Bitcoin, along with other cryptocurrencies, has been described as an economic bubble by at least eight Nobel Memorial Prize in Economic Sciences laureates, including Robert Shiller,[144] Joseph Stiglitz,[202] and Richard Thaler.[203][204] Noted Keynesian economist Paul Krugman has described bitcoin as "a bubble wrapped in techno-mysticism inside a cocoon of libertarian ideology",[135] professor Nouriel Roubini of New York University has called bitcoin the "mother of all bubbles",[205] and University of Chicago economist James Heckman has compared it to the 17th-century tulip mania.[204] Former Federal Reserve Chairman Alan Greenspan has also described bitcoin as a "bubble";[206] the investors Warren Buffett and George Soros have respectively characterized it as a "mirage"[207] and a "bubble";[208] while the business executives Jack Ma and Jamie Dimon have called it a "bubble"[209] and a "fraud",[210] respectively.

“If the trend continues, the average person will not be able to afford to purchase one whole bitcoin in 2 years. As global economies inflate and markets exhibit signs of recession, the world will turn to Bitcoin as a hedge against fiat turmoil and an escape against capital controls. Bitcoin is the way out, and cryptocurrency as a whole is never going away, it’s going to grow in use and acceptance as it matures.”
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The "Metropolis Part 1: Byzantium" soft[citation needed] 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.[citation needed]

Vitalik Buterin picked the name Ethereum after browsing Wikipedia articles about elements and science fiction, when he found the name, noting, "I immediately realized that I liked it better than all of the other alternatives that I had seen; I suppose it was the fact that sounded nice and it had the word 'ether', referring to the hypothetical invisible medium that permeates the universe and allows light to travel."[9]

1) Irreversible: After confirmation, a transaction can‘t be reversed. By nobody. And nobody means nobody. Not you, not your bank, not the president of the United States, not Satoshi, not your miner. Nobody. If you send money, you send it. Period. No one can help you, if you sent your funds to a scammer or if a hacker stole them from your computer. There is no safety net.

Mining is a record-keeping service done through the use of computer processing power.[f] Miners keep the blockchain consistent, complete, and unalterable by repeatedly grouping newly broadcast transactions into a block, which is then broadcast to the network and verified by recipient nodes.[79] Each block contains a SHA-256 cryptographic hash of the previous block,[79] thus linking it to the previous block and giving the blockchain its name.[7]:ch. 7[79]
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[92] and links it to Tulip mania.[93] American business magnate Warren Buffett thinks that cryptocurrency will come to a bad ending.[94] In October 2017, BlackRock CEO Laurence D. Fink called bitcoin an 'index of money laundering'.[95] "Bitcoin just shows you how much demand for money laundering there is in the world," he said.
Network nodes can validate transactions, add them to their copy of the ledger, and then broadcast these ledger additions to other nodes. To achieve independent verification of the chain of ownership each network node stores its own copy of the blockchain.[80] About every 10 minutes, a new group of accepted transactions, called a block, is created, added to the blockchain, and quickly published to all nodes, without requiring central oversight. This allows bitcoin software to determine when a particular bitcoin was spent, which is needed to prevent double-spending. A conventional ledger records the transfers of actual bills or promissory notes that exist apart from it, but the blockchain is the only place that bitcoins can be said to exist in the form of unspent outputs of transactions.[7]:ch. 5
^ Iansiti, Marco; Lakhani, Karim R. (January 2017). "The Truth About Blockchain". Harvard Business Review. Harvard University. Archived from the original on 18 January 2017. Retrieved 17 January 2017. The technology at the heart of bitcoin and other virtual currencies, blockchain is an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way.
As of November 2017, Bitcoin and other digital currencies are outlawed only in Bangladesh, Bolivia, Ecuador, Kyrgyzstan and Vietnam, with China and Russia being on the verge of banning them as well. Other jurisdictions, however, do not make the usage of cryptocurrencies illegal as of yet, but the laws and regulations can vary drastically depending on the country.
All of those factors make mining cryptocurrencies an extremely competitive arms race that rewards early adopters. However, depending on where you live, profits made from mining can be subject to taxation and Money Transmitting regulations. In the US, the FinCEN has issued a guidance, according to which mining of cryptocurrencies and exchanging them for flat currencies may be considered money transmitting. This means that miners might need to comply with special laws and regulations dealing with this type of activities.
Venture capitalists, such as Peter Thiel's Founders Fund, which invested US$3 million in BitPay, do not purchase bitcoins themselves, but instead fund bitcoin infrastructure that provides payment systems to merchants, exchanges, wallet services, etc.[162] In 2012, an incubator for bitcoin-focused start-ups was founded by Adam Draper, with financing help from his father, venture capitalist Tim Draper, one of the largest bitcoin holders after winning an auction of 30,000 bitcoins,[163] at the time called "mystery buyer".[164] The company's goal is to fund 100 bitcoin businesses within 2–3 years with $10,000 to $20,000 for a 6% stake.[163] Investors also invest in bitcoin mining.[165] According to a 2015 study by Paolo Tasca, bitcoin startups raised almost $1 billion in three years (Q1 2012 – Q1 2015).[166]
Like Bitcoin, Ethereum is a distributed public blockchain network. Although there are some significant technical differences between the two, the most important distinction to note is that Bitcoin and Ethereum differ substantially in purpose and capability. Bitcoin offers one particular application of blockchain technology, a peer to peer electronic cash system that enables online Bitcoin payments. While the Bitcoin blockchain is used to track ownership of digital currency (bitcoins), the Ethereum blockchain focuses on running the programming code of any decentralized application.
The first cryptocurrency to capture the public imagination was Bitcoin, which was launched in 2009 by an individual or group known under the pseudonym, Satoshi Nakamoto. As of February 2019, there were over 17.53 million bitcoins in circulation with a total market value of around $63 billion (although the market price of bitcoin can fluctuate quite a bit). Bitcoin's success has spawned a number of competing cryptocurrencies, known as "altcoins" such as Litecoin, Namecoin and Peercoin, as well as Ethereum, EOS, and Cardano. Today, there are literally thousands of cryptocurrencies in existence, with an aggregate market value of over $120 billion (Bitcoin currently represents more than 50% of the total value).
Transactions are verified by network nodes through cryptography and recorded in a public distributed ledger called a blockchain. Bitcoin was invented in 2008 by an unknown person or group of people using the name Satoshi Nakamoto[15] and started in 2009[16] when its source code was released as open-source software.[7]:ch. 1 Bitcoins are created as a reward for a process known as mining. They can be exchanged for other currencies, products, and services.[17] Research produced by University of Cambridge estimates that in 2017, there were 2.9 to 5.8 million unique users using a cryptocurrency wallet, most of them using bitcoin.[18]