Rasher Null

Thank you Strange for your generous comment ). I never thought I would be relieved by the strangeness of special relativity! But in a vaguely informationy sort of way it is a relief.

Well leaving out quantum scale things (for now at least), shall we say that an "object" is something that has a position? We could call it an "aardkarv" even - but some name would be useful if the definition of motion is based on a "change of position", because presumably that means a change of position of something and it would be convenient to have a name... FANFARE!! I may be in a position to resolve one aspect of "motion" that is bugging me - about being able to "freeze" a moving object and being able to discern its velocity. ... Can this not be done - by an external observer at least - by looking for relativistic length contraction?

Would it make sense to define an object , for now, as anything that has the property of occupying a position? (Objects might possibly then be subdivided into "classical" and "quantum")

OK, special relativity insists on time being a fourth dimension. So motion can be defined as "change of position over time". Position of what though? Is it only "objects" that can change position over time? Objects presumably come in two flavours - classical and quantum?

I've never thought about there being no maximum acceleration or frequency! If there's no maximum frequency, one could imagine certain state flipping changes being permissible without consideration of time??

What I write below is not to be argumentative for the sake of it or to try and "win" something. I guess I am taking a philosophical approach and all that and trying to get to the bottom of things, think things out slowly and thouroughly and all that... I'm declaring this as I am aware I have not come across well previously... hmmm, well it would seem to me then, that the most minimal definition of motion would therefore be either "change in position over time", or even "change in position". The latter definition is the more contentious one with you, given that you say that time is necessary for positions to change. But what is time if not defined by change? So is not the use of "time" introducing circularity into the definition?

That's obv a good and proper start, though I am hoping to delve deeper into the matter So some follow up questions 1) Is there such a thing as a "position" which is not "relative"? 2)In terms of a minimal definition, is not "Change in (relative) position" sufficient ... is the "time" bit necessary?

Sure. Motion is not wholly a property of the object and depends on the observer. But it is partially a "property" in the sense that 2 objects generally present different motions to the observer. One has to make a value judgement as to how "directly affecting" a post is. It is my experience from other fora that science topics contain certain technical terms or words that trigger a strong desire on the part of many posters to rattle off knowledge relating to the word without really having read and comprehended a post properly. This is human nature, I spose. (As is some impatience on my part, perhaps). Also, if one is "leading" a thread - even if one is the least knowledgeable - it is not practical to reply to every branching issue . I am probably guilty of having a poor thread title that maybe didn't help the thread get off to a good start .... Seems like a good question! Relative motion is observed, while non-inertial motion is experienced.... maybe??

OK, well I've just read through the first lesson from a series at Cambridge University (get me!!) on concepts of theoretical physics, and been introduced to POLA. Can't seem to post a link, but it's by a Daniel D. Baumann, and it's really well written - my how things have changed since my undergraduate days (maths)! I think I will attempt to work my way through all the chapters as a project. But anyway, the first one deals with POLA. I can see the relevance to motion, and certainly it's very interesting and would seem necessary to a proper grasp of modern physics. In terms of my query - which perhaps can be better phrased as essentially "what IS motion?" - there is still a lot of room for ruminating (including philosophizing on POLA of course ,as alluded to by Strange). But I still want to get my head around motion as a "property" ... objects seem to possess it yet they don't in isolation, because it requires time to be expressed. Contrast this with the property of mass - which you can deduce by isolating and totting up the mass of the constituent particles say. I hope you can see where I can coming from, even if you don't think it is very interesting. P.S. Am I a troll? Well I enjoy a good game of one-upmanship if that's what's on offer. And I do have a thick hide . But no I am not a troll.

hmmm well I studied the calculus of variations many moons ago, and so I will give Studiot's advice a go in the interest of restoring some good faith into this thread. Might take a while for me to swot up ... Meanwhile Studiot thinks I will obtain an answer .... does that mean he knows what it will be ... I ask because if he told me - or dropped hints to a beginner at it - that might be useful....

"Fairly meaningless" ??!!

Such defeatism!

Sorry for not being able to get the multiquote to work for me properly yet, so I have numbered your comments for ease of reference. 1) Yes, velocity is a sort of history of forces acting. But how much detail is there in the history I wonder? Classically speaking, there is only one piece of historic information - the velocity of the (rigid) body. In practice of course, objects aren't rigid; also reference frames are not inertial. One imagines that in practice a moving object is subject to all sorts of microscopic wobbles, waves, pushes and pulls etc as it moves at an approximately constant speed in nearly inertial reference frame. N1L is not true in any real sense, because objects aren't rigid and refrence frames aren't inertial. 2) Any theory of everything and all that must surely explain how macro velocity and quantum scales are related ....??

I have already posted that I was probably misguided linking to "information theory" simply because I am using the word "information". I've accepted my mistake and moved on! Your quoting of Newton was just a restatement of N1L . Your statements about inertia were not focused on helping me in any way, I felt. And now you won't accept my admission of a mistake in good faith.... But I assume you are still interested in the topic as you are introducing Newton's bucket - which I will look at soon. Thankyou.

A refutation might rest on mathematical truth being non-simulatable. The simulators couldn't have one over on us in that respect....

I do know about calculus and limits, honest! The thing for calculus to work is that you DO have the information about motion - in equation form. Objects don't carry equations around with them though, do they?

Zeno I guess...

Calculus is ....errrrrm classical.

I'm not saying they won't be moving in an instant of time! The problem is they are but where is the proof/information etc.... Also I though Zeno was all about repeatedly chopping his step length in half...

But there would seem to be no information "about" motion, only the existence of motion itself. This is at the root of my thinking there is a problem. Mind you - suppose in the future it proved possible to deduce information "about" motion by some means of microscopic examination of matter or space. Does such a supposition invalidate what we know already? (Yeah I know I could say suppose we discover little green men sitting on every atom ... but the former supposition (I daren't call it "my" ) is not quite as wild as that.... Note made re phase space.. thankyou.

When I say "freeze" them I mean take an instantaneous snapshot, so they are still moving. (It is a thought experiment remember!) No I'm not actually thinking about Zeno so far - that paradox is merely a mathematical one.

Thanks for that Strange. OK, well I don't have many ideas - certainly not well formed ones, so I am unable to present a coherent model or theory merely air my thoughts and hope that others do likewise. The "problem" I have is when I think about two rigid spheres that move differently in a perfect inertial reference frame. Conducting a thought experiment ... if one were to freeze each object and examine it in unlimited detail , would I be able to deduce in which direction, say, each object is moving? If I were to examine the space in and around each object would I be able to then? If the answer is no, then what accounts for the difference in motion? If "nothing" accounts for the difference in motion, then the next question is "what does that say about motion...?"

I feel you guys are missing a trick by being so dismissive and unwilling to think about it. I mean, reputable scientists have even speculated that space could be granular and discrete at the quantum level. Quantum weirdness abounds and there are several mysteries - I feel a fresh look at motion might be make for an interesting discussion. Sure motion can be successfully treated as a cut and dried concept in classical physics, but I was hoping to move away from that limited viewpoint.

It's the issue of motion that I am trying to draw attention to. I'm not an information theory specialist - just a layperson. Perhaps my association of "information about motion" with "information theory" is misguided .. but certainly I am puzzled by motion in terms of how it is "coded for", as it were. It seems that the state of motion of an object can only be deduced through observation of that motion, but psychologically at least, this is bizarre and unsettling, I suggest. What is it about the state of matter and or space that "codes" velocity? Has anyone ever considered what motion is at the quantum level?

I seem to have to touched a nerve!