when doing basic calculations of theories where the mass of a photon isn't a critical variable, it would be allright to assume a value of zero for the mass of a photon. however, when we delve into calculations of theories based on special realativity or quantum mechanics, where the mass of a photon becomes more critical, we must give a non-zero value to avoid anomolies such as infinities or absolute zero's. but, what is this non-zero value, and how can it be determined?
an ingenius experiment carried out by Jun Luo and his colleageus at Huazhong University of Science and Technology in Wuhan, China using a very sensitive torsion balance (a device with rotational torque) have been able to determine the mass of a photon. they aimed a beam of light at the apparatus, for which the value of the torque (or rotational energy) of it is known. when the photons hit the device, there is a measurable increase in the overall torque. this method is a 20-fold increase in the accuracy to determining the value of the mass of a photon over previous methods for determining the photon's mass. the newly determined estimate for thenon-zero valueof the mass ofa photonis 10<SUP>-51</SUP> grams or 7 x 10<SUP>-19</SUP> electron volts.
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photon mass
