Ballistic Theory, Progress report...Suitable for 5yo Kids
in [Relativity]
|
Prev: OWLS is not equal to c
Next: Mathematical Inconsistencies in Einstein's Derivation of the Lorentz Transformation
From: George Dishman on 7 Aug 2005 09:48 "bz" <bz+sp(a)ch100-5.chem.lsu.edu> wrote in message news:Xns96A560C154543WQAHBGMXSZHVspammote(a)130.39.198.139... > "Jeff Root" <jeff5(a)freemars.org> wrote in news:1122862205.456748.163740 > @g44g2000cwa.googlegroups.com: > >> George replied to Bob: >> >>>> The spectra seem to indicate that the single photons >>>> have very narrow bandwidth [as I would expect]. >>> >>> If a photon has a specific energy and that is >>> proportional to frequency, then a single photon >>> has a unique frequency hence zero bandwidth and >>> infinite duration >:-( >>> >>> At least it does with a semi-classical view. >>> >>> If you include Heisenberg, then the uncertainty >>> in the measured energy relates to the uncertainty >>> in the frequency which depends on the time over >>> which the frequency is measured, hence the >>> bandwidth is related to the method of measurement, >>> and I don't need to point out the crucial role of >>> measurement methods in QM. >>> >>> As a result, I don't think a photon has a specific >>> length or duration, but the idea of it as a single >>> cycle with hard ends at the zero crossings can be >>> ruled out as too simplistic. >> >> The notion that a single photon can have a bandwidth seems >> absurd to me. For reasons analogous to the notion that the >> North Pole can have a longitude. It seems obvious that the >> property of bandwidth only applies to statistical collections >> of photons, or waves. >> >> I'm not sure it makes sense to talk about the frequency of a >> single photon, either. Any photon has a particular, measurable >> energy which is associated with a particular frequency, but >> there is no way to measure that frequency. I disagree Jeff, we can take a single photon and fire it at a diffraction grating and measure the wavelength hence the frequency. (I'm not sure if single photons have had their frequency measured by the heterodyne method yet.) If you measure many photons, you can determine the bandwidth or the uncertainty of the energy. >> Only by analyzing >> the behavior of a collection of photons does the property of >> frequency become evident. The analysis shows that f = E/h, >> so you can *know* the frequency of a single photon within the >> limits of uncertainty, but you can't actually measure it. >> >> If you have enough photons to directly measure their frequency, >> then you have enough photons to detect their bandwidth. > > The question is 'how big'[long] is a photon. > > I can't see any reason that it should be more than one cycle in length. The reason I have offered several times is that interference effects occur with path length differences of many wavelengths even in single photon experiments. If you don't want to treat a photon as a point particle, you have to address that aspect in some way. > There is a paper > http://jchemed.chem.wisc.edu/JCEWWW/Articles/DynaPub/DynaPub.html#ref16 > That I disagree with. They appear to believe that each photon consist of > a wavetrain that is millions of cycles long. > > Their theory seems to be falsified by femtosecond laser pulses. They weren't using femtosecond pulses. Your argument doesn't stand, because if they were using femtosecond pulses, the pulse envelope bandwidth multiplies the carrier producing sidebands. The 'length' is inversely related to the bandwidth. George > There are some that would be less than 2 cycles at the frequency of the > laser. Also, the max keying speed of ELF transmission would seem to > preclude > any requirement for millions of cycled per photon.
From: bz on 7 Aug 2005 12:39 "George Dishman" <george(a)briar.demon.co.uk> wrote in news:dd53au$k6p$1 @news.freedom2surf.net: > > "bz" <bz+sp(a)ch100-5.chem.lsu.edu> wrote in message > news:Xns96A560C154543WQAHBGMXSZHVspammote(a)130.39.198.139... >> "Jeff Root" <jeff5(a)freemars.org> wrote in news:1122862205.456748.163740 >> @g44g2000cwa.googlegroups.com: >> >>> George replied to Bob: >>> >>>>> The spectra seem to indicate that the single photons >>>>> have very narrow bandwidth [as I would expect]. >>>> >>>> If a photon has a specific energy and that is >>>> proportional to frequency, then a single photon >>>> has a unique frequency hence zero bandwidth and >>>> infinite duration >:-( >>>> >>>> At least it does with a semi-classical view. >>>> >>>> If you include Heisenberg, then the uncertainty >>>> in the measured energy relates to the uncertainty >>>> in the frequency which depends on the time over >>>> which the frequency is measured, hence the >>>> bandwidth is related to the method of measurement, >>>> and I don't need to point out the crucial role of >>>> measurement methods in QM. >>>> >>>> As a result, I don't think a photon has a specific >>>> length or duration, but the idea of it as a single >>>> cycle with hard ends at the zero crossings can be >>>> ruled out as too simplistic. >>> >>> The notion that a single photon can have a bandwidth seems >>> absurd to me. For reasons analogous to the notion that the >>> North Pole can have a longitude. It seems obvious that the >>> property of bandwidth only applies to statistical collections >>> of photons, or waves. >>> >>> I'm not sure it makes sense to talk about the frequency of a >>> single photon, either. Any photon has a particular, measurable >>> energy which is associated with a particular frequency, but >>> there is no way to measure that frequency. > > I disagree Jeff, we can take a single photon and > fire it at a diffraction grating and measure the > wavelength hence the frequency. (I'm not sure if > single photons have had their frequency measured > by the heterodyne method yet.) If you measure > many photons, you can determine the bandwidth or > the uncertainty of the energy. > >>> Only by analyzing >>> the behavior of a collection of photons does the property of >>> frequency become evident. The analysis shows that f = E/h, >>> so you can *know* the frequency of a single photon within the >>> limits of uncertainty, but you can't actually measure it. >>> >>> If you have enough photons to directly measure their frequency, >>> then you have enough photons to detect their bandwidth. >> >> The question is 'how big'[long] is a photon. >> >> I can't see any reason that it should be more than one cycle in length. > > The reason I have offered several times is that > interference effects occur with path length > differences of many wavelengths even in single > photon experiments. If you don't want to treat > a photon as a point particle, you have to address > that aspect in some way. > >> There is a paper >> http://jchemed.chem.wisc.edu/JCEWWW/Articles/DynaPub/DynaPub.html#ref16 >> That I disagree with. They appear to believe that each photon consist of >> a wavetrain that is millions of cycles long. >> >> Their theory seems to be falsified by femtosecond laser pulses. > > They weren't using femtosecond pulses. Your argument > doesn't stand, because if they were using femtosecond > pulses, the pulse envelope bandwidth multiplies the > carrier producing sidebands. The 'length' is inversely > related to the bandwidth. That is true, by information theory. But, I doubt that information theory was designed to handle quanta of energy. If we look at femto second pulses, they must consist of bunches of photons at different frequencies [the frequencies of the side bands]. If we filtered those out, and attenuated the carrier so as to just allow one photon on the main frequency, would the photons suddenly get longer? I don't yet have any reason to think so. >> There are some that would be less than 2 cycles at the frequency of the >> laser. Also, the max keying speed of ELF transmission would seem to >> preclude >> any requirement for millions of cycled per photon. > > > -- bz please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set. bz+sp(a)ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
From: George Dishman on 7 Aug 2005 13:29 "bz" <bz+sp(a)ch100-5.chem.lsu.edu> wrote in message news:Xns96AB76C397DFCWQAHBGMXSZHVspammote(a)130.39.198.139... .... > If we look at femto second pulses, they must consist of bunches of photons > at different frequencies [the frequencies of the side bands]. > > If we filtered those out, and attenuated the carrier so as to just allow > one photon on the main frequency, would the photons suddenly get longer? > > I don't yet have any reason to think so. If you hit a narrow-band filter with an impulse, how long does it ring ;-) George
From: bz on 7 Aug 2005 14:42 "George Dishman" <george(a)briar.demon.co.uk> wrote in news:dd5g3h$out$1 @news.freedom2surf.net: > > "bz" <bz+sp(a)ch100-5.chem.lsu.edu> wrote in message > news:Xns96AB76C397DFCWQAHBGMXSZHVspammote(a)130.39.198.139... > > ... > >> If we look at femto second pulses, they must consist of bunches of photons >> at different frequencies [the frequencies of the side bands]. >> >> If we filtered those out, and attenuated the carrier so as to just allow >> one photon on the main frequency, would the photons suddenly get longer? >> >> I don't yet have any reason to think so. > > If you hit a narrow-band filter with an > impulse, how long does it ring ;-) That depends upon the Q. Since we only want one photon, we can tolerate a rather low Q. Aye? -- bz please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set. bz+sp(a)ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
From: George Dishman on 7 Aug 2005 18:21
"bz" <bz+sp(a)ch100-5.chem.lsu.edu> wrote in message news:Xns96AB8BB274B34WQAHBGMXSZHVspammote(a)130.39.198.139... > "George Dishman" <george(a)briar.demon.co.uk> wrote in news:dd5g3h$out$1 > @news.freedom2surf.net: > >> >> "bz" <bz+sp(a)ch100-5.chem.lsu.edu> wrote in message >> news:Xns96AB76C397DFCWQAHBGMXSZHVspammote(a)130.39.198.139... >> >> ... >> >>> If we look at femto second pulses, they must consist of bunches of >>> photons >>> at different frequencies [the frequencies of the side bands]. >>> >>> If we filtered those out, and attenuated the carrier so as to just allow >>> one photon on the main frequency, would the photons suddenly get longer? >>> >>> I don't yet have any reason to think so. >> >> If you hit a narrow-band filter with an >> impulse, how long does it ring ;-) > > That depends upon the Q. > > Since we only want one photon, we can tolerate a rather low Q. > > Aye? No, you can get single photons just by reducing the intensity to a low rate and using quite a wide (long duration) gate. You said "one photon on the main frequency". The question is how close to that frequency is "on"? Low Q means wide band. The duration of the ringing is of the order of 1 / bandwidth. Again we come back to the argument from duality, that the bandwidth is a measure of the uncertainty of the energy of a particular photon while the "length" is related to the uncertainty of location and the product is of the order of Planck's constant. Try to constrain the energy using a filter and ringing increases the uncertainty in location. George |