It is not that simple. Photons have energy but not contributed by a rest mass but by their relativistic momentum.
AAhhh, I see.
James,
Thus, as I said originally, the “rest mass” represents what the photon WOULD have IF absorbed (at rest). It is just a terminology issue.
But that’s wrong.
No, it’s not.
Well, then you need to argue that with Einstein. I didn’t invent the term. The explanation that I got many years ago for that term is still the same one they give today as far as I can tell.
Sigh! This really isn’t right, and your sarcasm is misplaced. The momentum of a particle with finite rest mass (for example an electron) is indeed mv (where the relativistic mass m=m0/(1-v^2/c^2)^-2 and m0 is the rest mass). But the photon cannot have finite rest mass because by definition it has v=c, and that would result in the photon having an infinite relativistic mass and carrying an infinite kinetic energy = 0.5 m0 v^2/(1-v^2/c^2)^-2 (and an infinite momentum) which is obviously nonsense. Since the photon travels, by definition, at the speed of light, its rest mass must be zero to avoid infinite kinetic energy. Using the expression for the momentum of a particle of finite rest mass with a rest mass of zero and speed of c, gives a momentum of 0/0, ie undefined, so we have to express the photon in another way. It carries finite energy and we know precisely how much energy is does carry, initially through considerations of black-body radiation – it is equal to h*nu where h is Planck’s constant and nu is its frequency. The photon also carries momentum which can be measured by radiation pressure: p=hbar k =h nu/c where h is Planck’s constant and nu is the frequency.AAhhh, I see.
If we just don’t write it as an “m”, but rather a “p”, then we don’t have to tell anyone that “p = mv” (which would also = 0 …shhhh), so we can get away with it… kewl.
The indigent?
This is not true for a photon, and it’s not true for a particle of finite mass.
You proposed an analogy that wouldn’t help anyone to understand anything because it conflicts in several ways with known physics.
You are wrong. The correct term is diffraction whether you are talking about waves or particles. Dispersion means something else as I have pointed out (a frequency dependent refractive index, or a frequency dependent group velocity, which is the same thing) - or in a completely different context the mixing of particles into a fluid.
Not - in the diffraction case there is energy in the geometrical shadow, and since the conservation of energy applies, that means there is less energy in the illuminated region in the diffraction case than in the geometrical case. When I said one finds less energy in the geometric shadow and more in the illuminated region than one would expect from geometry I managed to get it back to front. However, you cannot say that all photons are diverted towards the edge - first of all there is no way that you can create a single stream of photons (it’s physically unrealisable because a stream narrower than a wavelength does not propagate as a narrow stream but self-diffracts and the narrower the stream the wider the diffraction angle); and secondly, you can’t determine a unique path for any photon. If you look at it using classical wave theory, you get the sum of two terms - the geometric field which is a plane wave plus the diffraction field. The latter appears to arise from a line-source on the diffracting edge propagating into both the geometric shadow AND into the geometric illuminated region, in antiphase with the plane wave at the geometrical boundary.
You are confusing two entirely different phenomena: wave diffraction, which is a classical phenomenon is what we are talking about. Bending of stellar light by intervening masses is a gravitational effect and is relativistic – an entirely different thing.
Then, you are not talking about the OP’s question, which was about the quantised Young’s experiment where individual photons arrive many orders of magnitude longer than picoseconds apart and still produce fringes.
How do you know that?
How do you know that?
How do you know the relationship between the size of things and “that propagation effect” without observation? You have a bar of platinum in your hands. Its length at 20 degrees C is defined as a “stick”. Now what is the speed of light in sticks per second, and how do you determine it?
The size of things is caused directly by the propagation being measured by that size? You are not making sense. There is no way that you or anyone else can know from pure logic that light is always observed to be the same speed in different frames because it’s an observation.
Why would size not exist if the speed of light were infinite?hecd2:
Because SIZE would not exist at all.
Why would all things be the same thing if the speed of light were infinite?
Why do distances and dimensions exist in the first place? What metaphysical argument links the speed of light *necessarily *to the existence of distance and dimensions?
In that statement, perhaps misunderstood, I said “when they land”, meaning that they are no longer photons because a photon cannot actually land, but gets absorbed into another variety of energy. I stated clearly that when in flight “they have merely momentum”.They have what is called “rest mass” when they “land” or are absorbed. But while in flight, they have merely momentum. The distinction had to be made to make the math work out right.
EXACTLY in what way does it conflict? Don’t give me a string of equations that you think somehow won’t fit. Tell me in what exact way that physical model doesn’t apply to the physical situation. To do that, you need to come up with a physical picture yourself.
Oh give us a break and get a dictionary;
Yes you DID get it WRONG!!! {geeez}
Maybe YOU can’t, but it certainly CAN be done. But the truth is that it wouldn’t matter whether it could realistically be done anyway. We were talking about a theoretical situation.
Take a course or 2 in metaphysics.
Well I agree, of course, that it is not illogical and inferences and conclusions we make from observations should not unnecessarily violate logic - but that does not mean it’s derivable by pure logic without observation and I deny the possibility that it is so. I don’t know any way of doing that and neither do you. As he himself said, his argument has an *empirical *foundation
Yes – he and I agree that the fact that the speed of light is finite is an observation, not a question which can be settled by pure logic.
Asking for a number to represent infinity is a meaningless question and reveals a lack of mathematical knowledge.
You really don’t get it, do you? We only know something about the nature of light, for example that it has wave-like properties because we have *observed *it to be the case. There is no purely logical reason absent observation why it must be so. You are relying on (misunderstandings of) physical optics and special relativity to come up with your argument, but neither of these are purely logical metaphysical pursuits. They are science and thus based on empirical evidence.
Why is it that people like you have difficulty in understanding what you read. I didn’t say there was no logic. I said that the things you claimed to know by pure logic (ie that light must have a finite speed and what it is) *cannot *be known by pure logic. Everything, *everything *that we *know *about the nature of light has its roots in observations that we have built on with logical inferences and tested empirically. Without an empirical basis, we couldn’t begin to know anything at all about light.
Well, I have to say that I have very little respect for people who know nothing about a subject, who don’t even know that they don’t know what they don’t know, but who adopt a patronising and didactic tone, and ridicule those who do know. For example, your absurd tirade against quantum mechanics on this thread is absolutely ill-informed, you reveal no knowledge of the subject at all, you don’t know why it was developed, you have no conception of the beautiful, useful, surprising, disturbing and accurately predictive discoveries and concepts in it, you misrepresent probability, quantum uncertainty and entanglement (Schroedinger, Bell and Aspect mean nothing to you) - and you have the gall to satirise someone like Leonard Susskind for giving an undergraduate course on quantum mechanics. Your failure to understand him is your failure - not his.
So what is your source for knowing that such a thing “cannot” be known?
I see, so you are an offended worshiper of the quanta magi.
But your original statement was wrong, because photons have zero rest mass (as defined by Einstein in his relativistic momentum and energy relationships) for reasons that have been carefully explained to you in more detail and with more patience than you deserve.
I have no idea where your confusion is coming from, but you seem determined to hang on to it.
While they are still “photons”.