Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

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.

share|improve this question
    
The real reason is that Newton believed that matter was particulate, from the laws of motion, and he couldn't bear the idea that light was something else altogether. He wanted a unified vision. –  Ron Maimon Mar 24 '12 at 7:57
    
@RonMaimon Makes sense--nowadays we sort of think waves are a natural fundamental--er--thing. At that time I guess all wavelike phenomena (sound) could still be explained via particle means; so no reason to complicate stuff. –  Manishearth Mar 24 '12 at 8:10
    
It is actually remarkable how far Newton went along with this--- he had the light "pulsate" in a wave pattern to reproduce interference fringes, but this cannot reproduce spatial interference. Modern quantum mechanics would have made Newton pretty happy, it's a shame there was a bit of a lag between his day and ours. –  Ron Maimon Mar 24 '12 at 8:41
    
@Ron Yeah, I think that's the "eels" argument I'd read. Though I doubt modern QM would make anyone happy--it's too complicated, though beautiful. :P –  Manishearth Mar 24 '12 at 8:46
add comment

3 Answers

up vote 3 down vote accepted

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

share|improve this answer
    
Hmm.. But isn't diffraction of light a very easy-to-see phenomenon? That would debunk light-travels-in-straight-line. How did he explain diffraction? –  Manishearth Mar 1 '12 at 6:16
    
By something like sound waves, a collective expression of corpuscles due to changes in density they have to go through. After all he studied prisms. –  anna v Mar 1 '12 at 6:45
    
Oh, good point. But I still have the doubts in the comment in the below question; they apply here as well. –  Manishearth Mar 1 '12 at 6:46
    
Sure, but the question was how he got the idea, not why he did not change. I suppose the older one gets the more partial to one's own theories and not letting go, no matter how brilliant the new explanation is epicycles are sought to shore up the pet theory. Look at Einstein and QM. –  anna v Mar 1 '12 at 6:50
    
Oh looks like I mis-stated my main question. So it was his arrogance after all. Or something like that. Thanks! –  Manishearth Mar 1 '12 at 6:53
show 1 more comment

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.

share|improve this answer
    
Aah I forgot the obvious point :p. But I do recall reading that Newton continued to uphold his theory even after experiments were carried out. He modified it to make the corpuscules 'move in a manner similar to that of eels'. Also, see en.wikipedia.org/wiki/Wave–particle_duality#Huygens_and_Newton . It says 'this theory had difficulties in different matters'; that's more of what I'm looking for. Any idea what the difficulties are? –  Manishearth Mar 1 '12 at 5:35
    
@Manishearth No matter how brilliant the physicist, eels( epicycles) are a better choice rather than adopting newfangled theories that destroy his own. Even the great Feynman had a reaction against QCD when it first broke out, he was partial to his parton model.en.wikipedia.org/wiki/Parton_model –  anna v Mar 1 '12 at 6:56
    
Yep, I've heard of partons. I think Gell-Mann mocked that by calling them "put-ons". Yeah, I guess it's always better to play in home field. –  Manishearth Mar 1 '12 at 7:09
add comment

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.

share|improve this answer
    
Thanks, this helps as well. –  Manishearth Mar 1 '12 at 6:56
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.