Wallets and similar software technically handle all bitcoins as equivalent, establishing the basic level of fungibility. Researchers have pointed out that the history of each bitcoin is registered and publicly available in the blockchain ledger, and that some users may refuse to accept bitcoins coming from controversial transactions, which would harm bitcoin's fungibility. For example, in 2012, Mt. Gox froze accounts of users who deposited bitcoins that were known to have just been stolen.
The "Metropolis Part 1: Byzantium" soft fork took effect on 16 October 2017, and included changes to reduce the complexity of the EVM and provide more flexibility for smart contract developers. Byzantium also added supports for zk-SNARKs (from Zcash), with the first zk-SNARK transaction occurring on testnet on September 19, 2017.
Paul Krugman, Nobel Memorial Prize in Economic Sciences winner does not like bitcoin, has repeated numerous times that it is a bubble that will not last and links it to Tulip mania. American business magnate Warren Buffett thinks that cryptocurrency will come to a bad ending. In October 2017, BlackRock CEO Laurence D. Fink called bitcoin an 'index of money laundering'. "Bitcoin just shows you how much demand for money laundering there is in the world," he said.
Like other blockchains, Ethereum has a native cryptocurrency called Ether (ETH). ETH is digital money. If you’ve heard of Bitcoin, ETH has many of the same features. It is purely digital, and can be sent to anyone anywhere in the world instantly. The supply of ETH isn’t controlled by any government or company - it is decentralized, and it is scarce. People all over the world use ETH to make payments, as a store of value, or as collateral.
Cryptocurrencies have been compared to Ponzi schemes, pyramid schemes and economic bubbles, such as housing market bubbles. Howard Marks of Oaktree Capital Management stated in 2017 that digital currencies were "nothing but an unfounded fad (or perhaps even a pyramid scheme), based on a willingness to ascribe value to something that has little or none beyond what people will pay for it", and compared them to the tulip mania (1637), South Sea Bubble (1720), and dot-com bubble (1999). The New Yorker has explained the debate based on interviews with blockchain founders in an article about the “argument over whether Bitcoin, Ethereum, and the blockchain are transforming the world”.
This flexibility makes Ethereum the perfect instrument for blockchain -application. But it comes at a cost. After the Hack of the DAO – an Ethereum based smart contract – the developers decided to do a hard fork without consensus, which resulted in the emerge of Ethereum Classic. Besides this, there are several clones of Ethereum, and Ethereum itself is a host of several Tokens like DigixDAO and Augur. This makes Ethereum more a family of cryptocurrencies than a single currency.
If you decide to invest in cryptocurrencies, Bitcoin is obviously still the dominant one. However, in 2017 its share in the crypto-market has quite dramatically fallen from 90 percent to just 40 percent. There are many options currently available, with some coins being privacy-focused, others being less open and decentralized than Bitcoin and some just outright copying it.
The receiver of the first bitcoin transaction was cypherpunk Hal Finney, who had created the first reusable proof-of-work system (RPoW) in 2004. Finney downloaded the bitcoin software on its release date, and on 12 January 2009 received ten bitcoins from Nakamoto. Other early cypherpunk supporters were creators of bitcoin predecessors: Wei Dai, creator of b-money, and Nick Szabo, creator of bit gold. In 2010, the first known commercial transaction using bitcoin occurred when programmer Laszlo Hanyecz bought two Papa John's pizzas for ₿10,000.