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I've been thinking of the idea of creating and adding an alien species that's antimatter-based (being from a universe where antimatter became the majority instead of "normal matter").

However, I'm not sure what abilities or what their biology would be like. Leading to the question of, what would antimatter life-forms be like? Such as how their metabolisms work, their chemical make-up, muscles, etc.

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    $\begingroup$ Just like normal life except evil, duh! ;-) $\endgroup$ – Michael Nov 3 at 19:27
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    $\begingroup$ This is an interesting question. As many have pointed out, it would probably be very similar, or even the same. However that brings one more question. If there are matter and anti-matter, there should be so-to-say Universe and Anti-Universe, and this what we call Physics would be Anti-Physics, which implies physics would work the absolute opposite way as they do here. So, could anti-physics exist in our universe, and what could that mean? $\endgroup$ – Snop Doog Nov 4 at 14:06
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    $\begingroup$ Maybe it's just a morose morning, but my inclination would be to say "Just like normal life except good" :D $\endgroup$ – arootbeer Nov 4 at 14:54
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    $\begingroup$ Well, since pasta and anti-pasta really aren't that different, and can even exist in the same restaurant together, surely anti-matter life forms wouldn't be that different... $\endgroup$ – ConcernedHobbit Nov 4 at 18:06
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    $\begingroup$ They wouldn't call the stuff that they were made of anti matter. They would just call it "matter." (Assuming, of course, that they spoke English, which practically all ETs do.) $\endgroup$ – Solomon Slow Nov 4 at 23:18
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Potentially, it would be very similar to life made out of matter.

Antimatter is expected to have the same chemistry as normal matter, so any lifeforms would work the same way with the exception that if they even touched our world they would instantly annihilate.

However! There is a lot about physics we don't know. Under the assumption that antimatter is an exact mirror to regular matter, one would expect the Universe to produce antimatter and matter in equal amounts. The fact that it doesn't is one of the great unsolved problems in physics.

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  • $\begingroup$ I think it would be helpful to mention antimatter is expected to have the same chemistry because of the symetry of behavior of positive and negative charges. $\endgroup$ – Vaelus Nov 3 at 15:18
  • $\begingroup$ I suspect that it's similar to the chirality problem in biology. If any imbalance exists between 'normal' and 'anti' matter in a region that imbalance may tend to grow. Areas that have exactly balanced regrowth will tend to lose energy while those where chance favors one side or other will tend to gather more of that type. $\endgroup$ – Corey Nov 4 at 5:14
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    $\begingroup$ Even in the Standard Model, antimatter is not an exact mirror of matter. The difference is just too small to give as much matter as we have around us en.wikipedia.org/wiki/… $\endgroup$ – JollyJoker Nov 4 at 8:45
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    $\begingroup$ @JollyJoker The effect on chemistry is still completely negligible, though, even with the highest estimates/expectations of the asymmetry. $\endgroup$ – Luaan Nov 4 at 14:30
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    $\begingroup$ @opa having many models that could produce the outcome doesn't make the problem solved. Every single one of them could be wrong; see the various formulations for uniting General Relativity with Quantum Mechanics - many models exist to unite them, but the problem is most definitely not "solved". $\endgroup$ – asgallant Nov 4 at 18:10
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Just like us

But don't touch them.

Lots of science fiction likes to attribute special or near magical properties to antimatter. This is rubbish. The only thing special about anti-hydrogen, is if you touch it with hydrogen, they annihilate in a tremendous release of energy. Two atoms of anti-hydrogen and one of anti-oxygen would still make one molecule of anti-water. Anti-copper wires would still carry anti-electrons to power anti-tungsten filament light bulbs.

Really, an antimatter universe would be roughly the same as ours. Until the two came together.

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    $\begingroup$ This was confirmed experimentally by Dr. Edward Anti-Teller. $\endgroup$ – Sneftel Nov 3 at 16:58
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    $\begingroup$ "don't touch them" is only scratching the surface, as you pointed out in your last line there, referencing a whole separate universe. They couldn't ever get close. They couldnt breathe the same air, or stand on the same planet. They probably couldn't even travel through space to anywhere close to you - as space still contains 1 atom per cubic centimeter or so. $\endgroup$ – Nacht - Reinstate Monica Nov 3 at 22:26
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    $\begingroup$ @DVNO I remember reading this in Martin Gardner's The Ambidextrous Universe, which is well worth a read if you like this sort of thing. This Reddit post is a briefer answer to your actual question. $\endgroup$ – bornfromanegg Nov 4 at 10:59
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    $\begingroup$ You don't have to touch anti-hydrogen with hydrogen. Any matter brought into contact with anti-hydrogen will have positron clouds exactly like matter's electron clouds. Those positrons will seek out their electron counterparts and wipe each other out. Then the anti-hydrogen (mostly anti-protons, but some nuclei also containing one or two anti-neutrons) will be attracted to the nuclei whose positrons were just stripped away, and the constituent antiquarks of the anti-hydrogen will find their quark counterparts for some more mutual annihilation. A lot of energy will be released. $\endgroup$ – Monty Harder Nov 4 at 21:37
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    $\begingroup$ Tiny amounts of antimatter are created on Earth and in the atmosphere by some types of normal radioactive decay. These antiparticles are almost instantly annihilated. It doesn't create "a tremendous release of energy". You need lots of matter and antimatter for that to happen. $\endgroup$ – CJ Dennis Nov 5 at 2:48
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Probably just like us.

We still don't know some other (normal-matter) biology except our own (we don't even know all the dark corners of our own biology). It may or may not be similar to our own. Keep in mind that A LOT of our own biology is randomness fixed and multiplied by the inheritance. There is such a thing like a convergent evolution - except that it kicks in whenever it feels like and is not really predictable and rather won't apply to the whole ecosystem.

Given the proper conditions, antimatter biology may develop just like our own. Or just like some other normal-matter biology we are still not aware of.

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  • $\begingroup$ If you want to keep things more general, "we should expect it to be as similar to us as any other matter-based life in our universe that lacks common ancestry". The stars would be the same, the planets would be the same, the water would be the same... $\endgroup$ – Luaan Nov 4 at 14:33
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I don't think it would make a difference, except positive would be negative and negative would be positive. From our perspective.

Antimatter is the opposite of matter, kind of like the equivalent negative number, but only if they violently exploded when combined instead of just being zero. (It does end up as zero, but after the violent explosion.) It makes up antiprotons, antielectrons, and antineutrons, which are like the ones we have, just with the charges flipped. (Except for neutrons, which don't have a charge.) Antimatter isn't very stable in our universe, because seeing as how it's made of matter, it gets annihilated very quickly. In a world of antimatter, it's stable, and more or less would just from the same elements and thus the same structure that our universe does. Except with the charges flipped from our perspective.

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  • $\begingroup$ Don't anti-neutrons have opposite spin with respect to neutrons? $\endgroup$ – James Grossmann Nov 8 at 2:57
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Though the other answers are all correct, I'd like to add the following: there is one thing we don't know for sure yet, whether antimatter is subject to gravity as normal matter ! See Gravitational interaction of antimatter on wikipedia.

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    $\begingroup$ It's true we haven't directly tested every particle to make sure it doesn't fall up, but nothing in physics would make any sense if any did. Photons are their own antiparticles, and we know (from bending of starlight) that they fall down. Gluons (taken collectively) are their own antiparticles and account for much of the mass of nucleons and we know that nucleons fall down. The SM fermions are made of chiral fields and their antifields via the Higgs coupling. Antiness isn't a property of particles (for the same reason that being a mirror image isn't a property of shapes). $\endgroup$ – benrg Nov 3 at 22:21
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    $\begingroup$ It will probably not make sense for an antimatter to fall up. But what if it did fall down slower? Well, this may break relativity. And what if anti-carbon was a bit heavier, because of some still unknown asymmetry? Anti-stars will make less of it, probably. SM is pretty good and it still can fail for the next discovery, just like any other theory. $\endgroup$ – fraxinus Nov 4 at 9:20
  • $\begingroup$ One of Gene Wolfe's novels had an air car that levitated because it had anti-iron inside of it, suspended in a vacuum space via magnets. (IIRC correctly, Wolfe is an engineer and therefore probably knew that this was wrong when he wrote it.) $\endgroup$ – EvilSnack Nov 4 at 12:18
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    $\begingroup$ It would be an interesting mechanism to produce a universe where on the large scale, matter is repulsed by anti-matter; on distances where gravity dominates, it might allow pockets of anti-matter alongside pockets of matter without being painfully obvious to observation. But as benrg noted, most of the mass around you already comes from almost equal contribution of matter and anti-matter (either gluons as neither matter or anti-matter, or considering the virtual quarks arising from the strong interaction in pairs of quarks and anti-quarks). Inertial mass wouldn't be gravitational mass. $\endgroup$ – Luaan Nov 4 at 14:43
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    $\begingroup$ @fraxinus I don't see how new physics of this kind could have hidden from existing experiments. E.g. it's been suggested that there could be scalar and vector forces that couple to baryon+lepton number, which would cancel in pro-pro or anti-anti interactions but not in pro-anti. That works approximately, but I don't see how they could cancel to 15 decimal places. And I don't see how a CPT violation large enough to make a difference could have been missed by colliders. I hope I'm wrong, because I'd love to see new physics. $\endgroup$ – benrg Nov 4 at 18:29

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