Namaste Hamid,
thank you for the post and welcome to the forum.
Hamid said:
How do we know all what Buddha said is right and true?
before we really get into much depth, are you familar with the Buddhist teachings?
if you are, i will skip the "introduction" type of material and try to address your questions. if you are not, however, please let me know so that myself, and others, can provide the foundational understandings.
Basically, proving the opposite is very simple. A lot of people (and I) believe that even in the realm of sprituality, mystiscim and our preceptions, human is progressing.
i'm not sure what you are trying to say here. you are trying to say that Buddhism doesn't say that people progress? if so, that is pretty much the complete opposite of our view
If Buddha said something 2500 years ago, there is much progress on that during centuries from then on.
this actually represents a fundamental difference in our traditions. our teachings are not meant in a dogmatic sense.. they are words.. and the words are guideposts... pointers along the way, if you will. so, bearing this in mind, the literal meaning of the words is superceded by the intended meaning of the words, which is the lesson being imparted.
Buddhism is also a bit different in that if our teachings were to teach, say that the universe is expanding (which they do) and we discover that the universe is actually not expanding, or is contracting, then our teachings would change to be consonant with our observations. this is a strength of the Buddhist system of teaching.. there is nothing to be dogmatic about
Buddha was just a human and human perception is limited.
after Goatama became the historical Buddha Shakyamuni, he was asked if he was a God, to which replied "no". he was asked if he was a spirit, to which he replied "no". he was asked if he was a human, to which he replied "no". finally, the interloquer asked what he was, to which he replied "Awake".
this is an experience that is ineffable, outside the ability of lingusitic convention to convey... and not much more can be said of it.
I don't understand why the Buddhists think whatever he said is valid for ever!!
we don't. we aren't supposed to accept any of the teachings that Buddha gives without testing them like a goldsmith tests gold. in Buddhism, the Kalamaa Sutta is where this is expounded in it's most concise form:
"So, as I said, Kalamas: 'Don't go by reports, by legends, by traditions, by scripture, by logical conjecture, by inference, by analogies, by agreement through pondering views, by probability, or by the thought, "This contemplative is our teacher." When you know for yourselves that, "These qualities are unskillful; these qualities are blameworthy; these qualities are criticized by the wise; these qualities, when undertaken & carried out, lead to harm & to suffering" -- then you should abandon them.' Thus was it said. And in reference to this was it said.
"Now, Kalamas, don't go by reports, by legends, by traditions, by scripture, by logical conjecture, by inference, by analogies, by agreement through pondering views, by probability, or by the thought, 'This contemplative is our teacher.' When you know for yourselves that, 'These qualities are skillful; these qualities are blameless; these qualities are praised by the wise; these qualities, when undertaken & carried out, lead to welfare & to happiness' -- then you should enter & remain in them."
And this answer that " experience it for yourself if it's ture or not" is not a good answer because the chance that we get that far is very small and to get there -according to Buddhists - you have to believe/practice all what Buddha said.
have you ever tasted a parsimon before? lets say that you haven't and i have one in my hand. i take a bite of it and my facial expression is one of delight and i say to you "this is wonderful, it's the best fruit ever." can you tell if it is or is not without tasting if for yourself?
in the end, we are not required to believe anything more than we are capable. this is why you find a variety of schools and Vehicles within the Buddhist tradition. our teachings say that there are 84,000 Dharma Doors (Entryways to Truth), each according to the capacities of the individual sentient being.
as an aside, we have some decent threads that address some of your questions already on this wonderful forum. i would encourage you to avail yourself of them if you have the time and inclination as they may address some of your queries in a more thorough fashion.