And at the edge of the known universe, an expanding shockwave from a supernovae fuses hydrogen into oxygen, forming the largest known water bubble totaling ten trillion times all the water on earth.
For future reference, fusion happens in stars (and at the center of supernovas). H combining with O2 is a chemical reaction rather than a nuclear reaction.
On the other hand, the question regarding how supernovas combine/mix heavy atoms to form chemicals would be a very interesting PhD thesis. :D
And the other options are...? I can think of nuclear thermal, which has its risks, and Orion-like bomb propulsion which no sane civilization would use. What else?
Most non-chemical propulsive mechanisms considered for space travel do not have the ISP necessary to launch from the bottom of a deep gravity well. We will probably continue to use chemical rockets to leave this Earth, at least until the first space elevator is built, and that itself will require quite a bit of up mass.
Why would no sane civilization use Orion-like bomb propulsion? I imagine the cost-benefit analysis changes when liftoff is nearly impossible with available chemical rockets, though I'm not quite sure what your objection is.
If it occurs to them at all that the benefits may be greater than costs. I'm extrapolating here a lot from human condition, but we humans have a tendency to first do something and only then begin to understand its potential. It's not that we carefully considered all the benefits of artificial satellite network before inventing the first rocket capable of reaching orbit. So a hypothetical civilization living at the bottom of a deeper gravity well might not even consider spaceflight, and be forever stuck on their world.
Kerbals have it easy though. They can tour their entire solar system with the same amount of delta-v we need to reach Low Earth Orbit :/.
I was specifically wondering why the Orion-like bomb is so bad that no sane civilization would ever use it. The parent comment seemed to indicate that even if you knew you wanted to go into space and had the idea for an Orion-like system, you wouldn't use it unless you were insane, but I see no justification for that.
Those are all either solutions that require you to already be in space to set up (like space elevators), or at least require much more advanced technology than the early chemical rockets humans first used. A civilization that used those methods, rather than chemical rockets, would require much more technological advancement before they made it into space.
I can't jump from the bottom to the top of the hill.
I also can't throw a ball from the bottom to the top of the hill.
But I can ride a bike from the bottom to the top, and if I can't ride straight up then I can weave back and forth, taking a shallower and longer path. When I get near the top I can throw the ball to the top of the hill, or maybe even ride my bike all the way to the top.
So why can't large planet dwellers ride one optimized vehicle as close to orbit as they can get, and then launch another one or more stage vehicle (of whatever propulsion system) from there?
Humans have launched things like this as well. Orbital Sciences does it with their Pegasus rockets which are launched from high-flying airplanes. They are still chemical rockets though.
A key part of getting to space and staying there is going fast. Getting yourself above most of the atmosphere makes it easier to go fast, but you still need to get up to the same speed. Realistically that takes chemical rockets. We know of other options, as mentioned, but they have problems, as mentioned.
That's what rockets basically do today, use multiple stages optimized for the area they're operating in.
The issue with rockets is that they have to use a certain amount of energy to go up, and they have to carry their own fuel which adds weight and means it need to consume even more energy and so on. For certain values of gravity and type of fuel, this becomes hard, to impractical, to impossible.
Most non-chemical propulsive mechanisms considered for space travel do not have the ISP necessary to launch from the bottom of a deep gravity well.
You don't need much ISP to launch from the bottom of a deep gravity well and thick atmosphere. What you need more of is thrust. Ion engines have orders of magnitude more ISP than chemical rockets, but you can't launch off of many things larger than an asteroid with one.
On our planet, the relatively thick atmosphere makes those sort of solutions very difficult, if not impossible. The forces involved would also be problematic for human life, but those sort of systems could still be useful for raw materials.
Yes, Orion-like bomb propulsion will do it. Looks like explosions can be contained in a steel tube, and the resulting fall-out is almost nill (a giant, nuclear, rocket throwing gun!).
Launch-loops may also compose well with chemical rockets. That'll take much more adnvanced tech than simply using rockets, but the laws of physics permit them. (A smaller, electric, rocket throwing gun...)
Those civs won't be able to construct a space elevator. It's boderline impossible on Earth already, on any bigger planet it'll be completely impossible.
Most discovered planets to date are larger than Earth and closer to the star, but that's probably because it's easier to discover those planets given our current technology...
Interesting to think that the size of planets would limit exploration though (from the article):
If our planet was 50% larger in diameter, we would not be able to venture into space, at least using rockets for transport.
It's possible to do better than lump all of the discovered planets together and complain that the set is biased. For example, Kepler can detect a planet iff there is a chance alignment of its orbit with our line of sight, so for each discovered planet, it's possible to compute the probability that its orbit was correctly aligned, and divide by it to compensate. That way it's possible to make unbiased statements about the distribution of planet sizes and orbits, the fraction of stars with planets, etc.
Wasn't complaining. I'd be interested in a ref for this, most popular science I've seen has skated over the limitations of data collection and made lots of assumptions.
In that submission, astronomers including Mike Brown of Caltech, Steve Vogt of UCSC, and Sara Seager of MIT all make assertions about typical exoplanet composition. A HN reader asked about the biased sampling issue. You can bet they are not just ignoring the possibility of biased sampling.
On the other hand, Earth is a very dense planet (in part due to the accidental formation of the Moon), so bigger planets might still have a lower gravity on average. Also, if they spin faster, getting into orbit will be easier.
Maybe Earth is indeed at a comparatively bad place in the gravity spectrum of habitable planets. Getting things up there is difficult enough that we can't have big payloads, but it's still easy enough to justify not building a self-sufficient infrastructure out there.
It doesn't surprise me how much water there is in the solar system, considering how simple of a chemical water is. Life itself is a chemical reaction that takes much longer to complete (though I'm starting to think that it's more abundant than I think :P).
Water being common doesn't mean life is common. We have the intuition to be aware that the exact atomic configuration of a boeing 747 getting replicated by pure chance on a planet 500 light years away is impossibly low. So impossibly low that I'm willing to bet my life that it won't ever happen, not just on a planet 500 light years away, but on every planet in the universe. What are the chances of life being on a planet 500 light years away? Unfortunately the definition of life is vague and the chemical processes required by life aren't even completely understood.
Without knowing the processes/materials necessary to ignite the self replicating processes required for life we don't possess the information necessary to know whether life is probable or improbable. Even in a universe with plentiful water and plentiful habitable planets, without context on what started it all we can't make any meaningful prediction. Is life like the boeing 747 or is it not?
I always find it ludicrous when someone says the universe is just so vast that life has to exist somewhere else. We just don't have enough understanding/context to know.
Of course, there is a planet that astronomers and others are very familiar where 747s appear all the time. They just happen through complex chemical reactions. Apparently they do that near some hive of theirs called "Seattle"
To answer the question about if life is rare we need to visit Europa and Enceladus in our solar system. If those places have life, then life might be quite common in our universe. If they do not have life, then we are likely very alone in the universe.
Maybe the probability that that life will occur is one planet out of every thousand planets. Then the probability of Europa having life is small. However one out of a thousand in a universe with billions of planets is a meaningful number. If this is the case, then examining our own solar system for life, which is comprised of far fewer then 1000 planets, will not be a worthwhile endeavor.
I think the key is understanding the process itself. What does it take to create the minimal self replicating machines necessary to evolve into the complex forms we see today? Once we are aware of the processes involved in the formation of life then we have the context to hypothesize about the probability that these reactions will spontaneously occur.
Things like the Drake equation are meaningless and made up. You can easily make up an identical bullshit equation about the chances of a 747 spontaneously being thrown together on another planet. We can easily see that it's impossible because we know how the 747 is made, we have context. For life? We have no context, no knowledge of where it came from, and therefore the drake equation and any other statement about life on other planets is meaningless.
We have plenty of context for how life forms - organic chemistry! Lets not pretend life is some magical thing - its an organization of carbon, hydrogen, oxygen and nitrogen. And those things just adore linking up in enormous variety given the right temperature and water.
Early Earth was an unimaginably huge petri dish where every grain of sand on every beach was an organic experiment, with the sun, tides and seasons trying every combination of heat/cold/wet/dry/acid/base... in endless cycles. Those conditions are far from unique in the universe. You could argue its inevitable that life/chemistry will unfold in the same patterns on millions of worlds.
Organic chemistry is a incomplete description. The entire field of biochemistry is an incomplete description. Until we can create life from nothing in a petri dish we don't know whether it is an inevitable outcome or a lucky one.
You can argue that the entire earth is a petri dish for a boeing 747. We have all the necessary materials, all we need is a hurricane to throw all the materials together in the right configuration and boom! 747. With billions of planets in the universe it's bound to happen on another one! It's inevitable.
Perhaps this would be more clear: We don't have Enough context to talk about the probability of life on other planets. Perhaps the chemical reaction needed to create life was mind boggling complex, billions of steps needed to happen in the exact order, under conditions that are equally exacting . Or maybe it's devastatingly simple. We just don't know...
Lets take a look at the jet example from another perspective.
The jet is self assembled by proxy of humans being self-assembled. A 747 is the result of a trillion step chemical reaction that stretches across the history of life on earth itself. The chances of this reaction self-assembling on another planet under the same conditions and in the same manner are impossibly low.
What we don't know is whether or not the chemical reactions forming the first life form on earth happened in the same improbable way. Did it happen over eons? did it require a billion steps? I dunno. Nobody knows. It is not unrealistic to say that the chemical reactions necessary to form life are so rare that earth is the only planet in the universe with life.
When I was young, the big mystery of pop astronomy was: are there any other planets like Earth?
And does water exist anywhere outside Earth.
At some point during my lifetime, exoplanets have been discovered and at some other point, the idea that planets, including earth-sized planets are almost as widespread (or rarefied) as stars themselves. At least 10 billion earth-sized planets in our galaxy alone.
So it seems like the Universe is full of Planets and a lot of those planets contain water.
The next logical step is that extra-terrestrial Life is just as common as water, planets and stars.
If that is the case, that means that life is a natural consequence of star formation/runtime, which is extremely interesting.
Which, if we now really think about it, is not entirely out of the question, in fact, it's quite probable.
We have proof. So far we already have detected a planet with Earth-like conditions (called Earth). Life formed on it. Possibly several times independantly.
The statistics for life on very earth-like planets are staggering.
> The statistics for life on very earth-like planets are staggering.
1/1. Sample size seems pretty shitty. Maybe if we find any other form of life in the galaxy OFF this planet, we might be able to bound the probability of it forming at all.
But this line of thinking eventually leads to Fermi Paradox.
The apparent size and age of the universe suggest that many technologically advanced extraterrestrial civilizations ought to exist. However, this hypothesis seems inconsistent with the lack of observational evidence to support it.
Was this a big pop science mystery back in the day? The simplicity of the composition of water ("burned hydrogen gas") would lead me to think that we should expect to find it in some phase of matter fairly regularly. Caveat though: I'm not a chemist.
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[ 0.25 ms ] story [ 115 ms ] threadOn the other hand, the question regarding how supernovas combine/mix heavy atoms to form chemicals would be a very interesting PhD thesis. :D
If most planets are larger than we are, their populations will struggle even harder than we do, getting off their rock.
[1] https://www.nasa.gov/mission_pages/station/expeditions/exped...
[2] no link needed
Most non-chemical propulsive mechanisms considered for space travel do not have the ISP necessary to launch from the bottom of a deep gravity well. We will probably continue to use chemical rockets to leave this Earth, at least until the first space elevator is built, and that itself will require quite a bit of up mass.
Kerbals have it easy though. They can tour their entire solar system with the same amount of delta-v we need to reach Low Earth Orbit :/.
http://en.wikipedia.org/wiki/Non-rocket_spacelaunch
I also can't throw a ball from the bottom to the top of the hill.
But I can ride a bike from the bottom to the top, and if I can't ride straight up then I can weave back and forth, taking a shallower and longer path. When I get near the top I can throw the ball to the top of the hill, or maybe even ride my bike all the way to the top.
So why can't large planet dwellers ride one optimized vehicle as close to orbit as they can get, and then launch another one or more stage vehicle (of whatever propulsion system) from there?
A key part of getting to space and staying there is going fast. Getting yourself above most of the atmosphere makes it easier to go fast, but you still need to get up to the same speed. Realistically that takes chemical rockets. We know of other options, as mentioned, but they have problems, as mentioned.
The issue with rockets is that they have to use a certain amount of energy to go up, and they have to carry their own fuel which adds weight and means it need to consume even more energy and so on. For certain values of gravity and type of fuel, this becomes hard, to impractical, to impossible.
You don't need much ISP to launch from the bottom of a deep gravity well and thick atmosphere. What you need more of is thrust. Ion engines have orders of magnitude more ISP than chemical rockets, but you can't launch off of many things larger than an asteroid with one.
A maglev gun sounds equally problematic.
The inherent upside to onboard propulsion is you can apply power for the entire duration of escape, reducing both maximum speed and delta-speed.
Launch-loops may also compose well with chemical rockets. That'll take much more adnvanced tech than simply using rockets, but the laws of physics permit them. (A smaller, electric, rocket throwing gun...)
Those civs won't be able to construct a space elevator. It's boderline impossible on Earth already, on any bigger planet it'll be completely impossible.
Nobody knows. Consider:
1. We don't know everything about physics. 2. We don't even know how much we don't know about physics.
I'd be surprised if alien civs didn't do at least a few things that are hard to imagine on 21st century Earth.
Some would be more or less mainstream, like balloon staging:
http://www.gizmag.com/zero2infinity-balloon-rocket-launch/34...
Others could be much weirder - possibly incomprehensible without a few years of science exchange.
I realise this is idle speculation, but it's impossible not to wonder if aliens would be alien, technologically and in other possible ways.
Do you have a source for that assertion?
Most discovered planets to date are larger than Earth and closer to the star, but that's probably because it's easier to discover those planets given our current technology...
Interesting to think that the size of planets would limit exploration though (from the article):
If our planet was 50% larger in diameter, we would not be able to venture into space, at least using rockets for transport.
It's possible to do better than lump all of the discovered planets together and complain that the set is biased. For example, Kepler can detect a planet iff there is a chance alignment of its orbit with our line of sight, so for each discovered planet, it's possible to compute the probability that its orbit was correctly aligned, and divide by it to compensate. That way it's possible to make unbiased statements about the distribution of planet sizes and orbits, the fraction of stars with planets, etc.
https://news.ycombinator.com/item?id=5668324
In that submission, astronomers including Mike Brown of Caltech, Steve Vogt of UCSC, and Sara Seager of MIT all make assertions about typical exoplanet composition. A HN reader asked about the biased sampling issue. You can bet they are not just ignoring the possibility of biased sampling.
Maybe Earth is indeed at a comparatively bad place in the gravity spectrum of habitable planets. Getting things up there is difficult enough that we can't have big payloads, but it's still easy enough to justify not building a self-sufficient infrastructure out there.
Without knowing the processes/materials necessary to ignite the self replicating processes required for life we don't possess the information necessary to know whether life is probable or improbable. Even in a universe with plentiful water and plentiful habitable planets, without context on what started it all we can't make any meaningful prediction. Is life like the boeing 747 or is it not?
I always find it ludicrous when someone says the universe is just so vast that life has to exist somewhere else. We just don't have enough understanding/context to know.
I'd still bet against that museum though.
I think life is created right now on Earth from scratch (chemical elements), but we need to find proof.
I think the key is understanding the process itself. What does it take to create the minimal self replicating machines necessary to evolve into the complex forms we see today? Once we are aware of the processes involved in the formation of life then we have the context to hypothesize about the probability that these reactions will spontaneously occur.
Things like the Drake equation are meaningless and made up. You can easily make up an identical bullshit equation about the chances of a 747 spontaneously being thrown together on another planet. We can easily see that it's impossible because we know how the 747 is made, we have context. For life? We have no context, no knowledge of where it came from, and therefore the drake equation and any other statement about life on other planets is meaningless.
Early Earth was an unimaginably huge petri dish where every grain of sand on every beach was an organic experiment, with the sun, tides and seasons trying every combination of heat/cold/wet/dry/acid/base... in endless cycles. Those conditions are far from unique in the universe. You could argue its inevitable that life/chemistry will unfold in the same patterns on millions of worlds.
You can argue that the entire earth is a petri dish for a boeing 747. We have all the necessary materials, all we need is a hurricane to throw all the materials together in the right configuration and boom! 747. With billions of planets in the universe it's bound to happen on another one! It's inevitable.
Perhaps this would be more clear: We don't have Enough context to talk about the probability of life on other planets. Perhaps the chemical reaction needed to create life was mind boggling complex, billions of steps needed to happen in the exact order, under conditions that are equally exacting . Or maybe it's devastatingly simple. We just don't know...
The jet is self assembled by proxy of humans being self-assembled. A 747 is the result of a trillion step chemical reaction that stretches across the history of life on earth itself. The chances of this reaction self-assembling on another planet under the same conditions and in the same manner are impossibly low.
What we don't know is whether or not the chemical reactions forming the first life form on earth happened in the same improbable way. Did it happen over eons? did it require a billion steps? I dunno. Nobody knows. It is not unrealistic to say that the chemical reactions necessary to form life are so rare that earth is the only planet in the universe with life.
At some point during my lifetime, exoplanets have been discovered and at some other point, the idea that planets, including earth-sized planets are almost as widespread (or rarefied) as stars themselves. At least 10 billion earth-sized planets in our galaxy alone.
So it seems like the Universe is full of Planets and a lot of those planets contain water.
The next logical step is that extra-terrestrial Life is just as common as water, planets and stars.
If that is the case, that means that life is a natural consequence of star formation/runtime, which is extremely interesting.
Which, if we now really think about it, is not entirely out of the question, in fact, it's quite probable.
If this is logic, it's purely inductive. We have no evidence for how likely it is that life form under water-like conditions.
The statistics for life on very earth-like planets are staggering.
1/1. Sample size seems pretty shitty. Maybe if we find any other form of life in the galaxy OFF this planet, we might be able to bound the probability of it forming at all.
The apparent size and age of the universe suggest that many technologically advanced extraterrestrial civilizations ought to exist. However, this hypothesis seems inconsistent with the lack of observational evidence to support it.
http://en.wikipedia.org/wiki/Fermi_paradox
Was this a big pop science mystery back in the day? The simplicity of the composition of water ("burned hydrogen gas") would lead me to think that we should expect to find it in some phase of matter fairly regularly. Caveat though: I'm not a chemist.
It may be detectably frosted since the solar wind would push it in that direction.