Steve3007 wrote:I think it simply comes down to this concept that David has of "reference frames which misrepresent reality". I think (correct me if I'm wrong) we all agree that in an inertial reference frame the ring is moving relative to that frame, and the light as measured against that reference frame, using a clock and two detectors that are close together, all three of which are stationary WRT that reference frame, will be observed to have speed c. And I think (correct me if I'm wrong) we all agree that an observer riding along the ring, with a clock and a pair of light detectors riding with him and close together, would also measure the speed of light as c. Where David seems to differ is in thinking that one or both of those measurements is, in some sense, "misrepresenting reality". And since he thinks that SR says that reference frames assert things that are asserted to be true for all reference frames (rather than simply being used to make measurements that can be used to devise laws of physics) this is why he claims that SR contains contradictions.
David Cooper wrote:It's very simple. Frame A claims the speed of light relative to objects at rest in frame A is c in all directions. Frame B claims the speed of light relative to objects at rest in frame B is c in all directions. At least one of those claims must be wrong.
If frame A is an inertial reference frame then an observer who is stationary WRT that frame who measures the speed of light by referring to that frame will measure it as c. If frame B is another inertial reference frame then an observer who is stationary WRT that frame will also measure the speed of light with reference to that frame as c. Accurate measurements. Nobody asserts anything. No contradictions.
Steve3007 wrote:The first postulate [that the laws of physics are the same for all inertial observers] is not ambiguous if you understand what laws of physics are. Laws of physics are generalisations created from observing the patterns in measurements which predict future measurements. The first postulate simply predicts that those measurements, and therefore the laws of physics that derive from them, will be found to be the same when measured against any non-accelerating reference frame.
David Cooper wrote:But most people take it to mean that because the speed of light is represented as c relative to any frames, that is the actual physics too.
The first postulate does not mention the speed of light
. Remember: take things one step at a time. The first postulate, as I keep on saying, is simply a generalisation of the Galilean Principle of Relativity.
David Cooper wrote:The more important issue is the absolute frame, and that is necessary to avoid contradictions, unless you're very specific about which model you're using...
Forget all the supposedly different models for now. Make sure you know the pre-SR basics. If we don't agree about those, and we don't agree what words mean, and we don't agree as to what a law of physics is, there's no point trying to discuss the finer points of a specific example of one of those laws of physics.
David Cooper wrote:If one frame says something is stationary and another says it's moving, it is clearly impossible to tell whether something is moving or not, so your objection to that one is frankly ridiculous.
Steve3007 wrote:Which is perhaps one reason why frames don't say that. Movement is defined as the change in the spatial distance between two objects with respect to time. So, if you use the correct definition of the word "moving", clearly we can work out if we're moving.
David Cooper wrote:Frames do say that. You can measure movement in any way you like, but if something is not moving in one frame (no change in spatial distance between itself and any other object at rest in that frame) and is moving in another (with a change in spatial distance between other objects which are at rest in that frame), then we have contradictory claims from different frames about whether the object is moving or not, and we can't tell which one is wrong.
No we don't. We have an object that is moving with respect to one frame and not moving with respect to another. Your characterisation of this as "contradictory claims" seems truly mad. If I am driving a car and I find myself to be not moving with respect to the car but moving with respect to the Earth, I am not "making contradictory claims"! Yet that is what you're saying here.
Steve3007 wrote:If, for the sake of brevity, you don't make that clear in your explanation it wouldn't be so bad if it wasn't for the fact that you build on that omission rather than explaining it.
David Cooper wrote:The fact of it is that you can't tell if you're moving or not in an absolute sense unless you have an absolute frame...
you postulate the existence of an aether and if
you further postulate that it's impossible to measure the velocity of that aether with respect to any other object, then
you can't tell if you're moving with respect to that aether. If that's what you mean by the above, then maybe there's at least something that we agree on. But I'm not holding my breath.
...That doesn't mean that there isn't an absolute answer known only to that absolute frame...
It sounds like you're talking about a God-like concept again. The absolute frame moves in mysterious ways that it is not for us to know.
...SR ordinarily denies the existence of an absolute frame, but you claim it's open to the idea,...
Where did I say that?
Steve3007 wrote:I would have read his [Einstein's] words in context, bearing in mind the physics that went before him and the empirical nature of physics. If he simply said "you can't tell if you're moving", since I know that statement, taken in isolation, is demonstrably untrue, I would ask him more about what precisely he means by it.
David Cooper wrote:It is not demonstrably untrue - it is demonstrably true. You cannot tell if you're moving because there's always a frame that says you aren't, and it could be right.
Given the standard definition of movement (change in the position of one object relative to another with respect to time) you can tell if you're moving. As I said, given that definition I would ask Mr Einstein what he meant. He would then tell me that what he was referring to was the old Galilean idea that the laws of mechanics, and the measurements from which they are derived, are invariant when measured against different inertial reference frames.
Steve3007 wrote:A few pages ago, when I asked you some simple questions about it, here:
in your answers here:
you either didn't answer the questions or answered them wrongly.
David Cooper wrote:I answered them correctly. You just don't like my correct answers because you prefer your incorrect ones which are informed by a broken theory.
Since the above is self-evidently false, there's nothing more I can really say here. All I can do is point you again to the standard definitions of words such as "acceleration" and "velocity".
Steve3007 wrote:This seems odd because they're simple questions. Question 1, for example, could be on a high school Physics exam. But rather than simply giving the obvious answer you started going on irrelevantly about how "the universe supports only one underlying reality".
David Cooper wrote:It's called precision rather than regurgitation of dogma. The answers that you want to hear are the ones based on shackled thinking rather than free rational thought.
It's not "shackled thinking" to simply recognise the definitions of the words "acceleration" and "velocity", to recognize that they are vectors and to know how to add two vectors together.
Steve3007 wrote:This rings alarm bells for me. Maybe you somehow just misunderstood what the question was asking. But I don't see how. I tried to make it as plain and unambiguous as possible. It was a question about how a ball, thrown upwards, moves just after it leaves the hand that throws it.
David Cooper wrote:Your question has a bias built into it that you cannot see because of the way you've been trained...
What bias? A bias towards the standard definitions of words in physics?!?
Maybe you somehow think it's a trick question? It's not! It's just about the most straightforward question in mechanics that I could possibly ask! Think about it. Suppose when the ball leaves your hand it's travelling at a velocity of 50 ms-1
, straight up, relative to the surface of the Earth. Do you accept that as a possibility? (I'm learning to take nothing for granted about the way that you think.) Now suppose that the acceleration due to gravity near the Earth's surface is 10 ms-2
, rounded to the nearest whole number. What will be the ball's velocity, relative to the surface of the Earth, after 1 second? After 2 seconds? What will the magnitude and direction of the ball's acceleration, relative to the surface of the Earth, be?
Again, this is not a trick question. There is no hidden agenda.
...If you say that the ball decelerates, you're assuming a particular frame to be the absolute one, but you don't know it to be the absolute frame, so saying that the ball decelerates is an assumption based on something that may be an error...
No I am not assuming that. In the above example, what is the speed
(note: I said speed, not velocity) of the ball, relative to the surface of the Earth, after 1 second? After 2 seconds? What is the definition of the word "decelerate"? Now: Is the ball decelerating with respect to the Earth? Is its speed relative to the Earth reducing?
No tricks. No agenda.
...I'm not going to make a stupid mistake of that kind, but you think I should in order to conform to the stupidity you're pushing. I reject that stupidity. I do not give absolute answers to questions which I can't give absolute answers to without being able to measure the absolute, and the fact that you expect me to do reveals a massive error in your thinking.
Steve3007 wrote:Do you accept that an object in free fall in the Earth's gravitational field is accelerating towards the centre of the Earth and can be moving upwards (have its velocity vector pointing upwards), with its speed (the magnitude of its velocity) decreasing?
David Cooper wrote:Yes. If you want to word things that way, I have no problem with that. It doesn't make my way of wording things wrong.
?!? After all that talk of the "stupidity I'm pushing", you suddenly agree? How else would you word it?
Steve3007 wrote:Do you accept that any object moving in a circle, at constant speed, is, by definition, accelerating towards the centre of that circle?
David Cooper wrote:Yes, but I don't let that blind me to the fact that it could also be decelerating in an absolute frame (which is something you want to ban people from realising).
I don't want to ban anyone from anything. Obviously if the centre of that circle is itself moving relative to some other reference frame, then the orbiting object, in addition to accelerating towards the centre of the circle, is also moving relative to that other reference frame.
Steve3007 wrote:Original question (paraphrased):
1. If I throw a ball upwards, neglecting air resistance, as soon as it has left my hand, is it accelerating, deccelerating or both?
David Cooper wrote:The correct answer is not dependent on the coordinate system you're using, so the answer c is wrong. The correct answer depends on whether it's accelerating, decelerating, or doing one followed by the other, and that depends on its movement relative to the space fabric.
Steve3007 wrote:No. the correct answer is by definition that acceleration is the rate of change of velocity with respect to time, which means that it can result in the magnitude of the velocity increasing, reducing or remaining the same. If the magnitude of the velocity remains the same, but there is still a non-zero acceleration, then the direction of the velocity is changing and the two vectors are perpendicular to each other.
David Cooper wrote:The correct answer is the one I gave you. You asked an absolute question and I answered it on that basis...
I asked you a question about a person throwing a ball while standing on the surface of the Earth. I said something about the velocity of that ball when it leaves the thrower's hand. I said it was "straight up". Are you really telling me that you didn't realise I was talking about the velocity relative to the Earth?
...Your inclusion of the word decelerating also implies that your usage of the word acceleration there excludes cases where something is decelerating...
No it doesn't. Acceleration is by definition
rate of change of velocity WRT time, where both are vectors. Deceleration is by definition
reduction in speed. A change in velocity can result in speed increasing, staying the same or decreasing. These things are true by definition
...If you want your answer to be the correct one, you need to frame your question with greater care and spell out the definitions of the words you're using in it wherever they go against normal usage....
I was using all words according to their normal usage in physics. I was under the impression that we were having a discussion about physics.
...If told you before that the differences between our answers come down to one simple thing - you're asking absolute questions and demanding SR answers (i.e wrong answers) while I'm giving LET answers (i.e. correct ones), and I'm giving you LET answers because SR is broken and should not be given precedence over a rational theory that works.
I'll tell you again: this is nothing to do with SR or LET. It is pre-SR and pre-LET. It is part of the building blocks that you need in order to start tackling those subjects.
Steve3007 wrote:So an acceleration vector pointing in the opposite direction to a velocity vector means that acceleration is a deceleration, if we define "deceleration" as reduction in speed, which seems reasonable.
This is basic, basic stuff which comes before SR or LET.
David Cooper wrote:It is basic stuff, but if you keep asking absolute questions without realising that that's what you're doing, you're going to keep tripping up. You're mistaking your communication failures for mistakes in my understanding of physics - that is the root of your problem here...
I really wish that were true and we could establish that we've covered the basics of Newtonian mechanics so we could move on to SR and LET. But most of the evidence I've seen so far suggests otherwise.
...Did you ever bother to click through to my reference-frame camera program (from my relativity page)? Anyone who spends a few minutes exploring that should realise that it can only be put together by someone who really knows their stuff...
Then show me you know your stuff with your words.
...You're searching in the wrong direction. What you should be doing is defining your SR models and showing where they fit in with the ones I've identified. Then we can discuss each one in turn and I'll show you that every single one of them is broken. I can understand that you want to avoid going there, but that is what the invitation here is. If you're sure you have a model that stands up, why delay going straight for the kill. All I ask of anyone is to show me a working model of SR, but by heck it takes a lot of work to drag them towards that, and NONE of them can deliver.
No, we're nowhere near
Steve3007 wrote:There's nothing "non-genuine" about a non-inertial frame....
David Cooper wrote:There is. In the gravitational case they're fine, but when an object is actually accelerating, a non-inertial frame continually asserts that the speed of light relative to it in all directions is c, and that's a continual contradiction with the previous moment. Such frames are not valid in that they are automatically misrepresentations of reality.
And here is another example of the reasons why we're nowhere near it.
Steve3007 wrote:For future reference: Please don't tell me what I'm seeking to do.
David Cooper wrote:You are playing word games, and I will call that out every time you do it.
As I said: Take what I say literally and do not assume that I mean various different things that I didn't actually say. If I use a word and don't define it, assume I'm using that word in accordance with its standard definition in physics, because that is the subject we're discussing. If I talk about a person standing on the surface of the Earth throwing a ball upwards, then obviously I mean upwards relative to the surface of Earth, not relative to the surface of Venus or some kind of aether. If you still insist on telling me what I'm seeking to do, then it's not "calling me out" it's simply not reading what I said. If you're not going to read what I'm saying, there's really no point in trying to continue communicating with you.
Steve3007 wrote:When I ask a question I am seeking to get from you an answer to that question, as it is stated. Nothing more.
David Cooper wrote:You are applying a bias to them which you don't recognise.
And, of course, I can assert the same of you. And we'll get nowhere. Is that how you want the conversation to end?
Steve3007 wrote:I asked you if you accept the fact that velocity and acceleration are vectors. This is because I am seeking to know whether you appreciate that velocity and acceleration are vectors. If you don't, then it's really difficult to discuss any aspect of physics because we don't speak the same language as each other. I'm just trying to establish whether we speak the same language.
David Cooper wrote:And you're doing this because...?
For the reason I gave you in the words of mine that you just quoted! You give a very, very good impression, in your words, of someone who is muddled about these things. I wanted to give you a chance to prove my impression wrong.
...Why are you wasting time on that? It all came out of one little phrase which was transitioning from one idea to another one, momentarily mentioning acceleration and deceleration (but without that contrast being important to the discussion), and moving on to something much more clear cut involving the ticking of two clocks where both are asserted to be ticking faster than the other. So what do you do? You ignore the clocks, and fixate on the acceleration vs. deceleration issue instead. It is actually relevant, but it would be very hard for you to see how given the depth of your indoctrination. You've been taught that something can be accelerating and decelerating at the same time, and it would take a lot of work to deprogram you on that point, which is why I'm not going to bother trying. The ticking rate comparison is much harder to cover up through brainwashing though, because someone who believes that clock A can tick faster than clock B while clock B ticks faster than clock A is manifestly certifiable.
David Cooper wrote:By one very specific definition of the word, yes. It isn't necessarily a real acceleration though just because it's been given a label with a misleading name.
Steve3007 wrote:A label with a misleading name?!?!? This, perhaps more than any other answer, appears to me to demonstrate you lack of grasp of basic physics that it is essential to grasp if you're going to tackle more advanced subjects like SR and LET.
(This was exactly
the kind of example which led me to conclude that you're confused as to what acceleration is and what a vector is.)
David Cooper wrote:That's where you keep repeating the same mistake. You want me to answer absolute questions in a biased way which accepts SR and rejects the absolute frame...
I'll say it yet again: this has nothing to do with SR. It's pre-SR. There is nothing in the standard definition of the word "acceleration" that rejects that concept of an aether.
...I'm not going to let my brain function on such a bias - not for you, and not for anyone. Reason dictates that there must be an absolute frame (in some models) in order to remove the contradictions, and you want me to abandon reason...
In showing me that you accept the standard definition of the word "acceleration" I am not telling you to abandon the concept of aether. If you were clear as to what the word means, I would have thought you'd know that.
...You want me to parrot mantras from a religious cult instead of doing physics properly. Your cult has given its own definition to a word which I, as someone who is not a member of that cult, refuse to endorse. You are fully entitled to use the word the way your cult uses it and I do not question your understanding of physics on the basis that you do so. I am likewise entitled to use the word my way, and as it's the way that normal people outside of the cult use it, it should not be hard to understand...
So, to be absolutely clear on this point: You think that defining acceleration as rate of change of velocity with respect to time, and defining both of them as vector quantities is a "mantra from a religious cult"?
...When you ask absolute questions, I don't apply the unstated bias that you imagine onto it - I answer the actual question that's been asked. The difference between my answers and the ones you want does not reveal a lack of understanding of the physics on my part, but is actively driven by my understanding of the physics and my rejection of your cult. I am in the LET camp, and we have an absolute frame. When we talk about deceleration, we ruddy well mean a deceleration (where kinetic energy is actually being lost rather than gained). Otherwise, we're merely dealing with apparent deceleration.
Steve3007 wrote:It is true by definition of the words "acceleration", "velocity" and "circle" that an object moving in a circle has an acceleration vector which points towards the centre of the circle. This a function of the definitions of those words. It's not specific to any individual aspect of physics that we might be discussing. Please tell me that I've misinterpreted you and you understand this bit of basic physics and geometry! If not, as I've said, we have no language in common in which to communicate.
David Cooper wrote:It should be obvious from my answers that I don't accept your definitions as absolute ones. There are alternative ones which are preferable because they are more logical, and you should expect me to use those as standard. Your usage of some words puts a bias into them which allows you to frame things as absolute statements which are logically incorrect by the more rational definitions of the same words and which make precision harder. Your definitions actively warp your ability to understand what you're describing because of their inherent bias.
Yes, I'm starting to realise the full extent to which we don't speak the same language.
Steve3007 wrote:Regardless of whether you think there is such a thing as aether, movement is by definition a function of the relationship between objects.
David Cooper wrote:Movement (in the absence of any wording relating what it's relative to) is by definition movement relative to the absolute frame. You're using a biased definition in which the existence of the absolute frame is denied.
Nope. As I've said, you're more than welcome to talk about movement relative to an aether.
Steve3007 wrote:If you think there is such a thing as aether then the sentence is rendered meaningful by changing it to: "object A is moving at 5 m/s relative to the aether". And, like any proposition in physics (or science generally) that proposition, to be meaningful, needs to be empirically falsifiable/verifiable, either directly or indirectly. i.e. you need to show how that statement is useful for describing and predicting possible observations.
David Cooper wrote:It is meaningful in physics because not having an absolute frame generates contradictions and invalidates the model. Again though, instead of arguing over linguistics, you should be setting out your SR models and telling me where they fit into my set of models, or where you want to put them if you think they don't fit in my set. Then we can take each one in turn and demolish it.
I'm close to giving up now.
David, based on our conversation so far, I think we're going to have to leave it. Not because we disagree about Special Relativity. We haven't go that far yet. You don't appear willing to accept the standard definitions of basic words. If you just keep refusing to do so, then we quite literally don't speak the same language. So I'll just have to say it's been ... interesting and leave it there. I presume you'll want to chalk this up as some kind of victory over some kind of dogma (the dogma of words having agreed definitions, I guess). Be my guest.
All the best.