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It is not known whether antimatter is repulsed by or attracted to matter. For the purpose of this question, I assume that antimatter is repulsive to regular matter (otherwise this question makes no sense). This debate is not the point of the question.

If there was a massive (much larger than a galaxy) amount of antimatter at the center of the known universe, it would cause expansion of galaxies around it since it's repulsive force would be greater than galaxies attractive forces. This seems like a simpler explanation than positing the existence of dark energy. However, I am not knowledgeable enough to know if the kind of repulsion that would cause at all fits the repulsion that is actually observed.

Could a super massive amount of antimatter (assuming anti-gravity) cause the actual observed expansion of the universe?

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    $\begingroup$ According to Wikipedia, it is not confirmed, but it is not believed that anti-matter repels matter $\endgroup$
    – BioPhysicist
    Commented Mar 19, 2019 at 18:01
  • $\begingroup$ @AaronStevens I am aware that this is not the generally accepted position, I was just curious if it would fit the data, and wasn't sure how to verify this myself $\endgroup$
    – rtpax
    Commented Mar 19, 2019 at 18:06
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    $\begingroup$ there might soon be a measurement of how antimatter responds to gravity home.cern/news/news/experiments/… $\endgroup$
    – anna v
    Commented Mar 19, 2019 at 18:54
  • $\begingroup$ Related. $\endgroup$
    – rob ♦
    Commented Mar 19, 2019 at 20:35

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The annihilation radiation the would be generated where this enormous amount of antimatter comes in contact with normal matter should be all over the place. Besides antimatter should attract, not repel matter as both have positive energy.

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  • $\begingroup$ Why would we expect there to be any collision of antimatter when all antimatter would be inside the gravity well and all matter outside of it? With enough gravity to cause something as massive as the expansion of the universe, surely it would be penetrated very rarely if at all (I might be wrong, but please clarify why) $\endgroup$
    – rtpax
    Commented Mar 19, 2019 at 19:16

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