Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: EvaH on 15/11/2018 09:56:19

Title: Do aliens exist in other galaxies? Have they come to visit earth?
Post by: EvaH on 15/11/2018 09:56:19
Enock wants to know:

I wanted to ask what scientists think with regards to the possibility as alien civilisations somewhere in our galaxy or other galaxies, as well as the possibility of them having visited earth in the distant past? If there isnít evidence parse, how to we explain some constructions around the world, stone hedge or the symmetry of sphinx in Egypt or any other seemingly impossible engineering marvels certainly misplaced for the supposedly primitive life of those eras?

Can you help?
Title: Re: Do aliens exist in other galaxies? Have they come to visit earth?
Post by: Ophiolite on 15/11/2018 11:03:28
Exobiologists have expressed a very wide range of views on the possibility of alien life and alien intelligence. These views range from the view that the Earth may be a unique occurence in the galaxy and possibly even in the universe, to an expectation that intelligent life will arise readily on any planet with a reasonably stable and suitable environment. You might find interesting the book Rare Earth, by Ward and Brownlee, that takes an intermediate position: life itself is commonplace, but on most planets does not advance beyond the stage of single celled organisms.

Historians, archaeologists and antrhopologists do not consider the early civilisations to be primitive. While the construction of the pyramids and numerous stone circles demanded competent planning and skilled craftsmen there is no sound reason to believe these were not available at that time.
Title: Re: Do aliens exist in other galaxies? Have they come to visit earth?
Post by: alancalverd on 15/11/2018 11:47:23
Are there  extragalactic life forms? Probably.

Have they visited Earth? Probably not.

The pyramids were built by slaves in the service of human stupidity.

Stone circles were built by tradesmen for business.
Title: Re: Do aliens exist in other galaxies? Have they come to visit earth?
Post by: chiralSPO on 15/11/2018 12:37:06
I will second Alan on this one.

Given that there are >100000000000 galaxies, each with >100000000000 stars, and it appears that, at least in our galaxy, most stars have at least one planet: I think it is very unlikely that there is not life in another galaxy.

However, to have travelled to Earth from another galaxy would require one of three options:
1) Several million years of travel time at close to the speed of light (Andromeda, the closest galaxy, is 2.5 million light years away)

2) Longer than the age of the universe, as we know it, traveling at the speed of our fastest out-going spaceship (a measly 17 kilometers per second, meaning it would take about 750 times longer to get to Andromeda as there has been time since the big bang)

3) Or perhaps there is some very advanced technology that somehow allows faster than light travel--let's even assume that it is instantaneous.

Option 2 seems least likely since they would have needed to leave their galaxy to come to ours before the existence of their galaxy, our galaxy, them or us.

Option 1 is most likely to me, but has the major problem of: how could they possibly have thought of Earth as an interesting target millions of years ago? Presumably if there is life in another galaxy, then life is fairly common (on an intergalactic scale), so why Earth--even if we think humans are special, we still didn't exist, and certainly didn't have a civilization worth visiting (we probably still don't).

Option 3 has two issues, even setting aside that we have no idea how faster than light speed could be acheived, or if it is even possible. The first is: even if they can get here instantaneously, and even if Earth is "worth" visiting (see above) how do they know to come here? It still would take millions of years for information to reach them from Earth, so they would have had to decide to come based on what they saw millions of years ago (plus I don't know how one could observe mastodon from millions of light years away). And finally... if these aliens can travel between galaxies in a heartbeat--what the f**k are they doing rearranging rocks on the surface of the Earth?
Title: Re: Do aliens exist in other galaxies? Have they come to visit earth?
Post by: guest46746 on 15/11/2018 15:56:09
If aliens have come to earth, it is in the form of technology. Aliens inhibiting bots!

my citation: the movie avatar! lol
Title: Re: Do aliens exist in other galaxies? Have they come to visit earth?
Post by: guest46746 on 15/11/2018 15:57:24
Are bots 4 evah? lol
Title: Re: Do aliens exist in other galaxies? Have they come to visit earth?
Post by: miniguy on 18/11/2018 01:13:10
This is my view.

Since life first formed on earth there have probably been millions of different forms of life, from bacteria to plants, from ants to humans.  And yet only one species (us) has achieved this level of intelligence.  So I think our level of intelligence is  rare thing.  I believe there is probably other life on other planets, but I think the chances of find life with our level of intelligence is highly unlikely
Title: Re: Do aliens exist in other galaxies? Have they come to visit earth?
Post by: ukmicky on 18/11/2018 02:29:57
How many billions of years has the earth been around. And in all that time we only have evidence that life ,that initial event that has lead to every living thing on Earth today has occurred once. As everything living on earth from plant to animal is related itís possible  the conditions required are so unique and special that we just got lucky and we are alone in the universe.

Maybe in billions of years time the universe will be full of life and an alien life form will look at the question of how did lit all begin and  determine that we on earth were the seed that spread life to all other planets and galaxies
Title: Re: Do aliens exist in other galaxies? Have they come to visit earth?
Post by: chiralSPO on 18/11/2018 02:37:16
This is my view.

Since life first formed on earth there have probably been millions of different forms of life, from bacteria to plants, from ants to humans.  And yet only one species (us) has achieved this level of intelligence.  So I think our level of intelligence is  rare thing.  I believe there is probably other life on other planets, but I think the chances of find life with our level of intelligence is highly unlikely

For the sake of argument, I'm going to disagree with you here (in a friendly way).

We really can't make predictions on how common life is with any idea of our certainty--because we only know of life on our one world, i.e. we have a dataset of 1. We can't know how stringent the requirements are for life, beyond knowing that our star is not unusual, and the composition of our planet is not unusual, and it appears that life, in the form of simple prokaryotes first appeared about 1 billion years after the Earth cooled enough to have a crust and oceans. This suggests that life may be common, but again, we don't have any good way of putting error bars on that.

On the other hand, we know that intelligence is evolutionarily advantageous to multiple types of species that have evolved on Earth. As far as we know, we are the most intelligent life on Earth to date, but even that is not certain, and we know of multiple examples of independent evolution of highly intelligent species: in addition to humans, several species of primates, birds, and even octopuses are known to fashion and use tools in the wild, and there are many more species still that have complex languages and social structures. It would appears that (at least on Earth) intelligence is a natural consequence of the evolution of multicellular organisms. Now, based on the evolutionary history of the life on Earth, I am willing to grant that perhaps life on most planets stalls out at single-celled organisms.

It took about 109 years for the first prokaryotes to appear after the Earth cooled. It took about another 109 years for the first eukaryotes to appear. And then it appears to have taken another 2x109 years for the first true multicellular organisms to appear. After that, intelligent life arose within 2x108  years...
Title: Re: Do aliens exist in other galaxies? Have they come to visit earth?
Post by: evan_au on 18/11/2018 08:54:11
The question of whether aliens exist out there was summarised (for the purpose of stimulating discussion) in the Drake equation.

This equation is essentially a list of unknowns, for which we are only now finding solid values for the number of stars with planets, while many others remain a total guess.
https://en.wikipedia.org/wiki/Drake_equation

The flip side is a paradox stated by the physicist Enrico Fermi - if there are aliens out there, why aren't they here yet?
https://en.wikipedia.org/wiki/Fermi_paradox

This is discussed in the After On podcast:
https://after-on.com/episodes/008