Is there a fundamental upper limit on how fast we can communicate? If you're like me, that limit is set by your despised cable provider (in my case, Comcast, which avoids being the most disliked company in America only by virtue of being ranked ahead of Time-Warner in most of those surveys).
But recently, Raphael Bousso at the University of California has proposed that quantum mechanics sets an absolute upper limit on how fast information can be transmitted. The limit he proposes in his paper is not all that interesting, but the reason for the limit is rather astonishing.
Bousso's limit on the amount of information that can be transmitted is given by the energy of the transmitter, multiplied by the time over which the information is transmitted, and divided by Planck's constant. This is an enormously large number -- our communications come nowhere near this upper bound. But what's more interesting is the reason for the bound. In the world of quantum mechanics, the vacuum is no longer simply empty space -- virtual particles can pop into existence and then just as quickly disappear. It is these "quantum fluctuations" that mess things up as you try to violate Bousso's bound -- they lead to spurious signals that were never sent! I suppose eventually quantum fluctuations could lead to an entire spurious blog post, just like this one.