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Comment by orf | Hacker News Reader

People always talk about how vast space is, but rarely about how vast time is. We've been looking for life for the last what, 60 years or so? It seems like not only is space so vast which makes finding evidence of life hard, but this is made even harder by the small volume of time we are likely to be around to try and observe in the grand scheme of things. Alien life has to be relatively close in terms of distance as well as time.

What if our closest alien life became discoverable (started emitting radio signals or other signs) a million years from now? Would we be around to see it?

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Exactly. 13 billion year old universe. 5 billion year old solar system. Life on earth was effectively pond scum for 3 billion years. Humans went from banging rocks together to transistors and space ships within 500k years. We have been a civilization for a laughably small time on astronomical terms.

Given the timeframes involved it's entirely likely that any 'aliens' are half a billion years ahead or behind us. Our first encounter with life will likely be one of three things.

1. Pond scum millions of years away from being anything else.

2. Aliens who have been extinct for millions of years.

3. Aliens so hopelessly advanced they are deities

Even just a million year gap would be insurmountable. Which is nothing on the universe's timeline.

Excellent point.

I think that one advantage of interstellar distance is we can effectively look back in time a great distance, so in effect we don't have a visible radius, but a combination of time and distance.

We can see thousands of light years back in time, thousands of light years away. However, we don't have that picture of Tau Ceti at 11 light years away. Perhaps thousands of years ago there was a civilization there that flourished and died - and we'll never know because their signs of life are outside our distance/time perception.

A graph of Time/distance would be Time one axis, distance on the other and a diagonal line stretching up and to the right, showing what we could see at any given time.

Thoughts?

[edit: comment formatting ate my pretty ascii chart]

Or worse, we do intercept the radio signals, from hundreds of thousands of light years away, from a an alien race long since extinct.

> Would we be around to see it?

And how long does an average civilization broadcast radio?

On the "life is safe" end of the spectrum, maybe there's much better technology to be discovered. On the "life is dangerous" end, maybe you learn pretty fast not to broadcast your location to the galaxy.

Reminds me of the book, The Three Body problem

> maybe there's much better technology to be discovered

Obviously we don't have much to draw on, but it seems like our technological growth looks a bit exponential. I'd imagine a civilization that has been around for a million years would have discovered a hell of a lot of technology - but a million years is a blip in 13.82 billion years, the age of the Universe. It's like 0.001% if I've got my maths right.

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