QUOTE(shun @ Jul 20 2006, 01:45 PM) [snapback]1277009[/snapback]
You know squat about astro-chemistry, astronomy, and the Universe at large. You are a pretender to intellectual reasoning.
I may not know all there is to know about the universe but I do know this about the possibility of ET life. I do know that this possibility is surely tied to the frequency with which stars are born. Clearly, a greater flux of new stars will ultimately produce a larger number of planets with thinking beings.
What is the star formation rate? Well, there are roughly 200 billion stars in the Milky Way, and that means that the average rate over the last 13 billion years has been about 15 new stars per year. In fact, however, this average rate is two tads misleading. Anyone whos used a radio telescope to study galaxies knows that when you examine a big spiral like the Milky Way, you find that the total amount of interstellar gas is typically a few percent of the mass of all the stars. Since interstellar gas is the stuff from which stars are built, its obvious that theres little material around today for constructing new ones.
Sure, stars explode as they die, spewing some of their contents back into space. Even the Sun will blow off some steam as it heads for the stellar bone yard. But the great majority of whats inside the Sun will stay there forever, locked in by gravitation. The ingredients for new stars are sparse, and most of the stars that our Galaxy will ever make have been made.
Clearly, this must affect the roster for our club of intelligent beings. But how? There are two obvious possibilities. One is that intelligence is such a useful attribute that technological societies last a really long time billions of years. Heck, trilobites lasted a half-billion years, and they werent even smart (by any reasonable standard). So maybe the thinking-beings club is home to really, really old societies, and were like preschoolers surrounded by grad students.
The other possibility is that, no, technology doesnt survive for such long time spans. And while the Galaxy may have spawned great civilizations in the deep and distant past, they are mostly gone now. In this scenario, other club members are not quite so ancient, but theyre in short supply.
Which, if either, of these possibilities is true will only become clear when we have decoded a signal from elsewhere,or if they stop by to say hi.
And about astro-chemistry.Its question as common as brown dogs: will alien life be carbon-based?
If you remember your high school chemistry, youll recall that carbon has half of its outer electron shell filled. In other words, each carbon atom is able (and eager) to bond with up to four other electron-sharing atoms (most atoms prefer to have a filled outer shell of eight electrons). As a common example, a single carbon atom will eagerly take on four hydrogen atoms to make methane (CH4). And because carbons outer shell is both half filled and half empty, it can handily hook up with other carbon atoms, creating the sort of elaborate molecular chains and rings that fuel companies love to pump.
Carbon, in other words, is adept at making complex structures. And complex structures are the bricks of life.
Are there other contenders? Is carbon really so special, or did it just get lucky here on Earth? If you have a periodic table handy, youll note that the element situated under carbon is silicon, which also has four electrons in its outer shell. Ergo, silicon might also seem to be an obvious basis for life, a point that was first made at the end of the nineteenth century by the German astrophysicist, Julius Scheiner. The optimistic Scheiner was certain that other planets in our solar system (including roasty toasty Mercury) sported life.
But his sunny attitude was misplaced when it comes to silicon-based beings. Silicon may be carbons chemical cousin, but its a poor relation. Because the silicon atom is larger, its bonds with other elements are weaker. While carbon hooks up with two oxygen atoms to make carbon dioxide, a nice waste product for both humans and SUVs, the silicon equivalent, silicon dioxide, quickly assembles itself into a crystalline lattice. Its better known as sand, and would make exhaling a gritty experience. The weaker bonds of silicon also preclude the easy formation of those long, same-atom molecular chains that underlie many biological compounds. A slew of complex carbon-based molecules are easily produced in comets, interstellar dust, and university glassware. But if you check out natures chemistry lab for silicon (consider volcanic lava), the products are far less interesting.
If thats not enough to dissuade you from silicon, consider this: theres just a lot more carbon around. Cooked up in the searing interiors of stars.
You are calling me a "pretender of intellectual reasoning", ok, were are your thoughts on this matter.