The government in Egypt is cutting off communications networks, including mobile phones and the Internet.

The decision to get out and protest is a strategic one.  It’s privately costly and it pays off only if there is a critical mass of others who make the same commitment.  It can be very costly if that critical mass doesn’t materialize.

Communications networks affect coordination.  Before committing yourself you can talk to others, check Facebook and Twitter, and try to gauge the momentum of the protest.  These media aggregate private information about the rewards to a protest but its important to remember that this cuts two ways.

If it looks underwhelming you stay home, go to work, etc.  And therefore so does everybody who gets similar information as you.  All of you benefit from avoiding protesting when the protest is likely to be unsuccessful.  What’s more, in these cases even the regime benefits from enabling private communication, because the protest loses steam.

Now consider the strategic situation when you lines of communication are cut and you are acting in ignorance of the will of others.  The first observation is that in these cases when the protest would have fizzled, without advance knowledge of this many people will go out and protest.  Many are worse off, including the regime.

The second observation is that even in those cases when protest coordination would have been amplified by private communication, shutting down communication may nevertheless have the same effect, perhaps even a stronger one.  There are two reasons for this. First, the regime’s decision to shut down communications networks is an informed one.  They wouldn’t bother taking such a costly and face-losing move if they didn’t think that a protest was a real threat.  The inference therefore, when you are in your home and you can’t call your friends and the internet is shut down is that the protest has a real chance of being effective.  The signal you get from this act by the regime substitutes for the positive signal you would have gotten had they not acted.

The other reason is that this signal is public.  Everyone knows that everyone knows … that the internet has shut down.  Instead of relying on the noisy private signal that you get from talking to your friends, now you know that everybody is seeing exactly the same thing and are emboldened in exactly the same way.

It’s as if the regime has done the information aggregation for you and packaged it into a nice fat public signal.  This removes a lot of the coordination uncertainty and strengthens your resolve to protest.

Addendum: Tyler has some related observations.