Naked Science Forum
On the Lighter Side => New Theories => Topic started by: MikeS on 01/03/2012 10:44:39
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If we assume the Universe to be finite then it must have a shape, possiby spherical. All that exists (from our knowledge) is contained within the Universe. Even light cannot escape, just like light cannot escape from a black hole. Presumably then, just like a black hole, the ‘edge’ of the universe is effectively an event horizon where according to a distant observer ‘time stands still’. Unlike a black hole, the distant observer is inside the Universe trying to look out.
We have no idea of our position in the Universe. We might be near the 'centre' or we might be near the 'edge'. If we are near to the center then we would expect time to pass quickly as compared to if we were near the edge where it would appear to pass slowly in comparison.
Varying rates in the passage of time over great distance in the Universe must affect the Hubble red-shift. When we make very long distance observations of the Universe we have absolutely no idea of what correction factors we should use to apply to the Hubble red-shift to allow for this difference in time discrepancy.
So my question.
Does the Hubble red-shift really give a true indication of the size and age of the observable Universe?
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imatfaal
Whilst I have no real objection to you moving this thread I believe it to be a perfectly legitimate question that could should be answered in Physics, Astronomy and Cosmology. I don't believe it constitutes a new theory, it just asks what may be an awkward question.
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Hmm Mike, where did you get that statement from?
"we have absolutely no idea of what correction factors we should use to apply to the Hubble red-shift"
Imatfaal did the absolute right thing, either that's a 'main stream' statement and then you should have sourced it, or it is a hypothesis you've made yourself, and then it surely belongs here, until proven.
As for edges and centers, that's meaningless statements in a inflationary process, creating four dimensions bound together into one SpaceTime. We have no idea what the real 'shape' of this universe is, we can discus how it 'curves' of course but that doesn't define any 'size' of it, only how 'stuff' moves in it. This one is a pretty good explanation of how the main stream definition is thought to work. What is the Big Bang theory? (http://www.talkorigins.org/faqs/astronomy/bigbang.html)
As for 'time dilations' you need to differ between the 'expansion' stretching 'radiative waves', making them redshift relative the observer and the way mass do it. Then you also have the way a radiative wave can 'stretch' relative your 'relative motion' as you and that flash light move away from each other, that will also give a redshift.
The idea behind is that lights speed in a vacuum is a 'constant', it never varies. So how can a 'photon' express 'work done'? It redshifts relative the observer as it can't lose 'speed', and an acceleration then becomes a blue shift. Does that mean it really loses energy when it redshift? No, it is a effect between 'frames of reference'.
If you followed that photon, being at rest with it you would never see it change any 'energy'. It can't as it is 'time less', it have no possibility to 'change' in its own reference frame. So, is it then a illusion watching that red shifted photon hit the detector? No, it's a true effect in your 'frame of reference', detecting it. No different than if two cars collide head-on, as compared to one banging into another from the behind, creating a 'redshift' and so weaker collision/energy. Mass is equivalent to gravity, and so also to accelerations (and decelerations (which both describes a 'motion')) which is about 'displacements', and ultimately, 'energy', but always as related relative the observer/detector.
The expansion is one tricky one though, where I don't know what to think really? On the other hand, all distances are 'plastic' in relativity, always locally defined, always true but from your own 'frame of reference'.
And as always, finally it seems to be about what 'energy' should mean.
I wrote this somewhere else on TNS but it doesn't hurt to repeat it :)
Redshift as seen here is when electromagnetic energy is shifted towards its lower, less energy containing electromagnetic spectrum. It should be pointed out here that cosmological redshift and Doppler redshift is not seen as the exact same though even though you can use Doppler redshift for explaining both the expansion and redshift effects due to the relative motion between two frames of reference.
It is referred to as the Doppler effect from Christian Doppler who 1842 proposed that frequency and wavelength of a wave was a relation between any two frames of reference. A simple example of that is you hearing that ambulance passing you, receding in the distance (redshift), noticing how the sound changed from when it was approaching you (blueshift). "Doppler correctly predicted that the phenomenon should apply to all waves, and in particular suggested that the varying colors of stars could be attributed to their motion with respect to the Earth. While this attribution turned out to be incorrect (stellar colors are indicators of a star's temperature, not motion), Doppler would later be vindicated by verified redshift observations." http://en.wikipedia.org/wiki/Redshift and http://en.wikipedia.org/wiki/Doppler_effect
We tend to say that it was Edwin Hubble and Humason that discovered the redshift of galaxies but this idea existed before they presented their 'empirical Redshift Distance Law of galaxies' 1929 (Hubble's law). "In 1912 Vesto Slipher measured the first Doppler shift of a "spiral nebula" (spiral nebula is the obsolete term for spiral galaxies), and soon discovered that almost all such nebulae were receding from Earth. He did not grasp the cosmological implications of this fact, and indeed at the time it was highly controversial whether or not these nebulae were "island universes" outside our Milky Way".
In that 1929 paper, by Edwin Hubble and Humason, they suggested that if redshift would be a measure of the galaxies recession speed (withdrawal), then that was "consistent with the solutions of Einstein’s equations of general relativity for a homogeneous, isotropic expanding space." The theory proposed that the distance to a galaxy was proportional to its redshift. the farther away a galaxy was, the more redshifted its light as seen from Earth would become. A implication of that theory was that if the galaxies became more redshifted the further away they were, then that also implied that they once should have been much closer. Another implication was that we had an expansion of the universe. http://en.wikipedia.org/wiki/Edwin_Hubble
It was Georges Lemaître that 1927 presented his "hypothesis of the primeval atom". In it he suggested that the recession of the galaxies was due to the expansion of the universe (Expansion), and in 1931 he went further and proposed that if you backtracked those galaxies there should have been a single 'point' from where they all must have started, that then would have to be a 'state' of infinite density, a singularity in fact, meaning something we don't really know as our physics laws only starts after that moment (Big Bang).
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yor_on
When I wrote
"We have no idea of our position in the Universe. We might be near the 'centre' or we might be near the 'edge'. If we are near to the center then we would expect time to pass quickly as compared to if we were near the edge where it would appear to pass slowly in comparison.
Varying rates in the passage of time over great distance in the Universe must affect the Hubble red-shift. When we make very long distance observations of the Universe we have absolutely no idea of what correction factors we should use to apply to the Hubble red-shift to allow for this difference in time discrepancy."
It seemed to be common sense. We have no idea of our position in the Universe. The Hubble red shift can only gives a true indication of distance if the passage of time is constant both over distance and cosmological time. We know that the passage of time does vary on a local scale, why then assume that it doesn't vary over large distance and with the passage of cosmological time? You can call that a new theory if you like but it seems to me that it is just common sense. Unless I have missed something of course?
For the above to be wrong there would have to be evidence that the passage of time is (fairly) constant both over very long distance (in any direction) and constant over the cosmological passage of time. As far as I am aware no such evidence exists.
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imatfaal
Whilst I have no real objection to you moving this thread I believe it to be a perfectly legitimate question that could should be answered in Physics, Astronomy and Cosmology. I don't believe it constitutes a new theory, it just asks what may be an awkward question.
Unfortunately, it is a question premised on a misunderstanding of time dilation; it was also one in a long line of your posts that deal with this area - thus moved to New Theories.
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I can go with "We know that the passage of time does vary on a local scale" if you add "relative the observer". Your own local rate of 'change' :) as I call it, never varies. That mean that if you have two clocks at A and B, two meters between them, you being at A. You will see a 'time dilation' at B, but as soon as you move to B looking back at the clock you left at A, you again will see a 'time dilation' but now defining A as the place 'out of sync'.
If you now had a wristwatch, coupled to some process in your body that is very exact, chopping that 'local arrow' we all live by into very small, evenly made, chunks, you would find that your wrist watch always give you the exact same 'chunks' as measured relative that bodily process (biological 'clock'). That means that no matter if you're at A measuring B, or at B measuring A your own local 'time' as your 'arrow', never changes for you.
That lifespan you have will always be the same according to your wristwatch, no matter where you go, or how fast. So a time dilation is a description between frames of reference. And the comparison of 'time' can only be done using your own local time in any real, direct measurement.
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Galaxy Redshifts Reconsidered (http://www.astronomycafe.net/cosm/expan.html) is still a nice one to me.
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yor_on
From the link you mentioned above.
"A second phenomenon predicted by general relativity that also has no analog in special relativity is the cosmological redshift. Simply stated, the cosmological redshift occurs because the curvature of spacetime was smaller in the past when the universe was younger than it is now. Light waves become stretched en route between the time they were emitted long ago, and the time they are detected by us today."
http://www.astronomycafe.net/cosm/expan.html
Does this mean that the curvature was less as in smaller or the radius of the curvature less meaning the curvature was greater. If the latter then this fits in perfectly with my beliefs.
If the "curvature of spacetime was smaller in the past when the Universe was younger" then gravity must have been stronger in which case time would have passed slower (relative the present). This fits in perfectly with what I have always maintained that the passage of time is getting faster.
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:)
I can see where you're coming from there Mike, heh, and I beg to differ. If you don't have another frame of reference to compare 'local time' too there can be no 'time dilations'. The curvature of 'space' is like that elevator experiment Einstein thought up for GR. You have a little hole in the elevator, with a light beam coming through hitting the opposite wall. You then move the elevator very fast and watch the light 'bend' on the opposite wall of the elevator. That's a equivalence to the way relative motion/accelerations and mass (energy) can 'bend space'.
"The central equation of general relativity is called Einstein's equation. One side of Einstein's equation is geometrical and is related to the curvature of spacetime, and the other side is related to the distribution of energy/mass/momentum. Since this is an equation, it is impossible to change just one side: change the geometry side and this means that distribution of energy/mass/momentum must also be changed; change the distribution of energy/mass/momentum, and this means geometry must also be changed.
So, spacetime can be manipulated by moving masses and energy around." by George Jones..
Arthur Eddington (http://hhttp://en.wikipedia.org/wiki/Arthur_Stanley_Eddington#Relativity) made the first test of it at the island of Príncipe studying the solar eclipse of 29 May 1919.
"the geometry and evolution of the universe are determined by the fractional contribution of various types of matter. Since both energy density and pressure contribute to the strength of gravity in General Relativity, cosmologists classify types of matter by its "equation of state" the relationship between its pressure and energy density. The basic classification scheme is:
Radiation: composed of massless or nearly massless particles that move at the speed of light. Known examples include photons (light) and neutrinos. This form of matter is characterized by having a large positive pressure. Baryonic matter: In this cosmological context, this is "ordinary matter" composed primarily of protons, neutrons and electrons. This form of matter has essentially no pressure of cosmological importance.
Dark matter: this generally refers to "exotic" non-baryonic matter that interacts only weakly with ordinary matter. While no such matter has ever been directly observed in the laboratory, its existence has long been suspected for reasons discussed in a subsequent page. This form of matter also has no cosmologically significant pressure. Dark energy: this is a truly bizarre form of matter, or perhaps a property of the vacuum itself, that is characterized by a large, negative pressure (repelling force). This is the only form of matter that can cause the expansion of the universe to accelerate, or speed up.
One of the central challenges in cosmology today is to determine the relative and total densities (energy per unit volume) in each of these forms of matter, since this is essential to understanding the evolution and ultimate fate of our universe." from Nasa. (http://map.gsfc.nasa.gov/universe/bb_concepts.html) So the more mass/energy the more 'bent' upon itself you might assume a universe to be. This one explains the universe 'critical density' quite nicely Fate of the Universe. (http://www.astronomynotes.com/cosmolgy/s9.htm)
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I can go with "We know that the passage of time does vary on a local scale" if you add "relative the observer". Your own local rate of 'change' :) as I call it, never varies. That mean that if you have two clocks at A and B, two meters between them, you being at A. You will see a 'time dilation' at B, but as soon as you move to B looking back at the clock you left at A, you again will see a 'time dilation' but now defining A as the place 'out of sync'.
If you now had a wristwatch, coupled to some process in your body that is very exact, chopping that 'local arrow' we all live by into very small, evenly made, chunks, you would find that your wrist watch always give you the exact same 'chunks' as measured relative that bodily process (biological 'clock'). That means that no matter if you're at A measuring B, or at B measuring A your own local 'time' as your 'arrow', never changes for you.
That lifespan you have will always be the same according to your wristwatch, no matter where you go, or how fast. So a time dilation is a description between frames of reference. And the comparison of 'time' can only be done using your own local time in any real, direct measurement.
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Galaxy Redshifts Reconsidered (http://www.astronomycafe.net/cosm/expan.html) is still a nice one to me.
This is true and it is called "special relativistic time dilation"
http://en.wikipedia.org/wiki/Time_dilation
However it is not the same as gravitational time dilation which is real. Observer A on the Earth will see the clock of observers B in orbit to be running fast. Observer B in orbit will see the clock of observer A to be running slow.
If this applies on Earth which we know it does then presumably it applies anywhere that has a difference in gravitational potential due to mass. For it not to be relevant would require clocks to run at the same rate everywhere in the Universe and for all cosmological time. To the best of my knowledge that would be simply a huge assumption.
The Hubble red-shift to truly be a measure of distance and age of the Universe requires that clocks run at the same rate everywhere in the Universe and for all cosmological time. As I said that is a huge assumption.
According to the interpretation of the Hubble red-shift some very distant galaxies are moving away from us at many times the speed of light. As this is not possible it was proposed that space is being created. This may or may not be true but it still seems to me to be a 'patch' born out of desperation. Oh and the patch required another 'patch' 'dark energy' etc. to account for the necessary force of expansion. Is that another patch?
If the observed red-shift is due to a mixture of 'expansion' and the variable rate of time then no 'patch is required. Why adopt a complicated solution when there is a much simpler one?
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:)
Clip
I can see where you're coming from there Mike, heh, and I beg to differ. If you don't have another frame of reference to compare 'local time' too there can be no 'time dilations'.
I might not have said "relative the observer'' but 'local time' in this context implies in comparison to time elsewhere. Were this not so, there would be no point in saying 'local time'.
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imatfaal
Whilst I have no real objection to you moving this thread I believe it to be a perfectly legitimate question that could should be answered in Physics, Astronomy and Cosmology. I don't believe it constitutes a new theory, it just asks what may be an awkward question.
Unfortunately, it is a question premised on a misunderstanding of time dilation; it was also one in a long line of your posts that deal with this area - thus moved to New Theories.
I would be grateful if you could explain exactly what it is that you think I am misunderstanding?
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imatfaal
Whilst I have no real objection to you moving this thread I believe it to be a perfectly legitimate question that could should be answered in Physics, Astronomy and Cosmology. I don't believe it constitutes a new theory, it just asks what may be an awkward question.
Unfortunately, it is a question premised on a misunderstanding of time dilation; it was also one in a long line of your posts that deal with this area - thus moved to New Theories.
I would be grateful if you could explain exactly what it is that you think I am misunderstanding?
I have spent entire threads doing just that - but as you seem to refuse to read even basic texts on einstein's relativity and you wish to jump straight in to making speculative theories then my explanations seem to just wash over you with little effect. Every comment you make on gravitational time dilation is to a greater or smaller extent incorrect - whether it is through implication of time being measure locally as dilated, to still not understanding the difference between grav potential and grav strength
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Clip
"I have spent entire threads doing just that - but as you seem to refuse to read even basic texts on einstein's relativity and you wish to jump straight in to making speculative theories then my explanations seem to just wash over you with little effect. Every comment you make on gravitational time dilation is to a greater or smaller extent incorrect - whether it is through implication of time being measure locally as dilated, to still not understanding the difference between grav potential and grav strength."
imatfaal
If, it is true that I am misunderstanding Relativity then it is not for lack of trying and effort. I first read SR when I was 15, I am now67 and have read SR and GR many times. My thoughts on the Universe, time and gravity are rooted in Relativity. If I still don't understand your explanations then perhaps they could be phrased more clearly?
Where I have mentioned that, I believe it to be true. Where I have not said in a few instances "from the reference frame of a distant observer" it is never the less implied. Just mentioning 'local' time implies in comparison to 'non'-local time and that implies distance.
Gravitational potential (a term open to misinterpretation) or more correctly Gravitational Potential Energy can be interpreted as the negative of the work done by the gravitational field moving a unit mass in from infinity.
Whereas gravitational strength refers to the 'strength or density' of the gravitational 'field' in a particular location where physical bodies attract with a force proportional to their mass.
What is it about that you think I don't understand?
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Gravitational potential (a term open to misinterpretation)...
It is open to misinterpretation if you don't know what it means
or more correctly Gravitational Potential Energy
nope. Grav Time Dilation cannot depend on GPE as then heavier objects would be more dilated than light. It depends on Graviational Potential.
can be interpreted as the negative of the work done by the gravitational field moving a unit mass in from infinity
. Yay!
Whereas gravitational strength refers to the 'strength or density' of the gravitational 'field' in a particular location where physical bodies attract with a force proportional to their mass.
The gravitational field is the negative vector gradient of the grav potential - I am not sure what the density of a gravitational field is
What is it about that you think I don't understand?[/color]
You use magnitude of gravitational field when you should use gravitational potential. Grav time dilation depends on the gravitational potential - not the gravity.
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Gravitational potential is a term open to misinterpretation as it is often used when meaning gravitational potential energy. If you are going to use gravitational potential and gravitational potential energy to mean gravitational potential energy then clearly another name is required for 'strength or density' of the gravitational 'field' in a particular location where physical bodies attract with a force proportional to their mass.
"Whereas gravitational strength refers to the 'strength or density' of the gravitational 'field' in a particular location where physical bodies attract with a force proportional to their mass."
I don't see how that could be any clearer.
"What is it about that you think I don't understand?"
quote imatfaal
"You use magnitude of gravitational field when you should use gravitational potential. Grav time dilation depends on the gravitational potential - not the gravity."
I think that sentence demonstrates clearly the confusion of terms.
Where the term 'gravitational potential' is frequently used to mean 'gravitational potential energy', clearly this is wrong. Gravitational time dilation has nothing to do with gravitational potential energy. Yes it does have to do with gravitational potential but only if gravitational potential does not mean the same as gravitational potential energy.
Where I have used the term "'strength or density' of the gravitational 'field'" I am referring to the 'gravitational potential', not the 'gravitational potential energy'.
I much prefer the term 'gravitational potential' but it leads to confusion when it is often used by others to mean 'gravitational potential energy'.
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Mike, we don't look at relativity the same way, you have your own interpretation, but that's also what gives it flavor. Imatfaal is cool with you, as me. I'm pretty sure of that, but he has his view, which is grounded in the mathematics of it. But it is so with mathematics that sometimes there are more than one way of interpreting them, and? Good ideas are good ideas, and even ideas that don't work may lead to new that will.
One never knows.
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yor-on
I think we do look at relativity in basically the same way, I stretch the boundaries. But that is not what I am referring to in my last post. I am talking about what is basically a confusion of terms when referring to 'gravitational potential' and 'gravitational potential energy'. We can only discuss these things when using the same 'language' otherwise it leads to confusion which is what has just happened.
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There is a ambiguity to what a time dilation is. Sometimes you find otherwise knowledgeable guys describing it as time goes 'slower', relative some other frame, which in my view is incorrect. Times arrow has only one pace locally, the same everywhere, as far as I see it, but that's my view :) You think of it in terms of different frames of reference experiencing different arrows of time, although not measurable locally, if I get it right. You work your ideas from that assumption while I work mine from the opposite assumption. We may still meet in middle somewhere Mike, and until then we will have good discussions.
One might also express it as that you work from a definition of a 'wholly joined indivisible SpaceTime', where I work strictly from 'locality' assuming radiations constant to be what 'join' different frames of reference into a 'whole description' of SpaceTime. It's a subtle difference, but it gives us two perspectives.
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yor_on
That't not what this confusion is all about.
It' about the meaning of terms appertaining to gravity.
An object above the Earth has a certain gravitational potential energy. Release it and its GPE is converted into kinetic energy. The Earth's gravitational potential (strength of gravity at that location) varies from maximum at the centre of the Earth to zero infinitely far from the Earth. If you think of this distance as shells of time surrounding the Earth then each one has a different time dilation factor. These are not the same things at all but confusion arises because some people and web sites use these terms indiscriminately. Although I like the term gravitational potential as it says exactly what it is, I am loath to use that term because it can so easily be confused with gravitational potential energy.
There is a ambiguity to what a time dilation is. Sometimes you find otherwise knowledgeable guys describing it as time goes 'slower', relative some other frame, which in my view is incorrect. Times arrow has only one pace locally, the same everywhere, as far as I see it, but that's my view :) You think of it in terms of different frames of reference experiencing different arrows of time, although not measurable locally, if I get it right. You work your ideas from that assumption while I work mine from the opposite assumption. We may still meet in middle somewhere Mike, and until then we will have good discussions.
One might also express it as that you work from a definition of a 'wholly joined indivisible SpaceTime', where I work strictly from 'locality' assuming radiations constant to be what 'join' different frames of reference into a 'whole description' of SpaceTime. It's a subtle difference, but it gives us two perspectives.
Surely, both statements are correct. It is just a matter of perspective or frames of reference. However, the frame of reference you choose to use does give a different perspective.
That's true, I do think of time along those lines but with the proviso that the average time dilation factor of the universe is made up by averaging all of the local time dilation factors.
I think we are saying the same but from the opposite perspective.
True it does give different perspectives. Everyone lives in 'local' time and for most purposes that's all we need concern ourselves with. However, to understand 'time' we sometimes have to consider time from another (non-local) perspective.
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GPE relative GP huh :)
To find GPE you need a mass, the gravitational potential energy is the energy associated with the position of a given mass in the gravitational field. To find GP you also need a test particle of rest mass to define it from. The Principle of Equivalence when it compares Earths gravity to a rocket accelerating uniformly constantly at one gravity also uses a 'test particle', aka that rocket. Without the 'test particle' there can be no descriptions of a gravitational field as you have nothing to describe the field against as it seems to me.
Fields and relative motion gives me constant headaches.
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GPE relative GP huh :)
To find GPE you need a mass, the gravitational potential energy is the energy associated with the position of a given mass in the gravitational field. To find GP you also need a test particle of rest mass to define it from. The Principle of Equivalence when it compares Earths gravity to a rocket accelerating uniformly constantly at one gravity also uses a 'test particle', aka that rocket. Without the 'test particle' there can be no descriptions of a gravitational field as you have nothing to describe the field against as it seems to me.
Fields and relative motion gives me constant headaches.
Not necessarily so.
We weigh less on the Earth than on Jupiter and more than on the Mars because Jupiter's gravitational field is stronger that the Earth's and Earth's gravitational field is stronger than that of the Mars. That is a direct indication of the differences in the gravitational field. Our clocks on all three planets would indicate time passing at the same rate but relative to a distant observer they would all be running at different rates. This is an indirect indication of the differences in the gravitational field. No test particle required.
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I'm not questioning that Mike :) Fields vary, and the way to define that variation is to measure. Measuring though always will involve some 'test particle/detector' or similar from where you define the variations. It would be really nice to measure without one but that can only be done theoretically using what we measured already via detectors. But it is also so that your 'frame of reference' measuring will define what you measure, as 'free falling' in a gravitational field moving uniformly/gravitationally 'accelerating', relative accelerating locally. And that gores for all types of fields I can think of now (measurable ones that is)
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The point is the question what we mean by 'relative motion' here. If everything is exchangeable except locally defined accelerations then what you see and measure becomes a local result, dependent on your 'frame of reference', and that means locally defined here. I like it as it fits my 'strictly local' point of view, but it also gives me a headache when looking at what we think we see, 'SpaceTime'.