🚀 go-pugleaf

I am more convinced than I was before that this argument is more than a 
matter of different definitions of mass.  No matter which definition you
adhere to, you can't get the right physics by assuming that matter and 
energy are not interconvertible in the way that Bondi seems to suggest.

In article <1992Nov19.145532.34225@bas-a.bcc.ac.uk>, ucap22w@ucl.ac.uk (Martin S T Watts) writes...
> 
>	"It has come to our notice (for example Warren, 1976) that there is
>	quite widespread misunderstanding about the interpretation of
>	Einstein's famous equation E=mc^2. It seems that this is often
>	regarded as something rather like a monetary rate of exchange, such
>	as L1.00=$1.45, and that mass and energy are thought to be
>	interconvertible, each to the other. This is not so. Mass and 
>	energy are not interconvertible. 

No matter which definition of mass ("old" or "modern") you use, energy
and mass are still interconvertible.  When an electron and positron 
annihilate into a pair of photons, which are absorbed by a piece of lead, 
you end up with hot lead.  You can extract work from the temperature 
difference thus created.  The mass of the original pair (whether you 
count just the rest mass, or the relativistic mass) has been converted 
into work.  If this is not mass being converted to energy, what is it?

>	They are entirely different
>	quantities and are no more interconvertible than are mass and
>	volume, which also happen to be related by an equation, V=m*rho^-1.
>	Mass and volume are different quantities and have different 
>	dimensions. So have mass and energy. They feature differently in
>	equations.

That's just gibberish.  The equation you quote is not a physical relationship
between two physical quantitites.  It is the definition of density.  It
has no physics content.  E^2 = m^2 + p^2 tells you how much total energy
a system contains, i.e., how much work you can extract from it.  It includes
the physically necessary contribution from the mass, which, when converted
into energy, allows more work to be done than can be accounted for by 
just the kinetic energy of the original system components.

A question for Martin:

If energy and matter are not interconvertible, where does all the energy
of an atomic bomb blast come from?  

-Scott
--------------------
Scott I. Chase			"It is not a simple life to be a single cell,
SICHASE@CSA2.LBL.GOV		 although I have no right to say so, having
				 been a single cell so long ago myself that I 
				 have no memory at all of that stage of my 
				 life." - Lewis Thomas