4 ms·

If antimatter was created during the Big Bang (and it was, we actually just don't know why there is more matter than antimatter [1]) it could exist in issolated

by nuccy 5y ago

If antimatter was created during the Big Bang (and it was, we actually just don't know why there is more matter than antimatter [1]) it could exist in issolated-enough patches of the Universe. Photons, gravitational waves or neutrinos coming from those regions would not differ in any way, so we would not be able to identify those regions, up until they merge with normal-matter-filled ones (which is unlikely due to accelerated expansion of the Universe [2]). 1. https://home.cern/science/physics/matter-antimatter-asymmetry-problem https://home.cern/science/physics/matter-antimatter-asymmetr... 2. https://en.m.wikipedia.org/wiki/Accelerating_expansion_of_the_universe https://en.m.wikipedia.org/wiki/Accelerating_expansion_of_th... Edit: as a matter of fact experiments, like the one described in the posted paper, allows to shed some light on the properties of antimatter and why there is more matter in the Universe (matter-antimatter anisotropy).

jl6 5y ago
What a bummer - to send an intergalactic probe to a far-off supercluster only to find it’s made of antimatter and you cannot interact with it (if you survive the close encounter long enough to find this out).
- db48x 5y ago
  If you are paying attention, and on a trip of that magnitude I think you would be, you would notice the halo of gamma rays as the antimatter supercluster interacts with normal matter around it. That said, the Larry Niven short story “Flatlander” is pretty funny. You should read it.
breuleux 5y ago
> it could exist in issolated-enough patches of the Universe. Photons, gravitational waves or neutrinos coming from those regions would not differ in any way, so we would not be able to identify those regions, up until they merge with normal-matter-filled ones Interesting. So how do we know there actually is more matter than antimatter in the universe? Couldn't there be a roughly equal number of sufficiently isolated pockets of each?
- Sharlin 5y ago
  It is a well-known hypothesis, but space is not empty enough for it to be consistent with observations at least within our observable universe. If there really were antigalaxies or anticlusters out there, we would expect to observe characteristic gamma ray photons from the matter–antimatter boundaries where the extremely sparse but still existing intergalactic medium would interact and annihilate.
  - ncmncm 5y ago
    People have looked for evidence such annihilations, but the observations we have are not able to rule them out. Antimatter superclusters (of clusters of antimatter galaxies) remain very possible. Nobody wants to talk about them because they don't want to be ostracized for speculating on what cannot be settled by evidence. But people do check, now and then, when new information comes up.
    - ncmncm 5y ago
      ... It must be said, too, that nobody has identified any way for the antimatter to have become so far separated from the regular matter. All the processes we know of that make matter like to make both (exactly) equally.

by nuccy 5y ago

jl6 5y ago

What a bummer - to send an intergalactic probe to a far-off supercluster only to find it’s made of antimatter and you cannot interact with it (if you survive the close encounter long enough to find this out).

db48x 5y ago
If you are paying attention, and on a trip of that magnitude I think you would be, you would notice the halo of gamma rays as the antimatter supercluster interacts with normal matter around it. That said, the Larry Niven short story “Flatlander” is pretty funny. You should read it.

breuleux 5y ago

> it could exist in issolated-enough patches of the Universe. Photons, gravitational waves or neutrinos coming from those regions would not differ in any way, so we would not be able to identify those regions, up until they merge with normal-matter-filled ones Interesting. So how do we know there actually is more matter than antimatter in the universe? Couldn't there be a roughly equal number of sufficiently isolated pockets of each?

Sharlin 5y ago
It is a well-known hypothesis, but space is not empty enough for it to be consistent with observations at least within our observable universe. If there really were antigalaxies or anticlusters out there, we would expect to observe characteristic gamma ray photons from the matter–antimatter boundaries where the extremely sparse but still existing intergalactic medium would interact and annihilate.
- ncmncm 5y ago
  People have looked for evidence such annihilations, but the observations we have are not able to rule them out. Antimatter superclusters (of clusters of antimatter galaxies) remain very possible. Nobody wants to talk about them because they don't want to be ostracized for speculating on what cannot be settled by evidence. But people do check, now and then, when new information comes up.
  - ncmncm 5y ago
    ... It must be said, too, that nobody has identified any way for the antimatter to have become so far separated from the regular matter. All the processes we know of that make matter like to make both (exactly) equally.