Newtonian Relativity: Galilean Relativity & Beyond

[Ken G]

Again: I present the theory according to which a=b*c. How can you test my predictions if you refuse to check out my definitions of a, b and c?

You are missing the point-- that theory predicts a via the formula a=b*c, hence by the data that is inserted into the equation, not what you picture in your head when you write it down. The definitions of b and c can change, and indeed almost always do, in every physics theory. But a does not change, and the theory does not change, expressly because it predicts precisely the same outcome as did the original version. So it is with Newton's laws (have you ever seen the form of calculus that Newton used? That's a perfect example of how definitions change but the theory is still the same).

You seem to say that by ignoring his theoretical development and assuming that it is scientific, it is perfectly scientific.

Why on Earth would I say such a foolish thing? Why do you think I said any such thing? What I actually said is that Newton's path to his theory is of historical interest only-- what matters is the theory, which is defined by the mathematics it uses to make its testable predictions. Like all physics theories, that's what a physics theory is. Definitions almost always change along the way as they get cleaned up and clarified. Haven't you noticed this? It happens with all theories, yet does not spawn any new theories, it merely changes how we regard what we are doing when we do the mathematics that results from the theory. What changes is the interpretation, not the theory.

Since my post #80 I am trying to turn this thread into a constructive fact-finding conversation about Newton's theory on his own merit - not to be confounded with the theories of some unknown later writers or second-hand explanations by others.

Again you are badly misusing the meaning of the term "theory." Newton's "theory" is exactly the same today as when he formulated it, as I have explained, yet no physics book today that explains Newton's theory will look anything like a similar book from 1800. Does that mean the theory has changed in the interim? No it does not. This is just how physics is, it's perfectly routine. Why do you think no one teaches Newtonian mechanics from the Principia, or relativity from Einstein's papers? Are we all teaching different theories if we choose a different textbook that interprets the meaning of the terms in ways that seem more pedagogically effective?

So what you need to do is, decide if you want a fact-finding conversation of historical interest about what was going on in Newton's head, or if you want a fact-finding conversation about what the theory of Newtonian mechanics actually asserts. Those are quite different things, as I have stressed because it is the main source of inconsistency in the discussion. The bottom line is, a frame of absolute rest has nothing whatever to do with Newtonian mechanics, even though Newton himself did seem to believe in it. Read that as many times as it takes.

 

[harrylin]

"Eppur si muove"
See "Dialogue on the Two Chief World Systems", and "Two New Sciences". I would seriously urge you to study both of those carefully. [...]

I gave you a link to the one to read; it would be useful if you give a link to the other Dialogue as well.

[..] No one (certainly not Newton) disputes that Newtonain mechanics is perfectly relativistic, in the sense that it is invariant under Galilean transformations, meaning that it is indifferent to the choice of inertial reference frame. In fact, this is the content of Proposition V (from memory) of the Principia. [..] He was arguing for the need for absolute space as opposed to RELATIONISM in order to give an intelligible account of phenomena, because relationism cannot account for inertial phenomena. That's why he based his mechanics on Galileo's principle of inertia (now known as the principle of relativity), which he acquired by way of Gassendi and Descartes. The prejudice he was trying to dispel was the idea that we can base everything on the relations between material bodies, without reference to any underlying properties of space (and time). It is a very important point, and forms the basis of Newtonian mechanics.

That's what I meant with fact finding instead of quibbling: it's good to see that we actually agree on the basics! However, you disagree with actually trying that:

I don't think that will be useful or instructive. The way you repetitively post quotes, that you thoroughly mis-understand, and none of which support your position [...]

That's exactly what I think of you, such as by your claim that the ship's motion means acceleration; and so you may be right that such would not be fruitful in practice.

You are missing the point-- that theory predicts a via the formula a=b*c, hence by the data that is inserted into the equation, not what you picture in your head when you write it down.

Well, it happens to be me who made that point: without knowing the meaning of "a", "b" and "c", you cannot test anything at all. For example the Lorentz transformation formula can also be used in acoustics, but there both the meaning of the symbols and their application are completely different - same equation but nothing to do with relativity theory.

Definitions almost always change along the way as they get cleaned up and clarified. Haven't you noticed this? It happens with all theories, yet does not spawn any new theories, it merely changes how we regard what we are doing when we do the mathematics that results from the theory. What changes is the interpretation, not the theory.

Certainly I noticed those things, but to what extend that has happened only became clear to me many years after I finished my study. With an eye on the topic: Suppose some famous vacuum cleaner producer, let's call him Mr. Hoover, sells vacuum cleaners to you for distribution. You think that the motor is no good and replace it by a better one from China, selling the vacuum cleaners with the label "Hoover". Perhaps your customers are perfectly happy. Still there is a tiny risk that one day the police knocks on your door. But as we know, the standards are different in teaching (as well as in religion): many teachers consider such cheating not a crime but a virtue. Note the subtle but important difference with accreditation: it's the subtle difference between selling it as a Hoover, or selling it as "Hoover with China motor".

[..] Why do you think no one teaches [..] relativity from Einstein's papers?

I have news for you: in the relativity forum several of us are quite successful explaining relativity to newbees with help of Einstein's papers and books.

[..] decide if you want a fact-finding conversation of historical interest about what was going on in Newton's head, [..] The bottom line is, a frame of absolute rest has nothing whatever to do with Newtonian mechanics, even though Newton himself did seem to believe in it. [..].

As there is no common interest on anything to discuss (except perhaps the two of you), I now also leave this thread. Harald

 

[Russell E]

I gave you a link to the one to read; it would be useful if you give a link to the other Dialogue as well.

The links didn't work in my browser, but it doesn't matter because I have paper copies of the books. Like you, I wouldn't dream of making pronouncements on the subject if I hadn't already studied both of them thoroughly, along with the vast secondary literature. If I was only now just becoming acquainted with these works, I would be in the mode of asking questions and learning, not trying to explain things to people much more knowledgeable than myself.

That's exactly what I think of you, such as by your claim that the ship's motion means acceleration...

But our situation isn't symmetrical, is it?

Obviously there are relative positions and velocities between the ship and the earth, etc., but Newton's laws are indifferent to position and velocity, they recognize only alterations in motion, i.e., acceleration. If the ship was moving uniformly in a straight line, then Newton's laws would be fully satisfied by referring all positions and velocities and accelerations to the rest frame of the ship. The same applies to the Earth and to the Sun. Finally Newton arrives at the center of mass of the solar system, and since he regards this as the entire cosmos, he declares (by mere convention) THIS is the absolutely resting center of space (which of course it isn't). This just illustrates the fact that Newton's laws give no warrant for selecting any particular frame as absolute rest, other than that it be perfectly unaccelerated. So that's why I highlighted the acceleration aspect of the ship/earth/sun discussion, to help you understand how Newton's discussion in the Scholium relates to the physical theory that he describes in the Principia.

I am trying to turn this thread into a constructive fact-finding conversation about Newton's theory on his own merit - not to be confounded with the theories of some unknown later writers or second-hand explanations by others... Certainly I noticed those things, but to what extent that has happened only became clear to me many years after I finished my study... Suppose some famous vacuum cleaner producer, let's call him Mr. Hoover, sells vacuum cleaners to you for distribution... or selling it as "Hoover with China motor".

Okay, so your interest is not physics, per se, but the historical thoughts and beliefs of one specific individual (Isaac Newton), and you regard as untrustworthy the views of any scholars who have studied Newton and his works and might try to explain them to you. And you feel you've been swindled by unknown writers (shiver!) who expressed things differently than Newton did, and who you suspect of bastardizing Newton's actual theory.

That's kind of a weird form of obsessive conspiratorial paranoia, but to each his own. The real problem with what you said is the phrase "fact-finding". That's not a cut-and-dried process. For example, the second law refers only to acceleration, but when you scanned the text you saw the phrase "altered motion", so you gleaned the "fact" that Newton's second law refers to motion, not acceleration. The problem is that the phrase "altered motion" means acceleration. So the "fact" you found was not a fact at all.

You can spend the rest of your life gathering "facts" like that, but you still won't understand anything, because you aren't thinking about what the words mean. Newton certainly thought about and understood what his words meant, so if you really want to understand his thinking, you need to understand what he wrote, not just scan the text for individual words that superficially conform to your pre-conceptions and prejudices. And you simply must learn to distinguish between physical and metaphysical concepts.

 

[Ken G]

Suppose some famous vacuum cleaner producer, let's call him Mr. Hoover, sells vacuum cleaners to you for distribution. You think that the motor is no good and replace it by a better one from China, selling the vacuum cleaners with the label "Hoover".

The analogy has nothing to do with how physics works, so is irrelevant. Don't reason by analogy-- physics theories are the observables they predict, period. Do you think otherwise?

I have news for you: in the relativity forum several of us are quite successful explaining relativity to newbees with help of Einstein's papers and books.

I have news for you-- no one teaches physics that way in classrooms. Now why do you think that is?

 

[harrylin]

[...]you gleaned the "fact" that Newton's second law refers to motion, not acceleration. The problem is that the phrase "altered motion" means acceleration. So the "fact" you found was not a fact at all. [..]

Just a final clarification for any potential onlooker: As is easy to check, in post #89 I tried to explain to Russell that the term in the second law to verify with Newton's definition is not, as he claimed, "acceleration" but "alteration of motion"; and that, consistent with that fact, the "relative motion of the ship" does not mean, as Russell pretended, "the ship could be moving (accelerating) relative to the Earth" but, according to Newton's definitions, motion is a translation from one place to the other.

Obviously no reasonable conversation is possible and I will next unsubscribe from this thread to prevent myself from looking at more of such distortions and verbal abuse.

 

[harrylin]

The analogy has nothing to do with how physics works, so is irrelevant. Don't reason by analogy-- physics theories are the observables they predict, period. Do you think otherwise?
I have news for you-- no one teaches physics that way in classrooms. Now why do you think that is?

Ken, how physics works relates to the topic of scientific method on which I started a thread, and I think that I already answered your question there:
https://www.physicsforums.com/showthread.php?t=598724

And why no one uses any original papers in the classrooms (which I doubt) is again a totally different topic... if you start a thread on that (which will likely end go to "Social Sciences"!) I will be happy to participate.

 

[Russell E]

Just a final clarification for any potential onlooker: I tried to explain to Russell that the term in the second law to verify with Newton's definition is not, as he claimed, "acceleration" but "alteration of motion"...

But "alteration of motion" IS acceleration. That's the whole point. The second law is completely indifferent to absolute position or absolute velocity - it depends only on absolute acceleration, which Newton referred to as "alteration of motion". This is why the absolute value of motion itself is of no significance in Newtonian mechanics, as Newton himself says many times. The same for absolute positions. This is because Newton bases his theory (in the Principia) on definitions, postulates, and laws that refer only to accelerations, and they explicitly equate "rest" with "uniform motion in a straight line". Hence it was inevitable that Newtonian mechanics does not distinguish between these.

In addition to the numbered axioms, definitions, propositions, and laws that constitute the development and structure of Newton's presentation of his theory, he also interspersed several Scholia, providing somewhat informal commentary on the theory. In the first Scholium he admits that he hasn't actually defined space, time, velocity, etc., but he realizes that some guidance is needed, because his propositions clearly don't apply to arbitrary systems of reference. In light of what we said above, the necessary and sufficient condition is that we be able to identify true uniform straightness, because all the definitions and laws are expressed in terms of deviations from uniform straightness. So he needs to identify the class of inertial coordinate systems, which he does in a physically meaningful way by noting that forces causing acceleration, so we need freedom from external forces to be unaccelerated. Fine. This is the operational basis of the theory.

Now, he also includes in the Scholium some additional statements - the ones that have confused you - declaring the existence not only of absolute acceleration (which is all that is relevant to his theory of mechanics as he has described it), but of absolute velocity and absolute position as well. However, regarding these unsupported declarations, he also admits that they "by no means fall under our senses", and he admits that he is unable to give them any operational meaning, and he does not give any indication of how they might be determined or what they signify. Hence these are self-admittedly metaphysical notions. It's true that nothing in the theory of mechanics described in the Principia forbids us from asserting that one particular inertial frame is the "true" one, but it's also true that nothing in theory requires it or makes any use of it. It is a purely metaphysical and superfluous conception.

According to Newton's definitions, motion is a translation from one place to the other.

No, Newton's definition of the quantity of motion is the product of velocity and mass (so it is what we call momentum), but of course he doesn't define velocity. In the Scholium he admits that he hasn't formally defined the basic terms, but he gives an informal discussion, necessary to establish the physically meaningful concept of an inertial reference frame. Interspersed with this discussion he refers to "absolute places", but he does not define them, and indeed admits that they have no operational meaning, so his theory is not based on them. (It is fortunate that those things are irrelevant to his actual theory, because if mechanics depended on "absolute place" or "absolute velocity" it would be worthless.)

Obviously no reasonable conversation is possible and I will next unsubscribe from this thread to prevent myself from looking at more of such distortions and verbal abuse.

None of the comments that you regard as "distortions and verbal abuse" are anything of the kind. They probably seem that way to you only because you are unable to grasp the concept of indefinite integrals. Acceleration has absolute significance, so you think the integral of acceleration (i.e., velocity) must also have absolute significance, and the integral of velocity (i.e., position) must also have absolute significance. One could continue defining more variables by taking successive integrations, but you have not articulated any justification for assigning absolute values to them. Newton gave his reason: Space is the sensorium of God, and it would be absurd to think that the sensorium of God moves. But that is not part of his theory of mechanics, it is just a metaphysical belief.

 

[D H]

But "alteration of motion" IS acceleration.

Yes and no.

Newton intentionally did not use his calculus in his Principia. It was too new, potentially too controversial; Newton didn't want to pile one new thing atop another. He wanted his Principia to stand on its own. This is also why he barely used algebra in the Principia. His weapon of choice was instead geometrical reasoning. For the next fifty years or so following Newton's death mathematicians and physicists undertook rewriting Newton's concepts in terms of calculus and algebra.

There is no doubt that F=ma (better: F=kma; the idea of consistent units for force, mass, length, and time was a hundred years after Newton's death) is Newton's second law. It just isn't how Newton wrote it. Without words, Newton's second law as written by Newton is
\Delta \vec p \propto \int_0^{\Delta t} \vec F\,dt
In words, "The alteration of motion is ever proportional to the motive force impressed, and is made in the direction of the right line in which the force is impressed."

Since "quality of motion" is mass times velocity, another way to express Newton's second as expressed by Newton is
m\Delta \vec v \propto \int_0^{\Delta t} \vec F\,dt
There's no need for absolute velocity here. Just change in velocity.

Getting from the above to the F=ma that we use now is a trivial application of calculus, plus a not so trivial effort to turn that proportionality into an equality.

 

[Ken G]

And why no one uses any original papers in the classrooms (which I doubt) is again a totally different topic... if you start a thread on that (which will likely end go to "Social Sciences"!) I will be happy to participate.

Actually, it's completely relevant, and has a very simple answer. As you have chosen to duck it, I will give it to you: original papers are not used to teach physics because invariaby the exact same theory described in those papers is better understood in modern terms that have emerged later than the original papers. The reason this is clearly relevant is that you insist on equating the theory of Newtonian mechanics with Newton's mental pictures about frames of absolute rest, but the two are not at all the same-- the former being explained in very different terms in classrooms today, yet still being exactly the same theory. If you don't see that, then you do not understand what scientific pedagogy is (a rather separate topic from the scientific method, by the way).

 

[Ken G]

There's no need for absolute velocity here. Just change in velocity.

Exactly. Newtonian mechanics, as described by Newton and still applied today, requires no reference to any concept of absolute rest, nor is any such concept ever invoked in the teaching of Newtonian mechanics. Yet, it is clear that Newton himself felt that there was an essentially philosophical need for such a frame. So we can clearly differentiate the theory itself from Newton's own opinions about its interpretation. That also answers earlier objections about whether or not Newton was being scientific-- to the extent that he was creating a testable theory, he was certainly being scientific, and to the extent that he was choosing a mental picture to interpret his theory, he was under no responsibility to be scientific, because the rules of science become quite fuzzy in the realm of interpretations, and that is just as it should be-- science and philosophy as non-overlapping magisteria that nevertheless interact closely.

 

[D H]

Actually, it's completely relevant, and has a very simple answer. As you have chosen to duck it, I will give it to you: original papers are not used to teach physics because invariaby the exact same theory described in those papers is better understood in modern terms that have emerged later than the original papers.

This is a very important point. It is one of the key differences in how the sciences and the humanities are taught. Very little, if any, of basic science / math / engineering education involves reading the papers of the "Great Minds". We aren't subjected to the thrills of reading scientific literature until our junior or senior year in college, maybe even later.

It took more than 200 years of polishing to get Newtonian mechanics "right". Physicists and mathematicians spent the 1700s rewriting Newtonian mechanics in terms of algebra and calculus. The 1800s saw Newtonian mechanics rewritten again in Lagrangian and Hamiltonian mechanics. Vectors appeared just in time to find that all this cleaning up wasn't quite as clean as physicists thought.

Newton's views on absolute space and absolute time were amongst those concepts that were discarded during that 200 year span. There is no need for it. Even Newton had little need for it. He did not use it in any of his laws, lemmas, or analyses.

 

[Ken G]

I can't help wondering if Newton himself ever paused to notice that latter point-- did he ever think "I wonder, if this notion of absolute rest is philosophically important, why doesn't it show up anywhere explicitly?" He was too smart not to notice that, so I think we have to look very carefully at the "Newton's bucket" to see why he felt it was necessary. It might be similar to why Lorentz felt an aether was necessary, even though it never shows up as a requirement of his own transformations. Indeed, even Einstein, in his later writings, concluded that some kind of aether-like concept was necessary to understand what was enforcing the inertial paths of general relativity. Is this a prejudice that just won't die, even for the great minds, or will we someday discover why we actually do need the concept?

 

[Russell E]

Russell e wrote "But "alteration of motion" IS acceleration."
Yes and no.

Could you clarify the "no" part? Are you saying that alteration of [inertial] motion is NOT acceleration? I didn't see anything in the remainder of your post that would justify that assertion. You just talked about the well known fact that Newton expressed the second law in terms of impulses rather than continuous forces, so the acceleration is instantaneous, but it is acceleration none the less.

Original papers are not used to teach physics because invariaby the exact same theory described in those papers is better understood in modern terms that have emerged later than the original papers.

I'd like to add a note of caution here. But first let me say I agree that it's possible for ideas to be refined and clarified, and it's obviously true that even the greatest scientists have often been confused and mistaken in some of their beliefs, and obviously they have held some non-scientific ideas along with their scientific ideas, etc.,... all of which just shows how silly is would be to slavishly obsess over old texts of certain specific individuals. There is unfortunately a kind of misguided soul who conceives of science as an exercise in textual analysis of scriptural sources, like the Scholastics of the middle ages who parsed and disected Aristotle's every word and phrase for illumination. Sometimes there was uncertainty about whether particular texts had actually been written by Aristotle, or by one of his students or later interpreters (horrors!). This is quite similar to harrylin's revulsion at what he calls China Hoovers and later interpretations by unknown writers and (shudder) "second-hand explanations". To borrow a phrase from Newton, these people are "more addicted to philology than to the study of nature".

Having said all that, I think when talking to crackpots it's important to keep in mind that many of the "second-hand explanations" they have been exposed to actually ARE quite bad. They usually come from a background of having been taught science in their youth by someone who (to put it mildly) didn't understand science very well, using textbooks that, lamentably, are often not good at conveying the subtleties underlying scientific thought, and tend to give somewhat naive and over-simplified accounts - often portraying the "great man" approach to the history of science. (George Washington never told a lie, and Thomas Jefferson was a champion of freedom and equality for all people.) This is compounded when these individuals start reading gee-whiz science popularizations and pick up more misconceptions, to say nothing of internet discussion groups where they are lectured by people who hardly understand the subject either.

Later in life they may catch their first glimpses of how they've been ill-served by clueless high school teachers and oversimplified hero-worshiping textbooks and gee-wiz popularizations. So it isn't totally surprising that they develop a suspicious attitude toward secondary accounts. This can lead in two directions: They may begin to actually study the subject, examining the real scholarly literature, and THINK about the subject (which can have mixed results, depending on whether they have any aptitude for it), and develop a more sophisticated, grown-up, and informed understanding. (Thomas Jefferson owned slaves. Your parents had sex. ) Unfortunately, all too many of these unlucky individuals go in a different direction, their suspicions turn to paranoia, they seize on some particular juvenile "pet" idea and ride it into full-blown crackpotism, from whose bourn no traveler returns.

Newtonian mechanics, as described by Newton and still applied today, requires no reference to any concept of absolute rest, nor is any such concept ever invoked in the teaching of Newtonian mechanics. Yet, it is clear that Newton himself felt that there was an essentially philosophical need for such a frame.

Agreed, although I might say religious and/or metaphysical rather than philosophical (especially since in Newton's day science was called natural philosophy). He obviously understood full well the complete relativity of his theory. In fact, Corollary 5 of his Laws is essentially identical both to Galileo's and to Einstein's statement of the principle of relativity. Newton felt the need to assert the existence of an (admittedly unidentifiable and physically meaningless) absolute rest only because he thought the concept of relativity might mislead people into atheism.

It's also worth emphasizing that Newton's didn't just argue for SOME absolute rest, he claimed specifically that the center of mass of our solar system is at absolute rest, and at the absolute center of the universe. So, if someone takes Newton's words as the revealed truth, they are commited to a rather awkward belief in solar-system-centrism. The only escape for them is to point out that Newton actually admits the solar system could also be moving uniformly in a straight line... but of course by admitting that Newton acknowledged that the center of the universe could be moving uniformly in a straight line they admit the conventionality of Newton's concept of absolute rest, and the primacy of the principle of inertial relativity. This is why those who espouse etherism invariably flee the scene as soon as their views come under scrutiny.

Obviously no reasonable conversation is possible and I will next unsubscribe from this thread to prevent myself from looking at more of such distortions and verbal abuse.

Right.

 

[Ken G]

But first let me say I agree that it's possible for ideas to be refined and clarified, and it's obviously true that even the greatest scientists have often been confused and mistaken in some of their beliefs, and obviously they have held some non-scientific ideas along with their scientific ideas, etc.,... all of which just shows how silly is would be to slavishly obsess over old texts of certain specific individuals.

I'll add to that the fact that even one individual may have held different beliefs and opinions over their own life! So when we quote Newton or Einstein, we don't necessarily know which Newton or which Einstein we are quoting anyway. And should we rely on a person's final conclusion on some topic, formed late in their lives, or should we imagine their minds were sharper and more original when they were younger and less influenced by the effort of having to get other people to agree with them? So reference to "texts" is generally of questionable value in fields that embrace the evolution of interpretation, as does science, unlike in religion which tends to try to avoid changes in interpretation as much as possible.

Having said all that, I think when talking to crackpots it's important to keep in mind that many of the "second-hand explanations" they have been exposed to actually ARE quite bad.

Yes, we must watch out for the "telephone game" effect, where an expert explains something to a scientist who is not necessarily and expert, who then explains it in more colloquial terms to a science writer who is not a scientist at all, who then tries to find words they think the "layman" will better understand, who then explains the idea to their neighbor, who then goes off and creates a website about why science tells us we are all going to get hit by an asteroid or eaten by a black hole. So I agree that returning to authoritative "anchors" is important to prevent that kind of sliding into pseudoscience. But generally speaking, modern textbooks are sufficient-- there is rarely a need to refer to the original texts unless one desires the (highly worthwhile) sociological experience of getting the flavor of the original discoverer. And sometimes the sharpness of that original mind is worth stepping back before the various pedagogical improvements, and seeing how clearly they understood their brainchild. But there must also be a willingness to step away from the less well developed pedagogical approaches, in favor of modern improvements. Indeed, I have seen plenty of crackpots who constantly refer to original texts-- the obscurity in the original language helps them create a kind of smokescreen as to why their crackpot idea is more consistent with the "great mind" than is the modern description of the great theory!

Newton felt the need to assert the existence of an (admittedly unidentifiable and physically meaningless) absolute rest only because he thought the concept of relativity might mislead people into atheism.

I'm not really distinguishing "philosophy" from "religion" or "metaphysics", because people tend to apply those words differently depending on which view they personally hold. I'm just distinguishing a scientific theory, which is highly objective and subject to the rules of science, from the contextual interpretation attached to it, which is highly subjective and a function of the cultural milieu in which the theory appears, but not subject to the requirements of scientific demonstrability.

It's also worth emphasizing that Newton's didn't just argue for SOME absolute rest, he claimed specifically that the center of mass of our solar system is at absolute rest, and at the absolute center of the universe.

Yes, a classic example of cultural interpretation outside the realm of science itself.

This is why those who espouse etherism invariably flee the scene as soon as their views come under scrutiny.

And we should probably distinguish "etherism", as Lorentz and Poincare held it, from "geocentrism", in the modern religious context. One can be an etherist and still a Copernican (in the modern sense of no center, not heliocentric), and indeed we may all have to adopt that approach ourselves, if the next great theory requires it. But it certainly seems highly unlikely that any future scientific theory will underwrite the concept that the Earth or Sun is the absolute center of the universe, or at absolute rest, in regard to all the intelligent beings in said universe!

 

[Russell E]

I can't help wondering if Newton himself ever paused to notice that latter point-- did he ever think "I wonder, if this notion of absolute rest is philosophically important, why doesn't it show up anywhere explicitly?" He was too smart not to notice that, so I think we have to look very carefully at the "Newton's bucket" to see why he felt it was necessary.

The spinning pail and the revolving globes in the first Scholium were not arguments for absolute rest (which wasn't seen as an issue, per se), they were arguments for substantivalism as against relationism. In other words, they were arguments to say we can't attribute all the phenomena of motion to the relations between bodies. Inertia is a property of how an individual particle moves in absolute space and time, regardless of what other particles exist. Of course, Mach argued that Newton was not justified in claiming the water in the pail would still be concave, and that there would still be tension in the rope between the two rotating globes, even if there was no other matter in the universe. Mach said we have no way of knowing whether inertia is ultimately attributable to relations with other bodies, all we can do is note the coincidence that the inertial frames are those that are at rest or moving uniformly relative to the apparent average frame of the matter in the distant stars. But there are well known problems with Mach's argument too, and the whole debate becomes moot in the context of general relativity.

But for the purposes of this discussion, the point is that Newton didn't actually present any argument or rationale for the concept of absolute rest (or absolute position). All he said in support of that notion was "Spaces are, as it were, the places of themselves as well as of all other things. It is from their essence or nature that they are places; and that the primary places of things should be movable is absurd. These are therefore the absolute places; and translations out of those places are the only absolute motions." That's it.

In Newton's day the argument about absolute rest was cast in terms of the argument about etherism, i.e., the plenum versus the vacuum, which Newton wrote about elsewhere, but kept it out of the Principia.

It might be similar to why Lorentz felt an aether was necessary, even though it never shows up as a requirement of his own transformations.

Lorentz explained himself on several occasions, public and private. There were two aspects to his position. One was that he felt is was important to remain open to the possibility that Lorentz invariance might be violated, i.e., that it might, after all, turn out that we can identify physically some absolute rest. The other was that, even if we accept complete Lorentz invariance, it is still possible that one particular foliation is the one inhabited by a universal consciousness (God), just like Newton's "sensorium of God", and so we would be justified in calling that the true foliation -even though we can never know it, since we are not God-like. But of course he freely admitted that this was a purely metaphysical notion, outside the realm of science proper.

Even Einstein, in his later writings, concluded that some kind of aether-like concept was necessary to understand what was enforcing the inertial paths of general relativity.

Already in 1916 (if not earlier) Einstein was clarifying the sense in which spacetime could be regarded as an ether. This again is the rejection of relationism, which Einstein did as he gradually lost his enthusiasm for Mach's ideas, and returned to something like Newton's substantivalism. But we mustn't confuse Einstein's concept of the ether of spacetime with the question of whether there is absolute rest, because Einstein specifically explained that the "ether" he had in mind cannot have any state of motion or rest assigned to it, because the events of spacetime have no velocities and are Lorentz invariant. As he said, Lorentz had deprived the ether of all its mechanical properties except one, namely its immobility, and the theory of relativity (Lorentz invariance) demands that the ether relinquish even its immobility.

Is this a prejudice that just won't die, even for the great minds, or will we someday discover why we actually do need the concept?

I think it's difficult to talk about THE concept, because there are so many different conceptions of the ether and spacetime. It's almost inevitable that some interpretation of some of these ideas would have some relevance to some future theories, and also that they will be set aside again. The question of the Vacuum will always be at the center of fundamental conceptions of physical theories - as it has been for thousands of years - but whether we will converge on a single stable conception seems doubtful (to me).

 

[Russell E]

I'll add to that the fact that even one individual may have held different beliefs and opinions over their own life! So when we quote Newton or Einstein, we don't necessarily know which Newton or which Einstein we are quoting anyway.

Yes, Einstein is a good example of someone whose views were constantly evolving, and he frequently repudiated some of his earlier beliefs. He once said about himself (only half joking) that every year he retracts what he wrote the year before.

Generally speaking, modern textbooks are sufficient--

Sufficient for what? Generally speaking, most students don't need or want to understand the subtleties of the foundations of scientific theories, e.g., the circularities lurking in most naive definitions, and the difficult epistemological issues. So the fact that textbooks do an abysmal job of explaining those things may not be a huge drawback, generally speaking. But what we're talking about here is precisely the foundational issues of a scientific theory, such as the possible meaning and significance of the concept of absolute rest in the context of classical mechanics. I don't think very many textbooks on classical mechanics do a good job of explaining that (nor, to be fair, were they intended to).

In contrast, original works by great thinkers tend to at least pay some attention to the foundational issues, because that's what those thinkers have been wrestling with in the formulation of their theories. But of course, being at the earliest stages, they often have confused and emerging ideas, and often change their minds later, so even the original works of great thinkers can't be taken as definitive statements of that individual's views (as you noted above) - let alone as statements of the truth. Many of the great scientists have been likened to "sleepwalkers" who were guided more by spiritual beliefs, instinct, and intuition than by clear-headed ratiocination.

Needless to say, there IS a vast literature on the foundational issues, but it is in books devoted to the foundations of science, and crackpots hardly ever seem to be acquainted with that literature.

I have seen plenty of crackpots who constantly refer to original texts-- the obscurity in the original language helps them create a kind of smokescreen as to why their crackpot idea is more consistent with the "great mind" than is the modern description of the great theory!

Yes, although in most such cases I think the obscurity is more in the mind of the crackpot than in the original text. For example, Einstein says "for ease of reference, let's call this the stationary frame", and the crackpot says "Aha! Busted!" That's just the dementia of crackpots at work, not an obscurity in the text.

Of course, there ARE genuine obscurities and ambiguities in any text, but crackpots rarely notice those. This thread is a case in point. There are certainly obscurities in Newton's Principia, but on the question of absolute rest Newton was extraordinarily careful to consistently equate "rest" with "uniform motion in a straight line", and he explicitly states the complete relativity of his mechanics. And the fleeting mention of absolute position and velocity in the Scholia is carefully labeled by Newton as purely metaphysical ("the places of absolute space do by no means fall under our senses") and religious ("God constitutes space and time"). In addition, he rather carefully discussed the difficult foundational issues in the Scholia, making the crucial case against relationism with his pail and rotating globes examples. All in all, an incredible intellectual feat - which makes it all the more regretable to have it mis-represented by crackpots.

I'm not really distinguishing "philosophy" from "religion" or "metaphysics", because people tend to apply those words differently depending on which view they personally hold. I'm just distinguishing a scientific theory, which is highly objective and subject to the rules of science, from the contextual interpretation attached to it, which is highly subjective and a function of the cultural milieu in which the theory appears, but not subject to the requirements of scientific demonstrability.

I know metaphysics and religion fall withing the realm of philosophy, but my point is that science does too. Saying that Newton's concept of absolute rest was 'philosophical' doesn't really make the distinction you're trying to make (certainly not to antiquarian crackpots), because objective scientific thinking is philosophical too. Indeed, science in Newton's day was called natural philosophy, and even today the modern dictionary definition of 'philosophy' doesn't exclude "objective" thinking "subject to the rules of science". It's true that some people (especially scientists) use the word 'philosophical' in a limited and (dare I say it?) even slightly perjorative sense to mean "metaphyical" or "subjective" or non-scientific, but that's a specialized meaning that only some people have in their minds. (I recall that Feynman used to delight in referring to the Phil-AH-zofers.) And of course the very distinction between objective and subjective is subject to objective debate within philosophy. So, if your concern is to avoid words that "people tend to apply differently depending on which view they personally hold", I think you should avoid vague and all-inclusive words like 'philosophical' that mean different things to different people, and instead use more precise words like 'metaphysical' and 'religious' to signify (respectively) ideas that have no observable physical significance (does not fall under our senses) or are based on religious beliefs (e.g., the sensorium of God).

 

[Ken G]

In Newton's day the argument about absolute rest was cast in terms of the argument about etherism, i.e., the plenum versus the vacuum, which Newton wrote about elsewhere, but kept it out of the Principia.

The other was that, even if we accept complete Lorentz invariance, it is still possible that one particular foliation is the one inhabited by a universal consciousness (God), just like Newton's "sensorium of God", and so we would be justified in calling that the true foliation -even though we can never know it, since we are not God-like.

Thank you for these additional details. These positions seem to confirm that indeed Newton and Lorentz held philosophical views that they clearly distinguished from the stuff of their scientific theories. That seems like a natural state of affairs, and underscores the importance of distinguishing the theories from the mental pictures that their originators may have used for motivation.

The question of the Vacuum will always be at the center of fundamental conceptions of physical theories - as it has been for thousands of years - but whether we will converge on a single stable conception seems doubtful (to me).

I agree-- I think you and I are in the minority of people who don't view the progress of physics as being toward "the answer", but rather simply a progression of current answers that achieve ever-improving accuracy and generality, but that's it. That seems like a bitter pill for many to swallow, but I can't see what evidence anyone can use to support the former over the latter expectation! How ironic that many scientists seem to choose an unscientific abandonment of reliance on evidence whenever they discuss science itself.

 

[Ken G]

Sufficient for what? Generally speaking, most students don't need or want to understand the subtleties of the foundations of scientific theories, e.g., the circularities lurking in most naive definitions, and the difficult epistemological issues.

By "sufficient", I simply mean sufficient to understand and apply the theories in question, from the perspective of currently most-favored pedagogies. On the topic of epistemology, I have to agree that textbooks make little or no effort to elucidate those issues, nor to trace the historical debates that will likely go on forever, as an interesting kind of "back story" to the progress of physics. Most people just don't seem as interested in that as you and I, so that simply gets left out of the story, but I agree with you that this is something of a shame. Closer contact between physics and the ageless philosophical questions seems to me like a good backdrop against which to better understand the ramifications of the various theories (something that students are generally much weaker at than simply amassing a body of cut-and-dried problems that they know how to solve).

In contrast, original works by great thinkers tend to at least pay some attention to the foundational issues, because that's what those thinkers have been wrestling with in the formulation of their theories. But of course, being at the earliest stages, they often have confused and emerging ideas, and often change their minds later, so even the original works of great thinkers can't be taken as definitive statements of that individual's views (as you noted above) - let alone as statements of the truth. Many of the great scientists have been likened to "sleepwalkers" who were guided more by spiritual beliefs, instinct, and intuition than by clear-headed ratiocination.

I think there is a tendency for thinkers on the frontiers to use philosophy more than do the practitioners in their wake. Of course, the Nobel laureate Steven Weinberg doesn't agree-- he sees philosophical thinking as a kind of useless barrier that must first be removed before you can think scientifically. On the other hand, Weinberg may fall into the standard trap that "my metaphysical thinking isn't philosophy, other people's is."

Yes, although in most such cases I think the obscurity is more in the mind of the crackpot than in the original text. For example, Einstein says "for ease of reference, let's call this the stationary frame", and the crackpot says "Aha! Busted!" That's just the dementia of crackpots at work, not an obscurity in the text.

Yes, the "obscurity" is a moving target-- the language becomes more precise when one is a trained scientist who understands its intent, but for the crackpots, a little knowledge is a dangerous thing!

I know metaphysics and religion fall withing the realm of philosophy, but my point is that science does too. Saying that Newton's concept of absolute rest was 'philosophical' doesn't really make the distinction you're trying to make (certainly not to antiquarian crackpots), because objective scientific thinking is philosophical too.

Yes, the lexicon is tricky here. We can adopt the approach that science is a kind of "arm" of philosophy, created to answer certain types of philosophical questions using particularly well-suited means (which is the meaning you take and is certainly historically accurate). Or, we can adopt an approach that is probably more typical, which is to stress the way science has become a "prodigal son" of philosophy, advancing so far along its own independent path that it is no longer considered to be under the influence of its parent (that's certainly Weinberg's approach, though I feel he goes too far).

I see value in either picture, my intention was merely to stress the "two hats" that people like Newton and Lorentz wore, where at one turn they were describing some scientifically testable theory, and at another they were placing that theory into an essentially sociological context to help them understand what lessons they felt we might wish to take from the theory. The former is objective, the latter largely subjective, and since opinions in science are generally considered to be objective and in philosophy are more subjective, that was the distinction I wished to make.

And of course the very distinction between objective and subjective is subject to objective debate within philosophy. So, if your concern is to avoid words that "people tend to apply differently depending on which view they personally hold", I think you should avoid vague and all-inclusive words like 'philosophical' that mean different things to different people, and instead use more precise words like 'metaphysical' and 'religious' to signify (respectively) ideas that have no observable physical significance (does not fall under our senses) or are based on religious beliefs (e.g., the sensorium of God).

Since I agree with you that it is a shame to treat the term "philosophical" as perjorative in the context of scientific thought, I can see the value in this suggestion. It is a somewhat uphill battle however-- the horse may have already left that barn! Many people think science has so eclipsed its philosophical lineage that it should no longer be thought of as a branch of philosophy, rendering philosophy to the "all other" category. Slipping into that kind of language was like sleeping with the enemy, but that view has rather taken hold I would have to say.