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Post by carnyx on Dec 28, 2010 19:44:47 GMT 1
Abacus;
"Come on, you can do better than this."
Stop waffling, and have a go at the answers to the questions put to you earlier;
What is YOUR understanding of a photon? ... How big is it?
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Post by abacus9900 on Dec 28, 2010 22:30:04 GMT 1
Abacus; "Come on, you can do better than this." Stop waffling, and have a go at the answers to the questions put to you earlier; What is YOUR understanding of a photon? ... How big is it? I assumed you already knew the answer to this question and simply intended to engage in the philosophical aspects of the answer, but as you appear not to then the answer is that a photon is best described as an energy field which when 'unobserved, or 'measured' is 'spread out.' A photon may be described as both a wave and a particle so that an observation will cause it to 'collapse' into an entity best described as 'particulate' (in everyday terms) at a position calculated by a formulated probability. To venture into the meaning of this odd behaviour belongs to the realm of philosophical interpretations which, although fascinating, cannot at present be experimentally verified. It should be noted, however, that the adjectives we commonly use to describe the objects in our common experience are not really helpful in attempting to describe things like photons since it is mathematics that is the preferred language of physics. It is only natural to try to understand phenomena in terms of our experience but at best one can only use such experiences as a very rough analogy in order to convey a general meaning to the uninitiated. This is not meant to sound condescending or arrogant - it is simply the case and if anyone wishes to really come to grips with particle physics they have to master higher maths.
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Post by carnyx on Dec 28, 2010 22:54:08 GMT 1
Abacus, that's more like it!
I'd like to explore the idea of low-frequency radio 'photons'. If you put two receivers equidistant from the transmitting aerial on opposite sides, would they detect the same photon at the same time?
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Post by abacus9900 on Dec 28, 2010 23:27:45 GMT 1
Abacus, that's more like it! I'd like to explore the idea of low-frequency radio 'photons'. If you put two receivers equidistant from the transmitting aerial on opposite sides, would they detect the same photon at the same time? Well, low energy photons, such as radio waves, are more 'wavelike' than higher energy ones, so in a sense, at this level, a photon is 'everywhere', therefore, yes, it is all spread out (as I pointed out earlier) and may be said to be everywhere at the same time. It should always be borne in mind of course that it is an arbitrary definition of a photon we impose on it to conform to our commonsense notions of reality. It is like the state of the ocean. We can distinguish what we perceive as separate entities we call 'waves' but in reality these apparent separate aspects are really part of the greater body of water, and so with photons. Everything is connected in my view.
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Post by Progenitor A on Dec 29, 2010 10:34:13 GMT 1
Odd thing about the particle/wave duality is that ALL matter is , in effect (so I am told) really just an assembly of em waves - I suppose the exception to that might be neutrons which have neutral charge - but leaving that aside, I am told that matter is a manifestation of em energy.
Odd that. You see em waves do not normally interfere with one another - they simply pass through one another as if they are each not there (admittedly to an observer they add and subtract but they can nevertheless always be separated out - the subtraction bit gets a bit puzzling really as the addition of two em waves can produce a null- nothing - an absence of energy - what has happened to the energy?)
But some em waves do interact with one another - quite violently it seems. If an em wave is of short enough wavelength then it reacts with em waves of similar wavelength. And that reaction is just like two billiard balls bouncing off one another. Odd that really - why does this interaction only occur at very short wavelengths?
And that is where the particle bit come in, isn't it? If the packet of em energy at very short wavelength reacts violently with its kith and kin, then we call that reaction a particle interaction. Another odd thing. Low frequency em waves spread out a they move but very short em waves (apparently) do not. Why? What's going on? A photon is not diluted as it moves from the surface of the sun to the earth, is it? Other em radiation of lower wavelength is though, isn't it? What on earth is going on? What is going on in a glass block when light slows down? What is going on in a half-silvered mirror when some photons go through and others (of the same energy) are reflected?
But puzzling isn't it?
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Post by abacus9900 on Dec 29, 2010 11:04:21 GMT 1
Odd thing about the particle/wave duality is that ALL matter is , in effect (so I am told) really just an assembly of em waves - I suppose the exception to that might be neutrons which have neutral charge - but leaving that aside, I am told that matter is a manifestation of em energy. Odd that. You see em waves do not normally interfere with one another - they simply pass through one another as if they are each not there (admittedly to an observer they add and subtract but they can nevertheless always be separated out - the subtraction bit gets a bit puzzling really as the addition of two em waves can produce a null- nothing - an absence of energy - what has happened to the energy?) But some em waves do interact with one another - quite violently it seems. If an em wave is of short enough wavelength then it reacts with em waves of similar wavelength. And that reaction is just like two billiard balls bouncing off one another. Odd that really - why does this interaction only occur at very short wavelengths? And that is where the particle bit come in, isn't it? If the packet of em energy at very short wavelength reacts violently with its kith and kin, then we call that reaction a particle interaction. Another odd thing. Low frequency em waves spread out a they move but very short em waves (apparently) do not. Why? What's going on? A photon is not diluted as it moves from the surface of the sun to the earth, is it? Other em radiation of lower wavelength is though, isn't it? What on earth is going on? What is going on in a glass block when light slows down? What is going on in a half-silvered mirror when some photons go through and others (of the same energy) are reflected? But puzzling isn't it? You see, when people talk about 'waves' what they are really referring to are waves of probability, not real waves in the sense of water waves and so on. The Schrödinger equation is a mathematical construction that uses statistical methods to predict the motion of a particle over time in terms of a probability wave, in other words, it predicts the probability of finding a particle here or there but the point is that in this case, we are talking about a mathematical probability wave, not a real physical wave. So, what does all this mean? Well, to me it means that we cannot use ordinary terms with which to describe the fundamental nature of matter but have to turn to purely mathematical models to do the job. But, is mathematics not just a human construct, an abstract way of looking at things and not real in any physical sense? If the answer to this question is yes then it seems what we think of as reality is actually a construct of the mind, which seems to upset most of our traditionally ideas about reality and existence. I suppose what it does highlight is that what we have evolved to regard as 'the real world' is a combination of something ultimately unknowable and the way our sensory focus manages it and this prompts the question whether reality already exists 'out there' waiting to be discovered by species like us or whether in fact it is more a matter of our participatory role in 'filtering' our experiences (both in the everyday sense and the scientific sense) to produce what we will.
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Post by Progenitor A on Dec 29, 2010 13:41:24 GMT 1
You see, when people talk about 'waves' what they are really referring to are waves of probability, not real waves in the sense of water waves and so on. Both true and not true. When physicists talk of the wave/particle duality of light they are not talking of probability waves. They are talking em waves of which light is but a small part of the overall spectrum. The Schrödinger equation is a mathematical construction that uses statistical methods to predict the motion of a particle over time in terms of a probability wave, in other words, it predicts the probability of finding a particle here or there but the point is that in this case, we are talking about a mathematical probability wave, not a real physical wave. Fine as far as it goes, but a photon is the particle which at other times is a real em wave So, what does all this mean? Well, to me it means that we cannot use ordinary terms with which to describe the fundamental nature of matter but have to turn to purely mathematical models to do the job. Fine, but if we cannot use ordinary language (even if we have to invent a new language0 to describe what the mathematical equations are telling us, then that means quite simply, that we do not know wht the equations are telling us and that is highlighted by the schisms in the physics world over QM interpretations But, is mathematics not just a human construct, an abstract way of looking at things and not real in any physical sense? Yes, but is there any such thing as 'real' knwledge that has not been filtered through our preconceptions and interpretations?
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Post by abacus9900 on Dec 29, 2010 16:29:21 GMT 1
I think the crucial question is at what point, at what level of focus, does reality stop being real in any conventional sense? EM waves are real, as are ocean waves, but when science examines the most fundamental processes of matter, from which the world around us is all based, what is found are purely mathematical representations. Now this leads on to the next question: is mathematics real in itself or is it wholly a product of mental phenomena? If the latter then what is the nature of such mental phenomena? You ask if there exists any 'real' knowledge that has not been filtered through our preconceptions and interpretations. Personally, I would answer in the negative which means, in effect, that we human organisms are nothing more or less than 'measuring' devices shaped by the demands of survival in the environment. This is quite startling if true because it reveals to us that we can never really make a complete separation between 'us' and 'out there' since these two elements of reality seem necessary in producing the 'whole.' It also seems to imply that it is wrong to assume there already exists a 'set' reality waiting for us to stumble across because if I am correct the universe has to be shaped by conscious entities like us to evolve and attain meaning. Let us not forget that we ourselves are composed of 'star stuff' so in effect we are that part of the evolving universe that has attained consciousness and the ability to examine itself. A startling idea but I don't think one can produce any counter arguments with which to refute it.
So, if nothing is real in any conventional sense where do mathematical ideas come from? The obvious answer is that they emerge from consciousness, however, this simply begs the further question as to what consciousness is? Well, if consciousness cannot have any 'physical' structure, since the idea of a solid physical world is really an illusion, as I earlier argued, then it must exist at the same level as quantum non-physical, mathematical stuff does. This seems to me to lead on the conclusion that ideas are really a non-material, quantum 'reality' that interacts with the 'real' world but that is essentially based in some other realm. This might explain how new concepts get made, i.e., by original forms of patterns not necessarily implicit in existing physical phenomena but generated in a superimposed quantum state rather as a theoretical quantum computer is supposed to work. This would lead me to the conclusion that we humans are, in effect, biologocal quantum computers and this would also, BTW, account for Godel's idea that no formal mathematical structure is able to foresee all the implications of its axioms, for that, creativity is necessary, generated in the manner I have explained.
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Post by carnyx on Dec 30, 2010 18:05:30 GMT 1
We are told that a photon is a discrete packet of energy, and that all elecromagnetic radiation comes in these packets.
Now we know a lot about EM radiation at relatively low frequencies, so it must be possible to develop a concept of a photon that will allow a more general understanding than is found in QED equations.
For example, we know that EM radiation is made of sinusoidal electrical and magnetic waves. In other words, continual rates of change rather than say step-changes. So, for any given frequency there must be a given number of complete cycles in order to contain sufficient energy to make a 'photon'.
So, taking the typical BBC transmission on 1500 metres, how big would one of these photons be?
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Post by abacus9900 on Dec 30, 2010 18:39:48 GMT 1
We are told that a photon is a discrete packet of energy, and that all elecromagnetic radiation comes in these packets. Now we know a lot about EM radiation at relatively low frequencies, so it must be possible to develop a concept of a photon that will allow a more general understanding than is found in QED equations. For example, we know that EM radiation is made of sinusoidal electrical and magnetic waves. In other words, continual rates of change rather than say step-changes. So, for any given frequency there must be a given number of complete cycles in order to contain sufficient energy to make a 'photon'. So, taking the typical BBC transmission on 1500 metres, how big would one of these photons be? A photon does not have a 'shape' as such. The best way to visualize it is as a 'packet' of energy of a certain frequency and that varies with the medium it is travelling through. If you recall, in an earlier post I stated that what we call 'frequency' is only a mathematical construction anyway, so what you seem to be doing is thinking that a photon is a little bit of matter, like a pebble, or marble. However, the wavelength of a photon will be a rough guide to its 'size' when passed through a diffraction agent.
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Post by carnyx on Dec 30, 2010 19:16:50 GMT 1
Abacus,
... clearly you have no experience of electrical engineering. Frequency is a very physical property, I can assure you. You can actually feel it, and hear it, and see it.
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'?
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Post by abacus9900 on Dec 30, 2010 20:50:46 GMT 1
Abacus, ... clearly you have no experience of electrical engineering. Frequency is a very physical property, I can assure you. You can actually feel it, and hear it, and see it. 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'? Well, as the wavelength of a photon is a rough approximation to its size....
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Post by Progenitor A on Dec 31, 2010 10:13:16 GMT 1
Abacus, ... clearly you have no experience of electrical engineering. Frequency is a very physical property, I can assure you. You can actually feel it, and hear it, and see it. 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'? Well, as the wavelength of a photon is a rough approximation to its size.... Seems very large Abacus as the wavelength of light is about 10 -7 m. That is 0.1 microns That of course is its em wavelength You may be referring to its 'wave function' wavelength, but I do not know.
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Post by abacus9900 on Dec 31, 2010 11:07:24 GMT 1
Well, as the wavelength of a photon is a rough approximation to its size.... Seems very large Abacus as the wavelength of light is about 10 -7 m. That is 0.1 microns That of course is its em wavelength You may be referring to its 'wave function' wavelength, but I do not know. Well, the formula to find the wavelength of a photon is: Where the first term equals the wavelength, h equals Plank's constant (6.626068 x 10-34 m^2 kg./s.), c is the speed of light and E equals the energy of the photon.
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Post by speakertoanimals on Jan 11, 2011 18:12:51 GMT 1
Not quite. Taking this the wrong way then leads to people imagining that a photon is a definite, particle-like thing (carrying one packets worth of energy), hence asking what SIZE is it makes sense (the unsaid, mental billiard-ball picture is what is actually coming in here).
Things aren't that simple!
Discrete packet of energy can also mean that we have matter like stuff that possesses energy (energy in atoms, in molecules, in crystals, even in nuclei). we also have energy in radiation. ANd the energy in matter can be exchanged with the energy in the radiation field, BUT only definite amounts can be exchanged. And it is found that the smalest possible amount that can be exchanged at a definite wavelength is related to that wavelength. which leads to the simple picture that what has happened is that one particle-like photon energy packet of that wavelength has been created (or destroyed) at one particular place (the atom or molecule that lost or gained the energy).
But that definite particle-like ness of the handover process isn't quite the same as what a photon IS when that isn't happening! It is a subtle but important point.
So, you have to consider this as well -- we can talk about energy being emited at a particular frequency -- except we find that associated with whatever frequency we choose, there is also a fuzziness in time. If we say exactkly what the frequency IS, we are then cannot pin-down exactly WHEN it was emitted. If we are more strict about what time it happened, than the exact frequency becomes uncertain. The particle-ness seems to be getting a bit fuzzy here as well!
If we can't be certain about exactly WHEN a photon was emitted, we can't say for certain WHERE it is, hence size becomes fuzzy. If we become more certain about position and size (a proper wave-packet in the wave-like picture, which does have a more definite position), then the frequency (hence the ENERGY of the damn thing) becomes even more uncertain -- the more we try to pin down the position of the wavepacket, the more uncertain the energy becomes!
So, if we have a totally definite energy (ie a totally definite wavelength and frequency), then in effect we have an INFINITE wave of a single frequency, with NO END in either time or space! Hence no meaningful 'SIZE'. If we want something with a definite 'size' in time or space, then energy, wavelength becomes more and more indeterminate! A photon isn't a billiard ball that you can pin down like that, and the SIZE of a photon is seen as not being a totally sensible concept.
A more useful picture is waves on the sea. There MAY be some discrete wave-generating and wave-absorbing processes going on, so that the energy that can be added or subtracted from the net effect is only multiples of some basic bit of wave energy, but once emitted, you can't distinguish each little energy-bit in the whole heaving, complicated mass that is the sea-surface. Add enough different processes in that can absorb or emit energy at different wavelengths, and you can't see them in the sea. It's only if you take a single process, in an isolated bit of totally still sea that you can see the individual bits, and what you see exactly depends on how you set up the experiment -- so in some experiments, you see waves with definite energy, but no well-defined position, in others you see waves-packets with a well-defined position, but no definite frequency, and everything else in between! But that doesn't mean the whole haeving surface isn't a whole load of these bits, even if you can't talk about the 'size' of a single bit in meaningful way.
If you mean 1500 metres EXACTLY, then the answer is infinite. If you really mean 1500 metres plus or minus a bit, then it depends on how large the bit is!
As regards photons, the problem also is that the energy of a single photon at that wavelength is incredibly tiny, so any physical radio signal is actually an extremely large number of photons, and a few more this way or that is never going to be measurable at those frequencies!
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