how can light have no mass?

Question

how can light have no mass?

Answer 1

This is hard to explain...light has mass. Light is made if photons which are extremely small and are pretty much unseeable but when in a larger group they make light and you can't see through them(when you look at a bright street lamp look on the outside of it...it will be hard to see with all the light coming out near the glass casing around the bulb. Photons have mass but it's extremely small so it's considered weightless but it does have mass...



Btw I'm in 8th grade so I'm not sure if I can explain this to you

Answer 2

("how can light have no mass? ... but you you can feel heat on your skin from light")

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It is true that light possesses no mass because it is the only subatomic particle that is both its own matter and antimatter (i.e., electron and positron) annihilation; thus, pure energy. The photon has a way tiny rest mass (rest mass - mass detected by an observer in the same inertial frame of reference). However, the photon is never in an inertial frame of reference. Light is invariant in all frames of reference. That is why light moves away from any reference frame at a constant speed of 3.0 x 10^8 m / sec. (186,242 miles / second). The photon is a massless spin-1 boson with no charge and carries both energy and momentum, but no mass. The photon is massless because that was defined by the initial conditions set-down at the time of the big bang origin of the Universe. The photon, boson, is very nearly the opposite of all matter particles, fermions, which do carry mass and charge, with spin-1/2 and move at less than the speed of light. The characteristics of all known subatomic particles was determined by the initial conditions at the beginning of the Universe. Thus, the physics governing the Universe is an intrinsic part of the space-time continuum itself.



You feel heat from Sun light or radiating from a light bulb, because both sources radiate not only visible light (light you can see), but they also radiate some in the Infrared and ultraviolet spectrum as well. The heat you feel is mainly due to ultraviolet rays.



See: Photons as light quanta

http://www.pa.msu.edu/courses/1997spring/PHY232/lectures/quantum/index.html



See: Electromagnetic waves

http://www.science.uwaterloo.ca/~cchieh/cact/c120/emwave.html



Best regards

Answer 3

E=mc^2 is typically the rest energy of a massive particle. That is, if a mass could be converted entirely to energy (in the form of light and heat) this would be the value. But if the particle is moving, there is another term.

The total energy, TE=Sqrt(p^2c^2+m^2c^4) which simplifies to the above for p=0. p in this equation is momentum. the momentum for a light quanta is p=(h v/c) h is planks constant, v is frequency.



I don't know if you wanted math, but the point is light has energy because it is moving (has momentum) and no mass. Massive objects have intrinsic energy even if they are not "moving."



p.s. Moving is in quotes for relativity's sake.



p.p.s

If you want to measure the speed of light, put a large flat piece of meltable stuff (chocolate, marshmallows) and measure the distance between the hotspots. Those hotspots are the frequency of light (microwave radiation) in your microwave oven. The owner's manual or label on the microwave should tell you the frequency of the light.



c = d * f d is distance in cm, f is frequency in GHz (or MHz) or 10^9 (10^6)/second