Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Harri on 07/12/2018 22:47:18
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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?
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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.
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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
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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.
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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.
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.
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.
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Thanks, Halc. I put that post together in a hurry without due thought for the possibilities for misinterpretation.
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).
. 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.
Yes
Sigh of relief! :)
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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.
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Hi, Set fair; it's always good to look back to the OP when thread drift has moved the discussion away. Mea culpa :)
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.
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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.
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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?
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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.
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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.
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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)
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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)
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.
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And talking of death! If I die and no longer observe time passing and experience change no longer, does time still exist?
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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.
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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.
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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.
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I am the only person in existence and everything is in my imagination!? I'm not sure why, but I find that quite interesting.
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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.
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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'
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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?
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There is probably a meditation method somewhere that suggests this
Perhaps Fred Alan Wolf could find us a yogi who could help.
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. :)
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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.
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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.
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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..
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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'. 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)
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…. what causes you to think of events as separate.
Oxford Dictionary: Event: Physics: A single occurrence of a process.
. 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.
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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.
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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.
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.
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?
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This is not possible.
That was my initial reaction. I’ve explained, above, why I didn’t leave it at that.
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?
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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.
I interpreted “contiguous” as having nothing by which they are separated.
That would be the same point then.
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.
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.
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?
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.
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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.
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.
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”.
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. :)
The usual term is 'mind', which is is not the 'brain',
Barbour’s term, not mine.
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.
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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.
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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.
Areas of land are not points.
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.
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.
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.
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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”.
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.
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?
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?
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One of my favorite forum subjects.
A few questionable lines.
#3Each 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.
#6For 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.
#7It 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.
#12If 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.
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A few questionable lines.
Possibly some lines become more "questionable" when taken out of context.
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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.
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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'
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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.
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A few more questionable lines.
#27Presuming 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
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
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
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.
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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. 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.
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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.
Of course, your comment is correct, but you seem to have overlooked the fact that this was a thought experiment.
….. which may not be the case.
Not the case
Could we be on the same page? :)
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”.
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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.
Where would the few milliseconds come from if time didn’t exist?
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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.
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That makes good sense to me. My sticking point was that Phyti seemed to find a few milliseconds without time.
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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.
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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.
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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.
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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”.
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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,.
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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.
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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.
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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.
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The view is called eternal time (or block 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, eternity and 'eternal time' are 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.
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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
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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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.
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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.
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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?
Time is the separation of events.
Are changes not events?
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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
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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?
Are changes not events?
I really appreciate your taking a break from more pleasurable activities to answer possibly tedious questions. Thanks.
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A point is not a "something". It is by definition infinitesimal, and therefore smaller than any "thing".
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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.
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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:
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.
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?
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Small enough to be mathematically treated as one for the task at hand.
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.
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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.
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Halc #46;
My mistake for not catching the word "accelerating", gotta read slower!
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.
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."
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.
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Bill S #49;
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.
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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.
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Some good facts about time. They are what we can say about time in nature. I don't think anyone knows what time is.
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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.
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.
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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.
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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.
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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.
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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.
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.
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.
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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.
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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.
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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.
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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.
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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?
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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?
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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.
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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.