Please reopen this question per the discussion we had in the comments. What is the maximum possible temperature of a 1mx1mx1m cube that is the focal point of an array of mirror reflected, concentrated beams of sunlight?

Also, a link says it has been asked, which is untrue. The question asks what particular physics will limit what could be achieved in practice in an Alabama field (under earth’s atmosphere for one thing, without 360-deg access etc) on a specific object. It also asks how number of mirrors would scale. That would be affected by things that wouldnt affect the asymptotic limit to the radiating body, such as finding a way to differ the emissivity across the body. The linked question asks about the theoretical limits of solar furnaces approaching the temperature of the radiating body. Different question altogether

The question has the following unique twists (which are relevant because it was closed as being a duplicate):

1.Discussing the number of mirrors:

My new answer added physics but not engineering issues about this (nothing about materials or how to achieve it, but the concept of differential emissivity for example). From a physics standpoint will be the exponential increase in mirrors needed per Kelvin increase. I was about to add this to an answer. People have mentioned in related questions that the temp of sun is a limit, but this is an asymptotic limit.

  1. Asking about practical implications in an Alabama field:

Engineering questions aside, what hard limits might there be in the physics of doing this on earth (other than the second law limiting it to the temperature of the sun which has been discussed). For example, is there a limit imposed by losses through the atmosphere? If we assume constant atmospheric absorption, what does that do? What the atmosphere changes frequency profile?

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    $\begingroup$ Do you mean this question: physics.stackexchange.com/questions/660967/… ? (There's no link in your post.) $\endgroup$
    – Buzz Mod
    Aug 24, 2021 at 0:58
  • $\begingroup$ @Buzz Oh yeah that would help 😉. Yes i did $\endgroup$
    – Al Brown
    Aug 24, 2021 at 1:08
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    $\begingroup$ The reopen review for this question is underway. There is usually no need to request explicit reopening of questions on meta unless a reopen review has already failed once. $\endgroup$
    – ACuriousMind Mod
    Aug 24, 2021 at 8:31
  • $\begingroup$ @ACuriousMind Oh ok noted. I submitted an edit to the question (Or maybe i have privilege to edit) thatd help. Gnight 🙏🏻👍🏻🥱 $\endgroup$
    – Al Brown
    Aug 24, 2021 at 8:42
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    $\begingroup$ I don't see how "unique twists" relate to the question being open or not. $\endgroup$ Aug 24, 2021 at 11:18
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    $\begingroup$ Although the question is currently closed, you can add info to your existing answer. And that will bump the question to the front page and the top of the Active tab. Also, closure doesn't prevent people from voting or commenting on the question or its answer(s). $\endgroup$
    – PM 2Ring
    Aug 24, 2021 at 12:30
  • $\begingroup$ @PM2Ring I added number of mirrors in answer and physics factors affecting. Not covered other questions. Am I understanding that we are trying to see if is duplicate or not? $\endgroup$
    – Al Brown
    Aug 25, 2021 at 4:47
  • $\begingroup$ Related: physics.meta.stackexchange.com/q/13378/305718 $\endgroup$
    – ACB
    Aug 25, 2021 at 5:25
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    $\begingroup$ Sorry, I hadn't looked at the close reason. Thanks for updating the meta post to be more clear about that $\endgroup$ Aug 25, 2021 at 11:09
  • $\begingroup$ @BioPhysicist Thanks. Yes true, and good point, was not mentioned. $\endgroup$
    – Al Brown
    Aug 27, 2021 at 17:41

1 Answer 1


The question, in its original form, was correctly closed as a duplicate of the indicated question. The only theoretical limit is as previously answered.

Unfortunately, the edits change the reason but not the outcome. Under the edits it is no longer a duplicate, but it is now an engineering question. Engineering questions are explicitly off-topic here. So the edits still should lead to a closed question, but merely for a different closure reason.

I don't believe that there is a way out here. The only physics theory answer is as already answered. Any modifications you make to the question so that is not the answer will make it an engineering question.

  • $\begingroup$ Ok I responded in a separate answer $\endgroup$
    – Al Brown
    Aug 25, 2021 at 23:06

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