I’m guessing more like 1. Because they start replicating again when they reach our galaxy.
So yes the replicating probes idea is mostly talking about the possibility of a species littering its own galaxy. But FTR I don’t think your arguments have succeeded in ruling out intergalactic probes.
Then there is the issue of material failure. It takes 2.5 million years to travel from Andromeda to us at light speed. It’s a given it would take a probe considerably longer than that to make the trip. Is there any device that could remain functional for that long without failure?
Maybe? There’s a thing in information theory about self-repairing code. You could (arguably?) have a self-repairing machine.
(Well, why not? We mere mortals “heal” from all sorts of damage.)
Any that we have? Probably not. I just got a new Whirlpool dryer, I’ll let you know how it works out.
That can be built by a civilization much more advanced then our own? I don’t see why not.
It’s not like it has to keep running that whole time, it doesn’t even need to be running ever. It can jus be launched out of one galaxy, only to wake up when it starts getting near its destination.
Y’all may be correct. Maybe it’s theoretically possible for a device to remain functional for millions of years. But, there’s a lot of maybes in that supposition. What’s possible vs. what’s probable may be the reason we see no sign of advanced life.
As you said, there are 250 billion stars in our galaxy. If there is no advanced life on any of them, then the chances that it’s just the next galaxy over seems pretty remote.
We could easily detect any sort of K2 civilization in our own galaxy, and a K3 in any other, as long as it has been long enough for the light to reach us.
As far as probes, it’s less sending them out for the purpose of exploration, and more for the purpose of exploitation. It would be trivial for a galactic civilization to start sending probes out to nearby galaxies to start harvesting their resources and bringing them back.
And it would be necessary as well. Once we have reliable fusion, we will stop seeing all the stars in the night sky as romantic filaments of wonder, but instead as burning oil wells, squandering fuel that we will need to hoard against the coming eternal night.
Apparently, the fastest speed humans have achieved to date in an unmanned vehicle is 16.3 km/s, or 0.0054% light speed [New Horizons 1/2006]. That’s pretty darned fast.
I’m a lover, not an astrophysicist, but, by my calculations (and please correct me if I’m wrong), traveling at that speed, it would take us 462,962,962,962.96 years to reach our nearest major galaxy, Andromeda. Conversely, Andromeda would have had to send a probe ~448-billion years before the Big Bang for it to just now reach us.
Given those parameters, I envision this conversation between a NASA mission planner and his boss:
Bob: Hey, boss, my team wants to send probes to Andromeda. Are you ok with that?
Bob’s Boss: That sound’s reasonable. How much will this mission cost?
Bob: More money than has ever been printed by all the nations on Earth, for all time. But, it’s tax deductible!
Bob’s Boss: Ok, that sounds doable. How long will it take to reach our destination?
Bob: Just a smidgen under 463-billion years.
Bob’s Boss: Ok, and how long will it take to get the data back from the probes?
Bob: Well, that’ll take another 463-billion years, give or take a few millennia.
Bob’s Boss: Alright Bob, I’m going to green-light this mission, providing you keep it under a trillion years.
Granted, advanced civilizations have probably exceeded 0.0054% light speed. But, how much faster? 0.01%. 0.1? Nobody knows. There may be absolute speed limits inherent in the physical laws of our universe. There may very well be a ceiling to the speed any advanced species can propel matter, and that ceiling may be quite low, relatively speaking.
Maybe? As you’ve stressed yourself, interstellar space is very empty. It’s actually closer to a perfect vacuum than anything we’ve managed to create on earth, including CERN. So it’s not like it’s gonna rust up.
Well we don’t know either way. So it fails as a basis for ruling out trans-galactic civilizations.
I would disagree with this. We’d have to hypothesize a species so short-sighted that they have managed to consume the energy and resources of a whole galaxy but so long-sighted as to launch missions that won’t bear fruit for many millions of years.
If the former at least seems plausible to you, bear in mind that even if every planet in the galaxy had a population of a trillion aliens, and each alien used as much energy and resources as human beings do collectively, there’s still plenty of energy and resources to support that for the lifetime of the galaxy.
What’s the relevance of that number?
There are people alive today, indeed a number of posters on this forum, that were born before Sputnik 1. We’re really, really new to the whole space thing.
What matters is what’s physically plausible to construct.
Since there are already serious plans on the table to make a crude probe capable of 20% light speed, that’s more the kind of speed we can envision for a species even mere centuries ahead of us.
As for the cost, most of the cost right now is getting stuff out of our gravity well. The costs will be significantly less for a species with launch capability from orbiting bases or space elevators.
The fact is, we are so far from knowing all the things we need to know to make reasonable estimates that everything is just a guess right now. There is no ‘crisis’ due to the Fermi Paradox, because right now we don’t have nearly enough data to understand what might be going on out there.
For example, it could be that the interstellar medium is full of enough grains of dust and small rocks and such that any suitably fast ship would likely not survive the journey. There might be a fairly hard limit on how fast you can travel before the energy dissipated hitting small stuff along the way becomes an insurmountable obstacle. For instance, hitting something weighing 1 gram at near light speed would be like a ton of TNT going off. Or if there are lots of particles even smaller, say 1 microgram, then it would be like sticks of TNT constantly hitting your ship and causing drag.
So if we mapped a column the width of the ship between one star and another, and it turns out that there are millions of such 1 gram dust motes in that column, and maybe a few bigger pieces up to a kilogram or something, travelling anywhere near light speed, or even a fraction of light speed down that column would be extremely difficult.
A planetary Nebula has 100 to 10,000 particles per square centimeter. Even in open interstellar space there are unseen collections of dust and rocks and such floating around, and we have a poor handle on them. We know the parameters of the interstellar medium in bulk, but we are still learning things. For instance we now estimate there are roughly 50 billion rogue planets wandering around in interstellar space in our galaxy alone, thrown out of their systems through gravitational interactions with stars and planets. So how many little clouds of gas and dust are there out there that are too small to see? We’ve only found about a dozen of those 50 billion rogue planets. Our chance of discovering a planet-sized collection of gas and dust and rocks spread across millions of miles are zero, and yet such a collection would likely destroy a relativistic spceship.
So it might be that the interstellar medium limits us to some speed well below the speed of light (or limits maybe 99% of civilizations that could otherwise travel to the stars).
Or it may be that the space in some places is clearer than others, and fast travel is only available, say, far out in the spiral arms. Again, we really have no idea.
Sure, and no-one has called it a crisis.
The point of the OP is merely that a lot of potential explanations for the lack of evidence of ETs have been ruled out recently, and therefore the paradox is becoming more acute.
Although I’d agree with you that it’s “more acute” like 330 degrees is more acute than 350: there are so many unknowns hidden behind things like the drake equation.
Yes, they probably would. Here’s another article on the possibility that clusters of primordial black holes should account for the dark matter in our universe. The problem is that the existence of these clusters would prevent space travel from attaining speeds that would allow intelligent civilizations to detect one another and maintain contact.
You mean because of all the steering around black holes?
Black holes are not going to be that numerous that it’s like the asteroid field on star wars. There’s still going to be stupendous amounts of empty space, and hitting a black hole by mistake would be akin to winning a thousand lotteries.
I don’t know, but I think the chances of hitting a black hole (if they really pepper the universe as dark matter) increase with the distance. And if stupendous speeds are involved then we’re talking about ginormous distances, where getting lucky may become a common occurrence.
Well, consider this. We see the stars in the sky because light has travelled between them and us without hitting any black holes. If there were enough black holes in the sky to pose a navigational hazard, then we would notice that the light that travels between the stars is occasionally interrupted. We don’t see that, so black holes are not common enough to cause a hazard.
You wouldn’t have to hit a black hole. You’d just have to be close enough to it that gravity throws off your trajectory. Unless you have enough fuel to constantly correct for such things, one very slight encounter early on could cause you to miss your destination by billions of miles.
And don’t underestimate the cost of those course corrections. At relativistic speeds, a change in course could be very expensive in fuel. A light-sail craft with no propulsion once the laser switches off would have no way to course-correct at all.
There have been numerous surveys of gravitational microlensing within our galaxy and, for example, between us and Andromeda. They have all basically found that the number of black holes is probably insufficient to account for more than a fraction of dark matter.
So, to the extent that this hypothesis of clusters of black holes can be true at all, the lack of lensing still suggests that it’s pretty easy to plot a straight line over vast distances, since the vast majority of photons seem to be doing just that.
Quite a bit of speculation on your part.
But, even if it was 100% accurate, (which I doubt)it still does not rule out the gradual and leisurely expansion of a civilization.
You don’t have to go all that fast to fill the galaxy in a relatively short period of time.
Essentially, this is entirely an argument from incredulity.
You are correct that NASA is not going to greenlight a mission to andromeda. We’re barely getting things into our own solar system now.
However, you ignore the fact that with the exploitation of resources in space, such undertakings become trivial. It could even be the work of a single person who decides on a whim to hurl a probe off to another galaxy at a small fraction of the speed of light.
And also, as a K3 civ fills up its home galaxy, it will start to spread out to others. They don’t even need to make a particular effort.
Hell, Andromeda will be here in just 5 billion years.
Or a species that is long sighted enough to see the heat death of the universe, and start preparing for it early.
Once we develop some form of functional immortality, such things no longer are academic, but are real threats to our personal futures.
Besides, what else do you think that we would do? We are short sighted enough that we’ve managed to consume the energy and resources of a planet, but are long-sighted enough that we have individuals who are working on expanding our reach for more.
What you have described is any species that grows to fill its available resources, along with the technology to develop new resources as they come available. Or, us, optimistically.
My position is simple and boring:
Intergalactic travel: I don’t think we (in our civilization’s time frame) will ever make contact with beings from another galaxy because I don’t believe any civilization has/will ever achieve anything close to light speed travel. At the fraction of light speed that I think possible as the upper limit, it would take too long for an extra-Milky Way mission to have reached us yet, even if it came from one of the closer galaxies, because it would have had to launch before any species had time to evolve into an advanced civilization (~5+ billion years ago, depending on top speed).
Just how old could the oldest K1, K2 or K3 Civilization be, even if K-civs do/can exist (which is not certain)? A few billion years, tops? (you can’t build worlds and civilizations with hydrogen and helium; you need later generation supernova elements to do that). At a fraction light speed, that’s not old enough for them to have traveled billions of light years to reach the Milky Way by now.
That’s the primary reason I believe we have not seen evidence of extra-galactic life (i.e. too far; not enough time). Secondary reasons include:
Why would any civilization, or “the work of a single person” launch anything to another galaxy, knowing, for all intents and purposes, it’s a one-way journey, with no possibility for pay-off for billions of years? I don’t care how advanced a civilization becomes, sending a fleet of self-replicating probes to other galaxies is more complicated and costly than flying a paper airplane across the room. You just don’t do it as a lark. To say otherwise is wild conjecture.
Other road-blocks: Any number of engineering and/or physical law limitations may exist that we’re ignorant of, limiting or preventing inter-galactic travel. And, it only takes one limitation to render inter-galactic contact impossible for us (or them), at the present age of the universe.
Intra-galactic travel: I’m conservative with regard to the Drake equation. I believe there are more parameters to consider to plug into the equation than many/most people, making the probability of life more advanced than human in our galaxy very low, to non-existent. But, that’s just me.
Other road-blocks: the same engineering and/or physical law limitations, on a smaller scale, may exist within our galaxy as they do beyond our galaxy. Who knows? And, again, it only takes one to make us incommunicado with our Milky Way brethren.
Ah, the Andromeda v. Milky Way Cage Match! Vince McMahon will be ring announcing that.
The thought of this catastrophic event keeps me awake nights. I anticipate a break like this and calculate Earth will be carom-shot into Canis Major…or, maybe nothing will happen.
This places the speed limit as something like c / 2000. We are not aware of any such limit.
In fact, like I mentioned, there are plans on the table to make a crude probe that would travel around 400 times faster than your limit. So I don’t see any support for your assertion. Nor reason to bring in “billions of years” to this part of the argument.
Sending one self-replicating probe to another galaxy doesn’t cost any more than sending one to the next star. The ridiculous distances and timescales involved have little bearing on the kind of craft or propulsion required. So yeah, I think an advanced species could do it on a lark.
More-or-less agree.
My feeling on the Drake equation is that, while it is a useful formalization, it can also be misleading. Some terms in the equation actually represent many, many unknowns.
And there’s no apriori reason why it is necessarily the right framing; so while it looks complete on its face, I wouldn’t be at all surprised if there are aspects of this issue that either span multiple terms in the equation, or don’t fit into it at all.
But on the probability thing, we simply don’t know. It appears that the probability must be at least quite low to explain the lack of evidence of ETs, but we don’t know what it is, nor the reasons why it is. Personally I think it makes sense to discuss the possible reasons and withhold judgement on the actual probability or number of ETs.
It is long enough that we would see them. K3 civs are pretty obvious.
And it is only your assertion that is the limiting factor on the speed of a probe. I see no reason why 10% or greater couldn’t be achieved.
Even assuming that they are not effectively immortal, and assuming that your asserted speed limit is a law of physics, people do do things that will benefit future generations that they will never see the results of.
And, if they are effectively immortal, and there is not such an imposed speed limit, then it could be the equivalent to us having to wait 6-8 weeks for mail order catalogue orders.
Just a thousand years ago, just crossing a small body of water like the Mediterranean was an undertaking that required the work and sponsorship of a nation. Now people fly solo around the world because they think it will be fun.
There is nothing in the laws of physics as we know them, not anything from a purely engineering standpoint that would impose such limits. Who knows? Sure, but you are declaring, “Here be Dragons” in areas where we’ve already more or less ruled out dragons.
There are a few thousand galaxies within a billion light years, most of which are substantially smaller than our own.
While I agree that life as advanced or more than we are is probably non-existent, it is only a few orders of magnitude more to assume that so is the local supercluster.
If there is life comparable to our own out there, it’s probably hundreds or thousands of billions of light years away, well outside of the observable universe, well past the point where we could never communicate or detect them as they are accelerating away from us at well over the speed of light.
The problem with the Drake Equation is that people tend to look at it backwards, that it is a mathematical tool to determine how many technological species are out there.
But that’s not what it is, it is an algebraic equation. The left side represents the number of technological civilizations that we can detect. And that number is 0. (Until or unless we do detect one or more, in which case, it is no longer relevant.)
The right side of the equation is all the unknowns. All it is is a formalization of the unknowns that we don’t know. If for some reason, we learn of a new unknown, then it doesn’t break the Drake Equation to add it to the right side. It’s general enough that it shouldn’t need much adding to, unless we learn something unanticipated, but there is no reason why some of the variables cannot be broken down into their own equations as well.
The idea is, however, that by formalizing these unknowns, it gives us a roadmap of what to look for. It starts with stars, which we actually can see pretty readily, and get a good idea of how many there are. The next is how many of those stars have planets, which at the time was unknown. We kinda assumed that most stars probably did, but we had no evidence of that, other than the fact that our solar system had planets, and it would make sense that others would as well.
In the last couple decades, we’ve started to fill in that variable. Turns out that most, if not all, stars have planets.
The next couple are about the potential and realization of life on those planets, and that’s what we are currently starting to dig into, we may have answers for that within the next decade, as we learn more about where life is able to survive and thrive in our solar system, and as better telescopes come online and we are able to detect biosignatures on extrasolar planets.
The last 3 will be a long time before we are able to get a handle on, if at all. We may get f(i), if we are able to detect signatures in extrasolar planets that we determine must be technological in nature, but that one’s more than a bit iffy. The last cannot be determined until we actually do communicate with a technological civ, and time it as it ages and dies.