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is gravity actually 'known' ? i mean not like defined like time , but is it understood like do you know what causes it , where it originates from ?

The strength of the gravitational interaction is known. From that, we know that whatever is its exact form at the fundamental level, the effect is roughly 0. What do you mean by "originate from"?

well if electricity comes from electrons and light from fotons, so to speak, where does gravity come from ?

Electricity comes from the motion of electric charges. The corresponding fundamental interactions behind this phenomenon is electromagnetism that is modeled, at the most fundamental level, by photon exchanges between charges particles. We can correspondingly assume a graviton exchange for modeling gravity at the most fundamental level. However, the formalism does not work. Which is why the embedding of gravity in elementary physics consists in one of the present challenges.

allow me to be the layman for once and ever

do gravitons exist

i mean have they been confirmed, observed and detected ?

has anyone "seen" them ?

i know i have obnoxious questions but ... its a bit what i do , like me

is there any proof of a "graviton" as such ? or are they just part of the mathematical model ?

Gravitons have never been observed. They may or may not exist.

o dear ...

sayonara-zetsubou-sensei-nozomu-itoshiki-teacher-japanese-manga.jpg

the universe DOES really hang by a theoretical thread doesn't it :)

(sayonara zetsubou sensei picture one of my alltime favourite anime)

so if gravitons don't exist the whole model is ... is wrong again ? which makes me assume you're hunting gravitons too at lhc ?

i mean ... its basically "what makes the world turn"

Gravity is not included in the Standard Model, because we don't know how to do it. This consists in an entire field of research. There are several propositions, and those are currently being tested.