Do you believe we are alone in the universe?

The universe is far, far, far too big and ancient a place to reasonably rule out life elsewhere. Even if the galaxy is currently lacking intelligent life other than our own (and I'm not convinced it is - our expectations of what intelligent life should be doing with itself is, obviously, prejudiced toward our own ideals), I don't think it was nor will be. I'm also much more optimistic about FTL.

 

[Ryujin]

This poll is missing the scientific answer #3 which is that "We're still looking, and I'd hate to say yes without direct and compelling evidence, and I'd hate to say no when it's hard to prove a negative like this."

But by the mere fact that we are on a world teeming with life, and the poll does not ask "are we the only sentient life in the universe," I'd have to vote for aliens being out there. They just may not be sentient, technological aliens.

Sentience may, in fact, turn out to be a disease that is its own cure.

 

[Morrus]

The galaxy is around 200,000 light years from end to end. At 0.1 it would take 2 million years just to cross the galaxy, let alone visit every planet in the entire place.

100,000 light years.

And if it took a million years to cross the sister, if you’re radiating out like a virus in every direction at that speed (assuming no stops) it takes only half that to cover the galaxy completely, on average, assuming you start from near the centre.

The current estimates are closer to 10M, though, as it assumed that each probe takes a long time to acquire local resources and replicate itself multiple times over.

 

[Dannyalcatraz]

This is an important element - the presence of one such species likely suppresses others from developing. Historically, when tool-using humans enter an area, extinctions of larger fauna follows. So, the probability of producing one intelligent species could be high, but the probability of producing a second while the first is around may be very low. This makes the 1-in-8-million to be a bit simplistic.

Technically, aren’t Neanderthals considered a separate species from us? If so, our planed was home for 2 sentient species simultaneously and in close proximity at least once, briefly, in the past.

 

[Umbran]

Technically, aren’t Neanderthals considered a separate species from us?

Yes. Neanderthals are one of those examples that tell you that the definition of "species" isn't too simple. In one way, yes, different species - loads of clearly evident different anatomical traits. In another sense there was some interbreeding with early modern humans - it is expected that if you aren't of African stock, 5% or so of your DNA is either Neanderthal or Densiovan.

If so, our planed was home for 2 sentient species simultaneously and in close proximity at least once, briefly, in the past.

And by "briefly" we are talking from 200,000 to 350,000 years or so that Neanderthals and Homo sapiens overlapped on the Earth. We might also include the Denisovans and Homo floresiensis, which might bring the number up to 4. We co-existed with other intelligent species for something like 20 times longer than we have been civilized.

 

[Celebrim]

@Morrus;The observable universe is of finite size. The observable universe is also of finite age, and thus finite size is the reasonable estimation of the size of the universe from known facts. It's possible that there exists an unobservable universe but anything outside our light cone might as well not be in this universe, so lets assume the universe is finite. We can estimate the number of atoms, galaxies, planets and so forth in the universe. We come up with very large numbers, so 10 to the 60th power or 80th power or whatever. The exact number doesn't matter for the next reason.

However, these seemingly large cosmological numbers for the breadth of time and space are trivial compared to the complexity of the information contained in the most primitive life forms we are aware of. Indeed, they are trivial compared to simplified DNA structures which we know are insufficient to support life. For example, the number of possible combinations of mitochondrial DNA in a typical vertebrate species is something on the scale of 10 to the 1000th power. Worse, the number of combinations that fold into any sort of protein, much less ones helpful for promoting homeostasis, energy consumption, and all the other things necessary for life to function is known to be very much smaller than the scale of possible combinations. Add to that the complexity of the surrounding hardware necessary to process that information, and it becomes incredibly unlikely that life will spontaneously generate from non-life. It is so incredibly unlikely that there is no reason to believe that it has happened more than once in the universe, and at the least there is no reason to believe that it has happened so often that any two planets in the universe support life at the same time. The frequency of spontaneous generation is probably so low, that it is lower than average life span of a living world before it gets wiped out by some cosmological catastrophe. Barring the discovery of some previously unknown self-organizing principle that causes life to appear at rates faster than random chance, we are almost certainly alone - the first technologically advanced species in the history of the universe. It's likely that not only is nothing else out there that can hear us, but that every other world is sterile.

There are various objections you can make to this line of argument, but they all prove to be very weak upon inspection. The most common to come up is to say that I'm only speaking of "life as we know it". But the more we know about how life works, and the more we realize life is actually nothing more than very complex machinery that processes information, the fewer alternative possibilities for arranging life exist. If you start looking at variant chemistries that might support life at other temperatures and pressures, they all turn out to have immense problems for sustaining life compared to the carbon/water based sort we do know about. It's not at all clear that any other sort of life can evolve in this universe, and if it could it's equally clear that the possibility of it evolving is even lower than the sort we do know about. Hence, "life as we know it" likely to be the only sort that exists.

 

[Dannyalcatraz]

Yes. Neanderthals are one of those examples that tell you that the definition of "species" isn't too simple. In one way, yes, different species - loads of clearly evident different anatomical traits. In another sense there was some interbreeding with early modern humans - it is expected that if you aren't of African stock, 5% or so of your DNA is either Neanderthal or Densiovan.



And by "briefly" we are talking from 200,000 to 350,000 years or so that Neanderthals and Homo sapiens overlapped on the Earth. We might also include the Denisovans and Homo floresiensis, which might bring the number up to 4. We co-existed with other intelligent species for something like 20 times longer than we have been civilized.

Yep. And if past is prologue, I might just get my Bonobos with crossbows.

Or, more seriously, if we can have multiple sentient species on a planet simultaneously, the question of the odds of sentient life being present elsewhere/elsewhen in the universe gets a new wrinkle.

 

[Eltab]

If you can build a probe that takes 40 years to get to Alpha Centauri and still successfully operate a 3-D printer programmed to make a copy of the probe, you probably also had an asteroid-based industrial capacity. That is where in the system to tell the probe to stop moving and turn on the printer. It probably loses a lot of time finding the needed resources before it can build its first copy.

But nothing says it cannot stay put and build more copies, launch them in different directions, thereby saving time in the long run.

 

[Umbran]

Or, more seriously, if we can have multiple sentient species on a planet simultaneously, the question of the odds of sentient life being present elsewhere/elsewhen in the universe gets a new wrinkle.

There's also the question of uplift (in the David Brin sense). We are starting to get into genetic editing. That gives us the option of helping other species over the hump. Gorillas don't use language in the wild, but can be taught basic sign language and express themselves. How much would it take to bring a gorilla or chimpanzee or bonobo to full language use?

 

[Yaarel]

This is an important element - the presence of one such species likely suppresses others from developing. Historically, when tool-using humans enter an area, extinctions of larger fauna follows. So, the probability of producing one intelligent species could be high, but the probability of producing a second while the first is around may be very low. This makes the 1-in-8-million to be a bit simplistic.




You are misusing the term "instinct". An instinct is a fixed behavior that does not need to be learned. Humans are born with the capacity to use language, but actual language use is a learned behavior. Some of our language capacity is developmental - exposure to language impacts how our brains grow and develop early in life, and a human who is not so exposed to language until after the brain is mostly developed seems to have a hard time picking up the trick. We have blessedly few examples of this, but a few children growing up in isolation have displayed the problem.

I meant instinct when saying instinct. It seems to me, our ‘unconscious’ continues to operate by means of biologically preprogrammed instincts. The capacity to learn a language is an instinct and makes language possible in the first place. The way you describe it − the difficulty of learning a language if without exposure while young − would suggest an example of imprinting.

 

[Yaarel]

If FTL is denied us by physics, this is unlikely, as moving viable colony-sized groups across interstellar distances may not be tractable for any species.

Actually, to travel *faster* than the speed of light seems theoretically possible. Some scientists suggest ‘tunneling’ thru the lightspeed barrier. There have been some quantum experiments along these lines, but nothing promising yet.

I suspect, at some point in the future, humans will figure out how to do this.