As I noted earlier, the Senate Judiciary Committee’s Subcommittee on Privacy, Technology, and the Law held a hearing this morning entitled: “Protecting Mobile Privacy: Your Smartphones, Tablets, Cell Phones and Your Privacy.” In it, Sentor Richard Blumenthal (D‑CT) engaged in a fascinating colloquy with Google’s Alan Davidson.

Blumenthal pursued Davidson about the year-old incident in which Google’s Street View cars collected data on the location of WiFi nodes and mistakenly gathered snippets of “payload data”—that is, the data traveling over open WiFi networks in the moments when their Street View cars were passing by.

Some payload data may have contained personal information including passwords. Google has meekly been working with data protection authorities around the world since then, hoping once and for all to delete this unneeded and unwanted data.

Blumenthal was prosecutorial in tone, but made a classic prosecutor’s error: He asked questions to which he didn’t know the answers.

Isn’t “payload data” extremely valuable for mapping WiFi networks?, queried Senator Blumenthal.

Davidson’s answer, and the consensus of panelists: Ummmm, no, not really.

(If you were to map pay phones, it wouldn’t matter whether people were talking on them, either, or what they were saying.)

Despite looking foolish, Senator Blumenthal persisted, asking Davidson whether collecting “payload data” should be illegal. Davidson demurred, but it’s a fascinating question.

Should it be against the law to collect data from open WiFi networks? That is, to observe radio signals passing your location on a public street? Should the government determine when you can collect radio signals, or what bands of the radio spectrum you may observe? What should you be allowed to do with information carried on a radio signal that you inadvertently capture?

If the government should have this power, the same logic would support making it illegal to collect photons that arrive at your eyes or that enter your camera lens. The government might proscribe collecting sound waves that come to your ears or microphone.

Laws against observing the world around you would certainly protect privacy! Let the government blind us all, and privacy will flourish. But this is not privacy protection anyone should want.

To understand privacy, you have to understand a little physics. As I said in an earlier comment on Google’s collection of open WiFi data:

Given the way radio works, and the common security/​privacy response—encryption—it’s hard to characterize data sent in the clear as private. The people operating them may have wanted their communications to be private. They may have thought their communications were private. But they were sending out their communications in the clear, by radio—like a little radio station broadcasting to anyone in range.

Trying to protect privacy in unencrypted radio broadcasts (like public displays or publically made sounds) is like trying to reverse the flow of a river—it’s a huge engineering project. Senator Blumenthal would start to protect your privacy by blinding you to the world around you. Then narrow exceptions would determine what radio signals, lights, and sounds you are allowed to observe…