Quick -- how much cash do you carry around with you? With the ubiquity of credit and debit cards, odds are it's not as much as it used to be. Is paper currency headed for obsolescence?

Curiosity contributor Susan Sherwood took a look at the state of paper money in the 21st century.

Is paper money going the way of arcade-based video games, camera film, typewriters, rotary-dial telephones, automobile cigarette lighters and public phone booths? A 2011 study by the Federal Reserve System found that between 2006 and 2009, electronic payments numbered 84.5 billion, for a value of $40.6 trillion. That was an almost 10 percent increase in just three years. According to wired.com, 2007 was the first year that cash and check payments were surpassed by debit and credit card usage. PayPal alone has 110 million active accounts to help deal with the estimated $224.2 billion that will be spent online in 2012. Not satisfied with computer-based commerce, PayPal is also expanding into brick-and-mortar stores, such as its presence in more than 2,000 Home Depot locations.

These changes are signaling the end of a convention that has endured for centuries. Paper currency was first used in China, in 806 A.D, although it would be another 300 years before it was common in many other parts of the world. In the New World, the Continental Congress issued paper notes (“Continentals”) in 1775. Without gold and silver stores to back them, though, the new currency soon floundered. It was not until the start of the Civil War in 1861 that the U.S. government printed “Demand Notes” to fund the military campaign. “United States Notes” replaced these the following year. Several other variations appeared until 1913, when the Federal Reserve Act was passed, paving the way for Federal Reserve notes, which are still used today. As of November 2012, $1.1 trillion of these notes are in circulation. But for how long?

These notes are costly; the Federal Reserve’s 2012 budget for new and replacement currency was $747 million. Although the Federal Reserve Bank of San Francisco insists on its website that “public demand for currency continues to grow,” another of its pages suggests that “smart cards,” which are being used in trials across the country, might be replacing paper money. About the size of credit cards, they are able to store personal financial information.

Another potential payment method: cell phones. Cell phone subscriptions around the world are estimated to rise to five billion by the end of 2012 and are already used by millions of people to send and receive money. Need another concrete example? Thirty McDonald’s restaurants in France are involved in testing PayPal purchases made from mobile phones or computers. Yeah, there’ll be an app for that.

But wait; not so fast. Electronic payments have a potentially worrisome downside: lack of privacy. You pay cash for your groceries, wine or books and it’s hard to trace. But personal information transmitted via the Web is not necessarily secure -- just ask some high-profile merchants. Many major businesses and banks, such as Sony, Walgreen’s, Best Buy, Citigroup and Chase, have been hacked, and consumers’ data has been accessed. The expansion of cloud computing, where remote servers manage large amounts of data (e.g., Google Drive, Amazon’s Kindle Fire), allows the service provider to control information that can be accidentally or purposely released to outsiders. Prospective smart cards would come with that caveat: They'll carry a tremendous amount of information that could be at risk if lost or stolen.

Paper currency seems on its way out. We can’t surrender it completely until there are secure and accessible processes in place that are accepted by businesses and consumers, so it’s going to be a long, slow, circuitous route. But it’s a path that we are certainly headed down.