I think part of the problem is that people believe too much of the stuff they see on television. The concept of extraterrestrial beings in popular culture is very anthropocentric or, at least, Earth-centric. The universe is a very big place. Why should we think that life elsewhere in the universe, if any, would be anything at all like the life we are familiar with? It might be so different that we don’t even recognize it. Imagine a life form based on the piezoelectric property of quartz. (I just made this up for the sake of discussion. It probably makes no sense at all if you think about it too much.) And maybe for this quartz-based life form the passage of time is perceived very differently. What we perceive as the passage of one second might be similar to what the quartz-based life form “perceives” as the passage of 100,000 years. If some day in the distant future we encounter this life form on the other side of the galaxy (I don’t think we will ever get any further than that if we even get that far) we might look directly at it and all we see are inert quartz crystals. But in the “minds” of those quartz crystals they “think” they have created an advanced and wonderful civilization.
There’s always been a tension between the “what if [something really wild and “out there”]” viewpoint and the “Only carbon” viewpoint. There are chemical things that carbon does really, really well, and no other element does really anywhere near as well. A quartz lifeform may not be impossible – I’m not gonna say such a thing! – but there are many who would definitely rule it out on the basis of “yeah, chemistry.”
The same is true for, say, the sociology of aliens. What if they have a totally different suite of emotions, and we can’t comprehend them at all? Some would say that’s possible, even likely, while others would argue that “fear, anger, and reproduction” are just about the only meaningful emotions and any “intelligent” creature would need them…and be limited to them.
We just don’t have enough data to extrapolate from! The best “first step” toward solving some of these mysteries might be “uplift” of dolphins and chimps to human-level intelligence. Then we can just ask 'em how they feel.
I still believe life is common in the universe, but multicellular life is orders of magnitude more rare, intelligent life orders of magnitude rarer and technologically advanced life orders of magnitude rarer still.
Because the universe is so big, I’m confident there are countless super-intelligent civilizations out there. But, as discussed earlier, most of the universe is forever closed off to us (and visa-versa) due to vast distances and expansion that exceeds the speed of light.
This pretty much leaves us with being able to detect super-intelligent civilizations only within the Milky Way. (I think our ability to detect a > Kardeshev Type II civilization in another galaxy is wishful thinking).
Sure, our galaxy is big and riddled with star systems, but ~250-billion is not that big a number. Not when we’re talking about the likely progression of abiogenesis > single cellular >multicellular > intelligence > super-intelligence.
Add to this the probable fact that most of the star-systems within any galaxy are physically unable to create and/or sustain life (at least biological life as we know it) and it’s reasonable to conclude Earth may be the only show in town with high tech. We (and other galaxies) have a super-massive black hole at our galactic center. The great percentage of stars within and around the core are in relatively close proximity to each other. Therefore, those star systems being bombarded with radiation from close-by solar flares, pulsars, supernova, etc. are almost certainly forever sterile.
We live on a Goldilocks planet, in a Goldilocks star system in a Goldilocks part of a Goldilocks galaxy. I don’t expect to see any high-tech interstellar bears.
Well if you say so, but what about type iii?
It seems like you’re handwaving part of the fermi paradox for no given reason.
I don’t think we know this. Of extraterrestrial star systems studied so far, about half have at least one planet in the habitable zone. And there is debate about whether we should only be focusing on that band – you say “at least biological life as we know it” but of course we cannot rule out other forms at this time.
A lot rests on whether red dwarfs can host life; they are extremely numerous but their energy output may be too unstable.
Ok, but most stars are not around the core. Most of the mass of the galaxy is around the core, but not most of the stars.
Possibly, but I don’t think you’ve established good reason to suppose this.
Thanks for the reply. I’ll follow up more, but, for now I’ll just address this part of your response:
It’s common knowledge that the closest Kardeshev Type III civilization resides on a planet in a star system within the Hyperion Proto-supercluster. Unfortunately, we lost contact with the quarks and bozons that later became that supercluster of galaxies 10⁻³⁶ s after the Big Bang. It was indeed a sad Bon Voyage.
I’m kidding, of course 
. But, my point is that Kardeshev civilizations are often taken as matter of fact. But, they aren’t. There is no evidence that they can, or do exist. If we did have evidence that they exist, this whole Fermi paradox would be moot, correct?
Why don’t we see evidence of Kardeshev civilizations? Well, maybe they purposely cloak themselves from our monkey-like eyes and ears. Or, maybe they are too far away to see. Or, maybe they transmit in some realm other than the electro-magnetic spectrum with which we are familiar. Or, maybe their Star-Trek prime directive dictates we’re too primitive to be part of the Intergalactic Club (the Big IC)…
…OR, maybe the reason we don’t see them is because they don’t exist. And, the reason they don’t exist is because can’t exist, not by the hands of mortal beings anyway.
Not everything that sci-fi writers and theoretical physicists come up should be accepted as fact. Science mandates reproducible evidence before something can be deemed canon.
It may very well be that nothing short of the omnipotent power of God can harness the power of an entire galaxy. So, if God doesn’t exist (and, let’s face it, he probably doesn’t exist), a Kim Kardashian Kardeshev Type III civilization can’t exist, either.
So, why are we seemingly alone in the Universe?
Ok, but it seems to me that you’ve got the paradox backwards.
I am not familiar with anyone asserting that type III civilizations exist. No one is taking it as a matter of fact.
The point is, like the rest of the fermi paradox, is that from what we know for sure right now, there is no reason why we would not see evidence of type III civilizations. Clearly we don’t see such evidence yet, so something is wrong or missing from our picture (the smart money is on both).
You may well be right that such civilizations don’t exist. Or any of your other hypotheses.
However, earlier you asserted that we will only see evidence of intelligent life within our galaxy. That puts a burden of proof on you on how you can rule out type II or type III at this point.
Indeed, but many of those planets in the habitable zone are ocean worlds with very deep layers of water, on top of even deeper layers of high-pressure ice; or neptune-type worlds with vast layers of gas and volatiles overlaying a deeply buried rocky core. Among the thousands of worlds detected so far, none have been a good match to Earth, and few represent an environment where any multicellular organism could safely stand on dry land and look at the stars.
I don’t think astronomers have anywhere near the certainty about this that you seem to have. AIUI, our ability to detect small, rocky worlds far enough from an M-class star to have liquid water is still limited.
Also, as I already stated, no reason has been given for why we’d rule out intelligent life unlike on earth (eg an intelligent aquatic species on one of the ocean worlds you mention).
But anyway, let’s simplify things.
For the sake of argument I’ll concede that most star systems are not suitable for life to emerge. But at the very least, based on what we know, under the most pessimistic estimates, there are still hundreds of millions of star systems in our galaxy with a rocky world at a temperature suitable for liquid water.
So it doesn’t work as a fermi paradox solution in itself. We still need to find another, far finer, mesh to be our great filter.
Well, the data has been fairly extensively analysed, and no, there are no Earth-clone planets in the data. But you may be right (and I hope you are) that there are plenty of small rocky worlds that haven’t been detected yet.
If we only go with the ones that have been detected, there would be nowhere for humans to live comfortably. That doesn’t rule out the possibility of life emerging in non-Earth-like environments, but I suspect that aliens from non-Earthlike worlds would be psychologically different to ourselves in some, or many, ways.
If they are sufficiently weird, that might explain why we can’t see them.
What do you mean by this?
The fact is, planets in the habitable zone of their star are common; the estimate based on Kepler data is around 40 billion in our galaxy. Whether those planets have suitable composition, atmosphere, low radiation etc, we don’t know. There is still debate over whether the habitable zone of proxima centauri and alpha centauri is genuinely conducive to life, and they are our nearest neighbours after sol (I would wager not in the case of alpha cen, since it’s a ternary star system, but we don’t know).
You frequently use a jumping off point of earthlike worlds being incredibly rare and basing all your arguments on that, but we just don’t know that; it’s an assertion on your part.
We can compare the data with the data we already have for Earth, and make detailed predictions. None are Earth-like enough to be comfortable. There is a conflict between the way astronomers use the word ‘habitable’ and the way laypersons use it; as a layperson I would expect to find a nice solid surface and a temperate climate. Astronomers just mean there is a chance that the planet retains liquid water.
Here’s a nice list of potentially ‘habitable’ exoplanets. All of them differ from Earth in several significant ways. Radiation flux, expected surface temperature, mass, tidal locking, tidal heating - I wouldn’t want to move to any of these worlds without some sophisticated environmental protection.
I’ve seen several posters who have summarily dismissed planets exposed to high amounts of radiation. Sure, those planets would be bad news for you or me. But maybe the “life” on some of those planets crave the radiation and use it as a source of energy in order to “live.”
This is a double misreading of your own cite.
Firstly, the fact that we only have a relatively small list of candidates right now is down to the limitations in how we detect planets and what we can infer about them. So it’s not like of the 40 billion estimated planets within their stars’ habitable zone all but this list have been ruled out. These are just the ones close enough to have been studied somewhat.
But secondly, and more importantly, many of the planets in the list are earth-like to the limit of our current ability to detect. e.g. a star with the same proportion of metals, a surface gravity similar to earth and temperature similar to earth. It’s too early to say if they have water oceans. So, once again, your claim that none are as comfortable as earth is still just a baseless assertion.
(and again, this is putting aside the implicit assumption that only exact earthlike conditions can support (intelligent) life)
We have enormous amounts of radiation hitting this planet. We call it “sunlight”, and our flora and fauna have adapted to thrive on it (both directly and indirectly), including the parts outside the visible spectrum.
One of the underlying assumptions in many of these hypotheses is that all life must in some basic way be fundamentally earth-like and require roughly earth-like conditions, because it has to be based on carbon, the only element capable of forming extremely complex molecules. I don’t know how realistic that assumption is. We’ve built some pretty sophisticated stuff based on silicon, and in large-scale timeframes, we’ve barely even begun.
And ETA (missed the edit window) even if the carbon assumption is correct, which is probably a good bet, there are likely many millions of planets that meet the “earth-like” criteria sufficiently well.
Once again, I am only talking about the planets we have discovered so far. And if you think there are any planets in that data set that are remotely Earth-like, I’d be interested to see which ones you think fall into that category.
I am, as I have stated previously, optimistic that there are Earth-like planets out there- maybe millions of them in the Milky Way. But the examples we’ve found so far ain’t them.
Please- this is not a baseless assumption - I am trying desperately to find Earthlike worlds in this dataset, and it just can’t be done. If you know better please enlighten me. This might sound snarky, but I am also very interested in your opinion in this matter- there might be candidates that I’ve missed.
The problem is that you’ve already ruled out worlds with different mass, tidal locking etc.
No planet is going to be identical to earth. But the fact is, the data is showing that rocky worlds within the zone of their star where liquid water could be, are in fact common.
So there is no basis for your earlier assertions:
It’s admittedly controversial, but many cosmologists/astronomers do believe galaxies have a habitable (Goldilocks) zone .Too far from the core, there’s not enough metallicity to support life. Too close to the core, there’s too much organic-killing radiation and frequent bolide collisions to support life. We earthlings live in the habitable zone of a middle-of-the road galaxy.
…we have zero evidence that extraterrestrial life exists. Why?
It could be because advanced civilizations are purposely cloaking their existence because they are paranoid or perhaps planning some sort of “gotcha” invasion of lesser advanced civilizations like ours.
Or, perhaps super-intelligent civilizations have found some sort of means of communication that totally bypasses the electro-magnetic spectrum with which we are familiar. And if we could just tune into that bandwidth, we’d realize intelligent life abounds all around us.
…or, maybe the reason we don’t see them is because they don’t exist. At least they don’t exist anywhere close enough to us to detect.
That’s a boring and sobering thought, but probably true.