[jvmboi]

> But you still have to explain the observation that the night sky is empty of signs of life.

It's really not that hard to explain. The last time I looked into this it was the case that we wouldn't be able to detect ourselves more than a light year out. The closest star is the red dwarf flare star Proxima Centauri at 4.2 ly. So, the question really isn't "where is everyone?" but "why is no one doing active SETI right now in a way that we can detect?".

That's exactly OPs point, we are heaping assumptions upon assumptions and most people discussing this topic don't even know how mind bogglingly huge those assumptions really are.

[eru]

You are underestimating the Fermi Paradox. Active SETI is barely relevant.

The first part:

See how fast technology is developing, and especially the decreases in the cost of rocket launches.

Within the next few hundred years humanity (or our drones) will have spread to countless habitats around the solar system. Within a few thousand years, we will have started building a Dyson swarm that will obscure a measurable fraction of the light of our sun.

We don't need any new science for this, nor radically new engineering.

For this confident prediction, we only need a few key ingredients:

* Humanity doesn't blow herself up completely. (Civilisations blowing themselves up is one way to resolve the Fermi paradox.)

* At least some humans are interested in space exploration. (The proportion of the total population can even go down compared to today.)

A thousand years is nothing on cosmic time scales. It's not even much in terms of geological time scales.

Even today's technology could detect the humanity of 3024 from countless light years away: just point a spectroscope at the star and notice a vast excess of infrared (the waste heat of our solar collectors has to go somewhere) and an corresponding deficit of shorter wavelengths.

So we might not be able to detect ourselves at the moment, but we would be able to detect our 20-minutes-into-the-future selves already.

The second part:

As I already mentioned, our sensor are pretty close to good enough to measure the chemical make-up of the atmospheres of exoplanets via spectroscopy. Atmospheres that harbour life look very, very different from those of life-less planets.

(Or to steelman that argument against nitpicks: there might be some forms of life that do not push the atmosphere of their planet out of chemical equilibrium. But for that to resolve the Fermi Paradox, that would need to be the vast, vast majority of biospheres.

And I'm not talking about an oxygen-rich atmosphere necessarily. Just any sign of chemical disequilibrium.)

So, yes, humanity couldn't detect ourselves right now. But humanity in a only few years could already detect signs of life hundreds of light years away while still at the equivalent of the Cambrian explosion.

Strictly speaking my part two is not a problem right now in 2024, but I'm fairly confident in predicting it will become acute in the next ten years as our telescopes get better. Astronomers have already done some basic spectroscopy on some exoplanets. Their skills are only improving.

---

You are right to warn about making too many assumptions about alien life. However, not all assumptions are born equal.

For example, life is almost by definition associated with being far outside thermodynamic equilibrium. Being outside of chemical equilibrium isn't much of a stretch.

Similarly, my first part assumes that humanity (or our alien equivalents) will keep multiplying and expanding. And again, that's not much of a stretch: yes, at any given time only some portion of life might be interested in these activities, but future generations will be predominately made up of those that showed the greatest interested and skill in multiplying.

[jvmboi]

> See how fast technology is developing, and especially the decreases in the cost of rocket launches.

The past century of rapid progress is anomalous in human history. We made do with stone tools for 100k years. In the middle ages basically nothing technological happened for a 1000 years. Consequently, this view of eternally ongoing progress is an artifact of the specific time and place we find ourselves in and not something that really has to happen. While we had some good results from semi-conductors I see our progress as already slowing down. Most of our science doesn't reproduce. Our cosmology is in shambles (more on this later) and our engineering is surfacing issues around putting the correct number of bolts on airplanes.

> Within the next few hundred years humanity (or our drones) will have spread to countless habitats around the solar system.

Why? What is there beyond the gravity well that isn't on earth? Maybe there are some substances, such as deuterium, that we can exploit remotely but this idea of "space habitats" is just romantic science fiction. Maybe someone will make it happen but only because we humans are in love with space, not because it makes rational sense.

> Within a few thousand years, we will have started building a Dyson swarm that will obscure a measurable fraction of the light of our sun.

Again, why? Fusion and fission can supply all the energy we want. If we want to do mega engineering for more energy we could just bore down to the earth's core. I'd bet that's what intelligent aliens on Enceladus would do. Regardless, it's completely useless to predict the future a thousand years out. We simply don't know and we have no data to anchor our fantasies to reality. From this initial starting point, nobody ever made and predictions worth anything.

> We don't need any new science for this, nor radically new engineering.

So why don't we do it then?

> For this confident prediction, we only need a few key ingredients: > > * Humanity doesn't blow herself up completely. (Civilisations blowing > themselves up is one way to resolve the Fermi paradox.)

Like I showed, you are baking in more and more assumption. Basically every sentence of yours is one more huge assumption.

> Even today's technology could detect the humanity of 3024 from countless light years away: just point a spectroscope at the star and notice a vast excess of infrared (the waste heat of our solar collectors has to go somewhere) and an corresponding deficit of shorter wavelengths.

Some SETI and Fermilab people looked already back in 2006 and found 17 candidates. There is this flawed idea that we already have detected and interpreted everything that there is. But JWST is showing us right now that we don't know anything. Every piece of our cosmology is currently under reexamination because wherever we point JWST we see stuff we can't explain. Even just the question of cosmic distance measurement isn't simple and clean cut.

All our space science is based on the premise that we are doing natural science where natural things exhibit regular patterns that we can describe with laws. If the universe were to contain ubiquitous mega engineering we would, by definition of the science we are doing, not recognize it. For instance, your Dyson spheres detection assumes that we see an abnormal spectrum. But, abnormal compared to what? If the universe was full of Dyson spheres we would say that there are "infrared stars" and then we would hypothesize how these come about naturally until someone can crowbar in an explanation that sort-of-kinda could work. Cosmology is full of these kinds of after-the-fact explanations btw, just look at Tabby's star or Oumuamua.

So again, we end up at a place where the Fermi paradox isn't very impressive. If the aren't building (arguably pointless) mega structures, we won't see them. If they all are doing mega engineering we wouldn't recognize it. For us to see them the aliens must be doing things that are very 20th century western hemisphere human things.

[eru]

You are right that the time since the industrial revolution (or perhaps since the start of the scientific revolution) was especially fast and things might not continue at this blistering pace. However we are already on edge of being able to settle the solar system; or to transform it with unmanned probes. Not much more progress is necessary. (Especially no new science. Engineering advances are welcome, of course.)

> Why? What is there beyond the gravity well that isn't on earth? Maybe there are some substances, such as deuterium, that we can exploit remotely but this idea of "space habitats" is just romantic science fiction. Maybe someone will make it happen but only because we humans are in love with space, not because it makes rational sense.

My argument does not require space exploration (or even life in general) to make any 'rational sense'. It just requires that some fraction of people are interested in it.

> There is this flawed idea that we already have detected and interpreted everything that there is.

Huh? Who has that idea?

> If the aren't building (arguably pointless) mega structures, we won't see them.

The Fermi Paradox does not require that mega structures have a point that you can understand. You talk a big game about being careful about our assumptions, but you can't even understand that some of your fellow humans might do 'pointless' things?

> If they all are doing mega engineering we wouldn't recognize it.

I don't buy your argument. Aliens can't magically escape thermodynamics, even if they were super quirky and 'alien'.

We don't see these 'infrared stars'.

[jvmboi]

So the starting point of this conversation is the Fermi paradox. Your line of reasoning has a very long line of necessary assumption. I only show that how they might not be warranted.

> Not much more progress is necessary.

The more plausible you make the technology the more you have to explain why we aren't doing these things. We might go back to the moon soon but beyond that we don't have any plausible plans to do anything noteworthy in space, let alone activities that would be detectable from other star systems.

> Huh? Who has that idea?

You. Everyone else who holds up the Fermi Paradox. The further we look into space, the less we understand but somehow you guys are so very sure that we aren't seeing aliens.

> It just requires that some fraction of people are interested in it.

I don't know how this relates to the Fermi paradox. Is the argument that "as long as some people are interested there will be a Dyson swarm"?. I don't think that follows.

> but you can't even understand that some of your fellow humans might do 'pointless' things?

I can absolutely understand that. What I don't agree with is that we are on an inevitable path to a Dyson swarm (or similar scale engineering).

> I don't buy your argument. Aliens can't magically escape thermodynamics, even if they were super quirky and 'alien'.

That wasn't my argument but I don't know what aliens can do. They might be able to do things that look a lot like violating thermodynamics to our incomplete understandings of physics. They might be engineering on a scale that is so fundamental that we can't currently recognize it. They might just be on their planet(s) with eternally stagnant technology. The point is, we don't know. We don't have data. We won't be able to draw valid conclusion from almost total ignorance.

> We don't see these 'infrared stars'.

It was a hypothetical. But let's say we don't see dyson swarms, which I am not even sure of, then proper conclusion is that nobody builds dyson swarms and nothing else.

[eru]

Thanks for the enlightening discussion!

> The more plausible you make the technology the more you have to explain why we aren't doing these things. We might go back to the moon soon but beyond that we don't have any plausible plans to do anything noteworthy in space, let alone activities that would be detectable from other star systems.

We are doing these things! It's just taking longer than people had expected in the 1960s. But in the timescales we are talking about for the Fermi paradox, an extra 100 years don't make a difference.

Arguably, going to the moon was a big waste of money for some bragging rights. More recently, rocket launch costs have decreased dramatically, and lots of space projects are only now becoming economically feasible. At the moment that's mostly a greatly increased rate of satellite launches, but we can already see asteroid mining on the horizon.

Collecting energy in space and beaming it to earth might also soon become economically feasible. Or perhaps the opposite: putting up a big sunshade at a Lagrange point to counteract global warming.

> I don't know how this relates to the Fermi paradox. Is the argument that "as long as some people are interested there will be a Dyson swarm"?. I don't think that follows.

Yes, you understood that right. As humanity becomes richer and more capable and space flight become easier, we'd need to commit proportionally less and less of our total resources to make a difference.

Compare eg how building something like GPT-4 would have been impossible in the 1990s; would have been Apollo program level expensive in the 2000s; is a major corporate investment at the moment; and will probably be something within the reach of hobbyists in the 2030s.

> I can absolutely understand that. What I don't agree with is that we are on an inevitable path to a Dyson swarm (or similar scale engineering).

I guess that's the crux of our disagreement. I predict the only way to avoid a Dyson swarm would be for humanity to blow itself up completely. (And even an AI singularity that sacrifices everything to the great paperclip maximiser would not avoid a Dyson swarm; just the opposite.)

> They might just be on their planet(s) with eternally stagnant technology.

Some aliens might do that. But to resolve the Fermi paradox, almost all alien civilisations would need to do that. If even one in a thousand have technological paths that are only even a 1% as fast as ours on earth, you'll get Dyson swarms.

It's theoretically possible that aliens might be able to do something that looks like violations of thermodynamics. Just like there's some possibility they might be able to go faster than light. But I'm excluding those possibilities here. (Or for the Fermi paradox to be still acute, it's enough if there's even a small fraction of Aliens who are bound by the same thermodynamics and lightspeed limits as we are.)

> It was a hypothetical. But let's say we don't see dyson swarms, which I am not even sure of, then proper conclusion is that nobody builds dyson swarms and nothing else.

Yes, as far as we can tell, nobody has build dyson swarms. But looking at our own technology, it looks like building dyson swarms should be fairly inevitable, once you have a tool using civilisation. So the conclusion is that it looks like there just aren't any civilisations even remotely comparable to earth.

---

To operationalise into something concrete that we could theoretically bet on:

I think a dyson swarm is at least a hundred years out, so that's too far out to bet. But as a precursor, I predict that launch costs per kg to an orbit of your choice will keep coming down; and that the number of launches will keep going up.

See the graph on https://en.wikipedia.org/wiki/Timeline_of_spaceflight#Orbita...

At the moment, we might be in a phase of exponential growth. I'm not sure that will keep on. But I predict at least a sustained linear growth in the total mass to orbit per year over the next few decades.