Matter is mostly made up of the first generation of quarks and leptons: the up and down quark and the electron and electron neutrino.

There are two other generations that are heavier versions and are unstable.

How does string theory account for this?

Does it for example see the other two generations as 'resonances',

Does it predict an infinite tower of such resonances and thus higher generations?

  • $\begingroup$ Not really sure why this question has garnered a couple of down votes so quickly. Surely its important for string theory to explain the particles of the standard model? $\endgroup$ – Mozibur Ullah Jan 25 '18 at 15:48
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    $\begingroup$ Related: physics.stackexchange.com/q/22559/2451 and links therein. $\endgroup$ – Qmechanic Jan 25 '18 at 15:56
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    $\begingroup$ I didn't place the downvotes but I would imagine it could relate to the fact there is a very similar question already here. Or perhaps that the question is about string theory, a lot of people ask about it without really knowing what they're asking for (no offense). The summary of any answer will probably be "That depends who you're asking." $\endgroup$ – Lio Elbammalf Jan 25 '18 at 15:56
  • $\begingroup$ It's been a long time since I took that string theory class in grad school, but from what I recall one can draw a neat connection between the topology of the compactified dimensions and the number of generations in the low-energy theory. I wrote a review paper on the subject which my professor never bothered to take down, which might be useful and provide you with pointers to further reading. (Or it might be completely wrong; like I said, it's been a long time since I thought about this stuff.) $\endgroup$ – Michael Seifert Jan 25 '18 at 15:56
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    $\begingroup$ When a definite string theory model is decided upon, it will have to embed the standard model in its possible groupings. Thats the idea, that string theories with their vibrational levels have the group structure for the standard model groups. $\endgroup$ – anna v Jan 25 '18 at 16:39

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