Explaining The Universe on Instagram: "The speed of light is one of the most fundamental constants in physics, travelling through a vacuum at an exact value of 299,792,458 metres per second. At this incredible speed, a beam of light could circle the Earth more than seven times in just one second. What makes this constant so important is that it represents the ultimate speed limit of the universe—no object with mass can reach or exceed it. Light slows slightly when passing through materials like