A crafty MIT student, has just completed the latest iteration in a series of upgrades to his dorm room door lock. Now because MIT's administration doesn't like it if you hack the door locks or the strike plates, Dheera needed an innovative way to enter his own room without using a key. He's gone through a series of various door-opening mechanisms over the last couple of years -- our favorite one required scanning a barcode on a box of EZ Mac to gain entry -- but he's finally settled on the simplest design, a computer-less setup that involves a microcontroller, a motor, and a PS/2 (waterproof) keyboard. (He's got a much more technical explanation, including a circuit diagram and drivers on his website, in case your SO / parents / kids also have rules about messing with your house). We're now taking bets on how long it takes his MIT classmates to crack his password.
The short answer is "no", but it is a qualified "no" because there are odd ways of interpreting the question which could justify the answer "yes". Light is composed of photons so we could ask if the photon has mass. The answer is then definitely "no": The photon is a massless particle. According to theory it has energy and momentum but no mass and this is confirmed by experiment to within strict limits. Even before it was known that light is composed of photons it was known that light carries momentum and will exert a pressure on a surface. This is not evidence that it has mass since momentum can exist without mass. [ For details see the Physics FAQ article What is the mass of the photon? ]. Sometimes people like to say that the photon does have mass because a photon has energy E = hf where h is Planck's constant and f is the frequency of the photon. Energy, they say, is equivalent to mass according to Einstein's famous formula E = m
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