5 ms·

I think you're wrong here. Given an infinite amount of time and an infinite number of stars distributed evenly in an infinite universe, even the dust and planet

by drcube 14y ago

I think you're wrong here. Given an infinite amount of time and an infinite number of stars distributed evenly in an infinite universe, even the dust and planets will start to radiate[1]. The paradox hinges on the assumption that the universe is infinite in size with an even distribution of stars which have been radiating for eternity. So, it's only a paradox if you assume those things. Remember, this question was first asked in the 1600s. [1] https://en.wikipedia.org/wiki/Black_body_radiation https://en.wikipedia.org/wiki/Black_body_radiation

dredmorbius 14y ago
The dust and planets will start to radiate ... at the blackbody rate. On average, that's somewhere in the neighborhood of 3K.
- lutusp 14y ago
  Yes, true, but Olbers' Paradox was posed long before the Big Bang theory or the idea that the universe is expanding. In a static universe such as Einstein proposed in 1916, eventually the entire universe would heat up to the temperature of its stars. This made Olbers' paradox an important reality-test, and reality failed the test. It was only because of the Big Bang and universal expansion was Olbers' Paradox reconciled with observation.
  - psb217 14y ago
    Err, Einstein's static universe did not preclude the death of stars via exhaustion of their fuel. So, the entire universe would "heat up" to a uniform distribution (i.e. evolve according to the heat equation), with the future local heat being everywhere equal to the mean local heat at present. And, in general, the universe is overwhelmingly empty and cold. I'm not sure what the mean energy of the universe is, or what the minimal energy required to coax an electron to jump around and create visible light is, but it could well be that the values are such that an entire universe homogeneously set to the mean local energy of our current universe would be nowhere energetic enough to cause the birth of (naked-human-eye-visible) photons. (note: it would also be important to know the relative amounts of energy dedicated to mass and motion) In other words, given a perhaps dubious mixing of temporally diverse understandings of physics, the relevant homogeneously energetic universe would likely be nowhere energetic enough to cause light. Thus, perhaps we should be more surprised that everywhere we look isn't dark?
    - lutusp 14y ago
      > Err, Einstein's static universe did not preclude the death of stars via exhaustion of their fuel. Yes, by a process of radiating away massive amounts of energy. > So, the entire universe would "heat up" to a uniform distribution (i.e. evolve according to the heat equation), with the future local heat being everywhere equal to the mean local heat at present. No, not "at present" "At present" is the outcome of a combination of energy radiation and cosmological expansion leading to the present. Were it not for the factor of expansion, the universe would be much, much hotter than it is now. > And, in general, the universe is overwhelmingly empty and cold. Yes, it is -- because of cosmological expansion. Were this not the case, the universe's temperature would be equal to or or greater than it was at "recombination" time, i.e. when normal atoms formed and the universe first became transparent to radiation, at about 300,000 years and an average temperature of about 4000 kelvins. > I'm not sure what the mean energy of the universe is ... Don't you mean average temperature? One can speak of total energy, or average temperature, but "mean energy" doesn't make much sense. > ... or what the minimal energy required to coax an electron to jump around and create visible light is ... That's well-established. When the energy of an impinging photon is equal to that for a possible electron orbital transition, and ignoring for the moment a few other considerations, the electron will absorb the photon and move to a higher orbit. Conversely, if an electron should drop from its present orbit to a lower orbit, a photon will be emitted whose wavelength is proportional to the energy difference between the orbits. > In other words, given a perhaps dubious mixing of temporally diverse understandings of physics ... At any given time, there is one understanding of physics. It's obviously open to challenge as all scientific theories are, but each challenge must be accompanied by observational evidence. The point of science is not to have any number of theories, the point is to have one -- the one that best answers observation. > the relevant homogeneously energetic universe would likely be nowhere energetic enough to cause light. For a sufficiently comprehensive definition of "light" (meaning electromagnetic radiation), no, not possible. There will always be electromagnetic radiation, even for a universe at zero Kelvins, because of quantum effects. > Thus, perhaps we should be more surprised that everywhere we look isn't dark? Not in this universe, no -- not with stars converting mass into prodigious amounts of energy everywhere we look. Which leads, full circle, to Olbers' Paradox.
      - 14y ago

by drcube 14y ago

dredmorbius 14y ago

The dust and planets will start to radiate ... at the blackbody rate. On average, that's somewhere in the neighborhood of 3K.

lutusp 14y ago
Yes, true, but Olbers' Paradox was posed long before the Big Bang theory or the idea that the universe is expanding. In a static universe such as Einstein proposed in 1916, eventually the entire universe would heat up to the temperature of its stars. This made Olbers' paradox an important reality-test, and reality failed the test. It was only because of the Big Bang and universal expansion was Olbers' Paradox reconciled with observation.
- psb217 14y ago
  Err, Einstein's static universe did not preclude the death of stars via exhaustion of their fuel. So, the entire universe would "heat up" to a uniform distribution (i.e. evolve according to the heat equation), with the future local heat being everywhere equal to the mean local heat at present. And, in general, the universe is overwhelmingly empty and cold. I'm not sure what the mean energy of the universe is, or what the minimal energy required to coax an electron to jump around and create visible light is, but it could well be that the values are such that an entire universe homogeneously set to the mean local energy of our current universe would be nowhere energetic enough to cause the birth of (naked-human-eye-visible) photons. (note: it would also be important to know the relative amounts of energy dedicated to mass and motion) In other words, given a perhaps dubious mixing of temporally diverse understandings of physics, the relevant homogeneously energetic universe would likely be nowhere energetic enough to cause light. Thus, perhaps we should be more surprised that everywhere we look isn't dark?
  - lutusp 14y ago
    > Err, Einstein's static universe did not preclude the death of stars via exhaustion of their fuel. Yes, by a process of radiating away massive amounts of energy. > So, the entire universe would "heat up" to a uniform distribution (i.e. evolve according to the heat equation), with the future local heat being everywhere equal to the mean local heat at present. No, not "at present" "At present" is the outcome of a combination of energy radiation and cosmological expansion leading to the present. Were it not for the factor of expansion, the universe would be much, much hotter than it is now. > And, in general, the universe is overwhelmingly empty and cold. Yes, it is -- because of cosmological expansion. Were this not the case, the universe's temperature would be equal to or or greater than it was at "recombination" time, i.e. when normal atoms formed and the universe first became transparent to radiation, at about 300,000 years and an average temperature of about 4000 kelvins. > I'm not sure what the mean energy of the universe is ... Don't you mean average temperature? One can speak of total energy, or average temperature, but "mean energy" doesn't make much sense. > ... or what the minimal energy required to coax an electron to jump around and create visible light is ... That's well-established. When the energy of an impinging photon is equal to that for a possible electron orbital transition, and ignoring for the moment a few other considerations, the electron will absorb the photon and move to a higher orbit. Conversely, if an electron should drop from its present orbit to a lower orbit, a photon will be emitted whose wavelength is proportional to the energy difference between the orbits. > In other words, given a perhaps dubious mixing of temporally diverse understandings of physics ... At any given time, there is one understanding of physics. It's obviously open to challenge as all scientific theories are, but each challenge must be accompanied by observational evidence. The point of science is not to have any number of theories, the point is to have one -- the one that best answers observation. > the relevant homogeneously energetic universe would likely be nowhere energetic enough to cause light. For a sufficiently comprehensive definition of "light" (meaning electromagnetic radiation), no, not possible. There will always be electromagnetic radiation, even for a universe at zero Kelvins, because of quantum effects. > Thus, perhaps we should be more surprised that everywhere we look isn't dark? Not in this universe, no -- not with stars converting mass into prodigious amounts of energy everywhere we look. Which leads, full circle, to Olbers' Paradox.
    - 14y ago