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Back To The Future

Relativity tells us that Nature has a speed limit: no information can travel faster than the speed of light. That's quite fast, but not fast enough to travel the universe quickly enough. When you look at the Sun (please don't!), you see it as it was 8 minutes ago: it takes 8 minutes for light from the Sun to reach us. Stare at Saturn through a telescope: you are seeing it as it was 1 hour 30 minutes ago. The deeper you look into space, the further back in the past you are imaging... Our closest star, Proxima Centauri, is about 4 years in the past as we look at it today. We say it is 4 light-years away. Our nearest galaxy, Andromeda, is 2.5 million freaking years in the past! And the edge of the visible universe is 14 Billion years in the past... This means that when we look at the Cosmic Microwave Background radiation (see previous post), we are actually looking at the universe as it was starting out, in its infancy...

One of the strangest effects resulting from this time lag comes about when singular violent events occur far away: Supernovae or exploding stars... When a star exhausts its fuel and undergoes total (and I mean total) gravitational collapse, it typically undergoes a series of violent (and I mean violent) explosions... these are so nasty that near-by stars can be torn apart by the explosion... And we can see these events all the way from the safety of our Earth. They appear as a sudden brightening of an otherwise unspectacular star; and a subsequent dimming as the star starts to settle into a neutron star or, better yet, a black hole. The accompanying picture is that of Supernove SN2006X, before and after - much like pictures taken in hair transplant commercials. The star is 54 million years in our past. So, while the explosion was seen in 2006, it actually happened 54 million years ago... the star is there no more...

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