Whether you're a fan of "The Three-Body Problem" for its literary merit or not, you have to acknowledge the effort Liu Cixin has put into engaging sci-fi enthusiasts, grounding many elements of the novel in scientific plausibility.
For instance, the method by which the character Ye Wenjie establishes contact with the Trisolaran civilization in the novel involves using the sun's energy to amplify a broadcast signal, enabling it to reach the Trisolaran civilization located 4 light-years away.
Due to the extremely weak propagation of electromagnetic signals between distant celestial bodies, and the interference of various electromagnetic waves in the universe known as "space noise," it's nearly impossible to establish direct communication using electromagnetic waves.
Therefore, the only way is to find a method to amplify electromagnetic waves for contact. I can't recall the specific description of how this amplification broadcast was portrayed in "The Three-Body Problem," but in the real world, there is a very scientific method that indeed utilizes the power of the Sun to enhance electromagnetic waves. There is a chance to achieve interstellar communication with an error rate of only two millionths.
So, how is this achieved, and what is the role of the Sun?
This is actually accomplished through the gravitational lensing effect of the Sun.
We know that a glass filled with water will distort the light behind or inside the glass; in photographic lenses, if not corrected, images will bend and look unrealistic.
Basically, when light passes through an optical lens, it doesn't follow a straight line anymore, and gravity has a similar effect – to be precise, massive celestial bodies can achieve this effect too.
When light passes around a massive celestial body, it gets bent (the bending is negligible for small mass bodies), much like how light passes through a lens. This phenomenon is called gravitational lensing.
The reason we added a modifier in the previous text to specify that it's caused by massive celestial bodies is because it's well known that light has no mass. So, how does gravity bend it?
Spacetime Distortion Illustration by Mysid
Actually, the answer is quite simple. There's no such thing as gravity in the way we usually think of it. Gravity is more of a perception or something we conjure up in our minds. The real reason light appears to bend is due to the mass of celestial bodies causing a distortion in space itself. Thus, even light, which has no mass, gets bent because it's passing through this warped space.
This is precisely what Einstein's Theory of General Relativity tries to convey to us. In fact, the phenomenon of gravitational lensing was the first direct piece of evidence supporting the Theory of General Relativity. Of course, the detection of gravitational waves later on further confirmed Einstein's correctness.
Gravitational lensing allows us to see celestial bodies located behind massive objects, which would be impossible to observe with our current technology without the effect of gravitational lensing.
What we end up seeing depends on the distortion of light by the lens, primarily determined by the mass of the large celestial body, as well as its distribution in relation to the light source (imaging body) and the observer.
When we observe from Earth, the observer's position is fixed, so the image that forms is entirely dependent on the lens and the light source.
Temporal distortion diagram for Mysid
Image: Einstein Ring
Check this out - when a lens and a target light source align almost perfectly, we get to see a ring shape from Earth, known as the Einstein Ring.
Image: This image showcases a remarkable gravitational lensing effect resulting in distorted perspectives, yet amplifying background galaxies.
Certainly, gravitational lensing in a sense magnifies the target—effectively concentrating the distorted background into a point, much like the effect of an optical lens.
However, unlike an optical lens, the light rays in gravitational lensing do not diverge beyond the focal point (you can try with a convex lens where light diverges after focusing, unlike gravitational lensing), they instead maintain a fixed trajectory along the focal axis—implying that every point beyond the focal point is a focus of the gravitational lens.
Gravitational lensing can be seen as a crucial "tool" for observing the universe, but what does this have to do with the Sun? And how does it relate to communication?
Source: NASA Ames/SETI Institute/JPL-Caltech
In fact, gravitational lensing not only distorts light but also any electromagnetic waves, including radio waves, in the same way. This means that radio waves are also amplified.
The mass of the Sun is large enough to warp space around it, acting as a "lens". This implies that we can directly utilize the Sun's gravitational lensing for various purposes, including enhancing the radio waves we emit.
So, some scientists believe that the Sun is the best "communication device" humanity can find.
However, utilizing this "communication device" is not as easy as imagined. The first point is that we must send and receive signals beyond the focus.
The focus is where the light is concentrated after passing through the gravitational lens of the Sun. How far away is this distance?
Actually, there's a formula to calculate it. For the Sun, the closest distance is 550 AU – that's 550 times the distance from the Earth to the Sun. This distance is 14 times the distance between the Sun and the old ninth planet of the solar system, Pluto.
With current human technology, sending radio equipment to this distance is extremely difficult, and it would take quite a long time for the equipment to reach that location.
However, as early as 1992, someone proposed the FOCAL mission (Focal Operation of a CAlorimeter in Low gravity), attempting to send a probe beyond the gravitational lens focus of the Sun, and fundraising efforts have been made for this purpose.
One more thing to mention is that the Sun's corona can interfere with electromagnetic waves, but this effect diminishes as the distance increases.
As mentioned earlier, imaging with a gravitational lens does not disperse beyond the focus, which is great news, but the bad news is that sending equipment to a farther place will be even more challenging.
Nevertheless, using the Sun as a means of enhancing communication is an important tool for future deep space exploration, and it may even be the only means available.
Deep Space Communication Illustration, Image Source: Claudio Maccone
Additionally, scholars have calculated that if communication devices were also placed at the focus of Proxima Centauri (also known as Alpha Centauri C, which is larger than the Sun), the nearest star system to us, it could achieve a communication error rate of just one in two million between these two points (the Sun and Proxima Centauri). Moreover, the required transmission power is astonishingly low—just one-tenth of a milliwatt.
Finally
If we're now considering using the Sun as a communication device, does that mean civilizations more advanced than ours might be doing the same?
Indeed, most scientists agree that once a civilization reaches a certain level of development, driven by curiosity and the need to explore, it would naturally construct such communication devices.
Thus, although "Solar Boosted Communication" remains a concept for us, it's very likely that other civilizations have already installed devices at the focal points of their stars.
This means that by searching for specific wavelengths, we stand a chance of intercepting potential extraterrestrial civilization's radio signals. This is something some scientific teams are currently working on, though there has been no progress yet. However, the continued development of artificial intelligence could significantly aid this effort.
