Peter Hickman wrote:

Mike Williams wrote:

That's a rather anthropomorphic concept of aliens. I'd guess that most
intelligent civilisations wouldn't build cities.

Cities are quite logical, shorter lines of communication and distribution. However once you have matter transporters (or some such technology) and a good communications system then you might start to abandon cites.

Matter transporters will always be problematic, especially if they require destroying the original and making a copy, or even de-constituting the original and reassembling it.  This is the stuff of science fiction today, but even if it were possible I would refuse to use one myself, and I'm certain that millions or billions of people would likewise refuse on religious, spiritual, psychological or naturalistic terms.

In any case, there are lots of things we do today despite technological advances.  We have cars and trains, but people still walk and ride bicycles.  We can order almost anything online, but people still shop. We watch television and movies, but still enjoy live theater.  People can drink at home, but this is even somewhat stigmatized: many prefer drinking at bars.

Interestingly, many people believe that the American city reached its zenith around the 1910's or 20's, then fell.  There's a great book about Minneapolis/St. Paul by Larry Millet called "Twin Cities Then and Now" which shows photographs separated by 100-50 years from each other.  You see that the 1910's suggest a vibrant, bustling metropolis typically with highly developed mass transit, horses and cars alongside each other, people on sidewalks, lively storefronts, etc.  The 1950's, rise of the automobile, sprawl, and interstate system destroyed the city as we knew it.  Gone was the vibrancy, the ornate architecture, the center of social activity.  In its place: sterile, glass and concrete facades, empty sidewalks.

Clifford Simak (also of Minneapolis) wrote his award-winning "City" in 1952 which suggested that anti-gravity personal transportation might deal the final blow to the city: people would move to the countryside, roads would no longer be needed, and eventually they'd leave earth altogether.

I like this theory, and actually wish it were true (I can't stand my long commutes to work every day and would rather get a piece of land and zip 100 miles to work in a matter of minutes).  But cities remain, and I believe there's evidence that they are regenerating, recovering from the   war (of neglect and "modernization"), returning to being the in-place.  The X-generation, for example, is an urban group.  The "hip" places are clearly in the city, not in the mindless, template cookie-cutter suburbs invading the farmlands surrounding every major city.

If there's on thing that's for sure, though, it's that cities (as a whole, whatever their rationale) have persisted longer than radio communications.  They'll likely last longer than radio communications, if current trends in technology continue at such a breakneck pace.  And so maybe the most fruitful SETI searches will result from (when technology allows) search for extra-terrestrial cities.  Whether we can do this optically, chemically or via some other signature, a city is not necessarily required for a sign of intelligence (hermits, nomads and Simak's "City" are counter-examples), but when a city *is* found, we might certainly say that we have found intelligence...

Besides cities have a political dimension. People will want to be near the seat of power. Cities will happen if power is wielded from a given location. Also population pressure will create cities as people simply have less space between them. Then there is the fact that large concentrations of people allow sub cultures to flourish. If 1% of the population like theatre then a town of 1000 people will probably not have much of a theatre scene, now 1% of a multimillion city and you have a vibrant scene.

The Japanese have a saying about ex pat communities. 1000 people per restaurant. There will be no decent Japanese restaurant (that the Japanese would eat at) until you have at least 1000 people (Japanese) in the area to frequent it.

Cities are important for the development of civilizations.