101–106 of 106 posts
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That would imply a frequency shift, which clearly doesn't happen (mirrors don't redshift the light that hits them).
I balked at that too, because infinite mirrors and mirror houses also don't show any wavelenght shift no matter how many reflections they do. They do change perceived amplitude, as no mirror is perfectly reflective.
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Feynmann is very clear that the photons bouncing off a mirror are not the same ones that hit it. They are absorbed by electric oscillators (free electrons in the material) and destroyed; then new ones are created and emitted. He's also careful enough to point out that electrons don't really have an identity that would allow you to meaningfully define "not the same". :)
Electrons? We were just told that there is only one single electron in yesterday's posts. It's almost like they don't know what an electron is
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Does Feynman say that? If an electron absorbs a photon, why would it create another one of the same frequency, and with polarization perfectly rotated by 90°?
Because of the layout of the electron orbitals.
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Not to quibble about definitions of what "change" means, but I thought the red shift depended entirely on the relative speed of the emitting and receiving body? A laser beam for example could not be analyzed for its red shift, unless we knew the original frequency, because there would be no spectral absorption pattern to determine the shift. So we cannot tell how far laser light traveled before it reached our sensor.
Not a quibble at all. The redshift I'm referring to is the kind of redshift due to gravity, as opposed what you're describing which is redshift due to the Doppler effect.
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> I believe proton decay is still considered hypothetical Definitely. > [link] is a good overview That overview seems to overstate the likelihood of proton decay. In fact, it has it backwards. The default position is that protons are stable, per the standard model, not that they're susceptible to decay.
> The default position is that protons are stable, per the standard model, not that they're susceptible to decay. It's only the "default" in the sense that the simplest model explaining data gathered to date (the standard model) predicts no decay. However, most physicist do not believe the standard model is the last word (and surely it cannot be when you go to the Planck scale), and many models post-SM models predict…
I don't think it's the case that many post-SM models predict proton decay. A few do, but even those are now tightly constrained by observations that place the proton's half life at more than 10^34 years. A lot of models that previously predicted proton decay have been empirically falsified on such grounds, and those that remain are looking pretty shaky. So I don't know. If you run that survey, I believe that the average physicist would come out against proton decay. It would be an interesting survey, in any case!!
Earlier quoted context omitted.
Feynmann is very clear that the photons bouncing off a mirror are not the same ones that hit it. They are absorbed by electric oscillators (free electrons in the material) and destroyed; then new ones are created and emitted. He's also careful enough to point out that electrons don't really have an identity that would allow you to meaningfully define "not the same". :)
Electrons aren't unique in not having identities. Photons of the same wavelength are similarly fungible if I remember right, though it's a little more defensible to call the reflected light not the same photons since the original photons are transformed to something we don't call photons before photons are produced again.