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#11
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"Ifff you go out in the sun today..." Better make sure yourcamera/lens is metal!
John A wrote:
On Sat, 17 Jul 2010 21:19:05 -0400, "Peter" Since when does black radiate in any band? You've never heard of black body radiation? Apparently not. http://www.google.de/search?q=black+...ion+definition Think of a carbon filament lamp. It's black, and if heated (e.g. electrically) it radiates off heat and some light. Heck, even black holes apparently radiate. Bekenstein-Hawking radiation is a different mechanism, though. -Wolfgang |
#12
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"Ifff you go out in the sun today..." Better make sure your camera/lens is metal!
On Sun, 18 Jul 2010 15:51:22 +0200, Wolfgang Weisselberg
wrote: : John A wrote: : On Sat, 17 Jul 2010 21:19:05 -0400, "Peter" : : Since when does black radiate in any band? : : You've never heard of black body radiation? : : Apparently not. : : http://www.google.de/search?q=black+...ion+definition : : Think of a carbon filament lamp. It's black, and if heated : (e.g. electrically) it radiates off heat and some light. What makes that a poor example is that black-body radiation doesn't have to be associated with visible light. The human body is an excellent black-body radiator. Put a person in a sealed, lightless room, and the most you'll see is the luminous dial (if any) on his watch. But look at him through IR-sensitive glasses, and he lights right up. That phenomenon is the bane of terrorist guerillas sneaking up in the dark to blow up a target. Bob |
#13
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"Ifff you go out in the sun today..." Better make sure your camera/lens is metal!
On Sun, 18 Jul 2010 08:18:24 -0500, Doug McDonald
wrote: : On 7/17/2010 8:19 PM, Peter wrote: : "Robert Coe" wrote in message ... : On Sat, 17 Jul 2010 19:58:02 -0400, "Peter" : wrote: : : "Robert Coe" wrote in message : : ... : : : : Rich, did you sleep through high school physics? An object isn't black : : because it absorbs IR; it's black because it absorbs all *other* wavelengths : : and *radiates* in the IR band. That's why if you lay different-colored cloth : : squares on snow, the black square sinks into the snow fastest and the : : white square sinks hardly at all. Canada gets plenty of snow in the : : winter, so they must have showed you that in the seventh grade. Did you : : play hooky that day? : : : : Uhm! Black is the absence of color. : : Which is another way of saying that a black object absorbs all visible : wavelengths (and reflects none). Which is what I said. Your point is ??? : : : Since when does black radiate in any band? : : : Since the Big Bang. : : Anything radiates if it is hot. : : However, a "red hot" piece of silver or aluminum will not radiate : as much as a piece of tungsten at the same temperature, in the visible : region, because they are "whiter", that is, reflect more. : : At room temperature the same thing applies, only they radiate : around 10 microns in the IR. This is really true and is why, : for example, the old-fashioned glass Thermos bottles are : silvered on the inside. : : The thermodynamic proof of this is one of the classic examples of : physics, and is the obvious (to a physicist) fact that led Hawking : to his Nobel Prize: Black Holes are black, therefore the MUST : radiate. If you're right about that, the Nobel Committee should stop giving prizes in physics until they get someone on the Committee who knows any. (But we knew that when they gave one to Albert Gore.) Black holes are not "black" in the classical sense. They were a theoretical construct *defined* as emitting nothing at all, not even radiation. They're called "black" ("unable to radiate in the visible spectrum") because the English language has no common term for "unable to radiate at all". To turn around and use that definition to conclude that black holes must radiate because other "black" objects do is absurd. What little I know (and it is very little) about the putative radiation of black holes suggests that the argument is far more subtle and well-reasoned than what you suggest. The argument may also, by the way, be wrong. No one, Hawking included, fully understands the ramifications of black holes. Just for example, note that black hole theory and the current model of the Big Bang are absolutely contradictory. They can't both be correct, so at least one of them has to change. Bob |
#14
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"Ifff you go out in the sun today..." Better make sure yourcamera/lens is metal!
On 7/18/2010 1:03 PM, Robert Coe wrote:
On Sun, 18 Jul 2010 08:18:24 -0500, Doug McDonald wrote: : On 7/17/2010 8:19 PM, Peter wrote: : "Robert wrote in message ... : On Sat, 17 Jul 2010 19:58:02 -0400, : wrote: : : "Robert wrote in message : : ... : : : : Rich, did you sleep through high school physics? An object isn't black : : because it absorbs IR; it's black because it absorbs all *other* wavelengths : : and *radiates* in the IR band. That's why if you lay different-colored cloth : : squares on snow, the black square sinks into the snow fastest and the : : white square sinks hardly at all. Canada gets plenty of snow in the : : winter, so they must have showed you that in the seventh grade. Did you : : play hooky that day? : : : : Uhm! Black is the absence of color. : : Which is another way of saying that a black object absorbs all visible : wavelengths (and reflects none). Which is what I said. Your point is ??? : : : Since when does black radiate in any band? : : : Since the Big Bang. : : Anything radiates if it is hot. : : However, a "red hot" piece of silver or aluminum will not radiate : as much as a piece of tungsten at the same temperature, in the visible : region, because they are "whiter", that is, reflect more. : : At room temperature the same thing applies, only they radiate : around 10 microns in the IR. This is really true and is why, : for example, the old-fashioned glass Thermos bottles are : silvered on the inside. : : The thermodynamic proof of this is one of the classic examples of : physics, and is the obvious (to a physicist) fact that led Hawking : to his Nobel Prize: Black Holes are black, therefore the MUST : radiate. If you're right about that, the Nobel Committee should stop giving prizes in physics until they get someone on the Committee who knows any. (But we knew that when they gave one to Albert Gore.) Black holes are not "black" in the classical sense. They were a theoretical construct *defined* as emitting nothing at all, not even radiation. They're called "black" ("unable to radiate in the visible spectrum") because the English language has no common term for "unable to radiate at all". To turn around and use that definition to conclude that black holes must radiate because other "black" objects do is absurd. Indeed they ARE black bodies. Any photon that crosses the horizon is sucked in. What little I know (and it is very little) about the putative radiation of black holes suggests that the argument is far more subtle and well-reasoned than what you suggest. I actually know quite lot. It's on the edges of my business. The argument may also, by the way, be wrong. No, it rests on one of the absolute pillars of Physics: thermodynamics. No one, Hawking included, fully understands the ramifications of black holes. That's quite true, of course. But the theory of their radiating is actually quite simple in its essence. What Hawking did was to generate a QUANTITATIVE quantum relativistic field theory that gave the correct radiation spectrum, which agreed with (relativistic) thermodynamics. No one previously had done that. Doug |
#15
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"Ifff you go out in the sun today..." Better make sure yourcamera/lens is metal!
John A. wrote:
The human body is an excellent black-body radiator. Put a person in a sealed, lightless room, and the most you'll see is the luminous dial (if any) on his watch. But look at him through IR-sensitive glasses, and he lights right up. That phenomenon is the bane of terrorist guerillas sneaking up in the dark to blow up a target. Let's hope they don't train polar bears to do it. There are poisonous snakes that can indeed do it. Doug McDonald |
#16
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"Ifff you go out in the sun today..." Better make sure your camera/lens is metal!
"John A." wrote in message
news On Sat, 17 Jul 2010 21:19:05 -0400, "Peter" wrote: "Robert Coe" wrote in message . .. On Sat, 17 Jul 2010 19:58:02 -0400, "Peter" wrote: : "Robert Coe" wrote in message : ... : : Rich, did you sleep through high school physics? An object isn't black : because it absorbs IR; it's black because it absorbs all *other* wavelengths : and *radiates* in the IR band. That's why if you lay different-colored cloth : squares on snow, the black square sinks into the snow fastest and the : white square sinks hardly at all. Canada gets plenty of snow in the : winter, so they must have showed you that in the seventh grade. Did you : play hooky that day? : : Uhm! Black is the absence of color. Which is another way of saying that a black object absorbs all visible wavelengths (and reflects none). Which is what I said. Your point is ??? Since when does black radiate in any band? You've never heard of black body radiation? Heck, even black holes apparently radiate. The very definition of black is the absence of radiation. You are mistaking imperfect black, for pure. Hawking has stated that possible emission of radiation by black holes it's just theory. At present, black holes are theoretical. It is possibly due to to some as yet undefined quantum effect. Until there is scientifically accepted proof I will go with my working definition. -- Peter |
#17
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"Ifff you go out in the sun today..." Better make sure yourcamera/lens is metal!
Robert Coe wrote:
On Sun, 18 Jul 2010 15:51:22 +0200, Wolfgang Weisselberg : John A wrote: : On Sat, 17 Jul 2010 21:19:05 -0400, "Peter" : Since when does black radiate in any band? : You've never heard of black body radiation? : Apparently not. : http://www.google.de/search?q=black+...ion+definition : Think of a carbon filament lamp. It's black, and if heated : (e.g. electrically) it radiates off heat and some light. What makes that a poor example is that black-body radiation doesn't have to be associated with visible light. Aeh, and why did I write "HEAT and SOME light" (emphasis added)? The human body is an excellent black-body radiator. Actually, no. Especially light skin reflects quite a bit of light and is thus not a black body radiator. Put a person in a sealed, lightless room, and the most you'll see is the luminous dial (if any) on his watch. But look at him through IR-sensitive glasses, and he lights right up. Try it with IR photography instead of thermography, then report back. That phenomenon is the bane of terrorist guerillas sneaking up in the dark to blow up a target. Can you please decide between terrorists and guerillas? -Wolfgang |
#18
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"Ifff you go out in the sun today..." Better make sure your camera/lens is metal!
"Peter" wrote in message ... The very definition of black is the absence of radiation. You are mistaking imperfect black, for pure. Hawking has stated that possible emission of radiation by black holes it's just theory. At present, black holes are theoretical. No they existed they have been 'seen' from observing matter falling in to them, they also radiate gamma radiation. It is possibly due to to some as yet undefined quantum effect. Until there is scientifically accepted proof I will go with my working definition. There seems to be lots of proof that black holes exist, they have even measured them. -- Peter |
#19
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"Ifff you go out in the sun today..." Better make sure your camera/lens is metal!
"Wolfgang Weisselberg" wrote in message
... Can you please decide between terrorists and guerillas? Whose side are they on -- Peter |
#20
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"Ifff you go out in the sun today..." Better make sure yourcamera/lens is metal!
Peter wrote:
The very definition of black is the absence of radiation. ITYM reflection. Just because usual black stuff radiates warmth on earth and you cannot see it, that doesn't mean no radiation. -Wolfgang |
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