The Universe as a Time Machine
Everything we see is always an image of the past
As many know, light does not propagate instantaneously but has a finite speed, just under 300,000 km per second. One of the strangest and counterintuitive consequences of this limit is that everything we see, even the closest thing, is always an image of the past.
Let us consider the Sun, distant 150 million km from Earth. Its light takes about 8 and a half minutes to reach us. At any moment, we see an image of what our star was like a little less than ten minutes ago. It is an unbreakable physical limit. Even if the Sun disappeared at this very moment, we would not be able to know it for the next 8 and a half minutes.
Since the whole Universe is subject to this same physical law, the deeper one looks into space, the more one looks into the past. In 1987, when the light of the supernova SN 1987A, exploded in the Large Magellanic Cloud, reached the Earth, it brought us the information of a cosmic catastrophe that took place 160,000 years earlier. At that time, the history of homo sapiens was just beginning. In fact, our satellite galaxy, the Large Magellanic Cloud, is precisely 160,000 light-years from us. So, the light of an object belonging to that galaxy can only take 160,000 years to reach Earth.
