Extremely shocked, Mark was stunned for half a minute before he came back to his senses and asked these two key questions: "...... you Why do you dare to be sure that thing sent it? And how dare you be an alien? ”

Sun Tan was not stumped by Mark's rhetorical question, but instead began his long explanation with an expression of "I already knew you were going to ask this".

The first question is about why this signal does not exceed the range of 3 light-years.

This is going to start with the medium-sized private long-wave receiving radio exclusively invented by Sun Tanzu's ancestor Sun Mingshi for more than ten generations, this device is just like Sun Tan's previous introduction, and the band it can receive and emit is something that no one or any organization on the earth can do except the Sun family.

And Sun Tan has been using it non-stop, whether on Earth or in the month since he arrived on the moon, at least he can be sure that this thing has never received any signal since he was born.

Sun Tan is 24 years old, which means that no object within at least 24 light-years has not emitted a signal that a radio station can receive in those 24 years. Why dare you say that? Because all the celestial bodies within 24 light-years have been completely mastered by the current means of human observation, humans can be sure that there are no signs of other extraterrestrial life and all extraterrestrial life activity within this distance.

And the day after the Earth was suddenly hijacked by the Cube, the signal was received by a medium-sized private longwave receiving station, and the message behind this was clearly self-evident.

Mark immediately retorted and asked, "How can you be sure of this?" Anyone with a modicum of basic physics and knowledge of the universe can hypothesize that the signal came from N light-years away and happened to be emitted in the direction of the Moon in N light-years. (here N>24)

For example, Taurus's famous Aldebaran, the Taurus α (Aldeba

a

Although it is a red giant star that is about to end its life in 500~10 million years, it has 5 planets and has been regarded by humans as one of the regions with the most likely occurrence of intelligent life.

Aldeba

a

The distance from the Moon is 68 light years, so what if the signal was sent by intelligent life on one of its planets 68 years ago and has just arrived on the Moon?

In response to Mark's question, Sun Tan smiled slightly and had already prepared the answer, which is the second question and what is this set of signals.

Sun Tan once again asked Mark to put on headphones and listen to the signal recording just now, but Mark was still at a loss and couldn't figure it out.

"Mark, the first thing I'm going to do is to make you understand the unbelievable fact that if there really are aliens, how do you think they will communicate with humans?" Sun Tan asked.

Mark thought for a moment and replied unimagibitively, "Words? A language with a sound? Or is it painting? Or create some astronomical phenomenon that we can observe? ”

Sun Tan shook his head and said, "Wrong, none of your answers are right, I'll explain to you why." ”

Communicate with words, not to mention whether it is possible for the other party to understand the hundreds or thousands of different words that already exist for earthlings, and even if they have the ability, it is possible that they will not use them at all, because aliens do not necessarily have such a thing as words.

As a simple example, if a certain alien is in a swarm, we imagine it as a bee swarm, and the whole swarm has only one person who gives orders, that is the queen bee, she has thoughts and can give orders, but it does not need words, only brain waves, and all the bees in the swarm except it receive orders unconditionally and carry them out, then does this kind of alien need words? The answer, of course, is no, and if they don't need words themselves, can they use words to communicate with earthlings? The answer, of course, is no.

In the same way, language is also a truth, if the other party does not have an auditory system and cannot feel the vibration of the air, or even take 10,000 steps back and say, there is no air in the environment where aliens live, let alone sound, then will it use sound to communicate with humans? More unlikely.

In the same way, it can be proved that what kind of painting, making astronomical phenomena and observing these things are all nonsense, because these assumptions have a premise, that is, to imagine aliens as a group with similar functions as humans.

Although we humans call extraterrestrial life extraterrestrial "humans", we do not say that it is really human!

"So, none of your assumptions are valid, and I'm going to tell you a hypothesis that hasn't been proven until now, but it's basically the most reliable hypothesis about how different groups of intelligent life interact with each other."

According to Sun Tan, the universe we live in is called the universe because it is composed of time and space, just like the most simple sentence in the ancient "Huainanzi" of Tonghua: "In ancient times, it is called the universe, and the four directions are called the universe." In other words, the universe is space and the universe is time, which is strikingly consistent with modern interpretations.

So what are the universal things or laws in the same universe? The first thing that comes to mind is things like the constant speed of light and absolute zero, which have become truth in the current universe.

But Sun Tan told Mark that if these contents are difficult to express for two completely different groups of life, the only law that can be expressed most easily is mathematics.

"Mathematics? Are you kidding me? So what if the aliens don't know math, according to what you just said? Sun Tanji asked.

Mark shook his head: "The expression may be different, but mathematics itself is part of the truth of the universe, and it is impossible to make an interstellar voyage or do more if you don't even understand the most basic mathematics." Didn't you hear that the recording was a sequence? ”

"Sequence?"

"Yes, if every 'tick' represents a 1, then you can listen to it all over again and write down the number it represents."

"Okay, I'll try." Mark put on his headphones again.

"2, 3, 5, 7, 11, 13, 17......" Mark read out the numbers as he listened, but the sound became longer and longer, and he couldn't remember it, so he took off his headphones and asked, "Then what does this have to do with your conclusion?" ”

"Mark, didn't you notice that this sequence is actually ...... A series of prime numbers? Sun Tan said the most crucial point.

"A series of prime numbers? It seems like...... Yes, indeed. ”

Sun Tan slowly threw out his astonishing judgment: "That's right, a prime number is a number that can only be divisible by 1 and itself, which is an iron-like mathematical definition that is universal in the whole universe. The purpose of sending a series of prime numbers in the signal is to confirm whether we are intelligent beings. ”

Only intelligent beings can understand what mathematics is, what prime numbers are, and what is a series of prime numbers!

And human beings who can understand the concepts of prime numbers and prime number sequences are at least no longer primitive people, right?

"Okay, even if you're right, then why did the aliens on that cube send these primes to the moon? What is their purpose? Mark asked rhetorically.