# Will a space alien civilization have died out by the time we receive their signal?

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The Drake equation,

N = R * Fp * Ne * Fl * Fi * Fc * L

Is used to estimate the number N of civilizations in the galaxy currently capable of extraterrestrial communication, given the seven factors on the right, which have to do with rate of star formation, fraction with planets, fraction on which life arises, etc.

The last term, L = the length of time for which such civilizations release detectable signals into space, and this is critical. We on Earth have only been sending out radio transmissions for about 100 years. Will we last, say, 10,000 years? If we don't, then by the time aliens more than 10,000 light years away hear our signals, we will no longer be around. Likewise, any signals we might hear coming from that distance or greater might well be from a long-dead civilization.

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I met an astrophysician from Grocka long time ago. I learnt something from him. If one twin go to space and return to Earth, he will be young but other twin old.

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Yes, but the space twin has to travel very close to the speed of light on his journey for this to be noticeable.

For example, if the space twin travels for 20 years (according to his clocks) at 90% of the speed of light, v = 0.9c, he will have aged 20 years, while the Earth twin will have aged 46 years.

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Yes, but the space twin has to travel very close to the speed of light on his journey for this to be noticeable.

For example, if the space twin travels for 20 years (according to his clocks) at 90% of the speed of light, v = 0.9c, he will have aged 20 years, while the Earth twin will have aged 46 years.

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Yeah, but new stars form and old stars die out every time. So, I believe there might be multiple alien worlds.

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If they even "want" to signal us. One look at our planet just might make them shy away but this book has another theory!

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Can't say as I'd blame them for wanting nothing to do with the likes of us.

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Hi OtherTink,

No, I think we will receive the alien signal okay...because I am betting on another paradigm shift, this time to take us outside of our bias for perceiving our universe ONLY within the narrow boxes of time and space.

So I was going to say all the rules will blow up, but no it's more that we will come to understand how tiny is our segment of reality where we are locked into the rules of time-space, and how vast our human horizons.

*  *  *

Think John Stewart Bell (with whom I am in love), Bell's Theorem, quantum entanglement and the failure of local realism.

Is the moon still 'there,' even when Albert Einstein is not looking at it? ...our confinement within the ideations of here & there, then & now, is compelling but unnecessary.

An' he had a sense of humour too...

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"... our bias for perceiving our universe ONLY within the narrow boxes of time and space."

There once was a physicist, Bell,

Who said, "Local theories don't gel.

It's all intertwined,

From in front to behind,

And what's past, now and future? — can't tell."

I looked for a cartoon about quantum mechanics that I saw once, but  couldn't find it. It showed a guy talking to an attractive girl. Then he momentarily glanced away, and she turned into a wave function.

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Ah Tink, it's a paean worthy of the great Bell himself...and the cartoon makes me laugh even without seeing it!