Looking for a basis of answer, life on Earth began once and only once relatively early in geologic history. Argument is that all life we know of depends on the same genetic alphabet, the same genetic language, and the same small set of organic acids and bases out of the hundreds that are available.

If probability is controlling then life should have several more beginnings on Earth and several more sets of biochemical components for construction. The implication is that life probably came to Earth from elsewhere, and a spontaneous new beginning of life is not likely to occur in the history of Earth.

Anything can be argued with statistics. These statistics are strongly inferring that life is existing elsewhere in space and predates life on Earth by many billions of years. It seems likely that Intelligent life is existing elsewhere and some societies may be so far advanced from us that we cannot even guess at their capabilities. Others might be less advanced.

The test is encounter. If we go to discover them, we are more advanced. If they come to discover us, they are more advanced.

Many claims of encounters are not verifiable. It looks more like a religion than a science fiction. Including legends the claims go back 10,000 years in Earth History, judging from coastal flooding at end of ice age. In all that time the apparent level of technology has not changed. It doesn't speak of distant travelers visiting occasionally. Technology improves with time. It speaks of timelessness.

In considering distant star travel, the difficulties are enormous. Present thinking is that local time and space must become warped by some new technology such as Todd Desiato and others write about. It means that space travel and time travel will be achieved together with the same new equipment in more than 4 dimensions and with many new discoveries.

Thank you very much, Jerry Decker for your excellent answer. Best regards. Hazim

Nobody knows.

I think nobo knows that.

Well, we hear and read on the news and social media that scientists believe that extraterrestrial life exists on other planets. However, there are no concrete evidence confirming the existence of extraterrestrial life.

Thank you very much, Dr. Abdullah Noori. The earth is just a dot in the huge universe in comparison to the giant planets and stars. However, the existance of life has been confirmed only on this small dot, the earth. Best regards. Hazim.

Dear Dr. Hazim Sir,

Please have a look at this useful PDF attachment.

Regards

For people who said: "nobody knows" --> The question was not: "do you know if there is life elsewhere" but rather: "do you think...". This is not the same question.

Second, I think that there is, in english, like in french, a difference between "believe" and "think". I think that the verb "believe" is not appropriate in science. I do think that there is extraterrestrial life, I do not want to believe or not because belief closes the discussion.

There are many reasons to think (or not) that there is life elsewhere in our Galaxy and/or in the universe. These reasons can not be summarized here. Several books have been written of that subject.

However, just think about this: imagine that an asteroid or a comet (50 km long or bigger) hits our planet tomorrow. It is then probable that all life on Earth would disappear because the mantle could be a huge magma ocean. And this, before than we could spread life elsewhere in the Solar System (if not already done...). It would be terrible that the unique place where the life arose disappeared just because of a "small" stone...

Just from a chemistry standpoint anyone who has written a chemical equation knows that if there are hydrogen and oxygen atoms in the different reactants in whatever configuration, the end result is water. It is a thermodynamically favourable reaction. We all know how essential water is to support life. That being said and the ease with which water can be formed from different chemical constituents, organic or inorganic, life should be supported in more places than we can think of. How intelligent that life form is is unknown at this point. As one colleague pointed out if they discover us they are more intelligent, if we discover them we are more intelligent.

Actually, life may have started on Earth many times during the earliest stages of its existence but have been wiped out by the heavy bombardment that extended until just under 4 billion years ago. Only the life that emerged after that still exists, albeit in multitudinous forms (though all with the same left-handed molecular structures and such).

However, the existence of intelligent life is a much more complicated question. If by intelligent life you mean things capable of basic reasoning, such as that exhibited by dogs, cats, pigs, horses, etc, then there are probably almost as many examples of that in the galaxy (let alone the Universe) as there are stars (since even one planet might have numerous examples). However, if by intelligent life you mean creatures capable of interstellar travel or communication, we have no way of knowing whether such life exists (or, for that matter, ever existed, since even we don't qualify for that yet, and may well destroy our civilization, if not all life on Earth, before we can reach that point).

Based on numerous studies, it appears to me that the general consensus is that intelligent life defined by a higher standard has probably existed at one time or another at a number of places in our galaxy, but that all such lifeforms have probably gone extinct within times too short to allow them to explore a significant portion of the galaxy, and by the time we ever detect any signals from such lifeforms, they will probably already be extinct. For even ignoring the question of self-destruction, the galaxy has proven to be a far more hostile place than we once thought, the length of existence of any life-form is probably distressingly short, and the difficulties (if not impossibilities) of interstellar travel may well make "interstellar travel" an irrelevant concept.

Taking into account the enourmous number of galaxies in the universe and each having maybe billions of stars then just by simple statistics I believe there is life somehwere else out there.

Earth is a good example to start with: on it one finds several types of intelligent beings and several types of intelligences that can hardly grasp the intelligence of the others (think about dolphins, whales, elephants, raven, apes, and the different kinds of humans over ages). Even among present humans one finds vastly different kinds of cultures impermeable to each others.

So my first bet is that if any kind of intelligence develop elsewhere in the universe we will struggle recognizing it.

My second bet is that when complexity is able to deploy, like with life, the combinatorial huge amount of possible states (where astronomical numbers like 10^22 stars are tiny in regard of combinatorial numbers like 10'^10000 kinds of carbonated molecules) makes that nature always explore new life forms. This is seen all over life history, despite some occasional convergences in evolution most of the time life tries new variations, already at the individual level.

I should note that my answer a couple of answers above was supposed to be broken into several paragraphs, to make it easier to read. I feel certain that other answers I've posted were broken into paragraphs, and am at a loss as to why this one wasn't. Perhaps it's one of the problems noted by ResearchGate at the top of the page.

Dear Courtney Seligma ,

Your answer has been divided into 3 paragraphs. RG is still having some technica problems. Best regads. Hazim.

One Strange Rock is a beautiful documentary series from National Geographic that explores our delicate and wondrous Planet. The series is hosted by Will Smith and strengthened by eight astronauts giving their personal experiences and perspective of Earth from a distance.

Episode 8 titled "Alien" gives a fine idea of the possibility of life elsewhere.

Episode 4 "Genesis", describes the difficulty, dynamic forces, coincidences and how everything had to fall in place for life to begin on Earth.

"For an alien planet out there to evolve over those billions of years and to be exactly like it evolved here on Earth... that's like rolling those dice and hitting a one a billion times in a row".

"The overwhelming probability if you find a planet with life on it, its probably going to be very simple life".

If you think about it life must have existed on other planets. At our level of development in human history we would not be able to find this out. However, we continue to develop habitable planets similar to earth example Kepler 62-e, 62-f, 442-b.

Humans have lost so much history, the Dogon tribe knew about the Sirius system long before modern astronomy.

There are questions we still cannot answer and this is one!

As previously written here, the mathematical probabilities are large if one considers how many stars in the Milky Way galaxy along with how many galaxies we know of. One tiny planet bound by gravity to a G2v class star in a galaxy of more than 200 billion stars; life exists on that tiny planet. Must be others.

We still don't know how life began although there are certainly a number of theories from Oparin's Coacervates to primordial soup and others. Each of these theories imply that there is a finite probability for the formation of life (given the appropriate starting conditions). Given the high probability of satisfactory circumstances it is probable that life exists elsewhere. As for intelligence, many would argue that intelligence evolves and, consequently it is possible for intelligence to exist elsewhere. Fermi's paradox remains unanswered unless you take Carl Sagan's posiition hat we are first (and there are some thoughts that suggest that the rate of life destroying GRB's has reduced sufficiently for life to get to the stage of space exploration just now)

As an aside, the archaean cellular membrane and ultrastructure is somewhat different from the other two domains of life raising the question of a secondary origin of life on earth. As suggested earlier in this thread, life may have started more than once on Earth.

I find it quite paradoxical that of all the millions of scientists on the planet only a handful has ever bothered to examine the details of reported UFO encounters to see what is the science behind them. None of these handful has ever published anything fearing a ridicule.

I examined one crop circle in 2003 and still cannot explain it fully and no other scientist took it seriously. On the other hand, non scientists believe it to be extra-terrestrial in origin and still are waiting for a serious evaluation.

It is almost inconcievable that we are alone in the universe. While it is probably the case that the conditions for sentient/intelligent life are very much a rarity there are so many possible places that life could originate that there must be huge numbers of 'thinking folk' out there. They probably even are asking themselves the same questions.

Whether we will ever meet them is a different matter. Unless we have got something fundamentaly wrong in our interpretation of physics it seems unlikely.

I would suggest that intelligence may not be such a difficult thing to evolve into given sufficient time. Accepting Darwinian evolution fitness involves adapting to maximize reproductive success which ultimately is a balance between collecting energy and not becoming a source of energy for something else. If behaviour (versus structure) is the means by which this is accomplished then evolution converging on intelligence will maximize fitness over time.

I do not think there is another life on a planet other than the earth. We never heard of a second life, and dear people Hazem al-Dulaimi with appreciation

I do not think there is a smart life exists on earth, therefore, I think do not have in another place.

Hi Everyone!

This is an interesting discussion. For the people who suspect that we are the only place with [intelligent] life, what informs your decision?

cheers, randy

Well, the predator hypothesis says that only the really stupid technologically advanced lifeforms go around advertising their existence to all and sundry, including to potential predators, and that if such predators exist, perhaps those stupid civilisations don't then last very long.

As far as human are concerned, our small planet is the only place in the universe to house thinking beings.

But this idea may be turned on its head as early as the middle of this century, as scientists up their efforts to search for intelligent life. If they are successful, then they will prove that Homo sapiens is just one of countless sentient species in the universe.

The idea of life in space is hardly new – even the classical Greeks were intrigued by the idea that unseen beings might populate the sky. What is new is our ability to detect the possibly subtle evidence for biology on other worlds. And while no one can guarantee success in these experiments, those involved in this effort think we will find something within a generation, including NASA’s chief scientist.

Ours may be the first generation to learn that Earth is not so special after all.

It's also possible that intelligent life might be scared of us. We're monsters. We even have a history of killing and enslaving fellow humans based on their having the "wrong" skin colour - how are we supposed to cope with actual aliens, whose social customs we might find nightmarishly repugnant? What if the standard "first contact" greeting involves leaders offering up their first-borns to the other side, to be ceremonially eaten? Would we really be up for that?

If I was a technologically advanced alien race, I'd put a very strict embargo on the Earth, nobody goes in or out pending reviews every hundred or so years, and I'd park a small planetary extinction device in Venus orbit just to be sure.

FAO Martin Smith, SETI Data Processing, Third Floor, cubicle 41.

Dear SETI,

Thank you so much for your last communication, and the speed with which you got back to us. We are currently beaming the requested information to you at 965 nm. This includes details of warp drive theory and design (which we were a little surprised that you needed), and the energy generators discussed.

Please be aware that under the current technology transfer regulations, Earth is now obliged to pay 50% royalty on the use of these or any other related technologies, along with a suitable percentage of planetary GDP (still to be assessed), on a standard 500-year starter contract.

Standard territorial rights extend out to three planetary orbital radii, so great news! You now own all the inner planets, plus Mars, and most of the asteroid belt! I think you'll agree that this is a sweet deal. The periphery of the belt and the outer planets will be dealt with by Orion Management Services, and all interstellar travel by Intersystem Services. Please be aware that there are strict penalties for trespassing outside your assigned 3AU limit.

Given that Earth is not really yet a spacefaring civilisation, and doesn't yet have access to the asteroid belt's mineral resources, might we ask how you plan to meet your initial payments?

The suggestion of our debt advisors is that perhaps we could forgo the first 100 years payments in exchange for some territory. How about North America? This could be cleared and maintained for us as a wildlife park, pending the arrival of our representatives.

Do you think you could give us an estimate of how long it would take to relocate or eradicate the populations of the US, Canada and Mexico? 2-3 years would be fine with us.

We are so pleased that SETI (and you, Martin, Supreme Leader of Earth) have absolute authority to carry out these negotiations on behalf of the rest of your planet. You would not believe how many species have much more involved consultative processes, it's so refreshing to be able to communicate directly with a real decision-maker such as yourself.

All the best in your reign, Martin,

Your Friends,

First Contact Services

(Ref: Galaxy Plz251xx36, Arm B)

“Do you think that there is intelligent life of other creatures on other planets?”

This problem is already discussed on some other RG thread, and is solved scientifically.

The answer is “Yes”, because of

“The biggest proof of existence of intelligent life in the Universe is the fact that so far no one has tried to connect with us”.

Sorry, but I don’t know – who is the author of the solution and can make only the anonymous quotation above.

Cheers

Even in a universe eventually flooded with life, some species will be the first to emerge.

And members of that species will look out at the stars and say: this is statistically ridiculous, it can't only be us.

And they'll be wrong.

How do you define civilization? If you think on it as possibility to transmit information then our civilization is not even 100 years old. And we are already facing extinction. Multi cell life on earth is maybe half a billion years old.

This means that probably most civilizations have a very small window of existens.