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In his De Anima (On the Soul), Aristotle writes, "And Empedocles was not correct, nor was anyone else who may have spoken as he did, in speaking as if light is in motion with respect to place and sometimes comes to be located between the earth and what surrounds it, but that such motion escapes our notice. For this is both contrary to the lucidity required of speech and contrary to the appearances. For while it might escape notice in a small interval, that it should escape notice [that light is traveling] from the region of sunrise to that of sunset is too big an assumption." (Book II, ch. 7, 418b) (Aristotle raises and discusses the question of whether light is in motion with respect to place also in On Sense Perception and the Perceptibles, 446a20-447a11.)

Aristotle seems to suggest that if light is indeed so fast that its motion escapes our notice, one would have a hard time accounting for what is responsible for light as it appears to us. Are modern scientists able to offer such an accounting? It seems they are unable to say with clarity whether light, as they understand it, consists of discrete particles or is a continuous wave, or if it is both (or neither), how that is possible.

user132918
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  • light is both a wave and a particle (photon) it can appear and act as both depending on the circumstance and how it is observed. but also... are you asking how the eye works? because thats what it looks like - voting to close – Alex Robinson Oct 13 '16 at 19:20
  • As it stands, this question is very broad and vague. Are you simply asking, "what is light?" Are you asking why the speed of light is so fast? – knzhou Oct 13 '16 at 19:21
  • @knzhou i think there are two questions here: what is light, and if light is so fast, how can we see it – Alex Robinson Oct 13 '16 at 19:45
  • Yes, looking for the modern physics to Aristotle's objection to Empedocles: hard to speak "lucidly" of what is responsible for light appearing as it does to the unarmed eye if we also say light's travel "escapes notice." Applied to modern physics, this would be a question about the clarity of the explanation of whether light consists of discrete particles or is a continuous wave (or neither, or both, and if so, how that's possible) and recognize this had been addressed, with further pointers here http://physics.stackexchange.com/questions/46237/is-th‌​e-wave-particle-dual‌​ity-a-real-duality – user132918 Oct 13 '16 at 22:12

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One would answer to an ancient Greek (or all ancients at that) since we have measured the speed of light, the question is moot.:

The first true measurement of the speed of light came in 1676 by a fellow named Ole Roemer (Rømer). Roemer was observing Jupiter's moon Io, the innermost of the Galilean satellites. As seen by an observer on Earth, Io suddenly disappears when it moves into Jupiter's shadow, and it suddenly reappears when it moves out of Jupiter's shadow (back into the sunlight). Roemer was interested in predicting the times at which Io would be observed to emerge from Jupiter's shadow. His goal was to use those observations to determine Io's orbital period more accurately; he was not initially trying to determine the speed of light.

Based on these observations, Roemer calculated that it would take light about 22 minutes to cross the diameter of Earth's orbit. Combining that value with earlier measurements of the Earth's semimajor axis (orbital radius) (described here and here) gives a speed of light of about 210,000 kilometers per second. This is about 30% lower than the modern value for the speed of light, but considering its antiquity, method of measurement, and 17th century uncertainty in the exact sizes of the planetary orbits, this value is remarkably close to the modern value of 299,792.458 kilometers per second.

anna v
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It seems to be both a particle and wave - light has wavelike properties as exhibited by phenomenon of interference. Light also seems to have the properties of a particle as exhibited in the photoelectric effect. That said, I am not sure how modern physics answers how light appears to the "unarmed" eye. Why would modern physics need to explain this given that it has calculated the speed of light at a quantity not easily "observable."

Also see:

https://www.google.com/amp/phys.org/news/2015-03-particle.amp

T Ye
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  • One might add that in his characteristic search for a definition or essence, Aristotle might not be satisfied with either waves or particle or wave-particle definition because such a definition would not give an account of the essence (the "light-ness") of light. To say that light is made up of photons is to push back the question about the character of light as light (or luminosity) onto the photon. Aristotle's definition of light is "the completion of the transparent." It resembles his definition of motion: "the actualization of the potential as potential" (obscure but not question-begging) – user132918 Oct 14 '16 at 13:19