Why did Newton believe light was a particle?

[Neo_Anderson]

Well?

 

[Feldoh]

Just taking a guess but historically did people of the time even conceive of a "wave" in any way that we currently think of a wave?

My guess is probably not. A particle is a lot easier to picture to me since it's a lot easier to think of motion with an object with a well defined position, etc.

 

[mgb_phys]

Because when you put your hand upto your eye you block out the sun.

 

[Neo_Anderson]

Just taking a guess but historically did people of the time even conceive of a "wave" in any way that we currently think of a wave?

My guess is probably not. A particle is a lot easier to picture to me since it's a lot easier to think of motion with an object with a well defined position, etc.

Huygens proposed the first wave model of light in 1690, which was when Isaac Newton was only 53 years old.

 

[arildno]

Just taking a guess but historically did people of the time even conceive of a "wave" in any way that we currently think of a wave?

My guess is probably not. A particle is a lot easier to picture to me since it's a lot easier to think of motion with an object with a well defined position, etc.

Completely wrong.

Christiaan Huygens, in his 1690 Traite de Lumiere proposed the wave theory of light, 14 years prior to Newton's corpuscular (particle) theory of light in Opticks (1704)

Fermat may have been even earlier than Huygens in formulating that some properties of light are most readily explained by a wave nature.



Besides, water waves have been observed for milennia...

 

[turbo]

Newton was developing mechanical theories, and he might have looked back to Greek atomism for inspiration, and came up with a corpuscular theory about light in which light is made of tiny particles emitted from objects, flames, etc. Not such a bad notion 300+ years ago. As for not being able to reconcile that with a wave theory, that probably came about as Einstein's ideas about the photoelectric effect were reconciled with wave theory in quantum theory.

 

[arildno]

It was Young's experiments that seemingly put an end to the raging debate between the two theories on light.

And then, Einstein came along to complicate the picture just a teensy bit, "re-justifying" Newton, so to speak..

 

[turbo]

It was Young's experiments that seemingly put an end to the raging debate between the two theories on light.

And then, Einstein came along to complicate the picture just a teensy bit, "re-justifying" Newton, so to speak..

Yes, in the 19th C, it was known that the effects of dispersion and interference were best described by wave theory. Then Einstein brought the corpuscular notion back into vogue. Not long after, the wave-particle duality was extended to other entities.

 

[Cleonis]

Well?

I once read the following answer to the question. I don't know whether it is a correct reconstruction of Newton's considerations.

Newton was a master lens maker. The lenses and mirrors he made for his telescopes were among the best of his time. As a lens maker, Newton knew how fine the lens surface needs to be polished. In working a surface the polisher uses finer and finer grained polishing agents. He has to manufacture the polishing agents himself, grinding them to finer and finer powders. (It seems plausible to me that Newton examined his grinding powders under the strongest magnification possible, such as the magnification that the dutchman van Leeuwenhoek achieved)

I assume that in Newton's time it was known that waves will be obstructed by structures that are smaller than the wavelength of the waves. For instance, if you have a pond, and a row of stakes in it, each one 5 centimeters thick and with a 5 cm gap between them, then water waves with a large wavelength will pass through unimpeded, but very small waves will be affected.

Polishing glass reduces the surface roughness to a level where the surface irregularities are smaller than the wavelength of light. Knowing the fineness of the polishing grains he needed, Newton had a good idea of what wavelength light would have to be if it was a wave phenomenon. Also, Newton had a good idea of the velocity of light; Newton was aware of Roemer's hypothesis, and he accorded with the reasoning.

If light would be a wave phenomenon then given its velocity it would have to have an extremely high frequency. To Newton that defied belief, and he concluded that light had to be a particle phenomenon.

Among the most difficult things to explain with a particle theory of light is the birefringence of calcite. It is my understanding that Newton put great effort in coming up with an explanation of how light particles are refracted by the calcite crystal.

(Incidentally, the details of the refraction of light in calcite crystals involve polarization. Early wave theories of light were based on longitudinal waves, so early theories of light propagation could not explain the birefringence of calcite either.)

Cleonis