New Estimate on likely no. of alien civilisations in our galaxy

[Montero]

Unless advances in physics on our side or theirs changes transport enough. All the wormhole theories and the like. I'd never say never. Would agree to "highly unlikely".

 

[Parson]

Or, maybe their society and/or individuals is so long lived that a journey of centuries is not out of the question.

 

[J Riff]

36 with interstellar space travel, more like a twenny thou civilized rocks or dirtballs out there.

 

[Astro Pen]

Fantasy writers, when stuck, pop up with, "magic". SF writers do not enjoy that luxury. If you are writing FTL, warp drives or alien military flotillas pitching up here you are suffering, to a degree, from genre slippage.
It's fun, so we do it anyway, but to pretend that it is in some way projected true science is delusional. Though many believe their own propaganda because physical reality is tediously limiting and means that we really do have to look after spaceship earth very carefully.
Inter galactic traveling biology is rather like reverse time travel, ( if it were ever going to be invented it would be here already.) We would have lost our planet to it long ago.

However, incredible distances, C, and cosmic radiation will stop any interstellar travel for anything but robotics. Even robotics will need to carry a bulky lead overcoat and some chronologically durable kind of power supply.
One thing that can be sent at light speed though. - information. Forget Greys landing in the woods, look for information.

 

[Justin Swanton]

Or, maybe their society and/or individuals is so long lived that a journey of centuries is not out of the question.

Interestingly enough, that's the theme of my SF novel. My starfaring civilisation first made themselves immortal, then built an interstellar ship. About the only remotely feasible way of doing it.

There is one argument against alien civilisations, at least against those capable of interstellar travel. Earth is one of the relatively few planets capable of harbouring life built on hydrogen, oxygen and carbon - the elements in the periodic table that allow for the most complex life forms.

Earth furthermore has been able to support life for hundreds of millions of years. Hence for a very long time it has been a valuable prize for any starfaring civilisation whose molecular biology is built on the same elements. If there was such an alien civilisation they should be here already - in fact they should be in charge (MIB anyone?).

An interstellar civilisation consisting of hundreds or thousands of inhabited worlds could not simply cease to exist, just as human civilisation has never ceased to exist once men learned to till fields and build towns. If the aliens make a mess of one planet they can always find another one to colonise. An interstellar civilisation should exist now if it ever existed in the past. But there is no evidence for such a civilisation. Therefore such a civilisation never existed.

I don't think alien life exists at all for other reasons that I won't go into here (most of you probably know them already).

 

[Justin Swanton]

However, incredible distances, C, and cosmic radiation will stop any interstellar travel for anything but robotics. Even robotics will need to carry a bulky lead overcoat and some chronologically durable kind of power supply.
One thing that can be sent at light speed though. - information. Forget Greys landing in the woods, look for information.

Machines actually do very well in space but they can't repair themselves and they can't generate offspring. They have a sell-by date. Re information you have the problem of transmitting a signal powerful enough to cross the impossibly vast distances in the galaxy without getting lost against background radiation. It's doubtful any planetary civilisation could generate the energy necessary for such a signal.

 

[Montero]

Machines actually do very well in space but they can't repair themselves and they can't generate offspring. They have a sell-by date. Re information you have the problem of transmitting a signal powerful enough to cross the impossibly vast distances in the galaxy without getting lost against background radiation. It's doubtful any planetary civilisation could generate the energy necessary for such a signal.

We Are Legion We Are Bob has human intelligence copied into machines, and the machines building more of themselves and replicating the intelligence. (Really fun series btw.)

 

[Venusian Broon]

Earth furthermore has been able to support life for hundreds of millions of years. Hence for a very long time it has been a valuable prize for any starfaring civilisation whose molecular biology is built on the same elements. If there was such an alien civilisation they should be here already - in fact they should be in charge (MIB anyone?).

I think this is pretty old-hat thinking. It would be far more efficient for a species to convert all the matter of their solar system into billions of 'O'Neil cylinders' or artefacts of the same sort of construction and you would have vast amounts of habitable space, millions upons millions times more area than a single earth-like planet. Put them into a Dyson swarm. Also much easier to adjust to however the star is evolving - for example ours is getting hotter. Even a continent-sized O'Neil cylinder will be easier to change orbit than a full Earth.

Why travel the vast distances to get to another star system only to maroon yourself on a planets gravity well??? (immediately making travelling off and on it incredibly expensive) plus it will extremely likely to need to be terraformed to suit your needs - a process that would take a very long time. Build an O'Neil cylinder instead or Bank's 'Orbital' with exactly what you need. Start small, then build more and bigger.

But fundamentally It would be far easier to make a Dyson swarm in your home system than to colonise another system. Even a relatlvely close one.

Matter is cheap. Oxygen, hydrogen and carbon is extremely plentiful in the universe. There are asteriods, moons and planets. And if you don't want to take the planets apart there are methods for mining the elements from stars - for example, there exists about 2 earth masses of Gold, say, in the sun. Sure, most of it will be flying about the core but the mining methods could also be used in conjuncture with fusion so that you could build up a whole range of materials that will be useful. And you would get more energy. (Also, although you'd need to extract a huge amount of mass, there is a good reason to 'slim down' the Sun. The smaller the mass of the sun the longer it's age gets, the longer life around it gets time to continue living!)

Of course, we need to learn how to take care of spaceship 1 - Earth - right now. And also hopefully learn how to solve a host of other problems that should be tackeled first - hunger, stopping war, disease, stewardship of the biosphere. And we don't have the technology now, and some of it will take more time to work on, but we're just right at the start of looking at being an interplanetary species.