Since Einstein published his theory of relativity, scientists have repeatedly observed weak deflections of light beams and radio waves when passing near the sun, confirming the gravitational bending effect predicted by the theory of relativity. However, the other two effects predicted by the theory of relativity have not been confirmed by direct measurement so far.
Einstein believed that the huge mass of the Earth would cause a "dent" in the originally straight space-time structure around the Earth. Gravity is actually the curved movement of objects along this "dent" in space-time. In addition, due to the rotation of the Earth, this "depression" in the surrounding space-time structure will be driven to move together, which can slightly distort this "depression" structure into a four-dimensional "vortex" structure. These two phenomena are called the geodesic effect and the inertial frame drag effect respectively.
These two effects are too weak on the earth's surface, and the distortion caused in one year is only one hundred thousandth of a degree, which is equivalent to people looking at an object as thin as a hair from 400 meters away. Due to limitations in measurement technology, scientists have been unable to make progress for decades.
Since it is difficult to observe on the ground, can the experiment be moved to space? In 1959, three American scientists first proposed the idea of ??using artificial satellites to detect gravitational effects. The basic principle is: rotate a A gyroscope is placed in Earth's orbit, with its axis of rotation aligned with a distant star as a fixed reference point. If space is warped, the gyroscope's axis will change slightly over time. Simply by accurately recording how much the gyroscope's axis changes relative to a reference star, the degree of distortion of space-time can be measured.
Almost half a century passed until April 2004, when the "Gravity Probe B" spacecraft used to test these two space-time effects was finally launched. The spacecraft is 6.4m long and has a mass of 3.1 tons. Its main instrument is a very sensitive ultra-high-precision gyroscope. Among them, four gyroscopic balls made of quartz are carefully crafted, with extremely smooth surfaces, and the roundness error does not exceed the size of a few atoms. They are called the most perfect and rounded spheres ever created by humans.
In order to provide an almost ideal space-time reference system, these gyroscopes must be in the quietest environment and not be affected by any external force. The rotating ball is suspended in the center of the gyroscope due to electric field force. In a vacuum state, it rotates at a speed of 10,000 revolutions per minute in a telescope aligned with a reference star. The outside of the telescope is wrapped in a superconducting lead bag, making it unaffected by external magnetic fields. These instruments are placed in an insulated vacuum container cooled by liquid helium, in an environment close to absolute zero, and there are four layers of lead protection outside to isolate any external interference.
If Einstein’s prediction is correct, the curvature of space-time caused by the Earth will cause the rotation of these gyroscope balls to become unbalanced, gradually deviate from the alignment, and cause the gyroscopes to rotate along the same axis as the Earth. Rotate in a direction perpendicular to the axis. Although these changes are subtle, they can be detected by the superconducting quantum interferometer inside the spacecraft. At present, the spacecraft has completed its data collection mission, and scientists are analyzing the data.