Opinion History,140 characters at a time

“Twitter is tens of millions of active users. There is no archive with tens of millions of diaries,” said historian Daniel J. Cohen. “Twitter is of the moment; it’s where people are the most honest.”

Last month, Twitter announced that it would donate its archive of public messages to the Library of Congress,and supply it with continuous updates.

The Twitter archive,which was “born digital,” as archivists say,will be easily searchable by machine — unlike family letters and diaries gathering dust in attics.

As a written record,Tweets are very close to the originating thoughts. “Most of our sources are written after the fact,mediated by memory — sometimes false memory,” Ms [Amy Murrell Taylor said. “And newspapers are mediated by editors. Tweets take you right into the moment in a way that no other sources do. That’s what is so exciting.” Twitter messages preserve witness accounts of an extraordinary variety of events all over the planet.

Ten billion Twitter messages take up little storage space: about five terabytes of data. (A two-terabyte hard drive can be found for less than $150.) And Twitter says the archive will be a bit smaller when it is sent to the library. Before transferring it,the company will remove the messages of users who opted to designate their account “protected,” so that only people who obtain their explicit permission can follow them. A Twitter user can also elect to use a pseudonym and not share any personally identifying information.

Each message is accompanied by some tidbits of supplemental information,like the number of followers that the author had at the time and how many users the author was following. While Mr Cohen said it would be useful for a historian to know who the followers and the followed are,this information is not included in the Tweet itself.

But there’s nothing private about who follows whom among users of Twitter’s unprotected,public accounts. This information is displayed both at Twitter’s own site and in applications developed by third parties whom Twitter welcomes to tap its database.

Alexander Macgillivray,Twitter’s general counsel,said,“From the beginning,Twitter has been a public and open service.” Twitter’s privacy policy states: “Our services are primarily designed to help you share information with the world. Most of the information you provide to us is information you are asking us to make public.”

Mr Macgillivray at Twitter said his company would be turning over copies of its public archive to Google, Yahoo and Microsoft,too. These companies already receive instantaneously the stream of current Twitter messages. When the archive of older Tweets is added to their data storehouses,they will have a complete,constantly updated,set,and users won’t encounter a six-month embargo.

Google already offers its users Replay, the option of restricting a keyword search only to Tweets and to particular periods. It’s quickly reached from a search results page. (Click on “Show options,” then “Updates,” then a particular place on the timeline.)

A tool like Google Replay is helpful in focusing on one topic. But it displays only 10 Tweets at a time. To browse 10 billion — let’s see,figuring six seconds for a quick scan of each screen — would require about 190 sleepless years.

Mr Cohen encourages historians to find new tools and methods for mining the “staggeringly large historical record” of Tweets. This will require a different approach,he said,one that lets go of straightforward “anecdotal history.”

In the end,perhaps quality will emerge from sheer quantity.

Randall Stross is an author based in Silicon Valley and a professor of business at San Jose State University

The New York Times