I thought dark and anti matter were kinda the same, but after saw a video, they mention that dark matter is not antimatter but their explanation is a little fast so I got doubts.

What are the differences between matter, dark matter and antimatter? Are they related? How they interact each other? Where can I see an example of this interaction? and also, in terms of percentage, how much of matter, dark matter and antimatter exist in the universe?


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    $\begingroup$ For most of us, itdoesntmatter. (Sorry, couldn't resist; good question) $\endgroup$ Aug 9 '15 at 12:38

Matter is the stuff you are made of.

Antimatter is the same as matter in every way, looks the same, behaves the same, except its particles have electrical charges opposite to matter. E.g., our electrons are negatively charged, whereas a positron (an antimatter "electron") is positively charged. The positron is the "anti-particle" of the electron.

When a particle meets its anti-particle, they "annihilate": the two particles disappear, and gamma photons are released carrying off their energy. For this reason, should a lump of matter touch a lump of antimatter, they would annihilate, and a giant explosion would result because of the huge energy released (E=mc^2).

Matter and antimatter are definitely related: same thing, but with opposite signs. Twins, but opposites.

It is not clear why, but it seems like there isn't that much antimatter out there, more like trace amounts. Definitely not as much as regular matter as far as we can tell. This is puzzling to physicists and cosmologists, because you'd expect the Big Bang to make roughly equal amounts of matter and antimatter. Scientists agree that the paradox of "excess matter" will advance physics even further once it's solved.

Dark matter - we don't really know what it is. It's not even sure it's "matter" in a conventional sense, or related to it in any way. We just know that galaxies are rotating in such a way that indicates there's a lot more mass out there, but it is mass that we cannot see and cannot be accounted for in the usual ways. Hence the name "dark" (as in invisible) matter.

Dark matter doesn't seem to interact much with regular matter, except gravitationally. Right now dark matter could be passing through you and you wouldn't notice. Dark matter also does not interact with light, so you can't see it. It doesn't seem to interact much with itself either, so for this reason dark matter cannot form "clumps" such as planets or stars. Instead, it probably exists in a diffuse form. Bottom line, dark matter interacts pretty much only via gravity.

The shape of galaxies is a proof of the existence of dark matter, and is a result of the interaction between matter and dark matter. Without dark matter, galaxies would be much less massive, and the outer parts would rotate much more slowly compared to the center. Due to dark matter, galaxies are quite massive, and they rotate almost as solid objects - the outer parts rotate approximately as fast as the central parts.

Estimates vary, but it seems like there's something like 5x to 6x more dark matter out there compared to regular matter.

  • $\begingroup$ do dark matter occupy space? sounds more like a force, is like "ghost matter" could be a less misleading name ¿? $\endgroup$ Aug 9 '15 at 3:01
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    $\begingroup$ It's not a force, it's a particle of some kind. The reason it behaves like a force is because when there's enough of it, it's gravitational effect is observed. It bends space just like regular matter. $\endgroup$
    – userLTK
    Aug 9 '15 at 3:16
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    $\begingroup$ Note that leading theoretical dark matter candidates are assumed to interact via the weak force as well as gravity. This isn't so much because we have a good reason to assume that, but because if they do we'll be able to detect them soon---looking for our keys under the lampposts. There are other candidates as well, but we've little idea how to proceed with checking on those ideas. Well, except for axions, which we understand but don't have the technology to hunt for in earnest. $\endgroup$ Aug 9 '15 at 3:32
  • $\begingroup$ So, if dark matter doesn't interact with itself or so doesn't clump, is the spread of dark matter uniform throughout the universe? Is there a contradiction here? I'm just thinking that if it "only interacts through gravity" with regular matter, than regular matter clumps would cause dark matter clumps. $\endgroup$
    – Dave G
    Dec 31 '15 at 0:19
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    $\begingroup$ @DaveG It still interacts gravitationally, so there's some amount of aggregation due to that. But it's nowhere near to the same extent as regular matter, which makes densely packed clumps. Basically, clumps of regular matter tend to be surrounded by diffuse "clouds" of dark matter, more or less. $\endgroup$ Jan 1 '16 at 2:36

A pretty good site for quick explanations is the Particle Adventure

Anti Matter

Dark Matter

Anti Matter is really quite simple and very similar to regular matter. It just happens to explode violently when it touches regular matter - like a positron (Positive Electron) and an electron (negative) will touch and evaporate into a pair of gamma rays. The Proton/anti Proton or Neutron/anti Neutron or Proton/antineutron or Neutron/antiProton (they interact because they have some quarks/anti-quarks in common). Those reactions are more complicated, but the gist is the same. They explode violently when they touch. So, because matter and anti matter tend to evaporate each other, there's really no primordial anti-matter left in the universe, cause there was slightly more matter.

But, other than the explosive interaction, Antimatter is almost exactly the same as matter, You could, in theory build a star, a planet, trees and life out of anti-matter.

Dark Matter is a lot more different. We don't really know what it is, but it's a different kind of matter, it's transparent and it's non binding but it has mass. Regular matter can bind together gravitationally, that's why it forms into things like stars, planets, comets, asteroids, etc. Dark matter doesn't do that. It loosely collects around galaxies, or, perhaps more accurately, galaxies collect inside large pockets of dark matter.

  • $\begingroup$ You're right. That was a typo on my part. Fixed. $\endgroup$
    – userLTK
    Aug 9 '15 at 3:46
  • $\begingroup$ Interesting page! it make ease to understand, thanks! $\endgroup$ Aug 9 '15 at 18:43

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