This is probably a dumb question. I guess what I'm trying to ask is if radio waves travel the same speed as gamma rays, how do gamma photons carry more energy than radio photons? Do they spin faster? What other energy sources could they carry if they are moving the same speed through space?
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$\begingroup$ Photons do not "carry other energy sources." What are you trying to ask? $\endgroup$– Carl WitthoftCommented Dec 18, 2017 at 15:03
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1$\begingroup$ Photons, if they exist, don't "spin." We assign a quantum property that we call "spin." Any more than quarks have "color." To those who object to "if they exist..." : I'm a moderate supporter of the concept that there is no matter and no particles, just highly concentrated locales of probability. $\endgroup$– Carl WitthoftCommented Dec 18, 2017 at 15:06
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3$\begingroup$ Massless particles are different from usual objects with mass. For objects with mass, your intuition "more (kinetic) energy is equivalent to higher speed" is entirely correct. For an object/particle with a given mass $m$, the energy is an increasing (hence invertible) function of the speed. Classically, it is $\frac12 mv^2$, and relativistically it is another (more complicated) formula. But for massless particles, it is different! $\endgroup$– Jeppe Stig NielsenCommented Dec 18, 2017 at 15:07
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$\begingroup$ @CarlWitthoft That seems a bit disingenuous. Bruce is trying to ask what the difference is between low and high energy photons, and without knowing what that difference is he cannot possibly ask in terms of the frequency, which is the answer. $\endgroup$– AaronCommented Dec 18, 2017 at 19:32
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$\begingroup$ @Aaron maybe -- I'm a bit concerned that his text is a mix of possibly useful question and significant misunderstanding of physics terminology. $\endgroup$– Carl WitthoftCommented Dec 18, 2017 at 19:36
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3 Answers
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Higher energy photons have shorter wavelengths. This means they are higher frequency. We can look at the equations, like E=h𝜈, and see directly that shorter wavelengths have more energy, but I think you're going to want a more intuitive example. Let's haul out the ropes!
Battle ropes are an exercise tool. You try to set up waves that propagate down the ropes. If we visualize ourselves pumping these ropes, we see that if we want to create higher frequencies and shorter wavelengths, we have to put more energy into the system. We have to accelerate the ropes up and down at higher rates, and that requires more energy. This is true even if we keep the amplitude of the ropes the same.
Photons don't move up and down like this, but they do create oscillating electric and magnetic fields (which are often visualized in a form similar to battle ropes). Oscillating this field more rapidly involves more energy, in the same way as the higher frequency battle ropes did.
Like with the battle ropes, the light waves travel at the same speed, regardless of whether they are high frequency (high energy) or low frequency (low energy). The energy is seen in how rapidly the rope changes position (or the fields change strength).
answered Dec 18, 2017 at 1:53
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1$\begingroup$ ...and even "oscillating" is quite a loaded word given the question. The OP seems to be asking exactly about the nature of such oscillation. I don't trust my own intuition of this enough to attempt an answer. I guess I'm imagining some potential flowing from one field to another and back. I'm not sure whether it makes sense to say that if the field is "stronger" (higer potential) at the maximum point, these swaps will happen faster. $\endgroup$ Commented Dec 18, 2017 at 14:04
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5$\begingroup$ @JirkaHanika "The exact nature of such oscillation" is actually not something science can provide, despite what they teach. All it can do is provide better and better models which describe how it could work, in theory. We do have equations which successfully model electromagnetic effects using waves, and we can use calculus to define the energy stored in those waves (if we know calculus). But really they're just models, not the exact nature of things. Visual images like the ropes are simply helpful if one doesn't want to dive into the calculus based models =) $\endgroup$ Commented Dec 18, 2017 at 14:24
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1$\begingroup$ And still, the mystery of photon-wave duality is persistent: why do we have to talk about the frequency or wavelength of a particle? I think your answer is good, but duality is still a mystery-filled model. Is it easier to teach than fields? Probably. $\endgroup$– Bill NCommented Dec 18, 2017 at 16:51
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1$\begingroup$ @BillN Duality is another beast entirely. I do think it would be easier to teach electromagnetism properly if we waited until we had college level math and were experts in quantum mechanics before tackling light ;-) Duality actually isn't as mysterious as they make it sound. It's actually a really fundamental thing: models aren't exactly the same as the thing they model. A schematic of an airplane is not the same as an airplane. Wave/particle duality is just what happens when you try to use simple models to describe electromagnetism. Sometimes they aren't 100% right. $\endgroup$ Commented Dec 18, 2017 at 17:06
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$\begingroup$ One blind man feels the ears of the elephant, and thinks an elephant is like a fan. Another blind man feels the trunk of the elephant, and thinks an elephant is like a rope. One experiment shows wavelike behavior of light. Another experiment shows particlelike behavior of light. Then, of course, there's modern QM, which is tremendously effective at predicting the behavior of light. It's like a seeing-man which can see the skin of the elephant entirely (and theorize what might be inside). $\endgroup$ Commented Dec 18, 2017 at 17:10
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All photons travel at the same speed (light speed) and carry the same spin (1). A gamma ray photon packs more punch than a radio wave photon, simply because its wavelength is much, much shorter. The formula is:
$\mathrm{energy} = \frac{\mathrm{planck's\ constant}\ \times\ \mathrm{speed\ of\ light}}{\mathrm{wavelength}}$
Which means as the wavelength gets smaller and smaller, the energy contained in each photon goes way up.
answered Dec 18, 2017 at 1:43
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$\begingroup$ Can someone please explain why my answer above shows a red -2 downvote on my user page? while it is nowhere near as detailed and thorough as cort ammon's, it is as far as I can tell factually accurate... $\endgroup$ Commented Dec 21, 2017 at 5:35
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There is a difference in wavelength and hence frequency. The energy is given by hv where h is Plancks constant and v is the frequency. Radio waves have a relatively long wavelength whereas gamma rays are much shorter.
