Waves and fields in bio-ontologies
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This document discusses waves, fields, and photons. It addresses whether waves should be considered portions of the medium they travel through or dispositions of the medium. It argues that waves are superposable and cannot be identified as either portions or dispositions. The document also discusses waves that do not require a medium, arguing that photons have angular momentum and are not simply energy. Finally, it addresses fields, noting that while many things can be described as fields, fields do not constitute a natural kind.
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Waves and fields in bio-ontologies
- 1. WAVES AND FIELDS IN BIO-ONTOLOGIES Colin Batchelor, RSC Janna Hastings, EBI / Geneva
- 2. OVERVIEW • Waves in a medium • Waves without a medium • Photons • Fields
- 3. WAVES IN A MEDIUM What is a wave? • A process? • A material portion of the waving medium? • A disposition?
- 4. AGAINST PORTIONHOOD Waves are superposable. A trough of one wave may physically coincide with a peak of another. Throw two pebbles into any pond if you need to be convinced of this.
- 5. AGAINST PORTIONHOOD Standing waves have portions of the medium that don’t move.
- 6. AGAINST DISPOSITIONHOOD Medium-borne waves need a medium and this medium needs the appropriate dispositions. A Mexican Wave is borne by a discontinuous medium. You collectively have the disposition to manifest a Mexican Wave. If you are not waving Mexican right now then the wave is not identical with the disposition.
- 7. WHAT ABOUT WAVES WITHOUT A MEDIUM?
- 9. NO.
- 10. Energy is not the kind of thing that can bear angular momentum.
- 11. Photons have angular momentum.
- 12. Spectroscopy only works because photons have angular momentum.
- 13. When a sodium atom undergoes a 3p → 3s transition, it loses angular momentum. The angular momentum is carried away by an orange photon. This is how sodium streetlights work.
- 14. MASSLESSNESS AND MATERIALITY Consider a massless, yet charged, cricket ball. It is repelled by the surface charges on ordinary objects. It is spatially extended, so can have angular momentum. Its passage through the air is slowed by induced charges on nitrogen and oxygen molecules. It will be visible because it is coated in dust and bits of grass. It has a history. But if you hit it for six you will never see it again.
- 15. WHAT IS A FIELD? A field, in the sense we are interested in, is something that has different values at different points in space. We can describe many things in terms of a field. It does not follow that a field is a kind, that the gravitational field of Uranus is of a kind with the electrical field of a van der Graaff generator is of a kind with the population density in Graz is of a kind with the direction of the hairs on my head at each point of my scalp.
- 16. ELECTROMAGNETIC FIELDS GRAVITATIONAL FIELDS describe the manifestation of a mutual disposition at a given point in space
- 17. ELECTROMAGNETIC FIELDS GRAVITATIONAL FIELDS describe the curvature of space– time at a given point in space and time
- 18. ELECTROMAGNETIC FIELDS GRAVITATIONAL FIELDS have a gauge boson we have actually detected
- 19. IN BRIEF Waves cannot be identified with the portions of their bearers, but wavefronts can. Waves cannot be identified with a disposition of their bearers. Photons are not energy. Fields are not a natural kind.