As said in the title, I am curious about the reported measurements for cooled black bodies. Any source is welcome.
I am neither interested in any thought experiment nor in the well-established law of blackbody radiation accentuated on hot bodies.
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asked Jun 10, 2020 at 18:09
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2 Answers
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Not sure what's the coldest black body ever measured, which would correspond to the longest wavelength, but it might be the cosmic microwave background at a peak wavelength of 1.063 mm. However, the spectrum of the cosmic microwave background has been measured at least to about 5 mm. The cosmic microwave background is the Doppler-shifted remnant of the black body corresponding to the universe about 370,000 years after the Big Bang.
answered Jun 10, 2020 at 18:30
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1$\begingroup$ This seems like more of a guess than an answer. Maybe someone has measured radiation from something in a lab cooled to 1 K. Or 1 mK. $\endgroup$– G. SmithCommented Jun 10, 2020 at 19:38
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$\begingroup$ Maybe, but the best anyone can do is point out the longest wavelength black body radiation measurement they know of. $\endgroup$ Commented Jun 10, 2020 at 21:19
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$\begingroup$ It would be interesting to calculate the rate of emission of, say, 10 MHz photons from a test tube full of solid helium at 1 degree Kelvin. I have a feeling those photons would come out v-e-r-y slowly. $\endgroup$ Commented Jun 10, 2020 at 21:35
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Cosmic Microwave Background is the most perfect source of blackbody radiation that exists in nature and has an associated temperature of 2.7K Source Wikipedia
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1$\begingroup$ This doesn’t answer the question. It didn’t ask about the most perfect source. $\endgroup$– G. SmithCommented Jun 10, 2020 at 19:52
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$\begingroup$ If you have read the question carefully you would have noticed that my answer perfectly fits the requests. It's not for a case that the other answer is about the same topic. The fact that it is the most perfect source of blackbody radiation present in nature is a property that sums up with the fact that is a very well measured radiation "cooled" by gravitational redshift. So, you are wrong, mine was a perfectly legit answer, but if it was incomplete, that's another thing. $\endgroup$– Rob TanCommented Jun 11, 2020 at 9:23
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$\begingroup$ I read the question carefully. Please do not assume that I did not. $\endgroup$– G. SmithCommented Jun 11, 2020 at 16:15