[hist-analytic] Materialism and mass as a unit of measurement

Roger Bishop Jones rbj at rbjones.com
Sat Jan 29 14:53:30 EST 2011

```Steve,

It looks to me like you did not take on board the very first
thing I said in my first response to you, viz. that photons
do have mass.

If you don't agree then I don't really know how to resolve
that.
If you do accept it then you need to revise your argument
and see whether there is still a problem.
The only problems I can see arise from your belief that
photons have no mass.

Generally, the equations should be taken to involve
"relativistic  mass", the only relevant equation I know of
which involves rest mas is the one which tells you how to
calculate relativistic mass from the rest mass and the
velocity.  This doesn't work for photons because it gives
you zero divided by zero.  For a photon you have to go to
quantum theory to get the energy (which is fixed by the
frequency) and use e = mc^2 to see how much mass that is
equivalent to.

On Saturday 29 Jan 2011 17:21, Baynesr at comcast.net wrote:

> "I don't see an ambiguity in e = mc^2 which applies
> really to both."
>
> Ok, then in the case of a photon which has no mass,

I can only repeat here what I said in my first post, which is
that a photon does have mass.  It doesn't have rest mass.

> what does 'M' in
>
> 'E=MC'
>
> mean? Is its meaning the same, then, as it is in
>
> 'P = MV'?

Yes.

In the first equation this is a general conversion which
could apply to rest mass or relativistic mass, whereas in
the second equation this is the definition of momentum and
the mass on the right must be the total mass not the rest
mass.

> Or, does it merely take different values? If a photon is
> massless

which it isn't!

> and M is 0 then then E is, likewise, 0. So
> either the mass of an electron is not zero or we
> "fiddle" with 'M' (the "equivocation").

The mass is not zero so no equivocation is required.

> We know that a
> photon has a great deal of momentum, so it does have
> energy, etc. However, I am pleased that you take it that
> the equation applied to both because the question of the
> meaning of 'M' in the characterizing the momentum of a
> photon becomes significant, given that it is massless,

no it isn't!

> although the value of M can't be 0 in the equation as
> long as the photon is said to have E.
>
> The question of units arises because a difference in
> units is the only way to justify attributing a value of
> M to a massless particle, assuming there is no ambiguity
> and, therefore (apparently on the view you take) we need
> not write it like this:
>
> E(rest energy) = M(rest mass)C^2.
>
> But if we DO require this emendation of the classical
> formulation then I would persist in saying there is an
> issue.

There is no emendation required.

> The problem with Kim (and I do have specific since there
> are as many flavors of physicalism as there is ice
> cream) is that he claims there is only matter; but he
> gives us no idea of what matter is.
> This is the fount of my skepticism.
> All accounts of what it is to be physical
> that I've seen depend on "realizers" of the laws of
> physics, which brings us to the question What are the
> laws of physics? The answer is usually "Generalizations
> over physical quantities." Circularity prevails. Physics
> is concerned with mass, not "material objects." But
> there may be a version of physicalism that identifies
> the two. I think some philosophers such as Kim make this
> assimilation; it was against them that my remarks were
> directed. I don't believe there are material objects; I
> believe there is mass, whence the importance of
> justifying any assertion to the effect that a photon is
> either a massed "quantity" or a material object. It is a
> subject matter of physics, but why? I.e. if we assume
> that physics deals with objects having mass. If mass IS
> energy then the move we've been talking about is merely
> "pencil and paper" (dealing with the conversion of
> units); if they differ then materialism cum Kim et al is
> false or unexplained. They can differ even if there is
> an equivalence relation between them.

Unfortunately there is no unified theory of physics, so
physicists don't have an answer on what physically exists.

That doesn't stop a metaphysician from being a physicalist,
but it does mean he can't underpin it by a belief in some
accepted scientific theory with which it is consistent.

If I were to be a physicalist, then I would probably leave
to physics the question of what kinds of physical objects
exist.  In which case detailed argumentation about the
status of the theory of relativity would not be crucial.

However, its unlikely that I would ever be a physicalist.
Just like Carnap (who also was not a physicalist of course)
I can see some point in formalising science, but I think
multiple alternative physical theories should be compared,
and we should not expect any single one to suffice for all
purposes.

Roger Jones

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