I mean let’s say we discover a new, non-electromagnetic way to communicate reliably over vast distances using some kind of low power, high bandwidth signalling system. We’d abandon EM in a geological heartbeat. In cosmic terms we would emit a wafer thin EM shell just 150 light-years thick - and then we would fall silent.
So basically I just think we don’t know enough physics yet. We are perhaps a few discoveries away from being able to listen in on alien conversations.
I was going to say that of the 4 currently known fundamental forces, only gravitational and electromagnetic interactions lend themselves to long range communication.
However, there seems to be ongoing research about an actual fifth force that might be related to dark matter: https://en.wikipedia.org/wiki/Fifth_force
There are obvious things which feel possible and would revolutionise so many things, like room temperature semiconductors, which we don't have yet. Also things we've better understood since 2012 like detecting gravity waves.
I don't understand how anyone could think we've "discovered all the physics which could matter to us", when we know full well there are massive gaps in our understanding.
Carroll says strange things sometimes. Epistemology doesn't appear to be his strong suit.
I doubt if dark matter can be used to make things lighter, possibly dark energy could be used for that (which is even more elusive than dark matter). It could only make thing heavier if there is a method to confine it. But because it seems that dark matter does not interact with normal matter (at least not often), I do not see how it can be confined to ordinary matter. Take notices that neutrinos also cannot used for this purpose, because the simply zap through us by the millions everyday, without us noticing anything. We have not found methods that to confine neutrinos yet. They seem to fly at speeds close to the light speed.
This seems to be a case of "not knowing what we don't know", as Donald Rumsfeld would say.
His claim implies that we know what we don't know. The reality is that we most likely don't...
That brought down Rumsfeld, not that he ever suffered for it. Millions of other people did, instead.
A adopted a very fringe, unified physics model. From this perspective we are looking at none of the possible signals that would make sense for long distance communication.
(Cue Fed Saberhagen, *Berserkers".)
Of course there are a lot of assumptions there, and lots of hypothesis to explain it a way, but that's the crux of the Fermi paradox: there is something to explain away
So aside from being perfect in terms of energy capture so that the underlying stars emit absolutely no EM at any frequency, the proposed Dyson spheres would also need to be completely transparent to any background EM such as visible light picked up by sensors like Hubble.
I mean just imagine some alien engineer trying to use EM for a new mobile phone system when everyone else on planet Glerbulon is using DE. The other alien engineers on the team would be like “wtf are you using photons for? Are you nuts? Just use an off-the-shelf unobtainium link. Here I’ve got one in my pocket.”
...seriously though, I can't fathom why people are so caught up on the Star-Trek-like predictions where hyper-advanced aliens are still essentially humanoid. It's at least as absurd as [protocells](https://en.wikipedia.org/wiki/Protocell) assuming that all advanced life would be essentially protocelluar.
I can't fathom why people fail to realise that being bombarded for decades with pictures of hyper-advanced aliens still essentially humanoid somehow shapes the general public imagination regarding "aliens". /s
I thought also that some researchers claimed a star had signals consistent with a type II .
Communication itself might be of little interest to such beings.
> unless the effective probe launch time is greater than 270 million years, the galaxy is old enough for every system to have been settled from an initial single civilization
> When diffusive stellar motions are accounted for,they contribute to the Galaxy becoming fully settled in a time less than, or at very least comparable to its present age, even for slow or infrequent interstellar probes.
>While settlement wave crossing and fill-in times are short, consideration of finite civilization lifetimes in a steady state model allows for conditions in which the settled fraction X is less than 1. Thus the galaxy may be in a steady state in which not every settleable system is currently settled.
Conclusion basically says that if there are expanding civilizations in our galaxy, they spread very slowly, have filled the galaxy sparsely or have limited lifetimes. Assuming they are not avoiding contact.
I.e. the number of universes that are incapable of harboring life is many order of magnitudes larger than the number of universes that may accidentally harbor life (i.e. us)
which is still many order of magnitudes larger than the number of universes that actually have a more realistic chance of harbouring life.
So us being a singular "accident" may just be a likely consequence of being here and asking questions.
[update] see also https://en.wikipedia.org/wiki/Fine-tuned_universe
In particular, taking the "number of possible universes" seems problematic to me, as we can only obverse the one in which we interact. And even taking that for granted, what is so astonishing that the actual one is the one that is compatible with our existence? I mean, if any possible universe could have happened, then the one we live in had actually an equal chance to exist with any other. Since this perspective assume that at least one universe must actualize, then pure randomness by drawing of lots is enough to explain the result. No need for a teleological purpose. Apply Law of Parsimony and you are done: Anthropic principle add needless ad hoc assumptions to reach its predetermined conclusions, especially in its strong version.
Also, the anthropic principle stands on many assumptions, including that the simulated models of tweaked universes do reflect other conceivable world in a fiddle manner would they be actual things.
It also neglects that among an infinity of variation, you surely should be able to come with totally different forms of "life". That is, for example it takes life as a carbon based structure, so you need universes with constant tweaked for enabling star to produce and disseminate carbon before they collapse. But on the counterpart, it can't pretend if you take it seriously, that other universes could not have produced very different form of "life". To my mind, we have no idea if our current actual universe is not also populated with non-carbon based life form.
Also this kind of theory emphases greatly on what the world did allowed with these tweaking. But, among an infinity of other combinations, who would seriously consider that nothing better could have been produced than a mankind tormented in wars and questions which are at best extremely hard to solve for its limited cognitive abilities, if not definitely out of its reach?
You've just verbalized the weak anthropic principle. The entire point of it is that this is not astonishing (at least not without additional knowledge), but a necessity for the universe to be one compatible with our existence, irrespective of how rare the conditions are, given we're here to observe it. The prior probability of "us" arising might have been incredibly small (or not, we can't tell), but the posterior probability is 1 - we're here.
> I mean, if any possible universe could have happened, then the one we live in had actually an equal chance to exist with any other.
Yes, but that does not mean that the odds of any given configuration need to have an equal chance.
What GP is saying is if there is an infinite number of universes and if life is extremely unlikely, then the odds of any given universe with life only having one life form might be very high, even if there being even one life form might be extremely unlikely.
We know that the posterior probability of there being one suitable for us is 1, since we're here. But we don't know whether or not life is a rare event or not.
The antrophic principle explains why we "won the lottery" so to speak in being in one of the universes with at least one life form, but life being incredibly scarce might be one explanation for why we might be in a universe with only one life form.
Though of course we can not infer that life is rare across any given set of universes if we determine we're alone in this one, because we don't know how other universes would be configured.
Not necessarily, you could assume a universal prior distribution over possible universes and count how many of those that have life have more than one.
This might be a sort of a "last tool of science", a way to discover the laws of our universe without observing them.
E.g. even given that we know, say, gravity exists, we do not know if or how its strength varies in a set of infinite universes. Based on a sample of one universe, it could be constant or vary in an infinite number of ways.
I think you entirely missed my point (because you didn't read the link!). You could use the universal prior, that is, you could enumerate all possible computer programs (e.g. Turing machine programs) starting from the shortest and find the shortest one that generates our universe. Now, 2^L where L is the length of such program is the prior probability of our universe.
So to determine e.g. the average value of the gravitational constant across all universes, you would measure the gravitational constant in all universes and calculate a weighted sum where you weight the value of the constant by the prior probability of the corresponding universe. The same for the occurrence of life, etc.
Guess that one of the benefits of living in suburbs.
Back to the topic. Let's assume there is a space nomad nazi species out there right now, will that species survive long enough to conquer the entire galaxy?
You are referring to what is known as "The Great Filter". The more troubling question is, What if we are alone because all the more advanced civilizations have been culled?
Mass Effect Reapers, anyone?
As Douglas Adams wrote, “Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.”
We've been looking for alien life for, what, 50 years? And we've made various assumptions about what we should be looking for. Oh, and we've been doing so on a very limited budget, with the technology available to us, in a tiny part of the sky .
Think about it this way. If human civilization persists and continues to advance, what's stopping us from spreading out to nearby stars within the next thousand years? And that's nothing on the cosmic timescale.
People already get sucked up by Warcraft and not even 100 years after computers made their breakthrough we fiddle around with haptic dual-4K VR.
The Fermi Paradox requires that aliens think and behave like late-20th century humans. But early-21st century humans already exhibit slightly different motivations and behaviours. So it's really hard to imagine that early-201st century humans would be at all familiar, let alone late-736th tier Grabulons.
They also talk about civilization lifetime and interstellar resettlement. But interstellar resettlement doesn't make sense to me; simpler for machine civilizations to hedge their bets by putting resettlement sleeper ships in highly eccentric orbits with some desired period. Maybe there are civilization-killing effects that disable those resettlers, but they would apply to interstellar resettlement too.
- Did you look in the drawer?
- Why, I've searched everywhere! I can't find them!
- Well, then - you must have no socks. Your socks never existed.
Why is a mere "more than 100 years" considered a "very long lifetime"? Is there any reason to assume that the majority of intelligent species, capable of technological civilisation, that may inhabit the galaxy, will not have a lifetime measured in thousands, or even hundreds of thousands of years?
The lifetime of the averarge star is a few billion years. We can assume that mos species will not have naturally evolved lifetimes lasting bilions of years, but a) species may evolve lifetimes lasting millions of years, or, b) a technologically advanced species may extend its lifetime indefinitely.
A species whose individuals lived for a few hundred thousand years would have plenty of time to visit the Earth by travelling in sub-relativistic speeds, from a significant portion of the galaxy. A species whose individuals lived for a few million years would have plenty of time to visit the Earth and wait for our own civilisation to die out. A species whose individuals lived for billions of years could pay us an intergalactic visit and still have time for tea.
Extremey long lifetimes are not impossible and they are not even particularly improbably. Here we are wondering whether there are other technological civilisations among the stars. Why should we assume that they are anything like we are?
That said, I would imagine that once most life forms get to the point that they are able to extend their lifespans with technology, they probably always do. They just don't evolve anymore...
I'm not sure I see that. For example, humans live many orders of magnitude longer than bacteria and yet we have both evolved just fine.
Anyway, I don't see why a species is pressed to evolve quickly in absolute terms. If all species on a given world evolve lifetimes many orders of magnitude longer than on the Earth, then there's no reason for any particular species to hurry.
I think how long or short a species' lifetime is can only be understood in the context of the environment in which it evolves. In any case, we don't know anything about life on other worlds, and my point is that we can't really make such big assumptions based on the single example we're aware of.
Whether these are the laws of nature, the laws of a simulation, or the laws of some Gods playing around, it makes no difference.
Unfortunately, without these assumptions it is impossible to have any kind of scientific knowledge - if we can't assume that the sun rising for the last hundred thousand years means it will rise again tomorrow, or if we don't assume that the universe extends in the past as well as the future, there is nothing meaningful to study.
Note: the laws of physics I am talking about above could be very different from what we know today - just as QM and Relativity are to Newtonian physics - but that would not change the assumptions I'm talking about.
See also Omphalos by Ted Chiang.
Life in OUR planet was shaped by competitive evolution and we have reason to believe life in other planets has been as well— it's how natural selection works after all, and at least in our planet it's proven to be an effective way to go from primordial soup to complex, intelligent life that can out-smart its competition hoard all the resources.
But how do we know that this is not a behaviour that civilizations, well, outgrow once they've hoarded all resources?
Unbound growth is an effective strategy in a competitive scenario like the evolutive stage of species, in large part because it's also one of simple incentives. When a species becomes dominant though, it is very dumb, because the species will just end up reaching the limit of available resources and burning through them, thus killing themselves, like bacteria in a petri-dish multiplying until all the food has been eaten and they all starve to death.
The argument goes, that's when a civilization would expand. Those bacteria would try to find another petri-dish. The species finds more resources so it can keep growing, but, can this incentive of "we have to keep growing" stand the test of time?
Simply from a practical standpoint, Alpha Centauri is 104691 times further than Mars. The technological gap between sending a colony to a planet in your system, versus one in another star is gargantuan.
First of all let's consider that planets are all ballpark similar in size and resources, therefore value. Is the investment even worth it? Is traveling 104691 times more for the same resources a stronger incentive that simply learning to find equilibrium with the resources easily available in your system?
Even if for the sake of argument the civilization decides it is, could they even achieve it before running out their available resources? It'd be a race against the clock.
There is reason believe the civilization would be forced to find stability and equilibrium within their existing system before developing the technology to be able to feasibly colonize a neighboring star system for the purpose of extracting resources. And if not to extract resources, why put the effort to continue expanding?
Fear? Of what? A nonexistent galactic empire?
Pride? If their history is anything similar to ours (which, since we're talking about similar motivations, is perhaps a feasible assumption to make), they would've learned colonizing far and wide does anything but promote a stable, unified, timeless nation.
Therefore, my guess is one of two things might happen:
1. They achieve stability because it's the only way to survive, and the motivation to expand to another system dies off. Probe and explore, perhaps. But if in a stable system, there's no incentive to introduce instability once again by adding another habitat. On the contrary, the prospect of instability is incentive to not.
2. They don't achieve stability in their system, and so collapse.
In a nutshell, I don't think there's incentive for unbound expansion once stability has been achieved, and I don't think unbound expansion can be achieved before stability. Of course, this is all just my opinion, but it's worth thinking perhaps the entire premise of extrapolating primitive evolutive behaviors to an advanced civilization is out of frame.
Consider the future world of Brave New World by Huxley, or even the Time Machine by H. G. Wells. Neither seem to have galactic empires; instead opting for (very distinct) forms of stability (and decay).
Just look at SpaceX and co. and all the people interested in that. If the technology exists some people will go. This does not have to be a large number compared to the overall population. That's enough to kick-start the process in a chaotic and unplanned manner...
We might be the progenitors of other intelligent species who might look back at us fondly and remember our shepherding.
Again highly unlikely, but a good point that we should not kill ourselves beforehand.
Are we at the peak of what people achieve on temperate world's? Maybe technology doesn't meaningfully advance much beyond what we already know - you get a computing boom, Moore's law ends and then a couple decades of discovering no substantial alternatives to the silicon chip.
I'm not saying it's impossible we'll discover some amazing, paradigm shaking new physics that will upend everything. Maybe. But we can't bank on it and it's entirely possible no such civilisation shaping new physics exists.
If that's the case, then the future will all be about engineering based on parameters we already pretty much know. I often see the Daedalus project held up as 'proof' interstellar travel and even interstellar colonization are possible. That was a designs for a very modest space probe payload, but even so the resources required to build them would pauper our whole civilization. Even if, or when, we master the resources of our whole solar system, those probes would be a significant cost and it seems likely they're way too puny to deliver a robust self-replicating bootstrap infrastructure. There's nothing inevitable or necessary about interstellar colonisation. The universe doesn't owe us Star Trek.
The motivation for traveling in space can only be to decrease probability of extinction and to increase their knowledge. The later may include studying other life forms and what they have learned. As a consequence, I assume they would specifically target solar systems with a high probability to host well advanced life forms. I don't give much credit to a random expansion in the milky way.
Regarding the Fermi paradox, the only paradox is excluding the UFO phenomenon as possible extraterrestrial manifestation.
You can support many times more people in things like O'Neil cylinders, bishop rings, etc. than you can on planets, using less resources. If you're the kind of civilization that can settle a galaxy, you're also advanced enough that you're going to care about that sort of thing, because you're already working on huge timelines, and you probably want to stretch your existence out for as long as possible. Being efficient with resources is going to be important there - the universe isn't making any more of them.
But anyway, that already assumes there's tons of spaceships out there, enough to actually show up on our equipment. Even if there's a galaxy-spanning civilization out there, the chances of running into them are low. I mean for a close analog, look at the game Elite: Dangerous, that can give you an appreciation of the scale of the universe - and in that game it's basically cheating because you can jump from one solar system to the next in seconds. And even at those speeds it takes forever to get anywhere.