To maintain reliance on measurable physical quantities alone--that is, to make no reference to metaphysical entities such as subjective utility or labor value-- Sraffa attempts to calculate objectively the cost of production in terms of quantities of things used, the surplus being the difference between the things produced and the latter. One understands the turn to physicalist language as a rejection of the subjectivism of the marginal school. But Marx's language is neither physicalist nor subjectivist or phenomenological; it is realist but processual.
And for Marx this physical quantities approach would not only be reifying, it would also be unrealistic, for it requires the means of production not only to be the qualitatively same goods on the input and output side but also to have been produced with the same techniques so that their unit prices can be assumed to be identical. This has been Alan Freeman's and Paolo Giusanni's point for more than two decades, and I don't know of a good response to it.
Only if the goods are same can we easily subtract physical things from the gross output to arrive at the surplus described only as a quantity of physical things and do away with the putatively metaphysical (but entirely realist) category of value
And only if the goods which appear as both inputs and outputs have the same identical price due to having been produced with the same technique will there not be too many unknowns for the equations based on physical quantities to be solvable, making value redundant.
Only in this fantastically static world is value dispensable.
That is, one cannot by pass labor values which are the measures of real labor processes to build economic theory on physical quantities of things without making totally unrealistic assumptions about the static nature of the economy.
But this static economy has no relation to the capitalist world, so all that has been proven is that in such a fantasy world value is redundant in the determination of prices and profits. How such an approach is more materialist or realist than Marx's value theory escapes me.
So while the Sraffian school is physicalist, I would said that Marxian value theory is more realistic.
The physicalist language gives the veneer of tough guy scientism, but it only serves as a mask for anti processual, anti temporal theory which resembles Platonism.
Rakesh