space phone tapping
The invention of radio communication at the end of the 19th century paved the way for much more than a useful communication system. During the interwar period, people noticed that the sky was full of radio sources. Moreover, it turned out that radio waves come from invisible objects that cannot be seen in the optical range. For example, it was possible to detect Sagittarius A*, a powerful radio source associated with a supermassive black hole at the center of our galaxy. When scientists realized that you can see less of the universe with the help of antennas than with a telescope, a new scientific field emerged – radio astronomy.
Radio astronomy has been plagued with a problem since its early years. The large number of transmitters on Earth creates interference and drowns out the sky, and therefore they try to place telescope antennas in remote places, for example in the Chilean Andes. But in the late 1950s, astronomers had an idea: If a telescope recorded radio transmissions from Earth, could it detect radio traffic from a hypothetical alien civilization? This is how the decentralized SETI project emerged, in which enthusiasts analyze space signals and try to find something that is not produced by nature.
SETI participants start from the assumption that the extraterrestrial civilization is at least somewhat similar to humanity and, among other things, lives on land rather than underwater or underground; it requires long-distance communication rather than living in small communities, and finally it uses radio instead of cables and lasers to communicate.
So even if we assume that an exact copy of humanity lives on another planet, will we be able to detect their signals? For simplicity’s sake, we can turn the question around: Is there a chance aliens are eavesdropping on Earth’s radio?
Distinguish signal from natural noise
The main difference between artificial signals and natural signals is the use of a relatively narrow frequency spectrum. The easiest way to explain this is to use the scale of an old analog radio, where the listener used a wheel to move the marker of the selected frequency. Each station has its own radio frequency that you can tune into and not hear other broadcasts.
Natural radio sources almost always broadcast in a very wide frequency range. For example, active nuclei of young galaxies (quasars) are observed at all wavelengths from kilometers to centimeters. Although there are gaps in the spectrum, they can be heard at the entire receiver scale, even if expanded thousands of times. The same applies to the radiation of the planets: Jupiter, for example, can be “heard” from five kilometers to at least two centimeters.
For comparison, Wi-Fi 2G operates in the range from 12.13 to 12.43 cm, 5G – from 5.15 to 5.81 cm. Television usually uses waves with a length of one to ten meters, but each transmission is carried out at a fixed frequency.
Some natural processes are capable of producing radio emissions in a narrow band, but almost all of them have been well researched and described by scientists.
It will not be possible to spy on worldly news
If we consider the total power of the earth’s radio emissions alone, it has increased thousands of times since the times of Hertz, Marconi and Popov. However, not all of the power will be useful to the aliens. For example, recently to work It showed that it is unlikely that an extraterrestrial civilization with Earth-level development would be able to detect the radiation of a large number of cell towers. A standard antenna is placed on a mast or high-rise building and is designed to radiate only laterally across the ground where subscribers are located. Therefore the signal flows into space in only a relatively narrow, attenuated beam that is constantly moving due to the Earth’s rotation. After analyzing all the factors, scientists concluded that mobile communication towers would be undetectable by a civilization 10 light years away from the Sun.
The situation is completely different with television towers, whose transmitters are powerful, whose antennas have a wide radiation pattern and whose radio frequencies of the channels do not change for years. One of the best ways to discover humanity is through television and radio broadcasting.
“It is estimated that an extraterrestrial civilization with human-level development can receive our television signals within a 100 light-year radius. There are tens of thousands of stars in this region and The existence of alien intelligent life on one of its planets is quite possible. “They definitely won’t be able to get the TV picture, but they will be able to get the audio component, yes.” – Alexey Rudnitsky, deputy head of the Astrospace Center of the PNFysics Institute, told socialbites.ca. Lebedev RAS.
It is also unclear whether hypothetical aliens could reproduce this sound. In analog broadcasting, the volume of the voice (or music) directly affects (modulates) the carrier frequency of the radio signal. The receiving antenna receives these waves, converts them into alternating current through a series of filters and amplifiers, and transmits this current to the speaker. In other words, there is no need to decode the analog signal. However, it cannot be guaranteed that aliens have the same hearing as humans, or that they have electric speakers similar to ours.
The situation would be completely different if an extraterrestrial civilization received the signal of increasingly popular digital television. Even if the computer were familiar with binary code without any specific coding knowledge, decrypting this information would be a millennium task for the aliens. But a binary code with regularly repeated elements will clearly indicate the artificial origin of the signal.
Lighthouses of the World
Television is a good way to send signals into space about your presence, but nothing compares to military radar in this regard. The transmitting antennas of the locators of long-range anti-aircraft missile systems such as Patriot and S-400 have a peak power of tens of kilowatts. The radars of missile defense systems are even more powerful, emitting up to 500 kilowatts of energy upon impact. In terms of power, it is comparable to the Ostankino TV tower, but the radar beams have a very narrow directivity of the order of one square degree. These rays regularly pass through the same point and scan the space line by line (or according to another algorithm).
To an observer, this will look like incredibly powerful radio flashes, comparable in brightness to ordinary radio towers, in the same way as a powerful laser and a lighter pointed at the eyes. Moreover, each flash consists of several short pulses and is repeated regularly – it is unlikely that there is a natural process in the Universe that could do this.
“At the terrestrial technology level, radar pulses can be detected at a distance of approximately 100 thousand light. years. This is comparable to the diameter of the Milky Way, so the signal will be noticeable at the other end of the galaxy,” Rudnitsky explained.
Military radars acting as beacons may present an unexpected problem. Their work can be seen not only from the other end of the galaxy, but also from Earth, and the enemy in particular is trying to do this. When radar radiation is detected, the locator is in danger of being destroyed. Therefore, engineers are trying to make modern radar signatures as bad as possible, using a wide range of measures for this, most of which are secret. For example, the signal frequency, pulse repetition rate and pulse shape can change continuously according to a random law. The pulse power is “spread” across a broad band so that the radiation is weak at each specific wavelength. This fools military radiation warning systems while eliminating significant signs of artifact in the signal.
However, the technology of creating stealth radars appeared relatively recently, and in the 20th century, humanity unwittingly managed to send many clearly visible signals into space. So, paradoxically, the worst aspect of human life—war and the means to sustain it—will be most visible from the other side of the galaxy.