????去年12月初，隨著比特幣價格一路飆升，迅速突破1,200美元大關，社會對它的關注與日俱增。批評家們敲響了警鐘，聲稱比特幣價格已經出現泡沫。但包括金融記者菲利克斯?薩爾蒙在內的一些人意識到了加密貨幣的價值，認為比特幣只是估價過高，就像2008年以前的房地產一樣。

????其他人想得更遠，他們認為比特幣全是泡沫，幾乎不存在固有價值，認為它更像是當年荷蘭的郁金香效應，而不是房地產泡沫。持這種觀點的人士包括諾貝爾獎得主羅伯特?席勒和美國聯邦儲配委員會的前任主席艾倫?格林斯潘。

????數字貨幣沒有任何國家或現實世界商品的支持，遭遇這樣的質疑也是情理之中的事情。但對比特幣持樂觀態度的人則認為，“支持”比特幣的是它順暢、廉價、采用分散化編程的支付系統的實用功能。今年1月在紐約州金融服務局（New York Department of Financial Services）舉辦的調查聽證會上，數字貨幣公司Circle的首席執行官杰里米?奧萊爾就曾經說過：“比特幣價值增長是因為人們把它作為支付平臺的看跌期權。”

????一封在比特幣觀察人士和追隨者中瘋狂傳播的匿名電子郵件展示了比特幣幾種假想的簡單用途和它的投入使用之后的情形，以及比特幣價格隨后會出現的變化。如果亞馬遜（Amazon）采用比特幣作為所有商品的支付手段，那么將這家公司總價380億美元的商品除以（撰寫電子郵件時）約700萬枚比特幣的供應量，比特幣的單價將會達到5,400美元。如果有3,000萬美元的國際匯兌業務采用比特幣來完成，光這一項就會使得比特幣價格漲到4.2萬美元。將這些再加上在線撲克游戲和加油站的交易量，比特幣交易的總金額就會達到6,020億美元，就算按照如今1,200萬枚比特幣的供應量計算，每個比特幣也價值5萬美元。

????斯坦福商學院（Stanford Graduate School of Business）的經濟學教授蘇珊?埃塞目前正在研究比特幣，他表示：“這些數據是一個好的開端。從某種意義上說，就像是比特幣價值的上限。”實際上，幾乎沒人認為比特幣能在短期內應用于全部這些交易中，但總交易額與供應量的比率是理解比特幣價格的起點——隨著越來越多的消費者和機構選擇使用比特幣，總貿易額增長，比特幣的價格就會水漲船高。

????埃塞根據這個基礎公式，再加上各種變量，建立了一個分析框架。第一個變量是周轉速度，也就是使用比特幣進行消費的頻繁程度。由于比特幣與紙幣不同，摩擦費用很低，因此，假如供應商或貿易商只是短期地持有比特幣，同時把它與政府發行的貨幣進行雙向兌換，比特幣就可能擁有非常高的周轉速度。埃塞表示，如此一來，用少量比特幣就能實現大額的支付，比特幣的價格就會維持在較低的水平。

????還有一些難以預測的高風險變量。顯然，比特幣未來的價格很大程度上依賴于人們對加密貨幣模式的接受程度。埃塞相信，分散化賬目的加密貨幣模式是“比現有技術更為優越的真正簡單而強大的技術”，一些重要因素會推動這類模式為人們所廣泛接受。

????In the last year, and with increasing intensity following the early December price spike that briefly put Bitcoin above $1,200, critics have sounded the alarm that the price is a bubble. Some, like Felix Salmon, have recognized the value of the cryptocurrency, but argued that it is simply overvalued, much like pre-2008 real estate.

????Others haven't stopped there, claiming that bitcoin is all bubble, at the center of which is little or no intrinsic value -- something closer to a Dutch tulip mania than a real estate bubble. Those making the latter case have included Nobel Laureate Robert Shiller and former Federal Reserve Chairman Alan Greenspan.

????It seems reasonable enough to be skeptical of a digital currency unbacked by any state or real-world goods. But bitcoin optimists argue that what "backs" bitcoin is the functionality of its frictionless, low-cost, decentralized payments system. As Circle CEO Jeremy Allaire put it at fact-finding hearings held by the New York Department of Financial Services in January, "The growth in the value of bitcoin is a put option on its adoption as a payments platform."

????An anonymous viral e-mail circulating among bitcoin watchers and partisans lays out a few simple hypothetical usage and adoption scenarios, and their consequences for bitcoin's price. If Amazon.com (AMZN) adopted bitcoin for all payments, its volume of $38 billion, divided by a supply of (at the time of the email's writing) about 7 million bitcoin, would make each bitcoin worth $5,400. If $300 billion in international remittance was conducted in bitcoin, that volume alone would push the price to $42,000. Adding these, along with online poker and gas station transactions, would lead to a total transaction volume of $602 billion -- and a bitcoin, even at today's expanded supply of 12 million coins, worth $50,000.

????"Those numbers are good ones to start with. In some sense, that's like a maximum," says Susan Athey, a professor of economics at the Stanford Graduate School of Business who has been studying bitcoin. Few would realistically argue that bitcoin will service 100% of even these silos in the near term, but the volume/supply ratio is the starting point for understanding bitcoin price -- as more consumers or organizations choose to use bitcoin, increased volume will drive the price up.

????Building from that basic formula, Athey adds a variety of variables to build an analytic framework. The first is velocity -- how frequently a bitcoin can be spent. Because bitcoin, unlike paper money, is very low-friction, there's the possibility of a very high-velocity bitcoin, if, for example, vendors or traders only held bitcoin very briefly, cashing it in and out to government currencies on either end of transfers. That, Athey says, would allow a small volume of bitcoin to process a large volume of payments, keeping the price of bitcoin relatively low.

????Then there are even less predictable and higher-risk variables. Obviously, bitcoin's future price depends hugely on the adoption rate of the cryptocurrency model. Athey believes that the cryptocurrency model of distributed ledgers is "a really simple, powerful technology that is superior to existing technology," and there are major drivers that point toward wide adoption.