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Where did Newton get the idea that light had a particle nature and not a wave nature? At those times, AFAICT there were no phenomena that showed particle nature. But wave nature is much easier to detect. So, why didn't Newton change his theory to a wave theory? I recall something about "motion like Eels", but by Occam's razor, it makes more sense to just call it a wave and not a wavelike particle.

Was it just his arrogance? Or did he have some reason to stick to particle nature?

Edit: I actually wanted to ask why he didn't change his theory after wave nature was discovered. He instead complicated it with the Eels. I failed to see what supported the particle point. But it's answered now :D.

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From the paragraph Optics in the wiki article

Newton argued that light is composed of particles or corpuscles, which were refracted by accelerating into a denser medium. He verged on soundlike waves to explain the repeated pattern of reflection and transmission by thin films (Opticks Bk.II, Props. 12), but still retained his theory of ‘fits’ that disposed corpuscles to be reflected or transmitted (Props.13).

If you look at the history of optics it is dominated by ray optics, straight lines. Particles travel in straight lines . I think that was the correlation he must have made.

In his Hypothesis of Light of 1675, Newton posited the existence of the ether to transmit forces between particles. In 1704, Newton published Opticks, in which he expounded his corpuscular theory of light. He considered light to be made up of extremely subtle corpuscles, that ordinary matter was made of grosser corpuscles and speculated that through a kind of alchemical transmutation "Are not gross Bodies and Light convertible into one another, ...and may not Bodies receive much of their Activity from the Particles of Light which enter their Composition?"[24]

He was not far off actually, once photons were discovered. Just missed duality.

It seems Lucretius had had the same idea ceturies before

In 55 BC, Lucretius, a Roman who carried on the ideas of earlier Greek atomists, wrote:

The light and heat of the sun; these are composed of minute atoms which, when they are shoved off, lose no time in shooting right across the interspace of air in the direction imparted by the shove. —Lucretius, On the nature of the Universe

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Well, light travels in a straight line just like a particle on which no force is acting upon, and light bounces off a mirror just like the laws of conservation of momentum would dictate it for a particle.

The wave nature, on the other hand, requires you to do some interference experiments to understand observed phenomena in terms of waves. I think Huygens double slit experiments pretty much settled the debate over the nature.

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Newton gives two main arguments for a corpuscular view of light in his Opticks:

(1) Light consists of rays of inherent and inalterable dispositions (as regards colour, refrangibility, etc.). This is argued for throughout, but see esp. the classic prism experiments in props. I and II. Wave theorists, on the contrary, base their explanations on modifications of rays.

(2) The law of refraction "may be demonstrated upon this Supposition. That Bodies refract Light by acting upon its Rays in Lines perpendicular to their Surfaces" (p. 79 of Dover ed.), i.e., the law of refraction follows by assuming a gravity-like force attracting particles of light toward the heavier medium. (Of course this implies that light speeds up when it is refracted towards the normal, i.e., that light is slowest in vacuum and fastest in dense materials; a fact not experimentally disprovable at the time.)

(1) and (2) are elegantly combined if rays of different colours consist of particles of different sizes.

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