Abstract
Olaf Müller presents a supposedly empirically equivalent theory to Newtonian optics, which in his view is therefore threatened by underdetermination. This threat could even be expanded to modern physics, since this branch of physics is partly based on Newton’s theory. In this paper, I will show that Müller’s alternative theory contains an ill-defined concept, viz. the definition of whiteness as the absence of optical causal factors. This results from a fundamental property of whiteness: for every source of white light there exist metameric sources. I further argue that this cannot be reconciled by borrowing other concepts from modern physics, as is, I will show, tacitly presupposed in Müller’s argument. As a consequence, his alternative theory is not empirically equivalent to Newtonian optics and his argument in favour of underdetermination fails.
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Notes
In this paper, I will use the terms ‘Newtonian optics’ or ‘Newton’s theory’ instead of ‘geometrical optics’ because it makes the historical context clearer.
Hereafter, I will use the terms ‘absence of optical causal factors’ and ‘causal neutrality’ synonymously, as optical effects are the only kind of effect considered here.
I will mostly not distinguish between ‘light rays’ and ‘darkness rays’, which is how rays on the inverted theory could be termed, and speak only about ‘rays’, as it should be clear from the context which one is meant. The term ‘light source’ may also refer to a surface which actually emits darkness rays in the inverted theory.
From modern viewpoint, due to its temperature being non-zero, there will always be some kind of radiation in the optical part of the spectrum emitted by a dark surface. However, as this view forms part of theories which are far more advanced than Newtonian optics, I will not consider it here.
I am indebted to an anonymous reviewer for pointing out the importance of the non-local character of colour vision.
Of course, the accuracy of approximation also depends on the amount of light let in in order to conduct experiments like producing spectra. To simplify matters, I will assume here that only a very small amount of light will enter the dark chamber in order to produce spectra, as in Newton’s experiments. Larger amounts of light would then require either dark surfaces with higher absorption, or a larger chamber.
Of course, this phenomenon affects all colours, especially unsaturated ones like white, where the range of possible metamers is very large.
The only way to construct a white chamber where we do not see any kind of influence on the experimental outcome would be to construct a chamber that was so bright that we were completely dazzled by its brightness, making it impossible to make out any differences at all. Of course, in such a chamber, one could not observe any kind of spectra, which makes it impossible to conduct optical experiments. This disqualifies it as a suitable approximation of absence of causal factors. Why should the absence of causal factors prevent us from seeing optical effects like colour spectra? Being dazzled by the light of a chamber seems like an indication that the room is filled by too many optical causal factors.
I am indebted to an anonymous reviewer for pointing out the possibility of this kind of black metamer.
Such detectors do at least presuppose a theory which describes the photo effect.
For example, if we try to invert the concept of energy, the question remains as to how it is mathematically inverted, that is, how we should relate orthodox energy values—given by measurements carried out by orthodox physicists—to the energy values of the inverted theory. If we consider the level of measurement, energy is normally measured on a ratio scale. This type of scale only allows transformations by multiplying the scale by a constant. In that case, an inversion can only be achieved by multiplication with a negative number, which results in negative energy values. At first glance, this seems as difficult to interpret as is talk about negative mass or negative length.
References
Müller, O. (2015). Mehr Licht. Goethe mit Newton im Streit um die Farben. Berlin: S. Fischer Verlag.
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Schreiber, A. Metameric Whiteness and Absence of Causal Factors. J Gen Philos Sci 49, 503–513 (2018). https://doi.org/10.1007/s10838-017-9393-9
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DOI: https://doi.org/10.1007/s10838-017-9393-9