A few people have asked for this so here we go.
Firstly, this isn’t in response to the Neil deGrasse Tyson video about the presence of aliens in the universe, but it is something I think about a lot. If you’d like to watch it, the link is here.
It’s always a weird thing to consider. Humans seem to have this arrogance that if there is life ‘out there’ that they are not only able to communicate with us, but also that they want to communicate with us. It could be that they’ve received our messages but didn’t see it as worth replying for whatever reason.
There are a number of other reasons why we’ve not been contacted, of course. Maybe we’re going about it in entirely the wrong way. Humans can only see around 2% of the electromagnetic spectrum and hear around 1-2% of the acoustic spectrum. Even on Earth there are life forms that can’t communicate with one another. I’m sure we’ve all read that story of the lonely whale who could only make noises out of the hearing range of the rest of their species and was thus unable to communicate. Considering this happens on Earth it isn’t too far fetched for it to happen anywhere else. It could be life on other planets have tried to contact us and we’re just unable to ‘hear’ the message. Or they see a different 2% of the electromagnetic spectrum and as a result we’re just ghosts to one another.
Another thing is the timing of our attempts to contact alien life. Say it takes 50 years for our message to reach whoever may receive it, it would have to reach them at a time within their development or evolution where they’d be able to collect and interpret that data, then form a response that we’d understand. We’ve tried to send references for them to use in building their response, but what if they didn’t understand that was what it was for? There are ancient languages on this planet that we’re unable to translate. Given the universe is around 13.8 billion years old, we might be contacting a civilisation in it’s infancy, or conversely a civilisation where our technology is considered to be archaic. They might view television and radio the way we view ancient Egyptian methods of communication at the very least. And even if they are able to receive our message, decide to reply, manage to form a response, know where to send it then transmit it back to us, it would probably still take another 50 years to reach us. So from our original transmission we’re talking at least 100 years for it to get back to us, assuming the 50 year model. If we extend that to 500 years we won’t hear back for a millennium, at which point our technology may very well have moved on to the point we can’t receive those messages anymore.
To go back to Dr deGrasse Tyson, he’s been widely quoted as saying that with the universe as huge as ours, saying there’s no alien life based on the areas we’ve looked for it is like looking into a drop of water and concluding there is no life in the oceans. There are currently approximately 10-14 million species on Earth and over 5 billion species having ever existed. It seems bizarre that all of these will have been condensed onto one tiny speck in a universe that is billions of light years wide.