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Oh god, can we please get a real physicist in here? This entire thread is a mess of computer programmers “well actually”ing other computer programmers and every

Oh god, can we please get a real physicist in here? This entire thread is a mess of computer programmers “well actually”ing other computer programmers and everyone being wrong.

stcredzero 8y ago
It's just like the old USENET days. It's also how Slashdot used to work. Enough of us programmers would spout enough nonsense to make a real expert angry enough to inform the heck out of us.
CydeWeys 8y ago
The linked article is correct and the arguments are well known and accepted in the physics community and have been for a long time (much longer than Randall Munroe has been alive). A lot of the counter-arguments/speculation here in the comments is wrong. Reading this is is equivalent to reading a thread on a physics forum where with people arguing about an article saying that O(n*lgn) is really the best possible runtime complexity for a comparison-based sorting algorithm, and trying to disprove it. It's also worth pointing out that Randall Munroe is a physicist (to the extent an undergrad degree counts anyway).
- nkurz 8y ago
  The linked article is correct and the arguments are well known and accepted in the physics community and have been for a long time (much longer than Randall Munroe has been alive). It's interesting what bothers different people. While many of the statements in this thread are probably wrong, not many of them bother me. But I find the lack-of-self-doubt and appeal-to-authority in your message to be genuinely offensive. Where does your certainty come from? With that out of the way, could you give some links to well known arguments that you refer to? Specifically, I feel certain that one can start a fire with sunlight reflected from a room temperature mirror, and don't understand the difference between a mirror and the moon within Munroe's argument. His conclusion might be correct (in practice, you may not be able to concentrate moonlight enough to start a fire) but I don't think the details of his argument can be. I currently don't believe that the temperature of the reflecting surface can be the limiting factor, and I think this is central his argument.
  - mrbrowning 8y ago
    "Appeal to authority" is a fallacious rhetorical tactic only in an extraordinarily rigorous epistemological context, in which all truths need to be established from first principles. In practice, especially given the information asymmetry between the people that have devoted rigorous study to a thing and the people that think they know about it because making computers do things means they're smart (which is an intellectual pathology that I think ought to bother anyone who cares about the process of modeling physical phenomena accurately and honestly, even if it doesn't bother you), an argument like "physicists uniformly agree on this physical property" is a perfectly adequate assertion in favor of the claims made in the article. It would for sure be bolstered by the inclusion of sources, but you have to admit that you're throwing away a lot of relevant information towards the end of supporting your intuitive sense about how the optics here work. It's not impossible, in the absence of an argument from first principles to counter, that you're correct and that people who have formally studied physics and/or are familiar with the literature are wrong or misguided, but it sure isn't the most likely case by a wide margin. In that context, your certainty ("I don't think the details of his argument can be [correct]") seems much less well-founded.
    - nkurz 8y ago
      I agree on most of your points. There is nothing inherently wrong with an appeal-to-authority in this case. If any substantial number of "reliable" physicists have looked at this problem, and if they unanimously agree that there is no way to concentrate light reflected from an object to produce a temperature greater than that object, then my intuition is almost definitely wrong and their conclusion is almost definitely right. The nice part about physics though (like Munroe, I was also an undergraduate physics major) is that in simple cases like this, a suitable expert can usually defend their position with an argument comprehensible to a nonspecialist outsider. My doubt in this case is not that the experts are wrong, but that the experts haven't actually looked at the details of Munroe's argument and stamped it as "approved". I think the part I find "offensive" is that CydeWeys is not claiming to be an expert himself, but is claiming to have certainty in what the experts believe. I don't know exactly why I find this offensive, but I do. And yes, this may be a problem with me, and not with CydeWeys' argument. I would not be offended in the same way by someone claiming "I am an expert and I approve this argument". Still, my question to him is genuine: what gives him this certainty?
- ummonk 8y ago
  The discussion here doesn't really bother me. I feel like people are making a good faith effort to understand and are asking questions that help develop better intuition. And this is a good example that helps develop an understanding of thermodynamics. (Another favorite of mine is "why can't you have stealth in space?") I feel much more frustration when arguing about impractical engineering proposals (e.g. solar roadways, waterseer, hyperloop, or the ocean cleanup project), since people seem to have a much more biased drive to believe in their feasibility, and can't really be reasoned with.
mikeash 8y ago
My thoughts exactly. Know the limits of your knowledge, folks. You’re doing the physics equivalent of arguing that you can write a lossless compression algorithm that always reduces the size of the input no matter what it is, or that you can write a comparison-based sort algorithm that’s better than nlogn if you’re sufficiently clever.
analog31 8y ago
I'm a real physicist. But I've learned to avoid these debates because I'm not a good enough debater to avoid getting tied up in logical knots. My version of the argument involves turning it into a perpetual motion machine. On the other hand, this rule is incredibly useful in modeling energy transfer through optical systems, seeing what things are possible and what things aren't without having to make detailed calculations. It's a real world rule with useful applications. Instead, I'll just spout nonsense about programming. ;-)
nshepperd 8y ago
Real physicist here. The linked article is correct.
Dylan16807 8y ago
The article is basically correct but doesn't fully explain all the concepts it touches. So you should really be asking for a communications expert, not a physicist.

Oh god, can we please get a real physicist in here? This entire thread is a mess of computer programmers “well actually”ing other computer programmers and everyone being wrong.

stcredzero 8y ago

It's just like the old USENET days. It's also how Slashdot used to work. Enough of us programmers would spout enough nonsense to make a real expert angry enough to inform the heck out of us.

CydeWeys 8y ago

The linked article is correct and the arguments are well known and accepted in the physics community and have been for a long time (much longer than Randall Munroe has been alive). A lot of the counter-arguments/speculation here in the comments is wrong. Reading this is is equivalent to reading a thread on a physics forum where with people arguing about an article saying that O(n*lgn) is really the best possible runtime complexity for a comparison-based sorting algorithm, and trying to disprove it. It's also worth pointing out that Randall Munroe is a physicist (to the extent an undergrad degree counts anyway).

nkurz 8y ago
The linked article is correct and the arguments are well known and accepted in the physics community and have been for a long time (much longer than Randall Munroe has been alive). It's interesting what bothers different people. While many of the statements in this thread are probably wrong, not many of them bother me. But I find the lack-of-self-doubt and appeal-to-authority in your message to be genuinely offensive. Where does your certainty come from? With that out of the way, could you give some links to well known arguments that you refer to? Specifically, I feel certain that one can start a fire with sunlight reflected from a room temperature mirror, and don't understand the difference between a mirror and the moon within Munroe's argument. His conclusion might be correct (in practice, you may not be able to concentrate moonlight enough to start a fire) but I don't think the details of his argument can be. I currently don't believe that the temperature of the reflecting surface can be the limiting factor, and I think this is central his argument.
- mrbrowning 8y ago
  "Appeal to authority" is a fallacious rhetorical tactic only in an extraordinarily rigorous epistemological context, in which all truths need to be established from first principles. In practice, especially given the information asymmetry between the people that have devoted rigorous study to a thing and the people that think they know about it because making computers do things means they're smart (which is an intellectual pathology that I think ought to bother anyone who cares about the process of modeling physical phenomena accurately and honestly, even if it doesn't bother you), an argument like "physicists uniformly agree on this physical property" is a perfectly adequate assertion in favor of the claims made in the article. It would for sure be bolstered by the inclusion of sources, but you have to admit that you're throwing away a lot of relevant information towards the end of supporting your intuitive sense about how the optics here work. It's not impossible, in the absence of an argument from first principles to counter, that you're correct and that people who have formally studied physics and/or are familiar with the literature are wrong or misguided, but it sure isn't the most likely case by a wide margin. In that context, your certainty ("I don't think the details of his argument can be [correct]") seems much less well-founded.
  - nkurz 8y ago
    I agree on most of your points. There is nothing inherently wrong with an appeal-to-authority in this case. If any substantial number of "reliable" physicists have looked at this problem, and if they unanimously agree that there is no way to concentrate light reflected from an object to produce a temperature greater than that object, then my intuition is almost definitely wrong and their conclusion is almost definitely right. The nice part about physics though (like Munroe, I was also an undergraduate physics major) is that in simple cases like this, a suitable expert can usually defend their position with an argument comprehensible to a nonspecialist outsider. My doubt in this case is not that the experts are wrong, but that the experts haven't actually looked at the details of Munroe's argument and stamped it as "approved". I think the part I find "offensive" is that CydeWeys is not claiming to be an expert himself, but is claiming to have certainty in what the experts believe. I don't know exactly why I find this offensive, but I do. And yes, this may be a problem with me, and not with CydeWeys' argument. I would not be offended in the same way by someone claiming "I am an expert and I approve this argument". Still, my question to him is genuine: what gives him this certainty?
ummonk 8y ago
The discussion here doesn't really bother me. I feel like people are making a good faith effort to understand and are asking questions that help develop better intuition. And this is a good example that helps develop an understanding of thermodynamics. (Another favorite of mine is "why can't you have stealth in space?") I feel much more frustration when arguing about impractical engineering proposals (e.g. solar roadways, waterseer, hyperloop, or the ocean cleanup project), since people seem to have a much more biased drive to believe in their feasibility, and can't really be reasoned with.

mikeash 8y ago

My thoughts exactly. Know the limits of your knowledge, folks. You’re doing the physics equivalent of arguing that you can write a lossless compression algorithm that always reduces the size of the input no matter what it is, or that you can write a comparison-based sort algorithm that’s better than nlogn if you’re sufficiently clever.

analog31 8y ago

I'm a real physicist. But I've learned to avoid these debates because I'm not a good enough debater to avoid getting tied up in logical knots. My version of the argument involves turning it into a perpetual motion machine. On the other hand, this rule is incredibly useful in modeling energy transfer through optical systems, seeing what things are possible and what things aren't without having to make detailed calculations. It's a real world rule with useful applications. Instead, I'll just spout nonsense about programming. ;-)

nshepperd 8y ago

Real physicist here. The linked article is correct.

Dylan16807 8y ago

The article is basically correct but doesn't fully explain all the concepts it touches. So you should really be asking for a communications expert, not a physicist.