Do we know exactly what time is?

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Offline Alan McDougall

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Do we know exactly what time is?
« on: 18/06/2013 16:37:20 »
Hi

What is time?

Some say it is just measure of movement or an aggregation of events. Time is not a constant and I would like you guys to put forward your own ideas on the topic before adding my piece to the story.

Alan
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Online yor_on

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Re: Do we know exactly what time is?
« Reply #1 on: 18/06/2013 17:03:03 »
:)

locally it is a constant.

It's only when you compare over frames of reference you find it to give you a time dilation. Using gravitational time dilations your body can be defined to belong to different 'time zones' if you like. But from each position (loosely speaking) in SpaceTime its clock has a 'constant rate', definable as locally invariant, just as 'c' will be so for each of those 'frames of reference'. That as a 'gravity' can be translated, according to the equivalence principle, into a uniform constant acceleration. So you can consider all those 'points' of your body as 'differently gravitationally accelerating', although each one of them must present you with 'c' locally, as a 'constant', just as they must with that  'arrow'.

And that is a local definition.

Defining time 'globally', you have to measure over 'frames of reference'. Doing so you compare far away clocks relative your 'local clock', macroscopically defined as being 'at rest' with you (although still subject to microscopic gravitational time dilations). As you in your observatory, measuring, using the clock on the wall as your local reference. Then 'a far away arrow' becomes subject to Lorentz transformation, to fit your local one.

It's a very tricky subject, for example, where is a consciousness situated? Does it have a specific location, or is it a synthesis, undefinable to any single location, over a brain? If it is a synthesis and we assume that it should be able to define a 'frame of reference' as something meaningful in itself (physically). Then choosing Planck scale as the 'smallest common nominator' for both 'c' and that  local arrow. Then your brain, and subsequent thoughts, must handle 'time dilations' as well as 'Lorentz contractions', assuming that those two are complementary.
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corrected a question mark :)
da*n.
=

As I already destroyed the unspoiled beauty of my post, if you're considering presenting a new theory, TNS have a lovely spot for those in 'New Theories'.

And a simple proof for a arrow, as being a local 'constant', is the fact that wherever you go that 'local clock' follows you. And your lifetime, relative that clock, is a set one.
« Last Edit: 18/06/2013 17:32:36 by yor_on »
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Offline AndroidNeox

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Re: Do we know exactly what time is?
« Reply #2 on: 24/06/2013 22:05:18 »
This sort of metaphysical question isn't what contemporary physics excels at... the general mental rigor of natural philosophy has been replaced by mathematical expertise (even if the equations are often misapplied).

I think that a better question than "what is time?" is, "when we measure time, what do we measure?". The first includes the assumption that time is something. Time doesn't seem to be a "something" any more than space does. Neither are conserved quantities. Einstein felt that "space" had no meaning independent of the fields within it.

When we measure time we are counting a sequence of events: heart beats, pendulum swings, quartz vibrations, etc. When we time some process we are comparing counts of two or more sequences.

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Offline Alan McDougall

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Re: Do we know exactly what time is?
« Reply #3 on: 25/06/2013 10:03:59 »
:)

locally it is a constant.

It's only when you compare over frames of reference you find it to give you a time dilation. Using gravitational time dilations your body can be defined to belong to different 'time zones' if you like. But from each position (loosely speaking) in SpaceTime its clock has a 'constant rate', definable as locally invariant, just as 'c' will be so for each of those 'frames of reference'. That as a 'gravity' can be translated, according to the equivalence principle, into a uniform constant acceleration. So you can consider all those 'points' of your body as 'differently gravitationally accelerating', although each one of them must present you with 'c' locally, as a 'constant', just as they must with that  'arrow'.

And that is a local definition.

Defining time 'globally', you have to measure over 'frames of reference'. Doing so you compare far away clocks relative your 'local clock', macroscopically defined as being 'at rest' with you (although still subject to microscopic gravitational time dilations). As you in your observatory, measuring, using the clock on the wall as your local reference. Then 'a far away arrow' becomes subject to Lorentz transformation, to fit your local one.

It's a very tricky subject, for example, where is a consciousness situated? Does it have a specific location, or is it a synthesis, undefinable to any single location, over a brain? If it is a synthesis and we assume that it should be able to define a 'frame of reference' as something meaningful in itself (physically). Then choosing Planck scale as the 'smallest common nominator' for both 'c' and that  local arrow. Then your brain, and subsequent thoughts, must handle 'time dilations' as well as 'Lorentz contractions', assuming that those two are complementary.
=
corrected a question mark :)
da*n.
=

As I already destroyed the unspoiled beauty of my post, if you're considering presenting a new theory, TNS have a lovely spot for those in 'New Theories'.

And a simple proof for a arrow, as being a local 'constant', is the fact that wherever you go that 'local clock' follows you. And your lifetime, relative that clock, is a set one.

Even locality is not in absolute terms a constant, simply because the different parts of you physical body move at differently rates, relative to other parts of your body. Thus, your legs might be moving due to walking and your arms held over your head stationary to the rest of your torso. Thus, relative to each other they are moving at different rates and this effects time, albeit so infinitesimally tiny, that on our human macro scale it is meaningless, but, nevertheless real in the quantum world of the minute.

Time is really a mystery?

Alan

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Offline evan_au

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Re: Do we know exactly what time is?
« Reply #4 on: 25/06/2013 10:49:40 »
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your arms held over your head stationary to the rest of your torso
If your hands are over your head, then they are further out of Earth's gravitational field.
So time passes more rapidly for your hands than your feet (by an infinitesimal but measurable amount).

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Offline Alan McDougall

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Re: Do we know exactly what time is?
« Reply #5 on: 25/06/2013 15:30:30 »
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your arms held over your head stationary to the rest of your torso
If your hands are over your head, then they are further out of Earth's gravitational field.
So time passes more rapidly for your hands than your feet (by an infinitesimal but measurable amount).

What you stated is true, but so is my example!

I, however, disagree that it is possible to measure the difference rates of time, between your hand and feet due to the effect of gravity? The force of gravity is incredibly weak and the effect you are referring to is simply imperceptible to our very best measuring devices, even atomic clocks would not pick up this effect.

Alan

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« Last Edit: 25/06/2013 15:39:41 by Alan McDougall »
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Re: Do we know exactly what time is?
« Reply #6 on: 25/06/2013 15:38:26 »
Yep, you can use gravitational time dilations and their complementary Lorentz contractions to define 'time zones'. But to do that you need a 'local clock' from where to compare it. There are two ways to define one single frame of reference. You can either use being 'at rest', as we macroscopically can be defined being 'at rest' with earth in its relative motion. Or you can refer to some 'inertially defined' object.

Then there is a third that I'm wondering about, and that is in fact that 'local clock' you either way must use, no matter if you define it macroscopically or microscopically.

It exists, and you can't work around it. And that one, if possible to define, I would define as belonging to Planck scale, as that is where light 'freeze' :), holding at one Planck length in one Planck time. As well as it is there physics stops giving you meaningful answers.
« Last Edit: 25/06/2013 15:40:21 by yor_on »
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Offline Alan McDougall

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Re: Do we know exactly what time is?
« Reply #8 on: 25/06/2013 15:46:21 »
Yep, you can use gravitational time dilations and their complementary Lorentz contractions to define 'time zones'. But to do that you need a 'local clock' from where to compare it. There are two ways to define one single frame of reference. You can either use being 'at rest', as we macroscopically can be defined being 'at rest' with earth in its relative motion. Or you can refer to some 'inertially defined' object.

Then there is a third that I'm wondering about, and that is in fact that 'local clock' you either way must use, no matter if you define it macroscopically or microscopically.

It exists, and you can't work around it. And that one, if possible to define, I would define as belonging to Planck scale, as that is where light 'freeze' :), holding at one Planck length in one Planck time. As well as it is there physics stops giving you meaningful answers.

I agree at the Plank limits such as Plank time we can't get meaningful answers, however, do we know for sure that the Plank limits on time are really the absolute smallest possible division of time? Has this been proven in any scientific experiment?
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Online yor_on

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Re: Do we know exactly what time is?
« Reply #9 on: 25/06/2013 15:58:49 »
You can't prove anything, as none can probe that scale Alan, that is as far as I know. What makes me define that way is that it is a limit for what makes sense physically. Under it we meet a new regime. If you use 'c' (locally measured), and split it into even chunks of 'time', to define ones local arrow, then at Planck scale that arrows stops 'move' just as light. What then might be 'under it' must be 'something totally else'. You do not have a arrow (locally defined) under that scale as I expect.
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Re: Do we know exactly what time is?
« Reply #10 on: 25/06/2013 16:12:06 »
The problem with probing something is that you will use your local arrow (clock) to measure. So if we define it this way you will still measure it 'taking time' by the macroscopically, arbitrarily defined, 'clock' you do use in your measurement. To really define it, measuring by a experiment, should be impossible as we are talking about something at Planck scale, and measured strictly locally 'in itself', not by you using a macroscopic definition of a 'local clock' to measure it by. It becomes a contradiction in terms doing it by comparing. The only way you can define time as 'stopping' is relative another frame of reference, as you measuring a event horizon using that local clock of yours to compare it to. And that one is only true relative your clock, for someone at that event horizon, 'locally' defined, time is as always and ticks. But to measure inside a frame of reference, being at one Plank length, belongs to science fiction so far :) Never the less, my logic works for me. We all need that 'local clock' to exist, and it 'ticks' relative 'c', both locally defined as constants, but the clock is not well defined quantum mechanically.
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Re: Do we know exactly what time is?
« Reply #11 on: 25/06/2013 16:27:49 »
Using it this way moves 'c' from being a 'speed', to instead becoming a pure mathematical constant. Locally defined and locally true, wherever you go, however fast you find it, relative some other frame of reference. Every constant that exists must be true locally defined. We then compare our local descriptions with each other, and if we find them agreeing from our locally expressed 'repeatable experiments', we lift them up to constants. But locality and that clock, to me that is, starts at Planck scale, as 'c' begets a 'speed' over frames of reference, always locally defined. Although depending on choice of macroscopic clock, still arbitrarily done from a quantum mechanical point of view.
« Last Edit: 25/06/2013 16:34:41 by yor_on »
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Offline Alan McDougall

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Re: Do we know exactly what time is?
« Reply #12 on: 25/06/2013 16:39:34 »
You can't prove anything, as none can probe that scale Alan, that is as far as I know. What makes me define that way is that it is a limit for what makes sense physically. Under it we meet a new regime. If you use 'c' (locally measured), and split it into even chunks of 'time', to define ones local arrow, then at Planck scale that arrows stops 'move' just as light. What then might be 'under it' must be 'something totally else'. You do not have a arrow (locally defined) under that scale as I expect.

I wonder does time flow like a river or can it be broken down into smaller and smaller discrete moments , something like frames on a movie reel?
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Re: Do we know exactly what time is?
« Reply #13 on: 25/06/2013 16:53:36 »
From my thinking :) I think it 'flows', because as long as we introduce one more frame, comparing between two, you must find 'c', and that goes microscopically as well as well as macroscopically. you can only 'freeze' that arrow using one single frame of reference, and, as I think? How would one do that measurement? But you can also consider it a 'bit' as we, at least theoretically, might be able to define it as a 'quanta of time' at Planck scale.
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Re: Do we know exactly what time is?
« Reply #14 on: 25/06/2013 18:30:45 »
I, however, disagree that it is possible to measure the difference rates of time, between your hand and feet due to the effect of gravity? The force of gravity is incredibly weak and the effect you are referring to is simply imperceptible to our very best measuring devices, even atomic clocks would not pick up this effect.
Alan
If the distance between your head and feet is one metre or just under, then these chaps claim to have measured/detected the relative time difference over that distance.

Quote
We can now also detect time dilation due to a change in height near Earth’s surface of less than 1 meter. This technique may be extended to the field of geodesy, with applications in geophysics and hydrology as well as in space-based tests of fundamental physics.
From http://adsabs.harvard.edu/abs/2010Sci...329.1630C

Quote
In 2010, Chou et al. performed tests in which both gravitational and velocity effects were measured at velocities and gravitational potentials much smaller than those used in the mountain-valley experiments of the 1970's. It was possible to confirm velocity time dilation at the 10-16 level at speeds below 36 km/h. Also, gravitational time dilation was measured from a difference in elevation between two clocks of only 33 cm
from http://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment#Similar_experiments_with_atomic_clocks
« Last Edit: 25/06/2013 18:53:19 by lean bean »

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Offline Alan McDougall

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Re: Do we know exactly what time is?
« Reply #15 on: 25/06/2013 19:12:11 »
I, however, disagree that it is possible to measure the difference rates of time, between your hand and feet due to the effect of gravity? The force of gravity is incredibly weak and the effect you are referring to is simply imperceptible to our very best measuring devices, even atomic clocks would not pick up this effect.
Alan
If the distance between your head and feet is one metre or just under, then these chaps claim to have measured/detected the relative time difference over that distance.

Quote
We can now also detect time dilation due to a change in height near Earth’s surface of less than 1 meter. This technique may be extended to the field of geodesy, with applications in geophysics and hydrology as well as in space-based tests of fundamental physics.
From http://adsabs.harvard.edu/abs/2010Sci...329.1630C

Quote
In 2010, Chou et al. performed tests in which both gravitational and velocity effects were measured at velocities and gravitational potentials much smaller than those used in the mountain-valley experiments of the 1970's. It was possible to confirm velocity time dilation at the 10-16 level at speeds below 36 km/h. Also, gravitational time dilation was measured from a difference in elevation between two clocks of only 33 cm
from http://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment#Similar_experiments_with_atomic_clocks

If that is true, it is beyond amazing!
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Online yor_on

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Re: Do we know exactly what time is?
« Reply #16 on: 25/06/2013 23:47:31 »
You can see the universe we exist in two ways. The one we're most used to is the one in where we share a common universe. In that one we're 'here', all together. I can touch someone, they can touch me. We are 'here'.

In the other we're still here, but your definition of that universe is not mine. I can translate your definition to mine, you can translate mine to yours. If I would take a measurement of a distance in this universe it will be true for me, and my arrow of time, and life span, is directly connected to my measurement of 'c'. But to fit it to your description of a universe, 'time' and a distance we might need Lorentz transformations. We're still 'here' though, but what defines us is 'c', and frames of reference. I was stuck on this one for the longest time, and in a way I still am.

To reconcile those two definitions we use the same constant, 'c'. But looking at it my way simplify some things, your life span for example. And the way we define a repeatable experiment. It becomes two definitions, depending on what view you take of life, the universe, and all, as Douglas Adams would have said :)

It's not as much as one must be truer, it's just that I like to simplify it, as good as I can.
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Offline Alan McDougall

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Re: Do we know exactly what time is?
« Reply #17 on: 27/06/2013 13:26:45 »
You can see the universe we exist in two ways. The one we're most used to is the one in where we share a common universe. In that one we're 'here', all together. I can touch someone, they can touch me. We are 'here'.

In the other we're still here, but your definition of that universe is not mine. I can translate your definition to mine, you can translate mine to yours. If I would take a measurement of a distance in this universe it will be true for me, and my arrow of time, and life span, is directly connected to my measurement of 'c'. But to fit it to your description of a universe, 'time' and a distance we might need Lorentz transformations. We're still 'here' though, but what defines us is 'c', and frames of reference. I was stuck on this one for the longest time, and in a way I still am.

To reconcile those two definitions we use the same constant, 'c'. But looking at it my way simplify some things, your life span for example. And the way we define a repeatable experiment. It becomes two definitions, depending on what view you take of life, the universe, and all, as Douglas Adams would have said :)

It's not as much as one must be truer, it's just that I like to simplify it, as good as I can.

Although off topic, this does relate to your post above. How each person might perceive the same thing differently.

Take colour perception,do you see red exactly as I do RED or
BLUE. So long as our different perception are consistent with each other, how are we ever to know for sure, we are both observing the same thing in the exact same way?

Perception of time might be different from person , to person, under the exact same conditions?

Alan
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Offline Pmb

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Re: Do we know exactly what time is?
« Reply #18 on: 27/06/2013 16:27:07 »
Hi

What is time?

Some say it is just measure of movement or an aggregation of events. Time is not a constant and I would like you guys to put forward your own ideas on the topic before adding my piece to the story.

Alan
I would define time as the phenomena which pertains to different configurations of the world around us.

 
What then is time? If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know. - St. Augustine

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Offline Alan McDougall

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Re: Do we know exactly what time is?
« Reply #19 on: 27/06/2013 18:45:58 »
Hi

What is time?

Some say it is just measure of movement or an aggregation of events. Time is not a constant and I would like you guys to put forward your own ideas on the topic before adding my piece to the story.

Alan
I would define time as the phenomena which pertains to different configurations of the world around us.

 
What then is time? If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know. - St. Augustine



I would like to post a dream about time I had a few years ago, please!, I am not going metaphysical, my odd dream just shows how strange time and movement could be from different perspectives. It is not a reflection of reality

What I am now going to describe is very weird, but it is a lucid dream I have had and for which I simply have no explanation. I seem to go to another dimension or universe, where time and movement were reversed, relative to everything and me, in this alternate dimension, everyone was moving backwards in time and movement.

You might have heard the phrase, "In the land of the blind the one eyed man is king"

In this bizarre alternate reality, I who could move both back and forward appeared to be king as I could easily reveal or hide myself there. Take one example, I saw a man who was walking backward after a workday at 5 pm, to his bedroom when he got up at 9am.  As he started to walk backwards from his desk 5pm, from my perceptive, time and movement,I was walking forward. However, in his reality he was moving (walking) back in time to the morning when he left for work at 9am. (moment)

From my viewpoint, I arrived at the moment he began to walk backward from his work desk at 5pm, to the elevator, reversing back to the moment when he got up at 9am in the morning. As I watched him he synchronized exactly with the elevator the moment door of the elevator opened, without looking, he just backed into the elevator. Weird not really! If you play the scenario forward in time and movement, when the elevator reached his floor, it opened and he got out and went to his desk, as if anyone would in our reality.

To try and make him aware my presence, I walked forward in front of him, because from my perspective, he was reversed and walking backward, from his evening at 5pm to his morning at 9pm, when he got up for work. He became very distressed by me, because he saw me, as a being that suddenly appeared in front of him. From his perceptive as he walked forward to his desk, he saw me walking backward in front of him in, no matter how hard tried to get rid of this apparition, that was I, I was always in front of him, reversing by walking backward relative to him. During another moment, I got behind him as he was walking backward and stopped him by placing my hands firmly on his back, thus, in his world he was suddenly stopped by some sort of outside force with a weird sense that there was another entity behind him that he could not identify. I think the hairs on his neck stood up straight. I could really have fun here I was the phantom of the opera in that moment.

In my dream, he was a very real person and I could see he was confused even frightened by the apparition, that was I. To him, I had become an unpleasant ghostly thing from some alternate reality. The interaction between these two alternate reversed time dimensions, were so complex, I think maybe one would need more than an Einstein, to explain what was really going on.

For instance, I noticed that at moments he could see me and tried to rush at me and touch me. When he did that, I simply stood still and slowly receded out of view, from his perceptive. When he to rushed/ran toward me, the time, the time, distance and movement variations between our alternate realities just increased. When he ran faster and faster toward me all that happened was, I moved receded faster and faster backward in distance and time from him.

The harder he tried to touch or reach me, the more I receded. "Weird" very "Weird" From his perspective he was moving forward in time, and I was reversing time and movement. I following him back from 5 pm, the moment he was supposed to knock off work him, until 9 am when he left for work and got out of bed. The dream is hard to explain and confusing and convoluted, but it really gives one a glimpse of how strange time and movement can be from different perspectives and perceptions.

Alan  8D
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Offline RD

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Re: Do we know exactly what time is?
« Reply #20 on: 27/06/2013 20:09:17 »
... it is a lucid dream I have had and for which I simply have no explanation. I seem to go to another dimension or universe, where time and movement were reversed ...

Are you sure it wasn't the "backwards" episode of "Red Dwarf"  [:)] ...

Quote from: wikipedia.org/wiki/Backwards_(Red_Dwarf_episode)
Kryten and Rimmer think that the backwards world is wonderful, pointing out that when the second world war comes around again, millions of people will come back to life, and Hitler will retreat across Europe, liberating France and Poland. Lister though looks at the other side of the argument and states that in this universe St. Francis of Assisi is the petty-minded little sadist who maims small animals and that Santa Claus is a big guy who sneaks down chimneys and steals all the kids' favourite toys.
http://en.wikipedia.org/wiki/Backwards_%28Red_Dwarf_episode%29#Cultural_references
« Last Edit: 27/06/2013 20:19:24 by RD »

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Online Bill S

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Re: Do we know exactly what time is?
« Reply #21 on: 28/06/2013 03:07:59 »
Quote from: Alan
I following him back from 5 pm, the moment he was supposed to knock off work him, until 9 am when he left for work and got out of bed.

I assume you spotted the inconsistency here.  At 9am, had he been travelling backwards through time, he would have fallen backwards into bed, his alarm would have gone off and he would have gone to sleep.  Time reversal is a complex thing.  I'm very pushed for time at the moment, but I hope to have a chance to air a few of my thoughts on the subject.
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Offline evan_au

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Re: Do we know exactly what time is?
« Reply #22 on: 28/06/2013 06:40:23 »
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I, however, disagree that it is possible to measure the difference rates of time, between your hand and feet due to the effect of gravity
The aluminium clock experiment at NIST in 2010 were a significant advance in timekeeping. But I was referring to earlier measurements that were able to detect time dilation effects over altitude differences as small as 30mm (not 30 cm).

The earlier researchers had a coherent beam with a very short wavelength. They aimed it at a target which split the beam in 2 paths, and then recombined it, causing interference fringes.

By rotating the splitter/recombiner, they were able to make the two beams take paths with the same altitude or different altitudes, and they could see changes in the interference patterns. They interpreted the results as showing that when the beam was further from the Earth, time passed more rapidly, so the beam was out of phase when recombined with the lower beam.

This is a very difficult experiment due to the required mechanical tolerances, but was an ingenious way to demonstrate the effect of time dilation on human scales without requiring two calibrated clocks - you just need one stable source.

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Offline syhprum

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Re: Do we know exactly what time is?
« Reply #23 on: 28/06/2013 11:01:09 »
I wonder if it has been considered when we seek to communicate with aliens that they may have vastly different life times than us and that their conception of time may be very different from ours.
If they have the life time of a mountain 1 Hz would be supersonic but if they have the life time of a fly it would represent an extremely low frequency. 
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Offline Alan McDougall

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Re: Do we know exactly what time is?
« Reply #24 on: 28/06/2013 14:53:24 »
Quote from: Alan
I following him back from 5 pm, the moment he was supposed to knock off work him, until 9 am when he left for work and got out of bed.

I assume you spotted the inconsistency here.  At 9am, had he been travelling backwards through time, he would have fallen backwards into bed, his alarm would have gone off and he would have gone to sleep.  Time reversal is a complex thing.  I'm very pushed for time at the moment, but I hope to have a chance to air a few of my thoughts on the subject.

Yes it was difficult to write and keep in mind the two opposite arrows of time , within the alternate dimensions. I will look at your comment and correct the error.

Alan
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Offline Alan McDougall

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Re: Do we know exactly what time is?
« Reply #25 on: 28/06/2013 15:08:45 »
... it is a lucid dream I have had and for which I simply have no explanation. I seem to go to another dimension or universe, where time and movement were reversed ...

Are you sure it wasn't the "backwards" episode of "Red Dwarf"  [:)] ...

Quote from: wikipedia.org/wiki/Backwards_(Red_Dwarf_episode)
Kryten and Rimmer think that the backwards world is wonderful, pointing out that when the second world war comes around again, millions of people will come back to life, and Hitler will retreat across Europe, liberating France and Poland. Lister though looks at the other side of the argument and states that in this universe St. Francis of Assisi is the petty-minded little sadist who maims small animals and that Santa Claus is a big guy who sneaks down chimneys and steals all the kids' favourite toys.
http://en.wikipedia.org/wiki/Backwards_%28Red_Dwarf_episode%29#Cultural_references

I went to the link, but my dream had nothing to do with that movie, I have dreamed this type of dream a few times, and they are very disturbing, nightmares in fact.

Thinking about the dream again, the two entities in the dream , me and the person in the other backward realm, might only really observe each other in brief 'moments', when they stood still relative each other, (within visual range), or exactly when the exact "moment" the two arrows of times crossed paths in opposite direction.

I , think , however, they do give a sort of an indication how truly strange and complex time can be, if viewed from different relative perspectives :)
« Last Edit: 28/06/2013 15:11:03 by Alan McDougall »
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Re: Do we know exactly what time is?
« Reply #26 on: 02/07/2013 23:46:14 »
  On the subject of communication between beings who are travelling in opposite directions through time,  J. R. Lucas has argued they could not communicate,  even if they could meet. He states: "If two beings are to regard each other as communicators, they must both have the same direction of time.  It is a logical as well as a causal prerequisite".  This may seem almost self-evident and, perhaps, absolutely irrefutable.  The philosopher Murray MacBeath, however, disagrees.

Professor MacBeath explains, ‘While Jim and Midge are together a face-to-face conversation is hardly likely to get of the ground.  To make this clear let us say that they are together from t0 until t10 on Jim’s time-scale, and from T0 until T10 on Midge’s TIME-scale; t0 is then the same temporal instant as T10 and, in general, tn = T10 – n.  If Jim at …t2 asks Midge a question, and Midge hears the question at T8, she will answer at T9, and Jim will hear his question answered at t1, before he asked it.  What is more, if Jim is inexpert at interpreting backward sounds, and at t4 asks Midge to repeat her answer, Midge will hear this request at T6, BEFORE she has heard the original question; and her puzzled reply at T7 will again be heard by Jim at t3, before he has uttered the request.’

Lucas seems to be on safe ground with his denial of the possibility of communication.  MacBeath, however, shows how to refute all of Lucas’s arguments if Midge and Jim are allowed to be clever about how they send messages back and forth.  To follow the logic, it will be helpful to look at Fig. 1 (a simplified version of MacBeath's scheme, above) for the time direction for Jim and Midge:
 
We imagine that Jim and Midge will not actually talk and thus have to decipher backward-spoken language.  Rather, they will exchange messages via computer-generated text displayed on monitor screens.  We can, in fact, imagine that Jim and Midge are separated by a window that is proof against all penetration but light.  Now, at t0 Jim brings a computer to the window.  He programs it to wait for four days, until t4, and then to display the following message on the screen: "This message is from Jim, who experiences time in the sense opposite to yours.  Please study the following questions and display your answers on a computer screen three days from now."

                               Fig. 1

earlier                                          Jim (normal time)                                        later
t0                            t1                            t2                            t3                            t4

T4                                    T3                            T2                          T1                           T0                                                               LATER                                  MIDGE (reversed time)                               EARLIER

   
    Jim’s message ends with a list of questions.  Since this will appear at t4, Midge sees it at what we will now call T0.  As requested, she brings her computer to the window, enters the answers to Jim’s questions, and programs the machine to display them (after a three-day delay) on its screen.  Thus, at T3, which is Jim’s t1, Jim sees Midge’s computer screen light up with: "Hi, Jim.  This is Midge.  The answers to your questions are at the end of this message.  Now, I’ve got some questions for you.  Please display the answers two days from now."  Midge’s message ends with Jim’s answers and her list of questions.  Jim sees Midge’s message at t1, enters the answers to her questions and sets the machine to answer after a two-day delay, at t3, which is Midge’s T1 – and by now you see how the process goes.  It’s cumbersome, but, according to MacBeath, it does work.

I have very grave doubts about this and would be glad to hear what others think before going further.

Not least among my doubts is the length of time which they would have together.  This links us to Alan's moment in time.
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Re: Do we know exactly what time is?
« Reply #27 on: 03/07/2013 09:26:39 »
I would expect causality (and logic) to demand all processes to have one ('same') arrow (direction) in time. Although you can imagine scenarios in where comparing between frames of reference giving you answers not making sense in form of communicating.

To really have two arrows going in the opposite direction, relative each other, becomes to me a contradiction in terms. Just consider the implied entropy for it to happen, sharing a 'same' coordinate system, as it here is assumed.
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Re: Do we know exactly what time is?
« Reply #28 on: 03/07/2013 09:43:44 »
The only way I can see for me to assume such a thing is to invalidate the arrow of time. In such a universe you can't have entropy existing either. Neither will there be a simple logic to it, and it does not fit what we see. When Einstein called time a 'illusion' I do not read that as him meaning that it didn't exist, only that in comparing between coordinate systems (3 D + a arrow) you may get answers that surprise. But built in in relativity is a assumption of me the observer having a arrow of time, and causality, and a simple logic, making it possible for me to get meaningful answers comparing between frames. And a further assumption that the same exist for you too, observing me. That gives us all a 'same direction' in time, relative any local clock measuring other frames of reference. To prove this wrong you then need another universe, without arrows, and so without the logic we find, as all processes defined in this universe goes one way. To simplify, you should need a universe in where you can assume some 'infinite energy' to exist in a nothing 'entropically', to then 'disappear' as the causality process we assume reverse under that 'arrow' we define to exist. That would give us a really interesting universe I think, but it's not the one I see.
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Re: Do we know exactly what time is?
« Reply #29 on: 03/07/2013 23:43:04 »
There is one way though. That would be assuming that all events are 'fragments', unique in themselves. but to get to the logic defining our 'common, and 'shared' universe' you will still need something, joining them. and the simplest definition of that, should be a arrow.
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Offline AndroidNeox

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Re: Do we know exactly what time is?
« Reply #30 on: 04/07/2013 01:22:43 »
Yep, you can use gravitational time dilations and their complementary Lorentz contractions to define 'time zones'. But to do that you need a 'local clock' from where to compare it. There are two ways to define one single frame of reference. You can either use being 'at rest', as we macroscopically can be defined being 'at rest' with earth in its relative motion. Or you can refer to some 'inertially defined' object.

Then there is a third that I'm wondering about, and that is in fact that 'local clock' you either way must use, no matter if you define it macroscopically or microscopically.

Right.

Example:
A simple clock suitable for relativistic thought experiments might be a resonant chamber of known length with mirrors reflecting a pulse of light back and forth. Usually the reference clock is not under any acceleration (occupying an inertial frame). Since the speed of light is guaranteed to always be the same for all observers in all reference frames, a resonant chamber of known length would register one reflection of the light pulse every t seconds, (2 x Distance btwn. mirrors)/c.

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Online yor_on

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Re: Do we know exactly what time is?
« Reply #31 on: 04/07/2013 09:55:50 »
A 'light clock' is a nice idea, given that you only can define that arrow from a local definition. To someone not 'inertially based' it will present him with another rhythm. Different mass and speeds presents you with different measurements of that light clocks rhythm. This light clock can also be defined to all rhythms, co-existing sort of, 'simultaneously', depending on what observer that measure it. 'Simultaneously' as we should be able to assume that if the arrow has a 'constant' existence, and it has. Then, no matter where in space and time you define it to a certain rhythm, someone else should be able find another rhythm, relative his 'motion and mass', comparing.
==

This one is me using ideas from a 'globally same, common' universe, just as we normally find it to be. 'Locally defined' the universe becomes something different. And discussing a 'arrow of time' as something 'unitary', sweeping through the universe taking us with it, becomes a lot more tricky if we introduce 'locality' as the base from where we observe. But it also has to do with our definitions of dimensions, distances, etc.
=

To me it's all about comparisons, done relative ones own (local) clock. And joining your reference frame to what you measured, all clocks tick the same. That makes a local definition of a clock possible, equivalent to 'c'. Relative such a 'perfect' local(ized) clock, your life has a unchanging constant duration, your life span the same everywhere.

One can imagine it as a SpaceTime of perfect clock quanta, all set to a 'same rhythm' at some 'origin' (as proven by joining 'frames of reference' into one singular). Then introduce relative motion, accelerations/decelerations and mass/'energy', and comparisons between frames of reference..
« Last Edit: 04/07/2013 10:33:27 by yor_on »
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Re: Do we know exactly what time is?
« Reply #32 on: 04/07/2013 10:11:48 »
'Simultaneity' can be used in a locally defined SpaceTime. Equivalence is not wrong either, as you can define a locally unchanging arrow, of a same duration,  'shared' by all measuring, locally defined. It's like we have a overlay over that 'perfect origin of rhythm', redefining our observations of it, when comparing over frames of reference.

But it's also about what a 'frame of reference' represent. Take for instance being 'at rest' with something. Using gravitational time dilations nothing is perfectly 'at rest' with anything, as a guess. Not if I define a clock to a 'quanta', defining that as a smallest meaningful origin of a 'frame of reference'. But I think it is that way, anyway :)
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Re: Do we know exactly what time is?
« Reply #33 on: 04/07/2013 10:53:28 »
As for the examples, causality can't be exempted in this universe. Assuming that you get a answer to a question unasked, you first must disallow (as in exempt) causality. Imagine yourself changing the question, would now the, already perceived, answer change too? A universe of magic that would be, not our SpaceTime :) Although you might assume that it all is 'set', no free will existing etc, in which case you never change your mind, ever, as it all already must be set, and so 'foretold'. Not making much sense to me. And that's simple logic.

Don't mix this with QM and the idea of you changing a variable (outcome), through changing the measurement though. That one can be thought of a having a 'set pattern', but it also assume 'free will', meaning you changing your mind under that measurement.

The other way to see it is to assume causality not to be needed, in which case a arrow isn't there anymore, although you still presume a logic to exist to even define this idea. What would that logic be based on? Can't use statistics, that belongs to histories aka a arrow existing. What will you use?
=

Using scales we find QM, and new definitions, but scale related. Whatever allows you to grow old macroscopically, and see others doing the same, will be a arrow to me. That arrow is what defines causality. Without it 'energy' is for free, nothing is forbidden, limits won't exist, and wild magic runs free :). QM has rules just as relativity so there must be limits set there too, and causality, as everything you measure first must become a outcome to exist for us. Defining a unlimited energy to something over a too short period of time to be able to exist tells you the same, limits exist as well as causality. We are governed by this, outcomes define our universe and they follow a logic becoming our arrow, and causality.
« Last Edit: 04/07/2013 11:05:46 by yor_on »
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Offline Thibeinn

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Re: Do we know exactly what time is?
« Reply #34 on: 24/07/2013 19:27:35 »
I will use a Human holding a clock in my example...

As the velocity of the Human with a clock increases, the inertia of every atom in the Human's body and every atom in the clock increases.  This results in more and more energy being needed to move those atoms in such a way as for the Human's bodily functions and the clock's functions to continue with the result that both the Human's biological functions, and the clocks functions, slow down.  Another result is that the Human's rate of aging slows down.

Likewise, as the gravity increases, the weight of the atoms increases and require more and more energy to move them.


As the velocity of the Human with a clock decreases, the inertia of every atom in the Human's body and every atom in the clock decreases.  This results in less and less energy being needed to move those atoms in such a way as for the Human's bodily functions and the clock's functions to continue with the result that both the Human's biological functions, and the clocks functions, speed up.  Another result is that the Human's aging speeds up.

Likewise, as the gravity decreases, the weight of the atoms decreases and require less and less energy to move them.


Time is simply the measurement of this speeding up or slowing down due to increased or decreased inertia and/or weight brought about by increased or decreased velocity and/or gravitational force.

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Offline AndroidNeox

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Re: Do we know exactly what time is?
« Reply #35 on: 23/09/2013 21:03:26 »
I prefer to approach these problems by accepting science can only deal with the observable and to see if stepping back and examining my definitions in observational terms helps. While doing that I realized it's easy to show that time can only be observed in systems of increasing entropy (information content).

When we observe, or measure, time, we observe a sequence (ticks, pendulum swings,...). To observe a sequence, information about prior states has to be retained. The longer the sequence, the more state info is required. For a system like our universe in which time seems to be proceeding without end, the entropy accumulation would be unbounded.

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Offline Pmb

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Re: Do we know exactly what time is?
« Reply #36 on: 24/09/2013 03:05:36 »
Hi

What is time?

Some say it is just measure of movement or an aggregation of events. Time is not a constant and I would like you guys to put forward your own ideas on the topic before adding my piece to the story.

Alan
Time is merely what we associate and use to specify the way things in the world around us change. E.g. how long has it been since my last cup of coffee or how long has my coffee be cooling off.

A good discussion has been given by my friend at http://users.wfu.edu/brehme/time.htm
« Last Edit: 24/09/2013 03:08:30 by Pmb »

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Offline Yojimbo

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Re: Do we know exactly what time is?
« Reply #37 on: 18/07/2014 13:38:29 »
Time is a bi-product of the collapse of an absolute state existence. Light does not suffer from having a relative frame of reference, and travelling at c, it does not "feel" time. Wave function collapse only happens upon observation, which requires a connection, by definition a relation to something else. Time is simply an old metaphor for relativity.
« Last Edit: 18/07/2014 13:42:45 by Yojimbo »

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Online Bill S

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Re: Do we know exactly what time is?
« Reply #38 on: 18/07/2014 16:03:11 »
Time is a perennial topic in science discussion forums, and is one of those topics that never seems to go anywhere.

Like St Augustine, we all know what time is, if no one asks.  The problem is that people will ask.  This leads to countless personal animadversions and interminable discussions which tend to progress in circles towards the inevitable non-conclusion.

Does time exist?  Discounting diversionary responses like “define existence”, the answer must be “yes”.  Time exists, but does it exist as something independent, or is it only something that exists in our minds?  Compare questions such as: “Does truth exist?”.  Again the answer must be yes.  It exists as a concept that is relevant to human communication.  Without rational beings it has no significance.  We know what it means, but philosophers can argue interminably about it.  Time is very similar.  It is essential to our reasoning, our understanding of the Universe and every aspect of our lives.  It is essential to every measurement we make, but without something to measure, it has no significance.  Why do we need to ask more of it?   
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Offline chiralSPO

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Re: Do we know exactly what time is?
« Reply #39 on: 18/07/2014 19:42:48 »
I wonder if it has been considered when we seek to communicate with aliens that they may have vastly different life times than us and that their conception of time may be very different from ours.
If they have the life time of a mountain 1 Hz would be supersonic but if they have the life time of a fly it would represent an extremely low frequency.

I don't know how well lifetime correlates with perceived time (especially across species or across galaxies). But I agree with the premise that communication (or even recognition of intelligence or life) is limited by our perception of time. We are beings built of complex chemical compounds, and governed by chemical physics and chemical kinetics. I wonder if there could be life composed of complex nuclear states and governed by nuclear physics and kinetics (given that there is demonstration of catalysis in nuclear chemistry [see CNO cycle], I maintain that there could be life based on such processes. Their lifetimes would be very small, and the related energies and frequencies very large, so presumably they would have very short attention spans as well...

As far as beings (particles are a different matter) interacting with beings of opposite time flow, this is very tricky to think about, but I suspect that it would be impossible. There is no such thing as entropy for a system containing one immutable particle, but as there are more particles involved in a system, entropy begins to have meaning, defining a time arrow for that collection. If we consider transferring information from one system of interacting particles to another, then we have to consider the system containing both systems--in which direction does the whole system move? Whose rules are followed and whose are broken? The only way that the three systems behave with no contradictions is if there is no interaction. With photons, which do not experience time, there may appear to be a loophole, but for any photon that is exchanged, there would be a disagreement between the two systems, each believing it was the one that emitted the photon before the other absorbed it (or both thinking they had absorbed it after the other one emitted it). Conservation of energy is maintained, and no information was transferred.

I'm not really sure what the current theory is on how close particles need to be in space and time to interact--taking account of uncertainty, we have to put error bars on the spatial and temporal coordinates so there is essentially some 4-D spacetime sphere in which the particles need to be to interact. It might be possible for beings to communicate with each other for a brief instant when they are at the "same" time, but as they each move to substantially different times, they won't be able to interact anymore.

On the other hand, if one can think of a positron as an electron that is traveling backward in time, clearly it interacts with electrons moving forward in time (the electrons think the backwards moving positron is an electron and the positron thinks the "backward" moving electrons are positrons).

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Online Bill S

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Re: Do we know exactly what time is?
« Reply #40 on: 18/07/2014 21:11:40 »
The idea that an antiparticle is a particle travelling backwards in time is, perhaps, one of those unfortunate things that has arisen from a misapprehension.     

One might say: “It must be possible to travel backwards in time, because Feynman said that an antiparticle is just a particle travelling backwards in time.”  In fact, Feynman did not say that.  What he said was that the mathematics governing the evolution of a particle as time moves forwards is the same as the mathematics governing the evolution of an antiparticle as time moves backwards.  This is true, but it certainly does not mean that any physical object is travelling backwards in time.  Consider the electron and the positron.  We call the electron a particle and the positron an antiparticle; but that is simply convention.  We could equally well call the positron a particle and the electron an antiparticle.  Which of these would then travel backwards in time?       
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Re: Do we know exactly what time is?
« Reply #41 on: 19/07/2014 09:03:42 »
The idea that an antiparticle is a particle travelling backwards in time is, perhaps, one of those unfortunate things that has arisen from a misapprehension. One might say: “It must be possible to travel backwards in time, because Feynman said that an antiparticle is just a particle travelling backwards in time.”  In fact, Feynman did not say that.  What he said was that the mathematics governing the evolution of a particle as time moves forwards is the same as the mathematics governing the evolution of an antiparticle as time moves backwards.
Actually the idea was Wheeler's, not Feynman's.  Feynman just popularized it who himself attributed it to Wheeler who was his advisor. It's suspected that he meant it as a cocktail party joke. Not something to be taken seriously.

All of this is found in Introduction to Elementary Particles by David Griffiths, page 65-66. Griffith warns the reader not to take it too seriously.

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Re: Do we know exactly what time is?
« Reply #42 on: 19/07/2014 20:24:36 »
Space and time, opposites yet the same.  Photon is unchanging in time as it travels through space at c, yet it interacts with matter that is unchanging in space as it moves through time at 1/c.  Space and time are the terms we use to describe motion both are real measures of energy in the present. 

Mass is the past relative to us all, space is the present moment we all share as observers, and the force of gravity is us dilating into the future.

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Re: Do we know exactly what time is?
« Reply #43 on: 19/07/2014 21:45:44 »
Quote from: petm1
Space and time, opposites yet the same.
Woa! Where did you get that notion from? It's certainly not true. While in some respects space and time are treated on the same footing in relativity mathematical, it's certainly not true that their anything alike physically, that's for sure. Space is what you measure with a rod. Time is what you measure with a clock. You can go back in space but you can't go back in time. You can rotate one spatial axis (i.e. a rod) into another spatial axis but you can't rotate a rod into a clock.

Let me quote something Einstein said about this. From A Brief Outline of the Development of the Theory of Relativity by Albert Einstein, Nature, Feb. 17, 1921. page 783
Quote
From this it follows that, in respect to it's role in the equations of physics, though not with regard to its physical significance, time is equal to space coordinates (apart from the relations of reality).

Quote from: petm1
Photon is unchanging in time..
That too is also untrue. A photon moves through space and its phase changes with time. You're thinking about transforming into a photons frame of reference and making measurements there with a clock and comparing it to the photon's frequency, etc. However since it's impossible to do that you can't even speak of it. Therefore the only time that you can speak of regarding a photon is coordinate time. Just because you can't speak of a photons proper time it doesn't mean that it's unchanging. You'd never be able to step into a photons frame of reference to verify it and that's not science.
« Last Edit: 20/07/2014 01:13:53 by PmbPhy »

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Online Bill S

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Re: Do we know exactly what time is?
« Reply #44 on: 19/07/2014 22:49:26 »
Quote from:  Pete
Actually the idea was Wheeler's, not Feynman's.  Feynman just popularized it who himself attributed it to Wheeler who was his advisor. It's suspected that he meant it as a cocktail party joke. Not something to be taken seriously.

My apologies to Wheeler.  Of course, this is part of the pop-sci misapprehension.  Outside scientific circles, many people think Feynman was the originator and that he meant it to be taken seriously.  One can interpret this by saying that many people who read pop-sci books lack the discernment to realise the truth, and should educate themselves more thoroughly in scientific matters before reading pop-sci books; or one could say that scientists who supplement their income by writing books for non-scientists should run their explanations past (thinking) non-scientists to see if their readers are likely to hear what the authors intend saying. 
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Re: Do we know exactly what time is?
« Reply #45 on: 19/07/2014 22:58:40 »
Quote from:  Pete
Actually the idea was Wheeler's, not Feynman's.  Feynman just popularized it who himself attributed it to Wheeler who was his advisor. It's suspected that he meant it as a cocktail party joke. Not something to be taken seriously.

My apologies to Wheeler.  Of course, this is part of the pop-sci misapprehension.  Outside scientific circles, many people think Feynman was the originator and that he meant it to be taken seriously.  One can interpret this by saying that many people who read pop-sci books lack the discernment to realise the truth, and should educate themselves more thoroughly in scientific matters before reading pop-sci books; or one could say that scientists who supplement their income by writing books for non-scientists should run their explanations past (thinking) non-scientists to see if their readers are likely to hear what the authors intend saying.
You'd be surprised, my friend. Even some intelligent physicists think the same thing. I almost believed it myself in fact. When I heard it seemed dumb to me but I held off making a definite decision until I came to learn particle physics in much more depth. That's when I spoke to Griffiths and he told it to me. Griffiths and I communicate quite often in e-mail so I have a good source of information in many areas. He's a wonderful person and he's a great author.   

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Offline Ethos_

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Re: Do we know exactly what time is?
« Reply #46 on: 20/07/2014 20:00:10 »


I think that a better question than "what is time?" is, "when we measure time, what do we measure?".


I quite agree AndroidNeox. As you have said, Einstein determined that space has no meaning without the presence of the electromagnetic field. And likewise, in my estimation, time has no meaning unless we understand the significance of the words: Past, Present, and Future.

And as well, the term Past has no meaning without the memory of it which occurs in the Present. And likewise, the Future has no meaning without the cognizance of the Present in which the Future is anticipated.

The Present is the only true reality and it vanishes before us at the Planck scale. So how are we to measure it? Can we trust our memory? What is evident is that we all feel this passage of ours from the Present into the Future with varying degrees of trepidation and wonder.

John S. Mill's quote: "The more things change, the more they remain the same."

The passage of time is merely a measure of the change we record in our memory. Again I ask; "Can we trust our memory?"
« Last Edit: 20/07/2014 20:10:30 by Ethos_ »
"The more things change, the more they remain the same."

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Offline Alan McDougall

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Re: Do we know exactly what time is?
« Reply #47 on: 03/08/2014 19:34:21 »


I think that a better question than "what is time?" is, "when we measure time, what do we measure?".


I quite agree AndroidNeox. As you have said, Einstein determined that space has no meaning without the presence of the electromagnetic field. And likewise, in my estimation, time has no meaning unless we understand the significance of the words: Past, Present, and Future.

And as well, the term Past has no meaning without the memory of it which occurs in the Present. And likewise, the Future has no meaning without the cognizance of the Present in which the Future is anticipated.

The Present is the only true reality and it vanishes before us at the Planck scale. So how are we to measure it? Can we trust our memory? What is evident is that we all feel this passage of ours from the Present into the Future with varying degrees of trepidation and wonder.

John S. Mill's quote: "The more things change, the more they remain the same."

The passage of time is merely a measure of the change we record in our memory. Again I ask; "Can we trust our memory?"

Your response was more philosophical than scientific, but I agree that time is a mystery. Einstein once humorously said "time is something we invented to prevent everything from happening at once" What you presented in your post is the philosophical concept of "presentalism" look it up?
The Truth remains the Truth regardless of our beliefs or opinions the Truth is always the Truth even if we know it or do not know it (The Truth remains the Truth)

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Offline PmbPhy

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Re: Do we know exactly what time is?
« Reply #48 on: 03/08/2014 20:28:30 »
Quote from: Ethos_
And as well, the term Past has no meaning without the memory of it which occurs in the Present.
I disagree. To a small extent the past can be deduced from causality as well as memory.

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Online Bill S

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Re: Do we know exactly what time is?
« Reply #49 on: 03/08/2014 21:11:03 »
Quote from: AndroidNeox
I think that a better question than "what is time?" is, "when we measure time, what do we measure?"


What do we mean when we talk of measuring time?  Surely, time is the "thing" with which we do the measuring.
There never was nothing.