The classic Fermi paradox assumes no interstellar travel. The version which asks "Where are they?" is too easy to answer. Just because they COULD come to our solar system or solar systems similar to ours doesn't mean they're obligated to.

Maybe they only like colonizing systems with hot jupiters. Maybe they only like colonizing red dwarf systems. Maybe they only like hanging out in the cold Oort clouds of star systems. Maybe they prefer cruising around in interstellar space in ramjets and only ever briefly fly through star systems. There are so many possibilities.

Exactly. Would a creature with a life span of, say, 100,000 years consider a 75 or 150 year trip between stars to be impractical?

I know it is usually interpreted this way. But what if it turns out that multiplying the real factors gives a number <1? As long as you do not know the real factors, their product could be any number (randomly distributed in logarithmic space), even <1.

As the only large moon in the solar system orbits the only planet known to host life, it would seem that with a higher probability than not a moon (or, alternatively, the process that led to it) is indeed nescessary for the formation of life.

From simulations of planetesimal collisions, we know that only <2% of all collisions result in systems resembling the Earth-Moon system. So the chances of having a moon comparable to our own orbiting a life-bearing planet while it its presence is not nescessary for the formation of life is only <2%. On the other hand, chances of having a moon comparable to our own orbiting a life-bearing planet while it its presence is nescessary for the formation of life is 100%. This would give us a Bayesian probability of >98% that the presence of a large moon is nescessary for the formation of life.

No. Fermi's paradox postulates that given the enormous amount of time and stars, even if life were fairly rare, there should be evidence by now of ET. Yet there isn't. Why?

Fermi's paradox doesn't assume there is no Interstellar travel. It doesnt assume anything. It just states a paradox that describes a result we expect to see based on what we observe.

Other people postulate that Interstellar travel must be impossible, and that is an answer to Fermi's Paradox. However, I'd counter that just because humans dont live long enough to make relativistic travel viable doenst mean other species with longer lives wont. We just dont know.

No, There is no interpretation on this point. The Drake equation is specifically designed to estimate the number of civilizations in the Milky Way Galaxy. Not in the Universe. Therefore, Since we are on Earth a technological civiliation, and we are in the Milky Way Galaxy, then the minimum answer to the drake equation is 1.

edit: Thats why there is a factor for frequency of star formation.

There are large Moons other than Luna. Ganymede is larger than Mercury and Pluto, and Luna. Titan is also bigger than Mercury and Luna.

Mercury and Venus are the only planets we have that don't have moons, although a large one would be required to have the effect we are talking about.

I do agree a large moon is probably helpful to life, but there are also other ways to create energy and chemical imbalance necessary for Life processes. Titan is constantly prodded and pulled by Saturn, which could create the same or similar effects. There are likely other ways to get the energy required for life without a moon.

Moons dont have to be created by primary impact of the host planet. That's one way we know of. Double planets form, asteroids can be captured. There are likely other ways Moons can be bound to planets.

If you wish to quibble over which version of Fermi's paradox is the "right" one, then go ahead. I'll just go with whatever version you want.

The version you're talking about is simply too easy to answer. If we allow for the possibility of interstellar travel, then the easy answer is that there's already a single civilization which has dominated the galaxy, and we simply don't notice them for any number of plausible reasons.
No. The Drake equation calculates the expected number of technological civilizations at a given time, not the actual number. We could be lucky. We could be the only technological civilization currently alive among the nearest million galaxies.

Note that our "luck" is not so surprising if we assume technological civilizations only last, say, a few million years. The galaxy has been around for billions of years. If we're the only technological civilization in the galaxy and we're only going to last a few million years, then the corresponding Drake equation result would be 0.001, not 1. We could be perfectly AVERAGE and the Drake equation number could still be much less than 1.

(All of this assuming that the Drake equation's assumptions are valid, which I do not accept.)

Although we now have evidence that "many" supernovae were producing the CHON elements less than a billion (10^9 years) after the alleged big bang, we don't know how soon "sufficient" densities of CHON elements were present for the subsequent star building to include planets with sufficient iron and silicon-like elements along with the CHON ones to support the initiation and progress of life, Consequently we can't be sure of our guessing about the age of the earliest life initiating-supporting planet, hence our guessing about the relative age of Earth based civilizations with respect to reasonably probable other occurrences is severly impaired. For the initiation of life to be other than purely random, the dice must be loaded with an as yet unspecifiable abundance level of the elements involved in CHON-based life.

I have presented to several NASA centers and several universities a plan (in my opinion the only viable plan) for interstellar transportation and have received no serious response---not even one to show the obvious flaws in the plan as presented. The cost of plans similar to the one I advocate is astronomical in more ways than one amounting to many teradollars. Since a similar plan is required to ensure the survival of humans over the long haul, I think it to be economical, at least to the point of beginning a serious assessment of its technical feasibility. In addition to its huge cost, the system will require from 300 to 1000 years to implement; a serious detriment to those motivated by egos. The point of this is to suggest that my counterparts in other would be space faring civilizations have probably been met with similar levels of resistance which may contribute to their not being observable. Also, if they are not within 10 light years of a neighboring star, it will be extremely difficult to get into interstellar transportation.

__________________
For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?

Not in the universe, but in any galaxy comparable to our own.

As I say: you can not force the laws of nature for these factors to result in a product >1. Maybe the formation of life is a very rare process, unlikely to have taken place even once in the entire history of the Milky Way Galaxy (I consider that unlikely, but it is certainly not excluded). How would you deal - mathematically - with that?

Maybe its a question how you think of the factors: as "facts" to be plugged in (as in: "how many times exactly has this or that happend in the history of the Milky Way Galaxy?"), or as probabilistic factors deduced from planet formation models etc.

I agree completely with you that in the first case, this will and must result in a number >=1, but it will be very, very difficult to gather that information. We would have to analyze every star in the galaxy, every planet and moon, investigate its history, search for signs of early life etc. A task almost impossible to accomplish, even with interstellar spaceflight and millions of years time.

We are better off with the second case. We can observe large numbers of stars, and calculate how often they form certain types of planets, we can run simulations of the formation of life, of evolution maybe - this then results in probabilistic factors that can be plugged into the Drake equation. But if we do this, it is by all means possible that the resulting number is <1.

Yes, I know that off course. But Luna is special as it is the only body of its size orbiting a terrestrial planet (and we are talking about the effects of a large moon on terrestrial planets, not gas giants...).

Considering how unlikely the formation of a moon the size of Luna is, it seems odd that we observe it orbiting the only planet known to host life. It would seem it is highly probable that its presence (or at least an effect dependent on its presence, as you suggested with "tidal heating") is crucial for the formation of life.

Double planets form? How many double planets do we know of?
Captured asteroids are to small to have any effect on tidal heating.

I seem to recall a study which determined that massive collision formed moons like ours should actually be pretty common. The headlines were that moons like ours would be "rare", but in this case "rare" meant one in twenty simulations produced a moon like ours.

One in twenty is a lot!

Apparently, when you simulate planetary system formation using the science we know so far, massive planetary collisions are quite common; common enough to form large moons like ours regularly.

I'm going with Fermi's actual paradox, as stated by Fermi himself. It states (paraphrased of course. i wasnt there. ) that, based on the age of the galaxy, and the enormous number of stars, we would expect that there are are large number of technological civilizations, however, we dont see or hear from them. Where are they? It was a question he asked. He left it to others to answer. I dont know of any other versions of his paradox, but there are many proposed answers.

One answer excludes Interstellar travel. Another allows it. But these are proposed answers to Fermi'[s paradox, not the paradox itself.

Again, you are confusing an answer with a question. Fermi Asked a question. He didnt assume anything. You may be confusing this with the Drake Equation, which did make a lot of assumptions. It is all assumption.

It came later and was a tool to try to at least estimate the number of civilizations in the Milky Ways Galaxy at present time, to try to quantify at least how many might plausibly be out there. It's answer is not for a given time frame, as you suggest:

wrong.

- wiki article. If you dont like wiki, there are many references that say the same thing.


wrong. Again, The Drake equation specifically estimates how many we could possibly communicate with. Therefore, the minimum value is 1.

- link

Generally, if you think your plan is the only viable plan, then you should probably reevaluate your thinking. If your plan is viable, why not a plan which is similar to it? Why is it the only viable plan?

I would consider several different technologies as viable for interstellar propulsion*, and there would be a limitless variety of viable "plans" to utilize them.

* The list of technologies I consider viable includes Geoffrey Landis's RPB propulsion, my own relativistic kinetic impact powered rocket, various runway based systems, and some more esoteric concepts. It does not include any sort of electric ion thruster based system, because I really don't think electric thrusters will ever have the thrust/weight ratios you wish for.

Nope. Drake equation is defined specifically for the Milky way galaxy at the current time.
bold emphasis, mine. link.

agreed. we cant know until we begin finding life.


Pluto and Charon are often referred to as a double planet because the gravitational center is outside of Pluto, actually in between the two bodies. Earth and Luna have also been consdiered as such, however I dont agree with it.


It is possible that a very large asteroid could be captured by a planet and a stable orbit is reached. No, we dont know of any, but there is no reason mathematically to discount it as a possibility, nor even an unlikely one. its just physics.

So chances observing such a moon orbiting our home planet (or any other specific planet) while it really has nothing to do with the formation of life ist 1:20 or only 5%.

Makes it 95% likely that having a moon does indeed have something to do with the formation of life (or complex life, or intelligence, etc.).

So the result might as well be "0" (or any other number <1). As we don't have to come into contact with ourselves...

EDIT:

Okay, let me rephrase it: How many double planets capable of sustaining life (as we are talking about the effect of a moon on the formation of life...) do we know of? None.

It would have to be in the Luna ballpark to really have the same effect. It is not excluded physically, off course (although, form a dynamics perspective, the large asteroid would have to have a large moon it can loose while being captured).

well, I can't argue with that. (well, I could, but its not worth it. ) touche.

Whatever! I don't care what version of the paradox you wish to argue, I'll go with any of them!

The one you state above ignores the possibilites of interstellar travel, because one of the possibilites of interstellar travel is that there's only ONE technological civilization out there; it suppresses the others.
No, there are many answers, not just two.
The question implicitly makes a lot of assumptions.
The Drake equation merely seeks to make explicit the implicit assumptions of the Fermi paradox. WHY does the enourmous number of stars out there imply that there should be many technological civilizations out there?

If you only wish to address the Fermi paradox in the absense of all of its implicit assumptions, then the "real" answer would be--"So what?" Without the implicit assumptions, the Fermi paradox is utterly meaningless.
Where does this contradict anything I said?
You're simply wrong, on two levels--the two levels I already explained.

First off, it does not estimate the ACTUAL value, it estimates the EXPECTED value. Consider rolling a six sided die. The expected value of the outcome is 3.5 (the mean of six equally likely outcomes). Let's say you roll the die and it comes up a "5". Is this at all surprising? Of course not. There's a difference between the expected value and the actual value.

Second, even if we're perfectly average the Drake equation result could be much, much, less than 1. You're failing to take into consideration the final term in the Drake equation--the length of time the civilization lasts. The galaxy has been around for billions of years. How long will we be around as a technological civilization? A few decades, as pessimistic nuclear MAD predictions might fear? A few thousand years, as pessimistic and weirdly inappropriate "Roman Civilization" predictions might fear? A few million years, if we're just waiting for the next dinosaur-killer or supervolcano to wipe us out?

If we plug in a few million years, and we assume the minimum that we're the only expected civilization in the galaxy, then we get a result of 0.001.

(Personally, I think the final term of the Drake equation is bogus, and the weakest link.)

No, it doesn't. Probabilities don't work that way.

Let's suppose I roll a twenty sided die. It comes up 16. The chances of it coming up were only 5%.

Does this mean that there's a 95% chance that my die roll of 16 has something to do with the formation of life? Of course not.

This pretty much epitomizes the problems with extrapolating from such a limited data-set.

__________________
There are few left who
Stare at the skies with wonder
Wishing to know more;
The clouds still drift by above
But the eyes below are blind.
--Laura Lundberg

Check out my writing, maybe.

Of course, if we want to look at suspiciously rare Moon-related things, there's the coincidence in apparent size of the Moon and the Sun. Because of this bizarre similarity in size, we get to experience spectacular eclipse events.

And it's not like they were always so close in size. The Moon used to be a lot closer to the Earth. And yet we humans, with intelligence and technology, just happen to evolve when the Moon and Sun are exactly the same size in the sky? Hmm?

That is not the same.

What are the chances that any planet has a Luna-sized moon? Say 5%. So chances are 5% that the Earth has a Luna-sized moon.

We can now imagine two universes. In one, universe A, the presence of a moon is needed to form life. In the other, universe B, it's not. 100% of the observers in the universe A will observe a Luna-sized moon orbiting their planet, while in universe B, only 5% will.

If you observe a Luna-sized moon orbiting your planet and don't know whether you live in universe A or B, where should you place your bet?

We can now imagine two universes. In one, universe A, the roll of 16 is needed to form life. In the other, universe B, it's not. 100% of the observers in the universe A will observe I rolled a 16, while in universe B, only 5% will.

If you observe me rolling a 16 and don't know whether you live in universe A or B, where should you place your bet?

Or apply the same logic to the spectacular solar eclipse coincidence. See the problem?

Excuse me, but saying whatever doesn't help you here. I am using the only valid paradox as stated by Fermi, albeit paraphrased. Please show me links to other versions.

wrong. Again, Fermi's paradox doesnt give an answer. Just asks the question. You are confused.

Please point out where I said there were only two? I specifically said:
and
These are two possible answers. It does not say these are the only two.

Prove that. Asking a question doesnt mean assumptions are made.

Why? isnt it obvious?

- wiki

If you know anything about Fermi's paradox, you should know this. do your own research.

Im not ignoring assumptions. I am pointing out that you are incorrect in saying that Fermi's Paradox assumes no interstellar travel. It does nothing of the sort. Possible answers to Fermi's paradox do include that scenario. Please provide a reference that shows that Fermi's Paradox precluded interstellar travel.

I don't understand what is such a big deal for you. I have repeatedly said I'm perfectly willing to use whatever version you want.
Okay, I interpreted your statement wrong. Sorry.

It's just that there are only two possibilities--either interstellar travel is possible or it isn't. And as I explained, if interstellar travel is possible then that's an easy answer to the Fermi paradox. If interstellar travel is possible, then the easy answer to the Fermi paradox is that there's already ONE dominant galactic civilization, and we just don't notice them because they're not in our face.

You seem to honestly believe that the other possibility--interstellar travel is impossible--is an "answer" to the Fermi paradox.

So if one is an answer, and the other is also an answer, and there are no other possibilities, then voila! Only two answers.

But here's the thing--traditionally, interstellar travel is impossible is NOT an "answer" to the Fermi paradox. It's pretty much the basis of the paradox! If interstellar travel is impossible, then that means that all those zillions of star systems out there are free to independently evolve and they're free to transmit radio messages to us. There's nothing stopping them.

The point is, if there are millions of civilizations out there, then it's not enough that there may only be, say, a 1% chance that a civilization wants to contact other civilizations. If there are millions of them out there, then that still means thousands of chatty civilizations out there. Why haven't we been contacted yet?

Lack of interstellar travel isn't an "answer", it's the very starting point of the mystery.
Fermi's paradox doesn't consider the most obvious possibility of interstellar travel. I'll repeat it once more, for you:

1) If interstellar travel is possible, then it's possible for one civilization to dominate the galaxy.

2) If there's ONE civilization dominating the galaxy, then that one civilization may prevent other civilizations from rising up.

3) Therefore there aren't lots of civilizations out there, so there's no mystery why none of them have contacted us.

4) This hypothesis still leaves one big honking civilization out there, but there's no particular reason to think this one civilization has any interest in contacting us.

There are NO other versions of Fermi's paradox. There is only one. I dont know why you keep insisting there are other versions. If there are, show me.

You seem to think that with travel, its inevitable that one civilization has taken over the entire galaxy and suppressed anyone else from contacting us. WHile this is a possibility, IMHO it is by far the least likely. That seems a vast oversimplification based on no data, or pure speculation.

If Interstellar travel is possible, there could be many reasons why we haven't heard from them:

1. The Zoo Hypothesis (quarantine til we get out there by ourselves)
2. Prime Directive (They are forbidden by some law)
3. They are all machine intelligences and and don't consider us worthwhile.
4. They havent found us yet.
5. They are scared of us.
6. They dont want to scare us.
7. They arent driven by the same human need for exploration or contact as we are.
8. They know about David Hasselhoff. (self explanatory)

I dont know the answer to Fermi's paradox. If Interstellar travel is not possible, then that would be part, but not all of the equation.

without travel, there are other ways for them to contact us, yet they havent. you seem to think that when Fermi said "Where are they" he was explicitly asking why they weren't here, physically, ie they travelled here to Earth. He was asking why we have no evidence: Radio contact, artifacts, telescopic observations of Dyson Spheres, FTL tracks, and any other evidence that would allow us to conclude that there are other life forms. You seem to be hung up on Physical Contact. Even if there is a big meany civiliation suppressing everyone from coming here, could they really supress their ability to communicate? That seems a very far fetched scenario.

SO first you argue I am saying there is only two answers and I corrected you. Now you are arguing that there are only two answers. wow. your argument is truly dizzying.

At any rate, Nope. The answer will not be as simple as that. whether or not Interstellar travel is possible is only part of the answer, whatever it is.
Lack of Interstellar travel doesnt mean we would never hear from them, it would just mean we wouldnt meet them personally, unless they sent their DNA to be reproduced, as in Species.

I dont see how interstellar travel is the Basis for the paradox. The paradox is just a statement and a question: Aliens Should have been detected by now! Where Are They?

Assume Interstellar travel is impossible. Contact is still possible by:

1. Exchange radio signals or some type of sublight communication.
2. send robotic probes, or Von Neumann Machines.
3. Solar signalling (structures to periodically block the sun to tramsmit a beacon. )
4. Spectroscopy - alter the atmosphere of a planet with artificial elements to show that life is present.
5. Use of some communcation method undiscovered by humans.

Congratulations. You just re-stated Fermi's Paradox.

it is part of a possible answer. we don't know the answer. With Interstellar Travel possible, then that narrows the possible answers. Without it, it narrows it another way. Still many many answers out there using both scenarios.

I'll repeat it for you: A Paradox is a question. It doesnt assume or consider. Fermi was asking why we havent seen evidence yet. Period.

I don't know why you care.
I do think that it is highly likely that interstellar travel means that the first civilization to develop interstellar expansion capability will dominate the entire galaxy. The amount of time required to dominate the galaxy is not very long--perhaps on the order of a few hundred thousand to a few million years. So in my opinion, the first one to start will likely have had no significant competition.

And I do think that once one civilization has dominated the galaxy, any other civilizations--if they even have a chance to develop--will be dominated by that civilization. This domination may be as violent as merciless extermination or it may be as peaceful as cooperative merging. Either way, the "primitive" cultures--if any--are dominated.
Why, exactly? What do you think is more likely, and why?
This requires a dominant galactic civilization (which I do consider plausible).
This requires a dominant galactic civilization.
This does not necessarily require a dominant galactic civilization, but it's more plausible with a dominant galactic civilization. It's easier to accept that just one civilization is a machine intelligence than to accept that a million independently evolved civilizations are all machine intelligences.
This does not require a dominant galactic civilization, but it's more plausible with a dominant galactic civilization. A single civilization may simply not be that interested in finding us, which would explain why they haven't found us yet.
Really? This is, I think, a very implausible possibility. What are they afraid of? The forbidden dance of the Samba?

Still, if this is a serious possibility, then it's easier to accept if there's a single dominant galactic civilization. It's certainly possible that a single civilization has a weird cultural fear of something about us (We're scary meatlings who survive immersion in caustic oxygen gas!!!!!). But if that already strains credulity, then the idea that there are thousands of independently evolved civilizations out there which all have the same homo-s.-phobia breaks all credulity.
This requires a dominant galactic civilization, for the same reasons as above.
This requires a dominant galactic civilization, for the same reasons as above.

Basically, if there's just one dominant galactic civilization, then it's just too easy to explain away why that civilization hasn't contacted us. It could be any of the above and then some. I do not consider it necessary or even fruitful to try to list all of the possibilities. There are so many.

It's only when you assume there are thousands or millions of independently evolved civilizations out there that simplistic answers fail us.
I disagree. You seem to think that interstellar travel impossibility is part of the "solution", but IMO it's part of the "problem". IMO it's not only the biggest part of the problem, it more or less IS the problem.

Fermi's paradox isn't even a paradox if you assume interstellar travel is possible, and that as a result there's a dominant galactic civilization. It's too easy to come up with "solutions" to the problem in that case.

It's only when you assume interstellar travel is impossibly hard, that you end up with a puzzle.

There are so many ways in which they could suppress them, every step of the way:

1) Initial evolution. The galactic civilization may deplete resources from most of the desirable planets, directly via colonization or indirectly with resource mining. This reduces the number of untouched planets where other civilizations may evolve.

2) Survival. The galactic civilization might be hostile, and may simply exterminate other civilizations if they take notice of them.

3) Cultural extortion. The galactic civilization might not be implacably hostile, but might place demands on other civilizations if they wish to avoid extermination.

4) Cultural influence. The galactic civilization might be perfectly friendly, but contact with the galactic civilization results in absorption of the galactic civilization's cultural ideas and ideals. For example, absorption into a galactic civilization like Star Trek's Federation would imbue the contacted races with cultural ideals of the "Prime Directive".

Depending on how oppressive the galactic civilization is, there might be "mind control" technology preventing anyone from having contrarian thoughts. There might be "pervasive electronic surveillance" technology preventing anyone from acting on contrarian thoughts. There might be "secret police" techniques preventing anyone from getting away with acting on contrarian thoughts. Or there might simply be natural forces of peer pressure, market forces, and such which prevent contrarians from gaining much power/influence.

Even on the most liberal end of the spectrum, it could simply be that contrarians never accumulate enough power/wealth/influence to operate the sort of powerful interstellar communications hardware suitable for CETI.

A plucky band of alien hippies might take over a short range radio transmitter for a short time...but a huge interstellar comms dish? For the thousands or millions of years it would take to luckily send a beam specifically at us, while we happen to be looking in the right direction? Doesn't seem likely, even if the galactic civilization is pretty groovy about letting hippie hijinks slide.
I'm just explaining why I thought what I thought.
No, I'm saying that LACK of interstellar travel is the basis for the paradox. If you accept interstellar travel as possible, the paradox goes away. It's too easy to answer.
Where's your disagreement?
That's my point. You only get Fermi's Paradox if you assume there are zillions of civilizations out there. But if you accept that interstellar travel is possible, then it's too easy to answer that there's only ONE civilization out there, and there are limitless plausible reasons why we haven't been contacted by just that one civilization.

Just making a correction.

Why would you think this? Does one Society or nation on Earth totally dominate all others by force? No. Why? Because It would take too many resources to control everyone. Its been tried before, it didnt work. Even if someone took over the world, they couldnt hold it, it wouldnt be worth the trouble - nothing of any importance would get done for all the rebellion squashing and social controls.

Now, magnify that problem by a hundred billion times. One civilization ruling all others on a galactic scale? Come on. You just can't be serious.

That is your opinion, however I disagree.

Because of the great distances and time involved in managing a galactic empire, it would never work, especially if FTL travel or communication isn't possible. Think of Earth History, which is the only frame of reference we have: Europeans all sent colonists to the New World to establish colonies, or armies to invade, all expecting they could be controlled from across the sea. It was assumed the armies would stay loyal, the colonists be continue to identify themsleves with England or France, or whoever. However, because of long communication times, dangers of travelling, and evolution of attitudes over generations, It didn't last more than a generation or two. Colonists considered themselves different than Europeans, and instead identifed themsleves with their new country. They forged a new society. They went their own ways. Now, why would the Galaxy be easier to control, which is billions of time larger and more difficult? No, your explanation, while possible, is far, far and away more unlikely, in my opinon.

If interstellar travel isnt possible, then it is a big part of the answer, but not the whole answer.

If interstellar travel is possible, then its part of the solution. yes its easy to say there is one civilization that has taken over the entire galaxy and is able to control them despite the gigantic distances involved, as well as squash rebellions and prevent social evolution. I find that scenario very unlikely for the reasons stated above.

For these purposes, one civilization DOES dominate all others, our modern technological human civilization.

I know what you're thinking--we live in a free society. But that freedom only goes so far. We are constrained by market forces, political realities, cultural realities, and biological realities.

Why aren't we trying to contact OGLE-TR-123, or any of many other known star systems several thousand light years away? A sufficiently wealthy and/or powerful enough individual or group of individuals could try...for how long? Until they die only a few decades from now? Not nearly long enough to have a serious chance of success, and even if they were successful they wouldn't see any results (nor would any of their grandchildren).

The things which we humans have in common with each other far outweigh our differences. The relevant similarities which limit our desire/opportunity to perform long range CETI are not necessarily things which need to be imposed "by force".

You argue that Earthlings have more in common, and yet we dont have a single dominant culture on this planet? How does this argue that a Galactic civilization could dominate the entire Galaxy?

We don't even have One language in common. We dont have the same religion. Some societies barely even tolerate the others existance. We are bound by a world economy because we have to be -- we are on the same planet!

think on it: One culture, effectively controlling a thousand different species who live in different environments, have different motivations and needs, communicate in entirely alien ways, and each developed their own society before being assimilated? And they are all hundreds or thousands of light years apart? And they all are evolving independantly as societies? And yet one culture completely and efficiently controls all other civiliations and prevents them from contacting Earth or annoucing their presence? And not one of them managed to get out a signal? This is the most plausible scenario of why we havent heard from Aliens? Are you serious?

Do you think a Galactic society would be any different than the ones here on Earth? Some planets would likely have resources that are in high demand. Some races would be better slaves or workers than other. Still others would possess technology others wanted. Some would have more powerful weapons. And you think skin color or stature is a differentiator on Earth?? Think about racial or species level intolerance of each other. This force alone would likely make control impossible, let alone distances and different environments. Such an eclectic group of cultures would be harder, not easier to control. And they'd have to do it perfectly.

But, Lets assume for a microsecond you are correct. One civilization is controlling or supressing all others from contacting us directly. Fine. We could still theoretically observe large structure architectures, Dyson Spheres, FTL drives, Spectral signatures of pollution, Artifacts left by probes, solar signalling, or many other evidences that are left unknowingly or non-deliberately in the day to day workings of this empire. If you doubt we could detect these, then go read the paper in the OP that discusses these methods and provides references to detection methods for these things. Such a galactic civilization wouldnt likely be able to hide.

Your argument just proves how difficult a single galactic empire run by one civiliation would be -- Impossible.

We do have a single dominant culture on this planet. The modern human culture. Our shared patterns of behavior and values are far greater than our differences. Compare humans to any other known species!
We can barely detect large exoplanets, why should large structures be easy to detect?
Dyson Spheres may or may not be a good idea. They're expensive to construct, and it's not obvious whether there's anything to justify this expense.
FTL drives may or may not exist; if they do exist we have no idea what they'd look like. There's no reason to suspect they even exist, much less that they'd be noticeable to us.
We can just barely detect planets which are too large for what we consider habitability, much less sense the atmospheric characteristics of a polluted planet.
The only artifacts we'd have the slightest chance of detecting are ones left on Earth, and even then we would have to be amazingly lucky to find them.
Rather expensive to do. Not the work of a plucky band of idealistic alien hippies, it would have to be a government backed activity.
There's no particular reason to expect we could detect the day to day workings of a civilization in other star systems. We couldn't detect our own civilization even from the nearest of star systems.
We COULD, in principle, eventually develop the technology required to detect, say, pollution in Earth-like planets in other star systems. We do not have that technology yet, so the fact that we have not yet detected pollution in Earth-like exoplanets is not in the least bit surprising.

The only things on your list which would be detectable so far would be Dyson spheres or solar signals (which is about as expensive as a Dyson sphere but is pretty darn useless). Dyson spheres at least offer something for all of the expense, but it's still not obvious what would be the actual practical use of a Dyson sphere.

This still does not lead me to believing your premise any more than you think I should.

__________________
There are few left who
Stare at the skies with wonder
Wishing to know more;
The clouds still drift by above
But the eyes below are blind.
--Laura Lundberg

Check out my writing, maybe.

You are either missing the point, or purposefully evading it.

The modern human culture varies greatly between countries. ANY world with 1 dominant species could be said to have a global culture since they are all the same species, but that doesn't make it so.

You are saying that if Intersetellar travel is possible, then the most logical answer to Fermis Paradox is that ONE civilization is controlling all other civilizations in the galaxy and preventing them from contacting us. I am saying that that is a very unlikely scenario, and Occam's razor cuts that to shreds.

Based about what we know of different cultures on earth of the same species, despite our similarities, One nation has not arisen to control all others. We dont share a dominant religion, currency, or government. And we all live in the same environment, breathe the same air, drink the same water. Despite these similarities, despite these "shared patterns of behavior and values " that are "far greater than our differences" we cannot unite one world's cultures. I fail to see how your position on this forwards your argument.

I have pointed out that one civilization controlling many others who are different species, different religions, different requirements for life, different philosophies, different motivations, and all separated by hundreds or thousands of light years, and all undergoing cultural evolution is a problem several hundred orders of Magnitude greater than uniting one world where everyone is the same species.