Monday, November 15, 2010

Trade Off #15: Acquiring Info vs Altering Subject

Paradoxically, when you ask someone a question, their answer will likely be different because you've asked them. On reflection this phenomenon is remarkably general; in acquiring or assessing info about a property of a system, we must be willing to accept the consequences of altering that system. A smattering of examples follow: 
  • Increasing the energy voltage in transmission electron microscopy can lead to higher image resolution (meaning more info), but it also does more damage to the tissue. (see here; there are similar trade offs in lots of med imaging techs, like PET scans, see here)
  • When a model of a complex psychological phenomenon becomes widespread, reality often begins conforming to the model. This is often called performativity, and it is perhaps why Keynes called economics a "moral" science. (see here
  • The Heisenberg uncertainty principle says that the more precisely the position of a particle is measured, the less precisely its momentum can be, and vice versa. The explanation for this is controversial, but it's likely due to observer effects--the measuring apparatus delivers a force to the particle which alters it. (see here)
Most examples that fit into this category are true to at least some degree, but it's often tricky to determine precisely how much variance they explain. For example, even when you run a placebo-controlled drug trial, you must be wary of side effects that can tip the participants off to their treatment status (see here). Regardless, this is a widespread trade off, and it now assumes its rightful place in the canon.

(photo is of a peptide fiber, taken with EM, credit to Christoph Meier)