World, Writing, Wealth discussion
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Where the aliens or how do you solve Fermi paradox?
I'm sure most of the earth's population is from a different planet or at least acting that way. We only have one - let's try not to break it instead of current human trends
Wait a minute? Is this thread I was hoping for? Indeed! Okay, one sec while I park the car... ;)
Just to be an arse, I should point out that the Fermi Paradox states that given the assumed likelihood of there being advanced civilizations out there in the universe, that surely we should have heard from some of them by now. It's actually the Drake Equation that claims that life should be plentiful. One clever answer is the possibility that advanced civilizations will eventually hit a point of singularity where they will no longer need their physical bodies. If they can just upload their minds into massive swarms of tiny machines that simulate reality and draw energy from their sun - aka. a Dyson Swarm - why bother going out in spaceships into the cold depths of space?
I am out on a limb on this one, but for me there is no real paradox. One of the interesting things about planets is that the standard theory has no idea whatsoever how they got started. They assume there was an even distribution of planetesimals (large asteroids), and these collided (without breaking them selves up, which happens in the asteroid belt when two collide) and stuck together to make planets. There is a great industry of people with computer programs and good grants churning out various scientific papers.My theory is they start due to chemistry (or physical chemistry) which means they start in different temperature zones and have different compositions. What this means is to have a planet like Earth, you need a G-type star, or heavy K type, AND you need the star to shed its accretion disk within about 1 My (it can last up to 30 My for some stars) If the disk lasts too long, you get planetary giants because they just keep accreting. If you believe that, earth-type planets are rare because G type stars are only about 1% of the stars.
Of course there are plenty of G type stars, but you may well have to delete double stars, like Alpha Centauri because the disk may not be friendly during accretion - we just don't know. Alpha Centauri b has a planet very close to the star, but we don't know about a.
So, earth-like planets are very well separated. You need such a planet because you need oceans and plate tectonics, which in turn means you need granitic/feldsic cratons. Earth is the lonely planet in this solar system with oceans, and with the possible exception of Ishtar and Aphrodite Terra on Venus, the only place where there is well-separated large amounts of granite. That, in my model, is a consequence of how the planet accreted.
If they are well separated, it is a huge distance between them. I did a count of possible suitable stars within 15 light years, and the answer is maybe Alpha Centauri, Epsilon Eridani and Tau Ceti. The first may not have planets, the second is too young to have multicellular life, or life based on oxygen, and the latter one is unclear whether there is a suitable Earth. In my second trilogy, I had four planets beside Earth with life, BUT they were at least 300 light years apart, and that may be optimistic. Now, fancy yourself on a delightful planet, and you have the opportunity to know about a planet 600 light years away (because not all will have technology for interstellar travel - like we haven't) will you go? You have to travel very close to light speed, or you need several generations to get there. Do you set off on a flight when you know you will die on the ship? If you resort to near light speed, how do you pay for the huge engines needed to get the necessary power? What do you do when you get there and find all the food is poison?
My guess is, you don't travel to anywhere but the very closest stars for a very long time in your civilisation. Do civilisations last that long?? I don't think it is a paradox. It may not be impossible to travel through interstellar space, but it is very difficult. We may one day see such travellers, but we should never expect them.
Ian wrote: "I am out on a limb on this one, but for me there is no real paradox. One of the interesting things about planets is that the standard theory has no idea whatsoever how they got started. They assume..."The standard theory is that planets formed from asteroids? Not from what I've learned. The standard theory is that planets and stars formed from the same clouds of dust, gravitational collapse in the center trigger nuclear fusion, and then a circumsolar dust disk creates the planets through clumping. They come together because the material is still hot and molten.
They become spaced based on the TItus-Bode law, and their composition differs based on where they are in relation to the star. This is the standard theory (in other words) the current one, is it not?
And recent exoplanet surveys show that Earth-like planets are actually quite common around M-class stars. So up to 70% of stars in this galaxy alone might have terrestrial planets. No guarantee they are habitable, of course, but the numbers could be very high still :)
I said they formed from planetesimals, which are asteroid-sized bodies. A lot of people think the asteroids are relics of that period. Yes, the planetesimals had to form from the accretion disk, which is basically hydrogen/helium that is slightly contaminated dust which ranges from micron to millimetre sized. We have observed that size distribution. The dust did NOT come together because the material is molten until you get within 1 AU around a star as big as sol. But the standard theory still says all you get from this are bodies up to large rocks. A recent paper shows that from the dust/rock size, nothing can melt until the body gets up to 20 km radius, and it does that partly through gravitational collapse energy and partly due to decomposition of short-lived radioactive isotopes such as 26 Al, which are used to date what happened. As far as I am aware, the standard theory does not differentiate close planets composition. It does separate out the giants from the terrestrial planets, but that is obvious.The standard theory has the Titus Bode law as more or less accidental, because there could be up to three to five more rocky planets provided they are earth sized or smaller. Theories like the Grand Tack get the Titus Bode distribution, BUT only due to the assumed distribution of planetesimals. What goes into the computation determines what comes out!
Earth-like planets are not common - what are said to be common are
earth-sized planets, which is not quite the same thing. We have no idea whether many are rocky, although some seem to have a density that suggests they might be. But densities as high as earth are rare.
If you want to see the difficulties, I wrote an academic-style ebook called "Planetary Formation and Biogenesis". Besides detailing why I think my formation theory is right, I have over 600 papers referenced and analysed which encompass (as far as I could find) representatives of all the important papers up to 2011. I did not do multiple references of one idea, so you can see how many variations there are!
Ian wrote: "I said they formed from planetesimals, which are asteroid-sized bodies. A lot of people think the asteroids are relics of that period. Yes, the planetesimals had to form from the accretion disk, wh..."Yes, you said "planetesimals (large asteroids)", except that planets didn't form from asteroids coming together, but dust and gas that becomes molten due to the ever increasing force of its own pressure. I mispoke when I said "still" molten. I should have said because it becomes that way. Bottom line, comparison to today's asteroid collisions doesn't fly. Those remnants from the early Solar System came together in the same way that the planets did, they just didn't get enough material to achieve hydrostatic equilibrium.
And Earth-sized and rocky was precisely what I meant. Whether or not they are rocky is construed from their size and mass. Sure, we don't know for certain, but the indications are there and the numbers of candidates is growing exponentially. Around Trappist-1, seven were announced earlier today - all of which were similar in size and mass to Earth. And that's in one star system!
And no, I really don't want to hear more about your theory, no offense. We've talked about that at length and I am neither qualified to evaluate it, but am quite confident that the current crop of scientific findings is showing otherwise.
The classic paper is: Safranov, V. S.,1969. Evolution of the protoplanetary cloud and formation of the Earth and planets, Nauka, Moscow. (English translation, 1972. NASA TTF-677.)More details: Pollack, J. and 5 others. 1996. Formation of giant planets by concurrent accretion of solids and gas. Icarus 124: 62-85.
Why your concept of dust accumulation has problems: Weidenschilling, S. 1984. Evolution of grains in a turbulent solar nebula. Icarus 60: 553-567. (Basically, once they get to about 10 mm, unless there is a reason for physical strength, they start to get eroded apart.
For the temperatures in the disk (necessary for you to melt stuff) see Beckwith, S. U. V., Sarjent, A. I., Chini, R. S., Gusten, R., 1990. A survey for circumstellar disks around young stellar objects. Astron. J. 99: 924-945. See also Makalkin, A. B. and Dorofeeva, V. A. 2009. Temperature distribution in the solar nebula at successive stages of its evolution. Solar System Res. 43: 508-532.
That is only a tiny showing of the problems, and I guess there is no point in continuing.
This thread makes my brain hurt.
Ian wrote: "The classic paper is: Safranov, V. S.,1969. Evolution of the protoplanetary cloud and formation of the Earth and planets, Nauka, Moscow. (English translation, 1972. NASA TTF-677.)More details: Pol..."
This isn't MY concept, Ian. It's the current consensus among geophysicists and astrophysicists. And while there are unknowns and potential problems with it, it is the most widely-accepted explanation. What I was showing was that your understanding of it was based on a misunderstanding - comparing planetesimals forming planets to asteroids colliding.
You cited Safranov, and his work is the foundation of modern Nebular Theory, yes? How does this paper support your case? And to that, I would add Woolfson's theory of runaway accretion, which shows how accretion disks form planetesimal-sized objects, which in turn coalesce with other smaller ones.
http://adsabs.harvard.edu/abs/1993QJR...
And I already corrected the issue of temperatures being high enough to melt stuff. The temperatures are accomplished by the accretion of matter creating conditions of extreme temperature. They are not solely the result of heat from the star itself.
Sure, there are many unknowns and imperfections in the theory, but that does not make your alternate theory more plausible.
Elizabeth♛ Everyone Else Has a Super Long Name With a Symbol So I Might as Well Do it Too♛ wrote: "This thread makes my brain hurt."Yeah, we need to get to the Paradox itself, not competing theories on Solar formation (or planetary formation).
First up, are you familiar with the the Fermi Paradox?
Matthew wrote: "Elizabeth♛ Everyone Else Has a Super Long Name With a Symbol So I Might as Well Do it Too♛ wrote: "This thread makes my brain hurt."Yeah, we need to get to the Paradox itself, not competing theor..."
No, no, I understand what you guys are all saying, but it still is draining to read through it all.
Matthew wrote: "Ian wrote: "The classic paper is: Safranov, V. S.,1969. Evolution of the protoplanetary cloud and formation of the Earth and planets, Nauka, Moscow. (English translation, 1972. NASA TTF-677.)More ..."
The planetesimal is a body that gets to the size of an asteroid. What happens when rocky bodies collide is actually quite difficult to predict, BUT we know of a large number of asteroid families. To get different results back then, you have to have a reason why the conditions are different. The temperatures of disks are well understood, because astronomers have measured many such accretion disks. You also have to realize that "runaway accretion" is a mathematical model to show the size distribution of such objects as they accrete from dust, BUT it assumes they do accrete. As the Weidenschilling reference I quoted shows, there is currently no simple physical mechanism that gives the bodies the necessary strength to avoid erosion. The temperatures arising from gravitational accretion and radioactivity cannot melt rock until the body has a radius of 20 km, at least according to one of the most recent studies, because the heat loss is too great. The rock most certainly does melt if the body is big enough. You also have to realize that for every gram of dust the body accretes, it passes through tens of tonnes of gas, and that is a cooling bath.
As an aside, all my theory does is provide a mechanism that gives strength to the accretion of dust to small bodies, but is also fixes compositional factors for the planets. Now, since you are essentially saying you believe the standard model, which is quite OK - you are perfectly entitled to do that - but you are not addressing the issue of the strength of small accretion, and also the rate of accretion (there is no mathematical explanation for the size of the planet LkCa 15b - in the standard model it should not even be there within the age of the star.) I think it is better if we simply part company and agree to go our different ways.
Ok, as I understand the bottom line regarding the opening thread is that Ian doesn't see a paradox and assumes another life might be pretty rare and so distant - hardly worth traveling, while Matt argues that habitable planets according to known equations might be abundant...The scientific debate about planet formation is no doubt important, yet we are interested in aliens! Are they crossing disguised the Mexican border? Is Tunguska event connected to their arrival?
If we use the analogy of indigenous people in Americas haven't seeing visitors from other continents for a rather long time and then they just came, maybe those very few millennia of recorded civilization is just such a short spell of time that aliens might've just left 'five' minutes ago and there are 'ten' more before they come again?
Okay. After browsing though all of this great scientific back and forth, I am wondering why no one mentioned the distances to be traveled. A trip to Mars using current technology would take about nine months - assuming earth and mars are optimally aligned. How long would it take to reach Alpha Centauri?The new planets are 40 light years away. How long would that trip take?
It is possible that we haven't met our neighbors because they are still on the road.
Joe, I thought my comment on the fact that potential planets would be well spaced meant they were distant and it would take a long time to get there, but the discussion must have got distracted.How long it takes depend on how fast you go, and there is a catch here. This new system, TRAPPIST-1 is just under 40 light years away. If you travelled at light speed, it would take, perforce, 40 years. If you travelled with our current rocket technology it would take 700,000 years.
The catch? Suppose you travelled at light speed, according to Einsteinian relativity, the time for the traveller dilates and the traveller would feel that the journey was instantaneous. (This leads to the twin paradox, which is also not a paradox.) Of course you cannot travel at light speed because it takes an infinite amount of energy to get there, but if you travelled close to it, the aging would be acceptable. Of course you also have to accelerate up to it. I used this time dilation effect in my Scaevola novels where humans embark on interstellar travel and are still young enough when they get there to do things. Fred Hoyle wrote an SF book where people travelled between galaxies and came back and found billions of years had passed locally!
Ian wrote: "Joe, I thought my comment on the fact that potential planets would be well spaced meant they were distant and it would take a long time to get there, but the discussion must have got distracted.H..."
Well, as I'm sure I've said already, this is not something I can debate on too much. If not, I'm saying it now. While I do think the current scientific consensus is correct, I am hardly qualified to debate you on every single point.
Getting back to the Fermi Paradox, Nik, you are correct in those summations. We don't know just how many worlds out there are habitable and we've been going by assumptions and mathematical models that have unknown for quite some time. The picture that is emerging, though, is one where rocky planets are actually very abundant, and orbit around stars that are the most abundant. Assuming that these stars are stable, there are literally dozens of worlds within spitting distance of Earth that could hold life.
Joe wrote: "Okay. After browsing though all of this great scientific back and forth, I am wondering why no one mentioned the distances to be traveled. A trip to Mars using current technology would take about n..."Our best option right now for reaching Alpha Centauri is in the use of nanocraft which would be accelerated using a laser sail. Like a solar sail, it intercepts a laser beam and uses that force to get up to high speeds. Starshot is the concept that Breakthrough Initiatives is working on, and it would (theoretically) take 20 years to get to Alpha Centauri.
Bridging the gap between stars is a major headache. The amount of energy it would take is beyond anything our species can build. But, and here's the beauty part, we wouldn't necessarily have to go to a nearby star system to notice signs of an advanced civilization. There would be signs detectable from light years away.
We have been broadcasting at light speed for well over 100 years even if the first signals would be very weak. So a civilisation 50 light years away could have broadcast back in that time frame - if they can be bothered, if they are listening and/or they exist. Life is probably abundant in the universe, infinite number of stars and infinite number of associated planets in the C or H zone. How many might of developed a civilisation is a whole other level of reduction. If it took Earth 7 billion years and it took 6.5 billion before earth like planets formed from big bang then the chance are an earth like and level civilisation is a hell of a long way way and getting further away as the universe is still expanding.
Of course the likelihood of life and intelligent life nearby would increase dramatically if life is discovered on Mars e.g 1/8 or 9 (Pluto in or out) to 2/8 or 9. Other systems may have more or less planets
Bottom line is we don't know but it would be nice to find out.
Just a word on faster than light - who knows if it is possible - elements of string and quantum state theory indicate very strange behaviour perhaps harnessed they can give a way of bypassing standard dimensional travel. Yes I used that in my own sci-fi (I'm not the first) - shameless plug over.
The mathematics and physics of this is well beyond my brainpower but so once was nuclear fission or humble electricity. There are streams of physics working on teleportation - 3D printers anyone. Add in bio-chemistry to capture brainwaves and perhaps that is the travel answer. If a civilisation was 100 years ahead of us what would they know that we don't. How about 500? What about 5,000 all blips in the billions of years in the Universe.
Hint: keep away from Matthew - his spitting ability is unbelievable :-) The nearest possible planet is 4 light years away.My guess is the laser light sail is great in theory but maybe difficult to make it work because you have to hit the laser beam dead over the centre of mass, otherwise the sail will impart torque and the vessel will start turning. Once the sail gets at any angle other than normal to the beam, you import sideways momentum. Aiming the laser and then the vessel may be beyond us. However, the ion beam type motor that NASA is working on gives a good chance of sending very small craft to other stars within a reasonable time.
Philip, the possibility of life is very much higher than intelligent life. As I said before, there may be quite a number of water worlds around red dwarfs, and if I am right, the second known planet around Kapteyn's star should be plausible (except it is over 11 billion years old, and we don't know what happens over that sort of time.) As an aside, Earth is only 4.5 billion years old.
If faster than light travel is possible, then Einstein's relativity is wrong somewhere, because his theory puts an impossible to overcome barrier between here and there. Could be, but it is a big call :-)
Ian wrote: "Hint: keep away from Matthew - his spitting ability is unbelievable :-) The nearest possible planet is 4 light years away.My guess is the laser light sail is great in theory but maybe difficult t..."
That's what make it all interesting. The string theory and quantum particle stuff may bypass the whole accelerate requiring energy thus impossible relativity work. There is so little we know about magnetism, gravity, fusion, quantum states, dark matter, boson-higgs, etc. that we could all be in for a shock just like the Native American who got shot at. Sometimes scientific advances happen in a huge leap not a slow progression then it becomes normal. When I was a child mobile phones were sci-fi and Apollo had not reached the moon - showing my age. Now Space X does a vertical booster landing and it barely gets a mention. Satellite launches are two a penny, even if the theory has been known for centuries. Human beings have come a long way in 10,000 years what will happen in the next 10,000. How far would a society be that was 10,000 years ahead of us.
Ian wrote: "Hint: keep away from Matthew - his spitting ability is unbelievable :-) The nearest possible planet is 4 light years away.My guess is the laser light sail is great in theory but maybe difficult t..."
Cute, Ian! When I say "spitting distance", you know I mean systems that are conceivably possible to reach. Cheeky bastard! ;)
Of course, he has a point. Proxima b is the nearest exoplanet and the best proposal for reaching it is unmanned and would still take a few decades at the least. While it is exciting to think of exoplanets being in our cosmic neighborhood, its still a freakishly big place and even the closest planets would be very hard to reach within anyone's lifetime.
As for the technical challenges, yes they are many. However, Starshot has Philip Lubin from UC Santa Barbara working on that, the man who's dossier includes NASA's DEEP-IN concept, and a proposal for using lasers to take out asteroids (DE-STAR). He's handling the lasers while Prof Avi Loeb of the Havard-Smithsonian Center for Astrophysics is handling the physics end of things. They regularly put out papers and address studies by other groups about the technical challenges. Check em out if you like:
https://breakthroughinitiatives.org/News
Philip wrote: "We have been broadcasting at light speed for well over 100 years even if the first signals would be very weak. So a civilisation 50 light years away could have broadcast back in that time frame - i..."I keep getting hung up on the practicalities. Supposing the geniuses on Trappist-1 E started transmitting radio signals across one of their oceans one hundred years ago. Some energy from those transmissions would have reached earth 60 years ago assuming the signals were not blocked. But the already weak signals would be losing strength as it traveled and spread. The signal would weaken by a factor equal to the square of the distance between the two planets. In other words, detecting the signal would be about as easy as detecting a sub-atomic particle.
It is likely that both the strength of the signals and the sensitivity of our receivers would have increased as time went on. Is it possible that a random message sent between two points in the Trappist-1 system would ever have enough energy to be detectable by a random receiver on earth?
Would the received signal have sufficient SNR to be recognizable as intelligent commincations?
Would we be smart enough to make any sense of such a message?
The other issue that is bothering me is the return on investment. Assuming the other intelligent occupants of our universe - which may not be the only universe - think like we do, they must see the same difficulties that intelligent humans do. We barely have the technical and economic resources for a mission to mars. We have no real incentive for going there. The ROI for such an undertaking would be trivial. Even if we could find a vast deposit of some critical resource - e.g., lithium which is required for batteries for our phones, tablets and cars - we couldn't use it. The cost of transporting a ton of lithium from Mars to Earth is prohibitive. Only a billionaire could afford a battery made from martian lithium.
It's a good thing that this kind of analysis was carried out before Columbus' venture was authorized. Unless you are a Native American who would have been just as happy if Columbus had never sailed to America.
Wot? Me a cheeky bastard? Sorry Matthew, i couldn't resist it :-)And yes, the costs are prohibitive to us now. But maybe not forever. In my opinion, the key here is can we build appropriate motors? I mentioned previously that the energy required to get up to relativistic velocities gets to approach infinite, and of course to get acceleration, by the law of conservation of momentum, you need to throw an equivalent momentum out the back. However, if you have the energy source, by using magnetic effects you can in principle accelerate what you are throwing out up to near light speed, which means you don't need anywhere near as much mass. If such ships were reusable, while the initial cost would be huge, operating costs may be OK.
There is one other possible weird trick - FTL is possible within General Relativity according to Miguel Alcubierre. (https://en.wikipedia.org/wiki/Alcubie...)
The idea is to warp spacetime. This requires spacetime to be "something" capable of being warped.
Given the discussion above on mechanisms, I thought I should summarise some key points. The standard theory and mine agree that planets should be very common. Despite what Matthew says, the standard theory does not explain explicitly how dust aggregates. A key point here is that most of the dust DOES NOT AGGREGATE. We see the dusty disks, and of course most dust ends in the star. The major differences between the two concepts that is relevant to here is that my version suggests earth-like planets, so defined that they are rocky, have lots of water, have feldsic cratons and have plate tectonics will be much rarer. As an aside, it has recently been shown that water on Earth could not have come from comets or from the asteroid belt. So where did it come from. That observation encourages me because in my view, water in large amounts is associated with feldsic cratons. One other point about red dwarfs. Observationally, the planets are much closer to the star. If a planet is too close to a star there is a very good chance any water will be stripped away. As an example, Jupiter's moons are all icy, with lots of water, except Io, which has a much higher density. The reason is, Io is deeply embedded in Jupiter's magnetosphere, which means it lives in what is almost a perpetual electrical storm. Not a place to find life. Planets very close to red dwarfs will probably have an even worse time. Also, if they collected a lot of water, they could be water worlds, which could permit life, but not life that sends off electromagnetic messages.
Obviously, we don't know who is right. My view is that in the not too distant future we shall start to find out.
The above made for some interesting reading. But the truth is usually quite simple. Aliens don't come here because they abhor the hassle of having to fill out all the paperwork and interact with lawyers to obtain resident status. That's why they stick to kidnapping farmers and livestock in the dead of night.
Ian wrote: "Wot? Me a cheeky bastard? Sorry Matthew, i couldn't resist it :-)And yes, the costs are prohibitive to us now. But maybe not forever. In my opinion, the key here is can we build appropriate motor..."
I knew someone would be mentioning the Alcubierre Drive! And yes, NASA is actually looking at this through their Eagleworks Laboratory. When I heard they were taking a serious look at this, and that they had gone over the equations and thought they could work (with modifications), I became rather excited.
It was like, "No freaking way!" Sure, it's not exactly worked out or even close to that, but knowing that it might be theoretically possible is more than most of us expect with technology like this.
https://ntrs.nasa.gov/search.jsp?R=20...
J.N. wrote: "That's why they stick to kidnapping farmers and livestock in the dead of night. ..."We should probably simplify paperwork or abolish nights, for we need the farmers and the livestock back to feed the growing number of earthlings -:)
Simplifying the paperwork should be the easiest option, but I am far from convinced it is.
Nik wrote: "Where the hell are the aliens?"Probably mainly on their own planet. We can't travel between stars so why do we assume they can? The other point is aliens with technology will be rare, which means there will be large distances between them. If you follow the literature analysis in my "Planetary Formation and Biogenesis" life is restricted (other than by colonization) to planets around G and heavy K type stars that ejected their accretion disk within about 1 My of stellar formation, and these stellar disks can last 30 My. The reason for the first restriction is that only those will have planets that could supply reduced nitrogen and end up in the habitable zone, and the second is otherwise the planets get too big and you end up with Neptune-like planets.
So, if the likely planets are too far away, it isn't worth going the distance. It is all very well to propose (as I did in a few SF novels) going at extremely close to light speed, but the energy required is not promising.
What about wormholes? Aren't there any shortcuts as far as space travel is concerned? And why assume all life is carbon based?
I don't believe there are any wormholes - we haven't seen any sign of them, and even if there were some, the forces inside them, if you were not properly aligned with the centre, would probably tear you to bits.As for why carbon is necessary, in my opinion it has to do with reproduction. The chemistry is a bit tough, but if you remain interested I shall explain in more detail. The problem is you need a number of different sorts of bonds with around the same energy, and only carbon does that. For example, if you try for silicon, give it half a chance with oxygen and it turns into rocks.
I've probably watched too much Star Trek :-) Are there maybe unknown elements on which life could be based? Just a thought. I have no idea.
Scout wrote: "I've probably watched too much Star Trek :-) Are there maybe unknown elements on which life could be based? Just a thought. I have no idea."Good question, and one which we can't answer... yet. The reality is, all of our searches for life are based on the "low hanging fruit" approach. We look for the elements we know are associated with life based on the only life we know about - our own. To us, anything other than carbon based life (i.e. silicon or methanogenic) is strictly theoretical. But those are two other forms of life that have been speculated to exist.
Scout wrote: "What about wormholes? Aren't there any shortcuts as far as space travel is concerned? And why assume all life is carbon based?"Also, wormholes are indeed science fiction. It's an exciting concept, but they violate General Relativity and causality.
Scout, there are no unknown elements that are not highly radioactive.Matthew, methanogenic will be carbon based (methane is CH4). Silicon cannot produce life because with water, or anything containing oxygen, tends to turn it into rocks. Whatever you use, you have to have hydrogen bonding for reproduction, and that only works with oxygen and nitrogen (fluorine is bad because HF is just too hazardous).
Ian wrote: "Scout, there are no unknown elements that are not highly radioactive.Matthew, methanogenic will be carbon based (methane is CH4). Silicon cannot produce life because with water, or anything conta..."
Methanogenic (in this case) refers to life forms that would consume molecular hydrogen H2, metabolize it with acetylene instead of glucose, and exhale methane instead of carbon dioxide. So calling it carbon-based just because carbon is a component of methane kind of misses the point.
As for silicon, that has been theorized as a basis for life because it has chemical properties similar to carbon (as you are no doubt aware) and can create molecules large enough to carry biological information. However, I merely refer to what has been hypothesized, I have no opinions about the likelihood thereof.
Methanogenisis (see Wikipedia on it for more info) hydrogenates CO2 or decomposes acetic acid, and it goes through a rather complicated pathway in which the organism uses some quite complicated enzyme cofactors, etc. The basis of my statement was not because carbon was in methane, but because the necessary other factors require a carbon based organism, at least to evolve naturally.Silicon is nothing like carbon in its chemistry. Carbon makes strong bonds to carbon, hydrogen, oxygen and nitrogen, and all of them are of more or less the same strength, and this permits carbon to form an extremely wide range of compounds, all of which are stable, and there is no driving force sending everything in one direction. Silicon forms Si - Si bonds approaching half the strength of a C - C bond, but forms Si - O bonds approaching twice the strength of most carbon bonds. Silicon does not bind readily with nitrogen, and stay that way, and it is inconceivable that silicon - only structures could evolve to look anything like a nucleic acid and permit reproduction.
As an example, consider magnesium carbonate. It is rather unstable towards heat, and acetic acid will quickly convert it to magnesium acetate and dissolve it. Then there is the magnesium salt of silicic acid. It is called forsterite, and try doing something with it with either heat (melts at about 1750 from memory) or acetic acid. The average basalt is more reactive, and you can try leaving a piece in acetic acid for however long you like. The relevance is, as I pointed out above, with silicon, give it half a chance and it turns into totally inert rocks.
We can best infer from something known to us. I believe the universe contains a lot of surprises for us. Maybe a universe itself is alive and stellar systems are parts of an organism? -:)
Nik, I am not convinced that when the advice given was to "think big" they quite meant in that way :-) Meanwhile, the good news for any worried by this suggestion, I am quite convinced we are not in the "effluent stream" about to be excreted.
Ian wrote: "Meanwhile, the good news for any worried by this suggestion, I am quite convinced we are not in the "effluent stream" about to be excreted."I'll bet you were convinced that you would not end up drowning in a flood when you lived back in the days of Noah.
Ian wrote: "Methanogenisis (see Wikipedia on it for more info) hydrogenates CO2 or decomposes acetic acid, and it goes through a rather complicated pathway in which the organism uses some quite complicated enz..."Is that not what I just said? That these methanogens would consume acetylene and produce methane? And you're statement that it would carbon based was followed by a chemical formula, so my presumption was quite understandable. Perhaps I was wrong to differentiate it from carbon-based life, but the term still applies.
As for whether or not carbon is similar in its chemistry is not the point. Its that they are considered large enough, by some theorists, to carry information in a similar fashion. We're talking about theoretical forms of life, so us assessing whether or not it is possible based on the chemistry we are familiar with misses the point. These are the limitations we are currently dealing with, and which we are trying to shed in order to theorize about what else is possible.
Matthew, give me a break. Acetylene is not the same as carbon dioxide or acetic acid. One of the things life must do is to reproduce, and it is not sufficient to carry information - it must be transferred to a new polymer, which is most easily done by building the new polymer adjacent to the old one. They must hold together while this is done, and the magnitude of ΔH increases with polymer length, while ΔS is largely proportional to the number of molecules, so ΔG for separation becomes increasingly unfavourable as the polymer length increases. This can only be overcome by joining the polymers with hydrogen bonds, and having either water or ammoniacal water as the solvent, because then the solvent overcomes the unfavourable ΔH. (Sorry everyone else about the thermodynamics. ΔG represents the work done managing a process, and unless it is negative, the process does not go. ΔH is negative if the step releases heat.) Now you have to have two bits that complement each other, and as far as we know, only purines and pyrimidines do this, through forming hydrogen bonds between each other. Silicon - oxygen systems do not form hydrogen bonds - instead they form rocks.
Matthew, if the chemistry we are familiar with rules it out, then what is unfamiliar is irrelevant, It is no good saying something might be possible - you have to give a clue as to what it could be.
Ian said, "Scout, there are no unknown elements that are not highly radioactive." That seems to me to be a bold statement. How can you know what is unknown?
The difference between elements is the number of protons in the nucleus. We have now found or made all the elements up to number 118. After bismuth, they are all radioactive, although uranium does hang around for quite some time. But the heavier they are after that, the shorter their half-lives, and number 118 only lasts microseconds, if that. The reason is the nuclear binding per hadron (proton or neutron) gets weaker as the elements get heavier after iron, presumably due to the electric field repulsions of all those protons. Anyway, we see they get progressively unstable, and we have got so far out that they are incredibly unstable, so it seems hardly likely any more will be stable. Also, such elements are made in supernovae, and we know that nothing additional comes out of them that we don't know about.
That's what I was looking for: "Also, such elements are made in supernovae, and we know that nothing additional comes out of them that we don't know about." That's a good explanation. But how can we be certain?
Scout, look at it this way. Every solid in every planet came out of a supernova, and they are call more or less the same - huge concentrations of unknowable energy. We know what came out of the supernovae that made our planet - the rest will be the same because they were made the same way.
What could be the reason for such a boycott from Universal community or at least from the homies of the Milky Way?
Is there maybe an embargo from UN of the Universe on Solar system? Are aliens afraid of V.Putin or D. Trump or T.May? Are we too primitive for their lofty civilizations, too militant, too alcohol-consuming, indelicate, don't play football/soccer well? Or maybe those aliens are too haughty or introvert?
Or could it be that half of the Goodreads members and politicians to boot are from extraterrestrial origin and fooling us around?
Any thoughts on this vital question shall be appreciated -:)