Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception]

From	Gregory Ewing <greg.ewing@canterbury.ac.nz>
Newsgroups	comp.lang.python
Subject	Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception]
Date	2016-03-05 15:51 +1300
Message-ID	<djuvt8FlbhtU1@mid.individual.net> (permalink)
References	(11 earlier) <101Cy.1411363$QP2.758114@fx42.am4> <56d8d10e$0$1587$c3e8da3$5496439d@news.astraweb.com> <mailman.181.1457086788.20602.python-list@python.org> <87lh5yjzob.fsf@elektro.pacujo.net> <mailman.193.1457112929.20602.python-list@python.org>

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Oscar Benjamin wrote:
> If we want to be precise then
> it's pointless to even refer to the "rest mass" of something that is
> never at rest.

Which just shows that the term "rest mass" is a bit silly.
It came from some confused thinking very early in the
development of relativity. The physicists soon sorted that
out, but unfortunately the textbooks didn't catch up, and
we've ended up with several generations of confused
students as a result. :-(

  The masslessness of photons comes from an extrapolation
> that leads to a divide by infinity: strictly speaking it's just
> undefined.

No, it's not. The total energy of a particle is given by

    E**2 == c**2 * p**2 + m**2 * c**4

where p is the particle's momentum and m is its mass.
For a photon, m == 0. No division by zero involved.

For a massive particle at rest, p == 0 and the above
reduces to the well-known

    E == m * c**2

> Something I don't know is if there's some theoretical reason why the
> binding energy could never exceed the sum of the energies of the
> constituent particles (resulting in an overall negative mass).

Conservation of energy would be one reason. If you
put two particles together and got more energy out than
went in, where did the extra energy come from?

If you find a way to make that trick work, watch out --
the secret cartel of energy companies that's suppressing
all the free-energy inventions will want to disappear
you...

-- 
Greg

Thread

[Off-topic] Requests author discusses MentalHealthError exception Steven D'Aprano <steve@pearwood.info> - 2016-02-27 20:37 +1100
  Re: [Off-topic] Requests author discusses MentalHealthError exception Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-02-27 09:50 +0000
  Re: [Off-topic] Requests author discusses MentalHealthError exception Ethan Furman <ethan@stoneleaf.us> - 2016-02-27 14:06 -0800
  Re: [Off-topic] Requests author discusses MentalHealthError exception Jason Friedman <jsf80238@gmail.com> - 2016-02-27 17:00 -0700
  Re: [Off-topic] Requests author discusses MentalHealthError exception Larry Martell <larry.martell@gmail.com> - 2016-02-29 11:21 -0500
  Re: [Off-topic] Requests author discusses MentalHealthError exception Ian Kelly <ian.g.kelly@gmail.com> - 2016-02-29 09:47 -0700
  Re: [Off-topic] Requests author discusses MentalHealthError exception Ben Finney <ben+python@benfinney.id.au> - 2016-03-01 03:56 +1100
    Re: [Off-topic] Requests author discusses MentalHealthError exception Rustom Mody <rustompmody@gmail.com> - 2016-02-29 09:08 -0800
      Re: [Off-topic] Requests author discusses MentalHealthError exception Ben Finney <ben+python@benfinney.id.au> - 2016-03-01 04:33 +1100
        Re: [Off-topic] Requests author discusses MentalHealthError exception Rustom Mody <rustompmody@gmail.com> - 2016-02-29 09:54 -0800
      Re: [Off-topic] Requests author discusses MentalHealthError exception Larry Martell <larry.martell@gmail.com> - 2016-02-29 17:40 -0500
      Re: [Off-topic] Requests author discusses MentalHealthError exception Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-02-29 23:29 +0000
      Re: [Off-topic] Requests author discusses MentalHealthError exception Joel Goldstick <joel.goldstick@gmail.com> - 2016-02-29 18:33 -0500
      Re: [Off-topic] Requests author discusses MentalHealthError exception Steven D'Aprano <steve@pearwood.info> - 2016-03-02 04:05 +1100
        Re: [Off-topic] Requests author discusses MentalHealthError exception Rustom Mody <rustompmody@gmail.com> - 2016-03-02 09:02 -0800
          Re: [Off-topic] Requests author discusses MentalHealthError exception Steven D'Aprano <steve@pearwood.info> - 2016-03-03 13:27 +1100
            Re: [Off-topic] Requests author discusses MentalHealthError exception Chris Angelico <rosuav@gmail.com> - 2016-03-03 13:35 +1100
              Re: [Off-topic] Requests author discusses MentalHealthError exception alister <alister.ware@ntlworld.com> - 2016-03-03 17:21 +0000
                Re: [Off-topic] Requests author discusses MentalHealthError exception Ian Kelly <ian.g.kelly@gmail.com> - 2016-03-03 11:03 -0700
                Re: [Off-topic] Requests author discusses MentalHealthError exception alister <alister.ware@ntlworld.com> - 2016-03-03 20:20 +0000
                Re: [Off-topic] Requests author discusses MentalHealthError exception Ian Kelly <ian.g.kelly@gmail.com> - 2016-03-03 13:33 -0700
                Re: [Off-topic] Requests author discusses MentalHealthError exception William Ray Wing <wrw@mac.com> - 2016-03-03 18:02 -0500
                Re: [Off-topic] Requests author discusses MentalHealthError exception alister <alister.ware@ntlworld.com> - 2016-03-04 14:05 +0000
                [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Steven D'Aprano <steve@pearwood.info> - 2016-03-04 11:04 +1100
                Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2016-03-04 10:19 +0000
                Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Marko Rauhamaa <marko@pacujo.net> - 2016-03-04 12:38 +0200
                Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Dan Sommers <dan@tombstonezero.net> - 2016-03-04 13:10 +0000
                Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2016-03-04 17:35 +0000
                Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] André Roberge <andre.roberge@gmail.com> - 2016-03-04 11:12 -0800
                Re: [Still off-top] Physics [was Requests author discusses   MentalHealthError exception] Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-03-05 15:51 +1300
                Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Chris Angelico <rosuav@gmail.com> - 2016-03-05 14:13 +1100
                Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Marko Rauhamaa <marko@pacujo.net> - 2016-03-05 10:31 +0200
                Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2016-03-05 13:11 +0000
                Photon mass (was: [Still off-top] Physics) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-05 16:38 +0100
                Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Gene Heskett <gheskett@wdtv.com> - 2016-03-05 10:15 -0500
                Photon mass (was: [Still off-top] Physics) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-05 16:46 +0100
                Re: Photon mass (was: [Still off-top] Physics) Gene Heskett <gheskett@wdtv.com> - 2016-03-05 12:36 -0500
                Re: Photon mass (was: [Still off-top] Physics) Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-03-06 12:16 -0500
                Re: Photon mass (was: [Still off-top] Physics) Larry Martell <larry.martell@gmail.com> - 2016-03-06 09:21 -0500
                Re: [Still off-topic] Physics Steven D'Aprano <steve@pearwood.info> - 2016-03-06 16:36 +1100
                Re: [Off-topic] Requests author discusses MentalHealthError   exception Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-03-04 19:34 +1300
                Re: [Off-topic] Requests author discusses MentalHealthError   exception Marko Rauhamaa <marko@pacujo.net> - 2016-03-04 08:52 +0200
            Re: [Off-topic] Requests author discusses MentalHealthError exception Rustom Mody <rustompmody@gmail.com> - 2016-03-02 19:57 -0800
              Re: [Off-topic] Requests author discusses MentalHealthError exception Ian Kelly <ian.g.kelly@gmail.com> - 2016-03-02 23:44 -0700
              Re: [Off-topic] Requests author discusses MentalHealthError exception Steven D'Aprano <steve@pearwood.info> - 2016-03-04 02:50 +1100
              Re: [Off-topic] Requests author discusses MentalHealthError exception Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-03 16:21 +0000
      Re: [Off-topic] Requests author discusses MentalHealthError exception Anders Wegge Keller <wegge@wegge.dk> - 2016-03-03 08:23 +0100
    Re: [Off-topic] Requests author discusses MentalHealthError exception Paul Rubin <no.email@nospam.invalid> - 2016-02-29 16:35 -0800
      Re: [Off-topic] Requests author discusses MentalHealthError exception Ethan Furman <ethan@stoneleaf.us> - 2016-02-29 16:54 -0800
  Re: [Off-topic] Requests author discusses MentalHealthError exception Larry Martell <larry.martell@gmail.com> - 2016-02-29 17:36 -0500
  Re: [Off-topic] Requests author discusses MentalHealthError exception Larry Martell <larry.martell@gmail.com> - 2016-02-29 17:38 -0500
    Re: [Off-topic] Requests author discusses MentalHealthError exception Steven D'Aprano <steve@pearwood.info> - 2016-03-01 23:13 +1100
      Re: [Off-topic] Requests author discusses MentalHealthError exception "Sven R. Kunze" <srkunze@mail.de> - 2016-03-01 17:49 +0100
  Re: [Off-topic] Requests author discusses MentalHealthError exception "Mario R. Osorio" <nimbiotics@gmail.com> - 2016-02-29 20:11 -0800
  Re: Photon mass (was: [Still off-top] Physics) Gene Heskett <gheskett@wdtv.com> - 2016-03-06 16:46 -0500
  Re: Photon mass (was: [Still off-top] Physics) Larry Martell <larry.martell@gmail.com> - 2016-03-06 17:51 -0500

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