There is a method that can be used to calculate the distance of the universe called "parallax". The meaning of the word parallax is not difficult. You put a finger about 8 cm in front of your eyes, and you only look with your left eye, then with your right eye You will feel that your finger has moved the position for the distant scene, because when you go to see it twice, the angle is different. Now you move your finger away, for example, straighten your arms, and then look at the last method, this time you will feel that your finger is moving relative to the background, but the amount of movement is not so large. Therefore, the size of the finger moving relative to the background can be used to determine the distance from the finger to the eye. According to the article, the correct expression of the definition of "parallax" is:. ['The distance between the object and the eye is called parallax.', 'Parallax is the displacement of an object seen by the eye relative to the background.', 'Parallax is the visual difference caused by looking at an object from different angles.', 'Parallax caused by looking at objects from different angles is called parallax.']