The end of the earth seems far away for human beings!
But in 1985, Soviet astronauts discovered a strange phenomenon: the abnormal rotation of the nut, which made the Soviet Union suspect that the end of the earth might be close!
So what's going on here?
The Janibekov effect
It is said that in April 1982, the Soviet Union's second-generation space station Salyut VII began to operate in orbit. However, after less than 3 years of operation, on February 11, 1985, the main radio transmitter of Salyut VII was shut down.
At that time, the ground command center thought that as long as the restart could be solved, but what was never expected was that after the ground command center issued a restart command, the transmitter did not respond at all, and even the radio receiver went on strike. The Salyut VII completely lost contact and became a "kite with a broken line." So what to do?
Astronauts could only be arranged to go up for repairs, in order to avoid the United States from taking the lead. On June 6, 1985, the Soviet Union urgently launched the Soyuz T-13 to repair it.
The Soyuz T-13 spacecraft carried two astronauts, one named Vladimir Janibekov and the other: Victor Savinikh.
On this mission, Janibekov not only successfully completed the mission, he also discovered a phenomenon: in the microgravity environment of space, the butterfly nut will appear to be "periodically flipped". So what is a "cyclical flip"?
What we need to know is that in general, flipping needs to be flipped around an axis, the space we are in is three-dimensional, and all kinds of objects (rigid body, the same below) are also three-dimensional, so in fact, any object has three axes. In general, the flip of the butterfly nut should be rotated around one of its own spindles, which is a common phenomenon in our previous cognition.
However, Janibekov found that the spindle when the butterfly nut is flipped is unstable, and a 180-degree periodic flip occurs, which is also known as the Janibekov effect.
I believe that many people must be very confused when they see this, this "Janibekov effect" does not seem to be so unusual, why does it make the Soviet Union suspect that it is related to the end of the earth?
The Earth rotates
To understand this problem, we have to start with the rotation of the earth itself.
According to previous understanding, if an object is not affected by any external force, it should be rotating around a main axis, and the earth should be rotating around its own axis of rotation all the time. So the problem is, if this spindle is periodically flipped, it means that the Earth's axis of rotation may also flip. If the earth really flipped, then everything on the earth will definitely be reshuffled, and the mass extinction of organisms will certainly not be avoided.
A research team once published a paper in the academic journal Science, in which they found that in the process of geomagnetic field reversal, the extinction rate of species on Earth will be significantly accelerated, mainly because the reversal will lead to a significant weakening of magnetic field strength, ozone content reduction, and global climate changes.
So, when the Ginibekov effect was inadvertently discovered, Soviet scientists could easily link geomagnetic field reversal to the Janibekov effect. As a result, Soviet scientists at that time believed that the Janibekov effect contained the secret of the destruction of the earth, so it was kept secret for a long time.
Tennis racket theorem
Although the Soviet Union has been keeping this secret, in fact, 6 years later, in 1991, a research team explained the reasons behind the Janibekov effect and proposed the principle: the tennis racket theorem.
To understand this "tennis racket theorem," we need to talk about a physics concept: the moment of inertia.
"Moment of inertia" is actually very difficult to approach the concept of "inertia" in dynamics, it is mainly used to describe rotational motion, the specific definition is as follows:
Moment of inertia is a physical quantity that measures the ease with which an object in motion changes from a state of rotation to a state of rest, or from a state of rest to a state of rotation.
The research team found that if rotated around different spindles, the moment of inertia of the object is likely to be different. Take tennis rackets as an example, there are three different spindles that can be found in tennis rackets.
If the tennis racket is rotated around three different spindles, the moment of inertia of rotation of the rotational motion of the three spindles at this time is different.
The research team found that the moment of inertia is the second largest rotational motion, and its spindle is unstable and will flip. The rotational movement with the largest moment of inertia and the rotational movement with the smallest moment of inertia are stable, and there will be no spindle flipping.
Therefore, whether the earth will have a spindle reversal in the end, you only need to see whether the earth's main axis corresponds to the situation where the moment of inertia is the largest. Since the interior of the earth is not completely solid, there are also substances such as magma that require liquid state, which causes the earth to be the rotational movement with the largest moment of inertia, which is in line with the principle of minimum energy. Therefore, the main axis of the earth does not flip.
Not only that, due to the existence of the Moon, and the proportion of the Moon relative to the Earth is not small, its gravitational force can actually play a role in stabilizing the Earth's main axis.
Therefore, it is almost impossible for the earth's main axis to flip, let alone talk about the destruction of the earth.