The question of extraterrestrial civilizations seems to me entirely open.

外星文明的疑问对于我来说显然整个还是开始。

youdao

If advanced extraterrestrial civilizations are out there, why haven't they made themselves known by now?

倘若真有高级外星文明存在，为何它们到现在也不现身？

youdao

Where extraterrestrial civilizations may be rare, there is something that is seemingly rarer still: A girlfriend.

虽说外星生命及其稀少佳音英语，但还是有一种生命比它更稀少：女朋友。

youdao

Vakoch admits that the typical SETI approach has been to suppose that long-lived extraterrestrial civilizations would also be far-ranging technical wizards.

FORBES: SETI's 'L Factor':? Will E.T. Actually Be Around Long Enough To Phone Home?

But because earth is home to the only technological civilization thus known, we are severely hamstrung when making assumptions about the longevity of potential extraterrestrial civilizations.

FORBES: SETI's 'L Factor':? Will E.T. Actually Be Around Long Enough To Phone Home?

Thus, in an age when we have come close to destroying ourselves several times over, is it reasonable to expect that extraterrestrial civilizations would persist over lifetimes of hundreds of thousands if not millions of years?

FORBES: SETI's 'L Factor':? Will E.T. Actually Be Around Long Enough To Phone Home?