Simply put: because there is no practical significance, the fourth universe speed has almost no guiding significance for the current scientific development of mankind. In one sentence, it is: it is a pity that food is tasteless and discarded!
Why do you say that? Let's briefly understand the definition of the speed of the universe.
The first speed of the universe: the lowest speed orbiting the earth, which is 7.9 kilometers per second.
Any object on the ground wants to orbit the earth, the minimum flying speed must reach 7.9 kilometers per second, this speed is based on the earth as the reference frame, flying at this speed will not fall on the ground. Of course, 7.9 kilometers per second is only a theoretical calculation value. The speed of the satellite above the earth is usually slightly lower than the speed of the first universe.
The reason is very simple. The speed of 7.9 kilometers per second is calculated when operating close to the ground, but in fact, there is no satellite flying close to the ground. The atmosphere near the ground is very dense, and flying around the earth is not realistic, the lowest The altitude of the satellite is more than 100 kilometers.
As the altitude increases, the gravity of the earth decreases, and the orbiting speed also decreases, but not much, about 7.8 kilometers per second.
Second universe speed: 11.2 kilometers per second.
also uses the earth as the reference frame. When an object's flying speed reaches 11.2 kilometers per second, it can escape the restraint of the earth's gravity and become a "satellite" of the sun, so this speed is also called the earth escape speed.
All probes launched by humans to explore other planets must reach this speed, except for one planet, which is the moon, because the moon is still within the gravitational range of the earth, and it is a satellite of the earth. The speed of the probe flying to the moon is only about 10.8 kilometers per second.
Third universe speed: 16.7 kilometers per second, which is also the speed of escaping from solar system .
reached a speed of 16.7 kilometers per second,It can escape the gravitational restraint of the solar system, fly out of the solar system, and orbit the Milky Way. In fact, this speed can also be regarded as the minimum speed obtained by zero potential energy at infinity from the surface of the sun. This means that an object falling from infinity to the sun will reach the surface of the sun at a speed of 16.7 kilometers per second. Of course, this is an ideal situation.
Very few probes launched by humans reach or exceed the speed of the third universe. The famous probe Voyager 1 spacecraft is one of them. The probe launched by NASA in the 1970s is currently It has already entered the outer solar system (note that it is not outside the solar system), but it will take tens of thousands of years to fly out of the solar system.
Here comes the question, what is the speed of the fourth universe? How is it defined?
The fourth cosmic speed, that is, the speed of escaping from the Milky Way. According to Newton's theory of universal gravitation, this speed is about 120 kilometers per second. At this speed, you can fly out of the Milky Way.
However, this speed is obviously not very convincing, and it has not been accepted by the mainstream scientific community. why?
Because the escape speed is mainly related to the quality of the escape target. The diameter of the Milky Way is at least 200,000 light years , how big is its total mass? It is really difficult to calculate, and the scientific community does not have a clear answer.
At the same time, coupled with the emergence of dark matter and dark energy , which scientists don't know very well, it is even more difficult to calculate the total mass of the Milky Way!
And the fourth speed of 120 kilometers per second is only a value calculated according to Newton's theory of universal gravitation. In such a vast space of the Milky Way, it is inevitable that there will be large errors in universal gravitation.
There is another point. From the current traditional chemical energy used by human beings, it is impossible for us to reach a speed of 120 kilometers per second.Unless there is a radical change in energy (such as the nuclear fusion propulsion system), traditional chemical energy will never reach this speed. The efficiency of this traditional energy is too low!
In fact, in addition to the fourth cosmic velocity, there is a fifth and sixth cosmic velocity, but these two cosmic velocities are less convincing.
The fifth cosmic speed is the lowest speed to get rid of the local galaxy group, about 2000 kilometers per second. And the sixth cosmic speed is the lowest speed to get rid of this supercluster. This speed is almost close to the speed of light!
Of course, in terms of the vastness of the Milky Way, the local galaxy group, and the local supercluster, it is almost impossible to escape even if the escape velocity is reached. The speed of 120 kilometers per second spans a distance of 200,000 light years? too difficult!
Someone might think of how fast is the escape from the universe? This is even more sci-fi. Can you escape the universe beyond the speed of light? Perhaps, this is no longer in the scope of scientific discussion, and science does not allow to exceed the speed of light (absolute speed exceeds the speed of light), we can only indirectly "beyond the speed of light"!
.
