JMC@SAIL.STANFORD.EDU (John McCarthy) (09/26/88)
---- Forwarded Message Follows ---- Return-path: <@AI.AI.MIT.EDU:JMC@SAIL.STANFORD.EDU> Received: from AI.AI.MIT.EDU by ZERMATT.LCS.MIT.EDU via CHAOS with SMTP id 195020; 18 Sep 88 18:44:59 EDT Received: from SAIL.Stanford.EDU (TCP 1200000013) by AI.AI.MIT.EDU 18 Sep 88 18:50:15 EDT Message-ID: <cdydW@SAIL.Stanford.EDU> Date: 18 Sep 88 1543 PDT From: John McCarthy <JMC@SAIL.Stanford.EDU> Subject: common sense knowledge of continuous action To: fishwick@BIKINI.CIS.UFL.EDU, ailist@AI.AI.MIT.EDU If Genesereth and Nilsson didn't give an example to illustrate why differential equations aren't enough, they should have. The example I like to give when I lecture is that of spilling the water glass on the lectern. If the front row is very close, it might get wet, but usually not even that. The Navier-Stokes equations govern the flow of the spilled water but are entirely useless in this common sense situation. No-one can acquire the initial conditions or integrate the equations sufficiently rapidly. Moreover, absorption of water by the materials it flows over is probably a strong enough effect, so that more than the Navier-Stokes equations would be necessary. Thus there is no "scientific theory" involving differential equations, queuing theory, etc. that can be used by a robot to determine what can be expected when a glass of water is spilled, given what information is actually available to an observer. To use the terminology of my 1969 paper with Pat Hayes, the differential equations don't form an epistemologically adequate model of the phenomenon, i.e. a model that uses the information actually available. While some people are interested in modelling human performance as an aspect of psychology, my interest is artificial intelligence. There is no conflict with science. What we need is a scientific theory that can use the information available to a robot with human opportunities to observe and do as well as a human in predicting what will happen. Thus our goal is a scientific common sense. The Navier-Stokes equations are important in (1) the design of airplane wings, (2) in the derivation of general inequalities, some of which might even be translatable into terms common sense can use. For example, the Bernoulli effect, once a person has (usually with difficulty) integrated it into his common sense knowledge can be useful for qualitatively predicting the effects of winds flowing over a house. Finally, the Navier Stokes equations are imbedded in a framework of common sense knowledge and reasoning that determine the conditions under which they are applied to the design of airplane wings, etc.