Communications
on Earth and between celestial neighbors
The
circumference of the Earth is 40,075 km (radius of 6,378 km). Thus, the furthest distance along the surface
of the Earth, from any given point, is approximately 20,000 km. If global communication occurs via satellites
in a low Earth orbit (1500 km altitude), the furthest distance is approximately
24,750 km.
The
speed of light is 3.0 x 108 m/sec.
The length of time it would take to traverse the maximum communication
distance on Earth would be 0.082 sec, or 82 msec (ignoring any delay due
to communication relays).
One
of the fastest [neural feedback] loops is from arm sensors to spinal cord and
back out to arm muscles: it takes 110 msec for feedback corrections to
be made to an arm movement (William H. Calvin, "The unitary hypothesis: A
common neural circuitry for novel manipulations, language, plan-ahead, and
throwing?" in Tools, Language, and Cognition in Human Evolution, edited by
Kathleen R. Gibson and Tim Ingold.
Thus,
(curiously enough) the size of the Earth, the speed of light, and the nervous
system, are such that it is feasible to have remote sensing (communications),
in real-time, between any two points on Earth.
Even a planet as large as Jupiter (119,000 km radius) would have a delay
of only 0.4 sec for light to travel one-half the circumference.
However,
It takes approximately 1.267 sec for light to travel
between the Earth and the Moon, thus, communications suffer a noticeable delay. It takes approximately 10 min for a signal to
travel between the Earth and Mars, and real-time communications are not
possible.
Thus,
the simple fact is that as soon as you attempt to communicate with another
celestial body, you will not be able to do so in real-time.