As a sort of corollary to the previous thread I started, I got to thinking that if we can describe the universe as it was at a certain time, measured by light years, We see the universe changing extremely quickly...in sort of chunks of time. A bit like a speeded up camera recording outside the usual time frames we use to know if it is lunch time for example. Therefore it is entirely possible that we missed an (or some) entire planetary civilisations which rose and fell between our snapshots of time and which perhaps even visited our Earth. So if for example we can see the universe at 3 million light years in the past, and then at 2 million, something may have happened in the intervening years. and seeded the Earth we know today.
A "light year" is not a measurement of time. It is a measurement of distance... the distance light travels in one year. The distance light travels in one second is 3x10 to the eighth power meters. So multiply that by 60 (seconds in a minute) times 60 (minutes in an hour) times 24 (hours in a day) times 365 (days in a year).
A "light year" is DISTANCE... the distance light travels in a year. If you doubt that, look it up. Its been in every dictionary for a long, long time.
I agree with the principle here. We can't see every heavenly body that could have a civilization, not because of increments of time but because of dust, hiding behind other stuff, bodies that don't emit light, etc. But, there is a problem that is harder than that. We can't detect civilizations in this universe, even if they are in our own galaxy - essentially, immediate neighbors. Those civilizations would have to be doing something SPECTACULAR compared to anything we can possibly do in order for us to detect it. And, if they are a civilization that died out, that's monumentally harder, of course. There could have been (or currently be) advanced civilizations all over the place and we would never know.
Yes a lot of stuff can happen between what we can see and what is actually happening there at the current time.
Not true in principle. SETI was justified based on the argument that using radio telescopes, we could detect us. We could detect a civilization in our galaxy that is emitting radio signals we like we do. So it makes sense to look for them. The flaw in that argument is the assumption that distant civilizations would using radio for thousands and thousands of years. In fact we are now going radio silent - the age of radio on earth was just over 100 years. Now we use LASER and microwave, which is highly directed and would not be detectable. In 1977 it looked like we might have detected someone. But we never heard it again. It was called the WOW signal https://en.wikipedia.org/wiki/Wow!_signal
The problem with the radio emission approach is that they have to be either (A) a civilization with a level of technology similar to our own that is located quite close to us (i.e. a few light years away) or (B) a much more advanced civilization that has chosen to emit signals using stellar mass equivalent power outputs which could then be detected from thousands of light years away. Which begs the question why would they bother.
The OP is basically correct. The tools we currently have are too limited to find most civilisations. Finding ones in the past is impossible unless we come up with something like Star Trek. And if you think about it, even Star Trek was limited to our galaxy. There's a couple trillion galaxies...
When you go out at night and look up at the night sky and wonder if anyone is out there, be sure to wave. Given the numbers, there is about a 100% that somewhere out there in the universe, something is looking back and wondering if you exist.
Let's hope not! Unless we have similar DNA, not likely. But then there is panspermia. We might be related. We can only eat our relatives. Also Einstein's birthday AND the day Stephen Hawking died. Hawking was born on the 300th anniversary of Galileo's death.
That would make the speed of light 3.27 x 10^6 US football fields per second. Note that a metric football field is not the same.
LOL! Today, astronomers use parsecs - parallax seconds. A parsec is about 3.26 light years. The reason is that most measurements are based on measures of parallax angles, and it just ends up being less math to talk about parsecs rather than constantly converting between parsecs and light years.
If we did find life besides ours in the universe, the first thing we would do is figure out a way to have sex with it. Second, we would figure out a way to kill it...
