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I am working with some possible concepts for my world building project and had the idea for two alien civilizations. One made from regular matter and another made out of antimatter in their own solar systems made from their type of matter.

My question is, would it be possible for these two civilizations to communicate using radio or similar types of communication?

Venik Hue
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  • Since gravitational effects on EM radiation in physics is well known, I wonder what gravity would be like in an anti-matter galaxy, and what effect it would have on EM radiation? – Justin Thyme the Second Dec 05 '22 at 04:25
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    I wonder if the two civilizations would be able to tell. If not, they might decide to try to meet... – prl Dec 05 '22 at 04:59
  • YES but you will have to send all your messages in reverse -- the arrow of time experienced by antimatter runs in the opposite direction from the one experienced by ordinary matter. – A. I. Breveleri Dec 05 '22 at 09:49
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    @A.I.Breveleri That's not quite true. It's true that at the subatomic level, an antiparticle resembles a particle moving backwards in time. But at the macroscopic level, time-asymmetric effects like friction and heat transfer go the same way for antimatter as for regular matter. – Tanner Swett Dec 05 '22 at 11:07
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    @Tanner-reinstateLGBTpeople, Re, "...have to send all your messages in reverse." Even supposing there was some alien civilization whose future was our past and vice versa, the idea that we would have to send all of our messages in reverse in order for the aliens to understand them is silly. When the aliens receive our first transmission, they know nothing about us, or how we communicate. All they know is, we sent a pattern. It's up to them to find meaning in it if they can. Time-reversal of the pattern won't make their job any easier or any harder. – Solomon Slow Dec 05 '22 at 16:24
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    @SolomonSlow That's a funny thought! It reminds of one time when I played blind go with a group of people. Contrary to chess, go doesn't have a convention regarding coordinates on the board: we can use letters for columns and numbers for rows, or the other way around, and we can number from top to bottom or from bottom to top. When we were about to start the blind game, someone exclaimed: "Wait! We forgot to agree on which convention we were using for the coordinates!". Someone else laughed and explained there was no need to agree on a convention, since the game would exist only in our heads. – Stef Dec 05 '22 at 20:19
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    @Solomon Slow: When the aliens receive our first transmission, they know nothing about us - But we know a great deal about them, having been exchanging messages with them for decades. (Contrariwise, when we first hear from them, they already know all about us.) – A. I. Breveleri Dec 06 '22 at 03:37
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    Of course there is the much bigger problem of having matter and antimatter within reach of each other. What is the rest of the universe made of? Some kind of third state ? Because otherwise the anti-planet is going to be destroyed pretty quickly as everything ranging from particles to meteorites from the surrounding universe crash into it. – komodosp Dec 06 '22 at 08:49
  • @A.I.Breveleri, D'Oh! And to think, I've read Bearing an Hourglass, and I still didn't see it. – Solomon Slow Dec 06 '22 at 14:12
  • Radio or electromagnetic wave is the same regardless of the source. Be it matter or antimatter! So of course it would work. – stackoverblown Dec 06 '22 at 14:14
  • @komodosp, I think that's kind of the point of the original question. We could make radio contact with a distant civilization not knowing that we are opposite forms of matter, and then get a nasty surprise when we eventually try to meet up. – Solomon Slow Dec 06 '22 at 14:14
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    @SolomonSlow - My point was that the anti-planet would have been destroyed by the impacts from various objects throughout the ages long before radio was invented or life could even have begun... – komodosp Dec 06 '22 at 15:08
  • @komodosp, That might depend on how far away it is. In reality, if we were exchanging messages at the speed of light, they would have to be practically in our own back yard. But for thought-provoking-soft-sci-fi-entertainment purposes, we could say that they were in some far away (as in, "a galaxy far far away") "bubble" of anti-matter. – Solomon Slow Dec 06 '22 at 15:21
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    Indeed we could, but then we wouldn't worry too much about whether it's technically possible for an anti-matter radio to communicate with a matter one...

    I suppose there could be anti-matter and matter sections of the universe, and all the collisions that happened on the frontier between them wiped out all the matter (and anti-matter) in that area, leaving a vast emptiness between them, so big that it is extremely rare for an object (or anti-object) to go from one section to the other...

     – komodosp Dec 06 '22 at 16:11
  • I actually just heard a story about this, two galactic civilizations in distant galaxies learn to communicate over eons of time eventually they both launch ships to meet in the void between galaxies to make true first contact. When the two ships meet an astronaut from each floats out to meet. When the two touch they are instantly annihilated. Over all the time of communication the two civilizations never realized that one was from a galaxy of matter and the other of anti-matter. Because all the physics, chemistry and biology worked exactly the same in both galaxies they never even suspected. – Justin Ohms Dec 07 '22 at 05:56

5 Answers5

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Yes, for example, the electromagnetic radio wave produced by an antimatter dipole antenna would have an opposite polarity of the field since you could think of positive charge being moved instead of negative charges. But the receiving antenna would still sense the electromagnetic wave and the negative charge in the regular matter antenna would respond to that field. The fact that wave started out with a different polarity doesn't really matter since the relative phase also depends on the distance between the antennas and if you move the antenna a half wavelength distance away it would also change the phase 180 degrees.

UVphoton
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    Or, a photon is it’s own anti-particle, so photons are photons (no matter how small?). – Jon Custer Dec 04 '22 at 17:11
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    The polarization of a photon is not affected by the charge of the particle that produces it. https://en.wikipedia.org/wiki/Polarization_(waves) You are possibly referring to the phase, which is not ordinarily observable any way. – BillOnne Dec 04 '22 at 19:39
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    @BillOnne Phase of radio photons is easily observable, it just doesn't matter for radio transmission. This isn't wavefunction phase, this is just the phase of the electric field. It is true, however, that phase of high-frequency photons (roughly, infrared and higher frequency) is not possible to measure with current technology. – Hearth Dec 05 '22 at 05:30
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    @Hearth Relative phase is observable. Absolute phase is not. Ordinarily even relative phase is not observable for a radio reciever. – Boba Fit Dec 05 '22 at 13:58
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    Or, simply speaking, without a common reference system except their radio communication, they have no way to find out if both are of the same type of matter. – Karl Dec 05 '22 at 22:39
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The Photon is its own antiparticle

The radio works by shooting out and receiving streams of photons. The anti-radio works by shooting out and receiving streams of anti-photons. But anti-photons are the same as photons. So not only can the anti-radio communicate with the regular radio, it doesn't need to be modified to work.

Daron
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  • Surely you would need to either run the anti-radio backwards in time, or parity invert the radio... – Aron Dec 05 '22 at 04:11
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    @Aron Not really needed. Experiments with antiparticles (up to whole antiatoms) show pretty much consistent behavior of the antimatter in this regard. – fraxinus Dec 05 '22 at 08:19
  • @Aron Yeah the signal will be upside down. But the other radio doesn't care. – Daron Dec 05 '22 at 13:43
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    @Aron the idea that anti-matter is "runs backwards in time" is totally incorrect and a misconception. Tanner explains this in a comment under the question. – Fattie Dec 05 '22 at 15:05
  • @Fattie CPT symmetry. Reversal of C must (afaik) require an inversion of PT. EM is also reversible, meaning time reversal doesn't actually do anything. Seems you misunderstood my point.. – Aron Dec 06 '22 at 02:25
  • @Aron Matter that goes backwards in time is called "tachyonic matter" (because it consists of tachyons). It has nothing to do with antimatter. If tachyons do exist, then there could be matter-tachyons and antimatter-tachyons. – Philipp Dec 06 '22 at 09:37
  • @Philipp Again, no. I didn't say matter that goes backwards in time. Light is not matter. I noted that Daron was describing light as its own anti-particle. But more properly, P inversion would necessitate CT inversion. However, both C and T inversions for a photon/electron or photo/positron pair are the micro level are equilivent. Look at the Feymann diagrams. At a quantum level, the excitation of the photon on the anti-radio would actually be pi out of phase with a real radio... – Aron Dec 06 '22 at 11:09
  • @Aron I suspect the rest of us do not have advanced degrees in particle physics or know what CPT is. – Daron Dec 06 '22 at 11:50
  • @Daron you are one of the luck 10000 today then. CPT theory simply put, is that there are 3 discret symmetries in the universe, charge (anti-matter), parity (mirroring) and time. You may swap one of them in a system for it's opposite without swapping one of the other two... At least as a general rule, most systems are symmetric under C, P and T... – Aron Dec 06 '22 at 15:23
  • electricity/magnetism not beging a symmetry promised by CPT, I suppose it can't say much about a type of matter for which rotating the radio 90 degrees would "fix" the signal. – MatrixManAtYrService Dec 07 '22 at 17:13
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In general, it is very hard to tell the difference between matter and antimatter without actually annihilating it. Nearly every chemical could exist the same in both antimatter and matter. However, as previously posted the polarity of light would be reversed for antimatter. This couldn't be detected by a radio however.

Prime Price
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Before gamma ray astronomy, many physicists believed that the universe contained equal amounts of matter and antimatter. There is no way to tell from light or radio waves whether the radiation originates from matter or antimatter.

However, because even intergalactic space isn't a perfect vacuum, if there was much antimatter around we'd see 511 keV annihilation radiation all over the place. We don't.

John Doty
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In theory, yes. In practice, not that easy.

Sure you can receive the signal, IF you happen to be monitoring the specific frequency used to transmit it and are close enough that your receiver is powerful enough to pick it up.

But that's only the beginning of the problems. How are you going to interpret the signal you just received? And THAT problem is unrelated to whether your receiver and sender are made of matter, anti-matter, or unicorn dust. It's an eternal and universal problem communicating with disparate means. Heck, you probably don't even realise it's not a natural source when you first get the message, and after you do realise it's not a natural source you're going to have to do a lot of guess work, more or less at random, until you find out what encoding it's using, what modulation system is used (if any), what sidebands to consider, etc. etc.. And even after that, if you do happen to have a signal that's what was initially sent out, you're still having to decrypt (possibly) and interpret it. These anti-matter aliens won't speak your language, they won't use the same encoding of data that you use, the clear text message will be utter gibberish to you (and yours to them, they're going through the same problem at no doubt a different pace).

That's a big thing, a very big thing, that most first contact stories (as well as SETI) forget about.

jwenting
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    I disagree with the claim that fiction or reality near-universally disregards this. Starting with constants and building an alphabet from them is a solution that has been anticipated (and attempted, for our own transmissions). Similarly, keeping the encoding simple is something that has been deliberately considered. – Charles Duffy Dec 06 '22 at 15:25
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    Beyond that, detecting that there is something that carries information is something we have practically workable (entropy-measurement) theory and practice for. – Charles Duffy Dec 06 '22 at 15:26
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    Not an answer to the question. – toolforger Dec 07 '22 at 03:39