On Wednesday, January 29, 2025 at 2:10:53 PM UTC-7 Jesse Mazer wrote:
On Wed, Jan 29, 2025 at 9:27 AM Alan Grayson <[email protected]> wrote: On Wednesday, January 29, 2025 at 2:26:43 AM UTC-7 Alan Grayson wrote: On Wednesday, January 29, 2025 at 1:30:28 AM UTC-7 Alan Grayson 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* 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 source frame is always fixed if the LT is applied. If the rod is moving in some frame, it is contracted from the pov of the source frame. I'm not sure of the result in the case you posit. AG * I don't understand what you mean by "fixed"--do you mean we been given the coordinates of all objects in the source frame as a fixed starting point in the problem before applying the LT, or do you mean the source frame is designated to be "at rest" in your non-standard terminology, or something else? And when you say "If the rod is moving in some frame, it is contracted from the pov of the source frame", does "moving in some frame" just mean that in the coordinates of "some frame" (like the target frame) the rod has nonzero coordinate velocity? Or are you using your idiosyncratic definition where saying something is "in" some frame is supposed to mean it is *at rest* in that frame, while it has nonzero velocity in the source frame? If the latter, I agree the rod will be contracted in the source frame, but I thought your claim about the divergence between the LT's predictions and actual measurements was supposed to be in the case where the *target* frame (the one we are using the LT to make predictions about) is the one where the rod has zero velocity, since you kept talking about how actual measurements don't show any contraction of an object in the object's own rest frame. *If an object has length L in some rest frame, say wrt the Earth, you can imagine that frame and object at rest in that frame, moving fast enough wrt the Earth,* Again I have trouble following your terminology, how can you talk about a frame being a "rest frame, say wrt the Earth", but then say the frame is "moving fast enough wrt the Earth"? Are you using "wrt the Earth" not to talk about its velocity as measured in the coordinates of the Earth's frame, but just saying everyone in the problem including observers on Earth have agreed to verbally designate this frame as "the rest frame"? Or are you saying that the object does not remain inertial throughout, instead we have to imagine it starts out with a velocity of zero in the coordinates of the Earth frame and its length L is measured there, and then later is given a nonzero velocity in the coordinates of the Earth frame? Or something else? * so from pov of the Earth, its length is predicted as .5L.* OK, so I take it this means the object has a velocity of 0.866c in the coordinates of the Earth frame, or at least it does after an acceleration in my second interpretation above. * Thus, the LT does NOT, does NOT, does NOT, predict its length correctly from the pov of the Earth from which the LT is applied. DOES NOT!* That appears to be a non sequitur, *why* do you think the LT wouldn't predict the length correctly from the pov of the Earth? And when you say "the pov of the Earth *from* which the LT is applied", do you mean you want to start with the coordinates of the object in the Earth frame (so that the length of 0.5L would be part of the starting conditions), and then apply the LT to get a prediction about the coordinates in the object's own frame? In other words, treating the Earth as the source frame and the object's frame as the target frame? Or when you talk about the LT making a prediction about length "from the pov of the Earth frame", do you want to start with the coordinates in the object's own frame (treating that as the source frame) and then use the LT to go INTO, not "from", the Earth's frame (treating it as the target frame)? Your comment about the LT not predicting measurements in some frame correctly would be wrong either way, but if you clarify what you are imagining I can give you the math of the LT to show why you are wrong. * I tend to doubt any scenario where its length is predicted to be larger than L. AG* If L is specifically defined to be the object's rest length/proper length, there will never be a frame where the length is larger than L. But when I talked about the length of the object expanding after applying the LT, I was just talking about its coordinate length in the target frame compared to its coordinate length in the source frame, in the case where the object had nonzero velocity in the source frame so its length L in the source frame was *not* the same as its rest length/proper length. Jesse *This is my last word on this subject. In SR, the idea of an empty universe and two frames moving wrt each other, is found in virtually all textbooks, from which the concept of relative motion derives, where one frame is considered at rest, the other moving, and vice-versa. So when you object to my language, you're really ignoring basic concepts of relativity. And even when I say "relative to the Earth", you still object to my terminology. So there's really no satisfying your desires for what you call "standard terminology". Consequently, this discussion is, IMO, totally worthless. I've already clearly proved what you consistently deny, and I can't state it any clearer. If you wish, you can consider my arguments useless, and continue in your delusion that the LT necessarily predicts what the measurements will be in target frames when it predicts length contraction and time dilation. So, let's terminate this worthless discussion. 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