-Velocity-

The shadow would fall across the equator only around the equinoxes. For much of the year, the shadow would entirely miss the Earth. The Sun declination criterion for at least part of the shadow to hit the Earth is 1/2*angular width of the Sun + 1/2 angular width of the ring + parallax of the ring as seen from (roughly) the poles. This is about 0.25 degrees + (1/2 the unknown width of the ring) + 8.6 degrees. Assuming the ring is 1/2 a degree wide, then the total is 9.1 degrees. When the Sun's declination was more than 9.1 degrees or less than -9.1 degrees, then the shadow misses Earth. So the shadow only hits Earth between something like March 6 to April 10 and from like August 30 to like October 9th (going off a graph of Sun declination vs. time of year I found). And no, the ring can't be seen from the poles, but it can be seen from very close to the poles, I think about 81 degrees north/south. Otherwise you're right, the ring would reduce the sunlight Earth receives and modify the climate in ways that might be hard to predict. That said, you could counter it "simply" using orbital mirrors to increase sunlight to the areas where it is lost.

Most of your post I agree with or at least find your logic agreeable. However, the whole point of this topic was those ideas you by which you were predicting the form of an intelligent alien were largely based on the premise that the intelligent alien evolved in nature. My point is that once a civilization is established, the rules of nature become invalid. Creatures who have created a civilization are subject to wholly different rules and pressures. An advanced civilization probably just 100 years more advanced than ours also has access to the ability to radically and rapidly evolve themselves along routes of their own choosing. Such a civilization probably also has intelligent machines, and may be integrating biological and synthetic components together. So to reiterate, once a species reaches civilization and in particular, an advanced civilization, then we can forget about trying to use natural selection to predict what the species might look like, because they don't play by the rules of natural selection, and they have the ability to intelligently evolve themselves. Only with young civilizations- like ours- will the laws of natural selection be a sure indicator as to what an intelligent species will look like. For all we know, our descendants 10 million years from now will have ten legs, be covered in fur, stand only half a meter tall, have a brain 1/10 the volume of ours but that is 1000X more efficient than ours thus making them like 100X smarter than us, and reproduce by copulating with a "species" of intelligent machine that, instead of sperm, ejaculates artificial life forms/"nanites" that help to shape the developing fetus in ways nature couldn't have imagined. It sounds ridiculous, but as long as civilization is maintained for enough total time, then who the hell knows how we will evolve. Unnatural things can and WILL happen, because civilization itself is, by definition, unnatural.

Well, obviously, our silicon computers and our biological brains are VERY different kinds of machines. When I say our brains are computers, I only mean it in the sense that they are complicated, deterministic (except for potential influences by the uncertainty principle) systems that take in data, store data, and then, by the arrangement of neurons and the chemicals released, produce some kind of output that is a highly complicated function of the input data. Don't take the analogy too far. So yes, we can calculate an estimated computing power for the human brain, but, to at least some extent, we are comparing apples and oranges.

If the brain consists wholly of physical matter, and the supernatural soul does not exist, then of course the brain is nothing but an extremely powerful computer. What else would or could it be? In fact, our brains are actually immensely powerful computers, and have the type of computing power only perhaps exceeded by the most powerful supercomputer in the world (at least, last I checked)- a giant, parallel-processing supercomputer in China that consumes like 20 MW (yes, twenty MEGAWATTS). Silicon is still many orders of magnitude behind biology in efficiency and information processing density. The reason that silicon computers outperform us on things like adding numbers is because we did not evolve such an ability because we did not need such an ability. That said, there are of course many areas where we vastly outperform silicon computers.

First of all, the feeling of a constant existence, a constant self, tied to a specific piece of matter is an illusion on multiple fronts. First of all, we are in no way tied to a specific piece of matter. Your brain is constantly rewiring and replacing itself. The brain is like the proverbial "ship of Theseus"- by the time you die, your brain will have probably replaced and rewired almost everything between the time of your birth and the time of your death. Secondly, as the brain is constantly rewiring itself, the idea of a constant self is also an illusion. So you could majorly rewire the way your brain works, even wholly replace your brain with a new one (which would be at least mostly functionally identical) and you would still feel that you were the same person- though you might think a bit differently if the new brain was wired a bit differently. Anyway, the matter that makes up our brains is utterly irrelevant. Everything about who and what we are is nothing but the information in our heads. When I say "information", I mean all the information we store in memory PLUS the manners and rules by which that information and new information is processed, and the information that describes how our neurons are wired to make us think. In other words, the information that describes our memories plus the information that describes how to create our process of thought and self-awareness. To make a computer analogy, you are all your "save files" in memory PLUS the source code of the program that makes up you. Because we are information, a functional equivalent of you made on a computer simulation- a simulated brain- would be exactly you. NOT a "copy". Because you are NOT made of matter, you are made of INFORMATION that is described in matter. How exactly matter is made to describe the information that is you is irrelevant- be it a biological brain or a computer software simulation. (I already hear someone's lame-brained counter-argument: "But what if the simulation were to run faster than your original brain!?!?!!! It would be very different than the original you!" Well of course, then you haven't replicated your original brain. EVERYTHING about you is information, including how fast your brain processes information. The information that describes you includes everything needed to exactly replicate the function of your brain.) Some people have a hard time conceiving this, so let me give an example. Lets look at another piece of information, say the number 1,638. Like you, it is a piece of information. A VERY TINY piece of information. So here's a question, when I write the number 1,638, am I writing the number 1,638 or just a "copy" of the number 1,638?... It is idiotic to say that I'm writing just a "copy" of 1,638. The number is just the number, as all information that is exactly the same is exactly the same. Likewise, an exact copy of your brain- regardless of what medium it is realized in- would be you, because you are nothing but information, and thus all instances of that information are exactly you. So far, we don't have any real use for these ideas outside of the philosophy of the mind. But, we may find a way to replicate human minds in software. Such minds could be vulnerable to prejudice and denied the rights of human beings. The above reasoning would show us that we should treat such software minds with the same respect we treat a biological mind. We can also have fun applying these concepts to a silly science fiction debate about the Star Trek transporters. The argument goes that, if the transporters destroy the body at one point and then replicate it somewhere else, then every time a person uses a transporter they in fact "die". However, applying the knowledge of the mind as information, we see that you do not die when using the transporter, as the only thing you are is information, and that information does get properly transferred from place to place. The immense byte stream that is "Captain Kirk" does in fact get beamed up or down from the Enterprise. It's a silly debate, but it could eventually have real world analogs for humans if "mind scan" like technologies come into being. And of course, it would have immediate real world analogs for any machine intelligences we might create in perhaps the not-so-distant future. That they were nothing but information would be immediately obvious to them, however, in a way that isn't immediately obvious to (most) humans.

I'm pretty sure that the main problem with plant/animal hybrid idea (we see "green people" with photosynthetic skin all the time in science fiction) is that making such a hybrid is not very useful if the animal is mobile. Mobile animals use a tremendous amount of energy compared to what can be produced by photosynthesis. It would be like putting solar panels on a race car. The benefits are not worth the cost.

"There is as yet insufficient data for a meaningful answer." Since no one said it yet.

Batteries are chemical energy storage systems, so AT BEST, they'll face the same kind of limits in energy density as other forms of chemical energy storage. I'm not a chemical engineer or chemist, but I doubt batteries will ever even approach rocket fuel or high explosives in energy density. Though, some batteries (zinc-air) already "cheat" by taking oxygen from the air to help them generate electricity- but that's cheating, and it only works in a dense oxygen atmosphere. Also, the rate at which you drain batteries can greatly affect how much total energy you get out of them. The total energy you get out can really plummet FAST as you draw more and more current out of them. For example, you might hook some battery up to 1 ohm resistor, by the time it's dead, you only get like 1/10th of the total energy out of it than if you had hooked it to a 1 k ohm resistor and drained it fully. For pulsed-power applications, you need capacitors, not batteries. And capacitors are much lower energy density than even batteries due to dielectric break down.

People who have an education make more money on average. Do you really not believe this well-known fact? I'm just saying, you can make a case that knowledge does in fact lead to less violence through the action of increasing an individual's investment in a well-functioning society. Furthermore, knowledge of and acceptance of human rights, the advancement of moral theory, HAS in fact lead to a reduction of violence world-wide. People watch the news and think we're living in a violent time, but it's not true. We're living in a golden age, which began to take off with the Enlightenment in the 17th century. Our golden age hasn't even peaked yet. I'd be afraid if it ever did, the Fall could be very unpleasant indeed. So in your mind, very weak evidence == proof? Huh?! You asked for any evidence that a "prime directive" actually exists, and so I gave you what you asked for. You didn't ask that the evidence support only the "Prime Directive" explanation BTW, I was sorta teasing you, but I did find problems with all your statements

Small quibble- the Earth is 4.6 billion years old, not 4.4 billion Well, Neanderthals DID have bigger brains. It's certainly possible they were more intelligent than us. It's also possible they were dumber. Brain size does not equate exactly to intelligence, and neither does brain to body ratio. Well ignorant people do tend to be more violent, I would assume. This is because ignorance leads to poverty, and poverty leads to violence. Knowledge would thus suppress violence by allowing someone to have a good, productive job. But the true cause of the violence is poverty, not ignorance. The fact that Earth is uncolonized by aliens despite there being tens of billions of potentially habitable planets in the galaxy where aliens could potentially evolve IS evidence of a real-life equivalent of Star Trek's "Prime Directive". It's only very weak evidence, however, as there are many other possible explanations- and combinations of explanations- that also result in an uncolonized Earth.

Hmm... of course, if the ring were solid, and stiff enough, and supported by multiple tethers, then I suppose you could put it in low Earth orbit; it doesn't HAVE TO BE at geostationary orbit. However, in LEO, now the tethers have to support almost 100% of the weight of the ring, whereas, in geostationary orbit, most of the weight that the tethers would have to support is just the weight of the tether itself. It's hard to conceive why you would want an LEO ring as compared to geostationary ring. Strong enough materials almost certainly do not exist in this universe for an LEO ring, whereas a geostationary ring is possible if space elevators are possible.

Yea. An example from fiction is Larry Niven's Ringworld series. It's about a gigantic ring around a star that is habitable. I've only read the first book in the series, and it was merely OK. But supposedly, after readers pointed out that the ring was unstable, Niven wrote a sequel to Ringworld that deals with this. (I think he introduces a control system for the Ringworld to keep it stable, and so the plot might center around the system breaking down or malfunctioning.) It depends on how you build the ring. If you first create individual space elevators and then send the rest of the stuff on those elevators, then yes, it would slow down Earth's rotation. But the slowdown would not be significant enough to affect anything. In an extreme case, you might add an extra few milliseconds in a year (defined as 365 days), or something like that. Big deal. You'd have to send up a huge fraction of Earth's mass before it would have significant consequences for life... and by that point, just by the mining required to send up that much of Earth's mass (you'd have to strip the entire crust and work your way into the mantle a large distance), life would be long extinct anyway. The bigger environmental impact could be caused by the ring brightly illuminating the nighttime sky, disrupting all sorts of biological balances. Circadian rhythms of wild creatures, the navigation of moths, etc. Predators would find it much easier to hunt at night. You could cause many species to go extinct.

It need not rotate; in fact, rotation does not help you any to keep it suspended, assuming it's rigid. The main problem with this idea is that such a ring is not stable. Any disturbance from the perfect balancing point will result in a net force that leads to a larger disturbance, and so on. You could potentially add thrusters that thrust the ring back to the equilibrium point when there is a disturbance. This is a control system which acts to create a net restoring force when there is a disturbance from equilibrium. Such a system would require fuel and energy, of course. If you are willing to accept tethers, however, you can tether a ring around Earth with a radius larger than geostationary orbit, and it will be held up there by centrifugal force. It would be nothing but a ring of space elevators. Edit- an alternative to a thruster control system would be a if you had a ring that WASN'T rigid, but could be actuated. Say that one side of the ring started to drift away from the central gravitating body (which correspondingly makes the other side drift closer). Normally, this slight imbalance would be amplified till the closer side of the ring crashed into the central body. However, if you could actuate the ring- deform it at will- then you could move portions of it closer to the cental body to create a force imbalance in one direction, which you could use to keep the ring suspended. Again though, this would require energy. Another alternative control system I just thought of would be to spin the ring, and wind or unwind weights to various lengths on long tethers. As the rotation speed is fixed, unwinding the weights further out would cause them to exert more centrifugal force on part of the ring they were attached to. In this way, you could apply restoring forces to the ring to keep it suspended.

We don't really know for sure what will be useful and interesting, it's a new world. For all we know, if we take an image of Ceres' night side at the right time, there will be a back-lit plume of dusty water vapor or something, kinda like we see on Enceladus when Cassini takes back-lit images of it from a distance. One of the leading candidates for the bright spots is, after all, a water vapor plume. Honestly, wouldn't it be smart to try taking an image of Ceres from its night side when the bright spot is on the limb, just to see if it rises from the surface into space some?

There are tons of reasons why aliens might have existed for billions of years in our galaxy, and not colonized everything. The argument that Earth is not colonized so aliens don't exist in our galaxy assumes a very specific alien behavior- out of control colonization far beyond what is needed for certain survival. I was going to write a long rebuttal of this idea, but coincidentally, someone put this on io9- http://io9.com/beyond-fermi-s-paradox-ii-questioning-the-hart-tiple-1697244447 The entire article is text so I'll paste it here: Anyway, to add to all that, I'd like to point out that if we ever survive long enough to establish interstellar travel, it's quite likely we'll have found a way to live sustainably on Earth. We will have conquered our drive to expand without limit. By the time interstellar travel is ever likely, we'll probably already have self-sustaining colonies on Mars, possibly the asteroids, maybe deep space. The need to expand to another solar system to ensure the survival of the human race will disappear. We have plenty of space and habitat right here in the Sol system. We could survive even past the death of the Sun, especially if we learned how to live in the Oort cloud. If we do find aliens out there, and interstellar travel is possible, then what does it mean? It means that alien civilizations, at least the vast majority of them, do not expand without limit. It means that, codified or not, it is an expected behavior of intelligent beings to not expand too much, to give other alien life forms their space and a chance to evolve towards civilization. It could be very dangerous for us to start expanding without limit, aliens could rightfully see us as a threat to their existence and the existence and future diversity of life in the galaxy. They left our planet alone, and so we should be expected to return the favor. It is easy to see how this rule could naturally arise, even among beings who cannot communicate with each other, from the simple observation that while the opportunity to colonize existed, no one did it, and each different intelligent civilization (except for the first) owes its existence to that.

LV-Ns and Poodles are terrible engines for a lander in a high-gravity environment, with the LV-N being especially bad due to its extremely low TWR. Under high gravity, you need engines with a very high TWR, such as the 48-7S. The 48-7S is by far the best engine to use for Tylo, use a bunch of them unless you're landing something REALLY big, in which case, the KR-2L is better. But very few people are ever going to land something on Tylo so big that the KR-2L is the best engine to use. Just use a big group of 48-7S. 8X 48-7S is a common engine configuration to use for my single stage Tylo lander and ascent vehicles. Just don't take the wrong lesson from how bad the LV-N is under high gravity. The LV-N is the best lander engine to use for very low gravity bodies, and there's a number of those in KSP. Obviously, the TWR of the LV-N is much higher on low gravity bodies, so that's why it works well there. But it's HORRIBLE on Tylo.

You're wrong in why it's stupid to imagine that there could have been prior civilizations on Earth. It's dumb because there is no evidence for a prior civilization on Earth when a prior civilization would have definitely left abundant evidence documenting its existence. It is in no way analogous to alien civilizations, which could quite easily have existed for billions of years somewhere out there and not left any evidence that we have yet observed here. Indeed, this is the only sensible conclusion. And "tons of space" does not do it justice. The current estimate for the number of Earth-sized and super-Earth sized planets in the habitable zones of stars between the mass of the Sun and the mass of a red dwarf in our galaxy is 40,000,000,000 (forty billion). There are around 200-ish billion galaxies in the observable universe. Conservatively estimating that the Milky Way galaxy is an unusually planet-rich galaxy by a factor of four, then we can estimate that there should be on the order of 200,000,000,000 X 40,000,000,000 X 0.25 = 2,000,000,000,000,000,000,000 potentially habitable planets in the observable universe. That's a 2 with twenty one zeros after it. You're falling into the same folly that the Catholic church did when they prosecuted Galileo. You want to believe our place in the cosmos is special. I just want to believe whatever the truth is. For centuries now, we've been accumulating fact after fact after fact that shows our place in the cosmos is of no particular significance. First, we found out that we weren't the center of the universe, and that the planets revolved around the Sun. Then we found out that the Sun wasn't the only star. Then we found out that the Sun wasn't in the center of the galaxy, as early star censuses seemed to show. Then we found out that we weren't the only galaxy- there were hundreds of billions more in just the observable universe alone! Then we found out we weren't the only planetary system, that we weren't the only Earth mass planet, and that there are tens of billions of Earth and super-Earth planets orbiting in the habitable zones of yellow to red dwarf stars, just in this galaxy alone. At this point, not believing that aliens exist somewhere out there in the universe makes about as much sense as believing in magic. Once you understand the sheer numbers involved and the science of it, it truly takes an act of religious faith to not believe in aliens. This is why all astronomers feel very strongly (a "statistical certainty") that aliens exist. I'm serious- an act of God is what it would take to prevent aliens from existing somewhere out there. If aliens don't exist, then God certainly does.

Correct. Sentience is not something you either have or don't have- it's a spectrum. Every higher animal- say, vertebrates- will have a reasonably high level of sentience. Software on our computers can already be very minimally sentient. As I said before, a tapeworm or protozoa may have minimal levels of sentience (which certain software has probably already exceeded). This idea of a continuum of sentience has been around for decades, here's one variation on the idea- http://en.wikipedia.org/wiki/Sentience_quotient It can be useful to define a certain cutoff limit between sentience and non-sentience, and this is commonly assumed though people may not realize it- because too broadly defined, even a rock could be considered to have some near infinitesimal amount of sentience. Basically, like sapience, there is a problem of where to draw the line between sentience and non-sentience. If we want to draw the line at levels of sentience experienced by say, vertebrates, then there might not yet be a piece of software that is sentient. It might be possible to create, for example, a superintelligent being that has abnormally low levels of sentience- a sort of "philosophical zombie"- http://en.wikipedia.org/wiki/Philosophical_zombie Personally, I am skeptical such a thing is possible- but if it were, as I said, I'd rather be a highly sentient being with lower sapience that a being with almost no sentience as compared to its level of high sapience.

It's not either-or. Sapient beings are, mostly likely, always very sentient beings too. It might be very hard to impossible to separate the two, though there have been many examples in fiction of intelligent, "unfeeling"/"soulless"/"heartless" computers. Personally, I think this is likely more reflective of human psychology than reality. Asimov called it the "Frankenstein complex" in his fiction. Homo sapiens is two words, btw. All in all, I'd rather be a feeling, dumb being than an unfeeling super-intelligence.

I disagree, because it is quite possible to imagine (and demonstrate) a computer that can feel but is not sapient. For example, your computer already responds to stimuli. You strike a key, and it responds. It sends out a ping to a website and sends data back and forth. A computer already has a level of sentience, but it certainly has no sapience. It is not self-aware, and it cannot reason or plan. Imagine if a computer runs a neural simulation with as much complex thinking and feeling as, say, a mouse. This could be highly useful, for example, we might disperse a small fleet of UUVs with this level of sentience through the seas of Europa. They could try to sniff out organic molecules, and visually see the environment, and "instictually" know to return to "base" with whatever interesting things they could find (where their results would be radioed back to Earth). There was some article I read recently even talking about someone developing software to do something like this, specifically for Europa. It was software designed for UUVs (unmanned underwater vehicles) that made them look for "interesting" things in the ocean. A UUV was loaded with it, and when released into the water, it started taking pictures of corals and fish, and eventually "noticed" the scuba diver that was monitoring it and started following the diver around! So one can quite easily demonstrate that our artificial intelligence software has already achieved a reasonable level of sentience! So, again, sentient computers are not equivalent to sapient computers; in fact, sentient computers already exist.

Please stop incorrectly using the word "sentient". "Sentient" means the ability to sense and feel. A dog is sentient. A tapeworm is sentient even, though certainly less so than a dog. Supposedly even some single-celled organisms have shown signs of sensing the environment and acting in self-preservation. This is all varying levels of sentience. There are literally millions of sentient species on planet Earth. Yet over and over again, you see science fiction authors calling intelligent aliens "sentient aliens" and intelligent computers "sentient computers". Where in the heck did this come from?! Don't they know their English? If I was an alien, I'd be insulted to be compared to nothing but a mouse or a tapeworm The proper word for intelligence is sapience, which means the ability to reason- i.e., the possession of intelligence. Where the cutoff between sapience and non-sapience lies, however, is not as well defined. Some people contend- sometimes with some arrogance, in my opinion- that humans are the only sapient species on Earth. This does make sense to some degree, because we are the most intelligent, we are the only ones to use "high" technology, have a complex language, etc. However, if we define sapience this way, then there's no reason a more intelligent alien race (or, more likely, a machine intelligence we create ourselves) could come along and tell us that we are not sapient, and that only it and beings more intelligent than it are sapient. Personally, I'd prefer to define the minimum level of sapience to be based off of some measure of intelligence that requires sub-human sapience (such as self-awareness). This would help finally give intelligent non-humans the respect and protection they deserve (i.e., force Japan to stop the torture and murder of dolphins), and set up an important precedent whereby, if we ever encounter or create our intellectual superiors, the moral precedent exists for them to respect our rights as sapient beings. Of course, that doesn't mean that they would, but it might help to have the moral high ground. Otherwise, if we had defined sapient beings as simply being the smartest things around, how could we rightfully object to being slaughtered or otherwise repressed? So I think it's important to set up a fuzzy boundary (pun intended ) between human rights and animal rights. But I'm starting to seriously digress from the definition of "sapience".

I was originally going to post this as a response to that "requirements for civilization" thread, but I went off topic enough to warrent a new thread, IMO. I think most people are in pretty good agreement as to what it would take for a civilization to arise. Indeed, it seems pretty obvious that things like communication, the ability to pass on knowledge, and the manipulation of physical objects are probably requirements. Please see that other thread if you want to discuss that. Personally, I think it’s more interesting to imagine how civilizations, once established, could evolve. Most science fiction writers and futurists are stuck in an unimaginative mind frame, imagining aliens as essentially unchanged from their naturally-evolved forms. An example is this- http://www.newsweek.com/aliens-are-enormous-science-suggests-319448 I don't really wish to judge the accuracy of this thinking as applied to biological evolution. Though as a counter-argument to the whole idea that bigger animals are smarter, I’d like to point out that one of the few non-human animals in the world shown to be self-aware (and otherwise very intelligent) is the European Magpie, which, while it has a large brain for its body size, still only weighs at most 0.25 kg. Other birds in the same family (the Corvids) have been observed using and fashioning tools (and are probably also self-aware). All this intellectual capacity is packed into a tiny brain. It is also likely that the majority of that tiny brain is not actually devoted to intellect. In the end, what the intelligent birds show us is that sapient beings need not be large. Anyway, as the article I linked points out, there are likely natural evolutionary pressures that encourage longer lifespans in larger animals (such as, the larger you are, the less likely you are fall prey to predation, and thus, it makes sense to have a longer reproductive period). I am a bit less sold on the link between intelligence and animal size, but at the least, the longer lifespan encourages the possibility that civilizations will be founded by larger beings. This is where I think that the imagination of science fiction writers and futurists and all the like fail them. We already possess the tools to deliberately induce changes in our own evolutionary design (and those tools are only getting better and better with each passing year), and our civilization is at an infant stage compared to astronomical time spans. We are no longer subject to natural biological selective pressures (such as predation or limited food resources). In terms of our future evolution, as long as we maintain civilization, it is a folly to draw any conclusions based off of natural evolution. If we desire, we control evolution now, and we can evolve at a rate much greater than that of natural evolution. So the error of science fiction is to assume that we can predict alien bodies and minds based on the rules of natural Darwinian evolution. When aliens are thousands, millions, or billions of years more advanced than us, they are bound to have deliberately evolved themselves into something else, using artificial rules of their own desire. In fact, they are likely to evolve themselves in many directions. For example, what if you want to maximize the number of individuals living on a planet? What do you do? As shown right here on Earth by the Corvids, (and perhaps by the "hobbit people", Homo floresiensis, though this needs more study) a sapient being does not have to be large. It might also be possible to be able to improve upon the biological neuron even further, increasing its processing capability and/or decreasing its size. The biological neuron is far from the smallest data processing unit possible. Either way, physics and the real-life example of intelligent birds shows us that we have rather large brains compared to our actual intellectual capacity. Thus, it seems highly possible that we could decrease body size without adversely affecting intellectual capacity. Smaller bodies consume less resources, and we could thus increase the number of people the planet could support by a factor of ten or more! So- au contraire! Intelligent aliens might not be large at all- they could be tiny! Despite the physical size of aliens or future human descendants, there will still be the need to manipulate objects. This is where direct, brain-machine interfaces (BMI) could come in useful- controlling a machine by thought alone. So, an intelligent biological being need not even have hands, if there is always a BMI around to serve as a manipulator. (Though one would imagine that hands- or their equivalent- would be retained as a manual backup.) There is only one example in fiction that I am aware of- the sapient "Neo-dolphins" from David Brin's Uplift universe. They are dolphins that have been "uplifted" by genetic engineering to a level of sapience equaling humans, and manipulate the world and move about on dry land (when necessary) using BMIs. They do not have hands. So science fiction has not entirely failed in this regard. Anyway, you might be wondering- what about cyborgs and intelligent machines? Well, I have entirely ignored them so far! The point is- just from genetic engineering alone, we have reason to believe that aliens- and any future descendants of ours- would differ greatly from their natural progenitors, and would be subject to artificial, deliberate selective pressures that have nothing or little in common with natural selective pressures. Once you factor in the emerging technologies of merging machine and biology, and the possibility of sapient machines, you have even more reason to believe that it is folly to speculate on the appearance of aliens based on their natural, Darwinian roots. Civilization- by definition of being non-natural- gives Darwin the middle finger, follows its own rules, and has the capability of evolving a species at a rate vastly higher than natural evolution. It seems likely that the only way we observe aliens in their true, Darwinian-evolved forms is if we catch their civilization in an infant stage. This seems unlikely, as even if only 1 in 1000 radio/spaceflight-capable alien civilizations survive for greater than one million years, they will outnumber "infant" civilizations like ours. In the end, we should be careful when we try to draw conclusions about the forms of aliens from the natural world, because civilization itself is unnatural, and if the aliens have deliberately "adapted" themselves to it (nearly inevitable over thousands, millions, or billions of years), they may only have a passing resemblance to their original, progenitor forms, or even no resemblance at all. Our observations of natural selection are only applicable to predicting the starting forms of aliens. (It also seems possible that alien civilizations will consist of many different intelligent races sharing a common creator species, but that’s another topic.) Oh and one more thing- even if harmfully conservative civilization maintains a prohibition on self-modification for millions of years, they will still evolve. People with certain traits will still produce more children than others. This leads to selective pressure, and a species will still "naturally" evolve to the unnatural condition of civilization, which has entirely different selective pressures than nature. So even if a species deliberately prohibits genetic engineering of itself, it will still evolve away in a different direction than what normal, natural selection would dictate in the absence of civilization. So no matter what an intelligent race does- short of artificially preserving and maintaining an ancient genome- it will evolve in directions that cannot be predicted by natural Darwinian evolution!

I wouldn't be surprised if Earth life is the norm for naturally-occurring life forms. However, natural biological evolution cannot follow every single path of innovation. There could be radically different forms of life out there that had their genesis as artificial life created by an intelligence or intelligences. Such artificial life could even have inheritance and undergo natural selection and evolution. (And then there's a wide range of beings that could exist that could have a difficult time falling into a specific category, such as a race of intelligent machines.) Personally, I believe that at least somewhere out there in the universe, such life is likely to exist- unless we want to be racists and consider only naturally-evolved beings "true" life.

Not every human being thinks as you do. Here's an example- this is the way I feel about imaging- "Why in the world would someone want to image astronomical objects instead of see them with their own eyes?! If you're going to be looking at pictures of astronomical objects on a computer screen, what in the world do you need the telescope for? Sell it, and stare at Hubble Space Telescope images downloaded off the internet all night long instead!" So asking why anyone would want to own a big telescope that takes a long time to set up is stupid. Obviously, some people have different desires and opinions than you do, and those desires and opinions aren't any more or less valid than yours are. In my case, I've seen probably well over than 10,000 deep sky objects over the past 20 years, especially in the past 13 years when I've had an 18" telescope or larger (at first, I wasn't nearly as spoiled by dark skies as I am now, and I had more opportunities to observe as well). Considering that I like to always observe some new objects (or new details in old objects) in an observing session, I can't tolerate the ugliness of light pollution, and I feel like I'm wasting my time under anything less than very dark skies, of course I need a very large telescope now. From 2009-2012 I was living in central Texas, and I actually got to use my 25" scope quite frequently. Since moving back to the southeastern US, I've only gotten to use my telescope twice- the weather really sucks that bad (though bad luck- such as being sick with a cold when conditions outside were perfect- has also played into it). I'm looking to get a job in the Southwestern US, where lots of wonderful outdoor hobbies will be available to me (such as hiking and excellent weather and very dark skies for astronomy). Assuming I get that job, I'll likely be able to use my 25" scope at least once a month on average.

There is a huge difference between saying "it's highly possible that" and "it's certain that". I stated the former, meaning I think it's important to keep an open mind, but that we should not be surprised at all if we find extraterrestrial life to be similar to life on Earth, because there's a good chance that it will be. It's so easy to say it will be different, but those people who say so have had a very hard time coming up with truly viable alternatives for even a substance as simple as water.