We should certainly not be alone as we drift in the vast sea of ​​stars. It’s hard not to look at the night sky and not think about the possibility of other civilizations being there. From the philosophical thoughts of Giordano Bruno to the statistical predictions of Frank Drake, the more we learn about the universe, the more likely alien life seems. But still, in our search for this life, we heard nothing but silence.

Just as it is possible for other civilizations to be isolated or use communication technologies that we cannot see, it is always possible that we are the only creatures in space. But radio communication is also powerful and inexpensive, and we use it extensively. Our radio signals have been transmitted from Earth for decades. So why don’t other civilizations use radio?

Some think we are too optimistic. Although we emit a large number of radio signals into space, the power of radio light weakens as distance increases as it fills an ever-expanding sphere. Combined with interference from the dust and gas of interstellar space, it is likely that our signals could be heard only a few light-years from Earth with the radio receivers we have today. Several times we have transmitted powerful radio messages directly into space, such as the Arecibo message sent to the Hercules cluster in 1974. But even they will be very faint when they reach their destination, 22,000 light-years away.

Of course, we are young and simple-looking. Maybe an ancient, super-advanced species could pick up our messages from the dust of space. But will they be able to do it hundreds or thousands of light-years away? This question is addressed in a recent article published on the arXiv preprints server.

The author begins with the Kardashev scale for advanced civilizations. First proposed in 1964, the scale ranks civilizations according to their ability to use energy resources. A Type I civilization can access energy on a planetary scale, a Type II civilization at a star system scale, and a Type III at a galactic scale. Carl Sagan and others generalized this on a variable scale and rated people at about 0.73. Based on this, the author poses the following question: What scale should a civilization have to explore the remnants of human civilization, and at what distance is this possible?

Given that our man-made radio signals only penetrate space for about a hundred light-years, species will have a better chance of trying to identify man-made objects on Earth. City scale works or large earthmoving works. Consider the pyramids of Giza as an example. They have existed for thousands of years, and the base of the Great Pyramid is about 230 meters.

Given the amount of light reaching Earth, the pyramids cannot be seen beyond a few thousand light-years, regardless of the telescope’s power. Enough photons will not be able to travel this distance to allow anything. Assuming the mid-range of visible light (about 550 nm) and resolution at 10 meters, the maximum distance would be about 3000 light-years.

To distinguish pyramid-sized objects from this distance, you would need an optical telescope with a diameter of about 10a. It is slightly larger than the orbit of Saturn. A telescope of this scale can be made using an array of optical telescopes with millions of satellites orbiting Saturn. Of course, this is far beyond our current capabilities or the capabilities of any planetary civilization. At the very least, you will need to become masters of your star system.

As a result, Type II civilization will be able to see the great works of humanity from 3000 light years away. A large alien figure might know we’re here. But it will take thousands of years before we reach level 2 and see them again. Source