Do you think we are alone in the Milky Way?

[alberto91]

So.. recent estimations for the Drake Equation (Maccone, 2012) suggest that there could be around 4,600 civilizations in our galaxy that are able to release detectable signals.

I find this number a little bit excessive, so I plugged some of the values of our Solar System into the equation and I obtained a smaller yet more realistic result, in my opinion: 50 civilizations.

Just in case someone is interested, I made a video showing the values I used: youtu.be/j2AIWIcn7Ig

Do you think 50 is a more realistic number?

 

[Anachronist]

In my opinion, any nonzero number is a realistic number. But the opinion of one person trying to come up with an answer using the Drake equation using available known values for inputs is as good as anyone else's. The devil is in the details: i.e. the proper input values to use.

The Drake equation is an excellent example of garbage in, garbage out. If there is any uncertainty in the inputs, there is even more uncertainty in the output.

 

[PeroK]

What criteria are you using to judge "realistic"?

 

[phinds]

In my opinion, any nonzero number is a realistic number. But the opinion of one person trying to come up with an answer using the Drake equation using available known values for inputs is as good as anyone else's. The devil is in the details: i.e. the proper input values to use.

The Drake equation is an excellent example of garbage in, garbage out. If there is any uncertainty in the inputs, there is even more uncertainty in the output.

 

[rootone]

The Drake equation isn't meant to be formula from which a definite number could be obtained.
It was conceived as a way of determining what are the theoretical factors involved, as bases for discussion in themselves.
Some of them, such as the frequency of stars having planets are now known to a fair accuracy.
Others, such as how many planets capable of supporting life give rise to civilisations are not even reasonably guessable.
However the default value for this should be 1, just Earth alone, since there is no data whatsoever suggesting anything otherwise.

 

[Klystron]

Limiting the thread to our galaxy seems like a reasonable boundary on the search for life off Earth given technological limits. If this limit is acceptable, then to further simplify the question: Is there life other than earth-based within some reasonable boundary around our solar system?

If one criterion for 'realistic' is 'bounded by empirical data' where the boundary implies physical evidence, then limiting the question helps avoid speculation.

If you are collecting forum members opinions, mine also contains upper and lower bounds. On some days I think, "We are alone. The Earth is a tiny globe nurturing the only known life forms; therefore the only intelligent species." On more cheery days I reply, "Life is ubiquitous. Look at all the evidence for exoplanets. Our galaxy may well teem with life."

Realistically, I would be satisfied with evidence of single-celled organisms from Jupiter or its satellites, or growing in a Kuiper belt fragment, or beneath the rocks of Mars.

 

[Anachronist]

What criteria are you using to judge "realistic"?

I think that was pretty clear when I said "any nonzero number".

 

[PeroK]

I think that was pretty clear when I said "any nonzero number".

My question was to the OP. Your reply just got in before mine.

 

[rootone]

My personal wild guess is that the circumstances of Earth are in many respects unusual.
However if it can happen once it can happen more than once.
Given that the galaxy is so big though, I'd go for maybe one or two other civilisations existing (contemporary with us.)