And now jesss, you don't understand English 🤔🙃🤣 What's the goal here ? You know, I know, everybody here knows, that will lead nowhere, there is nothing to win here other than losing precious seconds of your life to a stupid person.
Le mer. 29 janv. 2025, 20:54, Alan Grayson <[email protected]> a écrit : > > On Wednesday, January 29, 2025 at 11:06:18 AM UTC-7 Jesse Mazer wrote: > > On Wed, Jan 29, 2025 at 12:37 PM Alan Grayson <[email protected]> wrote: > > On Wednesday, January 29, 2025 at 9:23:31 AM UTC-7 Jesse Mazer wrote: > > On Wed, Jan 29, 2025 at 3:30 AM Alan Grayson <[email protected]> wrote: > > On Wednesday, January 29, 2025 at 12:24:33 AM UTC-7 Jesse Mazer wrote: > > On Wed, Jan 29, 2025 at 1:24 AM Alan Grayson <[email protected]> wrote: > > On Tuesday, January 28, 2025 at 9:01:14 PM UTC-7 Jesse Mazer wrote: > > On Tue, Jan 28, 2025 at 8:54 PM Alan Grayson <[email protected]> wrote: > > On Tuesday, January 28, 2025 at 2:56:32 PM UTC-7 Brent Meeker wrote: > > On 1/28/2025 6:49 AM, Alan Grayson wrote: > > I figured you'd jump on my word "separation". You have no idea what I > mean? Of course, events with different coordinates are separated in a > physical sense. Otherwise they'd have the SAME coordinates! But separated > wrt spacetime events means no causal connections; whereas timelike events > DO have causal connections. Of course, you know this, so please stop > splitting hairs to make an argument. As for relative velocity, if you don't > know what I mean, then you don't know what the v means in the gamma > function. Again, stop splitting hairs. Oh, about GPS, I will look up this > issue, but I was informed of it from a Ph'D in physics from Brent's Ph'D > alma mater, University of Texas at Austin. It's surely NOT a distraction if > it establishes that results in SR are physically real, not just > appearances. AG > > > There's an unfortunate but common confusion. The un-intuitive aspects of > special relativity are physically real, but not it the sense that they happen > to the moving object. If SR predicts length contraction, is the object is > really shorter? (1) It's really shorter in the reference frame where it's > moving. (2) It's not shorter in it's own frame. And (3) it's a different > degree of shorter in other reference frames where it is moving with > different velocities. Just looking at (2) people assume that it means (1) > and (3) are just appearances. What's true is that > > *the contraction, relative to things in some reference frame, with respect > to which it's moving, is real. *Brent > > > *It's a baffling result. The LT doesn't tell us what will be MEASURED in a > moving target frame being observed from a rest frame wrt length contraction > and time dilation, so the result is just an APPEARANCE from the pov of the > rest frame; and yet, from the pov of GPS clocks, these effects are real and > measureable. This was the conclusion I argued, which is why I referenced > the GPS clocks. * > > > Brent's comment wasn't saying there was any disagreement between what > coordinates the LT predicts for a given frame and what is really true (or > really measured) in that frame, just like I wasn't saying that (see my last > response above). You're really deluding yourself by rushing to read every > explanation people give you as confirmation of your pre-existing fixed > opinions. > > Jesse > > > IMO you're deluding yourself in one important respect; your insistence > that the results of the LT from the pov of some rest frame predicting > length contraction in a frame moving wrt to it, can be measured in that > moving frame; > > > This statement is hard to follow because you ignore the distinction I made > between frames and objects-- > > > *I can't help you if you refuse to use your imagination. A rod or any > object moving wrt a fixed source frame using the LT, or an object in moving > frame at rest in that frame when the LT is applied from a fixed source > frame, will be predicted as contracted. Period. AG* > > > Your idiosyncratic way of talking is very hard to follow, > > > *One frame moving and another at rest is very very very hard to > understand? AG* > > > I don't really understand the phrase "an object in moving frame at rest in > that frame when the LT is applied from a fixed source frame". > > > *Again, very very very hard to understand? AG* > > > Can you please just use my terminology of v_rs representing the velocity > of the rod in the source frame's coordinates, and v_rt representing the > velocity of the rod in the target frame's coordinates? What I'm asking > about is a scenario where v_rs is nonzero in the source frame's > coordinates, then we use the LT to predict the coordinates of the > worldlines of the front and back of the rod as defined in the target frame, > and get the result that in the target frame the rod has v_rt = 0 so it's at > rest in the target frame (i.e. both front and back have position > coordinates which don't change with time in the target frame). If we then > calculate the predicted length of the rod as defined in the target frame > (where 'length' just means subtracting the position coordinate of the back > of the rod from the position coordinate of the front), are you saying it > will be predicted to be CONTRACTED compared to the length as defined by the > original coordinates of the source frame? > > > > > if we have some object whose length we want to talk about, and we know the > coordinates of the worldlines of the front and back of the object in the > first (source) frame and then use the LT to predict its coordinates (giving > us its length) in the second (target) frame, you can't make any general > statement about whether the LT will be "predicting length contraction" of > the object until you know the velocity of the object itself in each frame. > If the object has a higher velocity v_rt in the target frame than its > velocity v_rs in the source frame, the LT will predict the object will be > contracted in the target frame; on the other hand, if the object has a > lower velocity v_rt in the target frame (including the case I analyzed > where v_rt = 0) than its velocity v_rs in the source frame, the LT will > predict the object is EXPANDED in the target frame, not contracted, > compared to its length in the source frame. In the past you disagreed with > this, do you still disagree or have you changed your mind? > > Please give a clear answer on this, telling me whether you now AGREE or > DISAGREE that when the rod has v_rt in the target frame lower than its v_rs > in the source frame, the LT predicts the rod's length in the target frame > is expanded, not contracted. And if you disagree, please address the > questions I asked in my last reply to you (the one before my reply to your > comment on Brent's post). > > > *The target frame is moving wrt the source frame. Objects in the target > frame are at rest within that frame,* > > > More verbal confusion here, > > > *If you claim you don't understand my statement, you're either lying or I > can't help you to understand what I consideer to be a simpe statement. A*G > > > No, in this case I didn't say I had any trouble understanding your > statement, > > > *Then re-write it consistent with your preferred "standard terminology" > style. AG * > > what I was concerned with was that your terminology here might be leading > YOU to misinterpret MY previous statement "its length in the source frame", > since you were using "within that frame" to mean at rest in a frame but I > was using "in" a frame just to mean "expressed using the coordinates of > that frame" without presupposing the object is at rest in that frame. So, I > asked you to tell me what terminology you would prefer for my own statement > to avoid any potential for confusion between these two meanings of > within/in. > > As for the other statements of yours that I did have trouble understanding > because it was unclear whether you were using "moving" and "rest" in the > standard way or your own non-standard way (and why you seemed to suggest > the question of whether one frame is 'moving' would have any bearing on the > answer to my physics question, when I had thought that even in your own > terminology the choice to label one frame as 'at rest' and the other > 'moving' was purely intended to be a linguistic convention with no physical > significance), if you don't know how to translate them into statements > about coordinate velocity/coordinate length as I asked, then that implies > they are "not even wrong" as statements about SR, since as I said all SR > statements about velocity/length are understood to be purely shorthand for > such coordinate statements. (Do you disagree that this is how physicists > understand such statements?) > > > *This is getting tedious, very tedious. You don't seem to understand > simple English. In another very recent post of mine which you ignore, I > clearly established your error in interpreting what the LT implies when it > is applied in fixed frame, calculating what it predicts for measuring > lengths in a moving frame. AG* > > > Jesse > > > > when I said "its length in the source frame" I just meant the coordinate > length assigned by the source frame, whereas your last comment "Objects in > the target frame are at rest within that frame" seems to say you are using > "within that frame" to specifically mean a velocity of zero using the > frame's coordinates. If you don't like my wording, just tell me what > wording YOU would prefer for talking about the coordinates assigned to an > arbitrary object by a given frame, regardless of whether it has a velocity > of zero relative to that frame or not. For example if the source frame uses > unprimed coordinates x and t, and the position as a function of time for > the back of the rod as defined in the source frame is x = 0.8c*t while the > position as a function of time for the front of the rod is x = 7.2 + > 0.8c*t, then at any given value of t in the source frame the coordinate > distance between the x-coordinate of the front and the x-coordinate of the > back will be 7.2, so that is what I meant by "its length in the source > frame" even though the rod is not "at rest within that frame" according to > your terminology. (I would also say in this case the rod's velocity in the > source frame is 0.8c) Is it OK with you if I continue to say things like > "its length in the source frame" or "its velocity in the source frame" to > refer to coordinate judgments like this, and if not what wording would you > prefer? > > > > * and contracted according to relativity. One can also consider a moving > rod as the frame AND the object under consideration. This is how to model > and analyze a shortened trip to Andromeda. If you have a better way to > model it, I am all ears. AG* > > > You didn't answer my straightforward question: "Please give a clear answer > on this, telling me whether you now AGREE or DISAGREE that when the rod has > v_rt in the target frame lower than its v_rs in the source frame, the LT > predicts the rod's length in the target frame is expanded, not contracted". > Keep in mind that a lower v_rt in the target frame could include the case > we were discussing where the rod is at rest as measured in the coordinates > of the target frame (v_rt = 0)--do you AGREE or DISAGREE that in this case > the LT predicts the rod's length in the target frame is expanded, not > contracted? > > In your followup reply you said "The source frame is always fixed if the > LT is applied, so offhand I can't say I agree or disagree in this case. If > the rod is moving, it is contracted from the pov of the source frame. If > you want the source frame to be moving, then the only way to apply the LT > is to consider relative motion, with one frame at rest. Offhand I can't say > I agree or disagree, except to say that from the pov of whatever frame is > fixed, to new target is contracted. AG" > > Here your confusing terminology, where you sometime use "moving" and "at > rest" in a standard way (relative to a specified frame) and sometimes in a > non-standard way (where you arbitrarily designate one frame as "at rest" > and the other as "moving" thoughout the whole problem), again makes it hard > for me to follow what point you are trying to make here. What does it even > mean to say "if you want the source frame to be moving"? I thought in > Alan-speak the designation of one frame as "moving" and the other as "at > rest" in your terminology was supposed to be an arbitrary linguistic label, > one which therefore should have no effect on the answer to any physical > question like whether the rod is contracted in the coordinates of either > frame? > > Again, the standard terminology is just to use explicitly relative phrases > like "the rod is moving relative to the Earth" or "the rod is moving in the > Earth's frame", both of which just mean that the position coordinates > assigned to the rod by the Earth frame are different at different values of > the time coordinate (as in the example above where the back of the rod has > coordinates x=0.8c*t, so for example at t=10 it would have x=8, then at > t=20 it would have x=16 etc). Likewise saying "the rod is at rest in the > rod frame" just means the position coordinates of the front and back of the > rod are unchanging in the rod frame, they don't change at different values > of the time coordinate. Modern physicists don't use non-relative phrasing > like "frame A is moving", and it's not just a terminological matter because > in cases like the above where you talk this way I genuinely can't parse how > your statement would translate into a statement about the coordinates > assigned by different frames, which is all that the LT is ultimately > dealing with. Likewise "length" in each frame is ultimately just a > coordinate matter, defined purely in terms of the coordinate distance > between the ends of the object at any single value of coordinate time. > > If you think SR involves any concept of "velocity", "rest", "length" in a > given frame that is *not* just a shorthand for talking about coordinates > assigned to objects by that frame (with all coordinates based on local > measurements by a system of rulers and clocks at rest in that frame), then > you are confused. If you agree it's all ultimately about coordinates, you > need to find a way of talking that doesn't lead to so much confusion about > how your statements could be translated into coordinate terms, like my > request to speak in terms of v_rs and v_rt. > > > > > > So we're both correct from different points of view, but you were mistaken > to ignore my comments about GPS. Also, to be candid, I don't appreciate > your comment that I am rushing to accept an opinion that confirms my > pre-existing fixed opinions. You like to focus on coordinates, but the fact > is you were mistaken in claiming the LT makes a measurable prediction of > what a source frame predicts. It does in the GPS case, but not in the case > of what a target frame predicts internally. AG > > > You never addressed my response to you about the GPS in my post at > https://groups.google.com/g/everything-list/c/ykkIYDAL3mTg/m/ximYgKzKDAAJ > <https://groups.google.com/g/everything-list/c/ykkIYDL3mTg/m/ximYgKzKDAAJ> > -- any coordinate system covering a non-infinitesimal region of curved > spacetime is non-inertial, and the LT isn't relevant to non-inertial > coordinate systems. > > > *An object in free fall is in inertial motion, called a geodesic in GR. > The LT is probably applicable for infinitesmal motion notwithstanding that > this is occurring in curved spacetime. But I'm NOT an expert on how or why > SR is used in GPS to make clock corrections. What I do know is that it IS > used, that consequently the LT is likely applied in some way, and I gave > this example just to show that whereas the LT does NOT give predictions > concerning what is predicted for objects moving wrt a fixed frame, one > cannot categorically claim that it never does.* > > > If we're talking about a scenario where a GPS type system was used in flat > spacetime, the LT would certainly "give predictions concerning what is > predicted for objects moving wrt a fixed frame", as I said in the last > sentence below you'd just have to include the way the clocks are > artificially slowed down (relative to standard clocks) in the source frame > before doing things like calculating elapsed time on a clock for some > interval of coordinate time in the source frame, or applying the LT to > predict the clocks' behavior in the target frame. > > Jesse > > > > > > But looking into this a little more, it seems based on p. 2-3 of > http://math.bme.hu/~matolcsi/gpsmegjelentejp.pdf that at some point in > the GPS calculations they do use an approximation that treats the spacetime > around the Earth as flat so an inertial coordinate system can be used, and > then they add higher-order corrections to account for the fact that the > spacetime is actually curved and this is relevant to gravitational time > dilation. > > But even if there were no gravity and we were just trying to define a > GPS-like system to adjust clocks with various states of motion so they were > all synchronized in a single inertial frame (as in the 'Suppose for a > moment there were no gravitational fields' comment in the second to last > paragraph in 'the realization of coordinate time' section of the GPS paper > at https://pmc.ncbi.nlm.nih.gov/articles/PMC5253894/#Sec4 ), say the > frame where the center of the Earth is at rest, I still don't understand > why you think this would indicate any conflict between what the LT predicts > and what is measured--the whole point of a GPS system is that the ticking > rate of the clocks is being artificially adjusted so it no longer matches > the "proper time" of an un-adjusted clock following the same trajectory, > but instead matches the coordinate time in some preferred coordinate system > you've programmed the clocks to keep pace with. If you have a system of > adjustments like this for clocks in flat spacetime where inertial frames > can be used, then if you know the adjusted ticking rate of a clock in some > source frame (along with the coordinates of its worldline in this frame), > you can use the LT to correctly predict the adjusted ticking rate of that > same clock in a different target frame. > > 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 [email protected]. > To view this discussion visit > https://groups.google.com/d/msgid/everything-list/41deae7f-93b4-4da8-948f-881493c3b78fn%40googlegroups.com > <https://groups.google.com/d/msgid/everything-list/41deae7f-93b4-4da8-948f-881493c3b78fn%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "Everything List" group. 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