More on Heat Transfer and Thermal Imagers:
A number of commenters took issue with my claims about Justice Scalia's discussion about thermal imaging devices in Kyllo, and I wanted to blog more about it. I realize that there may be only 4 or 5 readers who actually care about this, but please pardon my geeking out: I spent five years before law school studying mechanical engineering, specializing (near the end) in heat transfer and fluid mechanics, so I'm probably a lot more sensitive to what I take to be Scalia's misstatement. But for whatever reason, it strikes me as an interesting issue.
A number of commenters agreed with Scalia's suggestion that a thermal imaging device tells you the relative heat of various rooms in a house, because hot rooms will mean hot walls, cool rooms will mean cool walls, etc. To be clear, I think that this is often true. That why police might want to use thermal imaging devices, of course; they may ultimately want to collect evidence that might help make a showing about what's hapening inside the the home. Certainly that was the subjective intent of the officers in Kyllo: they wanted to learn something about the inside temperature of the home. But the issue here is physics, not the intent of some narcotics investigators in a particular case, and as a matter of phsyics it seems to me that Scalia's statement is often untrue. The fact that it is often untrue is what I think makes the claim scientifically irresponsible.
For example, imagine a simple two-room house that is being monitored on a very cold day. Imagine we're looking at the house side by side, with room 1 on the left and room 2 on the right. Further, imagine that the walls on the left side of the house (around room 1) are very well insulated, that the walls on the right side of the house (around room 2) are very poorly insulated, and that the house has central heating that pumps an equivalent anount of heat into each room. If the police direct a thermal imaging device at the house, the device will tell them that the exterior of room 1 is relatively cold, but the exterior of room 2 is relatively hot.
Does this mean that the interior of room 1 is relatively cold, and the interior of room 2 is relatively hot? It seems to me that the answer is no — in fact, the opposite is true. In room 1, the well-insulated room, the heat is being kept inside; it is heating the room, not pumping lots of heat to the exterior of the walls. As a result, the room with the cooler exterior will be warmer inside. On the other hand, the poorly insulated room, room 2, will have hotter walls but be colder inside. Now imagine that the homeowner brings a space heater into the poorly-insulated room, room 2, to bring it to the same interior temperature as room 1. The space heater will heat the exterior of the walls around room 2 even more: the exterior walls around room 2 would be significantly warmer than the walls around room 1. But the interior temperature of the rooms would be the same. As a result, the thermal imaging device won't tell the police anything about the relative interior temperature of the rooms; in this case, it will just tell the police about the relative insulation of the walls.
As I said earlier, none of this is necessarily relevant to the constitutional issue. But it seems to me that Scalia's statement about what the imaging device necessarily does is really about what it can often be used to do, subject to a set of assumptions, and he was wrong to dismiss Stevens' point as somehow factually incorrect.
UDPATE: Commenter T. Gracchus has a very good point:
A number of commenters agreed with Scalia's suggestion that a thermal imaging device tells you the relative heat of various rooms in a house, because hot rooms will mean hot walls, cool rooms will mean cool walls, etc. To be clear, I think that this is often true. That why police might want to use thermal imaging devices, of course; they may ultimately want to collect evidence that might help make a showing about what's hapening inside the the home. Certainly that was the subjective intent of the officers in Kyllo: they wanted to learn something about the inside temperature of the home. But the issue here is physics, not the intent of some narcotics investigators in a particular case, and as a matter of phsyics it seems to me that Scalia's statement is often untrue. The fact that it is often untrue is what I think makes the claim scientifically irresponsible.
For example, imagine a simple two-room house that is being monitored on a very cold day. Imagine we're looking at the house side by side, with room 1 on the left and room 2 on the right. Further, imagine that the walls on the left side of the house (around room 1) are very well insulated, that the walls on the right side of the house (around room 2) are very poorly insulated, and that the house has central heating that pumps an equivalent anount of heat into each room. If the police direct a thermal imaging device at the house, the device will tell them that the exterior of room 1 is relatively cold, but the exterior of room 2 is relatively hot.
Does this mean that the interior of room 1 is relatively cold, and the interior of room 2 is relatively hot? It seems to me that the answer is no — in fact, the opposite is true. In room 1, the well-insulated room, the heat is being kept inside; it is heating the room, not pumping lots of heat to the exterior of the walls. As a result, the room with the cooler exterior will be warmer inside. On the other hand, the poorly insulated room, room 2, will have hotter walls but be colder inside. Now imagine that the homeowner brings a space heater into the poorly-insulated room, room 2, to bring it to the same interior temperature as room 1. The space heater will heat the exterior of the walls around room 2 even more: the exterior walls around room 2 would be significantly warmer than the walls around room 1. But the interior temperature of the rooms would be the same. As a result, the thermal imaging device won't tell the police anything about the relative interior temperature of the rooms; in this case, it will just tell the police about the relative insulation of the walls.
As I said earlier, none of this is necessarily relevant to the constitutional issue. But it seems to me that Scalia's statement about what the imaging device necessarily does is really about what it can often be used to do, subject to a set of assumptions, and he was wrong to dismiss Stevens' point as somehow factually incorrect.
UDPATE: Commenter T. Gracchus has a very good point:
"Scientifically irresponsible" seems a rather agressive dscription. Your case about inaccuracy does nothing to establish that Scalia was irresponsible. In neither post have you given a hint of what you intend by "irresponsible." Do you just mean inaccurate?Excellent point; the phrase "scientifically irresponsible" was Jim Chen's, and I was interpreting it to mean only "scientifically inaccurate" without the suggestion of a moral wrong that might be associated with the concept of irresponsibility. My apologies if that caused confision.
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