Is it possible that Bitcoin will be regulated? And if it will be, then how would we know 
I have heard stories, speculating that if someone holds 51% of the total amount of BTC they will have kind of a monopoly position and can make or break the coin alltogether. Is this true?
I have heard stories, speculating that if someone holds 51% of the total amount of BTC they will have kind of a monopoly position and can make or break the coin alltogether. Is this true?It is nearly impossible for anyone to "hold" 51% of all bitcoins and if they did it would mean little. It would cost 100s of trillions of dollars to buy 51%.
What you may have been referring to is a 51% attack:
https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_computing_power
the market cap is currently around 10 billion.. how would it cost hundreds of trilions to buy up 51% of the coins?
Only a small part of the coins is actually being traded. You can't go anywhere near 51% by just buying up all the exchanges and as soon as you start buying on and off exchanges, people will start asking more and more for their coins. Slippage.
hundreds of millions is 10 x 10 x 10 x 10 the value of what BTC is worth today. i dont' know exactly how the math would add up if one entity were to buy them all, but that would be 10,000 the value of the cap today.
if you were to factor in the bitcoins lost, that number would likely be something like 5 million bitcoins to own half.. very unlikely, but then again, there is a lot of parity and one address (satoshis') holds 1.5 million coins itself.