CC: Subj: RE: [math-fun] dirac scissors trick + balinese cup trick Return-path: <math-fun-bounces+mckay=vax2.concordia.ca@mailman.xmission.com> Received: from newclyde.concordia.ca (newclyde.Concordia.CA [132.205.1.11]) by vax2.concordia.ca (PMDF V6.2 #30759) with ESMTP id <01L8N682POJQ003UGC@vax2.concordia.ca> for mckay@vax2.concordia.ca (ORCPT mckay@vax2.concordia.ca); Wed, 07 Apr 2004 09:12:27 -0400 (EDT) Received: from mailman.xmission.com (mailman.xmission.com [198.60.22.29]) by newclyde.concordia.ca (8.12.10/8.12.10) with ESMTP id i37DCNtq015945 for <mckay@vax2.concordia.ca>; Wed, 07 Apr 2004 09:12:23 -0400 Received: from localhost ([127.0.0.1] helo=mailman.xmission.com) by mailman.xmission.com with esmtp (Exim 3.35 #1 (Debian)) id 1BBCXh-0003Td-09 for <mckay@vax2.concordia.ca>; Wed, 07 Apr 2004 06:52:33 -0600 Received: from mgr3.xmission.com ([198.60.22.203]) by mailman.xmission.com with esmtp (Exim 3.35 #1 (Debian)) id 1BBCXW-0003TW-00 for <math-fun@mailman.xmission.com>; Wed, 07 Apr 2004 06:52:22 -0600 Received: from [65.171.232.3] (helo=ldap.micgi.com) by mgr3.xmission.com with smtp (Exim 4.30) id 1BBCXT-0004RV-QE for math-fun@mailman.xmission.com; Wed, 07 Apr 2004 06:52:19 -0600 Received: (qmail 39785 invoked from network); Wed, 07 Apr 2004 12:52:17 +0000 Received: from unknown (HELO alan-oxyfzctp75.neondsl.com) (209.248.59.156) by ldap.micgi.com with SMTP; Wed, 07 Apr 2004 12:52:17 +0000 Date: Wed, 07 Apr 2004 07:52:21 -0500 From: Alan Schoen <alanschoen@neondsl.com> Subject: Re: [math-fun] dirac scissors trick + balinese cup trick In-reply-to: <013501c41a75$541e6370$a52efea9@TASSO> Sender: math-fun-bounces+mckay=vax2.concordia.ca@mailman.xmission.com X-Sender: alanschoen@neondsl.com@mail.neondsl.com (Unverified) q To: math-fun <math-fun@mailman.xmission.com> Errors-to: math-fun-bounces+mckay=vax2.concordia.ca@mailman.xmission.com Reply-to: math-fun <math-fun@mailman.xmission.com> Message-id: <6.0.1.1.2.20040407074303.01c3a118@mail.neondsl.com> MIME-version: 1.0 X-Mailer: QUALCOMM Windows Eudora Version 6.0.1.1 Content-type: text/plain; format=flowed; charset=us-ascii Precedence: list X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on mgr3.xmission.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=8.0 tests=none autolearn=no version=2.63 X-SA-Exim-Mail-From: alanschoen@neondsl.com X-SA-Exim-Version: 3.1 (built Mon Jan 26 13:00:24 MST 2004) X-SA-Exim-Scanned: Yes X-BeenThere: math-fun@mailman.xmission.com X-Mailman-Version: 2.1.1 X-Scanned-By: MIMEDefang 2.35 References: <013501c41a75$541e6370$a52efea9@TASSO> List-Post: <mailto:math-fun@mailman.xmission.com> List-Subscribe: <http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun>, <mailto:math-fun-request@mailman.xmission.com?subject=subscribe> List-Unsubscribe: <http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun>, <mailto:math-fun-request@mailman.xmission.com?subject=unsubscribe> List-Archive: <http://mailman.xmission.com/cgi-bin/mailman/private/math-fun> List-Help: <mailto:math-fun-request@mailman.xmission.com?subject=help> List-Id: math-fun <math-fun.mailman.xmission.com> Original-recipient: rfc822;mckay@vax2.concordia.ca Thane: Dirac visited SIUC around 1978 for an Einstein symposium. When I met him, I mentioned to him that I recalled having seen -- around 1965 -- a brief reference to his spinor-related trick in Time magazine. The article suggested that he had discovered it around 1932. He confirmed that that was probably about the right date. I suggest that you ask my physicist colleague Jerzy Kocik (jkocik@math.siu.edu) to fill you in on the details of the spinor connection. He has demonstrated the trick (with flailing arms) and he has expert knowledge of quantum mechanics. I'll send a copy of this email to Jurek (Jerzy). Alan At 01:47 PM 4/4/2004, you wrote:

...

(This is the same thing that says you can hold a full cup of coffee in one hand, and without letting go or spilling, turn it around twice and get back in the same position. However, if you turn it around just once, your arm will be in a different, probably awkward, position.)

I read that Dirac illustrated this fact, that a 360 degree rotation isn't the same as a 720 degree one, using strings tied to a pair of scissors, right?

My question: where/when did he do it?

Thane Plambeck 650 321 4884 office 650 323 4928 fax http://www.plambeck.org

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