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| ▲ | amluto 4 hours ago | parent | next [-] | | I haven’t tried to look up the history of this claim, but here are some guesses: 1. There’s a sort of diffusion process going on. Photons from the core have some mean free path as a function of radial position (and, obnoxiously, of wavelength as well, so maybe we ignore that). You could calculate the mean time for a hypothetical object emitted from the core and traveling according to those mean free paths to escape. 2. You could imagine you have marked a photon and watched it travel. This is quite problematic. First, photons in thermal equilibrium obey Bose-Einstein statistics because they are indistinguishable bosons, and anything that could mark them would change the statistics to that of distinguishable particles. But whatever, the temperature is high and maybe this doesn’t matter. Also never mind that those core photons are mostly much shorter wavelength than the photons we see. But you can still imagine. (The answer is probably quite similar to #1 since this is sort of the same problem depending on how you think about the interactions with matter in the sun.) 3. You could calculate how long it would take to notice anything if the core suddenly stopped fusing. | | |
| ▲ | gus_massa 3 hours ago | parent | next [-] | | I agree. I read the 5000 years time a few times and I don't like it. When you have a transparent medium like water or glass, the photon that enters and the photon that exit share a lot of properties, in particular energy/color/frequency. Perhaps they have a shift in the phase or a different polarization (like in water with sugar or if you want to be fancy a quarter wave plate). You can still split a beam before in enter and make interference experiments after half of it passed though water or glass, and other weird experiments, so I think it's fair to call them "the same photon". But in the Sun, the original photons in the center of the Sun have a few very specific values of energy/color/frequency, that are totally lost. (But the neutrinos have so few interactions that they don't lose this information, and it's possible to do neutrino spectroscopy!) Also, the photons emitted by the "surface" of the Sun have a wide spectrum of energy/color/frequency that is very close to black body radiation at something like 5000K-6000K. So in my opinion it's better to think that the original photon in the center is absorbed shortly after it's emitted, and transformed into heat. The heat takes 5000 years to get to the surface. And then the hot surface emits a few new photons unrelated to the original one. I'm not sure what is the main transmission method inside the Sun: conduction, convection or radiation. | |
| ▲ | amluto 41 minutes ago | parent | prev [-] | | belated edit: My comment about “whatever, the temperature is high” is silly. The mean photon energy is about 2.7kT, which scales in direct proportion the interest bits of the Maxwell-Boltzmann and Bose-Einstein distributions (see [0] and [1]). At 2.7kT, the curves are pretty close, but you don’t have to go down that far to get a big difference. So tagging all the light would cause a substantial change in the sun’s color. [0] https://scholarship.haverford.edu/cgi/viewcontent.cgi?articl... Eq. 16
[1] Handy plot at https://commons.wikimedia.org/wiki/File:Quantum_and_classica... |
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| ▲ | teamonkey 2 hours ago | parent | prev | next [-] | | Photons are generated in the star’s core but the core is dense. The photons move around the core, bouncing off other particles, a random walk. It takes a vast amount of time for that photon to escape the sun and reach the Earth, as per monte-carlo simulations of this random walk. However, as the photon collides with other particles during its random walk, some of its energy is transmitted to those other particles. Sometimes a collision transfers energy to it too. In a simple model, the energy that originally belonged to the photon gets transmitted from particle to particle through convection, and can escape the star through radiation long before the original photon reaches the surface. I don’t think that model is supposed to be physically accurate, rather to be an illustration about the convention process inside a star. | |
| ▲ | fsh 4 hours ago | parent | prev | next [-] | | Any interaction between light and matter can be modeled as absorption and re-emission (stimulated or spontaneous) of photons. In this picture, there is not much difference between a photon traveling through the sun or through a piece of glass, and the analog makes physical sense. Since photons are massless elementary particles, they are indistinguishable and their number is not conserved. The notion of "the same photon" is questionable in any case. | |
| ▲ | Hikikomori 4 hours ago | parent | prev [-] | | Similar to how infrared radiation works in our atmosphere, minus the timescale? |
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| ▲ | MyHonestOpinon 5 hours ago | parent | next [-] | | Oh, probably skipped physics too. I haven't seen the video (yet), but I would have bet that light on earth came out 8 minutes ago from the sun. | | |
| ▲ | pantulis 5 hours ago | parent [-] | | Light from the sun that is reaching us now escaped the surface of the sun 8 minutes ago, yes. But photons are generated in the core through nuclear reactions, where they take their sweet amount of thousands of years bouncing around until they get out. | | |
| ▲ | mikkupikku 3 hours ago | parent | next [-] | | I think this is right in a certain sense, but not precisely. From what I understand no visible light photons are created in the core from nuclear fusion, it's mostly a bunch of gamma rays that get almost immediately absorbed. The energy, but not the photons from fusion, gets transfered up through the layers of the sun, through radiation and convection, eventually heating the photosphere. It is then the photosphere, white hot, which ultimately radiates the visible light we see as sunlight. | |
| ▲ | gpvos 5 hours ago | parent | prev [-] | | And thats a fact you don't need to learn in high school, at least you didn't in my time. |
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| ▲ | JeanSebTr 5 hours ago | parent | prev | next [-] | | They probably meant, as explained in the video, "light from our sun" | |
| ▲ | smarf 5 hours ago | parent | prev [-] | | ...did you skip human socialization? |
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