Thank you all my fans for talking about me! Don't forget to check-out my revolutionary papers on consciousness: https://philpeople.org/profiles/cosmin-visan
On Friday, 20 December 2024 at 12:41:52 UTC+2 Alan Grayson wrote: > Actually, you and Cosmin have much in common; both have pretentions of > being mind readers. AG > > On Friday, December 20, 2024 at 3:35:05 AM UTC-7 Quentin Anciaux wrote: > >> Why bother answering a troll ? He will never admit anything, will change >> what he says if he's cornered. His sole purpose and pleasure is trolling. >> You end a troll by ignoring it. Ignoramus as him and cosmin are better >> dealt with plain silence, that's all these shitty human beings deserve. >> >> Le ven. 20 déc. 2024, 11:09, Jesse Mazer <[email protected]> a écrit : >> >>> >>> >>> On Fri, Dec 20, 2024 at 2:09 AM Alan Grayson <[email protected]> >>> wrote: >>> >>>> *Pedagogical" means what? * >>>> >>>> >>>> Relating to how the subject is taught, in this case specifically which >>>> concepts any teacher would see as important for students to understand. If >>>> a student doesn't understand that different frames agree on all local >>>> events, then they basically don't understand the first thing about how >>>> relativity works. >>>> >>>> >>>> *If car fits in one frame and not in another, isn't that what we would >>>> expect, and yet in my prior post I wrote that this seems contradictory? >>>> Why >>>> do you expect the frames must agree about this kind of local event? To >>>> avoid a contradiction? AG* >>>> >>>> >>>> As long as the laws of physics are Lorentz-invariant, that guarantees >>>> that when different inertial frames apply the same equations (including >>>> length contraction) they will get locally identical predictions, assuming >>>> they both are using initial conditions which are equivalent under the >>>> Lorentz transformation. >>>> >>>> >>>> *Presumably, in this problem, the laws of physics are >>>> Lorentz-invariant, but contrary to what you claim, they don't result in >>>> the >>>> same locally identical predictions. Maybe I don't understand what you mean >>>> by "same locally identical predictions". In fact, the results are >>>> diametically opposite, about whether the car fits in garage. AG* >>>> >>> >>> "The car fits" or "the car fits" are not statements about local events, >>> i.e. statements about things that happen at a single spacetime point in one >>> of Brent's diagrams. But the back of the car does pass the front of the >>> garage at a single point in spacetime in this problem, so if there was a >>> clock #1 attached to the back of the car and a clock #2 attached to the >>> front of the garage, all frames would have to agree in their predictions >>> about what each clock reads at the moment they pass through that one point >>> in spacetime. Likewise if a clock #3 is attached to the front of the car >>> and a clock #4 is attached to the back of the garage, those clocks would >>> cross paths at a single point in spacetime so both frames would have to >>> agree in their predictions about what they each read at the meeting, which >>> they do. >>> >>> You can also imagine there is a ruler Rg at rest relative to the garage >>> running along its length, and another ruler Rc at rest relative to the car >>> and running along the same axis, so the two rulers are moving alongside >>> each other at 0.8c. In this case, for any of the types of events I >>> mentioned above like clock #1 passing clock #2, both frames also must agree >>> about what marking on Rg this event coincides with in space, and what >>> marking on Rc it coincides with. These are all facts about things that are >>> happening at individual points in spacetime, not facts which require >>> talking about a range of positions of times, like whether the car "fits". >>> >>> In Brent's scenario, assume clocks #1 and #3 at the back and front of >>> the car were synchronized in the car's rest frame by the Einstein >>> synchronization procedure, and clocks #2 and #4 at front and back of the >>> garage were synchronized in the garage's rest frame using the >>> synchronization procedure. Also assume the localized event of the back of >>> the car passing the front of the garage coincided with both clock #1 and >>> clock #2 there reading t=0 and t'=0 respectively, and that this happened >>> right next to the x=0 mark on ruler Rc and the x'=0 mark on ruler Rg. All >>> frames agree on these facts, which are exclusively about what happened at a >>> single point in spacetime, namely the point where the back of the car >>> passed the front of the garage. >>> >>> Given these assumptions, according to relativity they will *also* agree >>> in all their predictions about a second event, the event of the front of >>> the car reaching the back of the garage. Specifically they will agree that >>> at the same point in spacetime as this second event, all the following are >>> true: >>> >>> --Clock #3 at the front of the car read t = -7.5 >>> --Clock #4 at the back of the garage read t' = 3.5 >>> --this event of the front of the car reaching the back of the garage >>> coincided with the x=12 mark on ruler Rc >>> --this event of the front of the car reaching the back of the garage >>> coincided with the x'=10 mark on ruler Rg >>> >>> There is no disagreement on any of these local facts. The only >>> disagreement is that each observer adopts a different *convention* about >>> which ruler and clocks to treat as canonical for the sake of assigning >>> coordinates--the car rest frame defines time-coordinates by the clocks at >>> rest in the car frame (clocks #1 and #3) and the ruler at rest in the car >>> frame (Rc), while the the garage frame defines time-coordinates by the >>> clocks at rest in the garage frame (clocks #2 and #4) and the ruler at rest >>> in the garage frame (Rg). Based on these conventions, the car observer says >>> the event of the back of the car passing the front of the garage happened >>> AFTER the event of the front of the car reaching the back of the garage, >>> therefore the car never "fit", while the garage observer says the event of >>> the back of the car passing the front of the garage happened BEFORE the >>> event of the front of the car reaching the back of the garage, therefore >>> the car "did" fit. But this is not a disagreement about any of the local >>> facts I mentioned. >>> >>> (BTW I earlier derived these numbers as the coordinates assigned to the >>> event in each frame at >>> https://groups.google.com/g/everything-list/c/gbOE5B-7a6g/m/43aKXeEUAQAJ >>> but here I'm just emphasizing that coordinate judgments can be grounded in >>> local readings on physical clocks and rulers, something I also talked about >>> at >>> https://groups.google.com/g/everything-list/c/gbOE5B-7a6g/m/BvxSA-b3AAAJ >>> ) >>> >>> >>> >>>> >>>> But are you asking a different question about what is the motive for >>>> demanding that any claims about how things work in different frames needs >>>> to pass the test of giving identical local predictions, in order to >>>> qualify >>>> as good physics? If so just consider that there are all sorts of local >>>> interactions in physics, like collisions, that cause changes that >>>> different >>>> frames couldn't disagree about without being obviously inconsistent. For >>>> example, say you have a clock that's wired to a small bomb that will cause >>>> a localized explosion, which will be triggered when it reads 100 seconds. >>>> And say you have another object in motion relative to the clock/bomb, say >>>> a >>>> glass of water, which is going in the opposite direction so they will >>>> cross >>>> paths. Imagine different frames could disagree in their prediction about >>>> whether the event of the clock/bomb crossing paths with the glass of water >>>> coincided was at the same local point in space and time as the clock >>>> reaching 100 seconds--like, one frame predicts the clock reads 90 seconds >>>> when they cross paths, a second frame predicts the clock reads 100 seconds >>>> when it crosses paths with the glass of water. In this case, the second >>>> frame would predict the glass of water was right next to the bomb when it >>>> exploded, and so predicts that the glass will be broken up after the >>>> encounter. Meanwhile the first frame would predict the glass of water has >>>> already put some distance between it and the bomb by the time the bomb >>>> exploded, so the glass would be intact after the explosion. This is a >>>> clear >>>> physical contradiction, no? They can't both be right, and you could easily >>>> falsify one frame's prediction just by looking at the glass afterwards. >>>> >>>> On the other hand, if all frames agree in all their predictions about >>>> local events as in relativity (assuming Lorentz-invariant laws of nature), >>>> then you don't get any contradictory predictions about such localized >>>> physical interactions which affect the state of objects later. You may >>>> find >>>> it counter-intuitive that they still differ in some kind of non-local >>>> bird's-eye account of what happened, but you can't point to any >>>> differences >>>> they will see on any measuring-instruments (since instrument readings are >>>> also local events), like what a clock mounted on the back of the car reads >>>> as it passes by the front of the garage. >>>> >>>> >>>> *You keep asserting that the frames agree in all their predictions, >>>> when in this problem they surely don't! So, I don't think we agree on >>>> this, >>>> if I understand what you mean. AG * >>>> >>> >>> See above about what I mean by localized events. >>> >>> >>> >>>> >>>> >>>> Do you disagree with my point that if different frames *didn't* have >>>> differing definitions of simultaneity, it would be impossible for the two >>>> frames to disagree about whether the car or garage was shorter without >>>> this >>>> leading to conflicting predictions about local events, like what the >>>> clocks >>>> mounted to front and back of the car will read at the instant they pass >>>> clocks attached to the front and back of the garage?' >>>> >>>> >>>> *I don't see how simultaneity or not helps in this situation. It seems >>>> impossible for the car to fit when in motion. AG * >>>> >>>> >>>> It helps by showing how the car can fit in the garage's frame without >>>> leading the garage frame and the car frame to disagree in a single >>>> prediction about local events. Does your "seems impossible" just mean you >>>> find it counter-intuitive, not that you have a concrete argument about why >>>> you think it *would* lead to disagreements in predictions about local >>>> events? >>>> >>>> >>>> *Well, in this case, using length contraction, the facts speak for >>>> themselves. What could be counter-intuitive is that there's only one real >>>> car, so how can Lorentz-invariant physics give us frame dependent results? >>>> This seems to be not only a weak point in your analysis, but seriously >>>> mistaken. AG * >>>> >>> >>> There is no frame-dependence in predictions about localized events, and >>> according to relativity these are the only real physical facts in the >>> problem, everything else is a matter of conventions about how you *label* >>> these events with position and time coordinates, no more problematic than a >>> classical physics scenario . >>> >>> >>>> >>>> >>>> >>>> And in a later post, I elaborated on why differences in simultaneity >>>> are critical to avoiding contradictory predictions about localized >>>> physical >>>> events: >>>> >>>> 'In an imaginary alternative physics where different frames had no >>>> disagreement about simultaneity but different observers still all believed >>>> the length contraction equation should apply in their frame, then this >>>> would be a genuine paradox/physical contradiction, because different >>>> frames >>>> would end up making different predictions about local events. Think about >>>> it this way--if there were no disagreement about simultaneity, there could >>>> be no disagreement about the *order* of any two events (this would be the >>>> case even if observers predicted moving clocks run slow like in >>>> relativity). But if observer #1 thinks the car is shorter than the garage, >>>> he will predict the event A (the back of the car passing the front of the >>>> garage) happens before event B (the front of the car reaches the back of >>>> the garage), and if observer #2 thinks the car is longer than the garage, >>>> he will predict B happens before A. If there were no disagreement about >>>> simultaneity this would lead them to different predictions about readings >>>> on synchronized clocks at the front and back of the car/garage at the >>>> moment of those events, specifically whether the clock at A would show a >>>> greater or lesser time than the clock at B.' >>>> >>>> Jesse >>>> >>>> >>>> *Jesse; in the near future I will try to address each of the issues >>>> you've raised,* >>>> >>>> >>>> OK, please prioritize answering the question about whether you >>>> understand the basics of how position vs. time plots work in classical >>>> mechanics, because that really is a crucial prerequisite if you want to >>>> hope to understand anything about spacetime diagrams in relativity. If you >>>> don't understand it I'm sure I could find a site that lays out the >>>> essentials. And as a follow-up, did you ever study the basics of algebraic >>>> geometry? Like if you had to plot a function like y = 4x + 5 on a graph >>>> with x and y axes would you know how to do it? Likewise would you know the >>>> algebra needed to figure out where that function intercepts with another >>>> one like y = 2x +10? >>>> >>>> >>>> *Sure, I have advanced degrees in math and physics. I'd solve for x, by >>>> setting 4x + 5 = 2x + 10, and then solve for y to get the point of >>>> intersection. (I sure hope I got that right!) I've seen spactime diagrams >>>> before, but I'm more comfortable with explanatory text.* >>>> >>> >>> OK, in a word problem if I say that in a classical problem, at t=0 >>> seconds a spaceship is initially at position x=7 meters away from the >>> origin, and it's moving in the +x direction at 12 meters/second, would you >>> know how to write down the equation for its position as a function of time >>> x(t), and plot this as a line on a graph with position in meters on the >>> horizontal axis and time in seconds on the vertical? If so, that's really >>> all that a "worldline" is. >>> >>> Likewise, if we have various such worldlines for different objects, and >>> we want to know the position of each object at a particular time like t=5, >>> do you understand why this would just be a matter of plotting a horizontal >>> line that goes through the t=5 mark on the vertical axis (a classical line >>> of simultaneity), and seeing the point it intersects each worldline? >>> >>> >>>> *Tell me this if you can; in Brent's spacetime diagrams, he often has a >>>> stretched car. Since there's nothing in the problem to indicate an >>>> elogation of the car, what's Brent trying to illustrate? AG* >>>> >>> >>> He's trying to illustrate a slanted line of simultaneity that connects >>> two events that are simultaneous in the car's frame, as graphed in the >>> garage frame. But the visual length of this line in the diagram is >>> not meant to correspond to an elongated length in either frame, it just >>> looks longer because it's being translated from relativistic (Minkowski) >>> geometry where the length of a spacelike line segment is given by sqrt(x^2 >>> - t^2) into a diagram in a 2D euclidean space (your computer monitor) where >>> if we label the two spatial axes x and y, then the length of any slanted >>> line segment is given by sqrt(x^2 + y^2). In Minkowski geometry the length >>> of a slanted segment should be *less* than the distance along the x-axis >>> between its endpoints, but in Euclidean geometry it's greater because of >>> that switch from a minus to a plus, and we are only capable of intuitively >>> visualizing Euclidean geometry so that's what we use for our imperfect >>> diagrams. That's why the diagram has to show the car as longer here even >>> though according to the relativistic math the proper length of that line >>> segment should really be shorter. >>> >>> >>> >>>> >>>> >>>> * but for now let me just say I don't understand how to resolve this >>>> issue, and my tentative pov is that relativity just isn't correct. Listen; >>>> we start in a rest frame of a car which is longer than a garage. and have >>>> no problem asserting that it won't fit. And that's how things seem from >>>> both entities with physical observers. So far so good. Now we imagine the >>>> car in motion and apply length contraction in both frames and we get >>>> opposite results; namely, that in the car's frame, it won't fit in the >>>> garage, but in the garage frame it does fit, and the fits gets easier as >>>> the car's velocity increases. If I imagine a real car and a real garage, >>>> from one frame it doesn't fit, the car's frame, and from the other frame, >>>> the garage, it does fit. So, if intially the car doesn't fit, from the pov >>>> of both physical entities should I expect contrary results when the car is >>>> in motion? Maybe so. But I still can't wrap my head around the alleged >>>> claim, that the observed reality will be frame dependent. I mean, how can >>>> two observers in different frames, looking at a real car, disagree on what >>>> they see?* >>>> >>>> >>>> What do you mean "see"? Are you talking about what they see visually, >>>> in terms of when light from different events reaches their eyes? If so, do >>>> you understand that when we talk about "simultaneous" events in any frame, >>>> we are *not* talking about events that are seen simultaneously in a visual >>>> sense by an observer at rest in that frame, unless the observer happens to >>>> be positioned equidistant from both events? >>>> >>>> >>>> *If we imagine observers in each frame, humans seeing or instruments >>>> measuring, how do you expect them to observe the same thing, when the >>>> final >>>> results differ hugely? The car fits when observed from garage frame, but >>>> not when observed from car frame! AG * >>>> >>> >>> All they see is the sum of light from multiple events which are >>> individually localized in space and time. Imagine for example that they are >>> watching an image of the car and garage on a screen (it makes no difference >>> to the problem), such that every bit of light they see was emitted by a >>> specific pixel at a particular moment in time. In this case, even in a >>> classical problem where there are no disagreements about simultaneity or >>> distance in terms of the coordinates each observer assigns, as long as the >>> light takes a finite speed to get from the pixel that emitted it to an >>> observer's eye, different observers may visually *see* events at different >>> times and in different orders. Even in this purely classical scenario you >>> could have *visual* disagreements about whether the car fits (i.e. one >>> observer sees the light from the event of the back of the car passing the >>> front of the garage BEFORE seeing the light from the event of the front of >>> car reaching the back of the garage, a different observer sees it AFTER), >>> even though classically they won't disagree once they correct for light >>> transit times in order to assign time-coordinates to these events. >>> >>> >>>> >>>> This was another point I made in an earlier post (at >>>> https://www.mail-archive.com/[email protected]/msg97741.html >>>> <https://www.mail-archive.com/[email protected]/msg97741.html> >>>> >>>> ) which you didn't respond to: >>>> >>>> 'Note that when we talk about what happens in a given frame this is not >>>> what any observer sees with their eyes, it's about when they judge various >>>> events to have happened once they factor out delays due to light transit >>>> time, or what times they assign events using local readings on >>>> synchronized >>>> clocks that were at the same position as the events when they occurred. >>>> >>>> >>>> *It could be both. I'm just asserting there is some objective reality >>>> about whether the car fits or not, and from this I conclude a paradox >>>> exists since results using contraction give opposite results. How do you >>>> fail to reach this same conclusion? AG* >>>> >>> >>> Do you definitely deny what I said about all observers agreeing about >>> all local events, now that I've clarified a little what I mean by "local >>> events"? Or are you saying that *even if* they agree about all local >>> events, you still think there must be a separate objective truth about the >>> question of whether the car fits, a fact of the matter that is somehow more >>> than the sum total of all the facts about localized events (including all >>> local readings on measuring-instruments)? >>> >>> >>> >>>> >>>> >>>> For example, if in 2025 I see light from an event 5 light years away, >>>> and then on the same day and time in 2030 I see light from an event 10 >>>> light years away, I will say that in my frame both events happened >>>> simultaneously in 2020, even though I did not see them simultaneously in a >>>> visual sense. And if I had a set of clocks throughout space that were >>>> synchronized in my frame, when looking through my telescope I'd see that >>>> the clocks next to both events showed the same date and time in 2000 when >>>> the events happened.' >>>> >>>> >>>> * Incidentally, I just noticed that in one of Brent's recent posts with >>>> two diagrams, he says there is a disagreement about simultanaeity, but I >>>> am >>>> not sure if he's referring to comparing the two frames, and when I >>>> interpreted this as his comparison, he got angry, denying my >>>> interpretation. My bias is that the frames should agree (on what a bird's >>>> eye observer would see?), but does that require disagreement about >>>> simultaneity? AG* >>>> >>>> >>>> What does "bird's eye observer" mean, if it's supposed to be something >>>> more than just the sum total of all local events? >>>> >>>> >>>> *Not a precise scientific term, so just forget it. It could be how God >>>> sees everything, the ultimate observer so to speak, and finds your >>>> conclusion baffling. AG * >>>> >>> >>> Do you think someone with such a God's-eye perspective would find it >>> baffling that different coordinate systems may disagree about which of two >>> events has a greater x-coordinate, and that there is no objective truth >>> about the matter independent of how we choose to orient our spatial x-y-z >>> axes for the sake of assigning position coordinates? If you're OK with >>> there being no objective truth about this, why are you suddenly *not* OK >>> with the fact that there might similarly be no objective truth about which >>> of two events has a greater t-coordinate, independent of our conventions >>> about how to define coordinate systems? >>> >>> 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/CAPCWU3LF4UVdejjmHbB7jQMQgGnbZ2N7aNAf2GMejfjy%3DQrw8g%40mail.gmail.com >>> >>> <https://groups.google.com/d/msgid/everything-list/CAPCWU3LF4UVdejjmHbB7jQMQgGnbZ2N7aNAf2GMejfjy%3DQrw8g%40mail.gmail.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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