Why real-time communication is not possible between Earth and other planets


Human beings communicate with each other in two ways. The first is the same used by other animals: the emission of sound waves.

But they are slow and do not propagate for more than a few tens of meters, due to the attenuation caused by the air. Therefore, we have been looking for alternative forms of communication over long distances since antiquity.

Smoke signals, flags and mirrors were some solutions, but they were inefficient with respect to the amount of data they could transmit. The letters, on the other hand, allowed transmitting much more information, but they were very slow.

The great leap was produced with the progressive dominance of electromagnetic waves. In 1791, Claude Chappe invented the optical telegraph – a system that allowed the transmission of a symbol every two minutes between Paris and Lille, France, covering a distance of 230 km. But this system depended on weather conditions and did not work at night.

In 1837, the electric telegraph was implemented, the creation of English inventors William F. Cooke and Charles Wheatstone. Within a few years, it was possible to connect the United States from east to west, and later transmit across the ocean via undersea cables.

In 1901, Guglielmo Marconi developed experiments with wireless telegraphy crossing the Atlantic Ocean.

The birth of the information society

As early as the 20th and 21st centuries, the application of fiber optics and modern wireless technology led to the creation of the information society, in which we can communicate with each other in real time.

All of this is possible because electromagnetic waves are transmitted much faster than sound waves. Sound, even if transmitted under ideal conditions, through diamond, reaches a speed 10,000 times lower than electromagnetic waves transmitted through the air or fiber optics.

A parameter that allows evaluating the quality of communications is the round-trip time (RTT), that is, the time elapsed from the transmission of a message by a sender to its receiver until the reply arrives. . Its approximate value is twice the distance between the interlocutors, divided by the propagation speed of the signal.

Scientists and engineers set the upper limit of RTT to have real-time communication quality in about 200 milliseconds. If we consider that the speed of sound in air is 340 m/s and that the RTT must not exceed 200 ms, we can calculate that the distance for a conversation between two people must not exceed 34 meters – a logical value, if we consider that the waves Sounds are intended for communication between people close to each other.

With respect to electromagnetic signals, it is now possible to make them propagate through guided and wireless media at a speed of about 2×108 m/s, which is similar to the speed of light (and in the case of optical fiber , the transmission is made by the light itself).

With this speed, in order not to exceed the RTT of 200 ms, the separation between the two interlocutors must be no more than 20 thousand kilometers, which is exactly the greatest distance between any two points on the earth’s surface. In other words, the propagation speed of electromagnetic waves is suitable for real-time communication between all the inhabitants of the Earth.

And in interplanetary communication?

Between Earth and Moon (384,000 kilometers away), the RTT increases to several seconds. This value is unacceptable for many of the applications used in our information society.

Already between Earth and the other planets, the RTT arrives in minutes. And not to mention the nearest star, Proxima Centauri, located 4.2 light-years from Earth. Its RTT is 8.4 years. That is, we would need to wait more than two Olympics to receive an answer from a hypothetical interlocutor on a planet that revolves around that star.

The speed of light would need to increase dramatically for us to achieve interplanetary or interstellar communication. On the other hand, if the speed of light were lower, it would not be possible to communicate two points on Earth without running the risk that the RTT exceeds 200 ms. In other words, real-time terrestrial communication would not be possible and the information society would collapse.

If the propagation speed of light in optical fiber were 2×107 m/s instead of 2×108 m/s, for example, the RTT between Buenos Aires, Argentina, and Seoul, South Korea (almost 20,000 km ) would increase from 200 ms to 2 seconds. This would mean having to wait every time someone spoke, while more demanding applications such as remote surgery or interactive video games would not be able to cope with this increased time.

The speed of electromagnetic waves is sufficient for human beings to communicate in real time between any two points on Earth, but it becomes insufficient as we move further away from the planet. The information society is only possible on planets whose diameter is not larger than the Earth’s and only an animal like the human being, capable of controlling the propagation of electromagnetic signals, can benefit from this technology.

This paradoxical coincidence raises questions such as the fine-tuning of the universe or the anthropic principle, as well as opening the way for other reflections. One of them is the reason why the human being converged on the development of the information society on a planet like Earth.

The 200 ms RTT, considered suitable for real-time applications, is valid because our brain, combined with other parts of our body, such as eyes and ears, reacts to different stimuli with response times that adjust to this value. .

Furthermore, this RTT value is the result of many years of evolution and the diameter of the Earth was also a result of the expansion of the universe. The third parameter, the speed of light, is combined with the RTT and the diameter of the Earth to create the information society, which basically consists of many human beings interacting with each other in real time on the surface of our planet.

Another reflection refers to what is the point of colonizing planets if it is not possible to communicate with them in real time. Will we be able to surpass the speed of light in the future?

*Ignacio del Villar Fernández is a professor of electronic technology at the Public University of Navarra, Spain.

This article was originally published on the academic news site The Conversation and republished under a Creative Commons license. Read the original version (in Spanish) here.

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