Re: definition of a clock in relativity theory
From: Henri Wilson (H_at_..(Henri)
Date: 09/06/04
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Date: Mon, 06 Sep 2004 22:03:19 GMT
On Thu, 26 Aug 2004 01:19:41 +0100, Eric Baird <eric_baird@compuserve.com>
wrote:
>On Mon, 16 Aug 2004 22:57:17 GMT, h@..(Henri Wilson) wrote:
>
>>On Sun, 15 Aug 2004 19:21:46 +0000 (UTC), Eric Baird
>><eric_baird@compuserve.com> wrote:
>>
>>>On Thu, 12 Aug 2004 09:59:00 GMT, h@..(Henri Wilson) wrote:
>>>
>>>>What matters is that neither the clock nor the rod actually changes in any way.
>>>>Therefore presynched clocks always read the same times when reunited no matter
>>>>how they are moved.
>>>
>>>
>>>Not neccessarily.
>>>If you take two presynched clocks, and dangle one in a high-gravity
>>>region, then pull it out and reunite the two clocks, then the
>>>gravitational time dilaiton effect ought to result in the dangled
>>>clock having aged less by the end of the experiment (even if we don't
>>>like and don't accept special relativity).
>>
>>A perfect clock is not affected by a gravitational field.
>>The best manmade clocks DO vary slightly when placed in a free fall situation.
>
>It depends on how we choose to define our "perfect" clock.
>
>In modern relativity theory, I think it's natural to take a "clock" as
>being an idealised physical process that can be used to measure the
>passage of time, whether that's the rate at which a known mass
>accelerates when a known force is applied, or the rate of an isotope's
>atomic decay, a natural resonant frequency, or the rate at which a
>lightbeam is supposed to bounce between two mirrors, or some other
>fairly "pure" idea of something that produces a measurable indication
>of apparent timerate.
>
>In studies of supposed changes in timerate in inertial physcs, it's
>also important to specify that the "clock" should be capable of
>functioning in freefall.
>That's why there's a footnote in the "Dover Press" republication of
>the 1905 "electrodynamics" paper (p50) reminding us:
>: "Not a pendulum clock ... "
>That footnote wasn't in the original paper, so it's presumably either
>been added in the German-language republication, or in the authorised
>Lawson translation, but it /is/ in there.
>
>>>
>>>Increasing the background gravitational field strength around a test
>>>object seems to be equivalent to increasing "inertial field strength"
>>>in the region,and increasing the object's inertia woudl seem to reduce
>>>the rate of the nuclear and chemical and inertial processes that we'd
>>>normally use to measure time. Increase the inertia of a pocket-watch's
>>>flywheel and it ticks more slowly. Increase the inertia of an atomic
>>>nucleus and its resonant frequencies drop, and it takes longer to
>>>decay.
>>>
>>>
>>>So gravity really /does/ seem to screw up preset clockrates, as a a
>>>matter of principle, even if we are still using Newtonian mechanics
>>>(and appending Einstein's 1911 gravity-shift argument).
>>
>>These are purely unavoidable mechanical effects. They are not related to any
>>silly known theory.
>
>Well, these calculated gravitational effects would /seem/ to be valid
>irrespective of what sort of clock is being used.
>
>If your "clock" floating out in space is constructed using
>marshmallows and elastic bands and mice running around on wheels
>chasing cheese, and it produces visible "ticks", then looking at the
>the optical signal stream leaving the clock and arriving at an
>observer who happens to have jumped into a stronger-gravity region,
>then if that observer sees the light to have increased it's energy as
>it moved into the gravity-well, and if that energy-change shows up as
>an increase in frequency and a reduction in wavelength in the received
>light, (as opposed to a change in amplitude), then if the EM signal
>leaving the clock contains a certain number of EM wavepeaks between
>the parts of the signal that contain the "tick" signal, then if this
>number does not change en route, if the deep-gravity observer sees the
>stream of wavepeaks to be compacted into a smaller amount of time
>(because of the frequency-shift), then they ought to also see the
>stream of clock-ticks carried on the back of that signal to be
>compacted into a smaller amount of time, too.
>
>So (by this loooong chain of arguments) the stronger-gravity observer
>ought to see the mouse-marshmallow-cheese clock to appear to be
>running at an increased rate, with an amount of apparent speed-up
>depending on the strength of the gravitational gradient along the
>viewing path, regardless of how the clock in question happens to be
>constructed.
That's completely false logic.
The number of ticks emitted will equal the number received.
>
>And if the strong-gravity observer can see the image of the clock to
>be apparently running "fast", and running at that accelerated rate for
>an arbitrarily long time-period, we seem to run out of explanations
>for how this situation could be sustainable in real life, unless the
>"natural" rates of clocks in the strong-gravity and weak-gravity
>regions is different by the same amount as the observational mismatch
>in apparent clockrates that we just worked out.
Look, the wavelength of light is unaffected by gravity but its velocitty
increases as it falls, just like anything else.
therefore the frequency at which the wavepeaks arrive at the ground observer
increases. The light itself is blue shifted.
However, that does nothing to the frequency of 'ticks'. If N ticks are emitted
per orbit of the clock, then N ticks will be received, even though the
frequency of the 'tick signal' itself increases slightly.
>
>I suppose that we could try to compensate for this effect in order to
>produce a "compensated" clock (which would be more like one of
>Newton's hypothetical "absolute" clocks), but Machian arguments
>suggest that if we try to calculate the rate of a clock if the
>gravitational field is taken away completely, we get a meaningless
>result (infinity, perhaps?).
>The more general principles of relativity seem to suggest that the
>gravitational field acts as a sort of physical aether and physically
>defines the local concepts of time and distance, and if you take the
>field away completely, there's nothing left: the field "is" space, so
>in the most extreme interpretation of gravitational time dilation, the
>gravitational field density is not messing up a "natural" underlying
>clockrate, it's _defining_ the natural underlying clockrate.
>
>
>
>>Until we can establish a direct connection between gravity, mass, magnetism,
>>time and god knows what else, there is nothing much we can say about the
>>subject except that all known clocks appear to be affected by gravity due to a
>>number of factors, one of which relates to their own self-compression when
>>restricted from free falling.
>
>The above argument was for free-falling clocks.
>
>The "stronger-gravity" observer could still be inertial and at a
>constant distance, for instance they could be floating at the centre
>of gravity of a compact double-star system, so that there is a
>definite gravitaitonal gradient between them and the cheese-clock, but
>both parties are still in freefall
>
>>>
>>>The next complicating issue is acceleration ... if we apply the
>>>principle of relativity in its most general form, acceleration effects
>>>ought to be equivalent to the effects generated by (a particular odd
>>>sort of) gravitaitonal field (= a Coriolis field), so if we have two
>>>spaceships coasting away from each other at a high proportion of the
>>>speed of light, and one fires its retro rockets and turns around, and
>>>catches up with its twin, then we'd expect the ship that turns around
>>>to have aged less when they meet up again, as an acceelration effect,
>>>and, again, we should probably expect this to be true even if we think
>>>that special relativity is rubbish.
>>
>>A perfect clock should not be affected by acceleration.
>>All manmade clocks appear to suffer in some way.
>
>Well, if acceleration affects the apparent background gravitational
>field-strength that the clock is effectively immersed in, then that
>can be used to calculate a clockrate change from those gravitational
>principles, with the gee-forces being used as an indicaiton of the
>expected equivalent change in background gravitaiton ... but if you
>also want to work out the more difficult issue of how physical
>accelerations themselves might screw up the particular operating
>mechanism of the particular type of "real-life" clock that you've
>built, due to the local physics now being verifiably different, in a
>way that the clock itself "sees", than yes, that sounds a lot more
>difficult.
Just run it in a centrifuge for a period.
>
>
>>>... and again, if we have a centrifuged clock, even if we think all
>>>the SR definitions and arguments are junk, the general
>>>gravitation/equivalence principle arguments would lead us to expect
>>>that the accelerated clock at the centrifuge rim should age more
>>>slowly than a non-accelerated clock hovering at the centrifuge axle,
>>>even if we know nothing about SR.
>>
>>Bull!
>>You are preaching SR.
>
>Nope it's the general gravity-shift idea, coupled with the equivalence
>principle.
>If it makes you any happier, most of the SR folks don't seem to like
>the idea of a "gravitational" explanation for the centrifuge test, it
>makes claims that the result can't be explained without SR look a bit
>hollow.
>
>For the record, I count myself a as relativist, but I don't like SR's
>partial implementation of the idea. I personally think that the
>special theory cuts too many corners, and that some of these
>idealisations probably have bad consequences.
The whole theory is obvious nonsense from top to bottom, start to finish.
>
>
>>Try centrifuging a pendulum clock.
>>It will go either slower or faster depending which way you lean it.
>>
>>>
>>>
>>>So I think that these arguments about SR's validity should not be so
>>>much about whether these effects exist or not ... they do /seem/ to
>>>exist, and we'd arguably expect them to exist regardless of whether SR
>>>was right or wrong ...
>>>... but rather whether the effects as predicted by SR can be
>>>distinguished from the similar effects that we get from more general
>>>principles, and that, when we find a situation where the two sets of
>>>predictions diverge and can in principle be told apart, which set of
>>>predictions is /really/ the most accurate.
>>
>>SR claims that TIME itself is somehow linked to a gravity field.
>
>I think that that this sort of claim pops up in General Relativity
>(and in general Machian theory), but I dont think I'd say that it's
>really an SR thing.
>Parts of SR do seem to overlap into gravitational territory, but SR
>itself isn't supposed to be up to the job of doing full-blown
>gravitational physics ... it can give indications of how parts of
>gravitational phyuscs /might/ operate, but those SR-based indicaitons
>won't /necessaily/ be completely right.
>
>
>>There could be some truth in that but no relationship has been found.
>>
>>One thing we CAN say however is that TIME is definitely not affected by the
>>characteristics of any clock.
>>You seem to be claiming that a clock DEFINES time flow.
>
>I think I'm saying that when you have a "real" difference in effective
>local timeflow between two regions, you can use clocks placed in those
>regions as a useful way of illustrating and revealing the existence of
>the difference, and you can also use the predicted change in frequency
>of light passing between those clocks (altered by gravitational
>shifts) as a way of calculating what the difference in "effective"
>timeflow between those regions ought to be.
>
>If there's no difference in timeflow between those regions, or if we
>are using a "gravity-compensated" idea of timeflow, and
>gravity-compensated clocks, then of course the whole exercise becomes
>a bit redundant. But even if you prefer to use gravity-compensated
>clocks showing a sort of agreed standardised time, then I think its
>still useful to be able to calculated the strength of the expected
>"gravitational time dilation" effects, so that you know what to
>compensate for.
>
>
>The situation with relatively-moving clocks, where there are also
>distance-change-related effects to be considered, and the issue of
>whether or not the existence of a moving mass affects light
>propagation (experiment says yes, SR says no), is more fraught, and I
>don't think that I'd be happy defending the way this is dealt with
>under SR.
All observers in the universe can use the same ONE BIG CLOCK IN THE SKY that I
suggested some time ago. That terminates the argument and puts an end to
Einsteinian relativity.
>
>>
>>>Unfortunately, the pro-SR crowd seem to be doing the opposite ...
>>>concentrating on the experiments and thought-experiments where SR's
>>>predictions are the most difficult to tell apart from more general
>>>theory, and then claiming those as being the important tests of SR,
>>>with the comparisons that /really/ might be capapble of either
>>>significantly supporting or breaking SR arguments being sidelined and
>>>forgotten about.
>>
>>Precisely!
>>They don't want to know. Too many heads would roll.
>
>Well, it seems that we do the circular storage-ring test, get the
>exact acceleration-shift result that the gravity-shift calculations
>give us, and then claim the entire effect for SR by saying that of
>course we "know" that the acceelration effects are negligible.
>I'd suggest that we "know" no such thing, and that the SR community
>seem to be misrepresenting the competing gravitaitonal math (knowingly
>or unknowingly) in order to make their favourite theory look good.
>
>If they are really certain that the verifiable centrifufge time
>dilation effect (known ring circumference, known number of clircling
>particle-pulses passing the observer per second, known number of
>circuits of the ring traversed by the particles before decay), is 100%
>due to the particles' speed wrt the lab, and not at all due to the
>geeforces, then it would be nice to see tham actually testing that
>assertion by seeing how long their "centrifuged muons" live when the
>storage ring incorporates some straight-line sections where we still
>have relative velocity, but where the geeforces are absent.
>
>I've never seen a physics person willing to even acknowedge the idea
>of this sort fo experiment, perhaps becuase they aren't 100% sure that
>it would give the sort of SR result that they'd want.
Precisely. Besides, when one has a very strong faith, one sees evidence that it
is true almost everywhere.
>
The only difference between a preacher and a used car salemans is that the latter actually has a product to sell.
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