In extreme shock, Mark was stunned for half a minute before he came back to his senses and asked these two key questions: "Why do you dare to be sure that it was posted by that thing? And why are you sure that it is an alien?"

Sun Tan was not disturbed by Mark's rhetoric. Instead, he looked like "I knew you were going to ask this" and began his long explanation.

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

This starts with the medium-sized private long-wave reception radio station exclusively invented by Sun Mingshi, a ancestor of more than a dozen generations, of Sun Tan. As Sun Tan introduced before, the bands it can receive and emit are something that no one or any organization on earth except the Sun family cannot do.

Sun Tan has been using it continuously, whether on Earth or within the month he has just arrived on the moon, at least he is sure that this thing has never received any signal since he was born.

Sun Tan is 24 years old this year, which means that no celestial body within at least 24 light-year distance has sent out a signal that radio can receive in the past 24 years. Why dare to say this? Because all celestial bodies within 24 light-years have been fully mastered by current human observation methods, humans can be sure that there are no signs of other alien life and all alien life activities within this distance.

And the day after the earth was suddenly hijacked by a cube, the medium-sized private long-wave receiving station received the signal, and the information behind it was obviously self-evident.

Mark immediately retorted and asked, how could you be sure of this? Anyone with a little bit of basic physics and cosmic knowledge can make an assumption: this signal comes from n light years away, and happens to be launched towards the moon in n light years. (Here n>24)

For example, the famous Taurus Aldeba

a

), although it is a red giant, and will end its life in 5 million to 10 million years, it has 5 planets and is regarded by humans as one of the most likely regions of intelligent life.

aldeba

a

The distance from the moon is 68 light years. What if this signal is that the intelligent life on one of its planets was sent 68 years ago and has just arrived on the moon?

Regarding Mark's question, Sun Tan smiled slightly and had already prepared the answer. This is the second question, and what exactly is this set of signals.

Sun Tan once again asked Mark to put on his headphones and listen to the signal recording just now, but Mark was still confused and completely confused.

"Mark, first of all, I want to let you understand an incredible fact, that is, how do you think if there were really aliens, how would they communicate with humans?" Sun Tan asked.

Mark thought for a while and replied without imagination: "Writing? Language with sound? Or drawing? Or creating some astronomical phenomena for us to observe?"

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

Use words to communicate, not to mention whether the other party is likely to understand the hundreds or thousands of different words that the Earthlings already exist. Even if they have this ability, they may not use them at all, because aliens may not necessarily have words.

To give a simple example, if a certain alien is in a group, we imagine it as a bee swarm. There is only one order sender in the entire bee swarm, that is, the queen bee. It has ideas and can issue commands, but it does not require words, but only brain waves. All bees in the bee swarm receive commands and execute them unconditionally. Does this alien need words? Of course, the answer is not. If they do not need words themselves, can they use words to communicate with people on earth? Of course, the answer is not.

Similarly, language is the same thing. If the other party does not have an auditory system and cannot feel the vibration of the air, or even take a step back, there is no air, let alone sound in the environment where aliens live. Then will it use sound to communicate with humans? It is even more impossible.

Similarly, it can be proved that drawing and astronomical observations are all nonsense, because these assumptions have a premise, that is, imagine aliens as groups with similar functions as humans.

Although we humans call alien life an alien "human", we have not said that it is really human!

"So, all of your assumptions are not valid. Let me tell you a hypothesis that has not been proven so far, but it is basically the most reliable assumption of how different intelligent life groups communicate."

According to Sun Tan, the reason why the universe we live in is called the universe is because it consists of time and space, just like the simplest sentence in the ancient Chinese "Huainanzi": "In the past and present, 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 surprisingly consistent with the modern explanation.

So what are the common things or laws in the same universe? What you can think of at the first time are things that have become truth in the current universe, such as constant speed of light and absolute zero.

But Sun Tan told Mark that if these contents are difficult to express for two completely different groups of life, the only simplest rule is mathematics.

"Mathematics? Are you kidding me? Then according to what you said just now, what if aliens don't understand mathematics?" Sun Tan asked.

Mark shook his head: "The expression may be different, but mathematics itself is part of the truth of the universe. If you don't even understand the most basic mathematics, it is impossible to sail interstellarly or do more things. In the recording just now, didn't you hear that it was a sequence?"

"Sequence?"

“Yes, if every 'beep' represents 1, then you now listen to it again and write down the number it represents.”

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

"2357111317" Mark read the numbers while listening, but the sound was getting longer and longer at the back, and he couldn't remember it anymore, so he took off his headphones and asked, "What's the connection with your conclusion just now?"

"Mark, haven't you discovered that this sequence is actually a prime number sequence?" Sun Tan said the most critical point.

"Price sequence? It seems to be."

Sun Tan slowly gave out his amazing judgment: "Yes, prime numbers are numbers that can only be divided by 1 and itself. This is an iron-like mathematical definition, which is common in the entire universe. The purpose of sending the prime numbers sequence first in the signal is to confirm whether we are smart creatures."

Only intelligent creatures can understand what mathematics is, what prime numbers are, and what prime numbers are sequences!

And humans who can understand the concepts of prime numbers and prime numbers are at least no longer primitive people, right?
Chapter completed!