On Earth, all inhabitants can communicate in real time, because the speed of propagation of electromagnetic waves allows it. But this is not possible beyond our planet, explains the specialist
Ignacio Del Villar Fernandez in The Conversation.
Humans communicate with each other in two ways. The first is the one also used by other animals: the emission of sound waves. However, these are slow and do not propagate beyond a few tens of meters, due to air-induced attenuation. This is why we have been looking for alternatives for communicating over long distances for a very long time. Smoke signals, flags and mirrors were thus used, but were quite ineffective in terms of the amount of information they could convey. Postcards allowed much more data to be transmitted, but were very slow.
A great leap forward has been made possible thanks to the progressive mastery of electromagnetic waves. In 1791, Claude Chappe invented the optical telegraph, a system capable of transmitting a symbol every two minutes between Paris and Lille, 230 km apart. However, it was weather dependent and did not work at night.
In 1837 the electric telegraph was introduced by William F. Cooke and Charles Wheatstone. Within a few years, it was possible to communicate east to west across the United States, and then, later, to communicate across the oceans by means of submarine cables.
In 1901, Guglielmo Marconi developed wireless telegraphy experiments across the entire Atlantic Ocean.
Communicate in real time in the information society
Already in the 20th and 21st centuries, the application of fiber optics and modern wireless technology led to the creation of the information society, where we can communicate with each other in real time.
If this is possible, it is because electromagnetic waves are transmitted much faster than sound waves. Sound, even under optimal conditions, such as through diamond, travels 10,000 times slower than electromagnetic waves transmitted through air or fiber optics.
A parameter for evaluating the quality of communications is the round trip time (RTT). It is the time that elapses between the moment a sender transmits a message to a recipient and the moment a response reaches him. It can be estimated at 2 times the separation between the partners divided by the propagation speed of the signal.
Engineers and scientists define RTT values of around 200 milliseconds as a quality threshold for real-time communications. If we take into account that the speed of sound in air is 340 m/s, and that the RTT should not exceed 200 ms, we can deduce that the distance for a conversation between two people should not not exceed 34 meters. A logical value if we take into account that sound communications are intended for conversation between people close to each other.
As for electromagnetic signals, today they can be propagated by guided and wireless means with values of the order of 2×108 m/s, similar to the speed of light (in the case of optical fiber, it is the light that is transmitted). For this speed, if one does not want to exceed the RTT of 200 ms, the separation between two partners must not exceed 20,000 km, ie the greatest distance between any two points on the earth's surface.
In other words, the propagation speed of electromagnetic waves is sufficient to communicate in real time between all the inhabitants of the Earth.
What about communication on an interplanetary scale?
For the Moon, which is 384,000 km from Earth, the RTT increases to several seconds. This is an unacceptable value for many applications that we use in our information society. For planets, the RTT is counted in minutes. Not to mention the nearest star, Proxima Centauri, located 4.2 light years away. His RTT is 8.4 years. We would have to wait more than two Olympiads to receive an answer from a hypothetical interlocutor on a planet in orbit around this star.
To allow interplanetary or interstellar communication, the speed of light would have to increase considerably. Conversely, if the speed of light were lower, it would not be possible to communicate between two points on Earth without running the risk of the RTT exceeding 200 ms. In other words, real-time terrestrial communication would no longer be possible and the information society would collapse.
The speed of electromagnetic waves is sufficient for humans to communicate in real time between any two points on Earth, but insufficient for us to continue to do so as we move away from Earth. The information society is possible only on planets whose diameter is not greater than that of the Earth, and only an animal such as the human being, capable of controlling the propagation of electromagnetic signals, can benefit of this technology.
This paradoxical coincidence refers to questions such as the fine tuning of the universe or the anthropic principle, while opening the way to other reflections.
The first is to know why the evolution of human beings has converged with the development of the information society on a planet like Earth. The RTT of 200 ms, considered suitable for real-time applications, is valid because our brain, combined with other parts of our body like our eyes and ears, reacts to different stimuli with response times corresponding to this value.
Moreover, this RTT is the result of many years of evolution, and the diameter of the Earth is also the result of the expansion of the universe. The third parameter, the speed of light, combines with the RTT and the diameter of the Earth to create the information society, which essentially consists of many human beings interacting with each other in real time on the surface. of our planet.
Another reflection concerns the meaning of the colonization of planets when it is not possible to communicate with them in real time. Will we be able to exceed the speed of light in the future?
Ignacio Del Villar Fernández, Professor Titular de Tecnología Electrónica, Universidad Pública de Navarra
This article is republished from The Conversation under a Creative Commons license. Read the original article.