NetNews Usenet Archive 1992 #27/NN_1992_27.iso/spool/sci/physics/19409

Internet Message Format | 1992-11-22 | 2.6 KB

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From: [e-mail] (Matthew P Wiener)
Newsgroups: sci.physics
Subject: Re: energy, mass, and all that
Message-ID: <[e-mail]>
Date: 22 Nov 92 17:51:48 GMT
References: <[e-mail]> <[e-mail]> <[e-mail]>
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Reply-To: [e-mail] (Matthew P Wiener)
Organization: The Wistar Institute of Anatomy and Biology
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In-reply-to: [e-mail] (SCOTT I CHASE)

In article <[e-mail]>, sichase@csa3 (SCOTT I CHASE) writes:
>>>If energy and matter are not interconvertible, where does all the energy
>>>of an atomic bomb blast come from?

>>Simple.  The energy that used to be binding is now blast, light, heat.
>>While it was binding, the energy was localized enough that we could
>>weigh it directly, and so the bomb weighed E-bind/c^2 more than it
>>would have otherwise.

>This follows nicely upon my previous post, in which Dan Platt stretches
>the definition of mass so as to never convert mass to energy.  Now you
>are going to stretch the definition of energy so that we never have to
>convert energy to mass.

Why don't we *define* energy and mass before complaining about definition
stretching?  The naive notion for energy is just the ability to do work,
ie, accelerate mass through a distance, and for mass it is just the
inertial resistance to an acceleration.  The two are distinct physical
notions.  In the 19th century, energy was defined and numerous versions
of it identified.  No one (or at least, no one once the dust had settled)
ever said electric current *was* energy, even though you could extract
energy from something containing a current.

In 1905, Einstein pointed out that there is an inertia associated with
energy.  T=E/c^2.  (Not E=mc^2.)  That meant that if you had two equal
systems vis-a-vis their _matter_, they would weigh differently if the
one was at a higher temperature than the other.

Of course, if you want to use other definitions of energy and mass, be
my guest.  Just don't express exasperation that other people can and do
understand atomic bomb explosions as something other than mass to energy
conversions.  See Taylor and Wheeler SPACETIME PHYSICS, for example.

>              You are willing to say that when we weigh atoms
>that we are weighing their energy and not their mass?  [...]

I never said anything like that.  Although that is, of course, the goal
of numerous theorists.
--
-Matthew P Wiener ([e-mail])