The question of whether there is other intelligent life in the Universe, especially technologically advanced life, is one that fascinates many. There is much discussion regarding such questions as how common such life might be and whether alien beings have the capability of contacting us. To date no convincing evidence exists to prove or disprove whether such beings exist, unless of course you buy into one of the various fringe theories floating about.
But one of the things that influences such discusssions, and perhaps hamstrings them, is our own experiences. The only civilisation we know of is our own, and so we tend to base our guesses on what aliens might do and how they might behave on our own, even though we know that they likely won't be much like us physically or mentally.
While walking about today I saw quite a few birds flying about. This got me thinking of a potential reason why we might not encounter alien beings even if they exist. What if they never decided to fly?
From the earliest days of humanity we've been surrounded by innumerable examples of flying beings, ranging from tiny insects to large birds like vultures. This no doubt led to the human wish to fly, which has been with us for untold centuries and was expressed in myths such as that of Icarus, who died when flying too close to the Sun destroyed his wax and feather wings. Numerous ideas were conceived of and some even attempted, but it was the Montgolfier brothers of France who created what is generally recognised as the first successful aircraft, the hot air balloon, and who conducted the first successful manned flight in October of 1783. This proof that human flight was possible led to two centuries of experimentation and development, resulting in today's modern aircraft and both manned and unmanned spacecraft.
But it's not hard to imagine a biosphere with few or no flying creatures. Absent the examples of our own world would intelligent beings come up with the idea of flying? Or perhaps a better question is whether enough "people" would come up with the idea, or think it was a doable concept, without easily visible examples in the world around them. The only "flight" beings on a planet without flying lifeforms would know would be objects and beings falling from high places, or being flung uncontrolled through the air by accidents, the wind, or explosions. Even the example of their world's equivalent of insects might not be enough, the assumption being made that the principles involved couldn't be scaled up to anything useful.
If aliens never came up with the idea of flying on their own world the idea of travelling to other worlds via vehicles would seem even less likely. At the very least any such speculation would probably involve methods like teleportation that so far appear not to be pratical.
Absense of flight doesn't mean such a civilisation wouldn't have advanced technology. Much of the technology we use would have developed much as it has, flight or not, because it was not directly influenced by the development of aircraft and spacecraft. But it wouldn't be one hoping to someday meet us in person, and perhaps wouldn't even consider indirect contact possible at all. So it's possible it's not just capability that will prevent us contacting our alien counterparts, but the failure to even consider the possibility by those on the other end.