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#101
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"vonroach" wrote in message ... | On Thu, 26 Aug 2004 08:33:58 GMT, "Androcles" | wrote: | | | "vonroach" wrote in message | .. . | | On Wed, 25 Aug 2004 17:31:09 +0200, "Volker Hetzer" | | wrote: | | | | Intuition is a dangerous tool. I don't recommend it. Better to prove a | | theorem mathematically and then see if intuition agrees. Thunder | and | | lightning arrive at different times, and a child's intuition is | that | | they are seperate events. | | It seems that vonroach is prepared to say Volker Hetzer wrote my words AND | Jim Greenfield wrote them also. | Androcles | | No as I've already said, I don't care who wrote them. They are false. Different people have different opinions on many subjects, and rely on intuition to have those opinions. Since some of those opinions are diametrically opposed (as are yours and mine), it follows that your intuition is as reliable as you are in incorrectly attributing my words to another. QED. | And you impress me, speaking to Andro. ,as a pompous little sophomore | getting a tiny sip of knowledge. Since your 'impression' is really your intuition and is completely wrong, once again you've proven my point. You (speaking to roach) impress me as a totally ****ing stupid argumentative moron without a clue of what you are arguing about, and as someone who doesn't care who he misquotes. *plonk* Androcles. |
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"Androcles" schrieb im Newsbeitrag ... "Volker Hetzer" wrote in message ... | | "Androcles" schrieb im Newsbeitrag ... | | "Volker Hetzer" wrote in message | ... | | | | "Androcles" schrieb im Newsbeitrag | ... | | | | "Volker Hetzer" wrote in message | | ... | | | | | | "Jim Greenfield" schrieb im Newsbeitrag | | om... | | | "Dave" wrote in message | | ... | | | | | | Intuition is a dangerous tool. I don't recommend it. Better to | prove | | a | | | theorem mathematically and then see if intuition agrees. Thunder | and | | | lightning arrive at different times, and a child's intuition is | that | | | they are seperate events. An adult sees it differently. Until | | | Copernicus, intuition told us the Earth is at the centre if the | | | universe. After all, we see the sun cross the sky daily, it MUST | be | | | going around us. With greater knowledge we revise our view that | we | | | are turning toward and away from the sun. Never trust intuition, | it | | | is bane of science and the boon of religion. | | | | | | But aren't you using intuition to discard relativistic addition of | | | velocities in your c'=c+v (or is that c=c'+v?). | | | | | | Car is parked by road, another passes. At the instant both are | | | alongside, each emits a photon (vaccum condition). I say each emits | | | the photon at c from source, and therefore magic is required for | each | | | photon to travel "with" the other. This is NOT intuition- try it | with | | | throwing stones off the back of a ute! c DOESN"T = c+v (car). | | | As for relativistic addition of velocities, this totally disregards | | | conservation of energy/momentum, so I "intuitively" reject that | | | nonesense to. | | | Maybe here's a better analogy: Sound. If that depended on the source | | | speed, the sound wall wouldn't exist. | | | | | | Lots of Greetings! | | | Volker | | Sound DOES depend on source speed. | | You snipped the explanation. | I'll return the courtesy. | Sound DOES depend on source speed. | Try moving through air toward a sound source such as a fire siren. | Relatively, the source is moving toward you. All speed is relative. | See | http://www.place.dawsoncollege.qc.ca...ph/Chap18B.htm | Solution to Problem 18.51 | Androcles | | There. I quoted you. And I don't see how 18.51 explains how a supersonic aircraft can outfly its own | sound under the condition that the speed of sound depends on the speed of the aircraft. | | So? In your aircraft example the speed of (engine) sound, as measured by the plane when the plane is moving at Mach 1 through the air, is zero. Thus the speed of sound, in this case zero, depends on the speed of the source. In this case the result of the measurement depends on the speed of the measurement device relative to the speed the medium carrying the sound. That's different from the speed of sound being dependent on the speed of the source. If you agree to go back to the speed of light, which is the same regardless of the reference system, you might regard a simple radar thought experiment: Assume you have two reflectors, one (A) stationary, and one (B) moving toward you at 0.5c. The radar beam hits both reflectors when they are exactly 1km away from you. Obviously, B's echo will be blue shifted but do you really think that B's echo arrives in about 2/3 the time of A's echo? Lots of Greetings! Volker |
#103
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"Volker Hetzer" wrote in message ... | | "Androcles" schrieb im Newsbeitrag ... | | "Volker Hetzer" wrote in message | ... | | | | "Androcles" schrieb im Newsbeitrag | ... | | | | "Volker Hetzer" wrote in message | | ... | | | | | | "Androcles" schrieb im Newsbeitrag | | ... | | | | | | "Volker Hetzer" wrote in message | | | ... | | | | | | | | "Jim Greenfield" schrieb im Newsbeitrag | | | om... | | | | "Dave" wrote in message | | | ... | | | | | | | | Intuition is a dangerous tool. I don't recommend it. Better | to | | prove | | | a | | | | theorem mathematically and then see if intuition agrees. | Thunder | | and | | | | lightning arrive at different times, and a child's intuition | is | | that | | | | they are seperate events. An adult sees it differently. | Until | | | | Copernicus, intuition told us the Earth is at the centre if | the | | | | universe. After all, we see the sun cross the sky daily, it | MUST | | be | | | | going around us. With greater knowledge we revise our view | that | | we | | | | are turning toward and away from the sun. Never trust | intuition, | | it | | | | is bane of science and the boon of religion. | | | | | | | | But aren't you using intuition to discard relativistic | addition of | | | | velocities in your c'=c+v (or is that c=c'+v?). | | | | | | | | Car is parked by road, another passes. At the instant both are | | | | alongside, each emits a photon (vaccum condition). I say each | emits | | | | the photon at c from source, and therefore magic is required for | | each | | | | photon to travel "with" the other. This is NOT intuition- try it | | with | | | | throwing stones off the back of a ute! c DOESN"T = c+v (car). | | | | As for relativistic addition of velocities, this totally | disregards | | | | conservation of energy/momentum, so I "intuitively" reject that | | | | nonesense to. | | | | Maybe here's a better analogy: Sound. If that depended on the | source | | | | speed, the sound wall wouldn't exist. | | | | | | | | Lots of Greetings! | | | | Volker | | | Sound DOES depend on source speed. | | | | You snipped the explanation. | | I'll return the courtesy. | | Sound DOES depend on source speed. | | Try moving through air toward a sound source such as a fire siren. | | Relatively, the source is moving toward you. All speed is relative. | | See | | http://www.place.dawsoncollege.qc.ca...ph/Chap18B.htm | | Solution to Problem 18.51 | | Androcles | | | | There. I quoted you. And I don't see how 18.51 explains how a supersonic | aircraft can outfly its own | | sound under the condition that the speed of sound depends on the speed of | the aircraft. | | | | So? | | In your aircraft example the speed of (engine) sound, as measured by the | plane when the plane is moving at Mach 1 through the air, is zero. Thus the | speed of sound, in this case zero, depends on the speed of the source. | In this case the result of the measurement depends on the speed of the | measurement device relative to the speed the medium carrying the sound. | That's different from the speed of sound being dependent on the speed | of the source. | | If you agree to go back to the speed of light, which is the | same regardless of the reference system, Here is why it isn't. S1---------------------O----x---------------S2 t0 S1----------------------y----O--------------S2 t1 S1 and S2 are sources of light, and O is an observer. In the interval of time from t0 to t1, O has moved a distance x in time t1 with some velocity I'll call v = x/t. Light from S1 to y will travel at c, reaching y in time t. Hence c = y/t Light from S2 will reach y (where the observer is) in time t also. Therefore the observer will percieve the signal from S2 before the signal from S1, and will calculate t2 = x/(c+v) from S2 and t1 = x/(c-v) from S1. So unless you think he has two different times recorded that are the same, the velocity of light in the observer O's frame of reference is not c. By way of confirmation, Einstein wrote: "But the ray moves relatively to the initial point of k, when measured in the stationary system, with the velocity c-v, so that x'/(c-v) = t." you might regard a simple radar | thought experiment: Thought experiments are something Einstein came up with. His contain errors. Real experiments are much better. However, I'll take a look. | Assume you have two reflectors, one (A) stationary, and one (B) moving | toward you at 0.5c. | The radar beam hits both reflectors when they are exactly 1km away | from you. | Obviously, B's echo will be blue shifted but do you really think that B's | echo arrives in about 2/3 the time of A's echo? In air, no. In the vacuum of space, yes. Androcles. | | Lots of Greetings! | Volker |
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Sam Wormley wrote in message ...
How Do You Add Velocities in Special Relativity? http://www.edu-observatory.org/physi.../velocity.html Read it Greenfield... it's right and you're wrong. Clearly explained to me by George D privately. If you, EG and George wish to immunise SR against the rules/laws of vector addition (or don't you think velocity IS a vector), go ahead! But it won't work in THE REAL WORLD Jim G c'=c+v |
#105
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On Thu, 26 Aug 2004 13:26:22 GMT, "Androcles"
wrote: You (speaking to roach) impress me as a totally ****ing stupid argumentative moron without a clue of what you are arguing about, and as someone who doesn't care who he misquotes. *plonk* Androcles. As I thought a pompous sophomore with little learning. Profanity doesn't add any weight to your adolescent note. |
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On Thu, 26 Aug 2004 15:01:17 +0200, "Dirk Van de moortel"
wrote: There. I quoted you. And I don't see how 18.51 explains how a supersonic aircraft can outfly its own sound under the condition that the speed of sound depends on the speed of the aircraft. So? So, well done, Androcles! You are in over your head, Andy. Speed of sound `depends' on speed of aircraft? ROFLMAO Dirk, you must be an idiot. |
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On Thu, 26 Aug 2004 13:54:12 +0200, "Volker Hetzer"
wrote: yes, but according to androcles the speed of sound is supposed to depend on the speed of the aircraft, right? wrong |
#108
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"vonroach" wrote in message ... On Thu, 26 Aug 2004 15:01:17 +0200, "Dirk Van de moortel" wrote: There. I quoted you. And I don't see how 18.51 explains how a supersonic aircraft can outfly its own sound under the condition that the speed of sound depends on the speed of the aircraft. So? So, well done, Androcles! You are in over your head, Andy. Speed of sound `depends' on speed of aircraft? ROFLMAO Dirk, you must be an idiot. Perhaps you don't know the meaning of the word 'fumble'? http://users.pandora.be/vdmoortel/di...undSource.html It is Androcles who claims that speed of sound `depends' on speed of aircraft. It is me who claims that Androcles is an idiot. Dirk Vdm |
#109
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Eric Flesch:
On Fri, 20 Aug 2004 17:34:31 +0000 (UTC), wrote: In sci.astro Eric Flesch wrote: You're missing the point. The stress-energy tensor is a classical description which assumes continuous motion. But QED shows that the photon path is the summation of all possible paths (diffraction gratings are an application of this) and the delayed-choice experiment shows explicitly that the travelling photon cannot be pinpointed to any particular location in its presumed path(s). The point is that the "travelling photon" can be modelled only by a quantum description, and the classical stress-energy tensor does not apply. Everything you say here is just as true of neutrons, or protons, or any other elementary particle. Are you saying that we should therefore not use GR at all? Of course not. Bosons classically manifest routinely and so their gravitational vectors can be described. But photons have *no* classical manifestation between emission and absorption. There is a real difference here in their behavior "in the wild". Say what? Neutrons and protons are fermions, i.e., spinors, not vectors. On the other hand, the photon _is_ a four-vector. ... You can write down a low-energy effective action for the gravitational field without knowing details of quantum gravity. "Details"? Quantum gravity is vaporware. You can't quote it as though it were a reference. ``Aspects of Quantum Field Theory in Curved Spacetime'', Fulling, S.A., ``Quantum Fields and Strings: A course for Mathematicians'', Witten, E., and others, ed., 2 volume set. You can't have it both ways here. If you want to talk about what ``QED shows,'' you have to allow standard techniques from QED. You mystify me. What have I said to limit the application of QED? I'm saying that where QED's description differs from GR, QED rules. I hate to break this news to you, but the spacetime of special relativity from which qed derives is no less ``continuous'' than the spacetime of general relativity. It is possible to formulate qed (and quantum field theories, in general) in curved spacetime, e.g., see the references above. GR is not, and was never meant to be, a description of the nature of light. But general relativity is a theory of the spacetime in which light propagates. Are you suggesting that there is something special about flat spacetime other than the particular value for the curvature, (i.e., zero) or that spacetime is relevant to the light which propagates in spacetime? No it won't be. The mass might have some miniscule effect on the local geometry, that is all. Are you serious? You claim that a mirrored box filled with radiation does not weight more than an empty box? Would you like to describe how a mirror works? How efficient mirrors are? What difference does that make? Every mirror that we've ever built, if we build the box that you describe, toss in some photons and close the box, the photons would be absorbed (and converted to heat) in an infinitesimal fraction of a second. The point being what? Then, the heat contributes to the mass. If you want to debate the point of how well insulated from heat leaks one can make the box, be my guest. All you need do is note that a decent 5 litre dewer of liquid nitrogen will still contain liquid after a week, to see that one can insulate the box pretty darn well - certainly long enough to weigh the box. [...] Here's a simple exercise. I assume you accept that electromagnetic radiation is red-shifted in a gravitational field, right? It depends on the vector. Photons departing the gravitational field are red-shifted, certainly. So consider a box with a mirror at the top and one at the bottom, containing radiation in a coherent state (you accept QED, right?) with an expectation value of momentum that's in the purely vertical direction and an expectation value of wave packet width (z^2-z^2) that's small compared to the size of the box. Compute the momentum transfer to the mirrors, using however much QED you like. You will find that the momentum transfer to the bottom, where the energy is blue-shifted, is greater than the momentum transfer to the top. That means ``the radiation will be attracted toward the mass.'' In that sense you are right. But I am reminded of one of Bohr's refutations of Einstein's gedankenexperimenten where Einstein's premise of increased mass was countered by the different rates of time flow in a differential gravitational field. Which was what, precisely? I suspect the same applies here. In any event, this does not show that the "in-flight" photon exerts gravitation. So, if I place a radioactive source which decays by positron emission in a thermally insulated box, then what do you predict the mass of the box to be, (1) before any of the nuclei decay, (2) after all of the nuclei have decayed and the positrons have anihilated with electrons in the walls of the box, via e+ e- - \gamma\gamma (In the interest of simplicity, I'll skip the bremsstrahlung prior to any anihilation which is only relevent if you have a very convoluted answer to this question), (3) times in between (1) and (2)? Also, in the interst of simplicity, you may ignore the neutrinos unless you really want to punish yourself estimating the fraction of the energy which is carried off by neutrinos which escape the box. If you are into self-abuse, then make sure you do it correctly by calculating the cross-section of the neutrinos with the box, and assume some material and thickness for the walls. If you're going to be pedantic, you might as well go all the way. You've already turned a simple, straightforward question into a something much more complicted than was necessary. |
#110
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