1. There is energy to get to speed
2. Mass of fuel to decelerate (and you have to accelerate that fuel in the beginning!)
3. Highly blue shifted CMB (that alone limits how close to c you can get before becoming plasma)
4. Collision with micrometeorites (so the “ship” has to be microscopic or probability of collision quickly goes to 1, and there is no way to survive even micro collisions while moving at c).
5. Limits on how fast you can give impulse (because your ship is made of matter with finite strength). Eg You cant reasonably railgun something to close to c without converting it to plasma.
There is also all the things you do when you get somewhere before sending more probes to expand, presumably it’s not a single location that seeds everything else (and if it is then the energy budget of that is also complicated).
Now, even at 0.1 c and with many pauses to replicate on the new worlds it would still take only a few million years to span the milky way, but if someone was mid-expansion we would see them way before the bubble hits. Being limited to 0.1c also means that those not in our galaxy will likely be unable to expand into ours (and vice versa).
It's more of a viral mode of expansion where (virus) seeds carry the operational commands to new worlds (cells) which host them until they are consumed by the continued expansion. The intelligence and power consumption are concentrated where it's available, while passive catalytic action and stored knowledge is transported at speed.
So you can use a laser beam to construct a 3D printer at a distance.
Rinse and repeat, and this is asymptotically expanding at c.
We are firmly in the realm of science fantasy now.
You also don't really need atom resolution anyway. You can build mechanical computers driven by rolling stones by abblating matter with powerful beams - lithography on continent size scale, etc.
However I do wonder why the fermi folks get all bent out of shape about not seeing other civilizations. How far do you think you could see a fusion or antimatter ship accelerating or deaccelerating from 0.1c? Unless they are zipping around our solar system (Expanse style) doesn't seem likely the we'd notice them.
If the aliens were curious about us and had detected our expanding RF emissions they might well be close by listening.
Seems far from clear that civilizations would bother messing with stars (that would be detectable from a decent distance) instead of just propagating to other solar systems. People are already talking about sending probes to our nearest star via laser propulsion.
Consider Earth. If we set T=0 at one year ago, and assume that there really is no way around the speed of light, then it follows that by year N, every human alive must be within a sphere of radius N light years.
The average human has a volume of about 0.06 m^3, according to a few sites I found on the net. If you divide the volume of a sphere of radius N light years by 0.06 m^3, you get an upper limit on the number of humans that can be alive in year N.
Given a fixed population growth rate, you can figure out at what year the population hits the upper limit. It is startling faster than you might guess.
At 1% annual growth, we hit it by year 12059, when we'd have a population of 1.04 x 10^62 needing to fit in a volume of 6.22 x 10^60 m^3.
At 0.1% annual growth, we hit it by year 127168, with a population of 1.27 x 10^65 needing to fit in 7.26 x 10^23 m^3.
At 0.01% annual growth, we hit it by 1341545, with 1.45 x 10^68 people needing to fit in 8.56 x 10^66 m^3.
It is clear then, barring faster than light travel (or expansion into other dimensions or parallel universes or something like that), that growth rates for an growing civilization must in the long run go down, and keep going down until growth is very very low if that civilization survives long term.
Keep in mind that my numbers above are the time to hit a ridiculously high limit (packing all space that could be reached at the speed of light starting last year with over 16 humans per m^3). If you use a limit not as ridiculous, such as the still ridiculous limit of all mass within that volume is used to make humans, you'd get a much shorter time to the limit.
I think this might be a candidate for the Great Filter. Lowering growth rates means getting some people not to reproduce, but millions of years of evolution have selected for reproduction. Maybe civilization hit a point where they must slow down growth more than their citizens are willing to do, and that leads to internal conflict that if it does not destroy them at least stops them from further advancing.
The result may be that there may be a lot of civilizations out there, but they get stuck at the first size limit that they hit where (1) they don't have the technology to get past that limit but (2) they have the technology to make war over that limit devastating.
Civilizations that avoid this have figured out how to thrive indefinitely without depending on growth. Such a civilization might not feel the need to expand into a large volume of space. They may be content to stay within their solar system.
Or we may just discover new risks to avoid. Our ancestors created new villages because the river dried up, we might want other planets due to extinction-level asteroids, and our descendants may need to sidestep The Interstellar Ooze or whatever.
Meaning a single individual would be and use the whole galaxy.
Deliver the printer, rest is just information.
The Drake equation is usually turned into the Fermi paradox via some estimations that show the average (mean) number of alien civilizations we expect to see is large (>1).
However, just because the mean is large does not imply that seeing 0 is low probability.
More concretely, suppose there were 10 possible 'parallel' universes. In 9 of them humanity is alone and in the tenth there are tens of millions of alien civilizations. The probability of appearing to be alone is 90% even though the number of alien civilizations we'd expect to see is in the millions.
Talking about the Hubble Deep Field kind of misses the point. The original Drake equation estimates the number of alien civilizations in our galaxy. I probably should have used galaxies in my example, but left it with parallel universes as that is the common phrase.
How will their paper work if we confirm life on Venus, especially if it independently evolved.
It's easy to think of reasons why this might be the case. There is acceleration, deceleration, and replication time, which seems like it would be substantial for any civilization that doesn't want to put most of its resources into replicating as fast as possible.
One day, in a small quadrant of the galaxy, we'd notice starts "shutting off", simply going dark. After a few months, our astonomers would confirm their new model: the amount of stars going dark is increasing. Days later: the rate of increase itself, is increasing.
One day we'd wake up, and a small portion of the night sky would be dark. A disk of darkness, right at the brightest part of the galactic plane. By then we would have figured it out of course: most stars in the galaxy were being turned into dyson spheres. They were spreading almost as fast as light, making it look almost instantaneous, even though the process had taken hundreds of thousands of years. In a few thousand years a large portion of our sky would be dark. And after that...
Almost immediately, they have no more use for small rocky gravity-well planets, or even for stars. They live in Oort clouds where thermal noise is low and cold is plentiful.
There's some evidence that this is already happening - with 6 billion humans on earth, the global economy is already showing specialization (similar to how cells develop into organs in a human) and complex emergent behavior, with parts of it dying off without killing the whole.
What if the reason are experience looks like it does, with life a full 1/4 of the age of the universe, because at later points in the universe's evolution, life at this scale becomes meaningless and the primary sentient beings are planetary civilization interacting at the speed of light through the galaxy? Or galactic civilizations interacting throughout the universe?
Another interesting idea he explores a bit is "ownership" of resources. Do the resource-rich asteroids in our solar system really belong to us? Or are they available to any alien race who happens to pass through? In the book, we first notice aliens by observing unexplainable infrared radiation from the asteroid belt (later revealed to be thermal emissions from their resource extraction). He suggests that these aliens will potentially crowd out humans; even if they are not overtly hostile, they could gobble up all the resources we would have used to expand our civilization.
Highly recommend this book.
This presumes that The Most Technologically Advanced Civilization sees virgin nature as nothing but raw material waiting to become something useful. That's possible, but probable? I think that it's likely that diminishing marginal utility still holds even for TMTAC, and therefore they are disinclined to convert all the universe's visible matter and energy into Dyson swarms of Space Product.
My favorite (not particularly testable) solution to the Fermi paradox is that TMTAC originated shortly after the first heavy elements and planets formed. It became space faring and expanded throughout the visible universe before our solar system formed. Its agents have been lurking in our solar system since before life first appeared here. Having long ago achieved immortality and technological supremacy, there's no motivation for plundering or trading with terrestrial creatures. They silently observe like space faring bird watchers. They'll intervene if/when we start to approach the capabilities of TMTAC, particularly if we show destructive paperclip-maximizer inclinations toward converting the universe into Space Product.
To borrow some terminology from Nick Bostrom's Superintelligence book, it's possible that the universe has been colonized by a singleton civilization -- the first one to become star faring. But it's not particularly chatty or inclined to let potentially competing star faring civilizations expand.
Of course, here I'm trying to think like an alien civilization that is far ahead from us in technology and scientific knowledge, besides having an alien way of thinking, but the same goes for the article.
In any case, if that is like any disaster spreading through the universe at the speed of light (big rip?) not only we won't have time to notice, we won't be able to feel the effects neither.
Scan an object, at atomic & energy vector level. Transmit that information to a destination’s printer. Expansion is then indeed at speed of light, capped only by need to physically move a small “seed” printer (rapid transport may have enormous energy cost, but that’s all that needs moving; everything else is just data).
Having seen tech go from digital imaging to 3D organ printing in a fraction of my lifespan, seems plausible.
Imagine you have a way to build von Neumann probes that can boost themselves to some high fraction of c (say, 0.9). You start pumping them out in your home system, and send them towards some stars - not necessarily the closest ones. You keep sending them. There's now a shell expanding at 0.9c that's shaped by your production capabilities. Of course, the probes will spend time accelerating and then decelerating towards their destinations. But even as they decelerate, other probes, going to further targets, pass ahead of them.
Any probe that lands in a system sets up a facility for building and provisioning more of itself, and sends those to further star systems, adding to the wave. Meanwhile, any technological advancement could be transmitted at the speed of light - so the probes receive improvement instructions as they fly, and the entire shell keeps upgrading itself as it expands.
What's the aggregate speed of that shell? Less than 0.9c, I think, but I'd say it's still a high fraction of it.
The main warning sign we could look for, assuming there are no crazy unknown physics allowing creation of silent drives, are deceleration plumes and associated thermal emissions. But then, civilizations like ours should be easy to spot from a distance. Don't bother with radio waves, just look at the spectral lines of the planets in a system; if you spot high concentrations of chemicals that don't have geological rationale to be there (such as oxygen in our case), this implies something is keeping the planet away from equilibrium - likely some form of life.
If we go by Dark Forest theory, the standard procedure upon detection of such "life signs" would be to send updated instructions to the von Neumann probe heading towards that system: "don't decelerate, ram the planet (or the star) at 0.9 c". If there's anything of use left there, another probe will come later and consume it.
So, by the time we spot the evidence of the von Neumann probes, we may just be about to get hit by a relativistic kill vehicle at the vanguard of the expanding shell.
(I'm tempted to build a toy model and play with the parameters to see how much of an advance warning we would have.)
Still you need time to stop, make your conversion, pick next target, accelerate and deaccelerate. And you may be turning everything into nodes, i.e. suns, exoplanets, etc. As we find stars pretty far away and exoplanets in far away solar systems, we are safe for some million years at the very least, even with relativistic speeds.
And still, it is about what we think with the wrong mindset and a lot of unknown unknowns to properly understand the problem. Expanding may be obviously wrong for advanced enough... something.
A lot of what we think is rational discourse is actually ingrained, unspoken ideology floating to the surface and being coated with a patina of post hoc rationalization. That’s why it’s so hard to do science properly, especially social science- people don’t even know that they have biases, let alone what they are. But biases aren’t something you can point at directly and say, this belief is not true, it’s more that you might be overestimating the probability of truth of a whole bunch of little things by 10 percent and that creates a self reinforcing network of probable facts that adds up to weird beliefs when they are all put together.
The author of the article believes on some deep level that progress is inevitable and will go on indefinitely, combined with the unconscious imagery of a lifetime watching science fiction films, and a life of watching progressively more impressive gadgets appear on store shelves. It all adds up to essays like this.
If you wanted to build a "terrarium" for sentient evolving life forms how would you keep them from escaping?
1. Make the distances really really big
2. Put a speed limit in the environment
Rolled up with the Fermi paradox this simulation has "smelled fishy" to me for some time. :)
Or 3. Don't give humans capabilities to see them. Hell, I'd go even further, what if the "others" are already living on our planet, but we can't see them?
> Only when the sphere’s thin outer shell had reached the earth—perhaps carrying radio signals from the extraterrestrials’ early history, before their rapid expansion started. By that point, though, the expanding sphere itself would be nearly upon us!
Wouldn't the problematic portion of the sphere be, by definition, millions of years away from us? Given that radio waves travel at the speed of light, and the alien civilization travels at slightly less than the speed of light, it seems like we should have at least however many million years it took for those aliens to get from producing radio waves to "maxing out" travel.
We started producing a lot of radio around 100 years ago.
And we are still a long way from expanding at near speed of light. Even with expodential growth in capacity.
2) expanding near speed of light is much less than speed of light.
Say 99% of the speed of light. And expanding civilization is probably going to be coming from far far away, just because there is a lot more far far away than pretty close.
So say they are comiy from 10,000 light-years away (still close by galactic standards, and incredibly Close by Universal standards). Then the radio they start transmitting when their grown begins has gained on their expansion ba lead of 100years by the time it reaches us
Sure on the million and billion year time-scales mostly talking about that 100+ years is very little but it is still generations.
It assumes that technology will get to the point where it becomes trivial to explore space. That's not an easy assumption to grant.
On the timescale of the universe, geometric growth in colonization is functionally hyper rapid.
So either colonization (and thus, geometric growth) is impossible or there's nobody else out there.
No human being has ever set foot on a different planet.
No man-made object has ever reached a star system outside our own, let alone landed on a planet.
We may still be quite a long way away from accomplishing those things at scale.
There is a related number, N_hamlet_universes. This is the number of universes needed in order for monkeys to type Hamlet typing as fast as they can, covering every planet spaced 6' feet apart (in case one gets sick). I think this is also a very large number but I haven't figured it out.
Open question: Are we likely to be able to detect the difference between large asteroids and a small swarm of habitable environments in a star.
And the second question is: Is it worth spreading out? An advanced civilisation can defend against or modify (maybe even focus) the damage that an imploding star would cause, and an Issac Arthur video on the topic of the amount of space we have in the solar system states clearly that there's more than enough for trillions of trillions of trillions of habitats. There doesn't seem to be much reason for spreading a civilization out whatsoever, given the cost of communication and the assumed cultural and informational lag between the settlement and the source civilization.
As the article states, it's unlikely to be the case that we see an expansive civilization until it's too late.
I really don't want to say anything to spoil the books but the series were so good that I devoured them last summer which is something I rarely do.
Any entertainment industry on its own has more funding than all of humanity's space pursuits. All the apps for tracking time, buying clothes, losing weight, scanning tomatoes, properly wiping, get more money than the ESA or JAXA (at least NASA has more than them heh).
All the speculation and dreams of a great space colonization are nice, but the reality is that most of us will die on this planet, and likely take half of the life on it with us.
Edit: Apparently I have violated a HN taboo in even daring to mention that bothersome little law.
Understanding it and its implications and applying that knowledge to our IRL situation on earth might not be fun, however IS fundamental to making plausible statements about perpetual motion and related topics (i.e."von Neumann probes.")
Now, all that remains to be seen, this being HN, is:
Will this comment be downvoted into oblivion without a good reason being proferred?
I'm tempted to whip up some numerical simulation to verify this to some extent...
> But here’s the interesting part: conditioned on all the steps having succeeded, we should find ourselves near the end of the useful lifetime of our planet’s star—simply because the more time is available on a given planet, the better the odds there. I.e., look around the universe and you should find that, on most of the planets where evolution achieves all the steps, it nearly runs out the planet’s clock in doing so.
The form of reasoning used is exactly that in the https://en.wikipedia.org/wiki/Doomsday_argument for why humanity is unlikely to last long, and almost certainly will not have a future where we break out and colonize most of the Solar System, let alone the stars.
If you believe both arguments, the most likely outcome is that there is one more step on the way to Robin's argument. And that outcome is the replacement of biological intelligence with mechanical. So indeed we give rise to an expanding wave of technological civilization. But we are close to peak population and will not ourselves see that civilization.
All hail our future AI overlords!
But there is no reason to expect better. All the signs point there. Global climate disruption destroys crop yields in tropical and subtropical places, creating political instability. Millions, then tens of millions, then hundreds of millions of refugees flee toward higher latitudes. Nations at higher latitudes elect fascists to repel them. Fascists start wars, wars disrupt trade, economies collapse, nuclear weapons come out, boom.
It would be nice to be wrong about this, but it has all started already. 70M+ Americans voted for fascism. Brazil, Turkey, Hungary, India already got it. Germany, France, UK, Italy, Poland threaten. China and Russia fell long ago. Europe is already strained by the first few million refugees.
Sending the hundreds of millions of refugees on to Siberia and the Yukon could work, in principle.
So... evidence? Argument? Just stating baldly that it is so is not very convincing.
So, yeah. Overselling the case, in the graph on the first screen.
HN discussion of paper: https://news.ycombinator.com/item?id=26045731
Like other commenters have already said, this scenario assumes that near-speed-of-light travel is workable.
But millions of years of technological evolution is plenty enough time to make grey goo (or light speed spheres of incoming civilization).
And even of that is true, wouldn't we expect a significant fuzziness in that on the order of a millenium, where we see signs but haven't yet been engulfed?
But believing that you understand the data when there are huge glaring inconsistencies in your understanding is... naive.
He says there are only 3 possibilities (the part starting with "then either" 1) ... 2) ... 3) ...
But that's ignoring category 4) which is that we have only a fraction of a fraction of a grain of sand of the real data, and might be a bit early to come to conclusions.
So not to say #3 is wrong, and heck it could very well be more probably than #1 and #2, but I wouldn't bet the house yet when we don't know if there's an option #4 - #4,000,000,000,000 because we haven't even observed data from dimensions we don't even know exist it.
Now I'll never know what it was about. Probably someone selling stuff.
On the other hand, if it was intentional, then they'll be informed that it doesn't necessarily work as expected.
You might as well claim that "The Social Dilemma" was spam because you can just choose not to open facebook today.