer would happen to ask others what they though the observers clock rate to be, the answers would vary widely. That's from what I call a 'global view', which I think you're evoking here?
Each observer sees clocks moving relative to himself to be running slower.  That is true for all observers, and for the global view as you say.  The outside observer has no clock.  He's outside time, but can see the relations within the spacetime structure.

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If we stop using that, and stay local then it doesn't matter where you are or how fast you go. your life expectancy will be the same relative your wrist watch, and that goes for all observers inside this universe.
I think you are saying that you can jump on spaceships all you want, but never experience more life by doing it.  Yes, that's true.  The twins reunite and one is 80 and the other 40, but both die at 82, they both experience 82 years, even if their deaths are 4 decades apart.

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The 'global view' is filled with traps.
=
Thinking of it even the 'outside' observer should have the same problem, presuming he's using a clock.
You fell into a trap already I see.  He is outside time, and thus has no clock.  If he exists in time and has a clock to measure it, he's not an outside observer, but just another internal one, not more special than any of the others.

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What physics offer in this case is Lorentz transformations, and they don't talk about a 'golden standard', they just prove that it's possible to translate that clock rate into another.
Exactly.  Lorentz transformations describe relations between frames, but do not involve any golden standard.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: MikeFontenot on 14/12/2018 15:28:00

Each observer "sees" [concludes that] clocks moving relative to himself to be [are] running slower.  That is true for all observers, [...]


Not true for ALL observers.  It is true for all inertial observers.  It is NOT generally true for accelerating observers.  Accelerating observers sometimes conclude that some distant clocks are rapidly running forward, and sometimes conclude that they are rapidly running backward.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: phyti on 14/12/2018 15:41:09
A few more questionable lines.


#27
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Presuming you to, at all times, accelerating you could use a lightbulb placed at some absolute center, inside your ship, and then check if it blue and red shift I think, but that will only tell you that you're accelerating, not your 'speed'.


Doppler shift requires a relative velocity between source and detector.


#31
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Using the “snapshot” idea I was trying to imagine a situation in which it would be possible to have “snapshots” that didn’t exist in time, but could be “interpreted” sequentially by the brain; using “unreal” time.

How could the Universe have a frame rate if time didn’t exist?


The mind requires a few milliseconds to register sensory input, which can be the duration of your snapshot.

Does the universe need a clock to exist?


#33
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If time doesn't exist, then there would be no meaning to my age, or the velocity of this here rock. 


The measurements of time and space have a purpose and thus meaning for the observer.


#36
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How can a snapshot be observed at any other time than the time of the snapshot?  I can't observer yesterday.  At 5 PM I have no choice but to observe the 5PM snapshot.  Introducing a second sort of time (one of the snapshot, and another for when it is observed) is dualistic:


There are 'a' events, the physical occurrence of the event E, and 'b' events, the awareness of the event E. In the SR theory, Einstein defines the 'time' of the event E relative to the local clock of the observer, i.e. the 'b' event. Since light is the messenger, for local events there is very little difference between 'a' and 'b'. For  'remote' events on an astronomical scale, the difference is many magnitudes of 'large'.

The 'a' time requires additional knowledge of the distance to E. All observations are therefore historical. Just as the time is recorded after the event occurs, the image of E can only be seen after E occurs. Astronomers observe the past every night.

----------------------------------------

My personal thought about the never ending debate of 'time', philosophical, scientific, or otherwise, is the desire for a permanence of life. Humanity wants an assurance that 'time' will not end, thus maintaining their  presence. There should be an (invisible) entity working behind the scenes, planning events. A psychological desire similar to wanting a solid foundation for security. When portions of the earth shift, people get anxious!
This security blanket makes it difficult to separate fact from fiction.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 14/12/2018 18:11:57
Quote from: Bill
Each physicist can see his own clock and the other’s with no time delay for information transfer.

Quote from: Phyti
If light speed is finite, there must be a time delay, which alters perception. Without a delay you can’t measure distance.

Of course, your comment is correct, but you seem to have overlooked the fact that this was a thought experiment.

Quote from:  Bill
….. which may not be the case.

Quote from: Phyti
Not the case

Could we be on the same page? :)

Quote from: Phyti
Time is not a causal factor. The time of an event is recorded after the event occurs, after awareness of the event. It's an historical account for a multitude of purposes.

Recall that I was trying to make sense of Barbour’s “Platonia”. 
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 14/12/2018 18:34:23
A few more questionable lines.
Questionable, sure, but not necessarily wrong.
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#27
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Presuming you to, at all times, accelerating you could use a lightbulb placed at some absolute center, inside your ship, and then check if it blue and red shift I think, but that will only tell you that you're accelerating, not your 'speed'.
Doppler shift requires a relative velocity between source and detector.
It wouldn't be doppler shift in this case.  Given a long ship, the lights in the front will appear to be blue shifted due to time passing quicker up there due to the front being further out of the equivalent gravity well.  Similarly, light from the back will appear red shifted to an observer further forward.
This is the same as lights at the top and bottom of a really tall building, with observers looking at each other's light.  Gravity can be detected this way, and hence so can acceleration.  Of course there are plenty of simpler ways to detect it, like noting that you're not in free-fall relative to the ship.

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#33
The measurements of time and space have a purpose and thus meaning for the observer.
One can argue that time exists if it is something that can be measured.
This is one of those questionable cases.  Perhaps you can suggest nonexistent things that nevertheless are measured.

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#36
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How can a snapshot be observed at any other time than the time of the snapshot?  I can't observer yesterday.  At 5 PM I have no choice but to observe the 5PM snapshot.  Introducing a second sort of time (one of the snapshot, and another for when it is observed) is dualistic:

There are 'a' events, the physical occurrence of the event E, and 'b' events, the awareness of the event E. In the SR theory, Einstein defines the 'time' of the event E relative to the local clock of the observer, i.e. the 'b' event.
For starters, I disagree with that.  Einstein allowed the definition of the time of event E to be relative to any frame of choice.  E itself has no frame of its own, so that doesn't work.  But I as an observer can choose to use a frame in which I am not stationary and conclude a different time for E.

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Since light is the messenger, for local events there is very little difference between 'a' and 'b'. For  'remote' events on an astronomical scale, the difference is many magnitudes of 'large'.

The 'a' time requires additional knowledge of the distance to E. All observations are therefore historical.
I had a different interpretation when saying those words quoted above.  I'd say that all observations are of here and now, not historical at all.  I look at this fossil here in the state it is now, and infer history of a million years ago from that.  I look at light that reaches me here and now, and infer a star that emitted it a thousand years ago.  I am looking not at the past, but at the present.  The past is simply inferred from that.  That's what I meant by the words above.

Of course it is perfectly legit to say that all observations are caused by past events, and causes are necessarily somewhere within the past light cone of observation event b.

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My personal thought about the never ending debate of 'time', philosophical, scientific, or otherwise, is the desire for a permanence of life. Humanity wants an assurance that 'time' will not end, thus maintaining their  presence.
Time simply needs to 'be' to assure one's presence in it.  It seems to be a bounded thing at both ends, but that is only a problem if the flow of time is real, not if time itself is real.
Yea, that's a pretty philosophical statement, I know.

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This security blanket makes it difficult to separate fact from fiction.
I don't buy the flow bit, and am surprised that the view gives me that security blanket.  I obviously exist in time, and no event (my death say) can change that.  That actually works for me.  Yes, it is in my nature to seek that security, however much I try to not let it cloud my attempts at separation of fact from fiction.  I like to think that I'm better at that than most.  So good in fact, that I know that I totally fail at it.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 14/12/2018 18:41:55
Quote from: Bill
How could the Universe have a frame rate if time didn’t exist?

Quote from: Phyti
The mind requires a few milliseconds to register sensory input, which can be the duration of your snapshot.

Where would the few milliseconds come from if time didn’t exist?
Title: Re: What does the term 'time' relate to in time dilation?
Post by: alancalverd on 14/12/2018 19:10:43
The few milliseconds is what we measure with our laboratory clock between the sequential events of stimulus and response. If you poke about with an electrode, you can find a number of intermediate events as the electrochemical signal passes along the nerves.

You can't turn the light on by thinking about it, but your brain always registers the fact that someone has turned it on. So we say that the stimulus precedes the response: A => B. This determines the direction of time increasing. It's an arbitrary but convenient and universal convention.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 14/12/2018 19:30:23
That makes good sense to me.  My sticking point was that Phyti seemed to find a few milliseconds without time.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 14/12/2018 19:40:30
Quote from: Halc
I don't buy the flow bit

That would seem to suggest “tensless” time, which I think equates, roughly, to John McTaggart’s “B series”. Have you read his “The Unreality of Time”?  It was a bit philosophical, not to mention pedantic, even for me. 
Title: Re: What does the term 'time' relate to in time dilation?
Post by: yor_on on 14/12/2018 19:59:59
Of course I could have made a treatise of it, I didn't. But what I say should hold even if you lift up accelerations as a special case Mike, and phyti, you will find more than me defining it this way. A acceleration is about displacements, and it will give you a red respectively blue shift. And you can talk about 'slices' of spacetime, which is not 'events' but just a 'slice' of it in time and space. Doing such a slice in a accelerating frame should keep the blue shift balanced relative the red shift as far as I see, expressed otherwise there is no energy added or lost in that slice. It's a equivalence to the idea of 'c' holding even in a acceleration, although the displacements make it look differently. And Halc, there is nothing like a privileged frame in relativity which put into question anyone talking about 'snapshots' as if the frame that represents that snapshot would be anything else than frame dependent.  We don't need to agree of course :) But that's the way I see it.
=

when it comes to me arguing that the local representation is the correct one :) Well, that's equivalent to someone arguing that 'repeatable experiments' works. When it comes to defining this 'slice' I used then it was from a observer being at rest with (inside) the 'black box', able to see the light bulb from both directions, aft and fore. It's a idealized situation naturally.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 14/12/2018 23:33:27
Quote from: Bill #16
Yes, otherwise your body would not decompose.

Of course, it’s not as simple as that.  If I’m a solipsist, does my body decay when I die?

The answer to that must depend on several possible factors. They are all philosophical, so I’ll not list them. Suffice to say that I would opt for “no”.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 15/12/2018 00:41:27
Where would the few milliseconds come from if time didn’t exist?
I know, right?

Quote from: Halc
I don't buy the flow bit
That would seem to suggest “tensless” time, which I think equates, roughly, to John McTaggart’s “B series”. Have you read his “The Unreality of Time”?  It was a bit philosophical, not to mention pedantic, even for me.
"Tenseless" is just a mode of temporal reference that avoids relations to the present, mostly because yes, that doesn't exist in a non-flowing view.  The view is called eternal time, not tenseless time.
I don't need to read McTaggart's book to know how it works.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: alancalverd on 15/12/2018 10:38:50
Since you could count microseconds between your milliseconds, the ticks of your millisecond clock are sequential events, separated by....time. Colleagues have rpoutinely counted femtoseconds between phases of chemical reactions, and AFAIK there is no essential granularity in the measurement of time,.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 15/12/2018 12:56:52
Quote from: Halc
The view is called eternal time, not tenseless time.


I tend to avoid the term "eternal time" because eternity and time are completely different concepts.  That's something which has probably been "flogged to death" elsewhere, without any resolution.   
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 15/12/2018 13:14:47
Alan, that's a good one to keep in mind for next time the question of the possible quantization of time rears its head. :)
It doesn't address the question of where any fraction of a second could come from if there were no time.

My feeling is that when we talk about time/timelessness, what we are really talking about is change/changelessness. Time is what we call the measure of that change.  If there were no change, we would not be able to take measurements, so a measurement system would be extraneous. 
Title: Re: What does the term 'time' relate to in time dilation?
Post by: alancalverd on 15/12/2018 14:20:28
A fraction of a second dooesn't "come from" anywhere. It's how we measure the gap between events. Just like a millimeter is the gap between the jaws of a caliper gauge.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 15/12/2018 15:38:22
Quote from: Halc
The view is called eternal time, not tenseless time.


I tend to avoid the term "eternal time" because eternity and time are completely different concepts.  That's something which has probably been "flogged to death" elsewhere, without any resolution.
Agree, they're totally different concepts.  Not talking about boundless time.  I mean Minkowski spacetime: Time and space are one thing.  Time lacks a preferred moment in the exact same way that space lacks a preferred location.  That's my opinion, and I've on occasion defended the opposite view when somebody claims to have a proof against it.  I don't think there is any empirical way to settle the issue.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 15/12/2018 15:41:33
If there were no calipers, that mm would have no meaning.
If there were no objects, distance would have no meaning.
If there were no change, time would have no meaning.

https://medium.com/the-physics-arxiv-blog/quantum-experiment-shows-how-time-emerges-from-entanglement-d5d3dc850933

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Time is an emergent phenomenon that is a side effect of quantum entanglement, say physicists. And they have the first experimental results to prove it.
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Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 15/12/2018 15:50:16
Quote from: Halc
Time and space are one thing.  Time lacks a preferred moment in the exact same way that space lacks a preferred location. 

I’ll have to ponder that a bit. My initial reaction is to wonder if it is just space that in influenced by relative motion, gravity etc. and that time – our measuring “instrument” – has to adjust to accommodate that change.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: alancalverd on 15/12/2018 22:40:47
If there were no calipers, that mm would have no meaning.
If there were no objects, distance would have no meaning.
If there were no change, time would have no meaning.
Distance is the separation of points, not objects. Time is the separation of events.

It is arguably the case that if individual words have no meaning, their combination is also meaningless, but that is fatuous philology or, even worse, philosophy. Unlike philosophy, physical masturbation is at least pleasurable.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 15/12/2018 22:50:05
Quote
Distance is the separation of points, not objects.

I can see that it is the separation of points, but isn't it also the separation of objects, places etc?  E.g. is there not a distance between London and Cambridge?

Quote
Time is the separation of events.

Are changes not events?
Title: Re: What does the term 'time' relate to in time dilation?
Post by: alancalverd on 15/12/2018 22:57:34
I'll take a short break from more pleasurable activities to explain that "London" and "Cambridge" are fuzzy patches on a map. Points within "London" and "Cambridge" are separated by all sorts of distances, mostly between 40 and 70 miles.You can define points within those fuzzy boundaries that are not associated with any particular object. In the absence of other data those points are conventionally located within Charing Cross and Great St Mary's respectively but if you want to navigate by dead reckoning from Cambridge airport to London City you  will need to choose two other points.

And the pedantry prize is awarded to the old fool who pointed out that the change from boyhood to manhood is not an event, nor two events, but it may be denoted by a single event, arbitrarily chosen at 13, 16, 18 or 21 years after birth
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 15/12/2018 23:09:37
Quote
Just like a millimeter is the gap between the jaws of a caliper gauge.

How small does something have to be to be a point rather than an object?

Quote
Are changes not events?

I really appreciate your taking a break from more pleasurable activities to answer possibly tedious questions.  Thanks.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: alancalverd on 15/12/2018 23:17:41
A point is not a "something". It is by definition infinitesimal, and therefore smaller than any "thing".
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 16/12/2018 01:35:14
Quote
Just like a millimeter is the gap between the jaws of a caliper gauge.

How small does something have to be to be a point rather than an object?
Small enough to be mathematically treated as one for the task at hand.

The lightning strikes in Einstein's train/platform thought experiment needed to be pretty precise and those events were as concise as Einstein could describe them.  But on the other hand, other events like the Chicago fire are quite large because they usually are not compared with more precise things.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 16/12/2018 13:14:23
Quote from: Alan
A point is not a "something". It is by definition infinitesimal, and therefore smaller than any "thing".

Infinitesimal is by definition: “an indefinitely small quantity; a value approaching zero.” My thinking is that if it is a quantity, and not zero, it must be something, but I am neither a mathematician or a physicist.

Experience teaches that trying to forge any kind of link between this sort of mathematical concept and the “real world” leads nowhere.  Possibly a “put-down” type answer like:

Quote
A point on a line has no length. A point on a timeline has no duration. What's the problem?

Where does it go from there?  Perhaps try saying what the “problem” is.  It’s always good to answer a question.

Quote from: Bill
I have no problem with either of those, in principle.  However, in practice, can you show me a point that has no length, but is still there?

Similarly, a point on a timeline that is defined as having no duration may be theoretically valuable, but both the timeline, and the point are mathematical tools.  What would be a physical example?

No reply.  This is not an isolated example; which makes me wonder if I am asking a pointless question?
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 16/12/2018 14:27:55
Quote from: Halc
Small enough to be mathematically treated as one for the task at hand.

Quote from: Sabine Hossenfelder
I love math, I just don't want it to be confused with physics.

You can’t lie with math.  But it greatly aids obfuscation. 
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 16/12/2018 14:58:34
Quote
Similarly, a point on a timeline that is defined as having no duration may be theoretically valuable, but both the timeline, and the point are mathematical tools.  What would be a physical example?

No reply.  This is not an isolated example; which makes me wonder if I am asking a pointless question?
7:15 AM, GMT is a physical point in time.  It isn't an event, since the location of where it is 7:15 is not specified and hardly unambiguous.

A physical event is something like 2 billiard balls hitting, which yes, is a process, but one can narrow it to a point by specifying say the point of maximum force between the two objects.

Both these things can be treated as mathematical points in a discussion of physics.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: phyti on 16/12/2018 19:55:47
Halc #46;


My mistake for not catching the word "accelerating", gotta read slower!
Quote

One can argue that time exists if it is something that can be measured.

It's motion that is measured and labeled as 'time'. From early history: astronomical bodies in motion, to today's quantity of light waves.
[/quote]

Perhaps you can suggest nonexistent things that nevertheless are measured. [/quote]

Time.
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Einstein allowed the definition of the time of event E to be relative to any frame of choice.
Yes he did, but the clock was 'local' from the point of observation, which becomes the basis for coordinate transformations..
A. Einstein, 1905 paper, par.1:
"It might appear possible to overcome all the difficulties attending the definition of ``time'' by substituting ``the position of the small hand of my watch'' for ``time.'' And in fact such a definition is satisfactory when we are concerned with defining a time exclusively for the place where the watch is located; but it is no longer satisfactory when we have to connect in time series of events occurring at different places, or--what comes to the same thing--to evaluate the times of events occurring at places remote from the watch."
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Of course it is perfectly legit to say that all observations are caused by past events, and causes are necessarily somewhere within the past light cone of observation event b.
That's essentially what I meant. All your observations are 'now'. The fossil is also in its current/now state. Observing an image of a nova, the star is in an historical state. The difference is between a and b.
Thanks for the conversation.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: phyti on 16/12/2018 19:57:29
Bill S #49;
Quote

 My sticking point was that Phyti seemed to find a few milliseconds without time.


Medical research in the past three decades has revealed the brain has multiple processes periodic and not, that serve as clocks, for most of the biological functions. There is an overall lag between sensory input and the consciousness of events. There is a mind-time connection. Comatose patients, amnesia, brain damage, etc, all interfere with ability to correctly sense intervals of time, short or long.

Title: Re: What does the term 'time' relate to in time dilation?
Post by: alancalverd on 16/12/2018 22:25:37
Experience teaches that trying to forge any kind of link between this sort of mathematical concept and the “real world” leads nowhere. 

Far from it. A rigorous treatment of infintesimals leads to differential calculus, whence we get the whole world of classical physics, mesoscopic engineering and just about everything that distinguishes enlightened men from priests, politicians, philosophers and all the other human dross we scientists scrape off our shoes.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 16/12/2018 23:40:05
Quote from: Halc
Perhaps you can suggest nonexistent things that nevertheless are measured.
Time.
So you assert, but that's the exact reasoning I use to say it does exist.
I was hoping for a different example.  I suspect there are some.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: set fair on 17/12/2018 02:57:31
Some good facts about time. They are what we can say about time in nature. I don't think anyone knows what time is.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 17/12/2018 18:03:23
Quote from: Halc
7:15 AM, GMT is a physical point in time.  It isn't an event, since the location of where it is 7:15 is not specified and hardly unambiguous.


Thank you, you make one of my points more eloquently than I.  7:15 AM, GMT is a concept that, as far as I am aware, exists only in the minds of rational beings (apparently not universally); it is an invented “point” on an imaginary line that, conveniently, charts progress of/through time.  Time, itself, as we have been discussing, is somewhat ethereal.  It’s a relatively simple matter to propose a point of zero dimensions in such a scenario. 

Quote
A physical event is something like 2 billiard balls hitting, which yes, is a process, but one can narrow it to a point by specifying say the point of maximum force between the two objects.

This is probably the nearest anyone has come to identifying a physical point of zero dimensions.  Unfortunately, the point of maximum force between the two objects has no independent existence, so could hardly qualify as a physical object.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: alancalverd on 17/12/2018 18:12:32
Some good facts about time. They are what we can say about time in nature. I don't think anyone knows what time is.
Oh come now! A cow is a bovine quadruped that moos and poos, with milk in the middle. Time is what separates sequential events. These are definitions. Only a philosopher would pretend not to know what a cow "is". Farmers and scientists have more important things to think about, because we work with animals and time.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 17/12/2018 18:23:31
Quote from: Alan
A rigorous treatment of infintesimals leads to differential calculus, whence we get the whole world of classical physics, mesoscopic engineering and just about everything that distinguishes enlightened men from priests, politicians, philosophers and all the other human dross we scrape off our shoes.

The original question remains unanswered.  Perhaps the cognoscenti believe they can blind with science/maths this “human dross” before superciliously scraping them from their shoes. 

Your post seems to say more about your personal prejudices than about the subject of the thread, but the former is something from which I would prefer to remain detached. 
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Bill S on 17/12/2018 19:12:03
At some point, I think, I hijacked this thread. I don’t feel guilty about it because it has been a fruitful discussion, at least until recently.  I’ve gained a lot from it, and would like to thank those who have coped patiently with my persistence.  Unfortunately, the thread is showing signs of the sort of degeneration that one does not expect of TNS, so I am opting out. 

I’m pulling together some thoughts, which will undoubtedly raise even more questions/objections. 
I’ll probably post these in a new thread, rather than stay with this one.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 17/12/2018 20:40:33
7:15 AM, GMT is a concept that, as far as I am aware, exists only in the minds of rational beings (apparently not universally); it is an invented “point” on an imaginary line that, conveniently, charts progress of/through time.
I'd hesitate to call it a line.  7:15 happens at every point in space.  Different frames make it happen at different events, but there's damn few points in space where 7:15 doesn't happen at all.

The line could be your worldline, with a watch strapped to you defining 7:15.  That worldline is not at all imaginary because it is completely occupied by you, as is nowhere else.  That line (in particular the orientation of it at 7:15) defines 7:15 everywhere else at that event.

Quote from: Halc
A physical event is something like 2 billiard balls hitting, which yes, is a process, but one can narrow it to a point by specifying say the point of maximum force between the two objects.

Quote
This is probably the nearest anyone has come to identifying a physical point of zero dimensions.  Unfortunately, the point of maximum force between the two objects has no independent existence, so could hardly qualify as a physical object.
Well I never suggested a point was physical object.  Heck, even physical objects are not physical objects when you get right down and dirty.  The event I described with the billiard balls has a nice defined location and time, so it seems to suffice.  But I agree, it isn't an object at all.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: PmbPhy on 17/12/2018 21:17:38
For those who know algebra see the derivation at http://www.newenglandphysics.org/physics_world/gr/grav_red_shift.htm

It may help some to understand the phenomena. Colin got it perfectly in the second post. The math adds better precision to hos response. I.e. adds precision to the description.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: set fair on 18/12/2018 03:13:53
Some good facts about time. They are what we can say about time in nature. I don't think anyone knows what time is.
Oh come now! A cow is a bovine quadruped that moos and poos, with milk in the middle. Time is what separates sequential events. These are definitions. Only a philosopher would pretend not to know what a cow "is". Farmers and scientists have more important things to think about, because we work with animals and time.


Fair enough they're definitions but I think definitions of elapsed time. What actual time is, we don't know. We don't understand the time line of particles involved in spooky action at a distance. We don't know if time is quantised.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: alancalverd on 18/12/2018 09:29:23
At the risk of being dragged into philosophy, the notion of "elapsed" presumes a direction. We are fairly relaxed about the scalar distance between A and B and the vector distance from A to B, because the context makes it obvious and for the most part |A→B| = |A←B|, but it isn't always so.

If we accept Eddington's "entropy is time's arrow" then we have an independent definition of the directon of sequential events (positive if the entropy of the universe has increased between A and B) and hence a concept of elapsed time. But history, archaeology, carbon dating and the whole of forensic science, is about reconstructing events in reversed time, not merely establishing a sequence but also calculating the scalar modulus of temporal separation.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 18/12/2018 11:53:21
At the risk of being dragged into philosophy,
The question asks what time is, not just how we find it useful.  So the question is already metaphysical, which is philosophy.

Quote
the notion of "elapsed" presumes a direction.
...
If we accept Eddington's "entropy is time's arrow" then we have an independent definition of the directon of sequential events (positive if the entropy of the universe has increased between A and B) and hence a concept of elapsed time.
Which is why I try to avoid the term 'elapsed'.  For space-like separated events A and B, one can measure the time between those two events no problem, but a measure of entropy is frame dependent, so the sign of the elapsed time is as well.  There is no objective way to determine the arrow: It is ambiguous if A or B occurred first, and the measurement of duration is, as it is even for time-like separated events, frame dependent.
So I have a hard time calling the measured time 'elapsed' when two different measurements have conflicting opinions as to which event was first.

The 'interval' is a frame-independent measure of the separation of events A and B, but there is no obvious entropic measurement to an interval calculation.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: alancalverd on 18/12/2018 13:49:17
Not sure why entropy is frame-dependent. It is a scalar quantity whose increase denotes a conventional increase in time. A specific example would be radioactive decay.

If c is constant, we can always determine the sequence of events A and B.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: Halc on 18/12/2018 15:46:51
Not sure why entropy is frame-dependent.
Poor logic on my part.  Yes, entropy is frame dependent (at event A, did distant line of dominos fall already or not?  Frame dependent question that yields different entropy depending on the answer), but entropy defines the arrow of time, not the objective ordering of events.

So given an arbitrary orientation for the time axis, entropy will tell me which way is forward on that line, but entropy renders no opinion on which way the axis should be oriented, so it isn't going to help me when I ask in what order events A or B occur.

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If c is constant, we can always determine the sequence of events A and B.
The constant speed of light is exactly why we cannot.  Einstein drove that one premise to the conclusion of the relativity of simultaneity, and the frame dependent ordering of events, both quite unintuitive at the time.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: yor_on on 28/12/2018 18:44:08
Well, we have Lorentz transformations giving us a 'eye of a God'.
What that means though is that although we have a logic defining SpaceTime we don't have answer to why it does it.

Unless logic is what makes a SpaceTime?
Title: Re: What does the term 'time' relate to in time dilation?
Post by: guest47899 on 28/12/2018 20:25:54
the ironic time dichotomy.  time is a measure of motion.  in the case of absolute zero, freeze/stop the motion of a particle and you stop time/aging from progessing for that particle.  motion as expressed in velocity has the same result. accelerate that same particle to the SOL and you have effectively stopped time from progressing/aging for that same particle. 

cryogenics in time/space travel.

so, if you were able to freeze a particle to absolute zero where motion ceased completely in it, and then accelerate it to the speed of light; would the lack of motion/energy within it negate the SR requirement that when accelerating to the speed of light, mass/energy increases proportionally?

Consider that same particle traveling at the speed of light, would that same motionless hadron particle then be considered a bosonic field/force?
Title: Re: What does the term 'time' relate to in time dilation?
Post by: jeffreyH on 28/12/2018 21:01:33
Entropy is NOT frame dependent. The entropy will always increase by the same amount for the same process IN ANY FRAME. The time required to accumulate the entropy may vary but the entropy itself won't. As Alan said it is a scalar quantity.
Title: Re: What does the term 'time' relate to in time dilation?
Post by: guest47899 on 28/12/2018 22:05:15
the ironic time dichotomy.  time is a measure of motion.  in the case of absolute zero, freeze/stop the motion of a particle and you stop time/aging from progessing for that particle.  motion as expressed in velocity has the same result. accelerate that same particle to the SOL and you have effectively stopped time from progressing/aging for that same particle. 

cryogenics in time/space travel.

so, if you were able to freeze a particle to absolute zero where motion ceased completely in it, and then accelerate it to the speed of light; would the lack of motion/energy within it negate the SR requirement that when accelerating to the speed of light, mass/energy increases proportionally?

Consider that same particle traveling at the speed of light, would that same motionless hadron particle then be considered a bosonic field/force?


so as not to cause confuse,  in the above please, substitute velocity of light for speed of light. doing so make the above a vector quantity rather than a scalar quantity.

without motion at absolute zero there no equalization of thermal energy, thereby rendering entropy a moot point.