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Post by speakertoanimals on Jan 11, 2011 20:43:17 GMT 1
No, a photon that is received by one receiver can't also be received by the other.
It's no more mysterious than the fact that at high intensities, there are so many photons in ordinary light that we can treat it as if the em field were actually continuous. But if we take the intensity down and down and down (and keep using more and more sensitive detectors), we can get right down to the point where we are detecting single photons. Which is obviously something that interests astronomers, who want to be able to detect the weakest possible sources!
Same goes for radio waves. For terrestrial receivers and transmitters, the intensity is large enough that we don't have to use quantum physics, and can treat radio waves using classical em fields.
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Post by carnyx on Jan 11, 2011 23:05:15 GMT 1
STA,
I have the suspicion that the photon is a theoretical construct that makes the sums come out, yet has no actual physical existence ... and also that QM is a set of mathematical tools yet not a complete framework.
I suspect that the real problem is that we are unable to measure things below a certain size, where the energy required to detect the presence/absence of the smallest packet of energy, is equal. Thus it is not possible to go beyond this limit without affecting the subject. And I suspect that this limiting case, or granularity of energy, is being labelled as 'a photon'. This is not to say that stuff cannot be explored via ingenious inferential methods, such as using vast numbers of experimental observations and analysis using statistical techniques, but there are limits to this methodology, in terms of drawing general conclusions that are meaningful for the culture at large.
Whilst the results of these methods are useful for application to the various nano technologies, and that is the only way that such delvings are ever going be properly significant. And, as far as I understand the history of technology it is rare to have theoretical constructs leading technological change. Rather, it is the practitioners who give the puzzle to the theoreticians, yet are not reliant on the academic answers for progress. The value of the subsequent academic framework is in fact more pedagogical that practical.
So, it really does seem that theoretical physics has also reached a kind of limit, and is reliant on progress from applied physics to feed it with puzzles as it were.
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Post by Progenitor A on Jan 12, 2011 9:34:28 GMT 1
I have the suspicion that the photon is a theoretical construct that makes the sums come out, yet has no actual physical existence ... and also that QM is a set of mathematical tools yet not a complete framework. I suspect that the real problem is that we are unable to measure things below a certain size, where the energy required to detect the presence/absence of the smallest packet of energy, is equal. Thus it is not possible to go beyond this limit without affecting the subject. And I suspect that this limiting case, or granularity of energy, is being labelled as 'a photon'. This is not to say that stuff cannot be explored via ingenious inferential methods, such as using vast numbers of experimental observations and analysis using statistical techniques, but there are limits to this methodology, in terms of drawing general conclusions that are meaningful for the culture at large. Whilst the results of these methods are useful for application to the various nano technologies, and that is the only way that such delvings are ever going be properly significant. And, as far as I understand the history of technology it is rare to have theoretical constructs leading technological change. Rather, it is the practitioners who give the puzzle to the theoreticians, yet are not reliant on the academic answers for progress. The value of the subsequent academic framework is in fact more pedagogical that practical. So, it really does seem that theoretical physics has also reached a kind of limit, and is reliant on progress from applied physics to feed it with puzzles as it were. There must be a lowest-possible energy content of a photon -indeed there is as we are told that energy is not infinitely divisable. I have tried looking for the lowest-possible energy state of a photon, but without success. If the lowest energy level of a photon can be found, then the lowest possible frequency of a photon can be found from the equation given earlier by Abacus, viz Lamda=hc/E where h is Plancks constant, c speed of light and lamda the wavelength of the photon This reduces to f=h/E The difficulty is then fining E where E is the lowest possible energy level of a quantum Anyway, there is a lowest-possible frequency at which a photon can be said to exist. Finding the lowest-possible energy level of a photon will tell us if a photon can exist at, say, the wavelength of 1500m that you raised earlier It would be very useful to have a physicist on board
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Post by speakertoanimals on Jan 12, 2011 14:09:02 GMT 1
Except we can MEASURE single photons! Hence claiming it has no physical existence is just daft -- we can measure it, end of story.
If you knew anything about this, you'd know this was daft.
So, take a metal box, consider black-body radiation within that box. In essence, the waves must fit between the walls. The size of the box then determines the LONGEST possible wavelength of the radiation (hence lowest energy).
When applied to quantum zero-point energy in the em field, the metal box gives a shorter wavelength between parallel plates than outside in teh rest of the universe (no metal walls). Hence the zero-point radiation between the plates is different to that outside, net result being a force between the plates (the Casimir effect).
So, in the universe at large, the longest possible wavelength (smallest energy) is set by the size of the universe, if it is finite.
Saying there MUST be a lowest-possible photon energy doesn't actually show that there must be.....................
Must try harder. 0/10
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Post by Progenitor A on Jan 12, 2011 14:54:39 GMT 1
Abacus, Anyway, the question remains. Given that a photon is a quantity of EM energy, and that EM waves are sinusoidal, then at a wavelength of 1500 metres, how many cycles are needed to make a 'photon'? Right After digging around Einstein tells us that the energy E of a photon is givenn by: E=nhf where: n=(0,1,2,3...... corresponding to the allowed valency levels) h=Plancks constant, 6.26068x 10 -34f= 250kHz (wavelength 1500m) substituting into E=1hx250x10 3, where n=1 , the lowest possible quantum energy for a photon at this frequency E =(approx)125 x 10 -28 Joules How many cycles are required in the transmitted photon to get this energy? Well the power per cycle is constant (by the RMS integation method), that is Power = J/s is constant for each cycle It follows that the Joules per cycle is also constant Therefore only 1 cycle is necessary for a photon at 1500m. This must be so otherwise the enegy level of the photon would increase as we get more and more cycles (and if the number of cycles were infinte we would have a photon of infinte energy). Of couse we cannot get a sinusoid of infinite extent as it would require infinte space to accomodate all those cycles! (Bloody infinity again) Now, here is a problem. Imagine we have an omnidirectional antenna with just enough power (125 x 10 -28 Joules/s) to emit one photon. Is it emitted in all directions or just randomly in any direction?
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Post by speakertoanimals on Jan 12, 2011 15:35:31 GMT 1
Wrong.
First thing to get your head round is that a photon with a definite frequency also has a definite energy (related to that frequency).
A definite frequency/wavelength ALSO means that the waveform must be infinite in extent. Just as when you do fourier analysis, to get a discrete wavepacket you must ADD a range of frequencies. a pure single-frequency wave is an infinite wave. A finite-length wave or pulse is ALWAYS composed of a range of frequencies.
For photons, it means that if you have a rough idea where and when the photon is, then there must ALWAYS be some uncertainty in both the exact wavelength and the exact energy of that photon. Same situation as for any other quantum particle!
This in effect isn't really quantum theory -- just basic fourier (frequency) analysis tells you that the only pure single frequency waveform is an infinite length waveform. Anything else (ie anything we ever come across in practise), involves waveforms which have finite lengths in both space and time. Then simple application of the Heisenberg uncertainty principle says that the photon(s) involved must have a corresponding (albeit very small) uncertainty in wavelentgth, in frequency, and in energy.
You can't chop up a continuous single-frequency waveform into individual peaks and troughs -- such a thing doesn't make physical sense (such a single peak can't propogate, isn't a solution of any wave equation, be it Maxwells for em waves, or simple wave equation for water waves!).
I think you have got totally the wrong idea as to what a photon is, keep trying to visualise it in terms of the little you do know about waves, which is why you keep coming up with these daft pictures, and the daft conclusions you are drawing from them.
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Post by carnyx on Jan 12, 2011 16:15:49 GMT 1
@sta, you claim;
Oh Really? Have you not heard of Scott Russel's 'wave of translation'?
Seems to me a very good analogy of a 'photon'; A single solitary wave which must therefore contain a solitary lump of energy.
Here is an interesting quote;
Isn't that fascinating, or what!
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Post by Progenitor A on Jan 12, 2011 16:30:02 GMT 1
@sta, you claim; Oh Really? Have you not heard of Scott Russel's 'wave of translation'? Seems to me a very good analogy of a 'photon'; A single solitary wave which must therefore contain a solitary lump of energy. Here is an interesting quote; Isn't that fascinating, or what! Yes, the same thing applies to travelling waves in a waveguide or in a TWT. Then we have standing waves in non-matched transmission lines where it is common practice to measure individual peaks and troughs Then we have water waves in the forms of Tsunamis - it is possible to actually travel on the peak of such a wavefront.
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Post by speakertoanimals on Jan 12, 2011 16:40:24 GMT 1
A soliton ISN'T a photon. It only arises when you have very specific cancelation effects that allow the pulse to travel without changing shape.
Under ordinary conditions, such a finite pulse (which consists of a wide RANGE of frequencies, as I've already said) would change shape, since the different frequency components travel at slightly different speeds (why we get coloured fringes when we use glass prisms, different colours/frequencies have slightly different refractibe indices hence speeds).
Solitons, rather than being an anaology for a photon, are actually a rather complicated and special phenomenon. whereras photons can be of various sorts -- localised or not, that is the point.
Try again -- and why don't you try some actual physics this time, rather than just hand-wavey pictures.................
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Post by speakertoanimals on Jan 12, 2011 17:00:37 GMT 1
To those who may be tempted by the soliton-like picture...................
double-slit experiment. We can do this with SINGLE photons. So, how does the isolated lump of energy picture fit in with the usual quantum description where a single photon passes through BOTH slits?
Answer -- it doesn't.
The real point is that even within classical wave theory, we have a range of waves we look at.
We have infinite, sinusoidal waves of a fixed frequency.
We have combinations of such to produce localised wave-packets.
And we have various things in between.
The point being that in the quantum theory, we also need to include such a range of possibilities.
So, when we do particular measurements, we have something particle-like (localised in space). When we do other experiments, we find things which are NOT localised in that way. We can do experiments that focus on either the wave-like (NOT localised in space) or particle-like properties of photons.
A sopliton-like picture, which has things localised, is not enough, even as an analogy, to capture what photons ARE.
Waves and particles, that's the essential fact that comes out of quantum stuff, and it's as true for electrons as it is for photons. Just as we need to drop the billliard-ball picture for electrons (since they can behave as non-localised waves), so we also need to resist the temptation to adopt a particle-like only picture for photons..........................
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Post by carnyx on Jan 12, 2011 17:36:53 GMT 1
Hahahahaha! Gotcha!
Caught out with a flat contradiction, you really don't like it! So you create a straw man and then start pummelling it ..
Who said it was ?
And with this property of non-locality, you also failed to answer the question as to whether the same photon can be detected by two equidistant observers.
Fact is, your 'photon' is a fictive thing that is used to get the theoretical sums to work, and you don't like that reality.
And so at the very small, and the very large, theoretical physics has diminishingly less important things to say .... and is becoming ever-more irrelevant.
..... Is this why the state is reducing the subsidy towards such a trivial pursuit?
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Post by speakertoanimals on Jan 12, 2011 17:56:53 GMT 1
Try reading.............
Ditto:
Ditto:
Utter tosh.
If quantum physics wasn't correct about what it has to say about the basics of matter and energy and how they behave, then (for one), the very computer you are using to post this rubbish would not work!
Come back when you have something sensible to say (and have at least bothered to skim previous posts..................
Cost-cutting yes, but science MAKES money, and we'd be in an even bigger mess if it wasn't for some of the products that were only able to be designed and built based on quantum physics (like your PC), and some of the spin-offs from science and particle physics research (like the internet).
I suggest you go back to pen and paper then, and leave the trivial pursuit that is the internet to the rest of us....................
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Post by Progenitor A on Jan 12, 2011 18:56:08 GMT 1
Abacus, Anyway, the question remains. Given that a photon is a quantity of EM energy, and that EM waves are sinusoidal, then at a wavelength of 1500 metres, how many cycles are needed to make a 'photon'? Right After digging around Einstein tells us that the energy E of a photon is givenn by: E=nhf where: n=(0,1,2,3...... corresponding to the allowed valency levels) h=Plancks constant, 6.26068x 10 -34f= 250kHz (wavelength 1500m) substituting into E=1hx250x10 3, where n=1 , the lowest possible quantum energy for a photon at this frequency E =(approx)125 x 10 -28 Joules How many cycles are required in the transmitted photon to get this energy? Well the power per cycle is constant (by the RMS integation method), that is Power = J/s is constant for each cycle It follows that the Joules per cycle is also constant Therefore only 1 cycle is necessary for a photon at 1500m. This must be so otherwise the enegy level of the photon would increase as we get more and more cycles (and if the number of cycles were infinte we would have a photon of infinte energy). Of couse we cannot get a sinusoid of infinite extent as it would require infinte space to accomodate all those cycles! (Bloody infinity again) Now, here is a problem. Imagine we have an omnidirectional antenna with just enough power (125 x 10 -28 Joules/s) to emit one photon. Is it emitted in all directions or just randomly in any direction?
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Post by speakertoanimals on Jan 12, 2011 19:12:20 GMT 1
Wrong. the energy of a single photon of frequency f is hf.
If we have n photons, the TOTAL energy is nhf, but the energy of EACH photon is still hf.
There is no such thing as:
Since THE photon energy is always hf, although the TOTAL energy of the whole set of photons is given by nhf.
You have totally failed to understand the BASICS...............
Nope, that is a CLASSICAL result about em waves, which does not apply at the quantum level! All it reallyn says is that if you have a classical em wave of a fixed frequency/phase and amplitude (which in quantum terms is actually billions and billions of photons of the same frequency), then ON AVERAGE over a time of one cycle, the number of photons that you would detect turning up is approximately constant.
Seems that again, you really don't get the fundamentals, and the fundamental difference between quantum physics and classical physics, and the fact that classical physics is just WRONG (and has been shown to be wrong).
Same problem with ANY quantum particle. Suppose I emit an electron, only one, but in a state which is totally symmetric as regards direction (ie direction anywhere, and equally likely in all directions).
Potentially in any direction, quantum state is NON localised -- that is really is a spherical wavefront, if you like.
You will only think this is daft if you're still stuck with the classical idea that a particle has to have a definite direction and a definite path...........
I should just point out, using single particle bit untidy in practice, but plenty of experiments that involve the generation of a back-to-back pair of particles (two photons, electron-positron etc), where although back-to-back, the wave function is actually spherical, and any direction is equally likely.
Even if we emit one pair, and only one pair, that doesn't mean that that pair has a definite direction BEFORE we measure it, basic quantum stuff. In fact, very similar to entangled quantum pair experiments, but using direction rather than spin.
I think yuou'#re stuck in classical physics, trying to understand an inherently quantum concept (like the photon) by using classical ideas. So no wonder you keep thinking the whole thing is daft, plainly wrong, or plain nonsense, because quantum physics IS daft in classical terms -- because quantum physics says classical physics is WRONG, hence no bloody surprise if quantum seems to contradict when we use classical concepts -- that is kind of the whole point!
So, a photon ISN'T a bit of a classical wave, because classical waves only exist as the approximate limiting case when you have billions of photons.
And you can't mnix up classicaland quantum concepts in your arguments, since if you apply a classical result (such as power per cycle) to what is actually quantum, or course you will seem to get contradictions and nonsense!
Just go and learn the basics, please, before trying to claim that photons don't exist..............................
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Post by carnyx on Jan 12, 2011 19:25:55 GMT 1
Another STA strawman post.
Solitons apart form being a single wave, [which condradicts your silly comment].. may be a good analogy for a 'photon'..
And how about this for total rubbish!
Hahahahaha! A classic post-hoc fallacy!
"If it wasn't for Newton invention of gravity, we'd all fall into the sun ....."
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