On Thursday, January 30, 2025 at 1:33:09 PM UTC-7 Alan Grayson wrote:
On Thursday, January 30, 2025 at 11:55:54 AM UTC-7 Jesse Mazer wrote: On Thu, Jan 30, 2025 at 1:35 PM Alan Grayson <agrays...@gmail.com> wrote: On Thursday, January 30, 2025 at 11:16:52 AM UTC-7 Jesse Mazer wrote: On Thu, Jan 30, 2025 at 12:47 PM Alan Grayson <agrays...@gmail.com> wrote: On Thursday, January 30, 2025 at 10:28:05 AM UTC-7 Jesse Mazer wrote: On Thu, Jan 30, 2025 at 11:59 AM Alan Grayson <agrays...@gmail.com> wrote: On Thursday, January 30, 2025 at 9:38:19 AM UTC-7 Jesse Mazer wrote: On Thu, Jan 30, 2025 at 11:05 AM Alan Grayson <agrays...@gmail.com> wrote: On Thursday, January 30, 2025 at 7:59:32 AM UTC-7 Jesse Mazer wrote: On Thu, Jan 30, 2025 at 9:16 AM Alan Grayson <agrays...@gmail.com> wrote: On Thursday, January 30, 2025 at 6:48:21 AM UTC-7 Jesse Mazer wrote: On Thu, Jan 30, 2025 at 12:51 AM Alan Grayson <agrays...@gmail.com> wrote: On Wednesday, January 29, 2025 at 6:52:47 PM UTC-7 Brent Meeker wrote: Whooo! Hoooo! Brent Another fool who doesn't get it? Another fool who can't think out of the box? Jesse claims that the LT preserves what it predicts for local events AND, according to his lights, using the LT it can be shown that lengths are EXPANDED. OTOH, it's universally predicted that lengths are CONTRACTED under the LT. No, it's universally predicted that length in a frame where an object is *in motion* (coordinate-motion using the term I coined in my previous comment, to distinguish from your alternate non-standard usage which I called 'designated-motion') is contracted relative to that object's "proper length" in the frame where the object is *at rest* (coordinate-rest), the L in the length contraction equation is always stated to be the proper length. So, if you use the LT to transform FROM the frame where the object is in motion (coordinate-motion) TO the frame where the object is at rest (coordinate-rest), treating the coordinate-motion frame as what you call the "source frame" and the coordinate-rest frame as what you call the "target frame" for the LT, in this case the length should be contracted in the source frame and larger in the target frame, *So, after our exhausting discussion, you still have no clue what I meant by source and target frames.* So "source frame" doesn't just mean the frame whose information we are given to start with (i.e. given coordinates values of length/velocity etc. for the objects we are analyzing) before applying the Lorentz transform to predict coordinates in the "target frame", i.e. it's not just that source=unprimed and target=primed in your description of the LT as giving us x-->x' and t-->t'? If that's not what you meant by "source" and "target", fine, but that's just a linguistic matter, you can delete all references to "source frame" and "target frame" in my comment above and change it to "starting frame" and "predicted frame" or whatever terminology you want to use for this; it changes nothing about the substantive point I was making. * I never said anything about a LT from a frame where the object is in motion. I alway stated I was transforming FROM a rest frame to a moving frame.* But you made a big deal of the fact that a ruler isn't measured as contracted in its own frame (and a clock isn't measured as running slow in its own frame), claiming this shows a divergence between what is PREDICTED by the LT and what is MEASURED. If you aren't actually using the LT to make PREDICTIONS about what should be true in the ruler's own frame (the frame where the ruler is in a state of coordinate-rest), i.e. using the ruler's frame as what I called the 'predicted frame', then how can this example be used to show a divergence between LT predictions vs. measurements? So you have no response to my comment above? If not, I can only conclude that your earlier emphasis on the point about what was measured in the ruler's own frame was completely incoherent since you don't actually want to use the LT to predict anything about the ruler's own frame. * Is there any textbook which makes your claim? I've never seen it, or heard about it, or hinted about it, and for this reason I ignored your mathematics. AG* I don't know that any textbook would go to the trouble of saying something like "the length of an object may be larger in the primed frame than the unprimed frame when you use the Lorentz transform to go from unprimed to primed", but I promise you that no textbook will say anything like "applying the Lorentz transformation to go from unprimed to primed always results in the length of any object being shorter in the primed frame than the unprimed frame". The only real reason to say something like the former would be to dispel a misconception like the latter, but I doubt this is a common misconception, I've talked to plenty of people who are confused about relativity on various forums over the years and never come across this idea of yours. If I looked around a bit I could probably find numerical examples in textbooks where just looking at the coordinates they give for some object in the unprimed vs. primed frame (or whatever notation they use to distinguish coordinates in the 'starting frame' from the 'predicted frame'), you could verify that the object was longer in the primed than it was in the unprimed. And no response to this? Are you secretly afraid that I would actually be able to find textbook examples like this where the length of some object is greater in the primed frame than the unprimed frame? *No. Go for it. I'm sure you'll find what I am about to write. While I agree that either frame can be considered moving since inertial motion is relative, the LT is NOT applied from the frame considered moving, and predicts length contraction in the moving frame, from the pov of the rest frame.* Most textbooks do not designate one frame as "moving" and one as "at rest" in the first place (they use only the terminology I called 'coordinate motion', not 'designated motion'--let me know if you have any trouble understanding this distinction), they just use labels like primed and unprimed for the two frames, and give both x --> x' equations that tell you coordinates in the primed frame if you start with coordinates in the unprimed, along with the corresponding x' --> x equations that tell you coordinates in the unprimed frame if you start with the primed. So while a typical textbook won't give an example where length is said to be greater in "the moving frame" since they don't use that terminology in the first place, they definitely would give examples where length is greater in the primed frame than in the unprimed frame, presumably including cases where this is accompanied by a spacetime diagram where the unprimed frame is the one with the vertical t axis and the primed frame is the one with the slanted t' axis (i.e. showing the spatial origin of the primed frame as moving in the coordinates of the unprimed frame). Do you disagree with any of the above? If so I can look for examples, both showing that typical discussions of the LT don't include any phrase like "moving frame" and that they give both x --> x' equations and x' --> x equations side by side, and also examples where the length of some object is greater in the primed frame and there's a spacetime diagram like what I described. Jesse *Frankly it's too tedious to read.* Hah, I guess claiming that a single short paragraph is "too tedious to read" is a good way to rationalize not addressing the simple question of whether I should look for textbook examples to back up my point that "typical discussions of the LT don't include any phrase like 'moving frame' and that they give both x --> x' equations and x' --> x equations side by side, and also examples where the length of some object is greater in the primed frame and there's a spacetime diagram like what I described" [where what I described was a diagram showing the the primed frame as moving relative to the coordinates of the unprimed frame]. I think you are desperate to avoid answering whether I should give textbook examples like this because saying "yes, go look for them" would leave open the scary possibility that I would find them and thus show a VOICE OF AUTHORITY who contradicts you (since you were unwilling to judge my own numerical example for yourself, citing a supposed disagreement with textbooks), and saying "no, even if textbooks do say that it wouldn't contradict me" would force you to acknowledge points like "textbook authors don't bother designating either frame as 'moving'" and "the length of an object can be greater in the primed frame even when we illustrate the primed frame as moving". So it's kind of a double bind for you, no wonder you squirm so much when I press this question. *I'm not desparate. Not in the slightest.* Then why do you keep avoiding answering my question of whether I should look for textbook examples of what I say above, or if you say that such examples would not actually be in conflict with your understanding of SR? * Although I seem to recall phrases like "moving frame" and "rest frame", I can easily live with this or that frame in relative motion, such that the V **in the gamma factor can be applied to it. In the final analysis, our core disagreement is not about terminology, but what the LT predicts, and I claim that whichever frame has a non-zero V is applied to it, lengths will be contracted in that frame. AG* When you say "whichever frame has a non-zero V is applied to it", is this just a way of talking about which frame's coordinates we start with initially and which frame's coordinates we then predict using the LT, with the second "predicted frame" being the one you're talking about when you refer to applying a non-zero V to one frame? If that's not what you meant, then I'd be unclear about what "whichever frame has a non-zero V" means, since in relative terms if frame B has nonzero velocity V in the coordinates of frame A, that always means that frame A has nonzero velocity -V in the coordinates of frame B. * But I have no objection to reversing the frame which is considered moving, * Do you have an objection to NOT CONSIDERING ONE FRAME AS "MOVING" IN THE FIRST PLACE, which as I said is not a designation that typical SR textbooks make at all when discussing the LT? (and again, just say the word and I will look for textbook explanations of the LT that make no statements that designate one frame as 'moving' and the other at 'rest', I can give you screenshots of pages and everything) *Fine. I am OK with speaking as motion of one frame relative to another, and reversing the frames from which the LT is applied. Why do you refuse to take YES for my answer? AG * I'm not "refusing to take YES for an answer" since this is the very first time you offered to drop the idea of designating one frame as "the moving frame" and the other as "the rest frame" and just use comparative phrases about the motion of one frame/object relative to another. But if you are willing to do this, does that mean you are also willing to consider an example where we start with the unprimed coordinates of a frame where a rod is in motion (i.e. its x coordinate is changing with the t coordinate in the unprimed frame), and then use the LT to go to the primed frame where the rod is at rest? (i.e both ends of the rod have x' coordinates that don't change at different values of the t' coordinate) If so, would you still claim the LT would give the prediction that the rod is SHORTER in the coordinates of the second primed frame than in the coordinates of the first unprimed frame? Jesse *If you use the gamma factor to determine length contraction, then the V in the gamma factor means the LT is making a prediction of the frame in relative motion. You can do the LT in reverse since Inertial motion is relative. BUT if you want to assume the reverse transformation FROM a frame now magined in relative motion, the predicted value in the frame which is the image of the LT has a relative motion of ZERO, or V=0 in the gamma factor, which implies no length change in that frame. So, both frames show no length contraction under the scenario you posit. AG* *BTW, relative motion means either frame can be considered in motion, but not both at the same time. I think this is where you're making an error. AG* *that is, if you want the V in the gamma factor to have any meaning, but the result will be as I have claimed; an object at rest in the frame considered moving will be contracted in length from its rest length in that moving frame (obtained by setting V=0 in the gamma factor). Otherwise, you've turned SR upside down and unrecognizable. AG* It's only unrecognizable to the confused version of SR in your head, actual physicists don't see any need to have one frame that's "considered moving" and another that's "considered at rest", they get along fine with purely comparative phrases like "A is moving relative to B" and "B is moving relative to A" without any need to "take sides". *I am not confused. I thought my language was clear, but I am comfortable changing it as you insist. But the result will be as I claim, not as you claim. AG* Jesse * And x ---> x' refers to a LT from the rest frame to the moving frame. If you want to reverse this process, and change which frame is moving and which is at rest, unless what all the textbooks and lecturers claim, the predicted result is length contraction in the frame considered moving. And, I should add, this situation present another apparent paradox which is presumably solved by appealing to disagreement about simultaneity. AG* *Since the primed frame is the moving frame, if that were true, then SR wouldn't predict length contraction! AG* Here you seem to be using your particular terminology of "moving" which I have called "designated-moving" (where you just designate one frame as 'the rest frame' and the other as 'the moving frame' and refer to them that way throughout the problem) which is distinct from the more standard comparative terminology which I called "coordinate-moving" (for example, to make the comparative statement 'the rod is moving wrt the Earth frame' would mean that in terms of the coordinates used by the Earth frame, the rod's position coordinate changes with coordinate time, and we could also make the symmetrical comparative statement that 'the Earth is moving wrt the rod frame'). Did you read my earlier post where I spelled out the difference, and also pointed to statements of yours that would make no sense if interpreted in terms of coordinate-moving? As I said above, the Lorentz contraction equation is comparing proper length L in the frame where the object is at coordinate-rest and giving the contracted length in the frame where the object is in coordinate-motion; which frame you DESIGNATE as "at rest" or "moving" is irrelevant. In particular, note that it is perfectly possible to have a scenario where the frame where an object is at coordinate-rest is the one we DESIGNATE as "the moving frame" (designated-moving), since these designations are completely arbitrary, like designating one frame as "Fred" and the other as "Barney". These designations should have no effect on any of our physical conclusions about the two frames, or on how we do our calculations (for example, there is no obligation to use the LT to go FROM the designated-rest frame and TO the designated-moving frame, you can just as easily go FROM the designated-moving frame and TO the designated-rest frame). There's nothing wrong per se with designating one frame as "the rest frame" and the other as "the moving frame" as a matter of linguistic convenience (Einstein did this at one point in his very first SR paper, though I think it's much less common with physicists nowadays), but if you think this merely verbal designation can have any effect whatsoever on actual predictions about physical quantities like length in one frame vs. another, or on the calculations to generate those predictions, it's obvious you have become totally confused by your own terminology. Jesse -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/everything-list/05ed9d95-765a-4806-96d3-cbb57e112f88n%40googlegroups.com.
