Is the current economic system, which relies on paper money instead of gold and silver (the Dinar and Dirham), unlawful (haram), and is acknowledging it considered polytheism (shirk)?

The use of gold and silver as prices for goods is not a matter of divine ordainment (tawqif), and the currencies used for transactions have changed many times since the Prophetic era. Scholars have established regulations for dealing with contemporary currencies, treating them like gold and silver. Therefore, forward buying (salam) is permissible with them, as is buying gold and silver with them, provided there is immediate mutual possession (al-taqabud). Similarly, buying some currencies with others at a difference in value is permissible, provided there is immediate mutual possession, by analogy with the hadith: "If the types differ, then sell as you wish, if that is hand to hand."