Didn't Newton's corpuscular theory fail to explain reflection?

  1. In 1637 Descartes gave the corpuscular model of light and derived Snell's law. This Corpuscular model of light was further developed by Isaac Newton in his famous book entitled OPTICKS and because of the tremendous popularity of this book, the corpuscular model is very often attributed to him and is called Newton's Corpuscular theory.

    Corpuscular theory predicted that if the ray of light (on refraction) bends towards the normal then the speed of light would be greater in the second medium. But the experiment of Foucault proved that, on refraction if the light bent toward the normal, then the speed of light will be lesser in the second medium. Thus, Corpuscular Theory didn't satisfactorily explain refraction. But, reflection is said to be explained by this theory.

    In case of reflection practically, when the light ray is incident at an angle zero with respect to the normal drawn at the interface, ray bounce back in the same direction with the angle of reflection zero. According to Corpuscular model, if corpuscle bounce back in the same direction (when angle of incidence is zero) it came from, there will be collisions with the corpuscles which are going to be incident later. Then, there will be random displacement of corpuscles. But, this is not what practically happens. So, didn't corpusuclar theory also fail to explain reflection? does wave theory explain this case?
  2. jcsd
  3. UltrafastPED

    UltrafastPED 1,912
    Science Advisor
    Gold Member

    The corpuscles were posited to be very small so that they could travel through glass; thus collisions are unlikely.

    You can look up the writings of Young and Fresnel to see if they discussed the shortcomings of the corpuscular model.
  4. jtbell

    Staff: Mentor

    Foucault's experiment was around 1850. I'd be surprised if many physicists still took Newton's corpuscular theory seriously at that point, after the experiments on interference and diffraction beginning around 1800 by Thomas Young and others, and the theoretical analysis of interference and diffraction using the wave model of light by Fresnel and others around 1820.
    Last edited: May 5, 2014
  5. I am adding the link to the same question, which I had posted in another site (confirmed from administrator to be legal)-Didn't Newton's Corpuscular theory fail to explain reflection? I feel it will energize our discussion.

    I hope during reflection, photons bounce back hitting the surface. Considering this, I feel that photons can't move without interacting each other (I mean with out colliding each other) , when they are incident at an angle of zero degree w.r.t the normal at the point of incidence.
    Last edited: May 6, 2014
  6. Drakkith

    Staff: Mentor

    Classical wave theory explains reflection extremely well and works for all types of waves, not just EM waves. However, only Quantum Electrodynamics fully explains the interaction of light with matter, especially at the atomic and subatomic scales.

    Photons are not particles in the sense that they are like small billiards balls. They are the quanta of interaction of an EM wave. Put simply, the EM wave travels through space like a wave but interacts with matter only in little finite chunks of energy that we call photons. Note that this packet of energy is not a physical packet of something. Energy is not a tangible substance. A photon is simply the transfer of a discrete amount of energy from an EM wave to matter or from matter to an EM wave during creations of the wave. For example, a photon of an EM wave with a wavelength of of 500 nm (green light) has approximately 2.5 eV of energy. This means that when an EM wave interacts with matter, it only transfers energy in multiples of 2.5 eV and never anything else.

    As such, when an EM wave is reflected, the photons do not interact with each other because they are not little particles bouncing off of a surface.
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  7. Now, I got my another question resolved. I used to think that we have the sea of photons around us, though how could we see the macroscopic world? In other words, the photons which came from a particular object (which we expected to see) might get collided with other photons and end up some where other than our eyes. Then, we wouldn't be able to see the object which we intended to see. But, the fact that photons pass each other without colliding, resolves it.

    Although, I agree that there is a complexity in understanding the mechanism of how we see. I feel this fact helps us to be near the true mechanism.
    Last edited: May 6, 2014
  8. It's a valid point, but if the first of a linear series of balls all travelling at the same velocity colllides with something immovable, it bounces back at the same velocity, thus bouncing with the second ball, however, when two equally heavy balls collide it's as if they go through one another.
    There's a puzzle of the this sort about ants walking on a stick.

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  9. Drakkith

    Staff: Mentor

    The "true mechanism" is that light is an EM wave first and foremost. Quantum theory and the development of the photon does not change this. It merely changed the way we thought the wave interacted with matter.
  10. According to me the true mechanism is not yet discovered. Nothing is first and foremost atleast at this moment considering what we know now.
  11. Drakkith

    Staff: Mentor

    Nothing of what you quoted means that an EM wave isn't a wave. No matter its "true" mechanism, it's still an EM wave just like a water wave will always be a water wave. New theories don't replace old theories so much as they add to them. When Quantum Mechanics was discovered it didn't mean an EM wave is any less of a wave, it merely added to the description and made it more accurate through the addition of photons. The EM field still oscillates with a frequency and a wavelength, just like a wave should, and no new theory will ever contradict that since it is an observable fact. (Just look at how any radio works)
  12. Every one will have their own opinion. We are dealing with different thread, I don't want to be off topic and be against the forum rules. We shall discuss about it in a particular thread, "which is first and foremost".
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