Saw 12 Assumptions for Extraterrestrial Life by Kevin Kelly.

“1) Life is rampant and common throughout the universe.”

Agree

“2) This ubiquitous life is single-celled and elemental, and remains at this level for very long periods. Most planets with life never advance beyond the single cell.”

It starts out fine. Clearly it takes considerable time for complexity to evolve in single-celled life, for a suite of enzymes that allow a cell synthesize the chemicals it needs rather than rely on scavenging them, to develop efficient processes for replication, mechanisms that preserve homeostasis and let the cell live in less friendly environments, etc.

I think multicellular life in various forms will be ubiquitous–cells interact with other cells just as they interact with the environment, and coordination at various levels–from chains of cells, to swarms of cells, and things like slime molds are inevitable. And I think interactions between organisms–symbiosis and and complex stable interactions like those found in protists and lichens will be ubiquitous.

“3) While life on some planets is seeded from outside sources, most life spawns independently. The conditions to hatch elemental life are relatively common.”

Agree

“4) Most life is DNA-ish, that is a double helix-based on DNA or DNA-like molecules. DNA is the most remarkable molecule in the universe. There may be other life-supporting molecules that can be designed, but none (or few) other than can self-assemble and self-create.”

I don’t think chemistry is well enough understood to assert this limit or expectation of a RNA/DNA basis of life. And even with RNA/DNA-like biochemistry, there are likely many variations–different nucleotide pairs, organisms with two bps, or more than four.

“5) Any natural non-DNA-ish life follows the same patterns of distribution as DNA life.”

Mostly agree. There may be non-carbon based life, but given we have no examples or ability to design/create life, speculation is pointless. Other carbon based, especially RNA/DNA based life will have similar requirements and limitations that Earth life does, and will thus live in similar environments.

“6) Multicellular life is relatively rare. The evolution of higher organisms requires goldilocks conditions to be maintained for billions of years. The mild variability and persistence of favorable planetary conditions is relatively rare — compared to single cell life. But even “relatively rare” events in a vast universe will yield hundred of billions of examples.”

While I think multicellular life is ubiquitous, life originating in the sea can take lots of odd forms. I think bilateral life forms are useful enough to be commonly arise, but may not be the dominant form on other planets. I think bilateral, walking land organisms won’t occur everywhere, and will often appear late in a planet’s history. It took 4 billion years for insects to evolve on Earth after life appeared.

“7) Advanced civilizations are relatively rare compared to multicellular life (and to life), but are countless in number.”

Agree. There are several hurdles, a) mobile land animals, b) land animals with brains, c) intelligent land animals, d) technology creating animals, and each one takes time to evolve and may not evolve on any particular planet with life. Also, the planet has to have suitable conditions for large land animals for hundreds of millions of years.

“8) Since most life begins with DNA, the evolution of life on a planet converges onto a limited set of shared development sequences until it reaches the threshold of self-direction. Once evolution begins self-direction, including migrating to new material substrates, its evolutionary path diverges widely. Naturally evolved life tends to be similar across galaxies; consciously designed life tends to be unique.”

Hmm. I don’t have strong feeling that either part of this is true, but it could be.

“9) Sufficiently advanced civilizations can synthesize, manufacture, or create any resources found naturally anywhere else in the universe. There is no material, or energy source that cannot be synthesized at home if you have the know-how.”

While the possibilities are the same everywhere, I think there are some big barriers, and life will mostly be limited to the resources available in one or a few nearby solar systems. It seems likely that the ability to create or change stars is mostly too difficult. Are technological civilizations likely to converge on similar end-point technologies, or are there too many possibilities, or some tech just very hard to execute, or unpromising at early stages, so rarely developed? For example, is a mastery of nanotech possible, and if so will it be ubiquitous?

“10) The only reason for an advanced civilization to visit another planet is to see if there is another civilization which has invented things it has not, and perhaps could not invent. Invented resources are thus unlimited in scale and scope, and can be discovered only in unique places in the cosmos. Interstellar travel is essentially not travel through cosmic space but travel through possibility space. You visit another planet to visit other possible minds to see if they have thought of fabulous technologies your collective minds cannot reach.”

Growth and expansion are natural characteristics of life, so I think the desire for exploration is common, as is curiosity. A planet with complex life or intelligent life will attract the attention of every alien nearby. There are enough possibilities for life, and the organization of ecosystems, not to mention things intelligent organisms can do, that other planets will life will always be a novel and a draw.

Only sub-light speed travel is possible. It may turn out that travel between stars is too difficult, that it takes too much energy and effort to be common, so interstellar exploration is rare, or rarely successful.

“11) Every day a few probes of these billions of interstellar civilizations visit our planet scoping out our technological state. These technological probes appear briefly in order to see us, and disappear once they have inspected our inventory. So far we have little to offer; nothing that can’t be found on millions of other planets.”

Strongly disagree. The universe is large, and it takes a long time to travel to other stars. The best average speed of travel may be 1% of light speed, or a tenth of that. Earth hasn’t been interesting for very long, and even ‘close’ aliens only 1000 light years away haven’t had time to travel to Earth. The only way for it to be likely for there to be aliens in the solar system is to assume that intelligent aliens have spread probes to every likely solar system to wait for intelligent life to arise (as Brin postulates in the novel Existence). This isn’t the case.

“12) Most life capable of meaningful interstellar travel is indistinguishable from technology.”

Huh? Kelly can’t mean that aliens would look and sound like a cell phone, so I can’t imagine what he means. That aliens are likely to be a ‘created organism’, with mastery of technology, and could look or sound like anything? That an alien could (and would?) successfully hide? This seems like one possibility, but it stands on a chain of assumptions, most of which seem unlikely.

An interesting question is, what is the limit of the telescope? What can be observed from our solar system? A ‘best telescope’ would be located in space, far from the sun, and could be large and precisely made. If there is life on neighboring or distant planets, can we detect it and learn any details about them from observations made from our solar system?