Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site brl-tgr.ARPA Path: utzoo!watmath!clyde!burl!ulysses!allegra!bellcore!decvax!genrad!wjh12!talcott!harvard!seismo!brl-tgr!gwyn From: gwyn@brl-tgr.ARPA Newsgroups: net.physics Subject: Re: Re: why FTL is illegal, in small words Message-ID: <6651@brl-tgr.ARPA> Date: Tue, 18-Dec-84 17:47:31 EST Article-I.D.: brl-tgr.6651 Posted: Tue Dec 18 17:47:31 1984 Date-Received: Sat, 22-Dec-84 01:13:43 EST References: <683@gloria.UUCP> <785@ariel.UUCP> <119@talcott.UUCP> <374@mhuxt.UUCP> <820@bnl.UUCP> <432@gitpyr.UUCP> Organization: Ballistic Research Lab Lines: 21 > > One of the postulates of physics is that any observer in an > > inertial frame must observe a universe that obeys the same laws of > > physics as an observer in any other inertial frame. Otherwise > > there is no point to physics since the universe depends on how > > you observe it, and not on any intrisic existence of its own. > > But I thought that QM says that events absolutely DO depend on being observed? A very common mistake. What quantum physics tells us is that observation affects the system being observed (specifically, the measured value of a physical quantity is an eigenvalue of the corresponding operator, with probability distribution of eigenvalues corresponding to squared amplitudes of elements of the operator applied to the system state, according to the usual QM computation rules). This is not the same as "depending on being observed". The physical occurrences propagate in the total absence of any observer. This is really not much worse than in relativity theory, where the actual results of observations are observer (state of motion) dependent projections of absolute physical objects. Relativistic descriptions can be done either using coordinates or coordinate-free; similarly for quantum physics.