Talk:Inertial frame of reference/Archive 1

Archive 1

Archive 2

Should merge with Inertial reference frame ?

I think this has been done now

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Following edit by 62.254.128.4 was removed from article to this talk page, as it seems like discussion. --Zigger 18:32, 2004 Apr 27 (UTC)

Correction:

It is not satisfactory to define an inertial frame as above: rotate or accelerate with respect to what? In the context of Newtonian mechanics we can define an inertial frame as one in which Newton's laws hold. (Note that the question of whether a frame is inertial requires us to decide what forces are acting; strictly speaking there is no absolute means of determining whether or not a frame is inertial, for additional forces can always be postulated to explain behaviour that seems to show the frame is non-inertial. In practice, we are agreed on when to say a body is free of external influence because we are largely agreed on the conditions for the action of the various forces that enter our physical picture of the world.) It is a simple consequence of this definition and the laws that all members of the family of inertial frames move with constant velocity with respect to each other. An object stationary in one inertial frame need not appear stationary in another but will move at constant velocity in that frame. (NB: the claim above that such frames are 'purely theoretical' is rather confusing as a reference frame is evidently an abstract entity in any case. Presumably what is meant is that few moving bodies (eg the earth) yield an inertial coordinate system when we locate our origin on, and orient our axes with respect to, them.)

(William M. Connolley 20:30, 27 Sep 2004 (UTC)) What fun. I too was just going to complain about the same text "The inertial frame is a space-time coordinate system that neither rotates nor accelerates." Because unless you say accelerate-with-respect-to-something, this is meaningless.

I have written an new article that addresses precisely that issue. How does a rotating planet "know" how much to bulge at the equator? That is: how does a rotating planet know it is rotating at all?

In the newtonian framework it is assumed that there is absolute space that acts upon matter but is not acted upon. In general relativity the untenable concept of absolute space is replaced by a field concept, a pervasive field. This pervasive field is perfectly transparent to velocity, but when there is acceleration there is interaction with this field. --Cleon Teunissen 11:25, 5 Mar 2005 (UTC)

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In my search of the definition of inertial system I came across this page. It seems to me there is no good definition. At least is a system in free motion, e.g. a free toward the earth falling spaceship an inertial system. Another ship, falling at the opposite side of the earth all the same. These two systems don't move uniformly with respect to each other. There seems to be a circular argument in stating that no force exerted indicates inertia. Am I wrong?130.89.220.52 21:39, 6 Mar 2005 (UTC)

A good definition is a definition that does not lead to self-inconsistency in the framework of thought in which it is formulated. In general relativity the assumption that space is Euclidian is relinquished. Einstein showed that it is nonetheless possible to formulate a consistent and rich theory of motion. Indeed, relativistic physics is richer and deeper and more versatile than newtonian physics. In general relativity, there is a dependency on the scale of the perspective. If a volume of space is considered that is about as large as the size of a spaceship, and that spaceship is free-falling, then in that volume of space the co-moving frame of reference is an inertial frame of reference.

However, if a volume of space is considered that is large enough to contain a planet and its moon(s), then the center of mass of that planet and its moon(s) is the local inertial frame of reference. And so on for an entire solar system, an entire Galaxy, until the astronomer has arrived at the size of the observable part of the Universe.

Methinks you feel a definition can only be "good" if it can somehow be reconciled with Euclidean, absolute space. Gravity alters the very fabric of space-time geometry, the gravitational influence of a gravitating body changes the rate of time in its neighbourhood, and that changes everything . However, although very counterintuitive, the universe appears to be perfectly self-consistent, judging from the fact that our self-consistent theories describe the universe with uncanny accuracy. To understand current physics theories you must be prepared to relinquish all the trusted newtonian and euclidean assumptions but one: the demand of self-consistency. And no, the definiton is not circular, because it is also a statement about how gravitational interaction is mediated, so it departs fundamentally from the newtonian concept of gravity. --Cleon Teunissen 22:59, 6 Mar 2005 (UTC)

Dear mr. Teunissen, thank you for your elaborate answer. Allow me some remarks. I want to restrict my attention to special rel. th., because it is there where I see problems with the definition of inertial systems. In general rel. th. as far as I know the concept of an inertial system has only locally meaning. In SRT however forces don't enter the theory, but inertial systems do and their definition is dependent on the concept of force. It seems to me that for the main part of the SRT only the concept of mutually inertial systems is relevant, a rather overdone term for systems at constant speed difference.130.89.220.52 08:54, 7 Mar 2005 (UTC)

Special relativity is universally valid in a universe without gravitation. Formally, universes with matter in it fall outside the scope of special relativity. (But experience tells us (and general relativity confirms) that within a sufficiently local volume of space, for example the 27 kilometer diameter of the CERN particle accelerator ring, the laws of special relativity will hold good.) --Cleon Teunissen 10:39, 7 Mar 2005 (UTC)

(Not a good example, on second thoughts: CERN is, like everything on the surface of Earth, accelerating, but that acceleraton is negligable for the particle physics being conducted.) --Cleon Teunissen 10:49, 7 Mar 2005 (UTC)

Newton's Third Law

The first line says: "An inertial frame of reference, or inertial reference frame, is one in which Newton's first and second laws of motion are valid." What about the third law? —Preceding unsigned comment added by 203.206.7.60 (talk) 05:25, 28 March 2008 (UTC)

Special relativity and acceleration

It seems to me that for the main part of the SRT only the concept of mutually inertial systems is relevant, a rather overdone term for systems at constant speed difference.130.89.220.52 08:54, 7 Mar 2005 (UTC)

Well, if you take two space-ships, both firing their thrusters, accelerating equally hard in the same direction, sending radio-signals to each other, and they adopt a co-moving coordinate system for performing calculations, then the laws of Special Relativity won't hold.

If they want to use Special Relativity, they must read their onboard accelerometers in order to establish their relation to an inertial coordinate system. Then they can correct for the artifacts of their acceleration. But in order to transform the measurements of their radio-recievers to what they would have measured if they would have moved inertially they need general relativity mathematics. --Cleon Teunissen 11:06, 7 Mar 2005 (UTC)

Major revert

I am not accepting the previous misconception-filled description of this subject!

I have reverted to the previous edit of 1/30/05 because, as inadequate as it is, it is still a better article than Cleon's rewrite is, even with the subsequent changes.

Cleon - I know that you mean well. I really do. However, I thought that we had settled the issue the geometrodynamics is a defunct theory long ago. Why was its mention left here? (Then again, why did anyone let it stay here?) Also, while a gyroscope can travel inertially, the rotataing frame of reference of an observer spinning with it is not inertial. As for general relativity, it seems that globally inertial frames of reference are a casualty of it. (They can exist locally, but even for a free-falling observer there are tidal effects not far away in any curved spacetime.) --EMS | Talk 02:33, 2 August 2005 (UTC)

I too have been unhappy with CT's "image two spaceships" style. Can I interest you in coriolis force? William M. Connolley 08:30:22, 2005-08-02 (UTC).

I hate to be one to complain without doing anything about it, but I think the reverted version is pretty miserable as well. Can't we succinctly and clearly explain what an inertial frame of reference is? And where is the mention of Galilean relativity, special relativity and general relativity, not to mention Mach's principle (a page I would really love to improve one day) and the equivalence principle? And what the hell does this mean: "By the very nature of human limits to a particular inertial frame, the various branches of physics are devoted to building functions that relate human observation to theoretical concepts of cosmology and quantum mechanics and the rules by which they interoperate to describe possible reference frames like our own." While I'm sure there's an idea in there somewhere, it sounds a lot like pseudoscientific obfuscation. –Joke137 03:40, 3 August 2005 (UTC)

In that case, you can do the rewrite.  :-)

Look at it this way: The current version beats one that spends half of its time talking about geometrodynamics. I know that this version is "miserable" too. I just think that it still is a substantially better article than whar replaced it. If nothing else, its introduction is much more on target and the explanatory text does much less harm than Cleon's rewrite did. I do not advise doing major reverts like this unless it is absolutely necessary, but in this case it was. --EMS | Talk 04:10, 3 August 2005 (UTC)

--Cleon Teunissen | Talk 07:47, 3 August 2005 (UTC) About the version of the 'inertial frame of reference' article that I wrote, I had become dissatisfied with it, I felt it should be rewritten. Good riddance.

About the name 'geometrodynamics', at some point in time I was under a misconception, I had come across the name 'geometrodynamics' several times at it appeared to be an alternative name for purely the general theory of relativity. Geometrodynamics as a name for the general theory of relativity made a lot of sense to me. It was EMS who pointed out to me that Geometrodynamics is actually the name of a avenue that was explored in theorical physics, an avenue that was abandoned. So then I knew it was no good to refer to GRT as geometrodynamics, and I edited acdordingly.

A short time ago someone added an external link: to the 'frame of reference' article in the Stanford encyclopedia of philosophy. I think that is an excellent article, I will copy that link.

I have decided some time ago to no longer write about relativity, there are many, vastly different interpretations of relativity around, leading to discussions that keep going in circles.

I removed the para that J disliked. I think this article badly needs a re-write by someone who really understands the subject. Thats probably not me. I would say that an inertial frame in Newtonian mechanics is one in which things subject to no forces move in straight lines, and that the frame defined by the fixed stars is such a frame, and that anything moving uniformly wrt that frame is too. I also think that under GR the concept becomes more tricky, and suspect that it gets replaced by local inertial frame. Unless I've missed something, Newtonian mech and SR agree on what inertial frames are (even if they have different xforms) so some of the distinctions made in the current article look odd to me. William M. Connolley 17:30:40, 2005-08-03 (UTC).

Major rewrite (6th Aug 2005)

People here seemed to be saying that a major rewrite was called for, so I thought I'd have a go. Tried to keep the basic points of the original and not expand the thing too much.

Do feel free to rewrite, criticise, delete big chunks or just revert the whole thing all the way back to how it was before I hijacked it! Whatever, ErkDemon 00:32, 6 August 2005 (UTC)

Inivitation accepted

I did some serious editting to that rewrite. Even so, let me first thank you for that work. Even though it was far from perfect, I was able to use it as a framework for creating a better article quickly. Without that framework, it would have been much longer before I did much with this article.

Much of what I did was the removal of excess text. For example, in the inroduction I took out the business of an inertial object moving at a constant velocity (or speed and direction): That does not apply in accelerated frames of reference and general relativity (GR). The remaining text was right on the mark however.

Beyond that, I pared down your relativity stuff a good ways (including the removal of the "Limitations" section) and added in some of my own text. I won't call the result perfect but it is a large step in the right direction.

This is very, very much the way that I prefer to do stuff here in Wikipedia. I am willing to do major reverts and rewrites, but I am much happier if I can just build on an existing article in an incremental fashion instead of running roughshod over everything that has gone before. --EMS | Talk 00:12, 7 August 2005 (UTC)

Yep, your edited version was definitely better than what I wrote. Agree with all your edits. Nicely done! ErkDemon 12:52, 8 August 2005 (UTC)

The problem of avoiding inconsistency

The opening sentence of the article states:

In physics, an object has inertial motion if it is moving under the influence only of its own inertial mass and momentum [meaning that no external forces are being applied to it (Newton's first law of motion)]

Here, the concept of frame of reference is defined operationally, which has the great advantage that the same definition can be used in the context of the three successive theories of space, time, and motion: Newtonian dynamics, special relativity, and the general theory of relativity. It is a theory-independent definition.

Recapitulating: all three theories work with the same definition of inertial frame, the difference is in the description of how inertial frames relate to each other. I am pleased to see that this is now in the article.

But what does this sentence mean:

moving under the influence only of its own inertial mass and momentum

How is "own inertial mass" an influence? The very idea of inertial mass is that it is passive. So the current definition contains an inconsistency.

I propose the following definition:

In physics, an object is assumed to be in inertial motion if its motion is not influenced by physical interaction with other objects. Physical interaction can for example be collision, tugging, or being influenced by electric or magnetic fields.

That definition slyly evades discussing gravitation, for discussing gravitation has to wait until later in the article. --Cleon Teunissen | Talk 06:42, 7 August 2005 (UTC)

I think that you had a point about the lead-in. However, the solution was to shorten it more, not expand it. Look at it this way: If you need to explain your explanation, something is wrong.

I don't know that we are being sly about gravitation. The basics are up front where they need to be. The details such as GR as brought up later once they become germane. --EMS | Talk 18:45, 7 August 2005 (UTC)

Newtons second and third law of motion

Currently the opening paragraph reads:

In physics, an object has inertial motion if no external forces are being applied to it (Newton's first law of motion). When such an object’s state of motion is extrapolated over a region of space to take in all other possible objects in the region with the same state of motion, and these are used to define a common coordinate system, we refer to this common system as a frame.

The Stanford encyclopedia of philosophy article discusses an interesting point. Newton assumed that the frame that is co-moving with the common center of mass of the solar system is an inertial frame of reference. Newtons assumption was recognized as justified because under this assumption we see that Newton's second law of motion and Newtons third law of motion hold good.

Newtons first law is not necessarily a law of motion: Newton's first law is rather about how in newtonian dynamics individual members of the symmetry group of all inertial frames of reference relate to each other. In hindsight we can recognize that Newtons first law relates to transforming between inertial frames of reference: motion that is seen from the co-moving inertial frame as being at rest, is seen as uniform velocity from another inertial frame. Newtons first law embodies The principle of relativity of inertial motion.

Newton convinced the scientific world, not by direct proof that newtonian gravity exists, (which cant be given) but by showing that the second and third law hold good if A) it is assumed that the frame that is co-moving with the center of mass of the solar system is an inertial frame, B) it is assumed that there is a force of gravity, described by the newtonian universal law of gravity. (This slots in well with the formulation that a 'fictitious force' is a force that is assumed so that Newtons laws of motion hold good.)

A discussion of the concept of inertial frame of reference is more cohesive if it is in terms of Newtons second and third law of motion. Newton's third law is also about relativity of inertial motion. If an observer applies a force to an object, then both the object and the observer will accelerate with respect to their common center of mass: the common center of mass will remain in inertial motion. It is a force when it comes as an action-reaction pair. Newton showed that the Earth and the Moon orbit a common center of mass, and he showed that it is actually this common center of mass that is orbiting the Sun. Newtonian gravity always comes as an action-reaction pair, that is what made such a strong case for categorizing Newtonian gravity as a force.

The current version of the article reads:

In physics, an object has inertial motion if no external forces are being applied to it.

To emphasize the connection with newtons third law of motion I prefer the formulation:

in physics it is assumed that objects are in a state of inertial motion when there is not an attractive or repulsive mechanical interaction with other objects.

Whenever the interaction is mechanical, then the accompanying acceleration is measurable by instrument. General Relativity describes A) why gravitation, while being an interaction, is not a mechanical interaction. B) why gravitation has in common with for example electrostatic atrtraction the property that it always comes as an action-reaction pair.
--Cleon Teunissen | Talk 20:49, 8 August 2005 (UTC)

Cleon - How massive objects interact is not the subject of this article. Instead the issue is one of how inertial frames operate. I really don't want this to go wandering any farther into GR or gravitational theory than it has. That material is already covered elsewhere. --EMS | Talk 04:02, 9 August 2005 (UTC)

Of course the issue is how inertial frames operate. My proposal is to discuss that as a part of the theory of motion as a whole. In newtonian mechanics it is assumed that addition of velocities is Euclidean vector addition. The way velocities are assumed to add coincides with the way the individual members of the symmetry group of inertial frames of reference are assumed to relate to each other. Mathematically, the galilean transformation constitutes a particular symmetry group. Likewise the Lorentz transformations describe how the group of all inertial frames of reference constitutes a partucular symmetry group.

How inertial frames operate is inseparable from the theory of motion as a whole. There is no such thing as first formulating a theory of motion and then deriving a concept of how inertial frames operate from that. --Cleon Teunissen | Talk 06:24, 9 August 2005 (UTC)

How's about we turn the phrase "inertial motion" into a link, and then if someone reckons they know how best to define it, they can write a separate page on it that people can look up, if interested? ErkDemon 04:30, 9 August 2005 (UTC)

As I described above, the concept of inertial motion and the concept of inertial frame of reference are inseparably interconnected. The question, 'what exactly should we recognize as inertial motion' is at the heart of every theory of motion, for it determines how inertial frames relate to each other. The definition in the article is an operational definition, which has the great advantage that it is theory-independent. The next question is the description of how to transform from one inertial frame to another: that is different from theory to theory.--Cleon Teunissen | Talk 06:24, 9 August 2005 (UTC)

From Newton to SR: was it due to clocks or frames?

After further consideration, maybe a couple of things could be reverted a little bit:

"Included in these rules of physics is the explicit assumption that time progresses at the same rate for all observers, meaning that clocks calibrated in one inertial coordinate system will not become uncalibrated due to one of then being moved into another inertial frame of reference. "

I think that this sentence was meant to be helpful, but I don't think that the first part of it is strictly true: Plenty of textbooks certainly say that space and time were absolute under Newtonian theory when they distinguish between NM and SR, but I think that's a convenient oversimplification: the "definitions" section of Principia makes a big deal about explicitly distinguishing between "absolute" and relative time, and Newton's "absolute time" is not claimed to be the rate at which clocks run - balance-clocks in Newton's day were lousy, pendulum-clocks were already known to run at different rates in different latitudes due to the variation in gravity, and the nearest thing we had to a perfect clock - the motion of stars and planets - was known to be wonky, too, and required correction after correction to obtain better progressively better accuracies. His "absolute" time was also declared not to be the speed at which clocks are seen to run, because lightspeed issues were already known to mess up our observations of solar-system clockwork (specifically, the eclipses of the moons of Jupiter). I forget where Newton mentioned the Jupiter thing, it's probably buried in Principia or Optiks somewhere.

In Principia's definitions, Newton also cedes that there might well be no real processes in the universe that proceed according to his "absolute time", so it's probably fairer to think of this as a mathematical, idealised rate at which clocks might be expected to run when all other complicating effects, optical and physical, are taken care of, in other words, an idealised, applied coordinate system.

More things that writers often forget to mention: Newton's variable-density aether model of gravity in Optiks was technically a curved-space model (mathematicians were apparently already attempting to apply Gaussian geometry to it in the C19th), and Einstein showed in 1911 that gravitational time dilation was an (overlooked) consequence of NM (which probably should have been pointed out a century earlier), so perhaps it's a historical accident that we didn't get a GR-type model from a Newtonian base before the C20th, without using the "inertial frame" concept (e.g. Rindler, "GR before SR").

Old-fashioned emission theory predicts a stronger transverse redshift effect than SR does, and if we use the SR "inertial frame, clock-synch" approach but substitute the emission-theory energy relationships for the SR ones, we actually get similar time dilation and length contraction effects to SR, but stronger ("Lorentz-squared" redshift and contraction components compared to "classical theory", rather than SR's "single Lorentz" version). I think that a lot of physicists now accept the idea that E=mc^2 is a result of Newtonian theory as well as of SR, and a few are now also starting to mention the existence of forgotten transverse redshifts in older theory but I don't think many of them are yet up to speed on the Newtonian counterparts of the SR ruler and clock stuff. It take as long time to override things that people have been taught.

Rather than get into an of these contentious issues, I think it's probably better just to snip this sentence. ErkDemon 04:55, 9 August 2005 (UTC)

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Next:

"However, the assumption of constant progression of proper time in all frames of reference is replaced ..."

Since the "proper time" between two events on a observer's worldline is one of the few things in SR that doesn't change between frames, maybe this is a bit confusing. I think I know what the sentence is supposed to mean, but perhaps it's a bit convoluted.

I still think that perhaps the divergence between NM and SR's implementation of the PoR is probably better described as being to do with SR's emphasis on the frame approach, and its definition of the "special principle of relativity" as being about the relativity of inertial frames rather than about the relativity of the inertial motion of individual objects. The new focus on lightspeed being fixed in a frame in SR (rather than just fixed locally) ruled out at least two types of Newtonian model: Newtonian emission theory on a flat background (where there's no single light metric) and light-dragging implementations of Newtonian theory (where lightspeed can be locally constant, but SR's frame-based lightspeed arguments still don't apply). There may be other fully-Newtonian variants, but I can't think of any.

When I was looking at the subject, I found that it seemed that one can't actually implement the default NM relationships (the consequences of p=mv) in a flat light-metric. With SR, the variation in wavelengths given off at all angles from a "moving" emitter produces a nice ellipsoidal shape that fits back into its original spherical volume with a tidy Lorentz contraction, but with NM the wavelengths grow larger than SR for high velocities (NM is "redder" than SR), and to pack all those wavelength distances back into the original sphere seems to requires a full extrusion out of the plane: Put another way: NM with a flat lightmetric doesn't seem to work, you either have to lose the lightmetric altogether (old emission theory) or introduce velocity-dependent curvature, in which case the SR concept of c being globally fixed in an inertial frame doesn't apply. Either way, the SR frame concept doesn't really work for NM.

Put yet another way: if SR is "the unique solution for the principle of relativity applied to inertial frames" (which I don't think many people would dispute), then if NM also obeys the principle of relativity, and allows a solution, then, pretty much by definition, that solution can't be compatible with inertial frames in the same way that SR is. Once we say that lightspeed also has to be constant in an inertial frame, we are effectively saying that lightspeed is globally constant for every legal inertial observer, and that design decision seems to immediately rule out Newtonian theory, and anything else other than SR or "clones" of SR.

So I think that the use of frames when discussing lightspeeds (and the expicit definition of the special principle as applying to the relativity of inertial frames) was critical in taking us from NM to SR in a single step - instead of arguing about what sort of variably-curved spacetime (if any) might be described by the NM relationships, we declared that we knew that the speed of light was constant, used frame arguments to turn that into a statement that we knew that the speed of light was globally constant, and then went straight to SR as the only possible solution to the problem, as it was now defined, as a problem in flat spacetime.

There's no way we want to go through all this in the article, but perhaps we could revert a little way and say that SR differs from NM in its emphasis on the use of frames and in its "framey" definition of the SPoR, and that this leads to the SR relationships as a unique solution, and leave it at that? ErkDemon 04:55, 9 August 2005 (UTC)

How to implement the principle of relativity

I still think that perhaps the divergence between NM and SR's implementation of the PoR is probably better described as being to do with SR's emphasis on the frame approach, and its definition of the "special principle of relativity" as being about the relativity of inertial frames rather than about the relativity of the inertial motion of individual objects. ErkDemon 04:55, 9 August 2005 (UTC

The emphasis on the frame approach is practical rather than fundamental. The question Einstein had been pondering was that the set of solutions to the Maxwell equations can be arranged in a symmetry group, with the individual members of this symmetry group related by Lorentz transformation. In each solution, the speed of light is the same: c. The Maxwell equations do not have a solution for an observer co-moving with propagating light.

In newtonian dynamics it is assumed that velocities of objects add according to Euclidean vector addition. In formulating SR, Einstein proposed to replace the newtonian assumption of addition of velocities with a rule of velocity addition that brings velocity addition in conformity with Lorentz transformation between inertial frames of reference.

Relativity of inertial motion of individual objects, and relativity of inertial frames are truly inseparable concepts. --Cleon Teunissen | Talk 07:02, 9 August 2005 (UTC)

On second thoughts: I am assuming they are inseparable concepts. I don't know whether that assumption can be dropped or not. --Cleon Teunissen | Talk 07:24, 9 August 2005 (UTC)

On third thoughts, I see no alternative, so back to the first statement: Relativity of inertial motion and relativity of inertial frames are inseparable concepts. --Cleon Teunissen | Talk 08:11, 9 August 2005 (UTC)

Inertial motion

The term inertial motion used in the lead para (definition) does not seem to be defined in WP. Oh dear!--Light current 01:53, 25 October 2005 (UTC)

An inertial frame is a coordinate system defined by the non-accelerated motion of objects with a common direction and speed.

This definition is riddled with problems. If you have a bunch of objects, how do you define a frame? non-accelerated motion, common direction and speed have meaning only within a frame. --MarSch 12:57, 7 November 2005 (UTC)

Is it right to say that an inertial reference frame is one that is moving at a constant speed? I know there's a problem defining what a constant speed is as you don't know what to define it with respect to, but if you defined speed with respect to the seemingly 'fixed' stars, then that should be a good approximation, shouldn't it? It's often used anyway.217.43.134.133 21:45, 8 December 2005 (UTC)

I haven't been following this, but FWIW, 217.43.134.133, your definition would be tricky to implement mathematically even in an asymptotically flat spacetime and would be obviously problematic in an expanding universe. The simple definition used in physics is that a test particle is in inertial motion if it experiences no forces. For example, a charged particle moving through at electromagnetic field will generally experience a Lorentz force which bends its world line away from the geodesic path followed by the world line of a similar but electrically uncharged particle. See also frame fields in general relativity ---CH 11:23, 10 December 2005 (UTC)

Is an inertial fram the same as a non-accelerating frame?--Light current 03:51, 15 January 2006 (UTC)

Inertial Motion (again)

There are links into this page for the term 'Inertial Motion'. However, there is no expalantion of this term on this page. I see that 'Light current' mentioned this back in Oct 2005. Can somebody please add this definition? P Koil (talk) 16:32, 4 January 2008 (UTC)

Lead para- should it be velocity?

Should it not say velocity instead of speed?--Light current 03:48, 15 January 2006 (UTC)

Reversion of major re-write? (7 June 2006)

Hi, I was surprised to find that my edits were reverted because they contained "serious misinformation". I looked over what I wrote and didn't find any gross errors, at least at the level of undergraduate physics. Perhaps the history of the Lorentz transformation (Poincare/Lorentz/Einstein) didn't get adequate coverage, and I should really have provided a reference for the "divine sense organ" thing (I didn't have my copy of the Leibniz-Clarke letters handy) or, better, eliminated that clause as un/impertinent to this article. I didn't change the general relativity section at all, just the Newtonian and special relativity sections. Where's the serious misinformation? Some refinements could definitely be made to satisfy cognoscenti of general relativity (the issue of "local reference frames in particular) but perhaps those could be added as further refinements?

Personally, I feel that at least the initial part of the article should be written as an introductory physics article for lay people (especially high-school and first-year college students), clearly written with bright lines and a strong sense of flow; the latter part could then be used to introduce high-level refinements such as those of general relativity. Do we all agree on the goal of making this article accessible at that level? WillowW 07:58, 8 June 2006 (UTC)

I reverted these edits and I apologize for not taking time to fully explain.

Oh gee... now I don't know what I thought the problem was. Sorreeee! Go ahead and revert my reversion. Sorry again. Not all my bugs have been worked out. ---CH 08:49, 8 June 2006 (UTC)

Singular they

I did a minor copyedit and removed references to the "singular they" usage. I sympathize with the motivation but it's rather incongruous to find ongoing grammatical issues wikilinked in a physics article. Is there an existing reason for this usage here? Opabinia regalis 23:21, 12 June 2006 (UTC)

Hi O, and thanks for your excellent edits! There was no real reason for the link to singular they, except that I wanted to spare the poor text from knee-jerk reversions by finicky readers. The plural subject "scientists" is a better solution, which I'll copy to my other articles -- thanks muchly! :D WillowW 14:36, 13 June 2006 (UTC)

Yeah, I don't blame you trying to preempt the grammar nazis :) I usually try for plural everything in those cases, but the English language really does need to work on that.

A bit off-topic, but I noticed you correctly corrected some of my bold-facing - have you (or anyone else) noticed an issue with scalars rendering at a very small size when interspersed with text? I realized after I made the change that this doesn't happen on my much lower-resolution screen, but does on my 1920x1200 one. I have a somewhat idiosyncratic setup so maybe it is just me. Opabinia regalis 07:45, 14 June 2006 (UTC)