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HKATER
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Sorry a typo. I meant FTL, not flt above. My take on time dilation is as follows, I welcome any corrections to my rudimentary calculations and thoughts. Every human being is moving at a very great and defined linear speed (m/s). We most likely have a rotational angular speed as well but that I will ignore. This is because we are on a planet orbiting a star with a linear speed. A star orbiting around a point in its galaxy, and a galaxy moving within a universe, relative to some fixed point within this universe (not sure what that point is), which means we have all of these combined velocities as well.

Therefore because a human on earth has a set and defined velocity, a person who leaves earth will have a "higher" net speed. This greater speed will result in a difference in time between the traveller and the earth resident, since time is dependent on speed. This suggests to me that our current human perception of time is due to our speed now (living on earth). The day we leave earth it will change, but it would seem that unless we travel at vastly greater speeds, says aporoaching FTL, we won't really notice the difference. The strange part about time dilation is it seems to point towards the possibility of time travel, which is something I have hard time believing in.

As part of my research for my fiction book, I have done various calculations of space travel near FTL, and came across a curious observation. It seemed that light speed (or rather the distance that light travels) is related to earth's gravity or g. I can't remember exactly the relation I saw, it was a few years ago, but I found that accelerating at g (9.81....m/s2) for very long periods of time, had a bearing on the distance over time, or light years. i think it was if you travel at g acceleration for one year, you will find a relationship with the number of light years you have travelled. Do 2 years and it appears again. That's weird because the speed of light and earth's gravity are unrelated? It seems obvious to me that space travel will be at g acceleration, the followed by g deceleration. Its what the human body needs. Weightlessness in space doesn't have to be an issue. Even Arthur C Clarke in the film Space Odyssey showed how rotating space stations can solve g forces for human habitability. Our only problem is finding an energy source capable of sustained acceleration, deceleration over years continuously.

By the way thanks for the explanation of the feather and the ball experiment. Yes I was thinking of experimental error too - not a good vacuum or something along those lines. I will look into that since I see there has been a more recent trial with impressive accuracy.

Watsisname
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Time dilation is real (it can and has been very reliably measured in experiments), but for most situations it is such a small effect that we can ignore it.  An exception lies in the Global Positioning System, which must account for the effect because its time keeping must be extremely accurate in order to locate your position as precisely as it does.  I describe the details (and what would happen to the system if it didn't account for time dilation) in a post here.

For different planets orbiting different stars, the difference in the rate of time between them is pretty small.  To be quantitative, let's compute how quickly time passes on Earth orbiting 1AU from the Sun, and compare with someone floating at rest very far away in interstellar space, far from any gravity sources.  The time dilation formula for an object in a circular orbit (accounting for both special and general relativistic effects) is

where G is the gravitational constant, c is the speed of light, M is the mass being orbited, and r is the distance from that mass.

For Earth orbiting the Sun, this comes out to a time dilation factor of 1.000000481, meaning time passes more slowly here by about 53 microseconds per hour compared to a clock that was sitting at rest very far from the Sun.  We might wonder if the surface gravity of Earth itself modifies this result.  It does, but not by very much (by a few parts in 1010 vs. a few parts in 107.)

Most planets that would be considered worth inhabiting probably have fairly similar surface gravity to Earth, though the size of their orbits around their stars, and the masses of their stars, may vary.  Let's imagine a planet orbiting 10 times closer to a Sun-like star.  In that case, the time there passes more slowly than here on Earth by about half a millisecond per hour.  This would be a problem for precise timekeeping across different planets, but otherwise unnoticeable.

Where would time dilation become very noticeable?  If interstellar travelers reach speeds very close to the speed of light.  But reaching such speeds is highly impractical.  (I can also confidently argue the speed of light cannot be exceeded, by principles of relativity.)

HKATER wrote:
Source of the post The strange part about time dilation is it seems to point towards the possibility of time travel, which is something I have hard time believing in.

Time dilation means clocks tick at different rates, but it does not allow anyone to travel into the past.  It does allow travel into the future, which can be weird to think about.

For example, we did a calculation a while back for Midtskogen, who had accumulated about 7 days of air travel, and we found that he experienced about 450 nanoseconds more time than the rest of us due to the combined effects of special and general relativity.  Overall his clock ticked faster than ours because of the weaker gravity at flight altitude.  Is this "time travel"?  Absolutely!  We can say he traveled into the future more slowly than we did, since he experienced more time during the trip than us.  If he had carried a precise atomic clock with him during his travel, this would be measurable.

HKATER wrote:
Source of the post As part of my research for my fiction book, I have done various calculations of space travel near FTL, and came across a curious observation. It seemed that light speed (or rather the distance that light travels) is related to earth's gravity or g. I can't remember exactly the relation I saw, it was a few years ago, but I found that accelerating at g (9.81....m/s2) for very long periods of time, had a bearing on the distance over time, or light years. i think it was if you travel at g acceleration for one year, you will find a relationship with the number of light years you have travelled.

I'm not sure what relation you found exactly, but I think what you're describing is true for any value of constant acceleration.  There's nothing special between c and g, at least that I'm aware of.

Constant acceleration can be a bit tricky to analyze correctly, and if you want to compare calculations I can refer you here.  But the jist of it is if someone goes on a trip with a constant acceleration (as measured by him), his velocity (again according to him) will trend to infinity (explainable either through length contraction or that his clock ticks more slowly), while we who are not making the trip will say his velocity approaches the speed of light.  We will say the distance he travels after some amount of time will trend toward 1 light year per year (same as a photon), while according to his measurements they will follow the hyperbolic cosine (cosh) function.

HKATER wrote:
Source of the post By the way thanks for the explanation of the feather and the ball experiment. Yes I was thinking of experimental error too - not a good vacuum or something along those lines. I will look into that since I see there has been a more recent trial with impressive accuracy.

Sure thing, and please share anything you find!

Stellarator
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HKATER wrote:
Source of the post i believe we will break the FTL barrier. Simply because if you can't travel faster than light, you won't be able to get there. But the topic is obviously controversial.

Technically we already have, at least theoretically. Miguel Alcubierre's warp drive is indicative of this, because it rather elegantly points out that space (not matter) itself can travel at any speed it needs to.  The only practical barrier to building this type of space-ship is the requirement of negative mass to warp space/time enough to slip us along a path, and the only issues with this design are the resultant time dilation effects with traveling that fast (along with gamma radiation bursts). We on the forum have talked about this many times, and I always have to remind people that known physics DOES NOT FORBID FTL. Hell, things in our universe are traveling faster the light right 'now' beyond the Cosmic Event Horizon (it's important to note that this is from our perspective. It's all relative).

In addition, I must also remind lay-people that the idea of "Faster-then-light" is a misnomer anyway, because light isn't that special in this context and is not the specific issue at hand. General and Special relativity are instead explicitly stating the absolute SPEED LIMIT at which MASSLESS PARTICLES CAN MAINTAIN CASUAL CONNECTIONS TO OTHER PARTS OF THE UNIVERSE. This gives us the effect of 'observing' the universe. If this goes wonky, as in the case of extreme time dilation with FTL, casual connections break down and things go south.

Watsisname wrote:
Source of the post     HKATER wrote:
The strange part about time dilation is it seems to point towards the possibility of time travel, which is something I have hard time believing in.

Time dilation means clocks tick at different rates, but it does not allow anyone to travel into the past.  It does allow travel into the future, which can be weird to think about.

You can't physically travel back in time, true, but here is food for thought: If you travel far enough away faster then light, you might be able observe events taking place before your launching time at your origin. By, say, building a powerful telescope, you could remotely observe your own past from your current position that you reached by superluminal means. This would unleash all manner of paradoxes, of course - the concept originally  being the subject of a thought experiment between Einstein and Sommerfeld. A more pedestrian example would be simply when you observe the night sky. Due to the vast distances involved, the object you are looking at how is how it looked at the time when those photons that are hitting your eyes were emitted or bounced off the object in question, not as the object is right now. You are looking back in time.

HKATER, if you really want to know how space and time interact from the perspective of the observer and the observed, then I'd suggest researching the Minkowski space/time diagram, divergent worldlines and the geometry of casualty. PBS Spacetime did an excellent series of interrelated videos about such concepts, and will help one greatly in understanding them. Yes some scary math is involved and yes your brain will hurt, but in theend it is worth it - especially if a book is involved .
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Watsisname
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Stellarator wrote:
Source of the post We on the forum have talked about this many times, and I always have to remind people that known physics DOES NOT FORBID FTL. Hell, things in our universe are traveling faster the light right 'now' beyond the Cosmic Event Horizon (it's important to note that this is from our perspective. It's all relative).

A big difference though: nobody directly measures such FTL motion of galaxies in the universe, or objects passing below a black hole's horizon, or other such instances where we might say velocities are faster than c.  There are no actual causality issues with those motions.  But with an Alcubierre drive, someone would measure that FTL motion, and it is trivial to construct a causal paradox with it.  Just imagine someone making a round trip FTL journey.  Then we're back to the grandfather paradox of special relativity.  In my view this is a pretty powerful reason for concluding the Alcubierre style of warp drive is not possible, even aside from the exotic energy requirements.  (We could alternatively say the exotic energy requirements are a symptom of this being a nonphysical solution of general relativity's equations).

HKATER
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I believe the relation I saw was a traveller accelerating at g continously for one year, has travelled a distance of one light year. Two years, 2 light years. What you said about 1LY makes sense. Maybe it was because my calculations were in light years, that is after one year you get to 1LY speed. It makes sense that a traveller at a speed of 1LY travels a distance of 1 LY, but what I found strange was that the traveller after one year "reached" a speed of 1LY and started at zero (relative to Earth), as their speed is changing constantly. I don't recall now what it was exactly, but if you do a calculation of a traveller at g acceleration continuously for one year, you might notice it as well.

I also found it odd (like a creator of a universe planned it this way?) that the speeds required to travel between stars (ie vast distances) can be easily achieved if a traveller accelerates at g, the normal gravity experienced by an earthling. It makes space travel comfortable. How to sustain g for prolonged periods is our problem. We need a power plant technology much greater than what we have now. What I found was that if you move around the galaxy at g acceleration/deceleration, you can get to beyond FTL speeds within a time frame of years, not centuries.

Great points on the possibility of FTL and the idea that somethings within our universe maybe be exceeding this speed now, I had the same thought when contemplating the velocity of a human now, orbiting around a star, which is itself moving within a galaxy, which is not stationary either. All of this is relative to some fixed point in the universe, which is a problem in itself. How to define a fixed point, that is a stationary and most likely imaginary and arbitrary point, in an expanding universe? But it does suggest that the human body, relative to this fixed point , is moving at a tremendous speed right now. Relative to the earth of course we feel as though we are stationary. I feel that is what defines earth time, with regard to dilation.

Time dilation and time travel. Yes I came to the same amazing conclusion. That time travel is possible only in the forward direction. That we can leave earth and return and have aged less than those on earth. The faster we travel the greater the time difference. Which means we could visit an Earth more advanced in time than we are (time has slowed down for us). Going backwards in time is blocked for us, but the concept of the telescope is an interesting work around. Being unable to travel backwards in time certainly solves any scifi fantasies of people say travelling back in time and coming back and making a killing on the stock market for instance. But going forward in time is still pretty amazing. The day I worked out that forward time travel was possible was an amazing day for me, but I see that I am not the only person to have worked this out.

Watsisname
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HKATER wrote:
Source of the post I believe the relation I saw was a traveller accelerating at g continously for one year, has travelled a distance of one light year. Two years, 2 light years.

We should be clear about whose frame of reference these measurements are being made in.  But in either case (whether measured by the traveler or by those staying on Earth), the relationship doesn't quite work that way, and this behavior also is not unique to an acceleration of 1g.  Let's see how it works in both frames of reference.  (I'll put up the formulas at the end.)

If travelers are on a ship that accelerates at 1g continuously (as they measured in its frame), then after 1 year (according to their clocks), they will have traveled 0.562 light years.  After 2 years, they have traveled 2.90LY.  3 years: 9.72LY, and 4 years: 28.9LY.  The relationship is highly nonlinear.  After a few years of constant acceleration like this, the distance traveled begins growing extremely rapidly.  It almost seems like the ship exceeds the speed of light (more than 1 light year per year)!  But this is because the clocks on the ship are slowing down (time dilation) compared to clocks on Earth.  People on the ship will say however that their clocks are fine, and the rapid trip is because distances in the direction of travel became shorter (length contraction).

Meanwhile, the times elapsed on Earth after 1, 2, 3, and 4 years of ship time are 1.19, 3.75, 10.6, and 29.9 years, respectively.  People on Earth will also say the ship's speed is approaching the speed of light, or 1 light year per year.  But that had nothing to do with the acceleration being 1g.  It would still be true if it had been 0.1g, or 100g.  All this rate of 1LY/year means is that the ship is approaching the speed of light.  The faster its acceleration, the more quickly its speed approaches c, and the sooner these relativistic effects start to take hold.

Let's turn this into some graphics.  Here I plot the velocity (first row) and distance traveled (second row) over time, according to timekeepers on the constantly accelerating ship (left panels) and by timekeepers on Earth (right panels).  The ship's acceleration is 1g (9.8m/s2) as measured on the ship, and it accelerates like this for 4 years (again as measured by its clocks).  The bottom two plots show the relationship between ship time and Earth time (bottom left), and the ship's acceleration as seen by those on Earth as a function of its velocity (bottom right).

This does in fact mean that if we could accelerate at 1g constantly, then we could reach the near stars in just a few years.  After 12 years, we would reach the other side of the Milky Way!  We would reach the Andromenda Galaxy, 2.5 million light years away, in just 15 years.  Make it 30 years if we want to start slowing down half way and come to a stop there.   Meanwhile, 5 million years will have elapsed on Earth (and in Andromeda!).  Of course, as you say, accelerating like this to reach speeds so close to light is very impractical.  But it does make for great (and scientifically accurate) fiction.

Formulas:

where d is distance traveled, v is velocity, γ is the Lorentz factor (time dilation or length contraction factor), t is time measured on Earth, τ is time measured on the ship, α is the acceleration measured on the ship, and a is the acceleration of the ship as seen on Earth.  I can also recommend this webpage, http://math.ucr.edu/home/baez/physics/Relativity/SR/Rocket/rocket.html, for more information on how relativistic effects come into play on this hypothetical rocket ride.

HKATER
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Yes you are correct of course. I dug out my old calculations and discovered the error. As luck would have it my first calculation was to Alpha Centauri which is 4.365 LY, and my second calculation was in error. It just so happens that to travel to Alpha Centauri, constant g to the half way point of 2.18 LY then decelerate at constant -g to the system, I calculate as taking 2.05x2 = 4.1 years, which is close to the distance in light years. But my second calculation to Epsilon Eridani of 10.446 LY was only 6 years.

You have provided some impressive results for travelling within our galaxy and beyond, faster travel times than I had assumed. It seems clear to me that travelling at g would be highly desirable, which suggests that our ability to do such things, if it is possible, is a very long way off. The transition from +g to -g for a traveller could be easily and comfortably acheived, potentially leaving the traveller ignorant of the transition with a simple rotation of a habitat capsule, maybe with a short interval of weightlessness at the half way point, for a duration only necessary to acheive the rotation, a matter of minutes or hours conceivably. By simply changing the orientation of the travellers feet while standing relative to the direction of the force, +g or -g will feel the same.

I strongly believe that the driving force that will propel humankind beyond our solar system will be the discovery of another earth. This is what my scifi book would be about. I also believe that optics will advance to such a point that we will "see/sense" what is out there long before we have the ability to travel there, whether by AI or human explorers. Imagine if Columbus had had a giant telescope and could have seen the new world before he got there. Convincing the King of Spain to fund an expedition would not have been difficult. Interstellar travel will be tough, but with a goal in our sights, it makes it easier to acheive. Optics right now is advancing very rapidly. It is transforming the battlefield. Wars are already now "beyond-visual-range." In the world of the future, the one-eyed man in the land of the blind will be king. Wars that are coming will be far more dependent on optics. The dark-side of the moon will probably be the first strategic flash point. A telescope mounted there will not be limited to size constraints of a space telescope. From a stand point of a geosynchronous orbit, its advantages for uninterupted and continous communications will be very important. The moon will effectively become a giant satellite for comms and optics purposes and its ability to hide its far side from earth observers is of great military strategic advantage. I expect to see US defence moves regarding the moon within my lifetime, and other nations.

Stellarator
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HKATER wrote:
Source of the post I strongly believe that the driving force that will propel humankind beyond our solar system will be the discovery of another earth.

Perhaps for initial investigation, but truth be told, an Earth-like planet will be of limited use to space colonization, and thus of flaccid motivation for mundane colonists. Let me explain: The presumed objective for space colonization in sci-fi is to find a planet and settle it in a manner that is comfortable for humans, due to population problems on Earth or a looming disaster. Realistically, the chances of us finding a exoplanet that shares enough basic properties (mass, atmospheric quality, stellar parent etc etc) with Earth to be considered safe and desirous for people and our required ecosystems to settle within a reasonable distance is virtually zero. No planet out there will be identical enough to Earth to be considered an "Earth-twin".

But the actual fact is that no colony effort was ever made just so that 'people have more room to live', at least not in the beginning. Colonial efforts were usually about political or ideological conquest, resources, available funds and more rarely a scientific curiosity (that could be expressed and conducted by the virtue of a competitive and economically healthy society back home). We see this now in our own world with current and past space exploration - the Apollo missions were, for instance, executed by a need to out-compete the Soviets technologically and end the Cold War (well, mostly), and also for scientific gain. The next big wave in space operations will probably be in asteroid or Moon mining for industrial inflation, and the driving force behind Mars colonization will most likely be a curious scientific, not societal, imperative. The very idea that we as humanity need to colonize other planets in order to stave off over-population or natural disasters is ludicrous, because as we have discussed elsewhere on the forum, population growth and its related hurdles aren't the issue most people think they are and it would be far more convenient and cheap if the resources asteroid mining provides was funneled to building artificial habitats in space that can, with no real engineering hurdles, exactly simulate the conditions on Earth. The very technology that we need to do these awesome things require that we pull ourselves together here on Earth with clean, cheap renewable energy and better infrastructure. Without those, we will never be able to escape to Mars or another planet because we'll lack the necessary technology to have much hope of getting to, and surviving long-term in, an alien environment. Everything requires resources and time to prepare, and interstellar travel will require more than most. It is a common, and essentially correct assumption by scientists and futurists that we'll have colonized most of our solar-system and even manage to create a partial Dyson Swarm (becoming a K2 civilization) before we will send out colonial (pure manned exploration might be possible) missions to interstellar space. Even if FTL technology was perfected, energy and cost would still be inhibiting factors to expansion. These missions would involve space-ark-type ships for maximum usability and would more often then not be directed to solar-systems that do not harbor any life-forms, for reasons detailed below.

If an extraterrestrial Earth-like world was discovered (most likely by space-telescopes and surveys, and most likely after other planets with life were discovered), then interstellar unmanned probes would be deployed to that system. Travel time would depend on the technology available, as well as the overall distance. If the planet is really far away, no probe would be sent and instead information would be gleaned by remote observation. Colonization for humanity's sake might still not be considered because despite all that, a problem still remains: how will you integrate the Earth biology into that of the exoplanet's and why would you justify such an disruptive action? Too many barriers exist between Earth-exoplanet biomes to review here, but suffice to say that for exploration's sake genetic engineering for compatibility is certainly an option, but excessive just for colonization. You as a civilization would have absolutely no reason to colonize a Earth-twin because you can mine all the materials you needs from a perfectly barren asteroid or moonlet, and all the living space from artificial habitats you need from mining thereof. The only reason a civilization or nation as a whole would take interest in a Earth-twin would be for research purposes, and this would perhaps warrant a permanent presence on the planet, at least in low-orbit. This logic would apply to not only Earth-twins, but also any other exoplanet with a potentially fragile biosphere.  Of course, there could be exceptions to the rule (and we haven't even discussed terra-forming planets!), but realistically I can't see any colonial justification for living on a Earth-like planet outside of writing a interesting story-arc .
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HKATER
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I am surprised that you mention the unlikelihood of an earth-twin, though I am not saying you are wrong. The simple answer is we don't know. I was reading an Astronomy Now article a few years ago that stated that due to the billions of stars in our galaxy alone, and the unknown number of galaxies out there, possibly limitless and without number, that statistically the probability of an earth like planet (similar atmosphere, size, chemistry and temperatures) was not only high, but potentially thousands within our galaxy.

I do agree with your thoughts on colonisation and our solar system and many others. I think that the moon, mars and the rest of our solar system will not be colonised for the same reason that Antartica will probably never be colonised. They are too hostile to our lifeform - no one wants to live there basically. That these habitats will be for industrial and research purposes. People may "work" there for a time, but will return to earth to live.

But it is precisely because a twin-earth would be hospitable that we would seek to go there. Potentially such a venture could be a one-way trip, with no possible communication or return to earth. A good parallel example in my opinion would be Columbus and the new world and I agree with your points about purposes "other" than colonisation. The new world was discovered and developed by Spain, at that time the Spanish Habsburgs (the Holy Roman Empire), and exploited by others, for primarily trade and wealth generation purposes (gold), but it also had a colonisation element to it. HRE ruled their known world, and therefore considered any part of it theirs. The major difference between an earth twin and another planet, would be the knowledge that it was virgin land prime for both settlement and exploitation.

Human beings have always settled new lands. I could well see us continueing the process in space. i have no trouble in imagining many earth like planets out there somewhere, very far away. But this is of course pure speculation - impossible to prove. Mathematical probability and vast numbers of solar systems and exoplanets and countless galaxies, is my only guide.

And of course your opinion is just as valid as mine and I can understand your position. I do not believe our solar system will be as useful to us as futurists imagine, at least not as far as alternate habitats go. For resources and energy sources yes.

Stellarator
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Thank you for your understanding HKATER, and weathering my barrage of rhetoric . I too agree that Earth-like worlds may exist in our galaxy, perhaps many thousands. Statistically it is certain. But I do not find it very likely that they will be hospitable (or even desirous by our standards) for unaltered humans, from a astrophysical and biological perspective.

HKATER wrote:
Source of the post The major difference between an earth twin and another planet, would be the knowledge that it was virgin land prime for both settlement and exploitation.

Not so, even if we consider the vast multitudes of potential Earth-like worlds. The mathematical probability of an exogenous biome sharing enough biological characteristics like animic acids, protein configurations and symmetry, cell structure etc with that of Earth's for the purposes of Earthly human integration via colonization is exceedingly remote. The dizzying array of organic (and inorganic) configurations on a planet that then manifest into the tissues and processes of organisms that share congruency with Earth life will not be terribly common. Diseases are often mischaracterized in sci-fi as deadly to humans from off-world, but due to their nature, diseases have evolved to infect specific metabolisms, and those bodies that developed off-world would be none-compatible and the disease wouldn't 'catch', at least not to it's full potential, unless the metabolic similarities are really close (don't confuse the decimation of Native Americans from Old World diseases to be the same in this regard).

For the sake of clarity, I'm not saying that future humans CANNOT live on an Earth-twin, I instead state that it just wouldn't be WISE to do so, and  further apply the notion to exoplanets with LIFE ON THEM. This is because no matter what, there WILL be enough differences between Earth and the 'analog' exoplanet to cause issues.  The actual dangers would include bacterial (or alternative organisms) and other microbiological infection/cross-contamination, invasive Earth species usurping the native ecosystem (if the environment is REALLY similar), unforeseen environmental anomalies (like imbalances in elements in the soil/water) or genetic deformities in those non-native species that breed there over generations. In addition, a planet's surface and atmosphere is not a homogenous masses that is uniformly bucolic. As we know from Earth's past (Earth being a true 'Earth-twin'  ), natural disasters can occur via internal processes like volcanoes, outside forces like asteroid impacts, or a mix of both like with some global ice-ages. These cataclysms can be extremely detrimental to colonial efforts.

As for 'exploitation', it is easier to exploit non-Earth-analog objects for their riches, whatever they may be. Water can be synthesized from asteroids and comets, or scooped out of the interstellar medium (if you're really desperate), and almost all elements useful to society or manufacturing technology can be likewise found on asteroids, small moons and moonlets. Why trash a planet with life if you can gather it cheaper from an object without even a microbe on it? This is especially a reasonable preposition if you are considering the bane of fuel costs for transporting all those goods: gravity wells. It takes a lot of energy to launch a ship and achieve escape velocity from the gravity well of an exoplanet of Earth-mass or larger. That is why our space-program has always been rather taciturn in development - we need more efficient ways to escape the planetary gravity well (as well as other concerns that we won't get into here).  Mining resources off of a an object of far less mass in a solar-systems by comparison doesn't require magical Clarketech or anything, just decent automation, basic transport services, energy sources (nuclear fusion, or efficient solar if in the inner system) and of course a reason to do it. After considering this, it would likewise seem that building artificial habitats in low-orbit, the Lagrange points or beyond the Roche limit is a lot easier then building structures on a planet that would be designed for extended human habitation and accommodate all of our needs and allow for environmental .

All in all, Earth-twin worlds harboring life would be valuable biological treasures, just the way national parks and marine habitats are here on Earth. Scientific study and exploration will surely take place on them once they are discovered, but it would be unlikely and unnecessary for the pioneers to live directly on the planet for any reason aside from novelty or obscure principles. Of course, this ENTIRELY DEPENDS on the reasons for going to that planet, and the maturity of the civilization discovering it. Maybe if we just can't contain ourselves or something makes us land, we will build actual colonies on the Earth-twin.

I am not tackling the idea of terra-forming non-inhabited planets, because detailing the logistics of that is very lengthy, and I have not likewise addressed the possibility of intelligent life existing on a planet and how that would greatly interfere with colonial efforts due to the endless moral debates that would entail .
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HKATER
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Interesting points raised. I suppose I fall in the camp that "possibly", our star appears to be a very average one, and therefore maybe our planet and its biotope is not that special. If that is the case then it is possible that earth like biotopes (and many other kinds) exist on other planets. Good point on diseases. I don't believe in sentient aliens because if there were it would seem that they would have found us, but then again the universe is a large place. I feel the aliens we will encounter will likely be lifeforms like bacteria or plants without an animal brain. So yes it could be hazardous.

I suppose you could say I am a bit mixed up since I believe in two opposites simultaneously - a non-unique planet and biotope, yet a unique animal world with man at its apex - the thinking ape. That is a contradiction, but it seems to rest happily in my mind. I find it hard to believe we will meet sentient alien species, as smart or smarter than us, but I guess only time will decide.

I like to think that there is nothing unique about our planet. Mars appears to have followed a similar course to earth but due to its orbit and proximity to the sun, its fate was different. I think the above summarises my thoughts and explains my optimisim with regard to an earth twin in our future, but your counter arguments are logical and well explained. MY OPINION is based on a belief that our world is not unique, nor is its chemistry and biotope and chemical processes, natural laws. I feel that these characteristics of earth (warm seas, green land, blue sky) are universal to the universe and other star systems, but may not be seen in most systems. Maybe the occurence of earth like planets is 10%? I don't know the percentage, but I expect future scientists will.

Watsisname
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I feel much the same way, HKATER.  I think the conditions that led to life on Earth are not overwhelmingly rare, and suspect that life is common in the universe (though technologically advanced life may be quite uncommon).  But ascribing numbers or probabilities to it is still beyond our ability right now.

I think the most exciting thing is that the data that may help answer those questions is very likely to come about in our lifetimes, maybe even within the next 10 years.

Stellarator
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Science and Astronomy Questions

HKATER wrote:
Source of the post  then it is possible that earth like biotopes (and many other kinds) exist on other planets.

I too believe that life is ubiquitous throughout the cosmos, and that intelligence (by our somewhat anthropomorphized standards) is also present, with some exceedingly rare examples being more advanced then us (some by only hundreds of years, others by many millions). But most life, as you assert rightly, WILL be simple, if not single-celled then at the stage of microbes. Great filters exist, and these stack against life higher and higher as it becomes more complex, reducing it's chances of survival in environments. Finally, the greatest filter will apply to intelligent and technological civilizations. At this latter stage, these filters are no longer inherent to nature, but instead are caused by the specie's own technological misunderstandings or abuse, or faulty societal structures.

HKATER wrote:
Source of the post , but then again the universe is a large place.

Exactly. Relativity holds us all captive under it's chains. The farthest stars see in the skies are not as they are now, but how they were. Any signals of artificial origin will not be present-tense, but potentially many hundreds or thousands of years old - millions if they are extragalactic. If all alien civilizations are bound by the rules of universal causality (i.e. the speed of light) in transport and communication, then it would be illogical of them to waste so-much energy trying to contact us directly and physically - like by sending a convoy of star-ships our way just to say hi, or to conquer us. If they want to study humanity, then they could full well do so without interfering with us in any way - either by sending swift, silent probes through the dim and uncharted reaches of our solar-system, or by observing from afar with massive arrays of telescopes.

I think I have established my opinion thus far on the prime motivations of space-exploration, so to tie in, I'll say that we shouldn't expect extraterrestrials of the technological level from which they could actually contact us to be interested in Earth. That being said, I don't think we can theorize much of the motivations and mindset of an alien civilization, suffice to say that they should be reasonably logical - otherwise they wouldn't have gotten very far technologically. But it would be a grave mistake for us to think they think like us and have the same anthropomorphic ideals and dreams. Some might, by evolutionary chance, but they would statistically reside beyond the causality barrier, disallowing us from direct meaningful communication with them due to light-lag.

To conclude, technological restrictions here on Earth mean that the only reason we haven't found any alien life at all, is simply because we have not been looking hard nor long enough.

Watsisname wrote:
Source of the post I think the most exciting thing is that the data that may help answer those questions is very likely to come about in our lifetimes, maybe even within the next 10 years.

Yes, it's a thought that keeps me up at night .
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HKATER
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Science and Astronomy Questions

My last thought is this - that the driving force for colonisation of another earth I believe will be earth politics and war. A nation with the technology to leave earth behind and seek their destiny elsewhere, free of earth government, might well take the chance. Tyranny and liberty are the twin themes of human political history, and its unlikely we will change. I don't subscribe to global warming, ecological distaster, pending doom as a factor. Simply greener pastures elsewhere. I could well imagine a future peoples of earth brave enough to take the plunge into the unknown on some sort of generation ship, with a twin earth as their final destination, never to return to earth or communicate with it in their lifetime.

No doubt there are going to be some terrible wars coming our way that will be worse than WW1 and 2. Imagine a 1980's Soviet Union and USA in a fight to the death kind of war and we are getting close.I don't expect we will see the next world war in our lifetimes, thankfully, but a future generation will. I suspect it will be all out "nuclear." Future tech will probably make a nuclear war survivable (missile defence). Not something pleasant to imagine. Wars like that will make people more likely to leave.

Stellarator
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HKATER wrote:
Source of the post that the driving force for colonisation of another earth I believe will be earth politics and war. A nation with the technology to leave earth behind and seek their destiny elsewhere, free of earth government, might well take the chance. Tyranny and liberty are the twin themes of human political history, and its unlikely we will change.

I find it difficult to imagine a nation on this planet (as we know them) having the available resources and experience to build and certify a interstellar ship, now or some hundred years in the future - especially when they are at war. That ship would need to be multiple kilometers long, stocked with the most expensive, cutting-edge life-support and environmental-control technology and almost certainly built in space, either in low-Earth orbit or in a Lagrange-point. The ability to build a space-ark would imply the following:

• This nation or group of nations has a significant presence in space, in order to supply the operation with the required orbital infrastructure (ship-yards and ways for people to actually get to the ship). In addition, they must also have stupendous amounts of resources for construction - resources that could only come from asteroids - and in wartime might otherwise be more useful to, you know, win the war. The only issue here is that if they can make to space, they could just as easily relocate elsewhere in the vast solar-system - unless their source of distress is solar-system wide.

• This nation or group of allied nations does not seem to care about their opposition sabotaging the elaborate operation of building an interstellar ship, or simply blasting it out of space whilst it is still under construction. War is very messy business, and building an interstellar vessel requires the most delicate attention to engineering and societal detail. Any screw-ups would be catastrophic. If this nation doesn't care about this, then they must have some sort of upper-hand on the conflict, which raises the issue of why they must flee in the first place.

These points assume that the vessel being built needs to support a biological, human population. There are several cheaper designs that do not need to. For example, you can digitally encode human genetics or upload minds into a databank, pack them into a small probe with a sophisticated 3d-printer and send it off to wherever. When the probe arrives at its destination, it then can manufacture biological (or technological) bodies for the uploaded minds or genetics, with alterations made to match and adapt to the planetary environment that the probe landed in. No Earth-twin would be needed! This destination could be only a few light-years away, in this case, since you're not looking for a suitable environment. An AI could also be present, to tutor any fledgling humans or oversee construction. All in all, this operation is very cheap and efficient. But as I have outlined elsewhere, I find the notion of colonizing a planet a waste of energy - colonizing space itself would be much more efficient.

HKATER wrote:
Source of the post I don't subscribe to global warming, ecological distaster, pending doom as a factor.

In light of my exposition in the above paragraph, these would literally be the ONLY reasons humanity would want to escape the solar-system altogether. I'll add nearby supernovae, extreme solar-flares and ice-ages to this list.  All also have solutions that don't involve calling a grand "RETREAT!" from the solar-system.

HKATER wrote:
Source of the post Future tech will probably make a nuclear war survivable (missile defense). Not something pleasant to imagine.

In the future, nuclear missiles may be under-powered, depending on how far into the future we are talking about. If point-defense systems are good enough to actually 'deflect' or diffuse nuke bombs, then the opposition will invent a newer, smarter and more destructive weapon. It is the evolution of the armsrace: you have a better weapon, they have better defenses that then begets a better weapon and so forth. The end of this race is still far away, with the 'ultimate weapon to end all wars'. Nukes are not the end in this sense, because they were not used, only implied. A war that results in both sides losing defeats the purpose of said war. The perfect weapon and the ultimate end to any armsrace is that which can attack and NEVER be used on its wielders.

Anyway, I hope I've given you something to think, and maybe helped dispel confusion around any unoriginal sci-fi tropes .
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