Winning the E.T. Lottery 80
Consul writes "Space.com has a cute story about the statistical probabilities that we have been visited by an alien civilzation. He seems to make a convincing argument."
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Winning the E.T. Lottery
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Vanishingly small probabilities (Score:2, Interesting)
The probabilities for either event are infinitesimal, at least in my opinion, yet here we are. Even if you discount the above two occurences and bring up intelligent design or pure creation you're faced with yet one more improbability:
If you look at any of the probabilities they seem to point to a vanishingly small probability that even the simplest forms of life exist, let alone any intelligent life. Yet we're here.
Re:Vanishingly small probabilities (Score:1, Informative)
Re:Vanishingly small probabilities (Score:1)
Re:Vanishingly small probabilities (Score:1)
Re:Vanishingly small probabilities (Score:4, Informative)
Are you ready for the answer?
The existence of intelligent life on this planet does not necessarily imply the existence of intelligent life on other plantes. Just because a quarter lands heads up 10 million times does not imply that the next toss will produce the same result.
The existence of life on any planet must be taken as an individual probability just as each individual quarter toss must be taken as an individual probability.
QED
Re:Vanishingly small probabilities (Score:1)
But the article itself dismisses the likelyhood of us having been visited based on a series of statistical arguments. My point is that applying those same statistics says that we don't exist.
Duh! (Score:1)
Re:Vanishingly small probabilities (Score:1)
i beg to differ (Score:1)
50% NOT - because probability is based on the facts - how a certain entity has behaved in the past and not on how *you* think it should behave.
Probabilities are meaningless (Score:2)
Re:Vanishingly small probabilities (Score:1)
2. What's the probability that intelligent life evolved?
Dispite the probability, I think a more interresting question would be if they are able to recieve signals from us, since all signals and transmitions degrade in power over distance.
And if the are within this distance do they have the technology to detect the signals.
Re:Vanishingly small probabilities (Score:1)
One.
2. What's the probability that intelligent life evolved?
Somewhere between zero and one. We're still waiting to see.
3. What's the probability of the spontaneous existance of a supreme being?
I'll let you know when it happens
Note that your statement of the chances being infinitesimally small are your opinion, without any supporting evidence.
I on the other hand subscribe to "there are probably quite a number of earth-type planets out there, somewhere, so the chances are pretty good". Of course, it also includes that any societies are likely to miss each other by millions or billions of years - I think the chances of such civilisations encountering each other are infinitesimally small.
But I don't have any evidence to back either view.
Re:Vanishingly small probabilities (Score:1)
Re:Vanishingly small probabilities (Score:2)
1. What's the probability that primitive life evolved?
2. What's the probability that intelligent life evolved?
The probabilities for either event are infinitesimal, at least in my opinion.
Well your opinion is wrong, the probability of both is 1, since as you quaintly put it 'here we are'.
He ignores one possible solution... (Score:1, Interesting)
Seems this scenario gets rid of all of his improbable probabilities. They started everything off, so they KNEW where to come to find us (well, not us, but whatever did come of their little project).
Heck, he convinced me, if aliens have visited us then aliens must have started life here. Everything else is just too unbelievable.
Re:He ignores one possible solution... (Score:1)
Re:He ignores one possible solution... (Score:3, Insightful)
Imagine if we found that life is unique to Earth, but there are tons of planets out there capable of supporting life. Now we build a probe that will go to one such system. This probe determines what planet in the system has the best chance of supporting life, and it goes into orbit around it. Over time, it launches capsules with increasingly more complex life forms. This is done in conjunction with monitoring of the planet's atmosphere to encourage Earth-like development. We mass-produce said probes, and launch one to each of our neighboring star systems, expanding our definition of "neighboring" as we continue to produce the probes.
Now when we get around to colonizing the stars, we have planets ready for us.
Re:He ignores one possible solution... (Score:1)
Re:He ignores one possible solution... (Score:3, Informative)
Seems this scenario gets rid of all of his improbable probabilities.
...And instead gives the improbable scenario of aliens stopping by tens or hundreds of millions of times over the Earth's history. This would take a significant expenditure of resources, to little end (especially since the hypothetical ant-farm alien could have seeded a barren world in their own system or otherwise closer to home for convenient visiting). It would also require lots and lots of patience and dedication that would probably be more entertainingly spent elsewhere.
In summary, I'm doubtful of this scenario.
Or just drop a probe (Score:2)
Why not just drop a probe in orbit after they dump the cake mix? E.T. phone home...
It's a heck of a lot easier, plus NORAD probably can't even detect them today. Heck, we can barely find grazing asteroids. Stick one at a LaGrange point, and I doubt we'd ever see it.
Re:He ignores one possible solution... (Score:1)
The way I like to look at it... (Score:3, Interesting)
1) Faster-than-light (FTL, warp, whatever) travel is possible, and nobody's invaded us because there's some overarching federation of planets that's keeping us protected from outside influence until we're ready, and that's way cool.
or
2) FTL travel is not possible, and so nobody's coming here 'cause it's just not worth the trip. And that's depressing as hell.
Am I missing anything?
Re:The way I like to look at it... (Score:2)
I think that is the most likely explanation. No civilizations make routine interstellar trips simply because it is so expensive.
-- Bob (hoping for another revolution in physics...)
Re: (Score:1)
What is 'time' (Score:2, Interesting)
Pioneer [animelyrics.com]
FTL travel. (Score:3, Insightful)
Actually, our existing understanding of physics suggests several interesting possible approaches to FTL travel. These are already being studied to some extent; time will show whether they're practical or not.
We also have enough gaps in our understanding to leave room for potential methods of FTL travel. We just know that it isn't terribly easy, if it is possible.
I think that is the most likely explanation. No civilizations make routine interstellar trips simply because it is so expensive.
That's one possibility.
Another is that life is uncommon enough that even frequent-FTL-travelling civilizations wouldn't be near enough to us to have found us.
Another is that the active lifetime of civilizations tends to be short enough that nobody happened to be alive (or at least interested in contacting people) during our history to contact us.
Or a combination of the above.
It will be interesting when we finally have enough information to be reasonably sure which is the case.
Re:The way I like to look at it... (Score:2, Interesting)
A href=http://www.metaresearch.org/cosmology/gravit
Way cool stuff.
Re:The way I like to look at it... (Score:1)
Speed of Gravity [metaresearch.org]
Re:The way I like to look at it... (Score:1)
gravity propogates at the speed of light but contains velocity and acceleration dependent terms (as it would have to to satisfy relativity)
Re:The way I like to look at it... (Score:2, Informative)
The most amazing thing I was taught as a graduate student of celestial mechanics at Yale in the 1960s was that all gravitational interactions between bodies in all dynamical systems had to be taken as instantaneous. This seemed unacceptable on two counts. In the first place, it seemed to be a form of "action at a distance". Perhaps no one has so elegantly expressed the objection to such a concept better than Sir Isaac Newton: "That one body may act upon another at a distance through a vacuum, without the mediation of any thing else, by and through which their action and force may be conveyed from one to the other, is to me so great an absurdity, that I believe no man who has in philosophical matters a competent faculty of thinking, can ever fall into it." (See Hoffman, 1983.) But mediation requires propagation, and finite bodies should be incapable of propagate at infinite speeds since that would require infinite energy. So instantaneous gravity seemed to have an element of magic to it.
The second objection was that we had all been taught that Einstein's special relativity (SR), an experimentally well established theory, proved that nothing could propagate in forward time at a speed greater than that of light in a vacuum. Indeed, as astronomers we were taught to calculate orbits using instantaneous forces; then extract the position of some body along its orbit at a time of interest, and calculate where that position would appear as seen from Earth by allowing for the finite propagation speed of light from there to here. It seemed incongruous to allow for the finite speed of light from the body to the Earth, but to take the effect of Earth's gravity on that same body as propagating from here to there instantaneously. Yet that was the required procedure to get the correct answers.
These objections were certainly not new when I raised them. They have been raised and answered thousands of times in dozens of different ways over the years since general relativity (GR) was set forth in 1916. Even today in discussions of gravity in USENET newsgroups on the Internet, the most frequently asked question and debated topic is "What is the speed of gravity?" It is only heard less often in the classroom because many teachers and most textbooks head off the question by hastily assuring students that gravitational waves propagate at the speed of light, leaving the firm impression, whether intended or not, that the question of gravity's propagation speed has already been answered.
Yet, anyone with a computer and orbit computation or numerical integration software can verify the consequences of introducing a delay into gravitational interactions. The effect on computed orbits is usually disastrous because conservation of angular momentum is destroyed. Expressed less technically by Sir Arthur Eddington, this means: "If the Sun attracts Jupiter towards its present position S, and Jupiter attracts the Sun towards its present position J, the two forces are in the same line and balance. But if the Sun attracts Jupiter toward its previous position S', and Jupiter attracts the Sun towards its previous position J', when the force of attraction started out to cross the gulf, then the two forces give a couple. This couple will tend to increase the angular momentum of the system, and, acting cumulatively, will soon cause an appreciable change of period, disagreeing with observations if the speed is at all comparable with that of light." (Eddington, 1920, p.94) See Figure 1.
www.metaresearch.org/cosmology/speed_of_gravity.a
Crazy stuff.
Re:The way I like to look at it... (Score:1)
Please critique this if you're still inclined:
If gravity and light originate simultaneously at the same source (e.g., the Sun) and propagate to the same target (e.g., the Earth) at the same speed (e.g., c), then aberration will be the same for both. (That is because tan (aberration) = vorbit /Vpropagation
where vorbit is the transverse orbital speed of the target body and
Vpropagation is the propagation speed of field regeneration. Approximately,
aberration vorbit /Vpropagation.) Therefore, gravity and light should produce 3-space accelerations in the same direction (or exact opposite direction, if push and pull are reversed), differing only in magnitude by a scaling constant. Specifically, the momentum transferred to or removed from the target to produce the acceleration is some constant
(usually a mass) times
Vpropagation, a vector, in both cases.
The only physical way to break this equality would require postulating some source of the momentum transfer other than, or in addition to, the propagation speed of the field. Such a postulate would seem to constitute new physics, and would appear to be in trouble with the causality principle because radial forces from the source mass are already spoken for. In the absence of any serious such proposal for a new force, and given that gravity and radiation pressure do not produce anti-parallel forces in experiment (4), one of our premises must be violated. The only premise open to question is the equality of propagation speeds of the two types of force. If gravity propagates very much faster than light, all experimental evidence is immediately satisfied.
We see that all relevant characteristics except possibly field propagation speed are common for the two types of force. Therefore their physical propagation behavior ought to be the same if field propagation speed is the same, or different if field propagation speed is different, because there is nothing else relevant that might distinguish the two types of force. Experiments show without ambiguity that the resulting accelerations are applied in different directions, which implies different field propagation speeds.
To clarify, note than an accelerating target is necessarily changing its momentum vector. Momentum is the product of mass times velocity (or energy over c2 times velocity, if the projectile is massless) for whatever "projectile" carries the force from source to target. The "velocity" in the momentum is the velocity vector of the carrier, whose direction of travel is along the radial from source to target. Because the momentum is necessarily directed along the radial direction, no part of the exchanged momentum could be applied in some other direction. Specifically, if the projectiles are photons and the force is radiation pressure, the target is pushed in the direction of the arriving photons. Whatever is the mechanism of gravity, how could the direction of its pull be other than along the radial to the source mass? The physics and the meanings of words such as "momentum = mass times velocity" dictate only a single possibility for the vector direction of momentum transfers: the radial direction between source mass and target body. And if that is true, the only physical way left to explain the different effective direction of the force is a different propagation speed for a retarded field.
The same remarks apply to electrodynamic forces between charges. If the field propagation speed were lightspeed, we would be forced to interpret the momentum transfers as applied in a different direction from the direction of travel of the momentum carriers because of aberration. That is why, when the details are examined closely, we hear statements such as "virtual 'photons' (the hypothetical carriers of electrodynamic forces, not to be confused with real photons) travel at infinite speeds". So this "lightspeed propagation" assumption is unphysical and unnecessary. One can have the same equations (to the accuracy of observations) and interpret them in a physically consistent way if the momentum carriers travel much faster than light.
Now that we know that Lorentzian relativity is experimentally viable [18 [slashdot.org]] and allows faster-than-light (ftl) propagation in forward time [19 [slashdot.org]], ftl propagation is no longer forbidden in physics, and ftl force carriers are the most reasonable interpretation of the equations. I expect that no one would ever have thought otherwise if they had not mistakenly believed that ftl propagation was forbidden in physics.
If the field around a charge propagated with lightspeed delays, then Maxwell's equations would be wrong because they neglect transverse aberration, the main manifestation of field propagation delay. The fact that the equations are correct to first order in v/c tells us that the field propagation speed must be very fast compared to lightspeed, because the neglect of transverse aberration is the logical equivalent of adopting infinite field propagation speed. If Maxwell's equations did work for fields propagating at lightspeed, then they would work for radiation pressure from light fields too, which they do not. If the field has a measurable delay in reshaping itself to register the motion or acceleration of its source, then one would need to add propagation delay into Maxwell's equations (for example, by taking partials with respect to retarded coordinates instead of instantaneous coordinates). The absence of such propagation delay in the equations means that instantaneous propagation of fields is already built in.
Carlip's paper
In the geometric interpretation of GR, gravity is not a "force" and cannot propagate because target body motion simply follows a curved geodesic path through "space-time" without any force acting. Experiment (5) disputes the possibility that this forceless interpretation of gravity could be correct. So does the dependence of the full GR equations of motion for a target body on that body's own mass. Both are failures of the weak equivalence principle - the notion that "gravity is just geometry".
In his paper [15], Carlip recognizes the concept of gravitational force, as in the field interpretation of GR. But he claims that the experiments (1)-(4) are not direct propagation speed measurements for gravity. They are, however, measurements of aberration or v/V, where the only unknown is the speed of gravity, V. This makes Carlip's point semantic because the "indirectness" of these measures is not significant.
Carlip claims that we have made an implicit assumption that gravitational acceleration is central and has no velocity-dependent terms. If aberration were non-zero, the acceleration would be non-central. However, observations all confirm that it is in fact central to order v/c; i.e., directed along radials from the source mass. GR implies that gravitational acceleration is target-body-velocity dependent at order v2/c2, as shown in equations (2) and (4); but velocity-independent to order v/c. It is also source-mass-velocity dependent in some of the small terms we omitted. However, all these velocity-dependent terms are typically orders of magnitude too small to cancel the aberration term if V = c. So Carlip's point is again irrelevant to this discussion because no velocity-dependent terms exist at first order in v.
If one never considers genuine retardation of propagation between source mass and target body, then infinite propagation speed for gravity is being assumed, whether one says so or not.
Carlip considers his key starting point to be his equation (1.8). Its first term, proportional to ni, represents the transverse aberration. The second term, proportional to vi, cancels this transverse aberration to first order. Similarly, in the GR part of the paper, the corresponding equation where this cancellation occurs is (2.2). These two formulas are the only places where transverse aberration enters Carlip's discussion. However, the alert reader will see that Carlip is beginning with a force vector that points closely toward the true, instantaneous position of the source (to first-order in v), when he should be beginning with a retarded position. In other words, he assumes what he proposes to demonstrate. Obviously, a vector toward the instantaneous source position can be decomposed into an arbitrary pair of component vectors. So it is unremarkable that Carlip decomposes the instantaneous position vector into a retarded position vector plus an update vector for motion during the propagation delay. This merely creates the illusion that he has begun with a retarded position vector, when in fact he has begun with a (nearly) instantaneous position vector formed of two components.
By omitting transverse aberration, Carlip (like many before him) has effectively adopted a field propagation speed . No physical or observational basis exists for postulating V = c.
Re:The way I like to look at it... (Score:2)
Re:The way I like to look at it... (Score:3, Insightful)
Anyone can come up with all sorts of a sci-fi explanations to dispute this (let me try - aliens put a space beacon on any planet, which activates when there is life created, so that's how they knew about us so soon), but overall, the article makes several well-stated and well-supported points.
Re:The way I like to look at it... (Score:2)
...
Anyone can come up with all sorts of a sci-fi explanations to dispute this
I assume, basically, that if FTL travel is possible, then at least one of these advanced civilizations will eventually wander by us, sometime, somehow. Maybe an annual (for some interplanetary definition of the word) survey of systems with life-supporting planets. Remember, I'm assuming very low cost for the travel on that survey.
So, I suppose there's a third possibility -- FTL travel is possible, but nobody's invaded us because nobody's noticed us yet. So, hopefully, by the time we *get* noticed, we'll have developed sufficient shielding to withstand the Romulan onslaught. But if they're nearby, we'll be wiped out and/or enslaved, which is also really depressing.
So, then, my modified conjecture points to a 67% requirement for depression when thinking about FTL travel and aliens visiting us.
Dang. I gotta stop posting from work.
Bombs-to-starships gap (Score:2)
Even today with the paltry stuff we practice, space travel is horribly energy-intensive. While it's believable that we'll get more efficient, we still don't have much interplanetary travel, much less interstellar. We will have to acquire the ability to control more energy.
My premise: If a species has more than the slightest tendancy to use weapons against itself, it will not survive to build starships. That includes us. We have the next few centuries to burn some of our most terrible aggressiveness out of ourselves, or else we'll use that same energy to blow ourselves up. Actually, the Cold War was a great success story, since we *did* develop a survival mechanism that held us through half a century. We've more work to do, because greater energies are on their way, with more chance for abuse. Moreover we've got to improve the common man, as rather common men turned relatively safe transportation devices into bombs last year.
One hole in the theory - alien psychology such as a highly xenophobic hive-mind.
The problem with this is ... (Score:3, Informative)
I can find good arguments for both why or why not other worlds may have life or intelligent life.
-Sean
Bit unimaginative. (Score:4, Interesting)
Such a system could cover the entire galaxy in a couple of million years easily (and cheaply after initial design/construction cost). They can do whatever you like; sit and watch, make contact, try to destroy any competitors (The Forge of God [gregbear.com] style; soon to become a set of movies [gregbear.com], yay), and call home (since you end up with a network of them; sure, it'll take a while to get back home, but it's one hell of a cheap way to learn an awful lot about the galaxy).
Given that it only takes one civilization to have done this, and given that our solar system is probably quite interesting given it's layout, I wouldn't put too high odds on there NOT being such a device hanging around near here.
Re: (Score:2, Funny)
Re:Bit unimaginative. (Score:1)
Re:Bit unimaginative. (Score:2)
There is, unfortunately it's buried under a ton of asteroid dust on the far side of the moon. We need to send another moon mission to dig it up. It should be rather easy to find, since its such a large magnetic anomaly.
Re:Bit unimaginative. (Score:3, Funny)
Re:Bit unimaginative. (Score:2)
Self-replicating? Yes.
Intelligent? I'm yet to see any evidence of this.
Re:Bit unimaginative. (Score:1)
What makes us sentient ? (Score:2)
This is not strictly speaking true evolutionary science has a pretty good hypothesis.
Evoloution is a balance between Natural Selection (survival) and Sex Selection (propagation). When a species achieves top carnivore status it is no longer predated it become possible to seek out alternative strategies. Natural selection become relatively less important than sexual selection. One such strategy is the development of intelligence, communications ability, even altruism. In the same way that Natural Selection can cause an arms race, Sex Selection drives a similar race in intelligence, communications ability and altruism.
A similar features appear in many top carnivores, Whales and African Wild Dogs for two examples exhibit a very high intelligence, unusual communication abilites and altruism.
Re:Bit unimaginative. (Score:1)
You mean like God when he made man? Or maybe it was the monolith ;-)
A lot of strange assumptions in that article. (Score:2)
However, if they do have the resources to do this, then it would be reasonable for them to be able to set up monitoring stations all over the galaxy (in the space of a few million years) to listen for the radio signature of a new intelligent civilization popping into existance (ours, sadly, was Adolf Hitler). Said monitoring station would use whatever technology allows them to exceed the speed of light, and send a message back to their home base letting them know that somebody just invented television.
After that, the aliens hop into their little flying saucers, head for earth, abduct people, and probe their nether regions.
At any rate, the article is bunk, because the assumptions it takes are a bit too selective, and it fails to explore some very obvious possibilities.
Wrong numbers... (Score:2, Interesting)
I thought the most popular view was that they have been visiting for thousands of years... depicted in writing and art all throughout history...
That's 55 years in a planetary history of 4,600,000,000 years.
What about their planet's history? It's possible that they havent been able to travel to other planets for that entire time... more like a couple thousand years? Then the ratio is more realistic. (I just love misleading journalists...)
it implies that there have been millions of expeditions to Earth! We may send the occasional anthropological research team to Borneo, but we don't send millions.
Think ratio and intrest... first, it doesn't emply millions (how long have they been able to get here?
And it's a lot easier to get to Borneo than to traverse hundreds or thousands of light-years.
Before our technology developed, we couldn't even get across the damn ocean... so boreno would be a pretty hard place to get to for us thousands of years ago (...from the US). It's probably pretty easy for them to traverse "hundreds of thousands of light-years".... if they even have to go that far. I doubt they come from the other side of the galaxy...
Let's set aside the question of whether advanced galactic societies would have the slightest interest in our wars, our pollution problems, or our reproductive systems.
Why do you think humans research organisims on our own planet? We even hold a great interest in organisims at the bottom of the sea where we thought that life couldn't exist... We're different from them, and they have a hunger for knowledge...
The real question is, how would they know about us at all?
...telescopes? Passing by one day? Sub-atomic microtransponder galactic scanners that they have and we havent even imagined up yet? There are plenty of ways to find us...
I'd comment on the microwave signals we've sent out and your opinion on that... but there are other ways of them knowing we're here... (that takes care of about 3 paragraphs)
One sided journalism gets to me... so now I had to go and balance it out...
Re:Wrong numbers... (Score:2, Informative)
What about their planet's history? It's possible that they haven't been able to travel to other planets for that entire time... more like a couple thousand years? Then the ratio is more realistic. (I just love misleading journalists...)
How do you know that there are any appreciable number of space-faring civilizations that have developed in the past few thousand years. Our sun is probably a second, maybe third or more, generation star. Many billions of years have gone by. After the first few billion, one would expect life to start reaching towards our level of complexity. That makes the chance of near-by systems developing high speed space travel nearly synchronized with our own technological revolution highly unlikely. This isn't like Star Trek where hundreds of civilizations all start developing warp drive around the same time. What you are saying is just as unlikely as the point the article was trying to make. Read Contact, that one is more likely.
Re:Wrong numbers... (Score:2)
Having civilizations grow up and be technologically off by a couple thousand years isn't that far fetched. Take nebulas (the "great pillar" nebula that is starting to fade because planets/stars are forming). The solar systems within there are forming within the same time frame... there have to be star systems that are about the same age as eachother and are pretty close by...
Even getting to the "micro" evolution of the planets... we (or a different organism on this planet) could have had technology to launch ourselves into space millions of years ago (which would throw off the "millions of years" timeframe from Contact to a couple thousand...) if the dino's didn't go extinct (assuming that evolution would continue and form a sentient being)...
Of course it is possible that other civilizations have looked at earth billions of years ago, but how likely is it that the same civilization is still around, doing the same old thing? The author assumed in his "numbers" that it was the same... but new ones could be popping up every thousand years or so...
Re:Wrong numbers... (Score:2)
Ofcourse this assumes complex chemistry is required for life. I think this is a fairly good assumption.
The Score (Score:1)
Actual Cold, Hard Evidence = 0
Math Nerds REJOICE!
Science Geeks LAUGH!
Re:The Score (Score:1)
abuse of mathematics (Score:2, Insightful)
It makes little sense to calculate the probability of something that has already occurred. If we have been visited (and as a self-described space nut, I'll admit I find the possibility positively knee-weakening), then that stands as evidence on its own that our being visited is possible.
I have heard similar arguments for why the end of the human race is very near. The reasoning goes, that since the human population is always growing, it is more probable that I would be born in the 20th century than in any century prior. But wouldn't it then be even more probable if I were born in the 25th century? In fact, the chances of my being born in the 20th century would be vanishingly small. Therefore, it is safe to assume that there will be no people in the 25th century.
You can prove nearly any crazy idea with this kind of "thinking."
Re:abuse of mathematics (Score:1)
The probability that you were born in the 20th century is either 0 or 1, since that particular event has already occured, so we should introduce a randomly selected human into the dialogue.
If a person (let's call him X) is chosen at random from the set of all people who have ever or will ever live on the earth, the probability that X was born in the 20th century is greater than the probability that he was born in any particular earlier century, since the 20th century saw more births than any previous century.
But wouldn't it then be even more probable if I were born in the 25th century?
Assuming that the 25th century will have more births than any previous century, X would have a higher probability of being born in the 25th than in any previous century.
In fact, the chances of my being born in the 20th century would be vanishingly small.
Hmmm. The problem goes back to the premise that the human population is always growing. This cannot continue to be true forever. It will eventually have to level off because the Earth only has enough resources, space, etc to support a finite number of people (which also limits the number of births possible in a given century). Also note that the number of centuries that humans will populate the earth (call it N) is finite.
This implies some important stuff about the probability distribution of which century X was born in. The probability distribution is discrete. Thus each century has a positive probability of being the century of X's birth.
If N is large enough for the population to level off, then the probability distribution must level off too. Although the probability that X was born in the 20th century could be made arbitrarily small, the proportion
(Probability X is born in 20th century)/(Probability X is born in nth century)
where n is any century in the distant future has a positive bound. In other words, the probability that X is born in the 20th century isn't so much smaller than the probability that x is bron in the 25th that it can be discounted.
Another hole (Score:1)
Perhaps "They" visited us some time ago, and decided the planet was interesting. This decision may have occurred millions of years ago; scientific optimism aside, I have a hard time swallowing the idea that Earth is a perfectly normal, usual planet with nothing exceptional about that fact that it is teeming with billions of varieties of life. So they leave themselves a probe that can be triggered by something, probably the same radio signals that everyone points out. (Detectable, and much easier to be certain of intelligent origination then nuclear blasts, which can look an awful lot like asteroid strikes from far away. You can do signal analysis on the radio...)
Then they pushed a grant through the Galatic Science Foundation, hopped into their FTL spacecraft, came here, and started anally probing lots and lots of drunk and mentally distrubed people.
Don't believe in aliens myself, but this scenario is a major gaping hole in the article. In fact, any intelligence half as curious as us would need some good reason not to leave a probe around something as interesting as Earth...
Re:Another hole (Score:1)
Re:Another hole (Score:2)
And even if it is perfectly common... so what? An advanced civilization would still leave a probe, just to see if anything interesting happens. It's not like a probe is very expensive on their terms.
Think like a scientist... Earth doesn't have to be interesting, just potentially be interesting at some point in the future. That's why I say it could have happened millions of years ago.
So how common is life in the universe? (Score:4, Interesting)
Aliens visit us all the time. (Score:2, Funny)
One in California bred with a dog, and a Chupa pup is wreaking havoc in Massachusetts.
http://www.uncoveror.com/chupa.htm
http://www.
http://www.uncoveror.com
http://www.uncoveror.com/chupa4.htm
They have attacked us with Solaranite.
http://www.uncoveror.com/invaders.htm
The Air Force and NASA know it, and are covering it up!
http://www.uncoveror.com/ufos.htm
http://www.u
http://www.uncoveror.co
http://www.uncoveror.com/zhtitikofft.
And we got UNIX from the computers on the Roswell UFO! Microsoft has even used this alien technology.
http://www.uncoveror.com/aliens.htm
http://www
We report this stuff on The Uncoveror all the time, but people still don't seem to know about it!
(music)It's my website, ans I'll deep-link if I want to!(/music)
Or.... (Score:1)
Here we go again (Score:1)
1) Detection--there must be a way, not necessarily technical, to determine from afar that Earth is of some interest to visit--random discovery just doesn't cut it in terms of a very large universe, and
2) Means--it must be possible to get here from there. This implies a way around special relativity or its disproval, or it implies close physical proximity, a case ignored by most researchers since Donald Keyhoe claimed there were aliens based under the surface of Mars.
Those two conditions are both necessary and sufficient to guarantee the presence of aliens on Earth. Everything else is just blowing smoke rings.
Is that the interesting question? (Score:2)
I suppose I wonder what void does this willingness to believe in E.T. fill? Does God seem remote and unbelievible to some, and they have this need to believe in something greater? Or does it flow from our secret belief that we are infinitely fascinating and deserving of attention? Now that we know our tiny blue home isn't the geographic center of the universe are some people trying to reinvent it as the social center?
spurious reasoning (Score:2)
The age of the earth doesn't matter for this kind of calculation. What matters is the propensity for space travel of aliens, the duration of trips, the prevalence of earth-like planets, the expected lifetime of spacefaring civilizations, and the ability of aliens to detect earth-like planets.
Re:spurious reasoning (Score:1)
We didn't visit the moon right at the same time a moon-sivilisation started to use electric signals and the like.
The whole point of the article was, that the aliens apparently visited us within the last 55 years, when we got technically adept.
(But then, as someone else pointed out, yes, the aliens could have vizitied 25 milion years ago, and left a probe, that started sending signals when man evolved)
Re:spurious reasoning (Score:2)
Yes, and the whole point of the article was wrong. If aliens visit at random, they are a Poisson process, and the number of visits you see depends only on length you observe. Civilization, using electricity, etc., enhances the probability of visits over the past 55 years.
it's a Poisson process at worst (Score:2)
It is true, of course, that if we see, say, 1 visit per year (the same spacecraft flying around the planet a few times, resulting in many sightings), there must have been 1 million visits over the last million years, but so what? A million years is a long time.
Of course, more likely, aliens pick planets to visit based on whether they might harbor interesting life forms, which means that the frequency of visits probably has increased greatly over the last hundreds of millions of years.