The Archaeology of Science in the Science of Archaeology

Abstract

The Archaeology of Science in the Science of Archaeology ALEXY D. KARENOWSKA Revolution is a claim that can rarely be made without controversy, but as a description of the effect of science on the discipline of archeology over the last half century its justification is beyond dispute. Of the many scientific and technological developments that have contributed to the rapid evolution in the scope and capacity of archeological and historical research, among the most significant and visible have come from the area of imaging. Off-the-shelf tools now available for application to archeological research span a remarkable range of scales and capacities. We have, for example, techniques like reflectance transformation imaging (RTI) and multi-spectral imaging (MSI) that allow the recovery and discovery of minute textural and structural information about surfaces; magnetic resonance imaging (MRI) which gives us, non-invasively, spectroscopic information about the composition of three-dimensional objects, and satellite imaging technologies that enable geophysical surveying and mapping over kilometer scales with a speed and spatial resolution which, just twenty years ago, would have passed for science fiction. Though diverse in purpose and capability, these imaging instruments are united by a common basis: they all rely on the physics of electromagnetism. The part of the electromagnetic spectrum that is most faarion 27.3 winter 2020 A version of this paper was given verbally at the Annual Conference of the Institute for Digital Archaeology in Oxford in May of 2015. This meeting, dedicated to the theme of digital imaging in archaeology, served both as a timely celebration of recent progress in the field, and an opportunity to discuss different perspectives on this progress with colleagues from a range of specialisms. There, as here, I explore a magnetician’s eye view. 8 the archaeology of science miliar to us is visible light. Visible light is made up of a combination of travelling electric and magnetic fields: a wave of electrical energy (red, figure 1) together with wave of magnetic energy, propagating in the same direction, but inclined at ninety degrees to it (blue). The colour that visible light appears to the human eye is related to the distance between adjacent peaks of the waves, this length is called the wavelength and is inversely proportional to the number of undulations up and down per second, a quantity that we refer to as frequency. The term “frequency,” when applied to light is exactly analogous to that which we meet in the context of sound waves: the higher the frequency, or pitch, of a musical note, the shorter the acoustic wavelength, and vice versa. In the case of visible light, the longer the wavelength (that is, the lower the frequency) the redder it gets; the shorter it is, the bluer. If we change the wavelength significantly in one or Figure 1. Electromagnetic excitations are made up of a wave of electrical energy (red) together with wave of magnetic energy (blue). The two propagate in the same direction, but are perpendicular to each other. The wavelength, usually represented by the symtbol λ, is the distance between adjacent peaks of the two constituent waves and is inversely proportional to the frequency; that is, the number of undulations (or oscillations) up and down per second. Image by author. Alexy D. Karenowska 9 another direction, the light ceases to be visible to the human eye. When we extend beyond the visible part of the spectrum in the direction of longer wavelengths, we first encounter infrared light, and in the opposite direction—the one of shorter wavelengths—ultraviolet. If we increase or decrease the wavelength further still, the electromagnetic waves start to interact with matter rather differently from optical ones. In the direction of longer wavelengths, they first become microwaves —the kind of electromagnetic radiation that both your microwave oven and your mobile telephone use; then radio waves—the electromagnetic waves of short, medium, and long-wave radio transmission. In the opposite direction , when we increase the electromagnetic frequency above that of light, what we get are X-rays and, beyond that, their high-energy counterparts, gamma rays. It is only in the last one hundred and fifty years that a proper understanding of how electromagnetism works has been...