# evolution on different planets with same oxygen mix and  intergqlactic travels



## snoockey (Jun 6, 2014)

Hello, few days ago my sister and i started disscusion in wich i stated that if another earth like planet exists ( more or less same gravity, same air mixture (oxygen and all other elements))  that on that planet species could take different evolution paths. But my sister claims that evolution paths would be the same, and that other "earth" would produce same species, and that we, humans would be the inteligent race! And in case different species could araise, would it be humanoid or is there any chance of non humanoid inteligent specie? So i would like to know who is right in this case? 

And my secong q is this: why is almost every scy fi  book/movie/game linked to this galaxy only? Can hyperspace be used to travel to another galaxy? And could you do it in one jump ( between galaxy is mostly empty spaceright? So theres no gravity forces that could affect your hyperspace jump?) Or would a whole new intergalactic drive would be needed?

Im sorry if my questions sound dumb, even dought i like sci fi a lot, im still new to this genre!
And sorry for all grammar or simmilar mistakes, but english is not my native language!
Thank you for your time!


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## The Judge (Jun 6, 2014)

Very good questions -- and I'm looking forward to reading the answers you get!  

In the meantime, this is such a science-based topic I'll move the thread over to the Science/Nature sub-forum, where our white-coated intelligentsia live (usually in very small cages...) so they can see it and respond more quickly.


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## Brian G Turner (Jun 6, 2014)

snoockey said:


> that evolution paths would be the same, and that other "earth" would produce same species



This would completely disregard the fact that catastrophic events have frequently caused mass extinctions, and also the way the environment has shaped evolutionary pathways.

Simply put, there may be shared biology and divergent evolution (ie, similar species) - but life on different worlds would necessarily be unique IMO.

If you'd like to see an example, simply look up "Pre-Cambrian explosion" to see what weird and wonderful complex species first erupted on earth. Alas, we've never seen anything like them since.


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## snoockey (Jun 6, 2014)

My knowledge on this thread is limted, but as far as i know oxygen levels are crucial to evolution? So rapid apperiance of complex beings in cambrian explosion could be linked to  milion of years in which algees and similar "plants" were producing oxygen? As far as i know bigger and more complex crature is , it demands for oxygen are higher? 
But as i sayed my  knowledge is limited on this thread and this is just my speculation on this subject!
How similar would that species be?
For a civilization to develop, is humanoid shape and  opposable thumbs a must?


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## Darth Angelus (Jun 6, 2014)

Welcome to the Chrons!

Years ago, I took a few basic university courses about the universe, one of the being about life in the universe. By no means does this mean I have a master's degree on the subject, obviously, but I believe I can answer your question.
Basically, I strongly disagree with your sister.

First of all, the exact conditions on Earth are very highly unlikely to exist elsewhere. Planets would vary in size, distance from their star, size of their star, length of year, quantity of water, axial tilt, size of moon(s) etc., all of which could and would affect life. The chances of any one of these alone being equal to the same variable on Earth may not be extremely low (except maybe the size of our moon, and it is extremely rare for a moon to be that large relative to the size of its planet, if I recall correctly), but taken in combination, then the odds become small.
The human species has only existed for a very small part of Earth's history, but even Earth fifty million years ago would definitely have been more similar to Earth today than an extremely large majority of planets in the universe are.
When life evolves, it does so to adapt to conditions. It stands to reason that if conditions are even slightly different, other properties will be more favourable than the ones that were favourable to survival here.

When you look at all the possible, hypothetical species there could be, as in all the "genetic patterns" life could take (and not just the ones that happened to mutate into existence and then proved their survivability here on Earth), it becomes near infinite, as well. The particular genetic pattern of humans is only one. Other species here have shown some clear signs level of a certain intelligence, as well, but ours is the most evolved one on Earth (in certain ways, at least), so it is clearly not the only genetic pattern, shape of life that can have intelligence.
It is important to realize that our human intellegence is highly unlikely to be entirely different by type, from other species. It is just that the brain as an organ that has evolved to different levels.

At the same time, we have to be aware that there is a fundamental shortage of empirical experience of the paths life have taken elsewhere. So, a speculative answer to your question is all anyone could come up with. But with that said, what is the basis for declaring as a universal truth that only a certain type of primate could evolve a brain on an equivalent level of sophistication as ours? I have certainly never seen any, or heard any scientist mention anything of the sort.

And again, the chances of primates coming up in the first place is exceedingly small. It is a long chain of mutations that takes life from single-cell organism to primate, and an enormous amount of other branches life could have taken, particularly under different conditions.




I said:


> This would completely disregard the fact that catastrophic events have frequently caused mass extinctions, and also the way the environment has shaped evolutionary pathways.
> 
> Simply put, there may be shared biology and divergent evolution (ie, similar species) - but live on different worlds would necessarily be unique IMO.
> 
> If you'd like to see an example, simply look up "Pre-Cambrian explosion" to see what weird and wonderful complex species first erupted on earth. Alas, we've never seen anything like them since.


Yes, there are catastrophic events and mass extinctions, too.
Geological events and objects from space crashing into planets could wipe out species. Not only would life taking the same path require conditions to be unrealistically similar to those on Earth, but the entire planet's history of natural disasters would also need to be that similar.


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## snoockey (Jun 6, 2014)

Thank you very much for your answers! 
Now i only need answeron my second q, and taken my lack of xp with this forum, should i leave it here or is there any other  place on this forum i have higher chance of getting the answer? ( its less science and more fiction oriented?)


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## Darth Angelus (Jun 6, 2014)

Hyperspace, as far as I have been able to tell, is a plot device to solve the problem of the extreme distances between stars. Within our known physical space, it is simply impossible to travel faster than the speed of light (although it is possible for space itself to expand faster than that), and that would mean traveling to another part of the same galaxy would take countless human lifetimes, even several millennia.
So, another parallell, fictional space has been invented for Science Fiction, that follow other laws, presumably making distances between places much shorter than in realspace.

There may be physicists who explore the idea of hyperspace. Theoretical physicists always have to be open minded to ideas and abstract concepts, and I am sure someone has bee thinking about. But I have never heard anything about that jumping over to some other parallell space should be possible in real life. Therefore, I confine hyperspace and any other form of travel speed higher than that of light entirely to the fiction department.

So, I guess that if one is going to use a wholly fictional plot device like hyperspace, anyway, there is little difference between travelling between galaxies (within reasonable time) from traveling within a galaxy, except possibly a tiny one of suspension of disbelief, for some people.


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## farntfar (Jun 6, 2014)

Hello Snoockey. Welcome to the Chrons.

For your second question, I'm not sure that its really the case.

The first line that appears on the first Star Wars film, for instance, is
*A long time ago, in a galaxy far far away.....*

I think also, that we often just assume it's in this galaxy, without it being empirically stated. It's on planet X, but no-one  said exactly where X is.

However apart from that, if we're assuming that the main characters are human, rather than just humanoid, it's much easier to stay in our galaxy when it is stated. 
(The Foundation series is. It's eventually got earth in it. for example).

Basically if you move to another galaxy, and the people are of earth descent, you have to do lots of explaining how they got there. 
Stargate Universe starts in another galaxy for instance  (I think ), but they do explain that.

Can you use hyperspace to travel to another galaxy?
You tell me?
My homemade hyperdrive won't even get me to the bathroom, and I don't think Stephen Hawking's one does any better. So I think we can assume that when they really get a hyperdrive working, they'll soon be working on longer range ones, if there's currently a limit.

If you want to know, because you're writing a story, I think it's pretty much up to you to make the rules. Call it a hyperdrive with SIS capability  (Snoockey Intergalactic Shunt) and we'll all accept it.

I find it interesting that you say that it's the matter, and therefore gravitic influence that limits its range. It sound like you're a lot closer to developping the SIS than I ever would be.

There are people here who can probably give you some real scientific answers, and who will almost certainly be replying soon.
In the meantime, I hope you enjoy your time on the Chrons.  You should find lots to think about, and to amuse you here. (And your sister is welcome too, of course)


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## snoockey (Jun 6, 2014)

Im aware of that, but by fictional theory gravity centres of celestial bodyes are causing some slight errors in destination koordinates ( closer you are to star/planet harder it is to make right calculations and higher chance of emerging in wrong solar system or end up inside of a star) so if u jump away few parsecs from closest celestial body and make a jump to few parsecs from other galaxys closes celestial body, would it be a precise jump or would you still end up on wrong coordinates?  Or do you have to travel that empty gap between galaxys in small jumps? ( we are talking about purly fictional scy fi physics!)
And is space between galaxys empty or does it have some kind of bodys between em? (Asteroids, few suns/rouge planets?)
Reply to  darth angelus


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## Mirannan (Jun 6, 2014)

snoockey said:


> My knowledge on this thread is limted, but as far as i know oxygen levels are crucial to evolution? So rapid apperiance of complex beings in cambrian explosion could be linked to  milion of years in which algees and similar "plants" were producing oxygen? As far as i know bigger and more complex crature is , it demands for oxygen are higher?
> But as i sayed my  knowledge is limited on this thread and this is just my speculation on this subject!
> How similar would that species be?
> For a civilization to develop, is humanoid shape and  opposable thumbs a must?



My opinion only, the answer to your last question: No and no. What _*is*_ needed is some sort of manipulative appendage that allows fine control; on this planet opposable thumbs seem to have won out, but other solutions to that problem are possible. An example might be that of the Fithp from the novel "Footfall" which (superficially) look like dwarf elephants with a complex set of tentacles (8 of them, IIRC) in place of the trunk. A hive entity using a few hundred subunits is another.

As for humanoid shape, mythology has quite a few viable designs - the centauroid body shape being fairly obvious, for example. And radial symmetry might have some advantages, 360-degree vision and high manoeuverability being two of them.

Incidentally, the fine control of objects is what matters - not how it's done. Assuming (big assumption!) that psychokinesis is possible, it would serve admirably for that purpose.

Regarding the issue of hyperdrive accuracy, the details of hyperdrive operation in fiction are completely arbitrary and driven by the author's plot purposes. A great deal of technobabble is usually a must, however. 

The nearest we have, currently, to a workable hyperdrive design is Sonny White's variation on the Alcubierre design, which has brought down the energy requirements from a Jupiter mass equivalent to around 700kg. For reference, that energy is roughly equivalent to a 15-gigaton nuclear explosion.


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## Venusian Broon (Jun 6, 2014)

Regarding your questions Snoocky, 

In your question* you postulate an 'Earth-like' world, so we're talking about liquid water and enough gravity from a rocky planet to stop an atmosphere leaking into space.

Just to stimulate a discussion about it, I think your sister is kinda right - in a way. Even here on earth completely different and unrelated animals develop quite similar physical traits. Birds and bats, eyes have appeared on all sorts etc... Look at whales - their ancestors I believe were quite elephant like, when they became more and more aquatic they lost features and appendages that were useful on land and became more streamlined and 'fish-like' 

That is because they all face the same basic conditions - i.e. how to move in a fluid (whether it is air or water), or how to sense in an environment that has light, or what is the best way to filter particles out of a liquid etc... 

And also there is an element of 'common sense'. For example if you are an animal that requires to feed on other animals the best place for your sense organs are nearby your mouth. Then it makes sense to coordinate your mouth/eyes/nose with something like a brain that can act quickly to this sensual information, hence put it close to these organs. Thus something like a head emerges.

So if I were to fall onto another Earth-like planet, I wouldn't be shocked to find bird or insect-like things flying in the air, or fish-like things swimming in the sea. Or even legged** things with watertight skins wandering about plant-like things on land. 

Of course you'll notice I've put '-like' next to most of the terms. Just because convergent evolution has produced similar shapes and traits does not mean you reproduce everything - biochemistry may be completely different etc... 

However, pulling myself back from the brink of taking an opposing position just for the sake of it! I would be utterly surprised if such an Earth-like planet were to guarantee to evolve life that was humanoid. Evolution just doesn't work that way. There is a large degree of luck to our existence too. 

---

Regarding your Oxygen question - yes it is useful for large multi-cellular life to breath an oxygen rich atmosphere (assuming your evolved a respiratory method of course! When Earth did become oxygen rich it was really a pollutant and was likely to have imitated the first mass extinction in life's history on this world.) It provides plants and animals the fuel for loads of energy. 

As for other worlds, that's the 64,000 dollar question. I think most scientists would now agree that if there's liquid water somewhere there is a good chance that there is life - and that's the first priority. But there are other chemical pathways that life can extract energy - anaerobic bacteria already do it here from a number of ways (I think there are more than one.) We certainly can't rule out large life forms breathing in hydrogen gas or some other strange concoction. 

---

Your second question re: Hyperspace - Well the people of the Stargate franchise nip about galaxies quite easily it seems... But hyperspace is well, not a scientific term i.e. currently we see no evidence for such a entity, but it is a science fiction term thus relies completely on your imagination! The distances between galaxies are just SO VAST. Take the Andromeda galaxy, in universal terms a next door neighbour to us - approximately 2.5 million light years away. That's a distance so huge as to be virtually impossible to imagine, I'd say.

But it depends what sort of SF your writing I suppose. If you are on the hard SF side of the spectrum and come up with a 'hyperdrive' that can 'plausibly' jump a craft from one galaxy to another, that pleases hard-SF fans I will doth my cap to you with great respect.  












*irregardless of how many Earth-like planets there are - yes we're unlikely to have many in the vicinity of us, but my guess is there is probably a very large number of them, somewhere in the universe, of similar mass and with liquid water and atmospheres of some sort.

** There's a good reason land animals on earth have the leg and arms that we do - they essentially evolved out of fish fins and the reason fish had fins in those places was because it was a very efficient solution for helping to propel fish through water. Which in a sense is a basic fluid dynamics solution that I'd expect to be 'found' all over the place where there is water.


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## snoockey (Jun 6, 2014)

Thanks ffarntfararntfarr the welcome! 
Yes, star wars says in galaxy far far away, but that doesnt mean they are humans!  and even if star wars says its in galaxy far far away, it doesnt say anything about galaxy travels! 
But for egz: foundation by isaac asimov, miles workosigan saga by louis mc master boujold, hitchikers guid to galaxy, Dune by peter/frank herbert, enders game ( ok, you dont have any ftl drives there so i guess  its not a valid point! XD), star treck,every sci fi movie, even doctor who ( i think, not entirely sure!), mass effect, a lot of small novels that you can find in titan/ sirius , all of that low budget pc/mobilephone games  they all talk about this ( when i say "this galaxy" i want to say that they are confined to one galaxy only!) galaxy only! 
Only game i heard taking place in other galaxy  is eve online, and they have traveled there by natural fenomen, and now they cant go back to our own galaxy! So basically no character is traveling between galaxys !
So the q araised, is it possible to travel between galaxys? 
And isaac asimov explains that gravity affects precision of hyperjump (everywhere you got hyperjump you have to get away from planets to jump!)
Yes, well me and few friends (wich all love sci fi) are "trying" to make a pc game , most probably nothing will ever get out of it, but its a fun project for us and we (specially I) now have something that will make us explore sci fi universums of all kinds!  and we  agreed we want our game to have a lot of details, that every technology is explained and have a "stronghold" in some kind of real or fictional theory!and to be as close to real as possible! And thats why im asking if it is possible! XD
One more q, are fictional technologys like warp, hyperspace, holtzmans effect, mass effect  patented by peoples who "invented" them? Or are they free to use ?
Reply to farntfar
When talking about hyperspace i mean only in fictional univers, not real one!


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## Darth Angelus (Jun 6, 2014)

Venusian Broon said:


> Regarding your questions Snoocky,
> 
> In your question* you postulate an 'Earth-like' world, so we're talking about liquid water and enough gravity from a rocky planet to stop an atmosphere leaking into space.
> 
> ...


While I would agree with what you have to say, I think calling snoocky's sister even "kinda right - in a way" is pushing it. It would be very "kinda" and "in a way", making just about the widest definition of what is "human" that I have ever seen.
Yes, similar conditions favour similar traits, but the word used was "human". All species of monkeys are similar to us, biologically. In the grand evolutionary scheme of things (considering every shape and form we know life can take), they would have to be seen as very similiar, greatly more so than those vague similarities you describe (being able to move in a fluid, having something akin to a head etc). Yet, I have never heard anyone call monkeys "human". The most dissimilar life form from us which I can remember having seen seen referred to as "human" are the now extinct neanderthals. The word isn't more inclusive than that.

Now, I am definitely not meaning to put you down or anything, especially as you said you were trying to stimulate discussion. However, the way I saw the question presented, it was a lot more specific than vague similarities to human, in the general sense you talk about biological similarities.


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## Venusian Broon (Jun 6, 2014)

Hi DA, 

I did say, somewhere in the middle...let me find it: _I would be utterly surprised if such an Earth-like planet were to guarantee to evolve life that was humanoid. Evolution just doesn't work that way. There is a large degree of luck to our existence too. 
_



I do write a lot sometimes, I know. I perhaps should have been a bit clearer. My 'kinda agree' was about traits and shapes that we might recognise from here in animals and plants, based on basic bio-mechanics and similar physical considerations assuming (reasonable I think) similarities in habitat conditions and the building blocks that make up life. 

That was my thinking anyway.


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## Darth Angelus (Jun 6, 2014)

Anyway, one variable about a planet I forgot to mention earlier was the time it takes to rotate around its own axis a.k.a. length of day.

We have evolved for a 24 hour day-night cycle, when it comes to our biological clock, sleeping patterns etc. For a being of our biology to live on a planet with, say, 19.76 hour* day would be a huge invitation to jet lag (or some effect very akin to it, with a slightly different cause, but which still has to do with confusion of the biological clock).
Since evolution is all about adaptation to the environment, that would not happen. Rather, a species evolved on another planet would have a biological clock programmed to that planet's day-night cycle.


* I am talking about hour as it is on Earth, here, because they are likely to have their own time units, based on their own day-night cycle.




Venusian Broon said:


> Hi DA,
> 
> I did say, somewhere in the middle...let me find it: _I would be utterly surprised if such an Earth-like planet were to guarantee to evolve life that was humanoid. Evolution just doesn't work that way. There is a large degree of luck to our existence too.
> _
> ...


Yes, I know, and I agree. That is just not what I think snoockey's sister was trying to say. Rather, she came off as far more specific.


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## JonH (Jun 6, 2014)

It's worth recalling that you don't need a hyperdrive to get you to another galaxy. An engine that can give you a constant one gravity acceleration (subjective) for about 34 years is good enough. Relativity will do the rest. You end up travelling at a huge fraction of the speed of light, the distance between the galaxies shrinks for you, and you can easily make it in a lifetime.

Well, the traveller's lifetime that is. Not only would everyone left on Earth be dead, given that millions of years on Earth would have passed, they might not even be human.

On the other hand, they may have invented a hyperdrive in the interim and could be waiting for you when you get there.


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## snoockey (Jun 6, 2014)

So VB,
I guess hard sf side of spectrum aprove isaac asimovs  foundation series of books? In wich ( in the last book , first foundation and earth ( that would be exact translation from my language)) trevize makes a 27 hyperspace jumps in less than an hour, and in this series says that you gotta have a lot of jumps in stead of one big jump because of gravity of stars and similar bodys. So if u have exact same  hyperspace technology  like asimov you would be able to to travel between galaxys almost only in time it takes you to make right calculation.  1. Asimovs hyperspace drive doesnt require fuel (all power from nucler generators)
2. 27 jumps in less than one hour prove  that  this drive cant overheat  and doesnt require recharge time so it alowes fast travel.
So andromeda is cca 778 kiloparsecs away (one kiloparsec is 1000 parsecs and 1 parsec is cca 3.26 light years) i think he sayed distance he covered by this 27 jumps is around  5 kp (if i remember right)  so you get that you could cover distance of 778 kps in cca 156h wich is around 6days and 16 h so it could be posible to cover galaxy distances in rather short time? Even if u stop every few hour to cool down the shipit could still reach andromeda in short time, right?

So would this explaining do for hard sci fi? 
And thank everybody else for replies! 
JonH that true, but its not really practical, right? XD


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## Dave (Jun 6, 2014)

I don't think I disagree that life (as we know it) on some parallel Earth-like planet must be based upon long-chain carbon molecules and with water as a solvent. That means using DNA to replicate. 

I also don't think that I would disagree that convergent evolution would tend to produce the same kinds of animals and plants in the same habitats - hence dogs and dingos, or  sharks and ichthyosaurs.  

So, there could well be bi-pedal, intelligent, omnivores with opposable thumbs and large brains that look vaguely humanoid but are not our distant cousins.

What I think you may have missed is this piece of news from a couple of weeks ago: Creating “alien” DNA on Earth: Lab creates life with genetic code outside our own - Salon.com

The fact that there could be life based upon different nucleic acid base combinations means that the possibility of truly 'alien' life is still a very real one.


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## Dave (Jun 6, 2014)

Darth Angelus said:


> Hyperspace, as far as I have been able to tell, is a plot device to solve the problem of the extreme distances between stars.


I think it is also a theoretical physics idea too. Space is curved and it is curved (warped) by gravity. Given enough gravity you can curve it enough to make a hole - a black hole. The idea is that you can curve space enough to make a kind of Mobius strip where you can go from one place to another by sidestepping, or that you can go through a black hole. 

Unfortunately, there is no 'other side' to black holes, as far as we know. It would just be some bottomless pit. Anyway, the passing through the black hole part would break down matter to subatomic particles and a spaceman would not survive the journey. 

The Mobius strip idea, while interesting, is beyond anything we can actually engineer at the moment or even the foreseeable future.

The other thing to consider is that there probably 12, 13 or more dimensions, certainly more than 4. Space isn't really curved, we just see it like that because we only think in the dimensions of length, depth, height, and time. In essence, we are like a 2D drawing of a stick man who cannot cross a line drawn on a piece of paper. If we could see all the dimensions we might be able to build machines to overcome the problems of travelling great distances easily, just as the cartoon man could easily jump over the line if he was 3D.


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## farntfar (Jun 6, 2014)

Ah now! Your description of hyperspace, Dave as being a curvature of space created by gravity, brings me back to a problem I was wondering about, relating to Snoockey's original question.

If the curvature of space, and thus the hyperspatial tunnel (or whatever x-dimensional shape it is) is created by gravity,  would that mean that it doesn't actually work very well in the spaces between galaxies, where there is very little matter, and therefore not much curvature?

Maybe this was the basis for your original question Snoockey?


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## Venusian Broon (Jun 6, 2014)

Hi S, 

What constitutes 'hard SF' could become a contentious issue , so let us tread lightly!

My personal definition would say, no Asimov's Foundation series doesn't qualify as 'hard', because 1) FTL travel isn't allowable and 2) I don't think a subject like psychohistory as described in the books would be plausible  and 3) I don't allow 'one rule/law can be broken'! 

A hard SF approach to travelling between galaxies, would be a bit like JonH's suggestion - my relativity is a bit rusty as I'm writing much softer Space Opera at the moment - but I think he's in the right ball park. Of course you have to generate 1G of acceleration non-stop for 34 years. It might be one of these problems that, even with the most optimistic engine design possible you would need so much mass/energy that it tips it back into impossible. There are bound to be people on this site that have pondered this question deeply that can answer that...

Anyway, the concept of this hyperdrive that works much much better in smooth spacetime when not perturbed by large local gravitational masses is an interesting one - but be careful. The obvious journey to go between stars in the same galaxy is not to go the direct line of sight route, but surely to jump out of the plane of the galactic arms (which Wikipedia tells me are on average 0.3kpc thick - tiny compared to the jumps your talking about) into smooth spacetime and then quickly jump back to your target. No? 

(i.e. Why did Asimov have this character footering about inside big star distributions then when he could jump up and over ) 

but hey, as long as you are consistent I probably wouldn't notice. Like I said, the characters in Stargate are travelling between loads of galaxies - as if they are trucks on motorways - and my hard SF warning light never comes on. If your fiction/game/idea is good I won't bat an eyelid


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## paranoid marvin (Jun 6, 2014)

Our genetic code is so complex that just a couple of alterations and we would be entirely different creatures; so the chances of inhabitants of others like us on other planets is (in my opinion) fairly remote.

Even on our planet, it was partly by chance that we became the dominant species. If it wasn't for an asteroid hitting the Earth, it could have been dinosaurs. If another asteroid hits the Earth, or we finally succeed in destroying ourselves, then an alien race visiting the Earth could find it ruled by cockroaches.

As for galaxies; personally I don't think we'll ever leave ours under our own steam. And when you consider just how huge our galaxy actually is, there really would be no need to do so anyway We still don't fully understand our own Moon, which in space-terms is right in front of our noses, so exploring the rest of the nearby planets would take milllenia. 

Which is probably fortunate for any intelligent life out there, because having the Human Race come visiting is like the neighbours from hell moving in; we're Bad News.


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## Dave (Jun 6, 2014)

paranoid marvin said:


> Our genetic code is so complex that just a couple of alterations and we would be entirely different creatures; so the chances of inhabitants of others like us on other planets is (in my opinion) fairly remote.
> 
> Even on our planet, it was partly by chance that we became the dominant species. If it wasn't for an asteroid hitting the Earth, it could have been dinosaurs. If another asteroid hits the Earth, or we finally succeed in destroying ourselves, then an alien race visiting the Earth could find it ruled by cockroaches.



Most of our genetic code is complete junk and serves no purpose at all. It is altered by random mutations frequently, and if that is to a part of the code that is useful, in the majority of cases it will be a detrimental change. However, it is wrong to say that a few changes would make us completely different creatures. Humans and bananas share 50% of our DNA. And we share 18% with Baker's Yeast. I just Googled this: National Geographic Magazine - NGM.com

Other planets won't have human beings, but as I explained already, they could have unrelated humanoid creatures. If the Dinosaurs had continued to evolve then there may have been a bipedal, large brained, opposable thumbed, binocular vision Dinosaur. Convergent Evolution would make this probable given sufficient time. They would not have our body temperature maintenance because they had never needed to evolve that.

Unfortunately, you cannot get large creatures with exoskeletons (like Insects) The problem with giant exoskeletons | Forest Azuaron

So, no giant cockroaches!


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## Darth Angelus (Jun 6, 2014)

Dave said:


> I think it is also a theoretical physics idea too. Space is curved and it is curved (warped) by gravity. Given enough gravity you can curve it enough to make a hole - a black hole. The idea is that you can curve space enough to make a kind of Mobius strip where you can go from one place to another by sidestepping, or that you can go through a black hole.
> 
> Unfortunately, there is no 'other side' to black holes, as far as we know. It would just be some bottomless pit. Anyway, the passing through the black hole part would break down matter to subatomic particles and a spaceman would not survive the journey.
> 
> ...


Yeah, you may very well be right about all this stuff. What I meant was mostly that hyperspace, as shown in fiction (which seems to be what the OP seemed to be asking about) is more or less a plot device. Since hyperspace isn't very well understood, it is very easy for a writer to set it up any way they imagine. After all, it is easy to write stuff into fiction that is well-known without getting questioned too much, so who is going to question a writer who fills in the gaps in our knowledge about a very abstract idea?

As for the number of dimensions, I have heard of the idea that there may be more than four, but not what number the most recent findings of the foremost theoretical physicists would indicate.
Curved space may very well be a simplification to make it easier to grasp. After all, our innate visuospacial ability only works with three dimensions in space, so any more is counter-intuitive to the human mind. Calling it curved space could still be a helpful stepping stone, to improve someone's understanding ever so slightly, before they can hopefully move on to understand it on another (higher) level.
Then again, I am far from sure the 2D drawing of a stick man is not a simplified analogy, too.
In any case, even though the visuospacial aspect of our minds is limited to seeing space in three dimensions, I think far more (if not an infinite number) are mathematically possible.

Whatever the true nature of what is called curved space is, as far as the foremosts physicists can tell, the phenomenon has been observed, in at least one example, gravitational lenses.


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## Mirannan (Jun 7, 2014)

Dave - Are you really sure that DNA is the only possible informational molecule? I'm not. At the very least, a DNA variant using different bases ought to be possible - as you said, I think. Ditto amino acids; after all, there are hundreds of those.

Also, water isn't the only good polar solvent. Ammonia is just about as good, at slightly lower temperatures. Of course, in an ammonia-based system then the whole chemistry would have to be different...

Incidentally, although the evidence is sparse to say the least, some palaeontologists think that dinosaurs might have been homoeothermic; some evidence of feathers on them has been found, too.


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## Dave (Jun 7, 2014)

Mirannan said:


> Dave - Are you really sure that DNA is the only possible informational molecule? I'm not. At the very least, a DNA variant using different bases ought to be possible - as you said, I think. Ditto amino acids; after all, there are hundreds of those.
> 
> Also, water isn't the only good polar solvent. Ammonia is just about as good, at slightly lower temperatures. Of course, in an ammonia-based system then the whole chemistry would have to be different...
> 
> Incidentally, although the evidence is sparse to say the least, some palaeontologists think that dinosaurs might have been homoeothermic; some evidence of feathers on them has been found, too.



I could never say never or rule out anything, but I'd think the informational molecule must be carbon based (no Silicon based Star Trek Horta) because Silicon just doesn't make the same long chains or the same variety of molecules. And after billions of years of evolution on Earth, DNA is what it came up with. However, I do think the possibility of other bases is really really interesting.

As for Ammonia - firstly Water is unique - study about Water - there is nothing quite like it for all sorts of reasons - that the solid is lighter than the liquid - the highest surface tension of any liquid - the strong cohesion
Unusual Properties of Water - Chemwiki

Personally, I think Water is a prerequisite for Life to occur simply because Water is so weird.

However, secondly, as you say, Ammonia is a liquid at lower temperatures. That means a planet colder than the Earth-like Goldilocks zone. None of the reactions necessary for life as we know it would take place at that temperature and those that do are slower. If such life does occur it will very different to us. 

And as for the Dinosaurs that evolved feathers, I thought they didn't all go extinct - they are Birds  I accept that some were homoeothermic though. 

That End-Cretaceous mass extinction is still debated, but it was certainly linked to temperature change. I've read that there was a nuclear winter that lasted 10 years following the Yuctan meteorite. I've also read that there was global warming following gasses escaping from the Deccan Traps. Either way, I would have thought that homeothermic animals would have had an advantage and been selected for, so they must have died for some other reason - competition for food, loss of habitats.


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## Dave (Jun 7, 2014)

Darth Angelus said:


> Then again, I am far from sure the 2D drawing of a stick man is not a simplified analogy, too.


I was deliberately trying to simplify for the benefit of non-scientists, but we do need visual models and simplifications in order to learn. I remember back at school learning about atomic nuclei with electrons spinning around them, then a few years later was told, remember that, well it's all completely wrong! Or the Wave versus the Particle theories of Light. Neither are correct, but both help us to understand something. Also, I didn't make up the stick man analogy, I read it somewhere a long time ago. If you are a mathematician (which I'm not) you can explain all these things with formulae and maybe you don't need to visualise them.


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## Karn Maeshalanadae (Jun 7, 2014)

This kind of issue I have seen before, at least in passing, and the trouble with it all is, I believe most people are still thinking too small. Thinking too much like humans.


What I mean by that is this: We, humans, have evolved on a planet where O2 and H2O are what gave us life. That is simply how our atmosphere wound up. Well, actually, most of our atmosphere is nitrogen, but we evolved to need oxygen and water.


I also believe that makes scientists assume that ANY kind of complex life will actually need oxygen and water to evolve. This is where I disagree. We know what planets look like far from out solar system, but only from the view of space. Putting aside the fact that most planets discovered are merely gas giants, I believe that evolution can take many different paths. Atoms and molecules mix, mingle, fuse together within a primordial ooze. If one partnership works out well in its environment, then it has a higher chance of remaining. I have no idea how many combinations went through on Earth before it gained complex, cellular life, but we did through oxygen and water.


But...I highly doubt that is the only possible combination. First off, I don't think we even know what molecular structures are possible out there. I'm sure that we on Earth do not naturally contain every single one out there. I'm pretty sure we don't even know every element or atomic particle. So, who is really to say with certainty that there isn't life that, for instance, evolved to breathe methane and inside, say, even hydrogen peroxide, for examples? Temperature does seem to be a factor, though microbial life here on Earth has been seen to be able to withstand extremely high temperatures.


And I always ask that question about other galaxies myself. In my own stories, my two main worlds are within the Andromeda galaxy, not out own.


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## Mirannan (Jun 7, 2014)

Dave - It didn't require billions of years of evolution to come up with DNA. DNA is present in all life-forms on Earth, including the most archaic. Except some viruses, oddly enough, in which the info molecule is the very similar RNA. Which doesn't tell us anything about whether another genetic molecule is possible.

You're quite right about carbon being the only atom that can form long chains by itself. However, there are other elements that can do it with some help. As an example, silicones (which are long chains of alternating silicon and oxygen molecules, essentially) are quite stable. Probably too stable at Earthly temperatures, but maybe at temperatures of 200 C or so?


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## JonH (Jun 7, 2014)

snoockey said:


> JonH that true, but its not really practical, right? XD



Depends on whether you are talking now or the future, or drama vs physics.

It's not practical now. But if I could place a bet on whether a constant grav drive or a hyperdrive would come first (ignoring the fact I'd be dead before either happened) I'd say constant grav drive is far more likely to happen first. Both need leaps in physics and engineering.

Dramatically, constant grav sublight drive sucks.


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## Venusian Broon (Jun 7, 2014)

JonH said:


> Dramatically, constant grav sublight drive sucks.




Works fine in Alastair Reynold's Revelations Space universe. 

You just have to have loads of hibernating devices for the crew and passengers and a timeline that jumps around a lot if you are following different characters on different worlds. (I ignored trying to work out the years and just focused on the plot - much easier.)


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## JonH (Jun 7, 2014)

Mirannan said:


> DNA is present in all life-forms on Earth, including the most archaic. Except some viruses, oddly enough, in which the info molecule is the very similar RNA. Which doesn't tell us anything about whether another genetic molecule is possible.



LOL. I was just about to say that to make exactly the opposite point. If there are two protein types that transfer inherited characteristics on Earth, why can't there be more elsewhere?  Typically there are zero, one, or many things. Never two.


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## JonH (Jun 7, 2014)

Venusian Broon said:


> Works fine in Alastair Reynold's Revelations Space universe.
> 
> You just have to have loads of hibernating devices for the crew and passengers and a timeline that jumps around a lot if you are following different characters on different worlds.



Then he's a better man than I am. I tried to write this and even with cold sleep and extended lifespans, keeping dramatic tension going is a nightmare.


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## Venusian Broon (Jun 7, 2014)

JonH said:


> Then he's a better man than I am. I tried to write this and even with cold sleep and extended lifespans, keeping dramatic tension going is a nightmare.



I'd definitely recommend then that you give _Revelation Space_ the novel a go. Maybe it might fire you up with other ways of dramatising the sub-light constant-g universe?


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## Dave (Jun 7, 2014)

Mirannan said:


> Dave - It didn't require billions of years of evolution to come up with DNA.


Sorry, it was a bit early for me when I wrote that. What I meant to say was that the Earth is 4.54 ± 0.05 billion years old, and in all that time the only thing that appeared was DNA. 


Karn Maeshalanadae said:


> First off, I don't think we even know what molecular structures are possible out there. I'm sure that we on Earth do not naturally contain every single one out there. I'm pretty sure we don't even know every element or atomic particle.


Sorry, but I'm afraid we do know every element and the ways in which they react - it's called Chemistry. These are fundamental standards that are a result of absolute values of energy states of subatomic particles that were set in stone following the Big Bang. Maybe in some alternative Universe where those values are different then everything would change. If we could even travel to such a Universe then we could not exist as we are.

The other thing is that the vast majority of reactions are in solution. Unless you can have another solvent (which Mirannan was postulating with Ammonia) then you are stuck with Water as a liquid and restricted to temperatures between 0 and 100 C. The Miller–Urey reactions are in solution.

As I said earlier, Water is just very, very weird. The only reason we don't think of it like that is that we are so use to it. Our whole world is shaped by water.

And there are plenty of bacteria that don't need Oxygen. Anaerobic bacteria that live in your gut and in sediments, and the weird ones around deep ocean vents that break down Hydrogen Sulphide. However, they all need Water.



Mirannan said:


> You're quite right about carbon being the only atom that can form long chains by itself. However, there are other elements that can do it with some help. As an example, silicones (which are long chains of alternating silicon and oxygen molecules, essentially) are quite stable. Probably too stable at Earthly temperatures, but maybe at temperatures of 200 C or so?


(I did mention the rock-like Horta from _Star Trek_.) Or you could have a _Clay Man_? 

I hadn't actually thought of life existing at 200 C or higher before, so you have me there. I know little about Chemistry at such high temperatures but I think a Silicon Oil could act as a solvent.

However, the Earth has plenty of places where temperatures of that level exist on a permanent basis and we haven't ever seen this Magma Man living inside a volcano. I'm not totally convinced!


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## Mirannan (Jun 8, 2014)

Incidentally, there isn't even as much of a temperature restriction with water as one might think. Freezing and boiling points both depend on pressure. At a high enough pressure, there is no such thing as liquid water but supercritical water has many of the characteristics of the liquid.

There is another general point. We tend to think that life requires temperatures roughly similar to Earth's and water. Basically, because that's what we are used to and know about. I can't really think of any good, general reasons why complex reactions and/or molecules shouldn't be possible in a non-polar solvent, such as those present on carbon planets and also on low-temperature moons (such as Titan). Why don't we know of any such? Because we haven't looked. Liquid methane, in particular, is rather difficult and hazardous stuff to work with.


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## Dave (Jun 8, 2014)

Mirannan said:


> We tend to think that life requires temperatures roughly similar to Earth's and water.


I'm not showing some kind of humanoid-alien chauvinism but it does make sense to think life might develop under the same conditions that we did, because we are certain (however unusual that event might be) that it did it once. That does make the other ideas pure speculation. Also, there is the possibility that DNA was seeded here by panspermia.


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## Venusian Broon (Jun 8, 2014)

Mirannan said:


> why complex reactions and/or molecules shouldn't be possible ... on low-temperature moons (such as Titan). Why don't we know of any such? Because we haven't looked. Liquid methane, in particular, is rather difficult and hazardous stuff to work with.



That is not quite true...

Could basic life exist on Titan? | IFLScience

A very interesting article I thought describing a number of experiments that set out to replicate the conditions on Titan. 

At least from my reading they seem to be suggesting that Titan may have a layer of carbon-based life that is similar to bacteria we can observe here on Earth deep below the surface in places where liquid water could be present. It seems that basic building blocks for carbon based life seem to quite easily pop into existence (from memory I seem to remember that comets might be good incubators for building carbon based precursor molecules for life etc...) - it's just then a matter of getting them to liquid water.

However I would fully admit though it must therefore still be possible for completely unexpected things of a completely different chemical heritage floating in the (very) chilly pools of liquid hydrocarbons on the surface. Perhaps one day we'll get a rover on Titan and will actually be able to see if that's the case.

I also agree with the temperature/water point you make - bacteria have been found in the ice of glaciers and other cold places, at temperatures that should not support life, because they actually produce an anti-freeze that gives them a tiny bubble of liquid water to survive in.


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## Ursa major (Jun 8, 2014)

Venusian Broon said:


> I'd definitely recommend then that you give _Revelation Space_ the novel a go.


I second that. But some of us, me included, found the first fifty or so pages a bit hard going. After that, things were much easier. (Oh, and I'd agree with not worrying too much that the books jump about a bit in time and simply following the plot. I let the author worry about sorting out what had to happen when. )


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