NASA; ESA; Nature; SETIand METI are all wrong;

There are simple and effective basic communication rules that exist between cosmic civilizations. 

I am Fanxing444, a science fiction author.

In the boundless universe, human civilization on Earth is the only lonely one!
Not a single intelligent civilization has ever existed in the universe's 13.8 billion-year history at the very least! 
I've discovered the Pulse of Civilization — the underlying code for communication between cosmic civilizations.

Since the Arecibo Message in 1974, humans have sent radio messages into outer space many times, and all carry humanity's "greetings" without exception.
For this, humans even created a cosmic language:
Starting from cosmic constants like atomic numbers and pi, to data, then binary conversion and compilation — these guides make it easy for “aliens” to decipher our messages. 
This language is logically flawless, even almost perfect.
But why are we so keen on playing guessing games with “aliens”?
So Why not keep it simple?

This is a partial waveform of the Arecibo Message:

Carrier frequency: 2380 MHz, the message's frequency offset range is only 10 Hz.
The core frequency window for galactic communication is 1-10 GHz.
When we put this message into the possible background frequencies of cosmic communication, it's so insignificant.
Will “them” receive the complete message in 2500 years?
Maybe like this:

maybe it's just a bit of noise.

Don't Earth scientists know galactic motion will make them miss the best position to receive the message in 2500 years?
Don't they know each byte of these messages passes a planet in less than 0.05 seconds, and the message may be unreadable if even a part is lost?
Don't they know the 2500-light-year interstellar space is still full of countless galactic matter that interferes with the message?
Don't they know about Doppler shift, gravitational redshift blueshift...?
Then hope that 2,500 years later, on some planet in the M13 globular cluster, there are 'humans' just listening to electromagnetic waves around 2380 MHz, and happen to detect the information within 3 minutes of its arrival?

No, even most ordinary people know these things!
So can 'they' still piece together that famous grid from such electromagnetic waves?
So, what exactly is the meaning of communicating across time and space?
Tell them our biological info, technological level, language, culture and art?
End with a greeting and wait for a reply in tens of millions of years?
No, this makes no sense at all. 

The only meaning I can think of is: to tell 'them' that there are 'people' here, 'kindred spirits' that you can recognize.
So why not make it simple? 
Simple enough that needn't to carry any information.
Like this:

Sure you might say it’ll still get interfered with even like this.
Yeah, "they" might get a signal like this.

But don’t you think it’s still special?
I believe when an intelligent being sees this waveform flickering on a screen, no one can deny this is the civilization mark left by another intelligent species.

This makes me think: when someone visits your home, they’ll knock politely first, instead of standing behind the door and saying, "Guess who I am."
Like the croaks of frogs in the fields, the howls of apes in the mountains.
Their calls carry no information, nor do they require any prior agreement.
As soon as the first call is made, it immediately resonates with others of its kind.
It’s not just frogs and apes—most living things on Earth, even plants, still communicate this way.
This is the most fundamental communication code that nature has bestowed upon all living beings.
Yet humans have forgotten this code ever since we learned to speak.
Humans are the odd one out!
So Shouldn’t interstellar communication in the universe be the same?
This is a consensus reached by cosmic civilizations without any prior agreement.
This is also the only underlying code for cosmic communication that I mentioned at the beginning of this article.

But the truly terrifying thing for me starts with this very code:
This isn’t hypothetical, it’s inevitable: 
all intelligent species, once they enter a technological civilization, will inevitably emit radio waves into the universe.
And they’ll also realize that once electromagnetic waves carry any information, their waveforms turn messy; after interstellar interference and attenuation, they basically turn into unrecognizable noise.

So this is the cosmic rule: Interstellar communication cannot carry any information.
That’s also why the underlying code for cosmic communication is unique.

Thus every civilization will realize the universe forbids sending information-carrying electromagnetic waves between civilizations—unless the two civilizations are very close. The only thing they can send is the simplest and most easily recognizable :"knocks".
This method is so simple.
So simple it’s like a pure axiom, needing no proof at all.

If this is the case, it proves another terrifying fact:
So many “people” in the universe must be doing this simple thing. It requires no advanced technology or massive resources, just a grasp of basic knowledge.
And any civilization that picks up this "knock on the door" will definitely respond.
Not just respond, but send out more "knocks on the door".
Like a frog can never croak just once.
Earthling have already done this many times, even if they haven’t done it my way yet.They’ll surely do it far more in the future, and starting today, they’ll also realize the method I’m talking about.

Now let’s assume this: if there are (or have been) countless civilizations in the universe, then the cosmos must echo with countless "knocks on the door".
In the cosmic time and space measured in billions of years, time passes, civilizations perish, even matter fades away—but the "knocks" never do. Whether in the past, present or future,
these "knocks" will only multiply as the universe ages, and the cosmos should grow ever busier.
This is the unspoken pact of all cosmic civilizations, a thing achieved without prior agreement, not to mention any communication.
All civilizations in the universe—those of the past, present and future—will together forge the radio wave background of cosmic civilizational communication.
It will be just like the cosmic microwave background radiation, never to be erased.

But it’s not the case.
Humans have never picked up a single such signal.

This method is so simple—it’s like a concise axiom, so simple it needs no theoretical support, so simple it defies all doubts!
So why has no “one” done this?
Thus I’ve come to the following conclusion:
We’ve never picked up any "knock on the door" because I’m the only one out of 8 billion people on Earth who’s thought of this simplest way.
Or rather, in the 13.8-billion-year history of the universe, no civilization has ever thought of this simple method.
If these two conclusions are absurd, then there’s only one logical conclusion left: since the universe came into being, only one civilization has ever existed—humanity on Earth.

[From 10 PM the night before to 4 AM now, the atmosphere in the conference room remains heavy.
The President, Prime Minister, Minister of National Defense...all with graying hair, yet not the least bit tired.
Fanxing pulled a sheet of paper from the documents and slid it to the center of the table; everyone’s gaze fell on it.
A single glance let them recognize what was on it,their expressions calm yet tinged with confusion.
This was a piece of information sealed away for nearly 20 years—strictly speaking, five months short of the two-decade mark.
Printed on it was a section of electromagnetic wave signals: three stepped, looping square waves.
"The Cetus Signal—I oversaw this project back then.Is there a problem?" the Prime Minister asked.
Fanxing understood their calmness;every human on Earth knew exactly what this was.
Twenty years ago, a cosmic electromagnetic wave signal that lasted three days stunned the entire world.
Scientists quickly pinpointed its origin: the Cetus constellation.
But strangely, this signal only consists of repetitive three-step square waves, along with those extremely precise intervals.

Everyone thought it was a message from another interstellar civilization.
But strangely enough, no one could decipher any message from it.
Even international organizations offered huge rewards, yet still, no one succeeded.
It’s not so much that the message was indecipherable as that there was no encoded information in it at all
—for the waveform was far too simple.
Unable to make sense of it, people’s enthusiasm faded with time,and so did the attention on this incident. 
What’s more, two decades had passed, with no further signals received in between.
Follow-up observations by the astronomical bureau brought no substantive findings either.
Still, many national organizations back then sent cosmic replies toward the Cetus constellation just as they usually did.
Fanxing: "maybe, I might have deciphered the message on it."
A flash of surprise and anticipation crossed everyone’s faces at once.

Twenty years ago,they weren’t the President or Prime Minister yet—
they were just like ordinary people.
Twenty years ago, that signal that drove the whole world crazy became a mystery in everyone's hearts.
And now, the answer was finally about to be uncovered. 
How could this not thrill them?
All eyes were on Fanxing, brimming with anticipation.
Fanxing said nothing.
He just raised his hand and tapped the table: tap, tap, tap.
A few seconds later, the anticipation on their faces turned to confusion.
“What?” the Prime Minister asked urgently.
“A knock...” Fanxing said.
“that...” The Prime Minister started to speak,then realization hit him at once...
The conference room fell into an eerie silence, so quiet that even heartbeats seemed to echo.
The eager excitement that had just lit up their faces faded into gloom—even a faint pallor and fear.
Yes. In that moment, everyone knew the answer.
“A knock.” It sounded ridiculous, yet it was the only logical answer at this point.
An answer beyond all doubt—the knock of another interstellar civilization, to its neighbor.]

In my story, Earth received a "knock" from another civilization. 
But right now, we haven’t.
Perhaps in countless epochs to come, the physical laws will still forbid humanity from building light-speed spacecraft. Light speed is an eternal prison; humanity will never break free from the solar system, and the so-called advanced civilizations simply do not exist.
Or rather, no matter how advanced a civilization’s technology becomes, no matter how many scientific laws they master, they can never act against the most fundamental ones of all.
Human existence is like a bug in the universe. No one cares about this bug, and the universe certainly doesn't, because spacetime will naturally fix it.
When the solar system meets its end, humanity will seek to send the mark of our civilization into the cosmos, to prove we once existed.

We will try countless methods: launch countless spacecraft into the depths of the universe, strive to build eternal monuments. But in a cosmos measured in billions of years, space and time will destroy everything. All matter will eventually break down into molecules, atoms, fundamental particles—either vanish into nothing, or form new matter to enter the next cycle.
Thus the only indestructible method we can conceive of is the most primitive electromagnetic waves. We will seek to inscribe our history into these waves, yet space and time will still erase all that information—for once information is encoded, the waveform turns messy, and ultimately fades into the cosmic background noise.
In the end, we have no choice but to accept the truth: we can only send out the simplest electromagnetic waves that prove a civilization stands behind them.
This is the only pulse a civilization can leave in the universe! Like an electrocardiogram, it will stand as proof that a civilization once existed there.