A constant speed of light in all reference frames? Surely you can't be serious.
in [Relativity]
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From: PD on 1 Mar 2010 18:25 On Mar 1, 5:21 pm, bert <herbertglazie...(a)msn.com> wrote: > On Feb 13, 1:32 pm, Sam Wormley <sworml...(a)gmail.com> wrote: > > > On 2/13/10 11:23 AM, bert wrote: > > > > Photons if ever slowed begs this question What energy brings them back > > > to c? > > > Photons ONLY exist propagating at c, Herb! > > Sam A lab in Cambridge Mass has slowed light Light, Bert, not photons. The speed of particles in a gas at room temperature may be a couple hundred meters per second, but if someone farts on one side of the room it will usually take a lot longer than a second to get to the other side of the room. Understanding why there is a difference is important to this other case too. > down to 3mph when going > through super cold sodium. This shows imperial thinkers can't reason. > treBert
From: Ste on 1 Mar 2010 18:33 On 1 Mar, 15:48, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 28, 12:54 am, Ste <ste_ro...(a)hotmail.com> wrote: > > [... big snip ...] > > > secondly > > the degree to which opponents seem to be unclear about the conceptual/ > > qualitative basis of SR, > > I'd be careful about this. It may be that they are clear on the > conceptual/qualitative basis, but are declining to present it to you, > out of a personal preference for using the clarity and condensed > efficiency of mathematics. This unwillingness to cater to your > pedagogical needs should not be construed as their being unclear. Paul, there is nothing "clear and efficient" about mathematical statements made without any indication as to their meaning. The argument here is not about the mathematical form of SR, but about its physical meaning. I'm willing to concede that certain posters may be unaccustomed to discussing anything but maths, and may therefore find it difficult to articulate the relevant information, and that's an allowance that must be made, but that's not a preference for being "clear and efficient" - in fact the effect is to make much of what is written utterly obscure and ineffectual. > > and thirdly the preconceptions and > > psychological style of many posters. > > In other words, your basis for deciding what is correct depends on the > manners of the people you discuss it with? No, I'm saying some of the personalities that one must grapple with here are not the sort of personalities who make good discussion partners. Indeed many posters seem to have preconceptions or styles that are designed to avoid or deter productive discussion and sharing of knowledge. > > > > If > > > > such a thing appears to happen, then it is obviously an artefact of > > > > subjective observation. > > > > I disagree. In science, if there is a conflict between experimental > > > observation and intuition, then it is *intuition* that becomes > > > suspect, not the experimental result, especially if the latter is > > > confirmed independently and by complementary means. > > > I'm afraid there is no room for a discrepancy between intuition and > > observation. > > I'm sorry, but I've got a lot of classroom experience that shows that > this is simply a bogus expectation. I can set up a series of simple > experiments on a daily basis in class where I can display all the > elements of the experiment and show them plainly how the simple set-up > is put together, and then I can ask everyone in the class what their > intuition tells them will happen, and at least have of them will get > it wrong, which the subsequent observation will show. Yes, because there is a discrepancy between intuition and observation. But as I say, there is no room for a discrepancy - in the sense of "this town ain't big enough for the both of us" - and inevitably intuition is the one which must leave town (which in practice means either refining an existing intuition, or overhauling it to a greater or lesser degree). > > > > > > > Your disbelief of SR stems from the fact that you don't understand it. > > > > > > > My disbelief, really, stems from the blatant lack of conceptual > > > > > > understanding of the theory. I mean, as I repeatedly point out, I > > > > > > don't know a single equation of relativity, and yet I can root out the > > > > > > conceptual contradictions immediately when people here have a crack at > > > > > > making meaningful qualitative statements in SR. The classic example, > > > > > > of course, was Paul's contention that "what is simultaneous in one > > > > > > frame can never be simultaneous in another", which of course isn't > > > > > > true according to SR. > > > > > > I'm sorry? It is very much true in SR that two spatially separated > > > > > events that are simultaneous in one frame are not simultaneous in > > > > > another frame moving relative to the first. > > > > > But I contradicted that when I pointed out that two observers can be > > > > moving relative to each other, and yet undoubtedly events can be > > > > simultaneous for both. > > > > Not spatially separated ones, no. > > > I'm confused, because I thought we previously agreed that two > > observers travelling along the same axis, maintaining equidistance > > from both events at all times, would both report each event as > > simultaneous with the other event. > > Not quite. What we said was defined what it means for two spatially > separated events to be simultaneous, by a procedure. The same > procedure can similarly tell you when two events are not simultaneous. > > Where we left off the discussion of the case I presented is that for > the same pair of events, one observer (which satisfies all the > criteria of being equidistant between the events and so on) concludes > correctly from his observations that the two events are simultaneous, > and the other observer (which also satisfies the same criteria) > concludes correctly that the two events are not simultaneous. > > We were about to show how this is completely consistent with the laws > of physics. Then you were labouring the point, because I already held this to be consistent with the laws of physics - as evidenced by my existing understanding, where I was able to identify a situation where simultaneity *is* present for both frames, because the changes in relative distances from each event are kept symmetrical for both observers. You've presented a situation where the changes in relative distances are not kept symmetrical, so simultaneity changes, but that's not inconsistent with my existing intuitions. > > And moreover, if they not only both > > maintained equidistance from both events, but if they maintained a > > separation which was equal for both observers (which, if both > > observers are moving relative to each other, requires either a > > collision course between observers, or travel in diametrically > > opposite directions), then there is no question that the signals are > > received simultaneously. > > > Illustration: > > > E1 > > > -------- > > > E2 > > > The line represents the line between events E1 and E2, along which the > > observers may move while always reporting both events to be > > simultaneous. > > Yes, I see what you are thinking of. And it is true that IN THIS CASE, > E1 and E2 will be viewed as simultaneous by both observers. I do > concede this. > > This is not the situation we were discussing before, however. I wasn't talking about the train case. I was talking about this specific scenario, which I had posted before, and which last time indeed you conceded without fuss. But for some reason everyone, including you apparently[1] but certainly not limited to just you, seemed to go back to talking about "what is simultaneous in one frame is not simultaneous in another", when in fact the veracity of that statement is contingent on the circumstances, and there are in fact cases (i.e. the one above) where what is simultaneous in one frame *is* simultaneous in another. It is that contingency that allows reconciliation with my intuitions. [1] I quote you from above "It is very much true in SR that two spatially separated events that are simultaneous in one frame are not simultaneous in another frame moving relative to the first".
From: PD on 1 Mar 2010 18:39 On Mar 1, 4:39 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > Lol. The difference being that gravity is obviously real even outside > of Newton. The effect of gravity does not disappear simply because > Newton's equations are falsified, and indeed one can describe the > essential features of Newtonian gravity without reference to Newton's > equations at all. That is, your fault is in assuming that gravity > never existed before it was quantified by Newton. The question is what > essential physical concepts are described by Minkowski spacetime, that > would exist independently of the mathematics of Minkowski spacetime. Well, I presume you're talking about curved spacetime, not Minkoski spacetime (which is not curved at all), since you're talking about gravity. And you're quite right that curved spacetime existed long before Einstein (not Minkowski) described it mathematically, and it is responsible for the effects seen that had been attributed to a mysterious but ephemeral "gravity" that was at one point described mathematically by Newton. You see, it is not at all obvious that there is a "gravity" at all, though the effects that we would attribute to gravity are certainly there. But perhaps there is no physical gravity at all. As you say, no one --- including you --- would be able to supply any undeniable description of gravity other than by virtue of its effects. Newton did not attempt. Thus it is open whether there is any such "thing" at all. And in fact, almost the same effects can be explained by a physical model involving the pre-existing curvature of spacetime, and which at some point was described by Einstein both physically and mathematically. I say "almost the same" effects, because there is some differences between the effects that would be seen with curved spacetime and the effects that would be seen with this ephemeral "gravity" stuff that Newton described mathematically. And when you actually measure those effects carefully, you find that they match those expected from a curved spacetime physical model. > The fact that no one here seems to be able to give an answer is to me > evidence that some people here don't really know, or certainly don't > have a well-developed and well-thought-out knowledge of what Minkowski > actually means. I don't know why you would conclude that. If you stood on a street corner on London, near a busy taxi stand, and demanded that someone explain alternation of generations in plants, and no one responded to you, would you be right in concluding that none of the people at the taxi stand have well-thought-out knowledge of alternation of generations in plants? Would it be true even if the taxi stand was outside a conference of biologists and you were doing the same? PD
From: Inertial on 1 Mar 2010 18:14 "Ste" <ste_rose0(a)hotmail.com> wrote in message news:160f8e95-4da4-4a8c-bc94-a5e4d2376e75(a)z35g2000yqd.googlegroups.com... > On 1 Mar, 15:00, PD <thedraperfam...(a)gmail.com> wrote: >> On Feb 27, 11:23 pm, Ste <ste_ro...(a)hotmail.com> wrote: >> >> > The point was to explain the theory to someone who hasn't already >> > implicitly internalised the conceptual model on which the equations >> > rest. This is, after all, the test of whether the equations are a >> > complete description of reality, as Paul contends. >> >> In this case, then, I do agree that this is a good goal. And this is >> in fact what physics students do all the time: get an explanation of >> the theory prior to their internalizing the conceptual model on which >> the equations rest. > > Perhaps that's the problem then Paul, which explains why people here > have such a poor ability to explain the conceptual model, because it > is either learned implicitly or not at all. I tend to put a lot of > work into ironing out the conceptual model as I go. So far you still seem very confused about some of the basics of sr, such as simultaneity. Clearly you need a bit more work (and time) > (Incidentally, I notice I referred to you in the third person above in > a previous post. I must have got confused and thought I was talking to > Peter.)
From: Inertial on 1 Mar 2010 18:41
"Ste" <ste_rose0(a)hotmail.com> wrote in message news:c5223f76-96b4-4a9a-8d13-4226d486d190(a)y17g2000yqd.googlegroups.com... [snip for brevity] > But for some reason everyone, including you apparently[1] but > certainly not limited to just you, seemed to go back to talking about > "what is simultaneous in one frame is not simultaneous in another", Which is generally the case. > when in fact the veracity of that statement is contingent on the > circumstances, and there are in fact cases (i.e. the one above) where > what is simultaneous in one frame *is* simultaneous in another. It is > that contingency that allows reconciliation with my intuitions. That doesn't alter the fact that there are an infinite number of cases where things simultaneous in one frame are not simultaneous in another. That you can find some that ARE, does not alter that. If you then choose to ignore all the cases where simultaneity is NOT absolute simply to satisfy your intuition, then you are putting on blinkers on your understanding. |