Is it possible that when we look into the cosmos that we are seeing into the past?
We hear all the time that we are looking into the past when we look out into space. But we can’t definitively say that! In the following I’ll explain why.
Astronomers say that because the speed of light is a finite value (c = 299,792.458 km/s ) it takes light 1 year to travel a distance of 1 light-year. On the surface of it that seems very reasonable.
That means that light leaving the star alpha Centauri, which is 4.3 light-years away, took 4.3 years to get to Earth and thus the information in that light is 4.3 years old by the time it gets to Earth. Thus they say we are looking back in time — into the past. And for distant galaxies this means we are looking back in time even billions of years.
But is that correct?