Neither, the glass is simply twice as large as it needs to be.
If you travel at the speed of light and you try to look in the mirror, will you see anything. And why do we always refer to a mirror as a definitive article, ie look in the mirror instead of a mirror.
Not that the speed of light is theoretically possible, because as speed increases mass increases meaning an infinate amount of energy would eventually be needed.
And why do birds suddenly appear, every time, you are near?