You apparently overlooked a few things.

The human physiology does require some gravity or similar force to function properly. But does it invariably require an acceleration of 9.8m/sec/sec? If not, what fraction of that would be acceptable while assuring proper functioning?

A possible solution might be something proposed about 40 years ago: the O'Neill Colony. More of a habitat than what people envision as a spaceship, an O'Neill Colony resolves many of the issues raised in your article.

The population could be large enough to handle psychological issues and provide the diversity, order and security of a society. This also handles the imperative of a rapid journey, allowing for sub-light speeds to avoid the issues with Special Relativity or invoking cryogenic storage, which is a very uncertain process at this time.

Free of the constraints of gravity, the huge O'Neill Colony could be constructed in a size adequate for proper shielding from radiation and micrometeor impacts.

This would be a long-term project as it would be important to first send robotic explorers to systems deemed likely to have inhabitable planets. Since these would travel at non-relativistic speeds, it might take a century or more to gather the needed data.

In the meantime, the O'Neill Colonies could be constructed and populated to see what would happen over a generation or two from a physiological, psychological, and engineering viewpoint.

With all of the data from the exploration and the long-term experience of colony living, these vessels would be as well-equipped as possible to serve as what would essentially be arks sent out in the hope of securing the future of the race.

We have known for years that we can't stay on Earth forever. There are enough easily foreseeable catastrophes to have legitimate doubts of human existence lasting as long as the reign of the dinosaurs. So we must go forth and multiply or chances.

This might also be the reason for the lack of contact by non-terrestrial intelligence. Species expansion for the purpose of racial survival instead of conquest would necessarily limit the spread and it doesn't take too many parsecs to achieve isolation.

Rather than saying "No" to the possibility of spacefaring civilizations, a more appropriate answer might be "Not yet."


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