At 12:00 UTC, the price of a single bitcoin crossed $18,000. At 19:16 UTC, it crossed $19,000. The cryptocurrency is trading at $19,215.56, an increase of more than 9% in the last 24 hours, at 19:58 UTC. 

Within the last 24 hours, its price has jumped by approximately $1,600. Last week, at around the same time, bitcoin was trading at $14,623.18. This means that its value has appreciated by approximately $5,400 in a week. On an overall basis, the cryptocurrency is up by 1,845% this year. At this rate, a price of $20,000 before the end of this year might not be unreasonable.

After registering significant run ups in their prices over the last week, other cryptocurrencies within the top 10 most-traded list traded for price losses or stayed constant. Cardano, a cryptocurrency for smart contracts, was the exception. It racked up price gains of more than 79% in the last 24 hours. (See also: Bitcoin Price Weekly Review: Altcoin Rally, Bubble Talk.)  

There haven’t been significant updates to bitcoin’s protocol or trading volumes in the last 24 hours. As always, miner rewards have kept pace with the surge in bitcoin’s price to enable profits. The most probable reason for a rise in bitcoin’s valuations is the prospect of institutional investors investing in it. TD Ameritrade has become the latest big name to enter the bitcoin sweepstakes by allowing customers to trade in bitcoin futures, starting Monday. The entry of institutional investors is expected to bring price stability to the cryptocurrency. (See more: TD Ameritrade To Launch Bitcoin Futures Trading Dec. 18.)

But prominent names are increasingly describing bitcoin's price rise as a bubble. In an interview with BusinessInsider, Nobel Prize-winning economist Paul Krugman said the bitcoin bubble was unlike the housing crisis bubble because the cost of producing new bitcoins has become more expensive (as compared to housing, which became cheaper due to greater supply).

“We’re waiting for a Wiley Coyote moment. Cartoon physics,” Krugman said. “He runs off the edge of a cliff and it’s only when he looks down and realizes there’s nothing under him that he goes Pchew!”  

In the meanwhile, the same publication has an interesting interview with a developer, who claims to run a “pump-and-dump” scheme for crytocurrencies using bots. According to him, they use messaging apps to perform a coordinated buy action to pump up prices for a given cryptocurrency and, subsequently, dump it en masse as other players enter the market. There are 17,000 traders in one messaging app Telegram group for such a scheme. 

A similar strategy may not work in the case of highly-traded cryptocurrencies because their high prices and volumes, which run into millions and billions of dollars, preclude manipulation by individual traders. Bitcoin whales, or people who own 40 percent of the market, might be more apt to perform a similar action. (See also: Why Do Cryptocurrencies Have Buy And Sell Walls?)