If live have evolved somewhere else (which is unquestionable for all SF fans),
very probably it is based on carbon chemistry and molecules similar to those
encountered on Earth.
Carbon atom is very special, it enables a large variety of strong chemical
bounds necessary to sustain complex organisms. Another, and probably unique,
possibility is life based on silicon, which chemical properties are similar
to carbon. I don't mean silicon electronic circuits, but organic molecules
based on silicone instead of carbon.
However probable alien life chemistry doesn't tell us a lot about shape, color
or size of aliens.
SHAPE - One is sure - most alien life forms will look very different from
all those humanoid green or grey creatures with big heads and weak bodies
repeated over and over in bad science-fiction stories and movies. Look into
Earth's life forms - how different & strange they are, despite they share
common ancestors. Aliens won't look as Mr. Spock.
So don't limit your aliens to kitschy convention, be as imaginative as you
can, invent something new, instead of copying old patterns, but in the same
time try to imagine a consistent creature, adapted to live in world in which
it evolved. Take inspiration from various creatures living on Earth, and you
will see a large variety of blueprints for an organism. (Ex starfish or octopus
have so different body structure from ours, why aliens should have a head,
2 legs and 2 arms while so many other schemes are possible? )
While creating an alien, be as imaginative as you can, only try to imagine
how it moves, how it grows, what are his receptive organs, and how they function.
You can also try to imagine how your creature evolved, what is the environment
it lives in, is it a predator or a prey...
All creatures must be based on atoms & molecules and it means they can
be destroyed = killed. Chemical compounds, which form an organism, are stable
only in very narrow range of conditions such as temperature and pressure.
Crossing this range results in organism malfunction, and destruction. Indestructible
superheroes are fruit of pure imagination and have nothing to do with science-fiction.
Robots also are extremely fragile creatures, often more fragile than organic
life forms.
You don't believe me? Try to drop your cat from 1 m and then do the same with
your camera or microwave. ;-) Although robots can function in wider range
of temperature and pressure - even in vacuum, their structure can easily be
destroyed by strike, punch or high-G force, and they have a serious disadvantage
- they wear (age) quickly as they can not repair themselves, as organic life
forms do. Electronics can be destroyed by radiation. Very high levels of neutron
radiation can transmute even the hardest materials, and destroy them.
SIZE - Godzilla could not exist on Earth - it would collapse under its weight.
Bones strength is proportional to its cross section. If you expand a creature
making it 2 times taller, its bones cross section will be just 2x2=4 times
larger, but it's weight will be 2x2x2=8 times bigger, so bones will have to
support 2 times more weight, and will broke easier. That's why small animals
as dragonfly can have a very weak, slim body, and big elephant needs massive
legs to support its bulk body. You may drop a small mouse from 1 m without
any harm, but such fall for an elephant could be lethal.
That's why alien life forms sizes are probably similar to what can be found
on Earth.
Creatures living on big planet surface, with higher G force, must be smaller,
with massive legs, or some sort of slugs stuck to planed surface by high G-force
unless they live in aquatic (fluid) environment enabling them to profit from
Archimedes law.
Creatures living on small planets, with lower G force can be bigger and can
have more fragile structure and limbs, but don't exaggerate - too small planets
can not keep an atmosphere. (ex. Mars - small planets cool down faster, their
core solidifies and stops generating magnetic field which protect planet from
radiation and atmosphere from blowing out by star wind)
EVOLUTION - Life appeared on Earth relatively quickly, that's why probably life is a common phenomena on planets apt to sustain it, but intelligent civilizations might be very sporadic (life on Earth existed for 4 billions years, but civilization for only a couple thousand years, and we are the only specie which developed civilization)
To evolve, life must be based initially on natural selection, which "automatically"
promotes best fitted organisms, and eliminates non successful "prototypes".
When intelligent life forms evolve enough to discover their own life code
(like our DNA), they can manipulate, modify and improve it. When such stage
is reached, an explosive evolution takes place. There is another possibility
- intelligent biologic life forms, can manufacture "electromechanical"
bodies, and then transfer their minds into such artificial devices. Theoretically
it should be possible to develop an electronic version of our brain, which
could function similarly or better than the organic form.
New, engineered organisms may by much superior to those created by blind laws
of evolution. They can be immortal (will not age, but still can be killed),
can be much more resistant, intelligent etc… Also some mixes of bio-electromechanical
characteristic are possible. (good example of such "body in body"
concept were aliens in Independence Day)
Long existing civilizations can not be too violent, otherwise they risks self-destruction. So extremely developed "bad alien invaders" intending to exterminate earth's life and conquer our planet, probably doesn't exist, or they must have some kind of instinct which effectively restrains their violenc towards individuals from their own specie.
HABITAT - Only medium and small size stars live long enough (billions years)
to let live evolve into complex forms. Only single star planetary systems
are stable enough to sustain life - in multiple star systems, planets orbits
are very chaotic. Even if a planet formed and survived in a double star system,
its orbit would change so often, that climatic conditions would made life
impossible.
Don't imagine too big planets on sky - when a moon approach a big planet too
close, the tidal force becomes so high that it may disintegrate. Saturn rings
probably were formed in such way.
probably were formed in such way.
There are three possible ways to travel:
Move throughout our space (in starships) and be limited by speed of light
(only possibility known to science)
Teleportate = read exact state of each atom of teleported object, send this
information with a signal traveling at light speed - reconstruct the object
at the arrival. (difficult to imagine a technique allowing to send in this
way complicated objects as living organisms)
Perform a hyperspace jump = travel through a tunnel inside hyperspace ( total
fiction without any solid scientific background)
As only first possibility - conventional traveling - is realistic, I will focus on this one.
Distances between stars are huge (several light years) - to navigate through
such long distances in a reasonable leap of time you have to voyage with high
speed, but to attain high speed you need huge amounts of energy.
How long does it take to accelerate to relativistic velocities (close to light speed)? If a ship would accelerate with 1G (Earth acceleration), it would take about a year, before it reaches relativistic speeds. The same amount of time would be necessary to decelerate.
Interstellar voyages will be very long and extreme endeavors - If living
organisms are to be sent on such trip, hibernation would be necessary.
Probably it will be impossible to effectively hibernate normal humans, but
some specially generically modified humans could be hibernated for long years.
Other possibility is to send a fully automated ship, with "grains"
of biologic life forms onboard (frozen embryos, or only DNA code).
Frozen embryos will be grown and then educated by artificial intelligence
near destination point.
To find suitable planet for exploration / colonization, very large space telescopes
could be build.
Fighter jet shaped spacecraft look cool, but if you shape them as steam engine, or a bike, credibility level would be similar….
Forces in atmospheric flight:
An aircraft flying in strong gravitational field inside atmosphere have to
fight two main forces : atmosphere friction & gravitational attraction.
It is shaped to such purpose: aerodynamic smooth shape, huge engine pushing
aircraft forward, air flow around wing creates vertical force which compensates
aircraft weight.
Forces in space flight :
Only gravitation from stars, planets and force created by spacecraft engines
are involved.
There is no atmosphere in space - ships don't have to be aerodynamic, wings
are useless, and engines can work only to accelerate it to speed which remains
constant after engines are cut off.
If ship is designed to accelerate quickly - its construction must be strong
enough to withstand such accelerations.
If its acceleration is very weak - so could be its structure
If normal humans have to live in a ship during months or years, artificial
gravitation should be conceived.
The easiest way to achieve it is to simulate gravitation by centrifuge force
or constant work of engines accelerating the ship. No other possibilities
are known to science - "anti gravitation" or "gravitation generators"
are just a fiction, and very probably it won't ever change. (all mass generates
gravitation, but "gravitation generator" should have low mass and
generate gravitational force without creating inertia)
WEAPONS
ULTIMATE WEAPON: In my opinion the weapon of ultimate destructive power was already invented and tested 60 years ago, and nothing more powerful was conceived since then.
Thermonuclear weapons seems to be the ultimate weapon. Explosion of tens of megatons can obliterate in seconds any city on the Earth. There is no material or "power shield" that can withstand temperature and pressure of nuclear plasma at ground zero. Theoretically there is no limit for thermonuclear warhead power - all depends on how much fusion fuel would be put in the bomb. The biggest H-bomb was soviet "Tsar Bomba" of 100MT yield. It was tested on October 30th 1961 at "only" 1/2 of its potential power, which was enough to place it ahead of the biggest american nuclear test "Castle Bravo" of 15 MT yield performed on 1st March 1954.It's pointless to use more destructive weapons than thermonuclear. Thermonuclear warheads can totally destroy any civilization, on any planet - it's useless to explode a planet (as Darth Vader did), while after a nuclear Armageddon the planet would become inhabitable for generations. During intensive nuclear war, huge amounts of dust would be ejected in atmosphere, as a result sun light will be reflected back into space, temperature would drop, and during few years the planet would be plunged into a glace age. Impact on life would be similar to Yucatan meteor crash which ended over 200 MLN years of dinosaur's reign - majority of species which might survive the fire of explosions, would die from cold, famine and radioactive fallout.
When we compare arsenals invented by "Science-Fiction" authors or film directors to actually existing strategic bombers or ICBM submarine launchers, such SF arsenals look rather stupid, more like toys than really horrifying weapons. Most "SF movie arsenals" could be easily destroyed by one F-16 with conventional weapons, not to mention a B-1 bomber with dozen of cruise missiles each carrying 200kT warhead.
The winner of "The Most Stupid Weapon Contest" could be famous AT-AT walker form "Empire Strikes Back" - Why Darth Vader decided to use such ineffective & vulnerable cavalry? Answer is obvious - he was the Jedi insider in Imperial Government and he wanted his son, Luke to escape safely… ;-) Totally stupid! Yeah, walkers attack looks pretty cool on screen and lasts longer than split second thermonuclear blast, but strategically & tactically it doesn't make any sense. By the way, why AT-AT walked instead of hovering, while in Star Wars everybody uses anti-gravitation? (even Jabba) Because they are WALKers….. obviously! LOL!
LIGHT ARMS: "Ray guns" from SF movies bear a resemblance to indian bows, and are equally effective - you can easily see relatively slow multicolored "rays" blasted from those fiction toys. Speed of "rays" is similar to arrow speed, probably to let good guys hide from it, and even if they are touched, result often is not more lethal than from an arrow hit.Laser is not very effective as weapon - as it disclose location of gunman - laser beam loose lot of energy in atmosphere, and is ineffective in fog or against smokescreen. Very high energy which is necessary to destroy shielded vehicle would ionize atmosphere, resulting in significant loose of power.
FUTUROLOGY: Future weapons will be more precise, selective and rather incapacitating than killing and destroying. An example of such weapon can be neutron bomb with very limited range of thermal destruction and extended range of killing radiation.
Probably military robots will appear when artificial intelligence is available - they will be destructible, but by their agility and intelligence will easily replace human soldiers in commando type actions. War machines will be remote controlled, or have its own artificial intelligence.Chemical weapons are very ineffective (it is easy to protect against them), so probably will not be used on large scale, except some commando actions. Instead very lethal artificial germs may be invented to silently destroy a population. It may not be noticed that attack begun before months or years. It's possible to imagine a virus which at first stage cause light infection similar to runny nose which helps it to spread easily and infect a lot of people, then it migrates to central nerve system, and attacks it with deadly effect after several months from infection.