Quote from engie_ninja
If something was orbiting the Earth at the speed of light, it would take it only 4 seconds to complete an entire orbit.
That depends on the altitude of the orbit. As someone else mentioned, it wouldn't be a real orbit since the speed of light far exceeds the escape velocity of Earth. However, for such an orbit to last 4 seconds, it would have to be very high up. Something moving at the speed of light could circle the surface of the Earth more than 7 times in one second.