Post #391,008
6/20/14 11:38:42 AM
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Are we alone in the universe?
When confronted with the topic of stars and galaxies, a question that tantalizes most humans is, “Is there other intelligent life out there?” Let’s put some numbers to it (if you don’t like numbers, just read the bold)—
As many stars as there are in our galaxy (100 – 400 billion), there are roughly an equal number of galaxies in the observable universe—so for every star in the colossal Milky Way, there’s a whole galaxy out there. All together, that comes out to the typically quoted range of between 1022 and 1024 total stars, which means that for every grain of sand on Earth, there are 10,000 stars out there.
The science world isn’t in total agreement about what percentage of those stars are “sun-like” (similar in size, temperature, and luminosity)—opinions typically range from 5% to 20%. Going with the most conservative side of that (5%), and the lower end for the number of total stars (1022), gives us 500 quintillion, or 500 billion billion sun-like stars.
There’s also a debate over what percentage of those sun-like stars might be orbited by an Earth-like planet (one with similar temperature conditions that could have liquid water and potentially support life similar to that on Earth). Some say it’s as high as 50%, but let’s go with the more conservative 22% that came out of
a recent PNAS study. That suggests that there’s a potentially-habitable Earth-like planet orbiting at least 1% of the total stars in the universe—a total of 100 billion billion Earth-like planets.
So there are 100 Earth-like planets for every grain of sand in the world. Think about that next time you’re on the beach.
Moving forward, we have no choice but to get completely speculative. Let’s imagine that after billions of years in existence, 1% of Earth-like planets develop life (if that’s true, every grain of sand would represent one planet with life on it). And imagine that on 1% of those planets, the life advances to an intelligent level like it did here on Earth. That would mean there were 10 quadrillion, or 10 million billion intelligent civilizations in the observable universe.
Moving back to just our galaxy, and doing the same math on the lowest estimate for stars in the Milky Way (100 billion), we’d estimate that there are 1 billion Earth-like planets and 100,000 intelligent civilizations in our galaxy.[1]
SETI (Search for Extraterrestrial Intelligence) is an organization dedicated to listening for signals from other intelligent life. If we’re right that there are 100,000 or more intelligent civilizations in our galaxy, and even a fraction of them are sending out radio waves or laser beams or other modes of attempting to contact others, shouldn’t SETI’s satellite array pick up all kinds of signals?
But it hasn’t. Not one. Ever.
Where is everybody?
http://waitbutwhy.com/2014/05/fermi-paradox.html
Satan (impatiently) to Newcomer: The trouble with you Chicago people is, that you think you are the best people down here; whereas you are merely the most numerous.
- - - Mark Twain ÂPuddÂnhead WilsonÂs New Calendar, 1897
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Post #391,010
6/20/14 12:10:07 PM
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Several things have been pointed out.
Powerful broadcast signals probably have a very short window. Powerful broadcast is already fading here, after less than 100 years, as more efficient carefully directed low power beams and cable based networks take over.
Some entities may feel that trying to call attention to themselves in an unknown universe may not be a wise thing to do, and others may be far more interested in their yoga classes.
Significant evolution depends entirely on sexual reproduction. How likely it is for primitive microbes to develop the joys of sex is totally unknown, but this single factor could greatly reduce the possibility of intelligent life in the universe.
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Post #391,022
6/20/14 5:45:15 PM
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dang, I wanted to open up an intergalactic brothel.
Any opinions expressed by me are mine alone, posted from my home computer, on my own time as a free American and do not reflect the opinions of any person or company that I have had professional relations with in the past 59 years. meep
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Post #391,026
6/20/14 7:17:34 PM
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Excellent points. Thanks.
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Post #391,028
6/20/14 7:29:58 PM
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Perhaps the noisy ones end up dead.
Regards,
-scott
Welcome to Rivendell, Mr. Anderson.
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Post #391,031
6/20/14 8:31:13 PM
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Yup, thirteen Billion Years+ of inter-galactic crap-shoots and
our species remains Undecided.. as to whether? or not? it could dispense with a few trillion toys, sorta
(at very least: replacing most-All of these with something/something using μWatt-hours.. for a start.)
OR
Keep adding more stuff exponentially, get roasted and die along with most mammals (and an unknowable roster of others.)
Tough Choices! there: anyone wonder which branch we'll go with? I mean.. {sniff} -- just ONE Veyron in a museum and no more vacation-plane-filled skies?
(Me? I'm hoarding Jack Armstrong Tru-flite™ model (paper) airplanes (© 1944) to be cut-out in caves, via fire-fly light.)
Bet I can trade one for a whole flagon of warm Merlot.. or some finely marinated insect-stew.
er, Carrion
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Post #391,032
6/20/14 8:45:46 PM
6/21/14 1:16:06 AM
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It's easy to forget how huge the Universe is...
Yeah, the numbers of planets is huge. But they're really, really, really far apart. The fastest spacecraft at the moment is probably Voyager 1 at 17 km/s. The speed of light is roughly 300,000 km/s. The closest Earth-size planet found around another star thus far is 493 light years away. It would take Voyager 1 a long time to get there: 493 * 300,000 / 17 = 8.7 million years. It takes a lot of energy for significant mass to go fast. Unless practical controlled fusion or some other similar power source is available, the distance are simply too vast to get there because there isn't enough power. What about radio and so forth? 1/r^2 is a killer. Signal power drop off at that rate. Double the distance and the signal strength drops by a factor of four. 100,000 watts is a lot for a US radio station. That's 80 dBm (dB relative to 1 mW). The minimum relatively easily detectable signal is -192 dBm (at 4K in space) - a ratio of 272. Increasing power by a factor of 10 increases the dBm value by an addition of 10. So some quick math with a dBm calculator gives (ignoring all losses and only considering the 1/r^2 falloff): 100,000 W --- 80 dBm --- distance = 1 25,000 W --- 74 dBm --- distance = 2 6,250 W ----- 68 dBm --- distance = 4 1,563 W ----- 62 dBm --- distance = 8 So each doubling of distance cuts the dBm by 6. 0.0000000000000000000001 W is -190 dBm. 80 + 190 = 270 / 6 = 45 doublings. 2^45 = 3.5E13. So if you're in space receiving 100,000 W at 1 km from the transmitter, you would be at the minimum detectable signal from that transmitter at 3.5E13 km = 3.7 light years. Anything farther away than that cannot be distinguished from noise. A factor of 4 in power only gets you a factor of 2 in distance, so it gets expensive quickly... So the other civilization would need a big-honking transmitter to have any hope of another planet around another star detecting any radio signal they transmit. Note that lasers have the same 1/r^2 falloff. Their advantage is they're directional, but that didn't affect the calculation above (I assumed I was detecting all of the power at the starting distance). Basically, you're painting the inside of a balloon. As the balloon gets bigger, the thickness of the pain[t] has to fall - less power. With luck, there aren't too many errors in this - that would be embarrassing. ;-) Bottom line: We may not be alone, but we're very unlikely to ever have contact with anyone else so we might as well assume we are (though looking and listening is not a worthless endeavor). [edit:] Missing [t] Cheers, Scott.
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Post #391,034
6/20/14 10:09:33 PM
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Some assumptions lurking in that.
It skips over the odds of other planets developing life and also the odds of life developing to a point at a time where we could detect it. One percent sounds small, but there are just no reasons supplied for that estimate. In the scales of the other numbers thrown around, one percent is enormous.
Wade.
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Post #391,042
6/21/14 8:20:59 AM
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I am reminded of a cartoon of two ants...
One is telling the other "We have been searching all the known pheromone trails for generations and found nothing! We are clearly alone."
We might just be missing the galactic obvious. Or maybe the ones that can talk over light years don't want to chat with juvenile brats on Facebook. "Religion, n. A daughter of Hope and Fear, explaining to Ignorance the nature of the Unknowable."
~ AMBROSE BIERCE
(1842-1914)
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Post #391,044
6/21/14 8:42:21 AM
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:-) Yup.
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Post #391,047
6/21/14 11:11:18 AM
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This is my opinion as well.
I mean, if they are good enough to be able to detect us and to "look" and be able to hear our stuff...
No way would they be curious with our anatomy or our childish behavior.
IMO, if it we me and I saw the atrocities perpetrated by us in the last 3000 years... I'd just "move along nothing to see here" with my kids on vacation. --
greg@gregfolkert.net
"No snowflake in an avalanche ever feels responsible." --Stanislaw Jerzy Lec
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Post #391,052
6/21/14 10:03:54 PM
6/21/14 10:04:12 PM
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The Drake Equation
N = R(*) x f( p) x n(e) x f(l) x f(i) x f(c) x L
N = the number of civilizations in our galaxy with which radio-communication might be possible (i.e. which are on our current past light cone);
and
R* = the average rate of star formation in our galaxy
fp = the fraction of those stars that have planets
ne = the average number of planets that can potentially support life per star that has planets
fl = the fraction of planets that could support life that actually develop life at some point
fi = the fraction of planets with life that actually go on to develop intelligent life (civilizations)
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = the length of time for which such civilizations release detectable signals into space
Edited by gcareaga
June 21, 2014, 10:04:12 PM EDT
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Post #391,059
6/22/14 3:25:06 PM
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Heard Carl Sagan explain it on stage in LA back in 1974.
We've come a long way baby! At least with n(e). Too bad he did not get to see the recent developments. I don't recall a specific number, but his estimates at the time were way low. Alex
"There is a cult of ignorance in the United States, and there has always been. The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that "my ignorance is just as good as your knowledge."
-- Isaac Asimov
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Post #391,060
6/22/14 4:07:49 PM
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From the source
I heard Frank Drake explain it in class in 1986.
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Post #391,063
6/22/14 4:53:53 PM
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Indeed the source!
Alex
"There is a cult of ignorance in the United States, and there has always been. The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that "my ignorance is just as good as your knowledge."
-- Isaac Asimov
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Post #391,069
6/22/14 5:50:21 PM
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Missed opportunity
When I heard the equation, it was just something else to remember long enough to regurgitate it onto an exam. I wish I had had the foresight to think to ask this question.
When Drake created the equation, I think there was a mid-century assumption bias that technologically advanced civilizations would be immortal (the civs if not the constituent biologicals). What about an extinction rate? Yeah, it could be partially accounted for in L, but I think it rates its own variable. Maybe c really is a hard wall and macro-biological travel across the gulf of stars is impossible. If this is the case, home stars will will eventually die, violently or slowly in the case of the sub-fusion brown dwarves.
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Post #391,070
6/22/14 6:10:42 PM
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Re: advanced civilizations would be immortal
I distinctly recall Sagan mentioning civilizations doing away with themselves because of some stupid act.
Frankly, between folks seeking rapture and those seeking 72 virgins, it's becoming an ever more probable event. Alex
"There is a cult of ignorance in the United States, and there has always been. The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that "my ignorance is just as good as your knowledge."
-- Isaac Asimov
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Post #391,071
6/22/14 6:46:10 PM
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Re: advanced civilizations would be immortal
It shouldn't be binary; all cigs endure or all perish. Okay, well maybe the latter, but if so what is the lifespan? Need a variable even if it is a blind guess.
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Post #391,072
6/22/14 7:16:11 PM
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Thanks for reminder 'extinction rate', also that bias.
Clearly noted (now!) re, in '50s: strong presumption that Techno implicitly could solve any problem ('you could parse in Boolean?' they may have meant; the smarter ones, anyway.)
My 'institute' was certainly rife with such bubbly optimism.
But for those not up to Drake's eqn., Sagan's audience: I thought he did a decent task of conflating such missing-parts? into that ominous phrase about
(Our!) tendencies to commit seppuku in the name of any number of cockamamie rationales.
(As with 'I.Q.' too..) I doubt that any number in an equation could capture such a species-wide defect, into some Probability #.
Besides if that blindness tracks "IQ", we're certainly doomed to a death of un-Natural kind, anyway.
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Post #391,286
6/29/14 11:31:29 PM
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Apparently Fermi had a version, too.
http://praxtime.com/2013/11/25/sagan-syndrome-pay-heed-to-biologists-about-et/A good starting point is Stephen Webb’s book “If the Universe Is Teeming with Aliens … WHERE IS EVERYBODY?: Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life.” It’s a fun romp through the history of the Fermi Paradox. From page 23: “it was a 1975 paper by Michael Hart in the Quarterly Journal of the Royal Astronomical Society that sparked an explosion of interest in the paradox. Hart demanded an explanation for one key fact: there are no intelligent beings from outer space on Earth at the present time.” Hart’s explanation was “we are the first civilization in our Galaxy.“
Hart’s 1975 paper is short and clear, and worth a quick read. Hart runs various scenarios, but for me the key insight is one of time scale. It takes (only) millions of years for intelligent life to completely fill the galaxy, but billions of years for it to evolve. So first out the gate should be everywhere before second out the gate. Logically if ETs exist they should be here. And they aren’t. So case closed. The Fermi Paradox literature since Hart could arguably be characterized as nonstop special pleading to avoid a common sense conclusion. I hadn't seen this argument before: And as quoted in Mark A. Sheirdan’s book, we have eminent Evolutionary Biologist Theodosius Dobzhansky (“Nothing in Biology Makes Sense Except in the Light of Evolution“) joining the fray:
In his article Dobzhanksy turned Sagan’s argument on its head. Dobzhansky cited the fact that of the more than two million species living on Earth only one had evolved language, extragenetically transmitted culture, and awareness of self and death, as proof that it is “fatuous” to hold “the opinion that if life exists anywhere else it must eventually give rise to rational beings.”
Now we’ve nailed it. It’s Evolutionary Biologists versus Astronomers. :-) See the original for lots of embedded links. (via Sean Carroll on G+ - https://plus.google.com/u/1/118265897954929480050/posts/PCTANMoxvb3 ) Cheers, Scott.
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Post #391,597
7/6/14 5:02:56 AM
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Great material for honing the fringe of what-ifs? of more practical aims, maybe.
(Speculation is that the growth to 'sentient adulthood' (after the first denizens multiply) is as iffy as right-here contemporary problems.)
How do you accelerate from some basic sentient inroads towards (adult-level for that species?) Can we improve on the n-billions years postulate
--from scratch/microorganisms--> to a level capable of launching asexual-reproducing robots for exploration?
Or, let's go down quite a few orders-of-magnitude--you'd think that would be simpler, no?
How do you get.. already well-developed creatures, most often engaged in trying to emulate kittens-at-play -vs- doing any chores, (especially assigned-ones?)
like, oh say: cleaning the litter-box; then preparing for imminent days: calculated to become too-hot to be outside. (While you still can be outside.)
and also too--before your common foods have also wilted ... and a few thousand other things that aren't what you wished-for.
Obviously 'we' haven't the chops to solve That dilemma yet, judging by all the interest in 900 BHP 'street cars',
but not even 10 min./week checking out thermodynamics' effects on personal essential-Meatware.
$B Super-Ball jackpot for best MOTIVATIONAL posters!! (Super-Bargain if they work.)
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