A document from the U.S. Department of Defense’s intelligence agency raised an unusual possibility: controlling a rover on Mars from Earth in real time. Written in 2010, the document has the author’s name redacted.
The document examined whether a connection between distant particles of light could transmit messages faster than light. It even considered whether a message might appear to have arrived in the past. This wasn’t a plan that had already succeeded; it was a question the document proposed testing.
A Connection Between Particles of Light
Particles of light created together can remain connected even after they move apart. This phenomenon is called entanglement. Put simply, a measurement of one particle is linked to results that can be measured for the other.
But a connection between results doesn’t necessarily provide a way to send a message. To test whether it could be used for communication, the document reviewed earlier experiments and proposed new ones. The idea was to find out whether a change or measurement on one side could produce a signal detectable on the other.
The Road to a Mars Rover
The document focused on a practical question: Could someone on Earth send a message this way and control a Mars rover without waiting for a response? With conventional communications, a signal to Mars can take about four to 20 minutes to arrive, depending on the planets’ positions.
The document also considered the possibility of a signal traveling faster than light, or even one that appeared to have arrived from the future. It described ways to test these possibilities and examined what might prevent them from working. This was an analysis of existing ideas, not a study demonstrating a new form of communication.
What Remains Unknown
The document says the central question had not been settled by experiment. It also discusses reasons known physics might rule out sending messages this way. According to the accepted understanding, a connection between particles does not allow messages to travel faster than light.
A rover on Mars, and a signal from Earth that may still be on its way.
