COMPUTING THE PROBABILITY OF AN ISOLATED HUMAN EXISTENCE

Ron Minarik
(January 2003; Updated October 2005)

Scientific claims for or against an isolated human existence are incomplete without a comprehensive system analysis that leads to a quantitative result. A quantitative approach can reduce subjectivity and focus deliberation of the subject.¹

In this paper human evolution is defined as everything associated with the process, including universe formation and evolution of the necessary environment. Human existence comprises everything within our range of observation.²

External intelligence, if it exists, is defined as intelligence that would exist regardless of humanity formation and which can reside outside our range of observation. We do not rule out the case in which external intelligence is able to move into or out of our observable range. However, we exclude any intelligence that was formed within our observable range (i.e., after universe formation) because ultimately we want to identify aspects of our existence that cannot be attributed to such intelligence.

An isolated human existence is defined as one for which external intelligence was not involved in any aspect.³

(For background material refer to

The procedures used herein are based on the book Search for Existence by Ron Minarik.

Suppose we can show that the probability of forming life by natural means⁴ somewhere in our universe in 20 billion years, from any reservoir of atoms we choose, is essentially zero. Can science then conclude that humanity did not evolve in isolation, that external intelligence was involved? The answer is no.

The problem is that we do not know if there are other universes, some of which had physical laws conducive to life. And, if these universes exist, we cannot confirm that the probability for naturally producing an initial life form in each of them is identical to zero. Given enough universes one of them could evolve the conditions to naturally produce life and randomly mutate it all the way to inquisitive intelligence. The right conditions would make such evolution a mathematical certainty. As the number of suitable universes approaches infinity, the probability for the isolated formation of the inquisitive intelligence we have called “humanity” would approach unity, regardless of the probability’s infinitesimal size for any one universe.

Conversely, suppose we compute a high probability for naturally producing life somewhere in our universe and, still without external help, evolving this life and its environment all the way to human intelligence.⁵ Can science then conclude that humanity evolved in isolation? Again the answer is no. We do not yet know if there was a high enough probability of naturally forming a universe suitable to life. And even if there was, it does not mean that no external intelligence was involved in the process. (An analogy is that biological molecules can be produced either naturally or in the lab with help from human “external intelligence.”)

Let p(NPSU) be the probability of naturally producing a suitable universe, one with the precise physical laws and innumerable physical constants needed to form elementary particles, atoms, molecules, galaxies, solar systems and planets containing the necessary ingredients for life. Let n be the number of attempts at naturally forming a universe. If p(NPSU) and n are small enough then there would be an insignificant chance of naturally forming a universe suitable to life. And the likelihood of producing humanity without external help is even lower because we must include the process of forming life and evolving it to inquisitive intelligence.⁶

Due to observational limitations we cannot directly verify that other universes exist, how they might come into being, or what properties they could possess. Too few suitable universes and isolated human evolution could be extremely unlikely with a probability near zero. Conversely, a sufficient number of suitable universes and isolated human evolution would mathematically be inevitable with a probability near unity. So by considering only human evolution we reach an agnostic dilemma, that science cannot determine if external intelligence was (or was not) involved in our existence.⁷

The Type I Method considers only human evolution. But suppose we include other aspects of our existence. Can we avoid the agnostic dilemma and obtain a quantitative answer we can trust?

At first glance, trying to compute the probability of an isolated human existence seems hopeless. Starting with the birth of perhaps many universes we must compute individual probabilities based on credible observations for an enormous number of microscopic evolution steps and potential evolution paths, not just for humanity but for all aspects of our existence. Even if we could do this in principle, and practical constraints like funding and computing power did not stop us, we may not trust the answer because we could not be sure we included everything. Moreover, we would still have the problem of not knowing if our universe was formed by a natural process, or if there were enough universes to guarantee the formation of humanity in one of them without external help.

But we need not give up. A solution is unrealistic only if external intelligence was not involved in any aspect of our existence. To obtain the correct answer in this case we must compute a high probability for evolving everything without external involvement, including universes. And we must base the computation on credible observations, some of which may be impractical to make.

On the other hand a solution may be attainable if external intelligence was involved in some aspect of our existence. Here we need not account for every microscopic step along the way, some which may have occurred outside our range of observation. We need only show that one or more observable phenomena had a low probability of occurring in isolation, that is, a low probability of occurring either naturally or due to intelligence that may have been formed by nature inside our universe. A low probability for the occurrence of a phenomenon could indicate external intelligence involvement.⁸

We can extend the Type I Method to overcome part of the agnostic dilemma. The new method (the Type II Method) will not let us conclude that no external intelligence was involved in our existence in any way, if such were the case. But if any aspect of our existence involved such intelligence we will have a procedure to test for it.

We start by giving the benefit of the doubt to an isolated human evolution. We assume that a sufficient number of universes eventually evolved inquisitive intelligence (i.e., humanity) in some universe with no external help.⁹ Then we search for credible phenomena¹⁰ that are independent of human evolution and that clearly have a low probability of occurring without external involvement in the same universe as ours, regardless how humanity was formed.¹¹

A phenomenon that meets this requirement is a Type II Phenomenon (TTP). It gives quantitative evidence of an existence that involves some type of external intelligence. But if we cannot compute a low probability for the phenomenon with sufficient confidence we will not consider it.

Fortunately, the Type II probability computations do not require high accuracy. It is only necessary to obtain a credible maximum value. We can make conservatively high probability estimates (including unity) for questionable parameters and see if the computation still gives a low overall probability using parameters that are accurately known. A lower maximum value would correspond to a higher confidence level for external involvement.

Based on the Type II requirement humanity is excluded as a TTP because we do not know how many attempts may have been made in an uncertain number of universes to form us without external help. As already noted, an unlimited number of attempts means external help was not required (i.e., there was a good chance of our natural formation and evolution), but the opposite is true if the number of attempts was insufficient (i.e., there was little chance of our natural formation and evolution). This creates an impasse. Without inquisitive intelligent observers (e.g., humanity) there is no search for phenomena that indicates external intelligence. But it is uncertain whether external intelligence was needed to create the observers in the first place. So to be safe we will not observe ourselves and claim that we are a phenomenon that indicates external involvement. We must find something that is independent of the observer, that is, independent of us.

Excluding humanity as a TTP also means that a TTP is not one that was produced by human intelligence. If we cannot confirm or refute that we evolved without external help it means that any phenomenon that was produced by us has an uncertain probability of occurring without such help.

Using the same rationale, a TTP cannot be one that was caused by any extraterrestrial (ET) life form that is linked to ours through interplanetary or interstellar travel. We want to know if our existence involved external intelligence, regardless where our evolution process began or migrated. However, as explained later, the discovery of ETs not linked to humanity may provide an excellent TTP.

Events associated with human evolution (sunrises, photosynthesis, etc.) do not qualify as TTPs because they could have a high probability of evolving naturally in a universe that evolved our type of physiology. (Many of these phenomena were necessary for human evolution.) The same holds true for phenomena such as meteor showers and the northern lights, despite how spectacular. Although some natural phenomena may not be required for human evolution, it would be difficult proving they were not probable byproducts of natural processes (e.g., galaxy formation) or physical constituents (charged particles, magnetic fields, etc.) that are associated with our evolution.

Also excluded as TTPs are good and bad fortune because they can be attributed to random chance.

It is conceivable that some terrestrial organisms had a low probability of evolving without external help, which could qualify the organisms as TTPs. It could be extremely difficult, however, to prove that any organism played no beneficial role in our evolution—either as a progenitor, a direct source of nourishment to us or one of our progenitors, or as an indirect but necessary benefit to our delicate ecology. And even if we could untangle all possible evolution paths and prove that a particular organism played no part in our evolution, some nonessential organisms may have evolved as natural offshoots to the many random mutations that are postulated to have occurred during the evolution of humanity and its necessary environment.

Search for Existence gives other phenomena that fail to meet the Type II criteria such as various wonders of the world. They could have evolved by natural means, been created by humanity, or perhaps were created by ETs linked to humanity. Sophisticated human “emotions” (e.g., indignation, egotism, and appreciation of beauty) are also excluded. Although they might not seem essential to human survival (as love and fear might be), sophisticated emotions may be necessary for inquisitive intelligence. Moreover, there do not appear to be specific neurochemicals that produce only sophisticated emotions. So we cannot compute the likelihood of sophisticated emotions by computing the chance of randomly mutating the genes that produce “sophisticated neurochemicals.”

There is, however, an aspect of nature that was not needed for human evolution, one that has an very low probability of occurring by natural means. When viewed from earth our sun and moon appear to be the same size. So even if we assume there were enough chances to evolve human intelligence on some planet in some universe without external help, there is little chance of that planet accidentally having a single moon that appears to be the same size as its sun.¹²

This phenomenon meets our credibility requirements to the fullest. Not only is the phenomenon highly predictable and repeatable, it is accessible to nearly everyone on earth.

We might ask why external intelligence would include this phenomenon in our existence. Questions like this belong in the realm of philosophy rather than science. Still, this unlikely occurrence is difficult to ignore. It shifts the burden of proof from advocates of external intelligence to those who say external intelligence does not exist.

There is the unlikely possibility that the “sun-equals-moon” phenomenon was created by ETs within our universe. Although the presence of ETs may make the natural formation of life seem common, and seem to corroborate an isolated existence, the discovery of ETs may actually do the opposite. ETs could provide another TTP and increase confidence in external intelligence.¹³

Suppose we find ET life that was not linked to our own evolution through interplanetary or interstellar travel, and suppose we also show there is a very low probability of naturally forming life in a single universe like ours. The ET would then be a Type II Phenomenon. The rationale is similar to that regarding the apparent size of the sun and moon: Even if we assume that without external help there were enough chances to evolve human intelligence at some location in some universe, there would be little chance of that same universe naturally producing life (especially the same kind of life) in an independent location.¹⁴

Although science may show that some aspects of our existence involved external intelligence, we should not use these aspects to scientifically justify additional involvement such as a planned humanity. A justification for additional involvement, however, may carry weight on philosophic grounds. Why would external intelligence cause our moon, when viewed from the place we inhabit, appear to be the same size as the sun and then stop there? And if we discover extraterrestrial life and determine that such life had to be planned in some way, why wouldn’t ours be also?

Regardless, detection of external intelligence involvement is the initial task for science, not the amount of involvement.

The Type II Method provides a foundation—a quantitative procedure for scientifically investigating a human existence that involves external intelligence in some way. The method should be evaluated on its own merits, irrespective of the initial candidates for Type II Phenomena.

Additional studies can complement research that is either planned or is in progress by various groups.

This paper computes a probability of 2*10^-4 for the apparent size alignment of our sun and moon, but some factors may considerably lower this value:

(A) The likelihood of creating a moon so large and so near the earth to produce the size alignment. (This factor may decrease the probability of size alignment by several orders of magnitude.

(B) The likelihood of creating the apparent size alignment at this point in time in the earth’s evolution, i.e., during the age of humanity.

(C) If deemed significant, the chance that a planet possesses a single moon on a par with its sun—in size and approximate speed of movement across the sky.

Implement Closer studies of Pluto and its moon(s).

Pluto and its moon Charon is the only other observable planet-moon system where the moon is not orders of magnitude smaller than its host planet. So a close-up study of Pluto and Charon is the best empirical way to determine how our moon could be so large. If our moon’s formation (e.g., by planet collision) was different from Charon’s formation (e.g., by planet capture) it would lower the random chance of our moon being large enough to cause the apparent size alignment.

The study also includes the search for multiple moons of Pluto. Finding them would mean Earth’s single moon is unique in our solar system and would lower the probability of forming just one moon around our planet.

We should complete the planned spacecraft mission to Pluto before the window of opportunity closes. Contemporary telescope data is not good enough.

Compute P(NPL), the probability of naturally produced life of any type (NPL) in our single universe..

Computing the actual value of P(NPL) seems unrealistic because we must accurately model all relevant processes. However, we can simplify the computations by choosing modeling parameters that error in favor of higher values of P(NPL) and by assigning a probability of unity to steps that are difficult to analyze. (For example, starting with the big bang we could assume a unity probability for the natural production of the ideal environment and reservoir of atoms to start life at a breeding site, the maximum number of breeding sites in the universe, life forms with an absolute minimum number of atomic slots, a maximum collision rate for randomly placing atoms in the correct slots, and the maximum amount of time available to start life somewhere in the universe.) Then, if we still compute a low enough maximum value for P(NPL) it could indicate: (1) the start of our own life required natural attempts in multiple universes, and (2) there is a low probability of finding naturally produced ET life that is independent of ours.¹⁵

The analysis is complicated by the fact there may be multiple ways (some perhaps hard to envision) that life can naturally form and evolve to inquisitive intelligence. (Regarding our own life, if we were not DNA-based we may be unaware of it and still call ourselves “human.”) Nevertheless, the probability of producing any kind of life by natural means may not be significantly higher than for just DNA-based life. This could be true if all types of life in our universe are based on atomic structure and there is a limited number of atoms that are available.

The analysis is more direct when we restrict it to the probability of naturally produced DNA-based life P(NPL/DNA). The major experimental/analytical tasks are to determine: the minimum number of atoms required by the simplest form of DNA-based life; the prebiotic molecules that could form via random collisions of atoms and molecules in postulated environments advantageous to life; the beneficial and detrimental reactions that increase or decrease the overall probability of naturally produced life in our single universe; and the maximum number of attempts that could have been made in various specified volumes, one of which is our entire universe.

P(NPL) is directly applicable to the probability of naturally producing two independent life forms of any type in the same universe. P(NPL/DNA) is related to the probability of finding DNA-based ET life that is independent of ours.¹⁴

This task is more ambitious than computing the probability of naturally produced life. But if we find an independent source of inquisitive intelligence (I2) in our universe then this computation may significantly increase our confidence that the formation of independent I2 involved external intelligence. I2 requires an organism with many orders of magnitude more atoms than the simplest NPL. So the probability of evolving the NPL plus I2 should be much lower than the probability for just naturally producing life.

The decrease in probability, however, may be somewhat less than expected based on the number of atoms in the NPL and I2. Once life is naturally produced, evolution to I2 may be aided by the presence of surrounding life, a benefit the NPL does not have during its formation. The onset of various life forms may stimulate the evolution to I2 by providing food. The process is still natural, but the reservoir of available molecules via the food may be better suited to I2 evolution than prebiotic molecules would be. Still, the evolution to I2 must overcome many serious roadblocks, including radical environmental shifts that extinguish food or sources of energy.

To simplify this calculation we can again be conservative in favor of an isolated evolution. For example, we first determine the minimum number of atoms that must be correctly placed in I2, a number we are confident cannot be lower. Next we assume that multiple NPLs are packed into the entire volume of every planet and moon in the universe, with a surrounding reservoir of optimum molecules and sources of energy at every stage of evolution. Then, similar to forming the NPL, we use a maximum collision rate to compute the probability of placing the required atoms in the correct atomic slots for evolving inquisitive intelligence with no external intelligence help. Unlike the NPL analysis, however, we must also include the probability of naturally obtaining environmental atoms and molecules needed by organisms at various steps of their evolution to I2.

We should attempt to model and refine the overall process from a prototype NPL to humanity. (The task must account for the possibility of multiple NPLs and multiple molecular interacting paths leading to an I2 result.) The object is not to obtain a convincing evolution map (which may be impractical at the molecular level) nor to determine the exact probability that such evolution could occur in our universe. The object is to determine the maximum probability P(NPI2) for naturally produced I2 in our single universe. P(NPI2) should be smaller than P(NPL). So relative to an NPL-only analysis we should have higher confidence that: (1) a natural production of our own advanced intelligence would require multiple natural attempts in multiple universes, and (2) there is a low probability of finding advanced ET intelligence that was produced independent of ours by natural means.

Search for extraterrestrial life that is not linked to our own evolution.

Suppose we compute an insignificant probability for the natural formation of life in our single universe and we find ET life that is clearly independent of ours. We might conclude the ET life was planned by external intelligence. Even if we assume there were enough attempts in enough universes to evolve our level of intelligence without external help, we cannot account for the natural formation of independent life in the same universe. (We could also search for a terrestrial form of life independent of ours, but we must also show it has a sufficiently low probability of occurring in the total ecology that was needed to develop humanity.)

The probability of finding naturally produced ET life independent of ours depends upon the type of ET life. Probabilities should tend to be lower for independent life based on our DNA/RNA protein-making process. The reason is there are fewer outcomes of natural processes that produce this specific type of life. But when including any type of life we must account for more outcomes, i.e., all the ways life can be produced. This could raise the probability of naturally forming some type of life.

It would seem easier to prove that DNA-based life is independent of ours if it outside our solar system or, better yet, outside our galaxy. We might show the life was too distant to have been in direct contact with us. On the other hand it may be easier to show that life (even terrestrial-based life) is independent of ours if it different from us in some way. It may have a different genetic coding system, a metabolism based on silicon rather than carbon, or even a minor difference in molecular structure (e.g., right-handed versus left-handed amino acids). But, as noted, considering life different from ours means the probability computations must account for all the ways that life can form.

The independent life could be simple or it could bear inquisitive intelligence. Finding the latter (e.g., transmissions from distant ETs) might be stronger proof of external involvement because the probability of naturally forming life and evolving inquisitive intelligence is lower than the probability of just naturally forming life. Furthermore, the probability should be lowest if the ET life possesses inquisitive intelligence and is also DNA-based.

Regardless of the type of life or its independence from ours, the search may help determine the simplest forms of life, knowledge of which is important for probability computations.

We must ascertain that passage of radiation, matter, or some undefined entity into our range of observation does not invalidate a TTP probability computation.

Suppose we compute a low probability for naturally produced life in two independent locations in a single universe like ours. (Again note the probability for naturally producing a specific form of life in some universe could be high if there were enough attempts in enough universes and the life form was in the lucky one.) Then we receive distant transmissions from ETs, that is, signals with information content that indicates they were sent by a form of intelligence.¹⁶ Regarding proof of external intelligence, does it make a difference if the signals came from a region that presently seems outside our range of observation, for example, from outside our universe?¹⁷

Reception of signals from a region we cannot physically reside due to physical law limitations could automatically indicate external intelligence, provided we could ascertain where the signals came from. And as already noted, signals originating inside our universe from intelligence not linked to ours could also indicate external intelligence, provided such intelligence has a low probability of natural production and evolution. Thus, if P(NPL) is low, it may be irrelevant where the signals originated as long as the evolution of the transmitting intelligence is independent of our own.

Even if we conclude an ET resides inside our universe, we should consider a situation in which life (or a major component thereof) could be produced naturally due to enough attempts outside our range of observation and then pass into it. We should study the ETs plus their location within our universe and try to determine where they could have originated. ET life forms based on molecular structure would not seem to survive a passage into our universe during its formation. But we might determine that life or a basic constituent thereof (e.g., a molecular catalyst or biotic subunit) could pass into our universe at a later time and jump-start a natural evolution.

The effect on a TTP probability computation of any entity passing into our range of observation should be evaluated on a case-by-case basis. If external intelligence was involved in our existence the involvement likely required passage of some entity (particles, radiation or entities presently unknown) into our universe. We might consider how various entities (possibly including various forms of information) would be affected by passage into our observable range.

The effect on a TTP probability computation of any entity passing into our range of observation should be evaluated on a case-by-case basis. If external intelligence was involved in our existence the involvement likely required passage of some entity (particles, radiation or entities presently unknown) into our universe. We might consider how various entities (possibly including various forms of information) would be affected by passage into our observable range.

Nevertheless, the first step is to detect external intelligence involvement, regardless of the mechanism for such involvement. Moreover, passage of entities into our range of observation should not be an issue regarding probability computations for some Type II phenomena. One such phenomenon would seem to be the sun and moon appearing to be the same size when viewed from earth.

Determine the impact of multiple Type II Phenomena.

A Type II Phenomenon (TTP) has a low probability of occurring without external involvement. But suppose there are events that never occur yet would become TTPs if they did occur and were observed. These potential TTPs could raise our chance of seeing one. Then, if we did, our confidence in external intelligence involvement would be reduced.

For example, there may be multiple ways to naturally produce life. This raises the chance of finding life independent of ours elsewhere in the universe. Or perhaps there are highly improbable events that have not occurred, such as the sun starting to rise in the west or the stars arranging themselves to spell out EXISTENCE IS PLANNED. Although these phenomena each have an infinitesimal chance of occurring naturally, they all add to the overall probability of seeing at least one TTP. The question is whether the collective chance of occurrence of potential TTPs can raise the probability of seeing one from essentially zero to a value that prevents us from claiming external involvement.

The math for multiple TTPs, each having the same probability, is straightforward using the Bernoulli distribution.

       w_n(m) = C_mⁿp^m(1-p)^n-m [1]

where:

       w_n(m) is the probability of occurrence of m observed TTPs,

       n is the number of potential TTPs, regardless how many actually occur,

       p is the probability that any single TTP could occur, and

       C_mⁿ is the binomial coefficient n!/[(m!(n-m)!].

Several cases illustrate the formula.

If there is only one potential TTP that could occur with probability p, the chance that one TTP does occur is:

       w₁(1) = p.

If there are n potential TTPs that could occur, each with probability p, the chance that all n occur is:

       w_n(n) = pⁿ.

If there are n potential TTPs that could occur, each with probability p, the chance that none occur is:

       w_n(0) = (1-p)ⁿ

and the chance that one or more occurs is:

       1 - w_n(0) = 1-(1-p)ⁿ

which is approximately np for small p.

Multiple TTPs (i.e., m > 1) have a lower overall chance of randomly occurring and being observed than does a single TTP. (The overall chance of occurring is proportional to the product of the individual probabilities.) So our confidence in external planning grows significantly as we observe more TTPs.

Conversely, there may be multiple (n > 1) TTPs that could potentially (but not necessarily) occur with no external involvement. This increases the chance that some TTPs actually do occur so observing one is more likely. (For low probabilities the overall chance of occurring is roughly proportional to the sum of the individual probabilities.)

The math seems to favor a lower overall probability of TTP occurrence with increasing TTPs (probability multiplication versus addition), provided a sufficient fraction of potential TTPs always occur. But we must be sure that a large number of nonoccurring potential TTPs does not push the probability towards unity, where we cannot claim external involvement. This could throw us back into an agnostic dilemma, where we need to know the number of nonoccurring TTPs with enough accuracy but are unable to make a good enough estimate.

To avoid the dilemma we should be able to partition potential TTPs into statistically independent categories. (For example, the apparent size of our sun and moon should be independent of the formation of extraterrestrial life.) Then we ascertain that at least one category has a sufficiently low probability of occurring without external involvement.¹⁸

Additional work is needed to: (a) designate potential TTPs and (b) refine the statistics, taking into account TTPs with different individual probabilities.

The Bernoulli distribution is also a valuable tool for eliminating commonplace phenomena that might undermine the importance of bona fide TTPs. Otherwise we might say that our existence provides many phenomena that have a low probability of occurring without external involvement and that phenomena such as the apparent size alignment of our sun and moon is not so special.

For example, suppose a wasteland has a high probability of forming mud cracks, but there is a very low probability that an existing crack is located exactly where it is to the nearest millimeter. We do not want to conclude that the crack indicates external intelligence involvement. And, according to the Bernoulli distribution, we will not. The probability of interest is not the probability that a specific TTP could occur (i.e., the probability that a crack is in its existing spot) but the probability that any TTP could occur. In this case there are many potential TTPs that could occur, i.e., cracks in other spots. Some of the other cracks may have also occurred but a very high number of them did not. When we include all the potential TTPs that could occur, the probability for the occurrence of at least one of them is about the same as the probability for cracks occurring in the first place.

Another example is that a vehicle has a one-in-ten-million probability of receiving the license plate it was assigned. This example might be handled in the same way as the crack in the ground but it can be immediately discarded because it involves human intelligence. Here the intelligence artificially fixes the number of observed TTPs at unity: the vehicle receives only one license plate. Also, the probability p that any single TTP could occur is artificially set equal to unity divided by n, the number of potential TTPs (in this case the number of license plates that were assigned). We must not cause an artificial relationship between n and p in the Bernoulli distribution.

The goal is to provide a quantitative test criteria for any observed phenomenon.

The book Search for Existence also requires a Type II observation to be significant in some way. This is a philosophical issue we would rather avoid in a scientific investigation. Still, philosophical issues regarding our existence are important, and this one may play a scientific role in multiple-TTP computations.

Take the case of a solar eclipse, one in which our moon appears to be the same size as our sun as seen from the surface of our planet. Although this phenomenon has an incredibly low probability of evolving at random, one might argue that this type of solar eclipse would likely occur on other planets in our universe. Should we add these eclipses as potential TTPs, which makes it more likely a TTP will occur? Or should we exclude other solar eclipses by saying they are not significant to us? The latter choice would mean our own point of observation affects the probability calculation.

We could try to avoid the issue by saying a phenomenon must occur within our present range of observation to qualify as a TTP. This requirement presents no problem for phenomena outside our universe because physical limitations prevent our observing them. And we could say that other eclipses in our universe should not be TTP candidates if they cannot be observed at this point in time.

Nevertheless, the observation of a phenomenon depends on our ability to see it. We could limit the number of potential TTPs in our probability computations by not looking too hard, which may be as unscientific as we can get.

We want our computations to be scientific, to be as objective as possible. But this does not mean we can completely separate ourselves from the observation. Indeed, quantum theory says we cannot do so. Even a simple observation of an object affects it in some imperceptible way. Of course we could choose not to observe an object, but then we could not be sure it exists.

Solar eclipses on planets in other galaxies fall outside our observable range. Although we can postulate the eclipses take place, we need to observe them to be sure. Perhaps there are no other eclipses and ours is unique, one that was planned for us to see. Or perhaps if we ever journey to other galaxies we will observe more TTPs, and increase our confidence in external planning.

So for now we say that potential TTPs must have a low probability of evolving within our observable range without external involvement. If we reduce our number of observations we theoretically lower the number of potential TTPs, but we also prevent ourselves from observing more of them.

Regarding the significance of a Type II observation, the following seems appropriate. When we observe something that clearly has a low probability of occurring without external involvement (and thus gives a high probability of external intelligence) we cannot avoid the fact that the unlikely observation is significant to us.

Once science has a viable method for detecting external intelligence plus some promising evidence, various questions gain significance. Why would external intelligence present obscure clues like the apparent size alignment between the sun and moon? Why wouldn’t the intelligence just come out and present itself in a more convincing manner? Must the external intelligence be as isolated as possible from us, which permits a measure of independence and creativity on our part?

What would be the purpose of the clues? Why give any at all? To give us hope in adverse times? Why aren’t there many of them? To maintain a high degree of isolation? Perhaps more importantly, can the way a clue is presented (or had to be presented) indicate our role in the scheme of things?

And how are the clues provided? Would the external intelligence find a suitable universe and then choose a planet that could not only host life but would also have the sun and a single moon appear to be the same size when humans are there to look up from the planet’s surface? To do this, how would the external intelligence find our universe and observe us? Could the external intelligence pass various entities, including itself, into our universe?

If we show there is an extremely low probability of finding naturally produced independent ET life that is similar to ours yet we find such life, does it mean that external intelligence chose a suitable universe to seed with life in various places?

Tying together questions like these may provide enlightening answers.¹⁹

1. System Definition
To quantitatively analyze human existence and the related topic of human evolution we define a system consisting of one or more universes that are specified in space and time. If our universe is the only one that exists then the system consists of only one universe. If there are multiple universes then the overall system consists of multiple subsystems, each with its own timeline.

The system space consists of the volume occupied by the universe(s) and the (composite) timeline starts with the birth of one or more universes and runs through the onset of inquisitive intelligence, the kind of intelligence that questions its own existence and which in our case we have called “humanity.” The system has a large enough number of components (particles with and without mass) to permit statistical methods, particularly the assignment of probabilities to various outcomes.

There could be processes related to human existence that lie outside the defined system, e.g., processes leading to the formation of one or more universes. But until we can verify such processes we restrict the analysis to the above system definition.

2. Our Range of Observation
Our range of observation includes everything that physical limitations do not preclude us from scientifically observing. Because of such limitations our scientific range of observation presently excludes regions external to our universe as well as any region that cannot be defined in terms of our 4-dimensional space, regardless if it is considered to be outside or inside our universe. This means some entities may be within our system—e.g., in other universes if they exist—yet outside our range of observation.

Unobservable regions could also include regions within black holes and fundamental particles. (For convenience we shall refer to these entities as being inside our universe and therefore within our system.) Regions within distant galaxies, however, are not classified as unobservable because humanity may eventually be able to observe or even reach them.

Scientific developments could change our range of observation and perhaps dictate a new system definition as well as a redefinition of our universe. (For example, we may later regard regions “within” fundamental particles to be outside our universe and perhaps even outside our defined system.) But this paper’s approach for determining the probability of an isolated human existence should still apply.

Some aspects of human evolution may occurred outside our range of observation, such as processes that formed a universe suitable to humanity. Likewise, external events may have affected human existence, for example, unobservable subatomic processes that are needed to form atoms which, in turn, comprise the various phenomena we observe. Unobservable events should not be a problem, however, because we need not observe everything to ascertain a low value for the probability of an isolated existence. We need only compute a relatively low maximum probability for at least one observed phenomena. (On the other hand, we would have to compute a high probability for the natural occurrence of everything we can observe to ascertain a totally isolated existence.)

3. External Intelligence Involvement
Previous material by the author referred to external planning rather than external intelligence involvement or, simply, external involvement. The latter terms are now used to include the case in which external involvement, if it exists, may have been unintentional rather than planned. However, the terms external help and external planning are occasionally used where external involvement would appear to be intentional.

Also, if external involvement exists it does not necessarily involve all aspects of human existence.

4. A formation of life by natural means refers to processes that take place according to physical laws and random collisions of particles. When we speak of a natural human evolution, however, we must account for the decision-making that intelligent species use to benefit survival. This creates a semantics issue. For example, is it “natural” for an advanced species to aid survival by hiding from predators or making weapons for protection? To account for “natural decision-making” we could broaden the definition of natural to denote a process that involves no external intelligence. Still, regardless where we draw the line in defining natural, the key point is that various aspects of human evolution and human existence can be regarded as statistical processes that can be analyzed in terms of probabilities.

For additional discussion regarding terms such as “natural” and “random” see NOTE 8, Semantic Issues in the paper

5. The supposition of a high probability for obtaining life and human intelligence in our universe without external help is given for discussion purposes and is presently unsupported by a comprehensive computation.

6. A “theory of everything” might one day show that a universe formed by natural means had to possess our set of physical laws. This could mean the probability of forming our universe in a single attempt is essentially unity. But unless such a theory is established, which means quantified and substantiated with credible observations, we will not embrace it. Moreover, there is also the question whether science will ever ascertain “everything.”

7. We must also consider a situation in which various types of inquisitive intelligence (some unimaginable) might be formed by natural means in universes with different physical laws. Assuming it were irrelevant how our intelligence was formed—e.g., if it were not DNA-based we would still call ourselves "human”—the number of suitable universes would increase and raise the probability of our natural formation. However, if we cannot verify this situation with credible observations we cannot use it to resolve the agnostic dilemma.

8. It is assumed that we cannot detect external intelligence that never interacts with our existence in any way, either directly or indirectly. Also, if external intelligence acted outside our present range of observation to affect our existence, (e.g., by creating our universe or by creating life prior to insertion into our universe) we cannot use such acts as credible evidence of such intelligence unless observational verification becomes possible.

9. We are not claiming that human evolution occurred without external intelligence being involved. When drawing conclusions from an observation we merely want to reduce the uncertainty related to our own presence, such as the uncertain number of universes that may have been involved in our formation. To be objective analysts we should not be part of the phenomena being analyzed.

10. Credible Phenomena
Credibility is enhanced when a phenomenon is predictable (we know approximately when and where to observe it), repeatable, and accessible to many observers who are preferably living today.

11. The Type II Method is somewhat analogous to holding a lottery where the chance of winning is very small for each ticket holder. Random drawings are held and we keep observing numbers until we obtain a winner (corresponding to humanity being produced after enough natural attempts). Then we hold a second lottery and it turns out the winner lives in the same house as the first winner—a highly unlikely coincidence that suggests an “unnatural” act occurred outside our range of observation.

12. Probability_of_Sun_and_Moon_Size_Alignment
When viewed from earth the moon’s apparent size fluctuates between plus and minus 8 percent of the sun’s apparent size. But the apparent size alignment at the center of the fluctuation is less than 0.1 percent. If we assume it is equally likely for the moon’s apparent size to be between zero and 1000 percent the sun's apparent size, then the chance of the fluctuation center being within +/- 0.1 percent (a total range of 0.2 percent) is 0.2 divided by 1000. This gives a probability of 2*10^-4 or 1 in 5000.

Our moon is also moving away from earth. It is believed that several billion years ago the moon was more than 20 times closer than it is now. One might then question the chance of the moon appearing to be the same size as the sun at the same time humans came into being. Of course it may be that life was improbable until well after the moon’s cataclysmic formation, when the moon had moved much further away. Nevertheless, the chance of such an exact alignment at this specific point in time may lower the probability still further.

Search for Existence incorrectly states that all other moons in our solar system have a volume that is less than 0.1 percent the volume of its host planet. The volume of Pluto’s moon Charon is about 14 percent the volume of Pluto. But we do not yet know if Charon was formed in the same manner as Earth’s moon, which was presumably formed by Earth’s collision with another planet.

We need closer observations of the Pluto-Charon system to help estimate the chance of forming a single moon like ours, one that is much larger than normal. Charon’s close proximity to Pluto could mean the formation of Charon was relatively recent, which can aid the investigation. And finding additional moons for Pluto would mean no known planet other than Earth has a single moon. This could indicate that when moons are created during a collision of planets there is a high probability of creating multiple moons, which further reduces the probability for randomly forming a planet with a single moon. Regardless, even if Charon is a single moon, we may determine it was captured by Pluto rather than formed like our moon. This would mean there are no moons other than ours that were formed via a collision of planets, which empirically reduces the probability for the natural formation of our moon.

It is also important to consider the relationship between the evolution of inquisitive intelligence and our moon’s geometry. If the moon’s size and proximity increased the chance of an isolated human evolution it might also increase the probability of the sun and moon’s apparent size alignment at the time humans came into being. Current theory says the moon was produced about 4 billion years ago by Earth’s collision with another planet, and that the moon started out much closer to the earth and slowly moved away. The effect of the collision could have prevented humanity from evolving too soon, when the moon would have appeared much larger in the sky.

There is also speculation that a large moon helped make Earth more conducive to life. For example, strong tides from a closer moon could have aided the movement of simple organisms between the sea and the land, although the tidal benefit to such movement may be insignificant. Tidal forces could have also created enough elevation differences on Earth such that an optimum percentage of Earth’s surface is covered with water, a feature that is highly dependent on the amount of water available. Then there is the notion that our large moon prevents Earth from excessive wobbling on its axis of rotation, which could hinder our type of life. Even if there is some truth to these speculations, it does not explain why the apparent sizes of the sun and the moon are essentially the same today.

On the other hand, some factors may considerably lower the overall probability of the apparent size alignment. As noted above, based on other moons in our solar system, there could be little chance of naturally forming a moon as large as ours. Also, the probability could be low for naturally producing life on earth at a specific time such that the life would have randomly mutated to inquisitive intelligence at the time the moon had moved far enough away to produce the apparent size alignment.

If we choose to attach significance to a single moon on a par with the sun—in size and approximate speed of movement across the sky—we could reduce the probability by the chance that a planet would have exactly one moon that moves in this manner. (With the possible exception of Pluto, all the other planets in our solar system have no moons or multiple moons.)

Although an accurate probability calculation may be impractical, we may be able to obtain a credible maximum value that is relatively small, especially since the era of humanity does not appear to require such an exact alignment.

13. Extraterrestrials
Humans reside on earth. Extraterrestrials (ETs) are defined as life that may exist outside Earth. ETs might range from the simplest of life forms to high levels of intelligence, perhaps more advanced than humanity’s and perhaps in a form much different than ours.

We distinguish among several (but not necessarily all) types of ETs and state their relevance to computing the probability of external intelligence. Although ETs do not presently meet the credible phenomenon criteria in NOTE 10, no observation to date refutes their existence. Nor can we claim ETs will not be observed in the future. Types of ETs may include:

(1) External intelligence residing outside our range of observation (e.g., outside our universe). Because we cannot directly observe these ETs, much less determine how many natural attempts were made to form them, they will not be used in probability computations for determining their existence.

(2) External intelligence that has passed into our range of observation and which thus resides in our universe. These ETs may be of computational interest as noted in (3).

(3) ETs that can only reside inside our range of observation and that are not linked to our own evolution. If we detect some of these ETs and, based on their physiology, compute a low probability for their natural formation and subsequent evolution it could indicate external intelligence involvement. The rationale is that regardless whether or not we evolved without external help in an uncertain number of universes, there is little chance of ETs not linked to us being formed without external help in the same universe.

Note that we may not be able to tell the difference between these observable ETs and external intelligence ETs, especially if we detect the ETs via distant signal transmissions. This should not be a problem, however, because either case would indicate external intelligence.

On the other hand, if we detect some ETs and can show they have a high probability of forming by natural means in our universe we still may not be able to claim that no external intelligence was involved. (External intelligence may have stepped in to aid some part of the natural process, analogous to our planting seeds rather than having seeds fall naturally upon fertile soil.)

(4) ETs that can only reside inside our range of observation and that are linked to our own evolution, for example, through interplanetary or interstellar travel. These ETs are not of computational interest because we do not know the number of natural attempts at forming humanity and ETs linked to humanity that may have occurred in an uncertain number of universes.

14. The Probability of Two Naturally Produced Independent Life Forms in Our Universe

If P(2NPIL) is the probability of two naturally produced independent life forms appearing in our universe then

       P(2NPIL) = P(NPIL₁) * P(NPIL₂)

where P(NPIL₁) is the probability of naturally producing the first independent life form (IL₁) and P(NPIL₂) is the probability of naturally producing the second independent life form (IL₁).

In general IL₁ and IL₂ could be any independent life forms but an important case is that one of them, IL₁, is humanity. The value of P(NPIL₁) is uncertain. It would be near unity if there were enough attempts in enough universes to evolve us in one of them by natural means, but this is something we may never be able to confirm or refute. So based solely on credible observations we can only say that P(NPIL₁) lies somewhere between zero and unity, that is

       0 < P(NPIL₁) < 1.

This means

       P(2NPIL) < 1 * P(NPIL₂).

For convenience we change NPIL₂to NPL where it is understood that NPL refers to life that is independent of ours and is naturally produced in the same universe.

(If we knew for sure there was only one universe then P(NPL) could represent the probability of naturally producing our own life, whatever type it turned out to be. However, this case is not of interest in computing the probability of external involvement because of the uncertainty regarding the number of universes that may have been involved in our formation as well as the uncertainty in how we were produced. But there is no uncertainty in the number of universes involved in the natural production of ET life that is independent of ours and residing in our universe.)

With the uncertainty in our own evolution out of the picture we focus our efforts on computing the probability of naturally produced independent life somewhere in our universe. Restricting the computation to our single universe restricts the number of natural attempts at producing life, which reduces the uncertainty in computing P(NPL). A low enough upper limit for P(NPL) could indicate that independent life in our universe was not produced by natural means.

We shall refer to DNA/NPL as naturally produced life in our universe that is based on our own DNA/RNA protein-making process. (NPL still refers to any type of naturally produced life in our universe.) Although it should be easier to prove that two forms of life are independent if they are noticeably different (e.g., DNA versus a different genetic coding system), P(NPL) could be higher than P(DNA/NPL). P(NPL) must include all the ways life could potentially form which could raise the probability of seeing at least one type of life. (The situation is similar to accounting for all TTPs that could potentially occur when computing the probability that a TTP will occur. See Determine the impact of multiple Type II Phenomena in the section Recommendations For Future Work.)

The computation for P(DNA/NPL) is not only easier to model than the one for P(NPL) (we need not account for every possible type of life) but initial results indicate an extremely low probability for naturally producing a minimal form of DNA-based life in a single universe like ours. (Initial results will be given in a separate paper. Refinements are needed, however. See Compute P(NPL), the probability of naturally produced life in our single universe in the section Recommendations For Future Work.) Furthermore, the probability would be even lower for naturally producing (and discovering) independent DNA-based life that is relatively advanced. The probability of naturally producing life and evolving it to a higher form (along with the necessary environment) is lower than just naturally producing DNA-based life.

Even if we discover DNA-based life that is independent of ours, such life may not be exactly the same as ours. For example, we may find an independent organism that employs the DNA/RNA protein-making process but the organism is different in some ways from any earth-based organism. Indeed, there are differences among the same type of earth-based organisms. We should take this difference into account when performing probability computations. (Actually, we would take into account the identical parts among organisms. In general it would seem the closer the similarity, the lower the probability.)

If there is a low probability of finding independent DNA-based life, finding such life could mean that our universe was “seeded” in various places by an external source.

15. We must not fall into the trap of observing our environment and, seeing that life flourishes everywhere, conclude that there is a high probability for the natural production of life in multiple independent locations within our universe. Specifically regarding humanity, if it indeed required many attempts in multiple universes to naturally produce us, we would need to be in a universe (and location within that universe) where life can flourish. But that does not necessarily mean that life independent of ours can routinely originate and flourish naturally in more than one place the same universe.

16. We shall generally refer to distant transmissions from an intelligent origin as “ET-signals." They might be anything from intelligently modulated radiation to a form of information that is presently unknown. Also, though an unlikely occurrence, we need not rule out distant transmissions that indicate the remote presence of what we might deem a non-intelligent life form such as a microbe. Signals emanating from an inanimate entity, e.g., some type of beacon, could also aid the search for external intelligence if the entity was created by an independent life form.

17. We might argue that our reception of signals or other information from outside our present range of observation thereby extends that range. Future observations of distant transmissions may necessitate a redefinition of our universe and range of observation.

18. One might argue that no two phenomena within our observable range are completely statistically independent. So a more rigorous treatment would show that the correlation between phenomena categories is insignificant when computing the probability for a specific TTP. In some cases, however, an insignificant correlation may be simply determined by inspection. (For example, the sun appearing to be the same size as the moon should have an insignificant effect on the probability of naturally forming intra-universe ET life that is independent of ours.)

19. We can also consider the formation of external intelligence—whether by enough natural attempts outside our range of observation or due to planning by a still higher level of intelligence. But such formation lies outside the scope of this paper, which is to take the initial step in a scientific search for any external intelligence that was in some way involved in our existence.

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