I have very little doubt that the universe in general and this galaxy in particular are "alive" with life forms other than those found here on Earth. My problem is that it seems incredibly unlikely that we have been visited by them. Before I begin to consider the possibility, there needs to be an incredible amount of proof to counter what I see as an incredible improbability that they've landed.  Why do I think it's so unlikely? Well, this conclusion is a fairly recent one.

First of all, this is an incredibly large and surprisingly empty universe. This planet (Earth) is infinitesimally small and there is very little to draw attention to it. So even finding it seems highly improbable. Secondly, speculation on the probability of other civilizations that are even capable of thinking about visiting are extremely wide. One guess puts the distribution of such civilizations no closer than 200 light-years away. Therefore, there are not that many looking. Third, current thinking on "warp-speed" is that it's pure science-fiction. So traveling vast distances just doesn't seem feasible, at least, not from a planetary sociological stand point. Ship-time might not be a problem because time will slow down for the ship occupants. But who'll care when you get back home, at least 400 years later, what you found? Therefore, of the few who might be looking, fewer would bother. Fourthly, maybe a life form based on a different chemistry (Silicon, maybe?) may find the distances and times less problematic. Aside from my inability to even imagine a way such a life form could emerge, this doesn't remove the inherent problem of the meaningfulness of any data collected here on Earth short of a Geological nature. Finally, the same distribution that put the nearest civilization 200 light-years away also suggests that their comparative level of advancement has to be way superior to ours. There may be one civilization in the whole galaxy that is merely 1000 years ahead of us, technologically. More likely, they'd have to be hundreds of thousands or millions of years ahead of us. It hardly seems probable that such beings would scruple to make their visitations clandestine. These reasons, in a nutshell, is why I find it not just improbable that we've had visitors but incredibly improbable. What follows are some details on how I've come to these conclusions.
 

My absolute earliest memory of wondering about UFOs must have been about 1953. I was 4 or 5. I remember seeing the old Buck Rogers serializations on television. We lived in Oakland, California not too far from an air field. I would frequently see Blimps flying overhead and they look a lot like the "space ships" that were on the Buck Rogers show. The first time I noticed one I ask if that was a space ship and the answer was, "No, that's a blimp." I wasn't told there were no space ships, just that that wasn't one. So I paid closer attention to Buck Rogers the next time I saw it and I could see that there were differences. Finally, after numerous blimp sightings, I finally asked, "How come I see so many blimps and no space ships?" The answer was, "Two reasons. First, we live near the air field where the blimps are parked. Second, there are no space ships." Oh? "What about the ones on Buck Rogers?" So mother would smile and say, "Honey, the TV's just pretend." It looked real enough to me. So I kept an eye out. I never did see a space ship.

Because of that, for most of my life, I would characterize my opinion on UFO's as agnostic. In that sense, I mean I just don't know; not that I don't think so; not that I doubt it; just I don't know. I'd be happy and open to arguments either way. I've been intrigued by the possibility since I found out there were other planets from where they might come (so parts of Buck Rogers wasn't "just pretend" after all). I just couldn't help wonder about the possibility of life elsewhere after looking into the night sky once I found out those were all (well, mostly) suns very far away. I was in fifth grade in 1958 when the theaters were bursting with a new Sci-Fi film almost every week. Of course, I guess it was the advent of Sputnik late in 1957 that first made me look up and wonder what it would be like.

It wasn't until the late '80s (I was in my forties) and first half of the nineties, I began reading popularized science books such as A Brief History of Time (Stephen W. Hawking), Coming of Age in the Milky Way (Timothy Ferris), The First Three Minutes (Steven Weinberg) and others. I also found a copy of Cosmos, the PBS Special, narrated by Carl Sagan on video (and also found the book). After that watching and reading, I've become a skeptic for a great many reasons (not about the existence of aliens, but their visiting us). The reasons all rotate around these three:

1. Interstellar travel doesn't appear practical given the vast distances involved

2. Relativity restrictions to light speed and super luminous travel

3. The longevity limitations to "life as we know it".

The size and amount of empty space of this galaxy is almost unimaginably large. Our galaxy is comparatively mediocre at just about 100,000 light-years across (each light-year is just short of 6 trillion miles; the distance light can travel in one earth year). In just our solar system, there nine planets orbiting the sun from 36 million miles (Mercury) to about 4 billion (Pluto). Carl Sagan said that trying to put the relative size of each planet and their relative distances from the sun on the same scale is, I believe he said, "impossible". Consider:
 

Planet	Distance from Sun in Million Miles		Diameter in Miles	Scale Distance In Pct.	Comparative Distance In Miles	Orbit Through	Comparative Diameter In Inches
Sun	0		4,324,882	000.0000	0.00	Chicago, IL	425.3982 (35.45 ft)
Mercury	36.0		3,030	000.9836	5.58	Chicago, IL	.2980
Venus	67.0		7,520	001.8306	10.38	Evanston, IL	.7397
Earth	93.0		7,927	002.5410	14.41	Wheaton, IL	.7797
Mars	141.6		4,210	003.8989	21.94	Gary, IN	.4141
Jupiter	483.3		88,700	013.2049	74.87	Milwaukee, WI	8.7246
Saturn	893.0		74,980	024.3989	138.34	Indianapolis, IN	7.3751
Uranus	1786.0		31,750	048.7978	276.68	Cleveland, OH	3.1230
Neptune	2794.0		30,750	076.3388	432.84	Martinsburg, WV	3.0246
Pluto	3660.0		1,367	100.0000	568.00	Washington, DC	.1345

I took the distance from the Sun to Pluto's orbit and called it 100%. I then adjusted the diameters on the same scale and converted it to inches. I then expanded the distance I'd use in order to make each of the nine planets visible. The first time I did this, I arbitrarily used a football field (100 yards) and put the Sun on one goal line and Pluto on the other. The percentages show through which "yard lines" the orbits of the planets would pass. The problem was that only the Sun would be visible to the naked eye.

What I came up with was putting a model of the Sun (a bit over 35 feet in diameter) in the middle of Chicago and Pluto in Washington DC (about 568 miles away). On this scale, the diameter of Pluto is a little over 1/8 of an inch.  I then tried to find a town at the specified distance from Chicago that might be recognizable to people. These towns are, obviously, not in a straight line, but they do approximate the distances that the orbit the particular planet would pass through (or close to). If you can almost get your head around that, then try this. On this scale, Alpha Centauri (which is actually about 4.2 light-years away) would still be nearly 4 million miles from Chicago (about one fifth the way to Venus on her closest approach).

That's probably why it's called Space, because that is chiefly its composition. The point is that even finding a place to visit is difficult enough, but there is a tremendous amount of distance to travel to get there. There is, of course, still the question of "Who's looking".

In the early 1960s, Frank Drake of Cornell University came up with a formula that, when filled in and evaluated, would give the approximate number of civilizations that we might be able to detect from their radio transmissions (and, therefore, provide at least a lower boundary on how many civilizations may exist). The formula is discussed in Sagan's Cosmos on page 299 or you can find it in Drake's book, Is Anyone Out There -- The Scientific Search for Extraterrestrial Life (Delacorte Press, 1992). According the Sagan, there has to be a great deal left to little more than guesses in filling out the equation and there is a large degree of differing opinions on some other more factual elements of the equation. But even holding most of those factors at a conservative constant, the last factor, which is the number of civilizations that arise to a technological level, is open to all kinds of speculation.

There are two problems.

One is that given life emerges at all, doesn't necessarily mean that it will evolve to intelligence (I'll set aside the opinion that some share that we didn't evolve, but were created). Some are of the opinion that intelligence isn't an inevitable trait of evolution. The term "evolution" carries a connotation of improvement when it really means "change". The mechanism of evolution is survival of the fittest. For Intelligence to win, it must first emerge and prove to be an advantage over other traits, such as brute force. The argument goes that it was no accident that mammals, and eventually intelligent mammals, did not emerge until after the dinosaurs had vanished.

The other problem is given that an intelligent species emerges and becomes technically capable, how long do they last? We, Sagan says, have been able to do radio for a few decades, but its not totally unlikely that we could destroy ourselves tomorrow. After 3.5 billion years of evolution, we wipe ourselves out within 25 or 50 years, that's about a millionth of a percent of the existence of life on Earth. Putting that factor into the last term of Drakes formula puts the number civilizations at about ten. Carl is all over the map on plausible reasons for the total number of intelligent civilizations at any given time to range from ten civilizations to, maybe, millions. He also suggests, if there are millions of civilizations out there (more or less randomly distributed throughout the galaxy), the nearest might be no closer than about 200 light-years away.

So one of the first questions which comes to my mind is given an area of 200 or so cubic light-years of space in which to search, what is the likelihood an alien civilization would pick us? Or more to the point FIND us? We've been in the "radio business" since, what, the 1920's? So if any of those earliest transmissions actually leaked out into space, they may have reached out to 80 light-years by now, but not 200. So what's the beacon that would draw their attention to us at all? A random search? You'd have to draw a sphere with a diameter of 200 light-years (about 1,200 TRILLION miles) and search the surface of it and beyond. That starts off at 18 million, trillion square miles (15,000 square light-years) of space. That's if it was exactly 200 light-years away (rather than 193 or 208). If you could stand back far enough to see the Sun and Pluto without turning your head, the earth would not even be visible. So a random search is trillions to one. Winning the California lottery is only 23 million to one and 1.2 billion to one if you hit the mega number also. That's a shoe-in compared to finding earth in all that.

The next problem is that of traveling time. As our understanding of the way things work currently stand, there is no "warp" speed. We are restricted to traveling less than the speed of light. This, apparently, is not merely an engineering problem, like the sound barrier. This appears to be, as Stephen W. Hawking said in his Brief History of Time "...a fundamental, inescapable property of the universe..." It has something to do with the equation E=MC². Using this formula as a basis and other laws of motion, mass and time, it can be shown that as the relative velocity a body accelerates, a very "real" effect appears on it's mass, physical dimensions and the rate at which time passes. At extremely high, close to light speed, velocities, bodies in motion become increasingly massive which takes more energy to keep them moving and more still to continue to accelerate. By the time it might be moving at the speed of light, it would be infinitely massive and would have taken an infinite amount of energy to get there. So it does appear that everyone, not just us with our limited knowledge, is bounded by the speed of light.

I might point out that there is no law that says we can't go faster than the speed of light. However, as far as we know, you have to through light speed to exceed it. There is, of course a problem with the mathematics that describes it to overcome. A portion of the model requires you to take the square root of a negative number which is not a defined operation. There is the possibility of using what are called "imaginary" numbers (the letter "i" is used as the Square Root of -1). Factoring out the square root of negative one solves the mathematical problems, but it isn't quite clear what "i" is supposed to represent in the model. But, I digress.

So, given that we are limited by the speed of light, it hardly seems practical that, even if we were found, that anyone would spend the time to get here. True, for those on the ship, traveling at near light speed, time will pass very slowly so that the two hundred years travel time would seem to be very short (a matter of moments or a few years depending on how close to the speed of light they traveled). But they, once they gather the data, and return ... to what? Their civilization has now seen 400 years pass. The travelers may have a difficult time fitting back in with their own culture. It would be like Galileo or Shakespeare showing up today and trying to blend. Even if they could, what possible use could anything they have to share be? Part of the reason for knowledge is to be able to apply it. There certainly would not be much technological advantage and any cultural information is already 200 years old by the time they return home and 400 years old if they immediately turned around and came back.

I guess it may depend, a little, on what is a normal lifespan for these aliens and how quickly their civilization advances. If, for instance, they lived thousands of years, a few hundred years, here and there, wouldn't make much difference. The problem with that is that you can't really expect organic (Carbon-based) intelligent life to live that long. Life based on something else that might have a longer life span, but such life doesn't seem probable. Even if they had a long life, all that does is show that when our aliens returned, their contemporaries would still be around. It doesn't make their news any more timely. Nevertheless, this leads me to the next topic -- Life as we know it.

"Life as we know it." Why life "as we know it?" Why not life as we don't know it? It would seem more likely that on some other planet life is bound to arise "as we don't know it" simply because there must be many more alternatives than what happened here. To read a book or see a film which suggested such an alternative, made me feel like I was not alone in my curiosity. Not only to make the suggestion, but to also evolve a story around the idea was absolutely fascinating. Because of the readings I mentioned earlier, I have lost that fascination to a degree. I have found the possibility of such alternate life forms seems less plausible.

It appears that organic (carbon-based) life is much more likely than I originally had thought. The composition of the universe seems to be quite literally "alive" with the stuff. Comets are a virtual warehouse of organic material. Aside from that, how would you go about searching for life as we don't know it? With organic life, if we don't find something moving around we look for things we know about it: look for waste material, foot prints, water, food stuffs, oxygen, carbon-dioxide. There are all kinds of hints for "life as we know it" because we have a pretty good idea what's involved to maintain it and what the consequences of life are. With life as we don't know it, we don't know what to look for and if we found it, how would we recognize it's significance? What might be a reasonable alternative life form? Silicon-based life? That seems to be suggested a lot. What might we expect from Mr. Sandman?

Take a look at a copy of the periodic table (which I lifted from the Chemistry Societies Network, CHEM SOC at http://www.chemsoc.org/viselements/pages/pertable_j.htm):
 

Carbon is element number 6, Nitrogen is 7, Oxygen 9, and there's Hydrogen up in the upper left as element 1. The thing about Carbon is that it would really like to get a hold of a couple more electrons in its outer shell. These other elements react nicely to form all kinds of proteins and other organic compounds and, finally, they thrive and ionize nicely in water (H₂0), which, incidentally, is ph neutral. All of these factors are important, in fact essential, in the proletarian stew we call "Life as we know it".

Life forms, based on something other than carbon, is an intriguing idea but falls apart under closer scrutiny. The speculation of a silicon life form may be plausible candidate because it has a similar make up as carbon. They have similar valences, they are both nonmetals and, therefore, silicon might "meld" well with other elements to form molecules. However, silicon is more than twice the mass as carbon. Chemically and electrically, it cannot interact as readily with other atoms to form the macro-molecules necessary for a complex being. The chemistry may support part of it. But then the physics would pull it apart and vise-versa. In any event, the abundance of the materials and the time for them to interact just doesn't seem to lend itself to support such an evolution.

Compare, for example, a sugar molecule to its "silicon" counterpart (pardon the graphics):

           OH H OH OH OH                          SLi Li  SLi  SLi  SLi
               |   |    |     |    |                              |      |     |      |     |
O = C - C - C - C - C - C              S = Si - Si - Si - Si - Si - Si
        |    |     |    |     |     |                      |     |     |     |      |     |
       H   H  HO H    H   H                     Li   Li   LiS  Li   Li    Li

            C₆(H₂O)₆                                       Si₆ (Li₂S)₆
where:

C = Carbon             Si = Silicon
H = Hydrogen         Li = Lithium
O = Oxygen            S = Sulfur
OH= Hydroxyl (?)   SLi= Sulfur Lithide ?
HO= ???                 LiS= Lithium Sulfide?

I am not a chemist by any stretch of the imagination. However, I am not bad at pattern matching. The carbohydrate on the left came from a chemistry book, the formula on the right was generated by taking elements from the periodic take offset the by the rows in which there counters parts resided. It is merely my speculation. The interesting thing about this is that sugar is carbon and water. The focus should not be on the Carbon (or the Silicon) but the nature of water. Water is a very unique compound. It is a perfect solvent and has an almost completely neutral PH (not too acidic nor basic). It is also unique in that it is one of the few compounds which is less dense in the solid state than it is in the liquid state (that's why ice floats (this isn't pertinent, just interesting)).

Though I have no idea what Lithium sub two Sulfur is, it must have vastly different properties than Hydrogen sub two Oxygen (water). The electron sharing to create this substance serves to use up the electron orbits for each other and not merely to co-mingle electrically. Oxygen needs two electrons to fill up an 8-electron orbit (L shell) and Hydrogen needs one to fill up its 2-electron orbit (K shell), so two hydrogens can coexist with one oxygen and make both shell orbits happy as well as balance the charge. Like Hydrogen, Lithium has only one electron its outer shell and like Oxygen, Sulfur has 6 in its outer shell. But the outer shell of Lithium is the L shell which isn't happy until it gets 8 and the Sulfur's outer shell (M) isn't happy until it gets 18. Consequently, though electrically neutral, it would not be stable in a multi-chemical environment.

The other more obvious problem is that if we assume that evolution is responsible for life in any form (whether it is "as we know it" or not), then one would expect the simpler compounds to occur first (if anything were to form at all). If the evolutionary environment was favorable to the application and replication of Silicon "organisms", it would have been more than conducive to Carbon based which would have formed much easier and used up the resources which may have spawned our sandman.

All this really means that (even if my picture is scientifically accurate -- which I do not claim that it is), maybe I have hit on an example of Silicon based life that doesn't work. That doesn't mean there isn't another combination that does work. Or that there may some other element-based organism that may arise rather than the life as we know it. But, for me, it just doesn't seem likely. The problem isn't my silly chemistry. The problem is that whatever "other" chemistry might be involved, the Carbon-based organisms would more naturally materialize first. Well, then, what if we were talking about a planet that didn't have the organic materials, but was rich is the other-base materials? That doesn't seem likely, either.

In the words of John Dobson (inventor of the "Dobsonian" mount telescope), "...the universe is just Hydrogen, Helium and the dust from exploding stars...." The Hydrogen, Helium and the dust are all the elements of the periodic table. Initially, a swarm of free hydrogen will "clump" together, become more massive and attracting more hydrogen until, at the center, the gravitational force is so large that the hydrogen fuses into helium. The energy released in this fusion is what makes stars shine. As more and more accretion of hydrogen continues, the more massive the star, the more gravitational force, the more fusion. Eventually, the hydrogen and helium fuse into other elements in the periodic table in varying quantities. Such a star may create most all of the elements up to and including Iron in this fashion.

Gravitationally induced fusion cannot create the heavier elements. This requires a supernova explosion. The force of that explosion creates the heavier elements. These elements (the "dust" from this explosion) again begin to coalesce  and the process starts over, but this time with more "material" to work with. Then it novas (but not necessarily a "super" nova) and, again, you have a bunch of scattered elements which begin to fall in upon themselves. This third generation star is something like our own sun, rich in a variety of material and stays stable for about 10 billion years. Smaller clumps, theory has it, form the planets. The interesting thing about this is that it is usual that the proportions of the amounts of the various elements are generally equal in the different bodies (sun and planets) which comprise the system. This is because they were formed from the same nebulae. The point is, that if a body were to have bunches anything, it would also, probably, have bunches of organic material as well.

Getting back to the life span of aliens, the reason for the discussion on "life as we know it", there is another time-crunch problem with carbon based organisms. We have two kinds of life here on Earth. What we call "Plant" and what we call "Animal". There are certainly "fringe" organisms that one might not be sure how it would be classified. For the lack of a better distinction, I'll say that plants breathe in Carbon-Dioxide and exhale Oxygen while animals breathe in Oxygen and exhale Carbon-Dioxide. The metabolism of plants is much less than animals and, therefore, don't require the energy that animals do. Oxygen is a much more potent "fuel" than Carbon-Dioxide. It burns, for one thing. For another, it is a carcinogen. I understand under absolutely ideal conditions, the human organism might be able last 160 or 170 years before it would "burn out". An organic race of oxygen breathers from somewhere else, however they've evolved, it is likely to assume, is bound by the same chemistry. So it would be very unlikely that another civilization would be of a species of life as we know it and  have a lifespan so long that two hundred years (Earth years) wouldn't be a significant chunk.

So if we were visited by aliens (if they knew where to look and if they found us) it doesn't seem likely that they'd be here to gather information to enrich the knowledge-base of the society they left behind. If they even planned to return, they'd be received by a society as different as we would see Galileo if he showed up today in Times Square. If we were visited I would expect they would do one of two things. They'd either place themselves at our mercy asking for a passport having learned that symbiotic relationships are beneficial or they'd just land, take what they wanted and swat us out of the way if we bothered them. I see no motivation for any alternative. Why? Because the likelihood that the aliens landing would possess a technology anywhere near our own is spectacularly ludicrous.

This solar system's been around for almost 5 billion years. The sun is about halfway through its life expectancy of 10 billion years. The current guess is that the universe itself is about 20 billion years old (certainly, no older). Our sun is probably a third generation star which is the first generation of star to be stable enough to support the time evolution takes to get a foothold. That is not to say that it takes 15 billion years to form such a star (that's the time our sun came into being). A first generation star takes only a few million years to form then supernova and a second generation a bit more than that. So it is conceivable that a third generation star could have gotten underway as early as 10 or 12 billion years ago. If this is true, then the "millions" of civilizations out there might be anywhere on the technology scale from that similar to ours or up to 5 billion years more advanced. Any visiting alien civilization MUST be more advanced that us (since we can't do intersteller, near light-speed travel yet, then a civilization at our technological level wouldn't be here). If the evolutionary process takes about 5 billion years to get as far as we have come, the likelihood that the level of technology of an alien visitor would be anywhere near our own, is astronomically remote. Taking, say, 5 million civilizations, and distributing them them along a 5 billion year history, at the vary least, any visiting civilization would be 1000 years ahead of us technologically (it would be like any of this planet's modern armies showing up an the Battle of Hastings in 1066). The chances are 5 million to 1 we'd be so lucky as to be out "gunned" by only one thousand years.

With all of this, what would an alien species be doing here? How were we found? What possible interest could we have to an alien species that would interest their society who would have to find it at least 200 years out of date by the time they even heard about it and 400 years out of date before they could act on it? True, as a species we, or any other organisms on the planet, could be considered a constant for the period in question. So what does that mean? Are they  building the Encyclopedia Galactica? Just to know? It seems awfully expensive and time consuming given that if the nearest civilization is 200 light-years away, there has to be millions of civilizations just in this galaxy that need to be visited (not counting the planets where life hasn't grown to a technological state). At 400 years per pop? I don't think so.

In conclusion, there is:

1. The extreme remoteness of our planet
2. The speculation that no civilization is nearer than 200 light-years away
3. The limitation of luminous or super luminous space-travel
4. The "what's the point" argument for a "knowledge" gathering species.
5. The vast difference in technology that aliens must possess

For me to seriously entertain the notion that we are being or have been visited, these suppositions have to be explained away. This, rant, for the lack of a better term is by no means meant to be proof that aliens do not exist. In fact, I'm not even proposing that (I assume they do exist, just that they don't visit other civilizations or, at least, not yet ours). However, because of all of the above I find it extremely unlikely that we have been visited. Consequently, I'll need to see some really extraordinary evidence before I can begin to take it on face value.

I would like to "qualify" some of this. The above is what I understand to be the truth. Whether it is or not, I don't know. Naturally, if any of this turns out to be wrong, then I'll have to re-evaluate. As it is, it is difficult for me to imagine an alien civilization, against all these odds, not only find us, but make the journey AND scruple to be quiet about it. There are, of course, all kinds of reports of sightings and visitations. This, of course, is the essences of the mystery. What are they, if not aliens? I don't know. But my ignorance doesn't make them aliens. Do I think these reports are fabrications or flat out lies? Well, probably not all of them. But they may be drawing the wrong conclusion about their environment just as I may have about the above. It doesn't make them nor me a liar. It merely means one or both of us are incorrect. What is certain is that we both can not be correct in our conclusions. To resolve this, I'll need something tangible to go on. Testimony is not tangible.