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Comment by vivzkestrel | Hacker News Reader

no matter how advanced the civilization is, proxima centauri will always be 42 trillion kms away. Our civilization in current stage is not even close to 0.1% the speed of light but lets say your advanced civilization goes at 99% the speed of light, still doesnt change the fact they need 4.25 years approx to reach earth. Still doesnt change the fact that unless they have a 1 billion km wide telscope, they cannot reliably tell if earth has life or not. So basically you are asking them to take a shot at coming to the solar system on a 5 yr trip when they have no idea what is found here. Now extrapolate the numbers for the average 100 light year trip between 2 points on our galaxy and you ll quickly realize why we dont have aliens

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If they came here and back at .99c it would be ~70 years "time debt"[0] for them (meaning 70 years would have passed for their relatives back home).

[0] Terminology from Dan Simmons's Hyperion. Would also recommend Joe Haldeman's The Forever War for more time dilation themes.

On a similar note, humans cannot colonize the galaxy. Sending a single message across would take thousands of years. Instead a human ancestor would split into various individual species.

When you think of it, light speed is really slow. Even on Earth we are capped by it.

> Still doesnt change the fact that unless they have a 1 billion km wide telscope, they cannot reliably tell if earth has life or not.

How come we’re making progress on this without a 1bn km telescope?

And even that notwithstanding, they could use a solar foci telescope. It's kind of a pain to orient, but it /does/ give you extreme magnification.

Where did you get the 1bn km number? I'm asking it seriously, I'd like to better understand how to calculate these things.

some calculation about resolution of the telescope to be able to see cities and people of another planet from a 100 light years away at the minimum. I forgot the exact calculation but it ll need a humongous sized telescope mirror

If their lifespan is 10,000 years, a five-year trip to exotic backwater Earth would be just a vacation.

Direct Multipixel Imaging and Spectroscopy of an Exoplanet with a Solar Gravity Lens Mission (with 1 km resolution)

https://arxiv.org/abs/1802.08421

...and someone made an awesome video about it:

https://www.youtube.com/watch?v=NQFqDKRAROI

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