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Numerous other ideas exist for alien life, but most of them have their shortcomings. It all boils down to chemical reactions and physics. Imagine a universe o
by at_a_remove 6y ago
Numerous other ideas exist for alien life, but most of them have their shortcomings. It all boils down to chemical reactions and physics.
Imagine a universe of only helium. No valence electrons would be readily available, so chances are you are not going to see helium molecules. Lithium, sure, as a metal. Continue examining various smaller (and more plentiful elements). Fluorine? Well, only one slot available, so you can make molecules with two atoms, but no chains. If you have two slots open, you can make a chain, but little else. Although try making a chain of oxygen -- even the three-link ozone is not particularly stable. Carbon can have four different bonds going at once, which is pretty crazy, and so you want something with three or four slots available.
But then you say, well, silicon could have four. And it could ... but for the fact that it is so huge by comparison to carbon (that whole other "electron shell") that it rarely has analogues to organic (carbon-based) compounds. Also, it doesn't like to do much until you get it fairly hot. So you climb back up a row and it looks like carbon, nitrogen, boron ... those are going to do your heavy lifting when you need multiple bonds, with hydrogen, oxygen, and the halogens or alkali metals somewhere on the outside. Hence carbon chauvinism. Carbon is something like the fourth most common element in the universe after all.
Then you start talking about solvents -- all of this stuff has to slosh around in something after all, your chemistry experiments take place in liquids -- and the field is a bit wider but dang, water has some crazy properties that make it quite a catch when it comes to solvents.
You've got temperature ranges: down in the single digits of Kelvin you're not going to have much chemistry happening, and up in the thousands of Kelvins even iron boils and then again, no more structure.
Once you start looking for these various "sweet spots" it all comes down to finding a place where you can have liquids (your solvent), solids (for structure), and gases (even if they are dissolved in liquids). Combine that with the more common elements (especially those that are friendly to complex chemistry) and you have something not entirely un-Earthlike.
There's tons of Wikipedia articles on it, but ... the restrictions of chemistry are the bulk of the culprit, I'm afraid.
- throwaway2048 6y agoAnother problem with silicon is that its basic oxide (Silicon Dioxide) is a solid that is non-reactive with virtually everything. If you assume water based life, there is almost certainly going to be oxides involved, such as how CO2 is involved with earth life. And I think water based life chemistry is an extremely good bet, because alternative liquids based off of light, common elements are either only liquid at very low temps, (ammonia, methane) extremely reactive ( Hydrogen fluoride, hydrogen sulfide), or both. Another consideration with silicon is that the earth contains vastly more silicon than it does carbon (in many ways life on earth is fairly carbon starved), yet life based on carbon arose, not silicon.
- thaumasiotes 6y ago> Another problem with silicon is that its basic oxide (Silicon Dioxide) is a solid that is non-reactive with virtually everything. I was amused once by reading an MSDS for silicon dioxide. As I presume is required, they do list some hazards of exposure, but if you read the sheets for other substances the contrast is pretty striking. Look at the health effects listed on https://fscimage.fishersci.com/msds/09890.htm https://fscimage.fishersci.com/msds/09890.htm : > Eye: Dust may cause mechanical irritation. > Skin: Dust may cause mechanical irritation. > Ingestion: May cause irritation of the digestive tract. > Inhalation: Dust is irritating to the respiratory tract. > Chronic: May cause cancer in humans. Prolonged exposure to respirable crystalline quartz may cause delayed lung injury/fibrosis (silicosis). > NFPA Rating: (estimated) Health: 1; Flammability: 0; Instability: 0 So yeah, as long as you're not inhaling sand, you're fine.
- erik_seaberg 6y agoI'm reminded of > [Chlorine trifluoride is] also a stronger oxidizing agent than oxygen itself, which also puts it into rare territory. That means that it can potentially go on to “burn” things that you would normally consider already burnt to hell and gone, and a practical consequence of that is that it’ll start roaring reactions with things like bricks and asbestos tile. It’s been used in the semiconductor industry to clean oxides off of surfaces, at which activity it no doubt excels. —Derek Lowe, “Sand Won’t Save You This Time”
- thaumasiotes 6y agoAnd from an MSDS for that... > Hazardous combustion products: None that are more toxic than the product itself. ( https://www.boconline.ie/en/images/chlorine_trifluoride_tcm674-55789.pdf https://www.boconline.ie/en/images/chlorine_trifluoride_tcm6... ) It's a fun read.
- erik_seaberg 6y agoMaterial Safety: None. The End. > Contains no other components or impurities which will influence the classification of the product. In the unlikely event you survive adding something, you won’t make it any better. You certainly can’t make it worse. > Unsuitable extinguishing media: Water, Foam, Halons > Specific methods: Move away from the container and cool with water from a protected position. Um. > May react violently with combustible materials. Specifically, everything. > Seek medical advice before using product. “Don’t.” > Ensure vehicle driver is aware of the potential hazards of the load Driving is a strong indication that he is not aware. > and knows what to do in the event of an accident or an emergency. “Run.”
- IgorPartola 6y agoThank you for that write up. What about non-chemical life. What I mean by that is something like a giant CPU with traces literally the size of freight trains? I recently finished the first Dark Tower book and it’s got me thinking about scale.
- hoseja 6y agoThen you run into speed of light issues. In one nanosecond, that is one 1GHz cycle, light travels only ~30cm.
- IgorPartola 6y agoHah, good point. The authors of our simulation really put a damper on things, huh?
- henearkr 6y agoYou only considered chemistry-based life. Cannot hold it against you of course. But some hard SF writers like Baxter also imagined life based on electromagnetic interactions, nuclear reactions (life in the mantle of a neutron star), fluid vortices and turbulences (life in liquid or gaseous planets), etc. Basically he included a lot of substrates that could be used to implement complexity. Also, a big drawback of searching only chemistry-based life is that it limits a lot the range of viable temperatures. Would be too slow and simplistic at low temperatures, and a complete uncontrollable chaos at high temperatures. In particular, finding a brine on an ice dwarf like Ceres is not very exciting, as the temperature is too low, and no interesting chemistry can happen. Whereas other substrates could be totally fine at different temperature ranges.
- Balgair 6y agoThat neutron star story is wild. Hard recommendation to read. One point I have with Baxter is that his premises are just bananas, but the people acting in them are pretty recognizable. To be fair, if the characters were also nutter-butter, no one would read it, as it wouldn't be a story anymore, just a strangely formatted research paper. https://en.wikipedia.org/wiki/Flux_(novel) https://en.wikipedia.org/wiki/Flux_(novel)
- gizmo686 6y agoFor another life on neutron star: Dragons Egg, Robert L. Forward
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- henearkr 6y agoI don't know if you read the other books from the Xeelee series, but the neutron star is probably not even the strangest life form Baxter considered :) I don't want to spoil too much though.
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- philipswood 6y agoEssay by Isaac Asimov considering viable chemistries for life: "Not as we know it. The chemistry of life" http://www.bigear.org/CSMO/HTML/CS09/cs09p05.htm http://www.bigear.org/CSMO/HTML/CS09/cs09p05.htm I was surprised to realise (that besides being N author) that he was a professor of biochemistry.
- philipswood 6y agoHe ends up with a "list of life chemistries, spanning the temperature range from near red heat down to near absolute zero: 1. fluorosilicone in fluorosilicone 2. fluorocarbon in sulfur 3.*nucleic acid/protein (O) in water 4. nucleic acid/protein (N) in ammonia 5. lipid in methane 6. lipid in hydrogen Of this half dozen, the third only is life-as-we-know-it. Lest you miss it, I've marked it with an asterisk."
- jacobkania 6y agoThis was fascinating to read, thanks for sharing! I hadn’t thought about how much harder it would be to create life out of other elements due to chemistry. Had previously believed the chances were small that other life would be similar to us, given so many options. You’ve convinced me that it seems more likely that other life would be carbon/water based as well due to those limitations.
- Johnjonjoan 6y agoThis is so non esoteric. I can't remember who said it but I'm reminded of the old saying: "if you can't explain something to a high school student then you don't understand it". You certainly understand it and I certainly appreciate you sharing your understanding in such an accessible way, thanks.
- marcodiego 6y agoI think it was Feynman: https://kottke.org/17/06/if-you-cant-explain-something-in-simple-terms-you-dont-understand-it https://kottke.org/17/06/if-you-cant-explain-something-in-si...
- RandyRanderson 6y agoAlso water has one of the highest heat capacities [0] of elements that are common so this makes a great solvent that is more resistant to freezing and boiling. For this fact and the ones above, I see it as very unlikely that complex life exists outside any region that doesn't have liquid h20 almost all the time. [0] https://en.wikipedia.org/wiki/Heat_capacity https://en.wikipedia.org/wiki/Heat_capacity
- qppo 6y agoAre there conditions in the universe where the chemistry required for life can occur with other compounds, that don't exist on earth? For example, extreme temperature, pressure, gravity, electro-magnetic field intensity, etc.
- frogperson 6y agoThis is an outstanding comment. You have made my day.
- Dragonai 6y agoTerrific comment. Thank you so much for the excellent explanation!