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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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A QED question
I was watching a lecture about QED given by Richard Feynman. Part of
the lecture was about the reflection of light. This is what I think he said, paraphrased: When shining a light at a reflective surface the probabability that the light will take the shortest path or the longest path to a detector, placed anywhere, is equal. However, the AMPLITUDE of the probability is not equal, but varies. The light particles with the highest amplitude are the ones we see when the incident angle and the exit angle are the same, the shortest path. So I think Feynman said the probablity can be the same but the amplitude of the probability can be different. Is that correct? If so, can anyone point me to a web site that explains this in a way a layman can sort of understand? Thanks, Eric |
#2
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A QED question
On Mon, 15 Oct 2012 09:10:47 -0700, etpm wrote:
I was watching a lecture about QED given by Richard Feynman. Part of the lecture was about the reflection of light. This is what I think he said, paraphrased: When shining a light at a reflective surface the probabability that the light will take the shortest path or the longest path to a detector, placed anywhere, is equal. However, the AMPLITUDE of the probability is not equal, but varies. The light particles with the highest amplitude are the ones we see when the incident angle and the exit angle are the same, the shortest path. So I think Feynman said the probablity can be the same but the amplitude of the probability can be different. Is that correct? If so, can anyone point me to a web site that explains this in a way a layman can sort of understand? Thanks, Eric Are you sure he didn't mean that the photon was the same everywhere, but that the amplitude of the probability was different from place to place? AFAIK, "probability" and "probability amplitude" are the same thing -- either quantum physicists use these terms differently than I'm used to (possible), or you misheard he said (presumably possible, although I don't know how many times you listened), or he _meant_ what I'm saying above (or something similar) but he didn't state it well. -- My liberal friends think I'm a conservative kook. My conservative friends think I'm a liberal kook. Why am I not happy that they have found common ground? Tim Wescott, Communications, Control, Circuits & Software http://www.wescottdesign.com |
#3
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A QED question
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#5
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A QED question
In article ,
wrote: On Mon, 15 Oct 2012 16:12:08 -0400, Joseph Gwinn wrote: In article , wrote: I was watching a lecture about QED given by Richard Feynman. Part of the lecture was about the reflection of light. This is what I think he said, paraphrased: When shining a light at a reflective surface the probabability that the light will take the shortest path or the longest path to a detector, placed anywhere, is equal. However, the AMPLITUDE of the probability is not equal, but varies. The light particles with the highest amplitude are the ones we see when the incident angle and the exit angle are the same, the shortest path. So I think Feynman said the probablity can be the same but the amplitude of the probability can be different. Is that correct? If so, can anyone point me to a web site that explains this in a way a layman can sort of understand? Feynman was stating Fermat's principle, but in a quantum mechanics framework. http://en.wikipedia.org/wiki/Fermat%27s_principle What Fermat actually said was that the actual path is an extremum, which can be the longest or the shortest. In practice, it's always the shortest. An extremum is a point where the slope of path length versus choice of nearby path is zero. If you want a bigger explanation, try posting the question on sci.optics. Joe Gwinn What I'm asking about Joe is the statement: The probabilities are equal but the amplitude of the probabilities are not. Is this correct? I understand that the light can be reflected along longer paths, that diffraction grating can be used to show this. It's this amplitude thing that I'm not sure about. Because the probabilities are complex numbers, they can be equal in magnitude and yet point in different directions. The animated drawing near Probability Amplitudes in http://en.wikipedia.org/wiki/Quantum...bility_amplitu des gives the general idea. Joe Gwinn |
#6
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A QED question
On 10/15/2012 19:10, wrote:
I was watching a lecture about QED given by Richard Feynman. Part of the lecture was about the reflection of light. This is what I think he said, paraphrased: When shining a light at a reflective surface the probabability that the light will take the shortest path or the longest path to a detector, placed anywhere, is equal. However, the AMPLITUDE of the probability is not equal, but varies. The light particles with the highest amplitude are the ones we see when the incident angle and the exit angle are the same, the shortest path. So I think Feynman said the probablity can be the same but the amplitude of the probability can be different. Is that correct? He refers to COMPLEX (number) propabilities.. http://en.wikipedia.org/wiki/Quantum...ity_amplitudes If so, can anyone point me to a web site that explains this in a way a layman can sort of understand? No. Kristian Ukkonen. |
#7
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A QED question
On Mon, 15 Oct 2012 23:56:48 +0300, Kristian Ukkonen
wrote: On 10/15/2012 19:10, wrote: I was watching a lecture about QED given by Richard Feynman. Part of the lecture was about the reflection of light. This is what I think he said, paraphrased: When shining a light at a reflective surface the probabability that the light will take the shortest path or the longest path to a detector, placed anywhere, is equal. However, the AMPLITUDE of the probability is not equal, but varies. The light particles with the highest amplitude are the ones we see when the incident angle and the exit angle are the same, the shortest path. So I think Feynman said the probablity can be the same but the amplitude of the probability can be different. Is that correct? He refers to COMPLEX (number) propabilities.. http://en.wikipedia.org/wiki/Quantum...ity_amplitudes If so, can anyone point me to a web site that explains this in a way a layman can sort of understand? No. Kristian Ukkonen. Thanks Kristian, the link you provided makes sense. I think I get it now. So even though you said there is no web site you pointed one out to me. I understand the joke even though I don't really understand QED. I'll keep plugging away at it though, it's so interesting and entertaining. Eric |
#8
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A QED question
I have the book. I advise getting one and reading a section - and you
can look it over and over to gain an insight when needed. Martin On 10/15/2012 11:10 AM, wrote: I was watching a lecture about QED given by Richard Feynman. Part of the lecture was about the reflection of light. This is what I think he said, paraphrased: When shining a light at a reflective surface the probabability that the light will take the shortest path or the longest path to a detector, placed anywhere, is equal. However, the AMPLITUDE of the probability is not equal, but varies. The light particles with the highest amplitude are the ones we see when the incident angle and the exit angle are the same, the shortest path. So I think Feynman said the probablity can be the same but the amplitude of the probability can be different. Is that correct? If so, can anyone point me to a web site that explains this in a way a layman can sort of understand? Thanks, Eric |
#9
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A QED question
On Mon, 15 Oct 2012 20:43:28 -0500, Martin Eastburn
wrote: I have the book. I advise getting one and reading a section - and you can look it over and over to gain an insight when needed. Martin On 10/15/2012 11:10 AM, wrote: I was watching a lecture about QED given by Richard Feynman. Part of the lecture was about the reflection of light. This is what I think he said, paraphrased: When shining a light at a reflective surface the probabability that the light will take the shortest path or the longest path to a detector, placed anywhere, is equal. However, the AMPLITUDE of the probability is not equal, but varies. The light particles with the highest amplitude are the ones we see when the incident angle and the exit angle are the same, the shortest path. So I think Feynman said the probablity can be the same but the amplitude of the probability can be different. Is that correct? If so, can anyone point me to a web site that explains this in a way a layman can sort of understand? Thanks, Eric That's what I'm gonna do. I have other books by and about Richard Feynman. Entertaining reading. So now I need to get all of his lectures in book form that are available. I did find a web site devoted to these works. Fo someone without a strong math background the stuff he talks about is a little hard to grasp sometimes. But it sure is fun! Eric |
#10
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A QED question
It is an interesting read - read the notes in the front of the book -
whence it came - and how and why - Friend, wife and himself!..... Martin On 10/16/2012 11:23 AM, wrote: On Mon, 15 Oct 2012 20:43:28 -0500, Martin Eastburn wrote: I have the book. I advise getting one and reading a section - and you can look it over and over to gain an insight when needed. Martin On 10/15/2012 11:10 AM, wrote: I was watching a lecture about QED given by Richard Feynman. Part of the lecture was about the reflection of light. This is what I think he said, paraphrased: When shining a light at a reflective surface the probabability that the light will take the shortest path or the longest path to a detector, placed anywhere, is equal. However, the AMPLITUDE of the probability is not equal, but varies. The light particles with the highest amplitude are the ones we see when the incident angle and the exit angle are the same, the shortest path. So I think Feynman said the probablity can be the same but the amplitude of the probability can be different. Is that correct? If so, can anyone point me to a web site that explains this in a way a layman can sort of understand? Thanks, Eric That's what I'm gonna do. I have other books by and about Richard Feynman. Entertaining reading. So now I need to get all of his lectures in book form that are available. I did find a web site devoted to these works. Fo someone without a strong math background the stuff he talks about is a little hard to grasp sometimes. But it sure is fun! Eric |
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