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alvaros
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When a photon is emitted it goes in all directions ? or just in one ? N, S, E..
Or there is a probability you can find it in any direction ?
Or there is a probability you can find it in any direction ?
Schrodinger's Dog said:A photon does not have a size in any real terms, it has no mass AFAIK or anyone else does, so if you're talking about how "big" is the wavelength or what is its direction that's not really indicative of size of a photon just it's path after emission, it's an unanswerable question. The question is phrased poorly I think...
alvaros said:Schrodinger's Dog wrote:
"The question is phrased poorly I think...", shure it is.
The cuestion arises from:
A dipole ( an antenna= aerial ) is just made up by two wires that can be very thin. A dipole receives photons from a surface much bigger than their surface ( length * whidth of the wires ). So, I infer, the photons whose path is not exactly through the wires of the dipole can be "captured". This will give us a size of the photons.
But, if you put another wire in front of your dipole, it will "capture" more photons. "In front" means in the line between the emitter antenna and the receiver. So, whith this device ( a yagui antenna, used to receive TV signals ) you receive photons from a bigger surface.
Where is the limit ?
meopemuk said:I guess you are confusing the size of the wavelength of photon's wave function with the particle size. The wavelength can be made as large as you wish. Still the photon should be treated as a pointlike particle.
Eugene.
alvaros said:No, I am not confusing the size of the wavelength of photon's wave function with the particle size.
The photon can't be a "pointlike particle". Remember the experiments about interference: a single photon goes through two holes.
Because it's related to the essence of QM weirdness and to dualism. If physicists talk about particles, and they never say these particles are in the detector, people will, rightly, think that these particles have to fly from source to detector. Then, the conclusion that they go in both slits is straightforward, as are the strange conclusions about their size.Gza said:Why does this question come up in every other post in this forum?
alvaros said:How big is a photon ? ( Where a single photon can be detected ? )
How does light propagate ? Indeed, isotropically...alvaros said:When a photon is emitted it goes in all directions ? or just in one ? N, S, E..
Or there is a probability you can find it in any direction ?
The photon size is a concept that does not exist because size is defined in terms of spatial coordinates. A photon however is defined as a chunk of energy. Energy is a concept that is NOT defined in terms of spatial coordinates. Do you see the contradictio in terminis ?alvaros said:No, I am not confusing the size of the wavelength of photon's wave function with the particle size.
Yes it can be because the particle (position and momentum) and wave (wavelength, frequency) nature are dual. They are like two different languages to say the same thing : ie a photon is a chunk of energy.The photon can't be a "pointlike particle". Remember the experiments about interference: a single photon goes through two holes.
marlon said:The photon size is a concept that does not exist because size is defined in terms of spatial coordinates. A photon however is defined as a chunk of energy. Energy is a concept that is NOT defined in terms of spatial coordinates. Do you see the contradictio in terminis ?
Yes but that does not imply the photon is a point particle in coordinate space, ie a particle with finite sized soatial boundaries. THAT is the point i was trying to make.Proof.Beh said:There is no sense for your answer. If a light ray emits from a lighting source, we allocate to that length, diagonal of light ray etc and know that a light ray made of the number of bounded photons.
How on Earth can you make this conclusion. Not only that, you are also talking about a photon's form. What is that ?Then the light has spatial coordinates and thus a photon also is this form.
Thanks.
Mr Beh
marlon said:The photon size is a concept that does not exist because size is defined in terms of spatial coordinates. A photon however is defined as a chunk of energy. Energy is a concept that is NOT defined in terms of spatial coordinates.
marlon said:Yes but that does not imply the photon is a point particle in coordinate space, ie a particle with finite sized soatial boundaries. THAT is the point i was trying to make.
besides, what are "bounded" photons. I always thought that photons do NOT mutually interact (at least up the the first orders of EM interaction).
How on Earth can you make this conclusion. Not only that, you are also talking about a photon's form. What is that ?
When you talk about form in this context, you are talking about a shape defined by finite spatial boundaries. A photon is NOT defined in this way. If you do not agree with me, i politely ask you to provide me with such a definition. Realise that you cannot use the wavelike photon concept to answer that question because of the reasons in gave in my previous post.
marlon
Sorry, but i don't get it :Proof.Beh said:"Bounded" imply to number of the photons in the length of a light ray that can reffer to finite.
I am sorry but according to me, there are no photons "osculating" with the surface. ISo if we consider the Photo-electric experiment, in a arbitrary time invertal, number of photons that osculate with the surface are bounded or finite.
It means that the accumulation of photons occupy a spatial region in coordinates of spase.
Therefor can you say me that what is your supposal for relating this subject to energy of a photon?
marlon said:Just ask yourself this: Suppose that a photon indeed has finite spatial boundaries, how would you measure them?
marlon said:But suppose you WOULD measure, you would indeed observe that there is a photon present through its interaction with the detector (emitted EM radiation for example : the light signal from the detector). The point is however that you are not observing the actual photon, you are not measuring the photon's (x,y,z) coordinates !
Shahin said:I think we can answer the question by another method. Has the photon a wavefunction? If it has, we can use |psi|^2 as a magnitude that can give us an idea of the size of the photon, considering, for example, that the photon size is "the volume" where, again for example, |psi|^2>1/10maximum (|psi|^2). It is like when you want to know the size of a nucleo, you can use several magnitudes to determine this, the mass, the charge... and you say: when the density is less than... i consider the nucleo has ended.
marlon said:Suppose that a photon indeed has finite spatial boundaries, how would you measure them?
alvaros said:I think it would be helpful if you speak about operational definitions instead of "chunk" "size" "bounded"...
If a photon has no size nor path, how can you get a photo ?
If a photon makes a spot on the photografic film we can infer that it collided in that point. How big can be this point ?
Shahin said:we can use |psi|^2 as a magnitude that can give us an idea of te size of the photon, considering, for example, that the photon size is "the volume" where, again for example, |psi|^2>1/10maximun(|psi|^2).
jtbell said:How about an electron? Consider a hydrogen atom in its ground state. Would you say that the electron in that atom has a radius that is roughly equal to the Bohr radius (or whatever result your prescription gives), which most physicists would say measures the size of the electron's ground state orbital?
Schrodinger's Dog said:Prof Beh, volume? What do you mean by this term? As I understand volume it would involve mass yes?
To be frank the question has been answered very well, there is no size, only a mathematical probability of where a photon will progress and this has nothing at all to do with an actual "size of the photon" I think you're confusing the issue.
Wavelength or direction or phase or whatever is the "length" in terms of this, but it does not denote an implication of size on the photon, at least as I understand it, all we're talking about is a spatial vector and that is not a matter of size per se just motion.
I could be wrong here, hell I often am, but size here is a matter of semantics, and is not really important when discussing the OP. I think we're talking about concepts that are not part of a "size" issue, merely vector progression.
It's irrelevant the point is energy not a point of size, of course energy will cause the measurement medium to produce a point ie where it hit, but that does not infer a size only a packet of energy or quanta no?
Because if we cannot measure the spatial concepts you are referring to then how can we prove they even exist ? Again i ask you, how do you measure a photon's size ?Proof.Beh said:Why you connect the structure of a photon (such as spatial coordinates) to the "measuring" concept?
Indeed photons propagate through the x,y,z plane. But that is about ALL you can say.You said that "they are the packets of energy only that we are observing them", so have these packets the spatial coordinates or not?
Which was ?You did not answer yet my essential question.
That's what we call distance, not length.1- length of a light ray means that if we consider a laser ray that emmited from its source, then we can measure its duration of arriving for example to point B ("A" is location of sourse), then by name its duration "T" and use the formula c.T=L ("c" is speed of light) we shall define L or length of light ray.
I don't get this.2- imply sth means PREDICATE to sth.
I am sorry but i really don't understand your English here. Besides, are you talking about volume of rays here ? How does one measure that volume and how does one measure the size of a photon experimentally ? Those questions, i ask YOU.3- Because I meant that show if we guess in the double slit experiment will constrict the diagonal of each slit, then the your energy packets because of their spatial coordinates and volume will cross for the first situation less.
You just wrote : a region in which there is a certain probability of finding the photon. That's correct. Then you say, the volume of that region is the size of the photon, right ? But then i can say, well you will always have probability 1 (ie absolute certainty) to find that photon in this region because the photon's volume is just as big as that region. Once you are in the region, you will observe the photon because it "fills up" they entire region. Clearly, this is incorrect.Shahin said:this wavefunction, has a maximun and a particular region in which it is very probable to find the photon, and outside this region we can neglect the probability of finding te photon. So we can conclude that, if the photon has size, a volume, it could be the volume of this region.
Shahin said:No no, i didnt mean that thing. You are talking about the bohr radius, that is the radius of certain orbit in a certain system of reference, and has nothing to do with what i wrote. In your example, |psi|^2 is not "big" in all the sphere that has the bohr radius centred in the nucleo, so the condition |psi|^2>1/10maximun(|psi|^2) does not hold. The correct analysis would be, for example, represent |psi|^2 as a function of r, and yo will see that |psi|^2 is only appreciable in a little region around the bohr radius.
Schrodinger's Dog said:To be frank the question has been answered very well, there is no size, only a mathematical probability of where a photon will progress and this has nothing at all to do with an actual "size of the photon" I think you're confusing the issue.
jtbell said:The wave function for the ground state of the hydrogen atom is
[tex]\psi = \frac{1}{\sqrt{\pi} a_0^{3/2}} e^{-r/a_0}[/tex]
with the corresponding probability density
[tex]|\psi|^2 = \frac{1}{\pi a_0^3} e^{-2r/a_0}[/tex]
where
[tex]a_0 = \frac{\hbar^2}{mq_e^2} = 0.0529 nm[/itex]
is the (first) Bohr radius.
Clearly the probability density is maximum at [itex]r = 0[/itex], with the value
[tex]|\psi|^2_{max} = \frac{1}{\pi a_0^3}[/tex]
Setting [itex]|\psi|^2 = 0.1 |\psi|^2_{max}[/itex] and solving for [itex]r[/itex], I get
[tex]r = - \frac{a_0}{2} \ln 0.1 = 1.15 a_0[/tex].
Using your criterion, then, the size of an electron in a ground-state hydrogen atom is (1.15)(0.0529 nm) = 0.0608 nm.
So the electron has no size but the photon has ? I really don't get why you think this is the case. How does this size determining method work ? I tried to reread your previous posts but i did not find a valid explanation. I guess this method does not work according to the stuff you wrote in the volume of the region in which you can find a photon.Shahin said:I have just mentioned it as an idea about how to know the size of a photon.