In his post below, Jonathan asks, "What is the most scientifically irresponsible passage in the United States Reports?" There are lots of contenders, but one nominee might be another contribution by Justice Scalia, footnote 2 in Kyllo v. United States.

  Kyllo considered whether pointing an infrared thermal imaging device at a home constitutes a "search" under the Fourth Amendment. Justice Scalia concluded that it did, it part because the device allowed the police to gather information about the interior of the home, namely, its temperature. In dissent, Justice Stevens argued that using the device was not a "search," in part because the device only revealed information about the exterior of the home. Justice Scalia responded to Stevens in footnote 2:

The dissent's repeated assertion that the thermal imaging did not obtain information regarding the interior of the home, post, at 3, 4 (opinion of Stevens, J.), is simply inaccurate. A thermal imager reveals the relative heat of various rooms in the home. The dissent may not find that information particularly private or important, see post, at 4, 5, 10, but there is no basis for saying it is not information regarding the interior of the home.

  Whether Scalia or Stevens had the better legal argument is debatable. But my understanding is that as a matter of physics, Scalia was wrong and Stevens was right. My research into this suggests that infrared radition is surface radiation: it emanates from surfaces, down to a depth of about 1/1,000 of an inch. See MIKE LLOYD, THERMAL IMAGING SYSTEMS 2-5 (1997). As a result, an infrared image only reveals the temperature of a surface, not the temperature of the space behind the surface. So the device really did reveal only the exterior temperature of the home, not the interior of the home.

  Of course, it is possible to draw reasonable inferences about the likely interior temperature of a home from the home's exterior temperature profile. Assuming a steady state system, we can make reasonable assumptions about how houses are usually built (for example, that there are no heat sources in the walls themselves) to find out information about the interior temperatures. But that information is only as good as the assumptions themselves. For example, if someone made a wall that had an good insulator and then a heat source on the exterior, the exterior would be hot even though that temperature would tell us nothing about the interior of the home.

  None of this necessarily means that Scalia was wrong as matter of law, of course, but I believe he was wrong as a matter of physics. That's my best sense, at least; I hope readers will let me know if I'm the one who is wrong here. (Of course, if it turns out that Scalia was right, I suppose I'll have to designate this "the most scientifically irresponsible blog post at the Volokh Conspiracy"...)