Classic logic would state that the "absence of evidence is NOT evidence of absence"... It is all but impossible to prove we are along.
In the folklore of the Oregon Stat Party there was a sighting of a triangular object with no lights that silently came over one night.. but a dark shape isn't much proof one way or the other.
Are we alone, doesn't seem likely statistically or otherwise if talking the universe or multiverse (;-) ) ...
As far as observing, all-sky cameras are getting pretty popular and a direct drive mount might have a chance of keeping up. Getting a setup in the right place and at the right time might be tough. Might want to consider a multi-messenger approach, UV, NIR, Radio, magnetic etc.
Take earth as an example, how would you detect earth? We sent out a lot of radio waves for 50-60 years. The spectrum spread then the power dropped dramatically. What we do have that is fairly high powered now is highly directional. With radio we have only been able to detect another civilization for th passed 50 or so years and have been detectable for maybe 70 or 80 years. That's a pretty narrow window of opportunity all things considered.
Precisely.
The absence argument is a philosophical one, not a scientific one. You can't say we are alone, you can't see we are not alone. So, no scientific study, no scientific observing.
Again, with the narrow window, you're saying can't test. So not testable.
Current science, and I mean science, not theories, weird ideas, wormholes, mathematical gimmicks that ignore the lack of physical data, says no. I'm afraid ironically astronomers of no sense of deep time. We are EFFECTIVELY ALONE. There is no way to tell one way or another if we are actually alone, so it is not testable. And remember, folk don't mean amoebae or archaeobacteria when they say life, they mean star trek or star wars plethora of advanced civilisations. Most more technically advanced "civilisations" in our history weren't overly benign to the intelligent life they met, whether we're talking Europeans in North and South America and Australia, or Slavs in the lands East of the Urals, where in all cases the meeting was not nice for the incumbent.
Of course there may be intelligent floaty things in the Jovian atmosphere, things crawling through the hydrocarbon gloop on Titan that take a century to complete one thought, there are all sorts of things you can think of, and science fiction authors sometimes have, it is not the same as being able to check for it.
As well as geologic deep time, the sheer amount of time needed to get significantly multicellular is four aeons ish here. Yet why does it have to be DNA? Most of these things purported, even when seriously, always are suspisciously at our scale, flying machines about the right size for hominid sized people. Yet there is no reason for arthropods to exist anywhere else, let alone vertebrates or molluscs or anything else. These views are usually stuck in the progression of life argument, whereas things didn't evolve, they have evolved via descent through natural selection, which isn't the same meaning. We often tend to phrase it as if it had purpose behind it, maybe due to a hangup of old religions making people all special like. A lot of natural selection on Earth in the past half aeon, and sometimes assumed prior, was accelerated at times due to niche changes, and especially major climate changes (usually massive ice ages that make the recent ones look like a few nights hoarfrost), all driven by plate tectonics, and neither 'habitable zone'/goldilocks planet either side of us has any real evidence of plate tectonics.
Really, not only is the popular Drake's Equation (popular no doubt as it is a simple multiplication formula) guilty of having terms that are not anywhere near being quantified meaningully, even before you get to the technical civilisation terms, but is entirely missing several, as it is heavily naive in its interpretation of what is needed for life, let alone intelligent life, etc, etc, etc.
There are amino acids out there in space, maybe RNA is an inevitability, and afterwards DNA, but the body forms don't necessarily have to follow. Even if something was out there, it might not be even capable of communicating with us, irrespective of technology. And even then, what's the common language? Not mathematics, ever tried to learn what all the symbols of mathematics are and mean? There are even more than one protocol at times to denote the maths, and binary numerical progression can only go so far.
We're effectively alone.
If 51 Pegasi has other planets, even an Earth one, its Sun is around six aeons old, does it always take around the same time to get to the radio window? Or the pulsing laser blasts at folk, both are still restricted by the speed of light and the immense distances. There are a lot of galaxies out there, you don't need parallel universes to assume there maybe some creature and civilisation akin to us somewhere in the universe, however, there is no universal here and now.
So we go back to being effectively alone, and having no way to test otherwise, scientific method wise.
Whilst we have a lot of circumstantial evidence to say that intelligent life coincidentally co-existing at the same time is at best unlikely at worst a meaningless statement in practice, even before designing any testing.
And stuff like that. It's so tempting it seems to people's thoughts. People even go around calling Astrobiology a science, utter drivel. There's barely enough measurable to have astrobiochemistry, and only just enough to have astro-organic chemistry. It is always surprising to me that when groups go multidisciplinary they tend to come out with drivel. If you're old enough your remember when geologists, palaeontologists, and astronomers got together and postulated planet Nemesis. You get a similar one today with planet IX, where Brown not satisfied with removing Pluto from being planet IX wants to be known as having found a real planet IX. This last bit more mentioned to show how even successful practical astronomers can get more and more unscientific, for the more this "bound to be" object isn't found, the more we haven't looked in the right place or looked properly, even now there is increasingly less places to look for it! Thus we're bordering on pseudoscience again. Nothing to stop folk thinking on it and enjoying the point, but it's only a science when you throw scientific method at it, philosophy isn't science, it's nearer maths, where you can have applied and "real" maths. With maths you can logically derive all sorts of things, and I suppose folk could assume that things currently without application in maths will have one found. Dubious.
Apparently, increasingly and massively complex self consistent systems of logic can be defined that lead to gibberish, as long as the "self-evident" or "intuitive" axioms are chosen appropriately. Etc, etc. You can get into stuff that science can't be relevant for quite easily, and you can also have pseudoscience. Most visitors from elsewhere concepts are about the same level as fairies at the bottom of the garden, just more modern.
The scale thing always annoys the heck out of me, by the way, because if folk reflected on it
No speculating on the Clapham Omnibus, to mix two old English sayings.
Are we alone? Nope, Google, Facebook, and for some Apple and Amazon, and the NSA are watching us all the time...
Or I could have summed this all up by just saying remember what Fermi said! But that's another pseudoscience trick, reference to what someone "specially clever" said (which is actually true in this case, the guy was specially clever, often it's just someone who's shoved out a popular book).
Absence of evidence is "well, we can't talk about it then, because there's stuff all to talk about".
