SilentP, it souldn't be necessary to see the alien species' planet in order to confirm the the aliens' existence.
Listening for their EM communications should be more than enough. We listened since the 1960s - and so far, nothing. The stars are strangely quiet.
Here's your first problem, we've only been listening since the 1960s. That means we've only listened up to 40~50 lightyears away from ourselves. It also assumes that even if something has been transmitted in our direction in the correct timeframe that the signal even has the correct strength to even register on any particular sensor we care to use.
Not quite, SilentP
We had powerful enough transmitters for ~60 years and that means that the radio transmissions we sent
are at the most ~60 light years away from Earth.
We could "hear" transmissions coming from civilizations thousands (or more) light years distant. That only means that these civilizations sent these EM signals a few thousand years ago and we're receiving them now.
See above point about signal degradation and dissappearing.
To be fair - most EM signals we have so far emitted should be incomprehensible to any alien astronomer (due to interference from the sun). But the carrier wave could be identified as being artificial. And, of course, we should be listening to EM signals from civilizations much more advanced than our own - the assumtion being that a more efficient/undetectable for us means for transmitting information (faster than light, that is) does not exist (according to relativity, such a thing can't exist).
Also, here lies the assumption that the species in question doesn't have some form of communication that isn't FTL. I'd throw out the example of the theoratical method using a 'split' particle and changing the spin on one halfs, which the other half responds to by spinning the other way. Anyone know what it is I'm thinking of?
Also, it may be possible that a form of FTL travel exists, but no capability for signals to do the same with pure EM signals, hence some kind of messenger craft being used instead.
Admittedly the previous two points are purely hypothetical, but then again, we can't assume that aliens haven't found ways around hurdles that we struggle with.
As I said, we should be listening for transmissions coming from civilizations more advanced than us - most of their transmissions will be powerfull enough to be coherent when they reach us, and, equally important, such civilizations should transmit EM signals continuously (more or less) - and I'm not talking just about transmissions sent specifically to some hypothetical alien species, but about transmissions that have other purposes, too.
About transmitting information/travelling with FTL speeds:
According to special relativity, NOTHING can travel faster than light (not matter, not even information) - this is because, according to the theory, one cannot determine a preferred frame of reference (and with FTL, one could do just that).
About the "split particle":
You're talking about quantum entanglement
. About this phenomenon was said that, "philosophically, it breaks special relativity, but practically, it does not".
You see, if you have two entangled particles and you measure one, the result you get obeys only probability - for example, you have 50% for the particle having spin up and 50% for the particle having spin down.
In this moment, the other entangled particle (which you did not measure) will "choose" to have a spin identical to the one of the measured particle - even if this not measured particle is at the other end of the universe! So, philosophically, entanglement breaks SR.
But you see, practically, you can't transmit any useful information this way. Why? Because you can't choose what spin the particle you measure will "choose" to have - this is a LAW of quantum mechanics. Only gibberish can be transmitted, you have no control over the transmitted information.
FTL or no FTL?:
If, in the future, a FTL form of transmitting information/matter is found, special relativity will be proven to be largely incorrect (so far, special relativity was experimentally verified again and again - it's one of the "safest" theories we have).
Of course, a FTL anything will enormously increase the probability that space-faring aliens are everywhere in the galaxy - a space-faring species can explore/colonize the entire galaxy in a few thousand years (and it had millions of years at its disposal)!
In this case - why are they not here