english: In this lesson, we'll add the single experimental fact that whenever anyone measures just how fast light moves, they get the same answer: 299,792,458 meters every second, which means that when we draw light on our space-time diagram, it's world line always has to appear at the same angle.
non_english: U ovoj lekciji, dodaćemo jednu eksperimentalnu činjenicu: kad god neko izmeri koliko brzo se kreće svetlost, dobija isti rezultat: 299.792.458 metara svake sekunde, što znači da kada nacrtamo svetlost na našem prostorvremenskom dijagramu, njena svetska linija uvek mora da se pojavi pod istim uglom.