I only recently realized that this "paradox" looking at the possibility not of "earth advanced" civilization but supposed advanced civilizations that would put out much more energy than humans put out.
The whole thing seems to rest on false-extrapolations of mid 20th century hard-science fiction authors. Our Western Civilization has experienced an exponential growth of some things, has expanded it's "frontiers" quickly in a variety of ways, conquering the rest of the globe and then labeling space "the final frontier".
But all this has been low-hanging fruit. We're reaching the end of population expansion, space is fundamentally hostile to human life in a way that would take tremendous progress to overcome and we're facing longer term consequences of the rapid expansions we have achieved (global warming is just one of the consequences). If humans survive this, we'll have to have somehow achieve a steady-state for energy consumption and related things. But once we do achieve that steady state, why would we want or need to suddenly start using the energy of an entire star (after the thousand years of scientific progress we'd need to under how to do that)?
We have the technology today to launch satellites into solar-orbits which would be capable of beaming power back to Earth. It would be clean, efficient and non-disasterous to the biosphere.
With any amount of space-borne industry, the costs would also plummet and get cheaper with every additional satellite. Once you can harness the energy of an entire star, there's almost no reason not to achieve it.
One of the assumptions of the article and of most serious scientific discussion of the topic is that the speed of light really is the fundamental limit that it appears to be. It's not mentioned because it's axiomatic. The only thing in favour of the speed of light not being an absolute limit is that people don't want it to be. And wishful thinking is a very weak argument.
This does not make interstellar travel impossible, just very difficult. It is not feasible for us at this time, but it does not "violate natural law".
At least, if you take a diff between typical beliefs at the time the Fermi Paradox was formulated vs. typical beliefs now, I would say the experience of the shutting down of Apollo and overall reduction of human space exploration is probably the most relevant new observation we have made since then.
[1] In the sense of: You don't need nuclear armageddon to stop humans from spreading to other solar systems; the price tag of interstellar travel is sufficient.
So you simply never (or rarely) get exponential cosmic expansion. There might be a few billions of that race roaming the stars, but their numbers do not increase.
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Date 1: Every two people produce four offspring.
Date 2: Every two people produce three offspring.
Between Date 1 and Date 2 the birthrate declined by 25%, but the total rate is still positive.
As an example, the European Conquest of the Americas was driven by competition between European nation-states, it might not have occurred so swiftly or at all without some kind of competitive pressure.
Said another way, imagine yourself waking up in the court of King James of England or Queen Isabella of Spain. You establish rapport and they believe you come from the future. You communicate faithfully what you know about history. What conclusion do you think they are more likely to reach?
1) They have done the right thing by colonizing the Americas.
2) They have created what will eventually become new competitors, of whom at least one (the USA) will have subjugated them under the disguise of an alliance called NATO.
In the crucible of 15th-century European politics, neither England nor Spain may have had much choice in their desire to acquire more resources and open new markets.
And maybe the 21st Century will have cheap space travel and good reasons to take the trip. But we shouldn't ignore the possibility that Earth's governments may just decide to not let anyone leave and blast anyone who tries. Let's call it the "Nitrogen Curtain" in honor of Winston Churchill.
Imagine a civ arising 50 million years ago (a majority of the other stars in the Milky Way are billions of years older than the Sun). It takes 50,000 years to become interplanetary, and then 1000 years later it's ready to launch a mission to the nearest neighbor, 8 light years away. It travels at 0.02c and then arrives 400 years later. After 2000 years it has colonized that system enough that it has local resources to repeat the process.
The galaxy is 100,000 light years across, so that allows a spread from one edge to the other in 30 million years, which is long ago for us. Forming closer to the center and allowing for the mixing of star systems with galactic rotation would shrink that number.
Wormholes or warp drive would actually explain the Fermi paradox for me: since the other civs are used to their stars that are older and hotter, and they only pay attention to the prime real estate. But limited to the speed of light, a civ will spread by filling each nook and cranny it can live in.
Just 2 million years ago, human ancestors were small-brained apemen. A million years is a long time.