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Offline yor_on

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Why is it important to believe time is relative?
« Reply #25 on: 13/11/2011 14:23:29 »
Time is a weird subject. Almost everything in Physics becomes weird when you take it far enough. Maybe that's why I enjoy it? You wake up a sunny morning well pleased with your world, then you open a physics book, debate, whatever :) and nothing is the same any more.

Let's see what we know of time. It has a direction for us, here and now, I will die some day.. If you don't agree to this one you're in trouble.. It might be a symmetry, or as Penrose suggested, an asymmetry, or just one way, meaning that it either communicates/commute in different 'directions', equally well or unequally, or that it doesn't communicate/commute at all. All of those questions are mathematical, coming from Einstein's field equations as I understands it, not experimental.

We have some very weird stuff, that I'm hung up on, existing. Entanglements, Tunneling's, Although personally I think Entanglement is the weirdest idea I know. But it's there, for real, no joke.

But time has a direction, so how do we measure that direction? It doesn't have any tags on it telling us when one 'swamba dimba' is gone, does it? We have to find our own ways of sorting it into 'quantities'. And physics is weird.

In physics you have Planck time, and Planck size and they are related to a ' smallest propagation of 'c' ' But why?

"The Planck time is the unique combination of the gravitational constant G, the relativity constant c, and the quantum constant h, to produce a constant with units of time. For processes that occur in a time t less than one Planck time, the dimensionless quantity tP / t is greater than one. Dimensional analysis suggests that the effects of both quantum mechanics and gravity will be important under these circumstances, requiring a theory of quantum gravity. All scientific experiments and human experiences happen over billions of billions of billions of Planck times, making any events happening at the Planck scale hard to detect."

And

In 1898, Max Planck discovered that action is quantized, and published the result in a paper presented to the Prussian Academy of Sciences in May 1899.[19][20] At the end of the paper, Planck introduced, as a consequence of his discovery, the base units later named in his honor. The Planck units are based on the quantum of action, now usually known as Planck's constant. Planck called the constant b in his paper, though h is now common. Planck underlined the universality of the new unit system, writing:

    ...ihre Bedeutung für alle Zeiten und für alle, auch außerirdische und außermenschliche Kulturen notwendig behalten und welche daher als »natürliche Maßeinheiten« bezeichnet werden können... ...These necessarily retain their meaning for all times and for all civilizations, even extraterrestrial and non-human ones, and can therefore be designated as "natural units"...

Planck's paper also gave numerical values for the base units that were close to modern values."

And it's to me a 'constant'. Constants are the closed doors you meet in Physics. There might be a key to open each one, but then you'll have to find a new way to walk up to it. They do not apologise, and they do not care that 'common sense' demands a answer for why they are there. They just are the 'rules of the game'.

So? We have 'two' constants here 'c' and the Plank units. And times measurement is a function of your choice of 'clock' measuring them. It's quite natural to combine them. The problem is that Relativity discuss a lot of other definitions for how time comes to be, relative the observer, and that catch peoples interest. Especially those of you mathematically inclined. And the idea of a time symmetry makes people forget what they actually see, that we all die.
« Last Edit: 13/11/2011 14:38:25 by yor_on »
 

Offline Geezer

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Why is it important to believe time is relative?
« Reply #26 on: 13/11/2011 19:36:00 »
There is something special about c - no object, no information, nothing can travel through space or be transmitted faster than c.  If c is not a limit then we either need to lose special relativity  or we need to lose causality - and both of those have stood fairly unchallenged.

And I don't understand what you mean by "light is synchronized" - synchronized with/to what.  The speed of light is a universal constant and the fact that it is finite and constant regardless of frame is fundamental to our physics. 

Matt - I completely agree that c is a speed limit imposed by spacetime. Now, nothing up my sleeves at all here, but notice that it's a "speed". It's a distance in time. It's always constant of course, but that just means that when we observe it, it always covers the same distance in a particular amount of time so we can use it to determine distances very accurately, or, if we know a very precise distance we can use light to tell time.

But that's not really any big deal - lots of other things are constant with respect to time too, so while c is a very special thing, there is nothing special about the relationship between light speed and time. The thing that is special is the fact that the speed is always the same.

Re. the synchronization thing - spacetime enforces rigid synchronization of all events including the distance light travels between two points! We can measure with finer and finer granularity and the events never seem to get out of order, until we get to a scale where they seem to have no order at all :D

The point is that when we do anything with time, we are always looking at it in terms of events, so all we can say with certainty is that, above certain scales, spacetime synchronizes events so that the relative ratios of events are always the same for a given set of conditions.

If we use anything other than events and drag time itself into the measurement, it all goes pear-shaped quickly. However, we are so conditioned to think of time as some sort of constant that it's really difficult to avoid the trap.
« Last Edit: 13/11/2011 19:37:47 by Geezer »
 

Offline yor_on

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Why is it important to believe time is relative?
« Reply #27 on: 13/11/2011 20:40:31 »
The idea is simple Geezer, and it works. That's why I like it.
 

Offline imatfaal

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Why is it important to believe time is relative?
« Reply #28 on: 14/11/2011 11:22:17 »
/snipped

Matt - I completely agree that c is a speed limit imposed by spacetime. Now, nothing up my sleeves at all here, but notice that it's a "speed". It's a distance in time. It's always constant of course, but that just means that when we observe it, it always covers the same distance in a particular amount of time so we can use it to determine distances very accurately, or, if we know a very precise distance we can use light to tell time.
It is a speed.  It is the fact that is is constant from all frames that is different
Quote
But that's not really any big deal - lots of other things are constant with respect to time too, so while c is a very special thing, there is nothing special about the relationship between light speed and time. The thing that is special is the fact that the speed is always the same.
  But very few are axiomatic to current thinking in physics
Quote
Re. the synchronization thing - spacetime enforces rigid synchronization of all events including the distance light travels between two points! We can measure with finer and finer granularity and the events never seem to get out of order, until we get to a scale where they seem to have no order at all :D
ok - what I would call causality

Quote
The point is that when we do anything with time, we are always looking at it in terms of events, so all we can say with certainty is that, above certain scales, spacetime synchronizes events so that the relative ratios of events are always the same for a given set of conditions.

If we use anything other than events and drag time itself into the measurement, it all goes pear-shaped quickly. However, we are so conditioned to think of time as some sort of constant that it's really difficult to avoid the trap.
  But that applies to all measurement - there are no absolute units of experimentation.  we may find it easier to visualize abstract length dimensions - but when we conceive of a cubic metre of empty space we are in effect bounding it by a frame of metre sticks, and we struggle to do that with time; but the measurements and movement along the dimension are the same.
 

Offline imatfaal

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Why is it important to believe time is relative?
« Reply #29 on: 14/11/2011 11:44:58 »
again, thank you for your responses.

imatfall

i will do this at my earliest opportunity, which at this point will be monday, since i don't seem to find an actual copy of einstein's work posted on the internet, but instead many attempts to describe or explain it which i have decided do not meet with the spirit of your instruction.  my apologies for misnaming the critical work involved, i knew it was the earlier publication but assigned the wrong general heading to that work.
Knock yourself out - it's a doozy.  You will come to a point where you lose the plot.  But the basics of SR are fairly accessible.  Wikipedia and Hyperphysics and the Physics FAQ are all excellent resources.
Quote
i do find myself, perhaps due to a weakness of character or intelligence, from making one argumentative point with regards to your response.  i would not be injured/offended if it was deemed unworthy of response.  The point:  in the various recountings of the circumstances leading up to the publication of einstein's 1905 that i have been exposed to, einstein is described as having had an insight or talomg a leap beyond our then current understanding with regards to the nature of time as relative, he then proceeded to work out the implications of that insight or leap.  rightly or wrongly, that strikes me as though he came to an intuitive understanding of the nature of time.  it may well be that einstein's innate intellectual capacity and his educational background prepared him to be able to gain the insight or make the leap and i may never be able to cross the conceptual distance einstein originally covered, but it does appear that someone's brain was wired by birth and experience to do so.  i make no claim to having einstein's educational background or intellectual capacity.  i'm not hoping to be able to turn the world of physics on its ear with some equally powerful insight, i'm merely attempting, by exposing myself to some of the same influences to gain the an equally intuitive understanding.  i reject the notion that, in general, the human brain is not capable of it, although mine may not be. 

/snipped
playaguess 

But Playaguess - you are not giving yourself even the chance that Einstein had.  We are constantly regaled by tales of Einstein the humble patent clerk, the poor mathematician, out of the academic milieu, a maverick who plucked his ideas from the depths of imagination and insight;  this is a romanticisation - Einstein was well versed in maths, had a physics/maths degree (and was working on his phd), and had a support network of friends who were good scientists at the point that he started publishing his great work. 

You need the basics - there is ground work to be done in all pursuits; to comprehend one of the greatest leap of imaginations in the history of our species (my opinion) you need to be up to speed, although def not superluminal.  I have to say that, on this and other fora I see an argument against special relativity about once a month - and not one of them is based on anything other than a argument of personal incredulity.  One point is that SR is mathematically internally consistent, completely consistent with experimental results, and has great predictive power; this means that thought experiments cannot overturn SR - a thought experiment that clashes with SR is wrongly founded, the only thing that will overturn SR is experimental results (this is why the preliminary results of OPERA/Gran Sasso are so interesting).
 

Offline simplified

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Why is it important to believe time is relative?
« Reply #30 on: 14/11/2011 12:40:45 »
Relativity is filter of guesses. :P
 

Offline yor_on

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Why is it important to believe time is relative?
« Reply #31 on: 14/11/2011 14:57:32 »
As almost everything worthwhile :)
Like guessing your girlfriends intentions and mood.

Dangerous, but worth your while, if lucky.

 

Offline Geezer

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Why is it important to believe time is relative?
« Reply #32 on: 14/11/2011 19:08:31 »

It is a speed.  It is the fact that is is constant from all frames that is different

Is that any different from "it's always constant"?

Quote
But very few are axiomatic to current thinking in physics

Apparently some might disagree. The SI unit of time makes no mention of the speed of light. 'c' is defined by atomic activity.

Quote
But that applies to all measurement - there are no absolute units of experimentation.  we may find it easier to visualize abstract length dimensions - but when we conceive of a cubic metre of empty space we are in effect bounding it by a frame of metre sticks, and we struggle to do that with time; but the measurements and movement along the dimension are the same.

But frames are an artifact. There are no real boundaries. And time may be an artifact too. All we know is that spacetime synchronizes events "locally" because, AFAIK, that is all we have been able to confirm by experiment.

 

Offline imatfaal

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Why is it important to believe time is relative?
« Reply #33 on: 15/11/2011 11:08:06 »

It is a speed.  It is the fact that is is constant from all frames that is different

Is that any different from "it's always constant"?
Yes - try measuring the electronic transition between the two hyperfine states of caesium-133 as you zoom past the clock in a space ship.  now try measuring the speed of light emitted by the leds on the top of the atomic clock


Quote
Quote
But very few are axiomatic to current thinking in physics
Apparently some might disagree. The SI unit of time makes no mention of the speed of light. 'c' is defined by atomic activity.
  Units - even SI - are just book-keeping and accountancy.  The speed of light is emergent from maxwell's equations and is axiomatic to einstein's relativity - whatever units you choose to work in.

Quote
Quote
But that applies to all measurement - there are no absolute units of experimentation.  we may find it easier to visualize abstract length dimensions - but when we conceive of a cubic metre of empty space we are in effect bounding it by a frame of metre sticks, and we struggle to do that with time; but the measurements and movement along the dimension are the same.

But frames are an artifact. There are no real boundaries. And time may be an artifact too. All we know is that spacetime synchronizes events "locally" because, AFAIK, that is all we have been able to confirm by experiment.
  I am not saying that time isn't an artefact - but in current physics it is no less an artefact than length


« Last Edit: 15/11/2011 11:09:48 by imatfaal »
 

Offline Geezer

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Why is it important to believe time is relative?
« Reply #34 on: 15/11/2011 18:22:30 »

It is a speed.  It is the fact that is is constant from all frames that is different

Is that any different from "it's always constant"?
Yes - try measuring the electronic transition between the two hyperfine states of caesium-133 as you zoom past the clock in a space ship.  now try measuring the speed of light emitted by the leds on the top of the atomic clock


Quote
Quote
But very few are axiomatic to current thinking in physics
Apparently some might disagree. The SI unit of time makes no mention of the speed of light. 'c' is defined by atomic activity.
  Units - even SI - are just book-keeping and accountancy.  The speed of light is emergent from maxwell's equations and is axiomatic to einstein's relativity - whatever units you choose to work in.

Quote
Quote
But that applies to all measurement - there are no absolute units of experimentation.  we may find it easier to visualize abstract length dimensions - but when we conceive of a cubic metre of empty space we are in effect bounding it by a frame of metre sticks, and we struggle to do that with time; but the measurements and movement along the dimension are the same.

But frames are an artifact. There are no real boundaries. And time may be an artifact too. All we know is that spacetime synchronizes events "locally" because, AFAIK, that is all we have been able to confirm by experiment.
  I am not saying that time isn't an artefact - but in current physics it is no less an artefact than length




Matt,

My point was that we don't "measure" time. What we do is count events, 'cos that's all clocks can do. Spacetime ensures that the ratios of the counts are always consistent. It's just another way of describing something about spacetime without having to use the term "time" itself (because that can lead to circular arguments.)

My other point is that the speed of light does not define time because the speed of light is controlled by spacetime, just like it controls everything else. (Not to say that we could not define time based on 'c' if we really wanted to, but it's not a very good method because of the uncertaintity of distance.)

While those points may not exactly conform with the axiomatic "conventional wisdom", is there anything wrong with either of them?

(BTW, the official TNS spelling is "artifact" ;D)
 

Offline Geezer

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Why is it important to believe time is relative?
« Reply #35 on: 15/11/2011 19:36:02 »
Yes - try measuring the electronic transition between the two hyperfine states of caesium-133 as you zoom past the clock in a space ship. 

I hope you realize that's not what atomic clocks actually do? There is no "measuring the electronic transition".
 

Offline imatfaal

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« Reply #36 on: 16/11/2011 09:52:37 »
You wanna try and phrase it in 4 words or under that is any better. [8D] 

You set up a feedback loop so that a electronic oscillator becomes synchronized with the transitions between states of caesium.  That's pretty much measurement - if in an indirect way; you can call it secondary observation if you are in a particularly hair-splitty mood .  You then count these oscillations and every 9 million or so click off another second on your clock.
 

Offline rhade

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Why is it important to believe time is relative?
« Reply #37 on: 16/11/2011 12:36:01 »
Geez, playaguess, you picked a nice, easy one for one of your first few posts! Of course, if the CERN observations about the neutrinos travelling faster than light check out as true, Einstein could be wrong and at least a part of what we thought we knew may have to be reconsidered.
 

Offline lightarrow

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Why is it important to believe time is relative?
« Reply #38 on: 16/11/2011 18:22:46 »
Why is it important to believe time is relative?
Physics is not religion. You don't have to "believe". If you want to find why and when physicists use SR, you can study it, and you'll discover yourself. 
 

Offline Geezer

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Why is it important to believe time is relative?
« Reply #39 on: 17/11/2011 02:06:25 »
You wanna try and phrase it in 4 words or under that is any better. [8D] 

You set up a feedback loop so that a electronic oscillator becomes synchronized with the transitions between states of caesium.  That's pretty much measurement - if in an indirect way; you can call it secondary observation if you are in a particularly hair-splitty mood .  You then count these oscillations and every 9 million or so click off another second on your clock.

I see. And what, pray tell, are the units of said "measurement"?

(As you are about to discover, this isn't anything like as hair-splitty as you seem to imagine ;D)

PS - I intentionally left out the bit about "there is no point in being precise if ........"
« Last Edit: 17/11/2011 07:25:14 by Geezer »
 

Offline imatfaal

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Why is it important to believe time is relative?
« Reply #40 on: 17/11/2011 09:46:21 »
Its dimensionless.  And it is hair-splitty - if we are to pounce on every elision of meaning we would be here all day.  So you say I am about to discover - enlighten me and stop being gnomic
 

Offline simplified

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Why is it important to believe time is relative?
« Reply #41 on: 17/11/2011 16:52:15 »
Why is it important to believe time is relative?
Physics is not religion. You don't have to "believe". If you want to find why and when physicists use SR, you can study it, and you'll discover yourself. 
Yes, in some cases relativity can be wrong,but it is useful in another cases.
 

Offline JP

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Why is it important to believe time is relative?
« Reply #42 on: 17/11/2011 16:55:03 »
Why is it important to believe time is relative?
Physics is not religion. You don't have to "believe". If you want to find why and when physicists use SR, you can study it, and you'll discover yourself. 
Yes, in some cases relativity can be wrong,but it is useful in another cases.

I'm probably going to regret this, but in what cases is it wrong?
 

Offline lightarrow

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Why is it important to believe time is relative?
« Reply #43 on: 17/11/2011 17:20:03 »
Yes, in some cases relativity can be wrong,but it is useful in another cases.
Another example: 2 + 2 = 4 in some cases can be wrong, but it is useful in other cases.
 

Offline lightarrow

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Why is it important to believe time is relative?
« Reply #44 on: 17/11/2011 17:25:34 »
Quote
Yes, in some cases relativity can be wrong,but it is useful in another cases.
I'm probably going to regret this, but in what cases is it wrong?
I assume he intended it's not valid...outside its range of validity  :)
Near big massive bodies, e.g.
 

Offline Geezer

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Why is it important to believe time is relative?
« Reply #45 on: 17/11/2011 19:04:43 »
Its dimensionless.  And it is hair-splitty - if we are to pounce on every elision of meaning we would be here all day.  So you say I am about to discover - enlighten me and stop being gnomic

Precisely! What we are actually doing is maintaining (or trying to maintain) a ratio (in this case 1:1) of event counts, which was my point about four posts ago.



 

Offline yor_on

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Why is it important to believe time is relative?
« Reply #46 on: 18/11/2011 12:51:17 »
Times arrow exist. What doesn't exist is the way we define it. That's a free decision for us in where we 'split' that arrow we observe into even durations. If I was to argue that it doesn't exist at the same time :) I know that every 'second' moves me one step closer to my death becomes rather meaningless.
 

Offline yor_on

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« Reply #47 on: 18/11/2011 14:15:50 »
Playaguess. "So I ask two new questions:

How do we know how far the light we are measuring the speed of has traveled?

How do we know how long an interval it took to cover the distance traveled?"

I think you are asking about if all radiation is a constant 'c'? Because it's from that you will get time dilations and Lorentz contractions, as well as 'frames of references' and Lorentz transformations.

That one is validated experimentally, over and over again. We define 'c' as '299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time. In imperial units this speed is approximately 186,282 miles per second.'

The metre is our own idea, seconds, hours etc is also our own definitions. But that 'c' is a constant is not our idea, it's a experimental fact. There's been a lot of attempts trying to find loopholes there but as far as I've seen. Nobody has succeeded so far (and that's in a hundred year-span, or more, if you use Maxwell as your first definition of it.). That you can define some 'stuff' as going faster than 'c' depends on what medium it 'propagate' in. 'c' is defined in a vacuum. If we changed our definitions of metres and 'seconds', 'c' could get a new value, but it would still be a invariant constant. And that's the real beauty of it, and why I connect it to 'clocks', as most of physics do, even if they don't define it full out as me. Why I do it is because I do expect it to be a constant, and nothing else.

To me you can just as easily use it as a 'clock', which also will fit so much better with it 'not existing', except as the recoil seen in a source as it 'leaves', and in its subsequent annihilation at a 'sink', like your eye. It was never a ball 'moving', and that's the reason we use 'propagate' instead of 'motion' too.

What is the experimental basis of Special Relativity. is rather cool to go through to see where the experiments are.

There you also can see.

"The Clock Hypothesis

The clock hypothesis states that the tick rate of a clock when measured in an inertial frame depends only upon its velocity relative to that frame, and is independent of its acceleration or higher derivatives. The experiment of Bailey et al. referenced above stored muons in a magnetic storage ring and measured their lifetime. While being stored in the ring they were subject to a proper acceleration of approximately 1018 g (1 g = 9.8 m/s2). The observed agreement between the lifetime of the stored muons with that of muons with the same energy moving inertially confirms the clock hypothesis for accelerations of that magnitude.

    Sherwin, “Some Recent Experimental Tests of the 'Clock Paradox'”, Phys. Rev. 129 no. 1 (1960), pg 17.

    He discusses some Mössbauer experiments that show that the rate of a clock is independent of acceleration (~1016 g) and depends only upon velocity."

Notice that it refer to 'relative motion' as the decisive action defining a time dilation and Lorentz contraction, not accelerations per se. Although you surely can argue that 'accelerations' can't be ignored as all 'motion' need something creating it, that one belongs more to philosophy than physics, which limits itself to observing and testing what we actually can see (and measure), and what hypothesises we can create explaining it, as well as test. Mach's empty universe inspired a lot of Einstein's thoughts about what 'relative motion' might be, but in the end he limited his descriptions to what we actually can measure.
« Last Edit: 18/11/2011 14:47:42 by yor_on »
 

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