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Archive 1: User talk:Harald88/Archive1
A dish for a relatively small mercury mirror can be manufactured in the following way:
Make a flat turntable with a rim. Spin the turntable up to the desired angular velocity. Pour a
resin in the pan, the liquid resin will redistribute itself. When the resin has finished redistributing itself then none of the resin flows towards the center or away from it. In fluid dynamics this is referred to as 'solid body rotation'. After several hours the resin has set into an actual solid.
The mercury layer of a mercury mirror must be as thin as possible, because of the weight. If the parabolic dish has been manufactured well, then a layer of one milimeter of mercury can be sufficient.
There is definitely an equilibrium at play: if the angular velocity matches then the layer of mercury is evenly thick all over the dish, and mercury is neither flowing towards the center, nor away from it. -- Cleonis | Talk 19:45, 15 January 2006 (UTC)
Thank you for your good suggestion. What you say is true, but on an other hand, it is in line with the precedent discussion. That's why I will 'wait and see' before moving it. Again, thank you.
Harald, I have been overwhelmed with helping to resolve another dispute about the Jehovah's Witnesses. Plus, my (real) work load picked up this week, so I have not been able to devote much time to Wikipedia. I went to the library, but they did not have the book I wanted about tired light on the shelf. I had to place a back order for it, it will be back next week some time. I am not a physicist by training so I will have to read some to get used to the terminology. If you cannot wait until then, then I will be happy to withdraw and let someone else help out.
Let me know.
Steve Mc
Hi Steve, I 'm not in a rush: the activity on that article is not big as long as I pause/slow down my part of the edit war. Harald88 21:09, 22 January 2006 (UTC)
Harald, I got the book yesterday and have done some reading. I can now be a little more active (and informed) in this discussion. SteveMc 17:52, 28 January 2006 (UTC)
Hi Harald,
I still owe you an explanation of what I referred to when I wrote: 'Minkowski metric signature'.
As you surmised, I was referring to the 1905 Einstein special relativity postulates.
Einstein wrote in his 1905 paper (my rendering, not verbatim quote): continuous light will propagate with speed c away from an omnidirectional source in a spherically symmetrical way. Pulses of light will propagate away as a spherically symmetrical shell. Let there be an observer A and an observer B with a velocity relative to each other. The expanding shell will expand spherically symmetrical with respect to A, and it will also expand spherically symmetrical with respect to B. (And so on for any pair of observers with a velocity relative to each other). Mathematically, the demand can be formulated as follows: Let:
that can of course be abbreviated with the convention:
Obtaining:
You can organize the set of all solutions to that type of equation into a mathematical group. The transformations to transform one member of the group in another are the sought transformations then.
In retrospect it can be seen that the idea of organizing solutions to an equation into a group was also applied by Woldemar Voigt. My understanding is that Voigt investigated a wave equation for a time-dependent field.
Where u is the propagation speed of the wave. The set of solutions to that partial differential equation can be organized into a mathematical group. In the specific case of the Maxwell equations, a useful group is the Lorentz group. A Lorentz transformation transforms a solution in which a wave expands symmetrically to another solution in which the wave expands symmetrically.
My understanding is that the transformations are not specifically a characteristic of the Maxwell equations, but a characteristic of the mathematics of wave-mechanics in general. The Maxwell equations were designed to describe processes developing over time, and given the nature of electromagnetism, some of the solutions of the Maxwell equations describe propagating waves.
Anyway, one way of mathematically rendering the lichtspeed postulates of Einstein's 1905 paper is above mentioned:
This shows that one of the basic theorems of special relativity the invariance of the spacetime interval.
Mathematically, it is equivalent to submit the invariance of the space-time interval as an axiom of the special theory of relativity, and take it from there.
The concept of the spacetime interval was not explicitly present in the 1905 paper, I think, explicit mention of it arose a couple of years later, but soon it took center stage in the perception as arguably the single most important concept in relativistic physics. The metric signature of the space-time interval is (+,+,+,-). In special relativity and in general relativity, the concept of the invariant space-time interval is identical.
In the context of space-time continuum, the separation between two points in space-time is measured in units of time. The only thing you can actually measure is how much time a journey takes. The closest thing to a space- odometer is measuring the duration of the journey. If the journey is not physically undertaken then spatial distance is inferred by measuring how much time it takes electromagnetic waves (light) to cover that spatial distance. But it is tricky. Inferring the spatial distance between two points in space-time is about attempting to measure something that is non-local; which gives rise to ambiguity. By contrast, counting lapse of time with a device such as an atomic clock is a local measurement.
I am sorry I have been butting in on the Twin paradox Talk page with cryptic remarks, and then not follow up on them. I think I had announced that I want to stay away from articles that involve relativistic physics, but I find myself drawn to it like a magnet. I shall once again try hard to stay away from involvement in wikipedia relativistic physics articles. -- Cleonis | Talk 12:23, 24 January 2006 (UTC)
Whether or not Einstein attached a 1-to-1 physical meaning to the space-time interval, the invariance of the space-time interval is what special relativity and general relativity have in common.
Do you know something about Minkowski's lecture that I do not? The parts of that lecture that I have knowledge of fit relativity. Is by any chance the content of that lecture available on the internet?
It dawned on me that although I am accustomed to writing 'space-time' the expression 'time-space' actually fits better. Also it would seem that the following expression for a timelike time-space interval is technically the correct one:
Separation between points in time-space is measured in units of time, so it makes sense to cast the expression in such a way that the dimensions fit.
I don't like it when it is suggested that 'time = length', because I think time is more fundamental than length. -- Cleonis | Talk 18:40, 24 January 2006 (UTC)
I am somewhat familiar with that allegory.
I wrote on the centrifugal force talk page:
All theories unavoidably contain elements that cannot be directly observed. For example, we cannot directly percieve the presence of a magnetic field. Charged particles behave differently when what we call a 'magnetic field' is present, that is the observable. The reason we take it for granted that such an entity as a 'magnetic field' actually exists is that it provides an efficient way to organize the body of knowledge about magnetism.
From my point of view, the physics concept of a field is inferred from the behavior of the silhouettes as seen on the wall of the cave. From my point of view it would be wrong to attach a feeling of absolute certainty to what is inferred from the behavior of the silhouettes. I follow Stephen Hawking when he says: 'I don't demand that a theory correspond to reality because I do not know what it is. Reality is not a quality you can test with litmus paper.'
I regard both the mathematical framework of a theory and its its interpretation as tools. The more versatile the tool, the better. Ideally, the best theory is like a swiss army knife that can handle any job. My philosophy of physics entails that interpretation of a theory does matter, in that it guides the thinking and it provides a way to organize the perceptions. But I do not demand correspondence to reality, for I don't know what it is.
The only demand that I make is that a theory of physics applies well, and that it is self-consistent. I don't want to have any pre-concieved notions of what is or isn't physically realistic, for I don't know what reality is. For example, I don't exclude the possibility that the concept of 'space' as it is applied in newtonian physics is a silhouette of something that cannot be adequately described as 'space'.
Maybe I do disagree with Minkowski. It is possible that before the introduction of relativistic physics some physicists were true believers in the concepts of Newtonian/Maxwellian physics. Relativistic physics may present a dilemma to some people: to either convert from newtonian faith to relativistic faith, or to stay away from the idea that one should have absolute faith in any theory. To me there is no dilemma, the only available choice being the the second choice. --
Cleonis |
Talk 11:07, 25 January 2006 (UTC)
I copy and paste from the twin paradox Talk page.
Geometry, when applied in physics calculations, is itself a theory of physics, of course. The Galilean transformations and the corresponding velocity addition rule are the foundation of the Galilean/Newtonian codification of the properties of inertia. The Lorentz transformations, and the corresponding relativistic velocity addition rule, are likewise the foundation of the relativistic codification of the properties of inertia.
I think physics textbooks ought to point out that according to relativistic physics, acceleration with respect to the structure of space-time is much more important than in Newtonian physics. According to newtonian physics acceleration is no big deal. But according to relativistic physics, to accelerate with respect to the structure of space-time constitutes an irreversable event. (Making two U-turns does not quite give the same end result as not making any U-turn. The second U-turn cannot entirely undo the consequences of the first U-turn.)
So Minkowski space-time is, if anything, more absolute than newtonian absolute space.
If textbooks would teach special relativity in that more logical way, emphasizing that the Minkowski manifold is absolute, then the perception of the twin scenario would be quite different. -- Cleonis | Talk 22:24, 27 January 2006 (UTC)
You might consider Wikipedia:Request for comment regarding 69. If he's causing that much trouble, there are probably admins more knowledgable about physics that can help you guys better. Last night he led me to believe it was a simple matter of moving a section. Apparently I was deceived, as there is a lot more material at hand now. I'm going to ask for some advice, and please feel free to message me in the meantime. -- DanielCD 14:41, 28 January 2006 (UTC)
Harald, I have posted an initial response and additional questions to clarify the dispute at Mediation Cabal: Tired Light. SteveMc 03:15, 29 January 2006 (UTC)
Harald, I do not know what is wrong with that email address. IT tells me it should work, I do receive email at that address, but apparently the email server kicks back some of it, sorry. I changed the email to reflect my new address, user ScienceApologist posted a web link to a URL where I was able to get the article.
I have posted a request for some outside help on tired light. This issue is really beyond me, even with the reading I have done. I will stay with it until I can find someone else more keen to the issues.
Thanks, SteveMc 14:37, 4 February 2006 (UTC)
The expression for the centripetal acceleration is derived in the article " Centripetal force". Why do you need to rederive it in section "Reactive centrifugal force" of the article " Centrifugal force"? Yevgeny Kats 23:28, 4 February 2006 (UTC)
Hello Harald88, thank you for reverting the vandalism of the g.o.mueller add, the biggest critical work ever.It is worth reading sooo much. Are you interested in an English translation by the way ? 80.138.158.108 01:35, 5 February 2006 (UTC)
"www.ekkehard-friebe.de/buch.pdf". 80.138.190.9 12:30, 6 February 2006 (UTC)
I copy from Talk:Relativity_of_simultaneity :
Let an atomic clock be put onboard an aeroplane that circumnavigates the world at a constant velocity, (such GlobalFlyer, in which Steve Fosset made a non-stop flight around the world.) Let the GlobalFlyer fly at constant altitude, with a constant velocity. Then the atomic clock onboard the Global flyer will on arival be seen to have counted 207 nanoseconds less or more time, depending on whether the flight was eastwards around the world or westwards around the world. (The time count does need to be corrected for gravitational effects.) -- Cleonis | Talk 10:42, 6 February 2006 (UTC)
I wrote that the time as counted by the travelling clock does need to be corrected for gravitational effects. The gravitational effects can be corrected for by having one GlobalFlyer fly eastwards around the world, and the other westwards. In an idealized case the flyers maintain a constant altitude at all times.
Other than that, the amount of difference in lapse of proper time after circumnavigation is independent of the relative velocity of the flyer and the clock that is co-moving with the equatorial surface of the Earth. Because it is a loop-closing scenarion (just as the twin scenario is a loop-closing scenario) the relative velocity drops out of the calculation.
In the case of a loop-closing scenario the only operative factor is the difference in spatial length of the path travelled.
So there is no need to know the velocity of the GlobalFlyer, the velocity only needs to be constant. (A trajectory with a non-constant velocity has an even longer spatial length, with a non-constant velocity the time difference is more than those 207 nanoseconds.) --
Cleonis |
Talk 00:35, 7 February 2006 (UTC)
I think the above example is in the Stedman review of the Sagnac effect. The link to the Stedman review is at the Sagnac effect. Anyway, the above example, the number of 207 nanoseconds, is from peer-reviewed scientific literature. -- Cleonis | Talk 00:35, 7 February 2006 (UTC)
Well, in the twin scenario the difference in amount of elapsed proper time at the point of rejoining is not a function of their relative velocity at previous stages the journey. The operative factor is the difference in the spatial length of the respective worldlines.
I get the impression that you have a different situation in mind than I have. I am thinking about difference in elapsed amount of proper time as seen when clock readings are comparded after rejoining. I am thinking about a variation of the twin scenario. One twin remains co-rotating with the surface of the Earth's equator, the other twin travels along a different worldline, a worldline with a different spatial length. -- Cleonis | Talk 21:59, 7 February 2006 (UTC)
In his 1905 article, Einstein discusses the comparison of a stationary clock (a clock on a non-rotating planet) and a circumnavigating clock. What I have in mind is two circumnavigating clocks; the clock that is stationary with respect to The Earth's Equator is circumnavigating (as it is co-rotating with the Earth), and a clock onboard an aeroplane that takes several days to return to the longitude of departure is also circumnavigating. -- Cleonis | Talk 23:17, 7 February 2006 (UTC)
Are you User:205.188.114.9? -- ScienceApologist 02:08, 7 February 2006 (UTC)
I don't know, as I use several computers (it's not the one I use now); but when I notice that the computer logs me out of Wikipedia, I sign in. I'll look if I can find a recent case where I overlooked it and if so, correct it. Harald88 08:05, 7 February 2006 (UTC)
Hi Harald, thanks for your note. I don't recall exactly when and where that phrase was first added, but it's certainly accurate. NOR, V, and NPOV are complementary in that they don't and can't stand in isolation from one another. Following NPOV does not mean we may add any and every opinion under the sun, because we're not allowed to add original research (no matter how beneficial it might be from an NPOV standpoint), and the only way we can show we're not adding OR is to cite sources in accordance with WP:V. Any attempt to interpret one of the policies in isolation will lead to problems. Hope this helps. Cheers, SlimVirgin (talk) 21:16, 7 February 2006 (UTC)
I have found two references for the comparison of synchronisation procedures that rely on signals, and portable clocks respectively, and that the correction factor of 207.4 nanoseconds arises in both procedures.
There is Neil Ashby's discussion of Relativity in the Global positioning system Enter the number 207 in the 'find a word on this page' function of your webbrowser to jump to where Ashby discusses signals and clocks
And there is
G E Stedman's review of ring laser tests of fundamental physics and geophysics
In section 1.2 Early history, on page 7 of the PDF document, Stedman mentions the comparison of circumnavigating signals and circumnavigating clocks.
From a newtonian (non-Lorentzian) point of view, you expect the Sagnac effect for circumnavigating signals. From a relativistic point of view you also expect a Sagnac effect for circumnavigating signals. In that sense the Sagnac effect for circumnavigating signals is a theory-independent phenomenon. The Sagnac effect for loop-closing signals is so fundamental that it is a theorem of every theory of physics.
On the other hand, when it comes to disseminating time with portable clocks, then from a newtonian (non-Lorentzian) point of view you do not expect an effect. From a relativistic point of view you do expect the clocks to have counted a different amount of proper time when compared on rejoining. It seems quite fitting to refer to time dilation effects for circumnavigating clocks as 'the Sagnac effect for clock transport' -- Cleonis | Talk 22:36, 7 February 2006 (UTC)
Recapitulating:
My mental picture is that I view the worldline of the clock that is co-rotating with the Equator as a
helix in a Minkowski space-time diagram. In other words: I map the worldline of the corotating-with-the-Equator-clock in an inertial coordinate system. Then I map the worldline of the airplane that takes several days to circumnavigate in that same Minkowski space-time diagram.
Maybe I should have announced explicitly that I was mapping the two wordlines in a single inertial coordinate system. As I have expressed before: I reject mapping of motion in a rotating coordinate system. (Well, I reject it for the purpose of theoretical understanding, it can on occasion be good calculational strategy.) -- Cleonis | Talk 00:48, 8 February 2006 (UTC)
Actually, the relativistic examination of the Sagnac effect plays a huge role in my commitments. I regard rotation as absolute. (I regard rotation as absolute in the sense that I regard the Minkowski manifold as absolute.) I may have expressed this before: I do not see relativistic physics as a theory of "motion is relative". I think of relativistic physics as the Theory of Invariance. -- Cleonis | Talk 01:49, 8 February 2006 (UTC)
Hey Harald. You're right, I agree that Wiki isn't the place to resolve accreditation disputes. But it does seem like the right venue for the facts about priority, and it really does seem to be the consensus that Poincare published first on a number of substantial issues. But as you say, those are simply the facts, and if they are laid out for people, they can come to their own conclusions. Lucidish 04:11, 8 February 2006 (UTC)
I asked what part of your question about the sources of the NPOV was not answered by this section, but, I have not seen any answer from you about this. I look forward to your answer: What question do you have that is not answered by the Wikipedia:Neutral_point_of_view#History_of_NPOV section? - 08:40 . . JesseW
I have just been reading the
Anti-relativity article.
In that article I encountered a distinction that I hadn't quite appreciated before, a distinction that possibly you edited into the article (but I haven't looked that up).
There is anti-relativism, and there is anti-relativityism. Very significant distinction there, for I oppose relativism, and I am committed to relativistic physics (in the sense that I am committed to Invariance Theory)
I follow wholeheartedly the opinion that the expression 'theory of relativity' is a misnomer (to my knowledge the name 'theory of relativity' was coined by Planck, who was the first to voice approval of Einstein's 1905 paper). It is known that Einstein would have preferred the name 'Invariance theory'.
Einstein was never interested in relativism, only in theories based on Principles of Invariance. In that sense Einstein is to be placed in the category of people who oppose relativism.
What I want to contrast is theories from a starting point that space should be eliminated from physics theories, and theories from a starting point that the structure of space and time is a player in the physics taking place. The three succesful theories of motion all have in common the concept of structure of space and time as a physical entity in itself, involved in the physics taking place: Newtonian dynamics, special relativity, general relativity. I see general relativity as the culmination of that structure-of-space-and-time paradigm.
A problem that I have is that I'm fed up with the matter of false expectation. I'm fed up with dealing with the burden of the wide-spread erroneous expectation that relativistic physics is meant to show that "everything is relative". I just don't have the patience to deal with people who have embraced that erroneous belief. -- Cleonis | Talk 12:24, 11 February 2006 (UTC)
I hadn't realized that the terminilogy 'anti-relativityism' is novel, but I guess it is. Because of its sheer usefulness, I would be in favor of retaining it. (Which may be going outside wikipedia policy, which personally I don't mind doing, but I will respect the opinion of others.)
I wanted to notify you that my assessment is that Einstein was never interested in "showing that everything is equally relative". As I wrote before, I have dug hard at information. The group of experts on the early history of relativistic physics is not very large: John Norton, John Stachel, Jurgen Renn, Michael Jansen. I may forget one or two here, but those authors are my main sources of information. Reading their papers takes patience, for they are very, very meticulous.
On the basis of the body of evidence that I have gathered, my assessment is that Einstein's aim in the years leading up to 1915 was to enhance the concept that the structure of space and time is an entity in itself in the theory. (There are Einstein remarks that appear to indicate that Einstein supported physical relativity. I have explanations for these appeareances that satisfy me.)
For now let me submit as evidence the mathematical structure of the general theory of relativity. In GR, the structure of space and time is a physical entity in itself. That was Einstein's starting point all along. To suggest that Einstein had the wrong starting point, and just happened to stumble on the GR equations would be like claiming that Sir Edmond Hilary and Tenzing Norgay happened to stumble to the top of Mount Everest on a caving expedition.
I think this occasion is a good opportunity try and do a good write-up of how I understand the history of GR. So: later more.
Cheers --
Cleonis |
Talk 08:45, 12 February 2006 (UTC)
As you know I dislike the expression 'fictitious force'. In my opinion that expression should be banned from physics textbooks, and it should be replaced with the expression 'coordinate acceleration'.
In this Sandbox article I explain the concept of coordinate acceleration. Can you check it out? It is related sideways to issues of the transition from newtonian dynamics to GR dynamics. -- Cleonis | Talk 11:51, 12 February 2006 (UTC)
Harald88, I wonder if you have some advice for me.... I am a bit puzzled about the way E=mc2 is presented in various Wikipedia articles and other references - it seems to understate the radical nature of Einstein's interpretation. I tried to encapsulate my puzzlement into a question at Talk:Special relativity. I'd appreciate your feedback. When you get back from vacation...? -- Alvestrand 21:29, 18 February 2006 (UTC)
Radiant! has yet again been removing the link to the proposed policy page.
Wikipedia policy requires that if user conduct is an issue, at least 2 users must have tried to resolve it first. I've done so already and failed. Could you have a go, and post a note on his talk page that this is an ongoing matter, and please not to disrupt the process or remove links to the page?
Thanks. FT2 ( Talk) 03:11, 19 February 2006 (UTC)
Where was this originally passed on to you? Was it in an email, or did someone post it somewhere on WP? Thanks. -- LV (Dark Mark) 19:04, 1 March 2006 (UTC)
It was sent to me by her family from her email address, probably because I had written to her recently about an alternative to the Copenhagen interpretation. I knew she had had cancer for some time now, but she sounded so upbeat about it that it really took me by surprise. :( Harald88 06:39, 2 March 2006 (UTC)
hope you had a good holiday!
Unfortunately, the Licorne show hasn't stopped playing yet - it's now at Wikipedia:Requests for arbitration/Licorne - and Licorne's invoking your name as if you supported him, amazingly enough.
Just thought you'd want to know. -- Alvestrand 06:59, 2 March 2006 (UTC)
Re your contribution to the Licorne "evidence" page:
just to be careful... Fastfission didn't introduce the idea that Bjerknes is a Holocaust denier into the discussion; I did. The basis for saying so is a speech given by Bjerknes in defense of David Irving - the link is on the Christopher Jon Bjerknes Web page.
I think the "talk" page of the RfA is a better place to discuss whether there are people who have behaved worse than Licorne, and whether that's a mitigating circumstance for him. -- Alvestrand 13:19, 2 March 2006 (UTC)
Hi,
I don't see that further discussion of this is relevant to Licorne or anything except mutual interest. In relation to your description of what you found childish, I reacted to that differently but also somewhat negatively. My reaction was simply (like yours on this) that it was basically irrelevant and made the article harder to follow (parallel critique of two versions, one of which was provisional and never public). The reason for doing it did not strike me as sufficient. I thought it a bit strange rather than childish, but mostly didn't give it much thought (to be honest; I was focused on following the arguments as carefully as I could). As to the shorter version, it is completely lobotimized and leaves out essentially all backing detail. I find this very unfortunate. The short version doesen't convince me of anything, while the longer version leaves me completely convinced until someone presents critical flaws that I couldn't see. In fact, I think it is a crucial piece of historical argumentation that is now hidden, and the primary sources are impossible for any non-expert to access (the preserved proofs in different versions, especially). -- Pallen 05:25, 4 March 2006 (UTC)
Hi Harald, I have been brooding on how to write about the history of General relativity concepts.
In preparation for the things I want to write about, I need to provide background.
I quote from a paper by John Norton,
Einstein’s Investigations of Galilean Covariant Electrodynamics Prior to 1905 (PDF-file 329 KB)
In a manuscript from 1920, Einstein recalled how this simple reflection had played
an important role in the thinking that led him to special relativity. The essentially relevant
parts of his recollection read:
In setting up the special theory of relativity, the following ...idea concerning Faraday’s magnet-electric induction [experiment] played a guiding role for me.
[magnet conductor thought experiment described].
The idea, however, that these were two, in principle different cases was unbearable for me. The difference between the two, I was convinced, could only be a difference in choice of viewpoint and not a real difference. Judged from the magnet, there was certainly no electric field present. Judged from the electric circuit, there certainly was one present.
Thus the existence of the electric field was a relative one, according to the state of motion of the coordinate system used, and only the electric and magnetic field together could be ascribed a kind of objective reality, apart from the state of motion of the observer or the coordinate system. The phenomenon of magneto-electric induction compelled me to postulate the (special) principle of relativity.
The origin of this Einstein quote is listed as a manuscript that was prepared for the magazine Nature, but eventually wasn't published there. It has been published in Einstein's collected papers. (Einstein, Albert (1920) “Fundamental Ideas and Methods of the theory of Relativity, Presented in Their Development,” Papers, Vol. 7, Doc. 31.)
Understandably I like the above Einstein quote; it is in perfect harmony with the mainstream understanding of special relativity.
There is the 'silhouettes on a cavewall' theme. Two observational viewpoints that are moving relative to each other cut a different slice through space-time. The 'cuts at different angles' theme is depicted in
this animation by Andrew Hamilton (that animation is on
this webpage.)
In Maxwell's theory of electricity and magnetism the two fields are described as separate entities. Each field can induce the other field, but nonetheless the two are described as separate entities. Einstein sought to develop a field theory in which there is a single electromagnetic field, a single entity. This single entity is then the mediator of magneto-electric induction. The class of separate accounts of the physics taking place that Lorentz Ether theory provides (a different story for each velocity with respect to the ether) is then seen as a class of cuts at different angles. This class of cuts at different angles is then seen as an equivalence class of mapping events in a class of coordinate systems. That theme is what I tried to embody in the animations of my Sandbox article about Minkowski spacetime.
Recapitulating:
According to the principle of relativity of inertial motion, when two objects collide non-elastically, (and sticking together after the collision), then the amount of kinetic energy that is converted to heat in the collision is a frame-independent quantity; an invariant quantity.
In Minkowski space-time, in order to shift the angle of cutting through space-time, a force must be exerted. The shift is called a 'Lorentz boost'.
The structure of space and time opposes shift to another angle of cutting through space-time; this is of course what we refer to as inertia. --
Cleonis |
Talk 08:58, 4 March 2006 (UTC)
PS I am bugged by your claim in that sandbox: "There is no theory to address the question of how the structure of space and time can be like that." As such a theory is inherently metaphysical, I take it to mean:
"There is no explanation of how the laws of space and time can be like that."
However, as you know very well, such a theory does exist, it's only impopular because of fashion and/or misunderstandings. Thus I'm curious what you do mean with that claim. Harald88 17:05, 4 March 2006 (UTC)
Cleonis |
Talk 19:30, 4 March 2006 (UTC) In my Sandbox article about Minkowski space-time, I write:
Harald:
I assume that you refer to the Lorentzian interpretation. I regard the Lorentzian interpretation problematic. In this I follow the mainstream view of the physics community.
One of my considerarions is the following thought experiment:
Cavendish measured the gravitational constant by measuring the gravitational attraction exerted by a lead sphere with a weight of 350 pounds. Description of the Cavendish gravitational constant measurement
We have good reasons to trust that active gravitational mass is always equivalent to passive gravitational mass, and that gravitational mass is always equivalent to inertial mass. No experimental evidence is known of a case of gravitational mass not being equivalent to inertial mass.
Suppose we assume that there is a Lorentzian ether. An Lorentz-type ether theory requires that inertial mass increases with increasing velocity with respect to the Lorentzian ether. Then it follows that a Cavendish gravitational constant experiment, onboard a spacecraft free-floating in space, will measure a different value, depending on the velocity of the spacecraft with respect to the Lorentzian ether. (Cavendisch happened to use a torsion balance, but there are of course lots of ways to perform the necessary measurement.)
On the other hand: according to the Einstein approach, in which velocity with respect to the Minkowski space-time does not enter the theory, we have that whenever the spacecraft is moving inertially (regardless of what it did before that; we assume motion to be memoryless), always the same gravitational constant will be measured.
It seems to me that a strictly Lorentzian theory only stands a chance of predicting the same as Einstein theory when the Lorentzian theory assumes that gravitation couples to rest mass, for it is rest mass that is, like coulomb charge, Lorentz-invariant. However, there is solid evidence that gravitation couples to the total inertial mass, not to rest mass.
The most extreme version of this thought experiment goes as follows: take a neutron star, teetering on the brink of collapsing into a black hole. In this thought experiment the neutron star is just below the mass limit for collapsing into a black hole. Now, increase the velocity of that neutron star. It seems to me that an ether theory must predict then that the increase of inertial mass will elevate the self-gravitation of the neutron star to the point of collapse into a black hole. -- Cleonis | Talk 19:30, 4 March 2006 (UTC)
Thanks for giving evidence in the Licorne arbitration. As a clerk to the arbitration committee, I have edited some of your evidence ( in this edit) to provide the kind of "diff" links that the committee will want to look at. If you give more evidence, but find yourself unable to produce such links, it would still be helpful if you could note the approximate time of day as well as the date of the edit. I can hunt the history and produce the diff more easily if you do that.
For the arbitration committee. -- Tony Sidaway 22:27, 4 March 2006 (UTC)
I couldn't make out from your previous reply whether I had been sufficiently specific in how I presented the thought experiment. It is unclear why you brought up the ECI frame.
Therefore I present the thought experiment a second time, with more specifics.
A characteristic of a Lorentz-type ether theory is that it is assumed that inertial mass increases as velocity with respect to the supposed ether increases. This has been explained by Poincaré in his 1909 Göttingen lecture. "On a constaté ainsi que la masse dépend de la vitesse et énoncer cette loi: L’inertie d’un corps croît avec sa vitesse qui reste inférieure à celle de la lumière, 300 000 kilomètres par seconde."
Let a spacecraft be somewhere in interstellar space, so far away from any star that any stellar gravitational field is negligable. In a hold inside the spacecraft, the gravitational attraction between two large, solid spheres is measured. The large spheres are centimeters apart.
Example of how the magnitude of that gravitational attraction can be measured:
A low pressure air cushion is supplied in the gap between the two spheres, so that the gravitational attraction cannot pull them closer. The low pressure air cushion would have to be provided by using a tiny, low mass tube, supplying a minute flow of air right between the two masses. The magnitude of the air flow that counterbalances exactly the gravitational attraction between the two masses is then a measure of the gravitational attraction between the two balls.
Let the spacecraft alternate between phases of accelerating and moving inertially. Everytime the spacecraft is moving inertially the gravitational attraction between the two spheres is measured. From an ether theory point of view, the respective measurements are conducted at a different velocity with respect to the ether each time. There is strong evidence that gravitational mass is always equivalent to inertial mass. From an ether theory point of view one expects that at each different velocity with respect to the ether a different gravitational attraction will be measured.
This thought experiment would not have been considered before 1915. In 1915, GRT put the concept of equivalence of inertial and gravitational mass on firm ground.
Lorentz ether theory works for electromagnetism because Coulomb charge is a Lorentz invariant quantity. On the other hand, according to GRT gravitation is a function of the total inertial mass. Rest mass is Lorentz-invariant, but the total inertial mass is not Lorentz-invariant. -- Cleonis | Talk 09:38, 5 March 2006 (UTC)
Hi Harald,
I've checked out what Alonso & Finn write about relativistic physics.
The location:
Alonso & Finn, second edition, volume I, mechanics and thermodynamics, Section 6.8, page 133
Alonso and Finn discuss the Michelson-Morley experiment at length, and write:
Lorentz and Fitzgerald independently proposed that all objects moving through the ether suffer a "real" contraction in the direction of motion
[...]
Of course, an alternative explanation is of the negative result of the Michelson-Morley experiment is to assume that the speed of light is always the same in all directions, no matter what the state of motion of the observer. [...] This position was adopted by Albert Einstein when he was formulating his principle of relativity. The student may, however, at this moment say that the "real" contraction assumed by Lorentz to explain the negative result of the Michelson-Morley experiment is exactly the same as the contraction we found in Eq. (6.35) by using the Lorentz transformation and the principle of the invariance of the velocity of light. There is however, a fundamental difference between, the two underlying hypotheses used for obtaining these two apparantly identical results. (1) the contraction (6.37) obtained by means of the Galilean transformations is assumed to be a real contraction suffered by all bodies moving through the ether, and the v appearing in the formula is the velocity of the object relative to the ether. (2) Contraction (6.35) refers to only the measured value of the length of the object in motion relative to the observer, and is a consequence of the invariance of the velocity of light. the v appearing in the formula is the velocity of the object relative to the observer, and thus the contraction is different for different observers. Einstein realized that the idea of an ether was artificial and unnecessary, an that the logical explanation was that the second one.
Admittedly, this exposition by Alonso & Finn is rather muddled, and several of their remarks are historically wrong, but there can be no doubt as to the philosophical commitment of Alonso & Finn.
There is always the distinction between the invariants and the variants. Electric charge, rest mass, and the space-time interval are invariants. When two objects collide, and remain stuck together after the collision, then the amount of kinetic energy that is converted to heat is an invariant, a frame-independent quantity. On the other hand: the quantity of length contraction is a coordinate contraction. Given an arbitrary choice of coordinate system to map physics events, an amount of coordinate contraction is assigned to each object that is moving with respect to the chosen coordinate system. But to this coordinate contraction no corresponding physics content is attributed; the coordinate contraction that is assigned is an artifact of the particular choice of mapping the events in a coordinate system. -- Cleonis | Talk 14:28, 5 March 2006 (UTC)
I copy and paste from above:
Presumably you mean: in GRT, what is the mutual attraction between the massive spheres when the spacecraft is in inertial motion? (This experiment would be very tedious when the spacecraft is pulling G's)
According to GRT, there is full blown equivalence of all inertial motion. GRT is by design a theory that has as its starting point full blown symmetry of all inertial motion. So in GRT there is nothing to calculate; in the mathematical framework of GRT there is no formula to slot in the velocity that you are referring to.
By contrast: in an ether theory, velocity with respect to the supposed ether matters, and if that ether theory wants to reproduce all relativistic predictions the laws of that theory must be such that in the end all ether effects cancel out against each other. As you know, that is what makes the ether theoretical discussion of for example the Trouton-Noble experiment so riddled with pitfalls. In an ether theory with Lorentz transformations, that machinery works out for electromagnetism, as the Lorentz transformations hold good for electromagnetism: in the end everything cancels out again. But gravitation is not Lorentz-invariant.
I was drawn towards this thought experiment precisely because of that difference. I have not encountered discussion of this thought experiment anywhere, which surprises me somewhat, because I think it is quite a probing thought experiment. -- Cleonis | Talk 19:03, 5 March 2006 (UTC)
Harald referred to:
rest mass/relativistic mass question as discussed on on sci.physics.research on 18 february 2006
When read as a whole (as opposed to taking a sound bite), I agree with the wonderfully clear expositions by Greg Egan.
Not surprisingly, my view coincides with the view that is presented in the Usenet Physics FAQ article about the question:
Does mass change with velocity? And the related article:
If you go too fast do you become a black hole?
In the above-mentoned thread: 'rest mass/relativistic mass question', Chalky asks a probing question:
Now, with a linearly accelerating mass, energy is definitely being spent on it. That energy is being transformed into kinetic energy (which is the other confusing concept because this meaure of energy seems to be frame dependant) which is as "real" as any other energy because it can be converted back if necessary to any other form of energy. However, this kinetic energy for some reason does not contribute to the stress-energy tensor.
Greg Egan's answer satisfies me in the sense that he shows to my satisfaction that there is no selfconsistency issue. -- Cleonis | Talk 19:42, 7 March 2006 (UTC)
You mention that unipolar magnets have weird effects in another thread on this page. What theory predicts that such a thing exists? Has it been observed? My physics is getting old.... -- Alvestrand 15:53, 4 March 2006 (UTC)
OK I found some of it back!
Very interesting experiments. The interpretation seems not fully settled. In contrast to Guala-Valverde's explanation, the following author claims that the effect does not occur for electromagnets, only for permanent magnets. This is seen to cause serious problems for Guala-Valverde's interpretation of his experiments. The author's alternative explanation is the analysis permanent magnets in terms of their magnetic domains, which represent small current loops: http://www.maxwellsociety.net/PhysicsCorner/CurrentLoopPolarization/ElectroAndPermanentMagnets.html However, because of the pitfalls of modeling an actually rather complex reality with oversimplified models, my sense is that there is not yet clear consensus on the explanation of these results. However, I would propose a different experiment (my own) to challenge the idea that if all parts of an e/m system are co-rotating, the rotation can't be detected. Consider two metal balls like those used in a van-de-graff generator, mounted on either end of an insulating rod. Have a large charge difference between them. Imagine spinning this apparatus rapidly like a baton. Imagine a radio detector some distance away, spinning identically with spinning charge apparatus - such that in an appropriate spinning frame, the whole apparatus including the radio receiver are stationary. SR, and most physicists, would predict that radio will detect radio waves if the spin is fast enough and the charge subsantial enough. My guess is that Guala-Valverde would propose that no radio waves would be detected. Of course, the electromagnet variant of his experiment already achieves detection of absolute rotation, electromagnetically (according to Dixon). -- Pallen 01:00, 7 March 2006 (UTC)
E-mail From: Chris Hillman To: Alberto Mesquita Filho
On Thu, 8 Jan 1998, Alberto Mesquita Filho wrote:
> In my original project I thought of a charge at rest, for example, a loaded spherical conductor on a table and of this separated by an insulating cylinder. However, the experience would be the same case if the charge it was in a rectilinear and uniform movement. Certainly, in the considered frame of reference, it is not being accelerated because "it doesn't emit electromagnetic radiation".
����������� You are still confused.� If the table is experiencing stresses because there is a gravitational force (or if you prefer, because the elevator is being accellerated), then the charge will radiate because it to is being accellerated.
Chris Hillman
Some sample papers debating this: http://arxiv.org/abs/gr-qc/9303025, http://arxiv.org/abs/gr-qc/0006037, http://arxiv.org/abs/gr-qc/9903052, http://home.omnisp.ru/mira/boulware/111.htm -- Pallen 15:51, 7 March 2006 (UTC)
Of these, on an initial read through, the 3d reference (Pauri and Vallisneri) seems the most convincing to me. Two of the others agree with the main conclusiong, but the argumentation seems less fundamentally convincing to me. The first reference takes a maverick point of view and argues that there is a genuine violation of the equivalence principle. My superficial initial analysis correctly noted that the comoving accelarated charge and detector has to be the same as a charge and detector supported in a gravitational field (by the equivalence principle). However, I wrongly concluded from an extremely oversimplified application of Maxwell's equations and SR, that the former case would produce radiation at the detector. This, indeed, leads to the bizarre situation you questioned. Reference 3 is very convincing that a proper application of Maxwell+SR predicts no radiation for the case of COMOVING accelarated charge and detector. There seems to be a good article opportunity here. I notice that the Physics FAQ chooses not address this question at all - I guess not surprising given how many great physicists (e.g. Pauli) have gotten it wrong over the years. -- Pallen 20:27, 7 March 2006 (UTC)
Welcome!
Hello Harald88/Archive2, and welcome to Wikipedia! Thank you for your contributions. I hope you like the place and decide to stay. Here are a few good links for newcomers:
I hope you enjoy editing here and being a Wikipedian! Please sign your name on talk pages using four tildes (~~~~); this will automatically produce your name and the date. If you have any questions, check out Wikipedia:Where to ask a question or ask me on my talk page. Again, welcome! -- Fastfission 03:53, 11 October 2005 (UTC)
Archive 1: User talk:Harald88/Archive1
A dish for a relatively small mercury mirror can be manufactured in the following way:
Make a flat turntable with a rim. Spin the turntable up to the desired angular velocity. Pour a
resin in the pan, the liquid resin will redistribute itself. When the resin has finished redistributing itself then none of the resin flows towards the center or away from it. In fluid dynamics this is referred to as 'solid body rotation'. After several hours the resin has set into an actual solid.
The mercury layer of a mercury mirror must be as thin as possible, because of the weight. If the parabolic dish has been manufactured well, then a layer of one milimeter of mercury can be sufficient.
There is definitely an equilibrium at play: if the angular velocity matches then the layer of mercury is evenly thick all over the dish, and mercury is neither flowing towards the center, nor away from it. -- Cleonis | Talk 19:45, 15 January 2006 (UTC)
Thank you for your good suggestion. What you say is true, but on an other hand, it is in line with the precedent discussion. That's why I will 'wait and see' before moving it. Again, thank you.
Harald, I have been overwhelmed with helping to resolve another dispute about the Jehovah's Witnesses. Plus, my (real) work load picked up this week, so I have not been able to devote much time to Wikipedia. I went to the library, but they did not have the book I wanted about tired light on the shelf. I had to place a back order for it, it will be back next week some time. I am not a physicist by training so I will have to read some to get used to the terminology. If you cannot wait until then, then I will be happy to withdraw and let someone else help out.
Let me know.
Steve Mc
Hi Steve, I 'm not in a rush: the activity on that article is not big as long as I pause/slow down my part of the edit war. Harald88 21:09, 22 January 2006 (UTC)
Harald, I got the book yesterday and have done some reading. I can now be a little more active (and informed) in this discussion. SteveMc 17:52, 28 January 2006 (UTC)
Hi Harald,
I still owe you an explanation of what I referred to when I wrote: 'Minkowski metric signature'.
As you surmised, I was referring to the 1905 Einstein special relativity postulates.
Einstein wrote in his 1905 paper (my rendering, not verbatim quote): continuous light will propagate with speed c away from an omnidirectional source in a spherically symmetrical way. Pulses of light will propagate away as a spherically symmetrical shell. Let there be an observer A and an observer B with a velocity relative to each other. The expanding shell will expand spherically symmetrical with respect to A, and it will also expand spherically symmetrical with respect to B. (And so on for any pair of observers with a velocity relative to each other). Mathematically, the demand can be formulated as follows: Let:
that can of course be abbreviated with the convention:
Obtaining:
You can organize the set of all solutions to that type of equation into a mathematical group. The transformations to transform one member of the group in another are the sought transformations then.
In retrospect it can be seen that the idea of organizing solutions to an equation into a group was also applied by Woldemar Voigt. My understanding is that Voigt investigated a wave equation for a time-dependent field.
Where u is the propagation speed of the wave. The set of solutions to that partial differential equation can be organized into a mathematical group. In the specific case of the Maxwell equations, a useful group is the Lorentz group. A Lorentz transformation transforms a solution in which a wave expands symmetrically to another solution in which the wave expands symmetrically.
My understanding is that the transformations are not specifically a characteristic of the Maxwell equations, but a characteristic of the mathematics of wave-mechanics in general. The Maxwell equations were designed to describe processes developing over time, and given the nature of electromagnetism, some of the solutions of the Maxwell equations describe propagating waves.
Anyway, one way of mathematically rendering the lichtspeed postulates of Einstein's 1905 paper is above mentioned:
This shows that one of the basic theorems of special relativity the invariance of the spacetime interval.
Mathematically, it is equivalent to submit the invariance of the space-time interval as an axiom of the special theory of relativity, and take it from there.
The concept of the spacetime interval was not explicitly present in the 1905 paper, I think, explicit mention of it arose a couple of years later, but soon it took center stage in the perception as arguably the single most important concept in relativistic physics. The metric signature of the space-time interval is (+,+,+,-). In special relativity and in general relativity, the concept of the invariant space-time interval is identical.
In the context of space-time continuum, the separation between two points in space-time is measured in units of time. The only thing you can actually measure is how much time a journey takes. The closest thing to a space- odometer is measuring the duration of the journey. If the journey is not physically undertaken then spatial distance is inferred by measuring how much time it takes electromagnetic waves (light) to cover that spatial distance. But it is tricky. Inferring the spatial distance between two points in space-time is about attempting to measure something that is non-local; which gives rise to ambiguity. By contrast, counting lapse of time with a device such as an atomic clock is a local measurement.
I am sorry I have been butting in on the Twin paradox Talk page with cryptic remarks, and then not follow up on them. I think I had announced that I want to stay away from articles that involve relativistic physics, but I find myself drawn to it like a magnet. I shall once again try hard to stay away from involvement in wikipedia relativistic physics articles. -- Cleonis | Talk 12:23, 24 January 2006 (UTC)
Whether or not Einstein attached a 1-to-1 physical meaning to the space-time interval, the invariance of the space-time interval is what special relativity and general relativity have in common.
Do you know something about Minkowski's lecture that I do not? The parts of that lecture that I have knowledge of fit relativity. Is by any chance the content of that lecture available on the internet?
It dawned on me that although I am accustomed to writing 'space-time' the expression 'time-space' actually fits better. Also it would seem that the following expression for a timelike time-space interval is technically the correct one:
Separation between points in time-space is measured in units of time, so it makes sense to cast the expression in such a way that the dimensions fit.
I don't like it when it is suggested that 'time = length', because I think time is more fundamental than length. -- Cleonis | Talk 18:40, 24 January 2006 (UTC)
I am somewhat familiar with that allegory.
I wrote on the centrifugal force talk page:
All theories unavoidably contain elements that cannot be directly observed. For example, we cannot directly percieve the presence of a magnetic field. Charged particles behave differently when what we call a 'magnetic field' is present, that is the observable. The reason we take it for granted that such an entity as a 'magnetic field' actually exists is that it provides an efficient way to organize the body of knowledge about magnetism.
From my point of view, the physics concept of a field is inferred from the behavior of the silhouettes as seen on the wall of the cave. From my point of view it would be wrong to attach a feeling of absolute certainty to what is inferred from the behavior of the silhouettes. I follow Stephen Hawking when he says: 'I don't demand that a theory correspond to reality because I do not know what it is. Reality is not a quality you can test with litmus paper.'
I regard both the mathematical framework of a theory and its its interpretation as tools. The more versatile the tool, the better. Ideally, the best theory is like a swiss army knife that can handle any job. My philosophy of physics entails that interpretation of a theory does matter, in that it guides the thinking and it provides a way to organize the perceptions. But I do not demand correspondence to reality, for I don't know what it is.
The only demand that I make is that a theory of physics applies well, and that it is self-consistent. I don't want to have any pre-concieved notions of what is or isn't physically realistic, for I don't know what reality is. For example, I don't exclude the possibility that the concept of 'space' as it is applied in newtonian physics is a silhouette of something that cannot be adequately described as 'space'.
Maybe I do disagree with Minkowski. It is possible that before the introduction of relativistic physics some physicists were true believers in the concepts of Newtonian/Maxwellian physics. Relativistic physics may present a dilemma to some people: to either convert from newtonian faith to relativistic faith, or to stay away from the idea that one should have absolute faith in any theory. To me there is no dilemma, the only available choice being the the second choice. --
Cleonis |
Talk 11:07, 25 January 2006 (UTC)
I copy and paste from the twin paradox Talk page.
Geometry, when applied in physics calculations, is itself a theory of physics, of course. The Galilean transformations and the corresponding velocity addition rule are the foundation of the Galilean/Newtonian codification of the properties of inertia. The Lorentz transformations, and the corresponding relativistic velocity addition rule, are likewise the foundation of the relativistic codification of the properties of inertia.
I think physics textbooks ought to point out that according to relativistic physics, acceleration with respect to the structure of space-time is much more important than in Newtonian physics. According to newtonian physics acceleration is no big deal. But according to relativistic physics, to accelerate with respect to the structure of space-time constitutes an irreversable event. (Making two U-turns does not quite give the same end result as not making any U-turn. The second U-turn cannot entirely undo the consequences of the first U-turn.)
So Minkowski space-time is, if anything, more absolute than newtonian absolute space.
If textbooks would teach special relativity in that more logical way, emphasizing that the Minkowski manifold is absolute, then the perception of the twin scenario would be quite different. -- Cleonis | Talk 22:24, 27 January 2006 (UTC)
You might consider Wikipedia:Request for comment regarding 69. If he's causing that much trouble, there are probably admins more knowledgable about physics that can help you guys better. Last night he led me to believe it was a simple matter of moving a section. Apparently I was deceived, as there is a lot more material at hand now. I'm going to ask for some advice, and please feel free to message me in the meantime. -- DanielCD 14:41, 28 January 2006 (UTC)
Harald, I have posted an initial response and additional questions to clarify the dispute at Mediation Cabal: Tired Light. SteveMc 03:15, 29 January 2006 (UTC)
Harald, I do not know what is wrong with that email address. IT tells me it should work, I do receive email at that address, but apparently the email server kicks back some of it, sorry. I changed the email to reflect my new address, user ScienceApologist posted a web link to a URL where I was able to get the article.
I have posted a request for some outside help on tired light. This issue is really beyond me, even with the reading I have done. I will stay with it until I can find someone else more keen to the issues.
Thanks, SteveMc 14:37, 4 February 2006 (UTC)
The expression for the centripetal acceleration is derived in the article " Centripetal force". Why do you need to rederive it in section "Reactive centrifugal force" of the article " Centrifugal force"? Yevgeny Kats 23:28, 4 February 2006 (UTC)
Hello Harald88, thank you for reverting the vandalism of the g.o.mueller add, the biggest critical work ever.It is worth reading sooo much. Are you interested in an English translation by the way ? 80.138.158.108 01:35, 5 February 2006 (UTC)
"www.ekkehard-friebe.de/buch.pdf". 80.138.190.9 12:30, 6 February 2006 (UTC)
I copy from Talk:Relativity_of_simultaneity :
Let an atomic clock be put onboard an aeroplane that circumnavigates the world at a constant velocity, (such GlobalFlyer, in which Steve Fosset made a non-stop flight around the world.) Let the GlobalFlyer fly at constant altitude, with a constant velocity. Then the atomic clock onboard the Global flyer will on arival be seen to have counted 207 nanoseconds less or more time, depending on whether the flight was eastwards around the world or westwards around the world. (The time count does need to be corrected for gravitational effects.) -- Cleonis | Talk 10:42, 6 February 2006 (UTC)
I wrote that the time as counted by the travelling clock does need to be corrected for gravitational effects. The gravitational effects can be corrected for by having one GlobalFlyer fly eastwards around the world, and the other westwards. In an idealized case the flyers maintain a constant altitude at all times.
Other than that, the amount of difference in lapse of proper time after circumnavigation is independent of the relative velocity of the flyer and the clock that is co-moving with the equatorial surface of the Earth. Because it is a loop-closing scenarion (just as the twin scenario is a loop-closing scenario) the relative velocity drops out of the calculation.
In the case of a loop-closing scenario the only operative factor is the difference in spatial length of the path travelled.
So there is no need to know the velocity of the GlobalFlyer, the velocity only needs to be constant. (A trajectory with a non-constant velocity has an even longer spatial length, with a non-constant velocity the time difference is more than those 207 nanoseconds.) --
Cleonis |
Talk 00:35, 7 February 2006 (UTC)
I think the above example is in the Stedman review of the Sagnac effect. The link to the Stedman review is at the Sagnac effect. Anyway, the above example, the number of 207 nanoseconds, is from peer-reviewed scientific literature. -- Cleonis | Talk 00:35, 7 February 2006 (UTC)
Well, in the twin scenario the difference in amount of elapsed proper time at the point of rejoining is not a function of their relative velocity at previous stages the journey. The operative factor is the difference in the spatial length of the respective worldlines.
I get the impression that you have a different situation in mind than I have. I am thinking about difference in elapsed amount of proper time as seen when clock readings are comparded after rejoining. I am thinking about a variation of the twin scenario. One twin remains co-rotating with the surface of the Earth's equator, the other twin travels along a different worldline, a worldline with a different spatial length. -- Cleonis | Talk 21:59, 7 February 2006 (UTC)
In his 1905 article, Einstein discusses the comparison of a stationary clock (a clock on a non-rotating planet) and a circumnavigating clock. What I have in mind is two circumnavigating clocks; the clock that is stationary with respect to The Earth's Equator is circumnavigating (as it is co-rotating with the Earth), and a clock onboard an aeroplane that takes several days to return to the longitude of departure is also circumnavigating. -- Cleonis | Talk 23:17, 7 February 2006 (UTC)
Are you User:205.188.114.9? -- ScienceApologist 02:08, 7 February 2006 (UTC)
I don't know, as I use several computers (it's not the one I use now); but when I notice that the computer logs me out of Wikipedia, I sign in. I'll look if I can find a recent case where I overlooked it and if so, correct it. Harald88 08:05, 7 February 2006 (UTC)
Hi Harald, thanks for your note. I don't recall exactly when and where that phrase was first added, but it's certainly accurate. NOR, V, and NPOV are complementary in that they don't and can't stand in isolation from one another. Following NPOV does not mean we may add any and every opinion under the sun, because we're not allowed to add original research (no matter how beneficial it might be from an NPOV standpoint), and the only way we can show we're not adding OR is to cite sources in accordance with WP:V. Any attempt to interpret one of the policies in isolation will lead to problems. Hope this helps. Cheers, SlimVirgin (talk) 21:16, 7 February 2006 (UTC)
I have found two references for the comparison of synchronisation procedures that rely on signals, and portable clocks respectively, and that the correction factor of 207.4 nanoseconds arises in both procedures.
There is Neil Ashby's discussion of Relativity in the Global positioning system Enter the number 207 in the 'find a word on this page' function of your webbrowser to jump to where Ashby discusses signals and clocks
And there is
G E Stedman's review of ring laser tests of fundamental physics and geophysics
In section 1.2 Early history, on page 7 of the PDF document, Stedman mentions the comparison of circumnavigating signals and circumnavigating clocks.
From a newtonian (non-Lorentzian) point of view, you expect the Sagnac effect for circumnavigating signals. From a relativistic point of view you also expect a Sagnac effect for circumnavigating signals. In that sense the Sagnac effect for circumnavigating signals is a theory-independent phenomenon. The Sagnac effect for loop-closing signals is so fundamental that it is a theorem of every theory of physics.
On the other hand, when it comes to disseminating time with portable clocks, then from a newtonian (non-Lorentzian) point of view you do not expect an effect. From a relativistic point of view you do expect the clocks to have counted a different amount of proper time when compared on rejoining. It seems quite fitting to refer to time dilation effects for circumnavigating clocks as 'the Sagnac effect for clock transport' -- Cleonis | Talk 22:36, 7 February 2006 (UTC)
Recapitulating:
My mental picture is that I view the worldline of the clock that is co-rotating with the Equator as a
helix in a Minkowski space-time diagram. In other words: I map the worldline of the corotating-with-the-Equator-clock in an inertial coordinate system. Then I map the worldline of the airplane that takes several days to circumnavigate in that same Minkowski space-time diagram.
Maybe I should have announced explicitly that I was mapping the two wordlines in a single inertial coordinate system. As I have expressed before: I reject mapping of motion in a rotating coordinate system. (Well, I reject it for the purpose of theoretical understanding, it can on occasion be good calculational strategy.) -- Cleonis | Talk 00:48, 8 February 2006 (UTC)
Actually, the relativistic examination of the Sagnac effect plays a huge role in my commitments. I regard rotation as absolute. (I regard rotation as absolute in the sense that I regard the Minkowski manifold as absolute.) I may have expressed this before: I do not see relativistic physics as a theory of "motion is relative". I think of relativistic physics as the Theory of Invariance. -- Cleonis | Talk 01:49, 8 February 2006 (UTC)
Hey Harald. You're right, I agree that Wiki isn't the place to resolve accreditation disputes. But it does seem like the right venue for the facts about priority, and it really does seem to be the consensus that Poincare published first on a number of substantial issues. But as you say, those are simply the facts, and if they are laid out for people, they can come to their own conclusions. Lucidish 04:11, 8 February 2006 (UTC)
I asked what part of your question about the sources of the NPOV was not answered by this section, but, I have not seen any answer from you about this. I look forward to your answer: What question do you have that is not answered by the Wikipedia:Neutral_point_of_view#History_of_NPOV section? - 08:40 . . JesseW
I have just been reading the
Anti-relativity article.
In that article I encountered a distinction that I hadn't quite appreciated before, a distinction that possibly you edited into the article (but I haven't looked that up).
There is anti-relativism, and there is anti-relativityism. Very significant distinction there, for I oppose relativism, and I am committed to relativistic physics (in the sense that I am committed to Invariance Theory)
I follow wholeheartedly the opinion that the expression 'theory of relativity' is a misnomer (to my knowledge the name 'theory of relativity' was coined by Planck, who was the first to voice approval of Einstein's 1905 paper). It is known that Einstein would have preferred the name 'Invariance theory'.
Einstein was never interested in relativism, only in theories based on Principles of Invariance. In that sense Einstein is to be placed in the category of people who oppose relativism.
What I want to contrast is theories from a starting point that space should be eliminated from physics theories, and theories from a starting point that the structure of space and time is a player in the physics taking place. The three succesful theories of motion all have in common the concept of structure of space and time as a physical entity in itself, involved in the physics taking place: Newtonian dynamics, special relativity, general relativity. I see general relativity as the culmination of that structure-of-space-and-time paradigm.
A problem that I have is that I'm fed up with the matter of false expectation. I'm fed up with dealing with the burden of the wide-spread erroneous expectation that relativistic physics is meant to show that "everything is relative". I just don't have the patience to deal with people who have embraced that erroneous belief. -- Cleonis | Talk 12:24, 11 February 2006 (UTC)
I hadn't realized that the terminilogy 'anti-relativityism' is novel, but I guess it is. Because of its sheer usefulness, I would be in favor of retaining it. (Which may be going outside wikipedia policy, which personally I don't mind doing, but I will respect the opinion of others.)
I wanted to notify you that my assessment is that Einstein was never interested in "showing that everything is equally relative". As I wrote before, I have dug hard at information. The group of experts on the early history of relativistic physics is not very large: John Norton, John Stachel, Jurgen Renn, Michael Jansen. I may forget one or two here, but those authors are my main sources of information. Reading their papers takes patience, for they are very, very meticulous.
On the basis of the body of evidence that I have gathered, my assessment is that Einstein's aim in the years leading up to 1915 was to enhance the concept that the structure of space and time is an entity in itself in the theory. (There are Einstein remarks that appear to indicate that Einstein supported physical relativity. I have explanations for these appeareances that satisfy me.)
For now let me submit as evidence the mathematical structure of the general theory of relativity. In GR, the structure of space and time is a physical entity in itself. That was Einstein's starting point all along. To suggest that Einstein had the wrong starting point, and just happened to stumble on the GR equations would be like claiming that Sir Edmond Hilary and Tenzing Norgay happened to stumble to the top of Mount Everest on a caving expedition.
I think this occasion is a good opportunity try and do a good write-up of how I understand the history of GR. So: later more.
Cheers --
Cleonis |
Talk 08:45, 12 February 2006 (UTC)
As you know I dislike the expression 'fictitious force'. In my opinion that expression should be banned from physics textbooks, and it should be replaced with the expression 'coordinate acceleration'.
In this Sandbox article I explain the concept of coordinate acceleration. Can you check it out? It is related sideways to issues of the transition from newtonian dynamics to GR dynamics. -- Cleonis | Talk 11:51, 12 February 2006 (UTC)
Harald88, I wonder if you have some advice for me.... I am a bit puzzled about the way E=mc2 is presented in various Wikipedia articles and other references - it seems to understate the radical nature of Einstein's interpretation. I tried to encapsulate my puzzlement into a question at Talk:Special relativity. I'd appreciate your feedback. When you get back from vacation...? -- Alvestrand 21:29, 18 February 2006 (UTC)
Radiant! has yet again been removing the link to the proposed policy page.
Wikipedia policy requires that if user conduct is an issue, at least 2 users must have tried to resolve it first. I've done so already and failed. Could you have a go, and post a note on his talk page that this is an ongoing matter, and please not to disrupt the process or remove links to the page?
Thanks. FT2 ( Talk) 03:11, 19 February 2006 (UTC)
Where was this originally passed on to you? Was it in an email, or did someone post it somewhere on WP? Thanks. -- LV (Dark Mark) 19:04, 1 March 2006 (UTC)
It was sent to me by her family from her email address, probably because I had written to her recently about an alternative to the Copenhagen interpretation. I knew she had had cancer for some time now, but she sounded so upbeat about it that it really took me by surprise. :( Harald88 06:39, 2 March 2006 (UTC)
hope you had a good holiday!
Unfortunately, the Licorne show hasn't stopped playing yet - it's now at Wikipedia:Requests for arbitration/Licorne - and Licorne's invoking your name as if you supported him, amazingly enough.
Just thought you'd want to know. -- Alvestrand 06:59, 2 March 2006 (UTC)
Re your contribution to the Licorne "evidence" page:
just to be careful... Fastfission didn't introduce the idea that Bjerknes is a Holocaust denier into the discussion; I did. The basis for saying so is a speech given by Bjerknes in defense of David Irving - the link is on the Christopher Jon Bjerknes Web page.
I think the "talk" page of the RfA is a better place to discuss whether there are people who have behaved worse than Licorne, and whether that's a mitigating circumstance for him. -- Alvestrand 13:19, 2 March 2006 (UTC)
Hi,
I don't see that further discussion of this is relevant to Licorne or anything except mutual interest. In relation to your description of what you found childish, I reacted to that differently but also somewhat negatively. My reaction was simply (like yours on this) that it was basically irrelevant and made the article harder to follow (parallel critique of two versions, one of which was provisional and never public). The reason for doing it did not strike me as sufficient. I thought it a bit strange rather than childish, but mostly didn't give it much thought (to be honest; I was focused on following the arguments as carefully as I could). As to the shorter version, it is completely lobotimized and leaves out essentially all backing detail. I find this very unfortunate. The short version doesen't convince me of anything, while the longer version leaves me completely convinced until someone presents critical flaws that I couldn't see. In fact, I think it is a crucial piece of historical argumentation that is now hidden, and the primary sources are impossible for any non-expert to access (the preserved proofs in different versions, especially). -- Pallen 05:25, 4 March 2006 (UTC)
Hi Harald, I have been brooding on how to write about the history of General relativity concepts.
In preparation for the things I want to write about, I need to provide background.
I quote from a paper by John Norton,
Einstein’s Investigations of Galilean Covariant Electrodynamics Prior to 1905 (PDF-file 329 KB)
In a manuscript from 1920, Einstein recalled how this simple reflection had played
an important role in the thinking that led him to special relativity. The essentially relevant
parts of his recollection read:
In setting up the special theory of relativity, the following ...idea concerning Faraday’s magnet-electric induction [experiment] played a guiding role for me.
[magnet conductor thought experiment described].
The idea, however, that these were two, in principle different cases was unbearable for me. The difference between the two, I was convinced, could only be a difference in choice of viewpoint and not a real difference. Judged from the magnet, there was certainly no electric field present. Judged from the electric circuit, there certainly was one present.
Thus the existence of the electric field was a relative one, according to the state of motion of the coordinate system used, and only the electric and magnetic field together could be ascribed a kind of objective reality, apart from the state of motion of the observer or the coordinate system. The phenomenon of magneto-electric induction compelled me to postulate the (special) principle of relativity.
The origin of this Einstein quote is listed as a manuscript that was prepared for the magazine Nature, but eventually wasn't published there. It has been published in Einstein's collected papers. (Einstein, Albert (1920) “Fundamental Ideas and Methods of the theory of Relativity, Presented in Their Development,” Papers, Vol. 7, Doc. 31.)
Understandably I like the above Einstein quote; it is in perfect harmony with the mainstream understanding of special relativity.
There is the 'silhouettes on a cavewall' theme. Two observational viewpoints that are moving relative to each other cut a different slice through space-time. The 'cuts at different angles' theme is depicted in
this animation by Andrew Hamilton (that animation is on
this webpage.)
In Maxwell's theory of electricity and magnetism the two fields are described as separate entities. Each field can induce the other field, but nonetheless the two are described as separate entities. Einstein sought to develop a field theory in which there is a single electromagnetic field, a single entity. This single entity is then the mediator of magneto-electric induction. The class of separate accounts of the physics taking place that Lorentz Ether theory provides (a different story for each velocity with respect to the ether) is then seen as a class of cuts at different angles. This class of cuts at different angles is then seen as an equivalence class of mapping events in a class of coordinate systems. That theme is what I tried to embody in the animations of my Sandbox article about Minkowski spacetime.
Recapitulating:
According to the principle of relativity of inertial motion, when two objects collide non-elastically, (and sticking together after the collision), then the amount of kinetic energy that is converted to heat in the collision is a frame-independent quantity; an invariant quantity.
In Minkowski space-time, in order to shift the angle of cutting through space-time, a force must be exerted. The shift is called a 'Lorentz boost'.
The structure of space and time opposes shift to another angle of cutting through space-time; this is of course what we refer to as inertia. --
Cleonis |
Talk 08:58, 4 March 2006 (UTC)
PS I am bugged by your claim in that sandbox: "There is no theory to address the question of how the structure of space and time can be like that." As such a theory is inherently metaphysical, I take it to mean:
"There is no explanation of how the laws of space and time can be like that."
However, as you know very well, such a theory does exist, it's only impopular because of fashion and/or misunderstandings. Thus I'm curious what you do mean with that claim. Harald88 17:05, 4 March 2006 (UTC)
Cleonis |
Talk 19:30, 4 March 2006 (UTC) In my Sandbox article about Minkowski space-time, I write:
Harald:
I assume that you refer to the Lorentzian interpretation. I regard the Lorentzian interpretation problematic. In this I follow the mainstream view of the physics community.
One of my considerarions is the following thought experiment:
Cavendish measured the gravitational constant by measuring the gravitational attraction exerted by a lead sphere with a weight of 350 pounds. Description of the Cavendish gravitational constant measurement
We have good reasons to trust that active gravitational mass is always equivalent to passive gravitational mass, and that gravitational mass is always equivalent to inertial mass. No experimental evidence is known of a case of gravitational mass not being equivalent to inertial mass.
Suppose we assume that there is a Lorentzian ether. An Lorentz-type ether theory requires that inertial mass increases with increasing velocity with respect to the Lorentzian ether. Then it follows that a Cavendish gravitational constant experiment, onboard a spacecraft free-floating in space, will measure a different value, depending on the velocity of the spacecraft with respect to the Lorentzian ether. (Cavendisch happened to use a torsion balance, but there are of course lots of ways to perform the necessary measurement.)
On the other hand: according to the Einstein approach, in which velocity with respect to the Minkowski space-time does not enter the theory, we have that whenever the spacecraft is moving inertially (regardless of what it did before that; we assume motion to be memoryless), always the same gravitational constant will be measured.
It seems to me that a strictly Lorentzian theory only stands a chance of predicting the same as Einstein theory when the Lorentzian theory assumes that gravitation couples to rest mass, for it is rest mass that is, like coulomb charge, Lorentz-invariant. However, there is solid evidence that gravitation couples to the total inertial mass, not to rest mass.
The most extreme version of this thought experiment goes as follows: take a neutron star, teetering on the brink of collapsing into a black hole. In this thought experiment the neutron star is just below the mass limit for collapsing into a black hole. Now, increase the velocity of that neutron star. It seems to me that an ether theory must predict then that the increase of inertial mass will elevate the self-gravitation of the neutron star to the point of collapse into a black hole. -- Cleonis | Talk 19:30, 4 March 2006 (UTC)
Thanks for giving evidence in the Licorne arbitration. As a clerk to the arbitration committee, I have edited some of your evidence ( in this edit) to provide the kind of "diff" links that the committee will want to look at. If you give more evidence, but find yourself unable to produce such links, it would still be helpful if you could note the approximate time of day as well as the date of the edit. I can hunt the history and produce the diff more easily if you do that.
For the arbitration committee. -- Tony Sidaway 22:27, 4 March 2006 (UTC)
I couldn't make out from your previous reply whether I had been sufficiently specific in how I presented the thought experiment. It is unclear why you brought up the ECI frame.
Therefore I present the thought experiment a second time, with more specifics.
A characteristic of a Lorentz-type ether theory is that it is assumed that inertial mass increases as velocity with respect to the supposed ether increases. This has been explained by Poincaré in his 1909 Göttingen lecture. "On a constaté ainsi que la masse dépend de la vitesse et énoncer cette loi: L’inertie d’un corps croît avec sa vitesse qui reste inférieure à celle de la lumière, 300 000 kilomètres par seconde."
Let a spacecraft be somewhere in interstellar space, so far away from any star that any stellar gravitational field is negligable. In a hold inside the spacecraft, the gravitational attraction between two large, solid spheres is measured. The large spheres are centimeters apart.
Example of how the magnitude of that gravitational attraction can be measured:
A low pressure air cushion is supplied in the gap between the two spheres, so that the gravitational attraction cannot pull them closer. The low pressure air cushion would have to be provided by using a tiny, low mass tube, supplying a minute flow of air right between the two masses. The magnitude of the air flow that counterbalances exactly the gravitational attraction between the two masses is then a measure of the gravitational attraction between the two balls.
Let the spacecraft alternate between phases of accelerating and moving inertially. Everytime the spacecraft is moving inertially the gravitational attraction between the two spheres is measured. From an ether theory point of view, the respective measurements are conducted at a different velocity with respect to the ether each time. There is strong evidence that gravitational mass is always equivalent to inertial mass. From an ether theory point of view one expects that at each different velocity with respect to the ether a different gravitational attraction will be measured.
This thought experiment would not have been considered before 1915. In 1915, GRT put the concept of equivalence of inertial and gravitational mass on firm ground.
Lorentz ether theory works for electromagnetism because Coulomb charge is a Lorentz invariant quantity. On the other hand, according to GRT gravitation is a function of the total inertial mass. Rest mass is Lorentz-invariant, but the total inertial mass is not Lorentz-invariant. -- Cleonis | Talk 09:38, 5 March 2006 (UTC)
Hi Harald,
I've checked out what Alonso & Finn write about relativistic physics.
The location:
Alonso & Finn, second edition, volume I, mechanics and thermodynamics, Section 6.8, page 133
Alonso and Finn discuss the Michelson-Morley experiment at length, and write:
Lorentz and Fitzgerald independently proposed that all objects moving through the ether suffer a "real" contraction in the direction of motion
[...]
Of course, an alternative explanation is of the negative result of the Michelson-Morley experiment is to assume that the speed of light is always the same in all directions, no matter what the state of motion of the observer. [...] This position was adopted by Albert Einstein when he was formulating his principle of relativity. The student may, however, at this moment say that the "real" contraction assumed by Lorentz to explain the negative result of the Michelson-Morley experiment is exactly the same as the contraction we found in Eq. (6.35) by using the Lorentz transformation and the principle of the invariance of the velocity of light. There is however, a fundamental difference between, the two underlying hypotheses used for obtaining these two apparantly identical results. (1) the contraction (6.37) obtained by means of the Galilean transformations is assumed to be a real contraction suffered by all bodies moving through the ether, and the v appearing in the formula is the velocity of the object relative to the ether. (2) Contraction (6.35) refers to only the measured value of the length of the object in motion relative to the observer, and is a consequence of the invariance of the velocity of light. the v appearing in the formula is the velocity of the object relative to the observer, and thus the contraction is different for different observers. Einstein realized that the idea of an ether was artificial and unnecessary, an that the logical explanation was that the second one.
Admittedly, this exposition by Alonso & Finn is rather muddled, and several of their remarks are historically wrong, but there can be no doubt as to the philosophical commitment of Alonso & Finn.
There is always the distinction between the invariants and the variants. Electric charge, rest mass, and the space-time interval are invariants. When two objects collide, and remain stuck together after the collision, then the amount of kinetic energy that is converted to heat is an invariant, a frame-independent quantity. On the other hand: the quantity of length contraction is a coordinate contraction. Given an arbitrary choice of coordinate system to map physics events, an amount of coordinate contraction is assigned to each object that is moving with respect to the chosen coordinate system. But to this coordinate contraction no corresponding physics content is attributed; the coordinate contraction that is assigned is an artifact of the particular choice of mapping the events in a coordinate system. -- Cleonis | Talk 14:28, 5 March 2006 (UTC)
I copy and paste from above:
Presumably you mean: in GRT, what is the mutual attraction between the massive spheres when the spacecraft is in inertial motion? (This experiment would be very tedious when the spacecraft is pulling G's)
According to GRT, there is full blown equivalence of all inertial motion. GRT is by design a theory that has as its starting point full blown symmetry of all inertial motion. So in GRT there is nothing to calculate; in the mathematical framework of GRT there is no formula to slot in the velocity that you are referring to.
By contrast: in an ether theory, velocity with respect to the supposed ether matters, and if that ether theory wants to reproduce all relativistic predictions the laws of that theory must be such that in the end all ether effects cancel out against each other. As you know, that is what makes the ether theoretical discussion of for example the Trouton-Noble experiment so riddled with pitfalls. In an ether theory with Lorentz transformations, that machinery works out for electromagnetism, as the Lorentz transformations hold good for electromagnetism: in the end everything cancels out again. But gravitation is not Lorentz-invariant.
I was drawn towards this thought experiment precisely because of that difference. I have not encountered discussion of this thought experiment anywhere, which surprises me somewhat, because I think it is quite a probing thought experiment. -- Cleonis | Talk 19:03, 5 March 2006 (UTC)
Harald referred to:
rest mass/relativistic mass question as discussed on on sci.physics.research on 18 february 2006
When read as a whole (as opposed to taking a sound bite), I agree with the wonderfully clear expositions by Greg Egan.
Not surprisingly, my view coincides with the view that is presented in the Usenet Physics FAQ article about the question:
Does mass change with velocity? And the related article:
If you go too fast do you become a black hole?
In the above-mentoned thread: 'rest mass/relativistic mass question', Chalky asks a probing question:
Now, with a linearly accelerating mass, energy is definitely being spent on it. That energy is being transformed into kinetic energy (which is the other confusing concept because this meaure of energy seems to be frame dependant) which is as "real" as any other energy because it can be converted back if necessary to any other form of energy. However, this kinetic energy for some reason does not contribute to the stress-energy tensor.
Greg Egan's answer satisfies me in the sense that he shows to my satisfaction that there is no selfconsistency issue. -- Cleonis | Talk 19:42, 7 March 2006 (UTC)
You mention that unipolar magnets have weird effects in another thread on this page. What theory predicts that such a thing exists? Has it been observed? My physics is getting old.... -- Alvestrand 15:53, 4 March 2006 (UTC)
OK I found some of it back!
Very interesting experiments. The interpretation seems not fully settled. In contrast to Guala-Valverde's explanation, the following author claims that the effect does not occur for electromagnets, only for permanent magnets. This is seen to cause serious problems for Guala-Valverde's interpretation of his experiments. The author's alternative explanation is the analysis permanent magnets in terms of their magnetic domains, which represent small current loops: http://www.maxwellsociety.net/PhysicsCorner/CurrentLoopPolarization/ElectroAndPermanentMagnets.html However, because of the pitfalls of modeling an actually rather complex reality with oversimplified models, my sense is that there is not yet clear consensus on the explanation of these results. However, I would propose a different experiment (my own) to challenge the idea that if all parts of an e/m system are co-rotating, the rotation can't be detected. Consider two metal balls like those used in a van-de-graff generator, mounted on either end of an insulating rod. Have a large charge difference between them. Imagine spinning this apparatus rapidly like a baton. Imagine a radio detector some distance away, spinning identically with spinning charge apparatus - such that in an appropriate spinning frame, the whole apparatus including the radio receiver are stationary. SR, and most physicists, would predict that radio will detect radio waves if the spin is fast enough and the charge subsantial enough. My guess is that Guala-Valverde would propose that no radio waves would be detected. Of course, the electromagnet variant of his experiment already achieves detection of absolute rotation, electromagnetically (according to Dixon). -- Pallen 01:00, 7 March 2006 (UTC)
E-mail From: Chris Hillman To: Alberto Mesquita Filho
On Thu, 8 Jan 1998, Alberto Mesquita Filho wrote:
> In my original project I thought of a charge at rest, for example, a loaded spherical conductor on a table and of this separated by an insulating cylinder. However, the experience would be the same case if the charge it was in a rectilinear and uniform movement. Certainly, in the considered frame of reference, it is not being accelerated because "it doesn't emit electromagnetic radiation".
����������� You are still confused.� If the table is experiencing stresses because there is a gravitational force (or if you prefer, because the elevator is being accellerated), then the charge will radiate because it to is being accellerated.
Chris Hillman
Some sample papers debating this: http://arxiv.org/abs/gr-qc/9303025, http://arxiv.org/abs/gr-qc/0006037, http://arxiv.org/abs/gr-qc/9903052, http://home.omnisp.ru/mira/boulware/111.htm -- Pallen 15:51, 7 March 2006 (UTC)
Of these, on an initial read through, the 3d reference (Pauri and Vallisneri) seems the most convincing to me. Two of the others agree with the main conclusiong, but the argumentation seems less fundamentally convincing to me. The first reference takes a maverick point of view and argues that there is a genuine violation of the equivalence principle. My superficial initial analysis correctly noted that the comoving accelarated charge and detector has to be the same as a charge and detector supported in a gravitational field (by the equivalence principle). However, I wrongly concluded from an extremely oversimplified application of Maxwell's equations and SR, that the former case would produce radiation at the detector. This, indeed, leads to the bizarre situation you questioned. Reference 3 is very convincing that a proper application of Maxwell+SR predicts no radiation for the case of COMOVING accelarated charge and detector. There seems to be a good article opportunity here. I notice that the Physics FAQ chooses not address this question at all - I guess not surprising given how many great physicists (e.g. Pauli) have gotten it wrong over the years. -- Pallen 20:27, 7 March 2006 (UTC)