Going back to the OP, does anyone know how many stars are within 20 light years of Earth? From memory, I think it’s only a handful. Does anyone know the average density of the milky way (stars per cubic light-year)?
106.
Well, if we perfect the generation of practical power from nuclear fusion, about the only potentially limiting resource is deuterium, of which there is a vast and easily extractable supply here on Earth. With all that essentially free energy, creation of large usable stores of antimatter is basically just an engineering problem, and so now the mass:energy part of the equation is small enough that interstellar travel is quite feasible on a colony vessel of some sort. Maybe some folks wouldn’t like the idea of leaving Earth forever, but I’m sure there are plenty who would be clamoring for a place on board, probably some of the same sorts of people who might set off across the ocean, believing they might fall off the edge if the round-Earthers goofed.
There aren’t any Earth-like planets that we know of nearby; but there are lots of gas giants, some of them far enough away from their stars that if they posessed moons (which seems altogether likely), some of those moons could meet all the habitation requirements of human colonists capable of making the journey in the first place; and such worlds could be reached in just a few generations at even fairly modest speeds (like maybe 20-30% the speed of light). Given our colonial history on Earth, I see no reason to assume any of the above is impossible or unlikely. Would other civilizations be so indifferent as to refuse the adventure of the great beyond? One can only speculate.
We have not done so. We once sent a single signal in a very specific direction which could be detected by our own technology at Galactic distances. I believe that the resolution of the Araceibo telescope is approximately one degree; if this is accurate, then we’ve only transmitted to one part in 40,000 of the sky. If this is the same sort of effort that ET is devoting to the task, then it’s no wonder at all that we haven’t heard him call.
Well I will throw out my ignorance for all the World to gawp at, not to revel in it but to be disabused. I am not tracking.
If there are 700 billion solar masses in the Milky Way
http://www.astronomycafe.net/qadir/q76.html
How on earth (so to speak) can they all be visited in 1 million years at sublight speeds? Isn’t that a rate of visiting 700,000 unique Stars a year?
Isn’t a more logical number that they would visit, say 350 new Stars a year, and to do this steadily this presupposes many, many thousands of ships making journeys at once. At 350 new Star falls a year, with no repeats, wouldn’t that take 2 Billion years? At 700 new stars a year a Billion years …
I am now mathematician or cosmic theoretician, and am certainly not being chesty with anyone – show the dumb guy what he isn’t tracking
The idea is that a single colony seeds multiple colonies, which in turn seed their own colonies, etc. It’s not a purely linear process, but rather the number of colonies increases, at least for a while, geometrically, and so the species (or more accurately, its sundry descendants) spreads out in all directions where worlds lie until virtually all habitable worlds are occupied.
I can’t remember the name of the book, but some British theoretical physicist wrote a sequel to H. G. Wells’s The Time Machine, the book basically serves, really, as a way of him explaining cosmological theory, and I only mention it so that if someone out there knows who it is, they can supply the name and a few more details.
Anyway, in one of his non=fiction writings, he states that if it’s impossible to develop some form of FTL travel, then a spacefaring species will essentially strip themselves out of resources and collapse. This, of course, will happen to non-spacefaring species that much faster. I’ve not read the original piece by him, so I’ve no idea as to how plausible his statement is. Certainly sounds reasonable to me (but then again, I’m a space geek), and if we’re unable to find a loophole in Einstein’s theories, then it’s pretty obvious why no one’s shown up: They’ve collapsed before they could get here.
There’s also the paranoid explanation for this deafining silence : others civilizations exist but they know it’s very unwise to be noticed. So, they stay silent and if they explore anything, it’s in a very discreet way.
IOW : there’s something out there that all other civilizations are afraid of.
(or at least exploring the galaxy systematically ends up very badly for some reason, so the only existing civilizations are the silent and/or cautious and/or unadventurous ones)
I heard this explanation being advanced seriously, but I can’t remember at all by whom.
Presumably as Hungarians.
One solution that might be plausible is simply disease. As it is, medical technology is giving us severely decreasing marginal returns. Over the last couple centuries, average lifespans could increase by a dozen or more years through the simple use of soap and other means of sanitation we now take completely for granted. Most of the remaining diseases humans normally succumbed to were then virtually or completely eradicated by antibiotics and vaccines. When did we last see such a leap?
The really nasty pathogens we know of out there, things like Ebola and other hemorrhagic fever viruses, have the nice built-in safety of killing their hosts too quickly for them to spread it around widely. It’s relatively easy to quarantine the remaining infected so that the virus never gets too far from its source.
But say you get something like an AIDS virus that can survive in aerosols and enter the body more easily. It’s not impossible. All you need is one deadly, incurable, easily communicable virus that waits a few years before it finally kills its hosts, and is contagious while subclinical, just as HIV is. Millions could be infected before we were even aware, and billions could die before we found a way to manage it.
The more dense, widespread, and mobile the human species is on Earth, the more vulnerable we are to the uncontrolled spread of deadly pathogens, if they cannot be detected quickly enough to avoid a pandemic, and/or we cannot rapidly find a cure. We have thus-far avoided such a disaster with AIDS because it’s so difficult to transmit. If we do encounter another “superbug”, we may not be so fortunate next time. I sometimes wonder if the “better mousetrap” rule holds inexorably for microbes and viruses, such that as soon as new hosts present themselves in large numbers, the rapidity with which microorganisms/viruses can reproduce virtually guarantees the evolution of new pathogens that can take advantage of the available habitat. Given this continual problem, it’s basically a numbers game until we either lick all disease for good, or we finally come into contact with something that licks us. The human species may be periodically knocked down such that it makes it very hard for us to devote our resources to major endeavors like interstellar travel; and what holds true for life here would likely hold true for life elsewhere, if it fits similar paradigms.
Would Contact with Extraterrestrials Benefit or Harm Humanity? A Scenario Analysis
Seth D. Baum,1 Jacob D. Haqq-Misra,2 & Shawn D. Domagal-Goldman3
- Department of Geography, Pennsylvania State University. http://sethbaum.com 2. Department of Meteorology, Pennsylvania State University 3. NASA Planetary Science Division
Acta Astronautica, 2011, 68(11-12): 2114-2129
This superbly entertaining article is about how to even formulate questions such as “do they eat us or milk us” or “can we do it to them” [my quote marks, my examples, i.e. not in paper].
The introductory material has rich references to scientific and fictional approaches to the Fermi Paradox, and that section I excerpt and condense here. [“ETI” is “extraterrestrial intelligence” and “METI” "messages sent [by us] to extraterrestrial intelligence.]
The Fermi paradox
So far, no extraterrestrial civilization has been unequivocally observed by humans. …Enrico Fermi suggests that ETI should be widespread throughout the galaxy [8]. This conspicuous absence of extraterrestrials is often referred to as the Fermi paradox…three paradox resolutions are worthy of consideration in our discussion.
One: […] life, or at least intelligence, is rare […] If intelligence is rare, then it is quite unlikely that humanity would have detected ETI. In the extreme case, humanity is the only intelligent civilization in the galaxy or even in the universe. Along the same lines, other intelligent civilizations may be beyond the physical limits of contact even if they do exist [15-17]. These scenarios are of limited value to this paper because they imply that contact with ETI is impossible.
[Two:] A second possible resolution […] derives from the challenges of expanding rapidly throughout the galaxy. Perhaps rapid expansion is unsustainable at the galactic scale, just as rapid expansion is often unsustainable here on Earth. This suggests that the absence of extraterrestrials might be explained by the fact that exponential growth is an unsustainable development pattern for intelligent civilizations [18], a response to the Fermi paradox known as the Sustainability Solution [19]. [which states] rapidly expanding civilizations may face ecological collapse after colonizing the galaxy, analogous to the fate of Easter Island [20].
On the other hand, the galaxy could be teeming with ETI that expand too slowly to have reached Earth yet [21]. These slowly expanding ETI civilizations could still be detected by us or send us messages, and their nature as slow expanders has some implications for contact scenarios.
[Three:] ETI are actually already widespread throughout the galaxy but are somehow invisible to us. The ETI could be unintentionally [or intentional]. The intentional form of this solution is sometimes known as the Zoo Hypothesis [22] because it implies that ETI are treating Earth like a wildlife preserve to be observed but not fully incorporated into the Galactic Club. This idea has been popularized through the Star Trek series as the “prime directive” for non- interference with a primitive culture. […] They may be waiting until we have reached a sufficient level of sophistication as a society such as the start of a METI program or the discovery of light speed travel [22-23], or they could be applying a societal benchmark such as sustainable development or international unity. The possibility that the Zoo Hypothesis explains the Fermi paradox has several important implications for contact scenarios.
“ETA” [“extraterrestrial assumption”]: It too 12 years of an expanding Universe for Leo to contact the dead.
[BTW, how much has the Universe expanded in the last 12 years?]
Ninjaed.
For those who don’t get this, let me explain. When Leo Szilard heard Fermi’s paradox, his response was that they are already here. We call them Hungarians. (For the record, Szilard was Hungarian.)
Smaller scale, (first manned landing on Mars, disrupted by someone getting there from Earth through a wormhole): the beginning of Pandora’s Star, by Peter F Hamilton.
There is also the simplest of assumptions: *There is no one else around, and we are alone. * Until someone comes up with a convincing theory of how the first DNA was created and that it was not a freakish low-probability event, this is my zero hypothesis.
Nobody knows how big the universe is. It could be a little bigger than the edge of the visible universe, it cold be trillions of times bigger. So that isn’t an answerable question.
Leo, I gotta say you find the most amazing stuff. And on quite a wide variety of topics.
Part of me really wants to ask how you do it and part of me is afraid to find out.
I’m confused about time dilation here. Or else Hari Seldon is saying, like Maxwell Smart, he missed posting by that much…
I think **Hari **is saying that as you get older your lightning ninja reactions lose a step or two. He’s slowed down to swinging his rhetorical katana a mere 12 years too late to slay the enemy. He just needs to aim a little farther ahead of where the bad guys are.
Kinda the opposite of that old Viet Nam era chestnut:
Perhaps Leo is the ETI who has already arrived.