I don't see any assumption in anything I said that is unreasonable — RogueAI

Btw, 'the earth is flat' is a "reasonable" supposition during, say, the Bronze Age ... :roll: And you've not addressed the assumptions I'd objected to which you've quoted.

Btw, 'the earth is flat' is a "reasonable" supposition during, say, the Bronze Age ... :roll: And you've not addressed the assumptions I'd objected to which you've quoted.

Can you put your objections in numbered form? It's not exactly clear what you're objecting to.

but it's not, in principle, different from any other of the "revolutions" humanity has already been through. — Echarmion

What does this mean? Of course it is different than anything humanity has previously been through; if only because what humanity has previously been through is past, and hence already determined; whereas what humanity may go through is future, and hence indeterminable.

My argument is simply that there is no rational basis for the belief that human ingenuity will solve all problems, or that we will find the energy and the expertise, the resources, to travel to other planets. It is as much a mere faith without empirical support as any religion is.

Can you put your objections in numbered form? It's not exactly clear what you're objecting to. — RogueAI

Sure.

(1)

If advanced alien life existed even in tiny numbers, the universe is old enough for them to have colonized galaxies over and over again. — RogueAI

On what NON-TERRESTRIAL basis do you assume interstellar (or galaxy-wide) colonization by "advanced alien life"?

(2)

And we would have seen this, at least in nearby galaxies in our supercluster.

On what TECHNOLOGICAL basis do you assume "we" - in less than a century of predominantly ground-based optical & radio telescopy / physical cosmology - ever have had, or currently have, the computational resources, etc to detect EM signatures of "advanced alien life" (re: megaengineered structures e.g. 'dyson spheres', 'dyson swarms' etc) as distinct signals differentiated from cosmic background noise ... from "a nearby galaxy"?

(3) I've enumerated further objections on this previous post. Feel free to point out any or all that you take issue with. My position is sketched here and across a few more posts on this thread.

On what NON-TERRESTRIAL basis do you assume interstellar (or galaxy-wide) colonization by "advanced alien life"?

Several reasons:
1. Preservation of the species.
No species is going to keep all their eggs in one basket, if they can avoid it. The universe is full of existential threats. An obvious way to avoid extinction is to spread out.

2. Mediocrity principle.
We will eventually be colonizing (if we make it that long). There's no reason to think we're unique in that respect.

3. Traits of technologically advanced species
Technologically advanced races are going to be adventurous and curious. Disinterested species won't bother trying to discover new techs. Timid species won't take the risks necessary to discover new techs. Disinterested timid species certainly won't start a space-program.

If they do have those traits, they're probably not going to stop expanding when they've filled up their planet. Even if the race as a whole doesn't want to colonize, for whatever reason, there will likely be adventurous members of their species who do want to explore and colonize.

4. Population pressures
When the planet fills up, there's only one place for new members to go: space.

Now, which of those assumptions is unreasonable? Why?

On what TECHNOLOGICAL basis do you assume "we" - in less than a century of predominantly ground-based optical & radio telescopy / physical cosmology - ever have had, or currently have, the computational resources, etc to detect EM signatures of "advanced alien life" (re: megaengineered structures e.g. 'dyson spheres', 'dyson swarms' etc) as distinct signals differentiated from cosmic background noise ... from "a nearby galaxy"?

An alien race that's colonizing would be visible with the equipment we have now. You would see colonization waves radiating out from the homeworld as they fill up system after system with artificial habitats and energy collectors. Stars would dim and their energy spectrums would shift to the IR. Sections of galaxies would look like they're missing.

What does this mean? Of course it is different than anything humanity has previously been through; if only because what humanity has previously been through is past, and hence already determined; whereas what humanity may go through is future, and hence indeterminable. — Janus

In the same way as whether or not the sun will rise tomorrow is indeterminable, yes. But obviously no-one would refer to that as a "religious faith" or "fantasy". It seems to me you're trying to sneak in negative value judgements by using those terms.

My argument is simply that there is no rational basis for the belief that human ingenuity will solve all problems, or that we will find the energy and the expertise, the resources, to travel to other planets. It is as much a mere faith without empirical support as any religion is. — Janus

But we're not talking about solving all problems, are we? It's a specific set of problems. And the rational basis in that case is simply that it's possible, and within our rational interest to attempt.

The salient difference between thinking that the Sun will rise tomorrow, and that human ingenuity will enable us to colonize the Planets is that we have every reason to believe the sun possesses the energy resources to rise tomorrow and, apart from the question of whether we have good reason to have confidence that human resourcefulness will find ways to colonize the planets, resourcefulness requires adequate resources as well as ingenuity, and in a world of diminishing resources there seems to be little reason to believe that we have adequate resources to exercise our resourcefulness such as to be able to sustain our growing population and economy, let alone colonize the planets.

:up:

This just in! We have Breaking News from the constellation "way the hell out of where we thought was the farthest galaxy but found one ever further away than ever" that place we have recieved a message from a man in a star ship claiming to be Jesus and he sends the people of Earth this special message: "Dear humans, we finally here in heaven have reached the tantamount discovery have happiness! We have built a super space ship and have been traveling around in it now for about 1,000 years enjoying every bit of it! Anyway just to let you all of the hook I won't be coming back sorry I didn't send this message earlier just been having a blast flying around photographing amazing star clusters and simply lost my track of time! Check back with you all later love you all - and hey stay safe and sober for the holidays!" My guess folks is that we as humans do not belong originally to earth persay but we were created here by another intelligent life form who thought it trivial to tell us that they would be back since they couldnt even be sure they would be right? Or maybe they are still here (the ones that made us) or maybe a new advanced race arrived after the more advanced race (the ones that made us) took off to gather resources or find another place to colonize our race.. Or maybe children from ages 7 - 15 all of which cannot speak the same language decided over a 50 year span decide to lie that they were taken aboard UFO by bug eyed dudes and poked with tools only to all be put snugly right back into bed wouldn't that be a neat trick to conspire for the sport of parent expressions, doctor's entertainment and such right? And it is a whole other thing to say in French or in Japanese "Bug eyed midgets came to my room and took me away again to their spaceship to tell me things and poke me with long tubes until I scream so load the big one yells lets stop and let me come back home again!" Secondly it is another entire different account to say "I saw my sister / brother / cousin / friend or 'so and so' (neighbor) taken and says he always gets abducted and taken away into a spaceship" but they say it in Portuguese or Hindi totally different yet describe the same exact occurrence? And these statements are claims made in every language by all ages describing not just the same number of fingers (4 with pads s 4 ft tall and bug eyed deep black seems to know what you are thinking) but the fact that every abductee and eyewitness always includes a spaceship is just bullshit. They are all lying and also any actual videos or photos are also all fake and the people who have witnessed UFOs are all just conspiracy loony tools any special projects coordinators or black project ex-high security clearance personnel who is currently retired and claimed to have worked or coordinated with other scientists to back engineer technology of undisclosed origin is also just an old perv trying to get one last go at any first come first serve basis as long as you bring ID - lets party. What this rant all boils down to is - there is 100% no possible way in the universe that we are not cohabitation with several races probably of advanced forms of humanoids here on earth as well as likely our asteroid belt where surely we had some big ass war and blew our 9th planet into oblivion for practice. Earth was supposed to be the place of ignorance is bliss and we are the ignorant obviously. My philosophy on this comes from.. if you don't know someone that actually does have experience in what you are discussing that is that needs to get laid so bad he would say anything guy working for the aerospace company, you would discuss that man because you know him personally and want to verify he is legit.. or the contrary. Just like I know for fact the bug eyed alien pricks exist (whether they are actually physical and not phantoms who knows for sure since everyone that is abducted seems to me being out of body and able to move through walls or the ceiling) since I have a friend who was abducted and I have personally seen things which certainly were from another dimension as well as galaxy "just passing through" it wouldn't be possible to debate your way around actual knowing in conviction rather than if I was so stubborn to deny my own memory and require hard evidence would seem silly.

It's well known that even the nearest star beyond the sun (at 4+ lys.) is too far away to get to at rocket speed. What is not-so-well appreciated is that travel at relativistic speeds is as a practical matter impossible.. No one, then, is going anywhere under present understandings of physics. Discussions of such travel are not even sci-fi, rather they're sci-ignorance sugared with fantasy.

There's no contradiction in positing a galaxy/universe full of intelligent life and our never encountering it, nor them us - it's that big and empty out there. — tim wood

There is no contradiction here because the universe is likely full of simple bacterial life which comprises over 99% of life right here on Earth. Bacteria is where molecular biology meets life. Highly evolved intelligent life is likely to be so rare as to be unique for practical purposes. We will never encounter or be discovered by another civilization given the short life expectancy of any intelligence and the incomprehensible vastness of space and time.

We will never encounter or be discovered by another civilization given the short life expectancy of any intelligence and the incomprehensible vastness of space and time. — magritte

It would have to be rare to the point of basically being unique for this alone to work as the solution to the Fermi paradox.

As big as space is, when you crunch the numbers, you find that self replicating probes, generation starships etc could litter the Galaxy in a fraction of the Galaxy's age.
And humans are right on the cusp of achieving this technological level -- a few centuries or even millennia is nothing in the grand scheme of things.

Sure, we could wipe ourselves out totally between now and then.
But if so, we still got pretty close.

A primate species, more violent and tribal than most other primate species (or other near-sapient terrestrial species) got as far as launching crude probes out of its star system.
This suggests to me that if intelligent life is as common as, say, 1 in a billion star systems, distance and civilization lifespan is insufficient to explain the lack of evidence.

As big as space is, when you crunch the numbers, you find that self replicating probes, generation starships etc could litter the Galaxy in a fraction of the Galaxy's age. — Mijin

Actually it took about 3.8 billion years, which is about a third of the age of the universe, for intelligent life to appear here. But even then, a super-aggressive extraterrestrial culture could have sent out self-replicating probes all over the galaxy just to say hello. According to Fermi, we don't see them because that never happened. Either advanced civilizations never existed or we are close to the first.

The cheapest way to find out whether there are ET's is to look for them and send signals to them by radio and other electromagnetic waves. EM waves travel at the speed of light and they are plentiful.

The problem is time. When signals are sent out in all directions, the signals travel as a thin growing bubble. Only for the small fraction of time as the bubble passes a planet is the signal detectable. If we aim a laser at a likely planet only 2.3 light years away, the light will pass there in 2.3 million years. If they happen not to be looking they'll miss our signal. Worse still, when we aim, we'll have to aim at a planet that will be civilized 2.3 million years from now, then wait 4.6 million years for an answer.

It seems most likely to me that any "advanced civilizations" that don't come to grips with their heightened status; in other words, a sentient race that cannot clearly differentiate themselves from the predecessor species of the planet; in other words, a sentient race that continues to act like an animal; will destroy itself. Those advanced races that do survive are way beyond the destructive, brainless tendencies of their predecessors. They look on at the antics of the malformed semi-sentient races that have not attained discriminating, unobstructed views of existence and waits for them to implode.

You just need a source of ongoing propulsion like a nuclear reactor, lasers from space mirrors, or ramjet. If you don't have to propel a massive colony ship, then it's easier to get up to a faction of the speed of light. Send a swarm of small, intelligent self-replicating probes.

I can't find the YT video now, but there was a talk where the presenter discussed setting up an automated factory on Mercury to produce mirrors in orbit around the sun and swarms of spacecraft that could be propelled by the mirrors. He calculated that using only half of Mercury would allow us to spam every star system in every galaxy reachable by accelerating the probes to between 50% and 90% the speed of light.

I think that was basically Carl Sagan's view. In the movie version of Contact, Jody Foster's character is told by her alien-in-dad form that humanity was taking it's first step and would take another one in time after her brief visit with the wormhole machine. Maybe once we overcame our juvenile destructive tendencies.

is truly the irrationally imaginative stuff of science fiction; a kind of religiously adhered to fantasy. — Janus

There is a field called astrobiology and SETI is staffed by scientists. It's not just fiction writers who imagine aliens or that we'll become advanced enough to colonize other planets.

Elon Musk even has a company committed to that project, and NASA is now on board with setting up a moon base to facilitate going to Mars. Of course terraforming it is a very difficult, long term project, but given how much the world has changed in the last 500 years, who knows what might happen by 2520.

For advanced civilizations, if they exist out there, our timescales are puny. They would have had many millenia to figure things out.

art from the question of whether we have good reason to have confidence that human resourcefulness will find ways to colonize the planets, resourcefulness requires adequate resources as well as ingenuity, and in a world of diminishing resources there seems to be little reason to believe that we have adequate resources to exercise our resourcefulness such as to be able to sustain our growing population and economy, let alone colonize the planets. — Janus

If we successfully make it through this century with civilization reasonably intact, then we should have the resources and time to do things on a larger scale. As you pointed out, the sun has plenty of resources, which we can make use of. So do other planets and moons, in terms of raw minerals and gases.

Sagan suggested that other ETs go through the same adolescent stage we are going through. If a civilization makes it, then who knows whats ultimately possible. Maybe we stick to our solar system and setup a long term radio transmitter to let any aliens listening know we're here in case they wish to communicate. Or maybe our machine ancestors take to the stars.

In short, the desire to contact aliens is born at a stage in a civilization that has, on balance, a friendly disposition. So, the idea that we should be wary of aliens, though sensible in some respects, may not be completely accurate. — TheMadFool

That might be true. It's pretty much what the SETI researchers believe. Jill Tartar said there's no real threat from advanced aliens, because they have no need to come here to exploit us, since they are advanced enough to make anything they want in their own system. You have to be pretty advanced to undertake travel between stars.

However, in Liu Cixin's novels, the aliens inhabited a system that was about to be consumed by it's unstable ternary sun system. So they needed to find a new home.

How about shielding? If the question does not make sense, then you're out of your depth.

Imagine riding a motorcycle without a face shield through a rainstorm at 100 mph. Then make it worse by a factor of about nine magnitudes. Then there the problem of getting all that shielding out of earth's gravitational field, and then accelerating it, and so forth and so on. Dreaming up the starship Enterprise is a long way from building it. At the moment it is impossible, even in principle.

How about shielding? — tim wood

Sure, that's an important problem. What about magnetic shields?

Dreaming up the starship Enterprise is a long way from building it. At the moment it is impossible, even in principle. — tim wood

A starship, yes. But we already do have a couple spacecraft leaving the solar system. They're pretty crude compared to what should be possible in another century. And there are some proposals for how a warp drive might work.

Our technology is primitive compared to what's possible, if we stick around long enough and continue developing. The point of advanced ETs is that they've been around a long time.

Still, the Fermi Paradox remains, so maybe even advanced aliens find it impractical to travel to other star systems. That's what Frank Drake proposes as a solution. And maybe that's why there's no galactic civilization in the Milky Way or anywhere near us.

Everything depends on what a friendly disposition is. It involves high moral standards i.e. deep knowledge of right and wrong. Granted that a dying star spells total annihilation but advancement in technology, if you go by how it's played out on earth, seems to occur in tandem with a better understanding of morality. Advanced civilzations facing such a disaster would, I think, prefer to initiate a knowledge transfer operation between their now doomed planet and other civilzations to ensure these others don't meet a smiliar gruesome fate rather than conduct an interstellar/intergalactic invasion of other worlds.

They're pretty crude compared to what should be possible in another century. And there are some proposals for how a warp drive might work. — Marchesk

Anything that comports with the laws of physics - that is not pure fantasy?

Anything that comports with the laws of physics - that is not pure fantasy? — tim wood

No. A perpetual motion machine is, as would time travel to the past where you kill your grandfather. But wormholes or warp drives might be possible. An advanced civilization that sticks around long enough is going to be able tot explore the possibility space of what physics allows.

It's speculative, but not pure fantasy. It would be weird to think we're close to the pinnacle of technological advancement, given how much has occurred in the last several centuries. Surely a thousand more years would yield far more advances. Of course it might not happen for humans, but it could have happened for some aliens.

Are you suggesting currently understood laws are wrong? Subject to refinement in some areas - maybe many areas, sure. But there is a difference between advancement and breaking laws. And from what I read, I gather QM, Planck time and distance, and relativity are all very hard science indeed. Are you supposing the limits imposed by these will be contravened, somehow?

No, I'm saying warp drives and wormholes are not ruled out. It might be possible to construct them for use in travel.

Actually it took about 3.8 billion years, which is about a third of the age of the universe, for intelligent life to appear here. — magritte

I don't think you need the word "actually" there. I did not suggest otherwise.

But even then, a super-aggressive extraterrestrial culture could have sent out self-replicating probes all over the galaxy just to say hello.

Agreed, and indeed, it doesn't even need a whole culture to be like that, just a small group or even an individual. For a species not much more advanced than us, the energy, materials and AI required to launch a self-replicating probe project may be completely trivial.

According to Fermi, we don't see them because that never happened.

No; Fermi doesn't assert anything. The point of the paradox is to point out what we don't know, and let us try to figure out through discussion and investigation why we don't see evidence of ETs.

o; Fermi doesn't assert anything. The point of the paradox is to point out what we don't know, and let us try to figure out through discussion and investigation why we don't see evidence of ETs. — Mijin

Also, Fermi wasn't thinking in terms of radio astronomy. He was wondering why the aliens weren't already here (and everywhere else), given the age of the universe and how it would only take millions of years to colonize a galaxy.

No one, then, is going anywhere under present understandings of physics. — tim wood

this is true. The question begs itself, however unanswerable it may be, to be: is there understanding of physics that make space travel possible?

It's the same conundrum as time travel. We believe in a straight-line time line, only in one direction. The problem is, if it can be cheated, and the history altered, it is impossible to notice that we are not the universe that is developing the old way, but the same universe develping (unfolding, not as much as developing) a new way.

Space travel is a bit easier to visualize as for its impossibility, because once the impossibility is demonstrated to be false, the proof will be in our face, it will be the easiest thing to see.

I've often thought about that movie and book. In the movie, the alien states that humanity has such magnificent dreams ... and nightmares. That has always stuck with me. I'd kinda like to eliminate the nightmares and it seems completely possible to me.