Monday, 2 November 2015

special relativity - High speed and low speed photons


Looking at the discovery of the neutron, and I came across this page: http://www-outreach.phy.cam.ac.uk/camphy/neutron/neutron3_1.htm


The animation on the left, talks about low energy photons and high energy photons. And it implies the more energy a photon has the faster it moves. I don't understand the whole light is photons and waves at the same time thing, but I thought the speed of light was constant, that Gamma rays travel at the same speed as visible light, infrared, microwaves, etc.


So how is that some photons can move faster than others (with more energy)?




Answer



The animation is unfortunately misleading. The speed of light is constant and all photons, of any energy, travel at the same speed. Higher energy photons have smaller wavelengths (or, equivalently, higher frequency) but not a different speed.


Unfortunately, this is difficult to illustrate clearly. The reason the illustration shows the higher energy photons as faster is because of the naturalness of equating speed with kinetic energy of an object. It "makes sense" to most people that a more energetic particle would move faster, even if this isn't an accurate description of the phenomenon.


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