Can something exist if has no mass or cannot be converted into mass? The mass of a photon is zero, yet how can a photon have energy but not have mass? If this is false, would that it be true that a box with and LED in it would have more mass when the LED is lit? But, are there other types of being aside from energy and mass? A concept perhaps. How would a concept be measured? The word apple is comprised of certain wavelengths that are detected by the human ear. In the human body as a system, the energy that my body requires to produce those wavelengths at "regular" amplitude (assuming there can be a standard amplitude) could be converted into mass. Would this allow me to measure the mass of the word apple in the system of my body? Right now I'm sure many of you are thinking that the word apple could be represented in many other ways such as writing. This is why I used the word 'system' when I referred to myself saying the word apple. Since there is no standard for the writing and speech of the word apple. Is everything comprised of something? Could that something be converted into mass? Can I measure anything?