To a scientist the glass is completely full with matter.
That's technically-accurate while side-stepping the inherent philosophical perspective in a way. A "scientist" would try to determine the intial state of the glass, (whether full of matter such as air molecules or liquid forms of matter). The conclusion about "fullness" would then depend upon the criteria parameters which form the basis of that conclusion. If "air" is a defining parameter, then the glass is never empty. If liquid matter is defining parameter, teh scientist may ask, "hey, who drank half of my drink?"