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First consider the fact that the Deep Space Network could detect a cell phone if it were on Mars. Keep in mind that radio waves are of ridiculously low energy, so it doesn't take much energy to generate a massive quantity of them. So our transmissions that go in every direction are even powerful enough to reach at least some of the closer star systems.
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yes, im not denying that they could travel that far, but waves that begin with a fraction of a degree difference in travel could end up billions of km apart. so youd have to literally have to cover millions of trajectories to come even close to covering a significant portion of the sky we see.
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When I mentioned a cell phone, I implied that the waves go in all directions. The same is true for the big antennae used for radio and tv stations. (I may be mistaken since they might emit a donut of radiation, but it's still a large fraction of the sphere).
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oh, i see, i was mistaken. thanks for the correction.
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Is not drake equation purely whimsical?
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More like inadequate. A real Drake Equation would be extremely complex. And still generally useless.
Some useful links while MER are active. [url=http://marsrovers.jpl.nasa.gov/home/index.html]Offical site[/url] [url=http://www.nasa.gov/multimedia/nasatv/MM_NTV_Web.html]NASA TV[/url] [url=http://www.jpl.nasa.gov/mer2004/]JPL MER2004[/url] [url=http://www.spaceflightnow.com/mars/mera/statustextonly.html]Text feed[/url]
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The amount of solar radiation reaching the surface of the earth totals some 3.9 million exajoules a year.
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Useless.SETI may give something useful.
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I am told the Globe and Main featured the Drake equation Monday. This reminds me of the comments I exchanged on the old message board. The Drake equation predicts the existence of intelligent life that we can communicate with. The equation is:
N = R * fs * fp * ne * fl * fi * fc * L
R is the rate of formation of stars in the galaxy
fs is the fraction of stars that are suitable suns for planetary systems
fp is the fraction of those stars with planets (thought to be around
1/2)
ne is the number of "earths" per planetary system -- planets suitable for liquid water
fl is the fraction of those planets where life develops
fi is the fraction of planets with life where intelligence develops
fc is the fraction of those planets that achieve technology which releases detectable signals into space
L is the lifetime of such communicative civilizations
I choose to use a different formula, rather than dealing with rates of formation.
N = S * np * fe *fm * fl * fi * fc
S is the number of stars in our galaxy
np is average number of planets per star
fe is the fraction of planets in the ecozone -- capable of sustaining liquid water
fm is the fraction of planets with a magnetosphere - so it can hold onto its water
fl is the fraction of those planets where life develops
fi is the fraction of planets with life where intelligence develops
fc is the fraction of those planets that achieve technology which releases detectable signals into space
S - The number of stars in our galaxy has been measured fairly accurately: 400 billion.
np - The number of planets per star was estimated at 2: some have more (ours has 9 or 10, depending whether you call Quaoar a planet), some stars have none.
fe - The fraction of planets in the ecozone is more tricky; it depends on the size of a star, how hot it is, and the distance planets will form from the star. Our star has 3 planets in the ecozone, both Venus and Mars are within it. So for convenience let's use the fraction 1/3.
fm - Earth has a magnetosphere, and so do the gas giants, but Mercury, Venus, and Mars have a negligible magnetic field. It has been argued that Earth's strong magnetic field is due to our large moon, but most stars are quite small and planets close enough to a small star to remain warm may experience tides from their sun. For convenience, lets stick to the ratio in our solar system: 1/4 terrestrial planets. You could argue that Pluto is not a gas giant, but its not anywhere near the ecozone and we don't know if it has a magnetic field, so let's stick to 1/4.
fl - Life appeared on Earth as soon as conditions would permit life, so life may form everywhere it can. Radiometric dating estimates Earth is 4.65 billion years old, and the first archaea fossil is 3.5 billion years old, so life has existed for 75% of the age of the Earth so far.
fi - Intelligence is more rare. Life has existed on Earth for 3.5 billion years, but the oldest animal fossil is a jelly fish 680 million years old, the oldest vertebrate is 570 million years old, and the first mammal appeared 200 million years ago. The earliest humans ancestor was australopithecine, 4 million years ago. There are some fragments that show huminine diverged from apes about 5 million years ago, but none of those fragments have sufficient detail to assign a species. The evolutionary line that led to modern humans diverged from australopithecine about 2.5 million years ago. Rather than trying to guess which human ancestor was first intelligent, lets use 2.5 million years. 2.5 million / 3.5 billion = 0.00071
fc - The fraction with technology which releases detectable signals depends on how long a technological species survives, whether there is a better technology that does not release signals, and how long it takes to develop it. For convenience, lets use the time from the first radio on Earth until today. Guglielmo Marconi transmitted a signal from Cornwall, England to St. John's, Newfoundland, in 1901. 1901 to today is 102 years; divide that by 2.5 million and you get 0.0000408
Plugging in the terms you get: 400 billion * 2 * 1/3 * 1/4 * 75% * 0.00071 * 0.0000408 = 1,448
Last time I did this I got a much smaller number: around 32. You could add a term for the fraction of planets with life where multi-cellular life evolved (plants and animals), but that's implied in my estimation of intelligent life. You could add a fraction where catastrophes don't occur so often that significant evolution doesn't have time: for example a Jupiter-like planet to divert asteroids. You could add a term for the fraction of stars that have heavy elements in their accretion disk to form terrestrial planets. First generation stars will never have a terrestrial planet, the best they can hope for is a gas giant. Life cannot form from gasses alone; in addition to hydrogen it needs at least oxygen, nitrogen, and carbon. However; 1,448 is a small number in a galaxy of 400 billion stars.
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I found that I did miss something. I included a fraction for the number of planets that are the right distance from the sun so they are not too hot or too cold. However, I didn't include a faction for the number of terrestrial (solid) planets. Astronomers have discovered planets around other stars, but they are big planets so far because our technology isn't sensitive enough to detect small planets. However, they did discover a planet larger than Jupiter that is orbiting the same distance from its star as Earth. So gas giants can be close-in. I suppose a gas giant that distance could have a large moon which would develop life. Jupiter?s largest moon Ganymede doesn't have an atmosphere, nor Neptune's largest moon Triton, nor Uranus's largest moon Titania, but Saturn's moon Titan does. If we just include terrestrial planets large enough to hold an atmosphere, then our solar system has 3 out of 9. If we include moons then Jupiter and Saturn have so many that I've lost count, but most of them are small asteroids. If we count gas giant planets with at least one moon with an atmosphere then we have 1 in 4. If we say the fraction is either the number of planets that are solid and have an atmosphere, OR have at least one moon that is solid with an atmosphere, then the result is 4 out of 9. Or should we count Quaoar as a planet; then the fraction is 4 out of 10. Perhaps we should add up all the solid planets or moons that are large enough to be spherical (round), and count how many of those are solid with an atmosphere. That would include Earth's moon Luna, Jupiter moons Ganymede, Callisto, Io, and Europa, the Saturn moons Titan, Iapetus, Rhea, Dione, Tethys, and Enceladus, Neptune's moon Triton, and Uranus's moons Titania, Oberon, Umbriel, and Ariel. Saturn's moon Mimus and Uranus's moon Miranda are almost spherical but have heavy surface features so they're not quite. Images of Pluto and Charon are fuzzy, but new images are good enough to show them to be spherical. Pluto has a diameter of 2274km which makes it smaller than Mercury (4880km), and it's even smaller than Luna, Io, Europa, Ganymede, Callisto, Titan, and Triton. Charon is only 1172km diameter but that makes it comparable with Ariel at 1158km. Quaoar is about 1250km in diameter, so if we include Charon we have to include Quaoar. Ceres is the largest asteroid, and at 466km it is smaller than Miranda (472km). So if we add this list of 17 moons and 2 outer planets to the 4 inner planets and 4 gas giants, we get 27 objects. Only 4 of those 27 objects are solid with an atmosphere, so let's make the fraction of terrestrial planets ft = 4 / 27 = 14.8%.
I have discovered another reference that says the stone-age started 2.5 million years ago, when humans learned to make the first stone tools. It ended at different times in different locations of the world, but roughly 10,000 years ago. So I think we can use the 2.5 million year figure to estimate intelligence.
Recalculating the formula N = S * np * ft * fe *fm * fl * fi * fc = 214
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Another complication: our sun is a medium size star. However, most of the stars are small. As a rough rule of thumb, stars that are 1/10th the size of our sun are 10 times as numerous; stars that are 10 times the size are 1/10th as numerous. Most of the stars in our galaxy are smaller than ours. That means fewer planets per star, smaller planets, fewer moons, and less likelihood of a "Jupiter" size planet to protect a terrestrial planet in the ecozone. However, it also means fewer asteroids. Also, our star is 2/3rds of the way out from the centre of the galaxy. If the galaxy is a reverse centrifuge like our solar system, there should be more heavy elements near the centre than the edge. Another point: in the core itself and star clusters, stars are so close it may be difficult for a planet to maintain a stable orbit; and what planets exist may be bombarded with radiation. But there life may simply evolve to thrive in the additional energy.
I'm sure the galaxy is a marvellous place with countless wonders yet to be discovered. Let's start with Mars; it's close.
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fi - Intelligence is more rare. Life has xisted on Earth for 3.5 billion years, but the oldest animal fossil is a jelly fish 680 million years old, the oldest vertebrate is 570 million years old, and the first mammal appeared 200 million years ago. The earliest humans ancestor was australopithecine, 4 million years ago. There are some fragments that show huminine diverged from apes about 5 million years ago, but none of those fragments have sufficient detail to assign a species. The evolutionary line that led to modern humans diverged from australopithecine about 2.5 million years ago. Rather than trying to guess which human ancestor was first intelligent, lets use 2.5 million years. 2.5 million / 3.5 billion = 0.00071
There's a hole in that reasoning, though. From the way I understand it, it assumes that every elgible planet will evolve intellegant life. I think this a very naive assumption that a lot of people that go into SETI make at least partially. Let's look at it logically. First, porkyariotes, bacteria, were the dominant group for 2-2.5 billion years, a nice starting place. After that, eykariotes like ameboas and protizoans emerged and dominated for 400 million years. Next, invertibrate life took over, and once fishes emerged the body plan of the dominant phylum remained, just in different forms.
After amphibions fell out of favor, dinosaurs ruled, then mammals. In all this time, perhaps as many as 15-20 sentient (Dolphin intellegance or better) animals existed, but only one had the dirve and capibilities to leave the place. Obviously, you can be an incredibly succesful species without being to bright. For this reason, I think that at most we can expect one in 50 Earth-like planets to harbor human-quality intellegance, and that's a very generous estimate.
As for the Drake equation, I believe that it could be useful, but it needs a few tweeks. First, change the variable from rate of star formation to the number of stars. Also, there should be a variable for nuber of terrestrial planets with the resources to allow for heavy construction. You can be as smart as Einstein but you won't go anywhere unless you have something to build with. Other than that it appears pretty solid.
The problem of course, is that we don't know enough about the universe to fill in variables with any confidence. That's why I think we need to put some money into finding an Earth-like planet. Once we find one, and see how hard it is to do so, we'll have a better picture to work with. Right now we're working with an example of one, like trying to study the oceans with a cup of water. After finding another Earth, it would be like trying to assemble a puzzle with the picture to help, while before all of the pieces are upside down.
A mind is like a parachute- it works best when open.
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The problem of course, is that we don't know enough about the universe to fill in variables with any confidence. That's why I think we need to put some money into finding an Earth-like planet. Once we find one, and see how hard it is to do so, we'll have a better picture to work with. Right now we're working with an example of one, like trying to study the oceans with a cup of water. After finding another Earth, it would be like trying to assemble a puzzle with the picture to help, while before all of the pieces are upside down.
That's true. I remember when in the 1970s that astronomers noted the distance of the inner planets from the sun appeared to roughly follow an arithmetic progression, but they had no idea why. Was it just a coincidence? It wasn't a perfect match to an arithmetic progression, just very close. They thought the answer could not be found until someone found another solar system: planets around another star. But then someone had the bright idea to study the orbits of the moons of Jupiter. Just this second example permitted them to work out the orbital mechanics; it turns out gravity tugs them into orbits that have an arithmetic progression. The smaller size of the Jovian system made the effect more dramatic, the moons more closely follow the progression so it was easier to figure out.
By the way, I'm told the first mammals evolved before the dinosaurs. The larger ones (about the size of a lion) died out when the dinosaurs arrived while the small ones lived underfoot.
I guess for intelligence the term refers to tool-using creatures. I think a couple years ago I had a term for evolution of eukaryotic cells, which have a separate nucleus and mitochondria and/or chloroplast. That could add a prejudice to how life evolved here. A stromatolite is an organization of prokaryotic cells, cyanobacteria to be precise. Is it necessary for cells to engulf and enslave another cell with separate DNA sequence? Could prokaryotic cells organize into multi-cellular organisms? They haven't here, but?
The question of body form is an excellent one. Do tool-using creatures all require a spine and 4 articulated limbs with bones and joints, and 3-5 fingers at the end? Octopuses and squids don't have bones or fingers. Insects and arachnoids have multiple limbs, no fingers, and an exoskeleton instead of an endoskeleton. One argument I have against the so called "grey" alien is that it's too much like humans. Look at the variety of creatures in the Burgess Shale: at first palaeontologists didn't believe anomalocarus was a single creature. And those creatures evolved on Earth. Chances are life which evolves on another planet will be quite different from us.
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The question of body form is an excellent one. Do tool-using creatures all require a spine and 4 articulated limbs with bones and joints, and 3-5 fingers at the end?
This is an interesting question. The question of body form is something that can be at least generally predicted by following what it took to make humans what we are now. It goes beyond body form to other factors such as personality and habitat. Let's see what it would take to make another species capible of associating with humans. By that I mean a tool-using social planet leaving sentient race.
Okay, first let's look at what it took to make us what we are now. Humans arose because we lived in a harsh environment that demanded excellence and a body plan that supported tool-use. First of all, our ancestors were social. They had to be because one human by himself doesn't put up much of a fight against nature. Since they were predisposed towards intellegance, they capitalized on this, then it got kind of out of hand during the terrible climates of the ice age, and what do you know, we have homo sapiens. I think we can assume that this race would have to have these traits:
1: Social. Solitary animals never get anything done. By contrast, several types of communal animals produce increadible works of engineering. These include ant colonies, termite mounds, coral reefs, and human cities. Any aliens would have to by extroverts.
2: Agressive. It's true, nice guys finish last. Want proof, gorillas are extremely intellegant animals, yet are extreme pacifists, ergo you've never seen a gorilla city. However, humans are constantly trying to nuke each other harder than a box of Pizza Bagels, and it shows in our capiblities.
3: Terrestrial. The simple truth is no matter how smart you are, you aren't going anywhere if you live in the ocean. It's just not possible to make your mark when you live in an environment with zero-tools.
4: A dexterous origin. The only reason we developed our tool-creating abilities is because we came from a family where that was the next logic step.This necesitates something like tentacles, hands, or some other apendage.
5: An origin as prey. Back in the day, our ancestors were good eating for any prehistoric beasts, sabre-tooth cats, lions, etc. We evolved our enormous brains because we NEEDED them to fend off these attacks. Then we flipped around and got those wooly mammoths back big time.
6. Curiosity. Do I really need to explain this? Seems like a given to me.
Aside from that I don't see any other big restrictions. This new spices could come from some other evolutionary pathway, some coral-alge combo, or superfungus, perhaps, although those are extremes. However, no matter what they'll end up with a product about our size that's social, violent, curious race that we should be able to relate to pretty closely. What do you think?
A mind is like a parachute- it works best when open.
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I disagree with some of your conclusions. I would hope that aggressiveness is not a prerequisite for intelligence, social co-operation is very important. But the creature does need a dexterous origin, and must start as weak in a difficult environment. If the creature is strong, then strength will be accentuated. The creature must have an evolutionary selection pressure to make very effective and creative use of what ever capabilities it has.
Humans started as omnivorous apes, similar to chimpanzees, with limbs capable of climbing trees to escape predators. That gave is the dexterous origin: hands, binary vision with good depth perception, and excellent hand/eye coordination. Then the mid-Africa mountain range arose, cutting off east Africa from west and slowly turned the rain forest of east Africa into savannah. The lack of trees forced us to walk, so australopithecines evolved legs capable of walking long distances efficiently. The body plan of a chimpanzee favours 2-leg walking, but that could have evolved into knuckle walking like gorillas then 4-leg walking like other mammals. The reason our legs evolved for efficient 2-leg walking was to permit us to see over long grass of the savannah. Then lack of fruit forced us to become scavengers; australopithecines ate bone marrow and brains of carcases left by predators, primarily big cats. Stealing left-overs from a strong, successful predator like lions, jaguars and cheetahs required intelligence to avoid becoming prey themselves. To ensure they had enough food, australopithecines evolved from scavenging to steeling meet. Cheetahs store their prey in trees to keep it away from other carnivores, but apes are good at climbing trees. This is why our digestive tract is best adapted to meat that has aged for a few days rather than freshly killed. You will notice house cats don?t like the smell of well aged meat; to them it smells spoiled. Eventually, we learned to hunt for ourselves by making stone weapons to give us the equivalent of formidable claws and teeth.
This evolutionary path is not necessary. An octopus or squid could evolve in water with lots of loose rocks, caves and crevices. The key is raw material to work with, dexterous origin, weak natural weapons, and a changing environment to create evolutionary stress. An amphibious creature could evolve in coastal regions. A small dinosaur could evolve if in an environment with a superior carnivore, and shortage of its previous food. Birds on Earth have shown great intelligence; grey parrots have been taught to speak English with a vocabulary of over 100 words. They can even understand abstract concepts like colour, shape, size, and numbers. They can do single-digit addition and subtraction. But most birds on Earth lack a dexterous appendage. The terror birds of South America, after the dinosaurs but before mammals, had become flightless and evolved short arms with fingers. But they were the top predator of their ecosystem, so their evolutionary pressure was for stronger natural weapons (beak or feet), and not cunning. Many birds do build elaborate nests; if they had hands instead of wings they could have evolved into intelligent beings.
Many insects exhibit complex behaviour. They were the dominant animal on land before lizards. I suspect the limitation for insects was their size. Insects breathe through their skin/exoskeleton, they don?t have lungs. This limits their size due to mass to surface area ratio. The larger an object is, the less its surface area relative to its volume. Large insects can?t get enough oxygen into their blood. If they had evolved a lung, they could have become larger.
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too bad I don't have much time to elaborate on this famous equation and interesting topic. But, in short, how do you estimate Fl, fraction of planets where life developps ?
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fi - Intelligence is more rare. Life has existed on Earth for 3.5 billion years, but the oldest animal fossil is a jelly fish 680 million years old, the oldest vertebrate is 570 million years old, and the first mammal appeared 200 million years ago. The earliest humans ancestor was australopithecine, 4 million years ago. There are some fragments that show huminine diverged from apes about 5 million years ago, but none of those fragments have sufficient detail to assign a species. The evolutionary line that led to modern humans diverged from australopithecine about 2.5 million years ago. Rather than trying to guess which human ancestor was first intelligent, lets use 2.5 million years. 2.5 million / 3.5 billion = 0.00071
fc - The fraction with technology which releases detectable signals depends on how long a technological species survives, whether there is a better technology that does not release signals, and how long it takes to develop it. For convenience, lets use the time from the first radio on Earth until today. Guglielmo Marconi transmitted a signal from Cornwall, England to St. John's, Newfoundland, in 1901. 1901 to today is 102 years; divide that by 2.5 million and you get 0.0000408Plugging in the terms you get: 400 billion * 2 * 1/3 * 1/4 * 75% * 0.00071 * 0.0000408 = 1,448
I wonder if this method is really the right way to handle intelligence. I'd rather pre-suppose that increased complexity is an element of life and the evolutionary pattern itself. Look at life on Earth. As a whole, biological complexity and neural size for animals occupying a given niche has only increased over time. Provided the conditions are favourable enough to make a biosphere expand above the level of microbial life, intelligence appears to me a more or less pre-determined outcome. It's just a question of time.
Instead of dividing the number by the infinitesmal amount of time that intelligence has existed on Earth, maybe one should merely ask oneself here what fraction of star systems can be considered to have stable orbits with terran planets in the water range (no near gas giants in highly eccentric orbits for example or binaries too tight), a decent share of heavy elements and having existed long enough for intelligence to develop, i.e for about 4.5-5 billion years or more.
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