I was asked to write about extraterrestrial life. That's an approximately big subject that I'll approach with a few posts starting off with some context. An old friend wrote this about the Universe:
Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.
Hold a finger about a foot - thirty centimeters - from your eye and focus on it. It's part of you, but you're seeing it as it was about a billionth of a second ago.. the amount of time it takes light to travel a foot.1 The Moon appears as it was a bit over one and a quarter seconds ago and the Sun is about five hundred seconds in the past.
Generally we don't think about these things unless we have to synchronize events or consider the historical context of an event. It comes into play exploring the Solar System, but also when measurements are made of events recorded in more than one place. In experimental physics you worry about it all of the time, but it's important in high frequency market trading.
When you look at the closest star - Centauri Proxima - you're seeing something that took place about four and a quarter years in the past. A few years ago some of us studied weather patterns on a type of star known as a brown dwarf. One could make predications and we issued a weather report. The problem was we were looking at something that happened about sixteen years in the past and if some being near that star could read our report, they'd be looking at our history making the total out-of-dateness of the report about thirty two years. When I know when someone was born I sometimes send them a birthday greeting naming the star from which starlight that originated when they were born is just making it to Earth.
The farthest in the past you can usually see with your naked eye is the Andromeda Galaxy .. about two and a half million years ago. Telescopes take us farther back to about thirteen billion years ago when gravity was beginning to pull the primordial elements of hydrogen and helium into stars and organizing the earliest galaxies. Thi distant past is bizarre and quite foreign to anything more recent, but it's there for the looking if you have enhanced your senses properly. Getting that far back is difficult and many more recent histories exist, so most Astronomers work in different time periods.,
We're not at the center of the Universe. Rather we're at the center of our own perception. Our finger is a bit in the past and our friend on the other side of the room a bit father back. We look out into concentric layers of the past marking different epochs. The history of the Universe that is written in light and now even in sound in these layers until we get to the last layer.. the fire of creation.
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1 Assuming your perception is instant, which it isn't.. it adds 250 to 300 thousands of a second, but that muddies the point.
We also live in neurological and acoustic pasts. Those signals travel much more slowly than light, but over short distances so we tend not to think about them except during thunderstorms.
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