Proponents of the efficient market theory argue that the stock market responds immediately to new information. Days like today, though, seem to throw the cold water of reality on that theory, as the stock market erased all gains from Tuesday and fell even further. Apparently, investors were willing to put up with one day of a government shutdown, as they endured a single day of plunging over the fiscal cliff at the beginning of 2013 before the government found a successful resolution. This time around, though, the impasse looks like it could last for a while, and with a confrontation over the debt ceiling having a short two-week deadline, investors feel like they're in the middle of a big game of chicken. The Dow Jones Industrials (DJINDICES:^DJI) were the hardest hit among the major market benchmarks, dropping about 87 points as of 11:30 a.m. EDT.

McDonald's (NYSE:MCD) was one of the biggest decliners in the Dow, with a drop of 1.4%, despite an interesting initiative among its restaurant owners aimed at driving customer traffic. According to a Bloomberg report, hundreds of Golden Arches franchisees are working with a mobile-solutions company to introduce a loyalty program that would give repeat customers free food and other offers. Combined with efforts like accepting mobile payments and advance-ordering apps, the moves could entice younger customers to stick with the fast-food giant rather than moving to rivals that are seen as more in touch with the Millennial generation.

Coca-Cola (NYSE:KO) also fell 1.4%. Earlier this week, the company learned it lost its top-brand status after a 13-year reign at the top of the Interbrand global standings, as Apple passed up the beverage maker to become the most valuable brand in the world. The move only stresses the challenges that Coca-Cola has faced lately, as falling demand for its namesake carbonated soft drinks has made a substantial dent in its overall results. Attempts to diversify and appeal to more health-conscious consumers with noncarbonated offerings like water and juices have helped somewhat, but investors haven't felt as confident about the stock's future growth prospects as they have in past years.

Finally, some stocks outside the Dow showed their strength even in the face of the shutdown. Pandora (NYSE:P) climbed more than 6.5% after announcing its September business metrics, which included an 18% increase in listener hours from September 2012 and a 25% jump in the number of active listeners. With Pandora's radio market share rising by more than a percentage point to 7.77%, the company has defied skeptics and held onto its audience even in the face of rising competition from other players in the streaming-music industry.

Fool contributor Dan Caplinger owns shares of Apple. The Motley Fool recommends Coca-Cola, McDonald's, and Pandora Media. The Motley Fool owns shares of McDonald's. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.