Q what we can not doubt ?
A1 exist of our heart = answer, from Rene Descartes
A2 unit, we use at physical experiment
A3 phyhsic law, what are always common in phenomenon
A4 reasons of observation, if all experiment possible with our observation
A5 logic we use, at certification
what we can not doubt, are
[1] what we can trust
[2] what are not fake
[3] what we can confirm
[4] what we can certificate
[5] what we can always use
Lets find All answer to question, with thinking of Rene Descartes
the wiki, recommendable to
[1] who want to learn physics
[2] who want to learn logics
[3] who want to learn philosophy
[4] who doubt god = if one concept world exist, god exist
[5] who doubt magics => if energy become object, magic in bible (what yes jesus write) are really exist
true theory, will never betray you.
answerer777