Kepler Planet Signal

Frontier physicist Zhou Ze accidentally discovered a mysterious signal from the planet Kepler, and the whole world was filled with surprise and curiosity. This is the first time that humans have discovered that the deserted universe is full of intelligent signals. After three months of deciphering, they finally learned the meaning of the signal sent by Kepler: Hello, Earth! I believe you have received the signal. We have been following you for three thousand years. With the initial surprise, excitement. Zhou Ze found that there were no more signals coming. Even though the earth kept sending messages, he never received a reply. Humanity's top physicists are in panic. The other party has been paying attention to it for three thousand years. What does this mean? This is definitely not a friendly signal, more like a low growl before an animal attacks its prey. What does it mean? Is the earth falling into a crisis that it has already prepared for?