Why is there no dust in elliptical galaxies? Firstly the universe is rational and the rationality is proportion at large scale systems such as galaxies. Proportion means that the distribution of matters in the universe is orderly. For example there are four giants standing in array. Their heights are respectively A B C D and A B stand in the first row from left to right C D in the second row from left to right. Proportion requires that A divided by C be equal to B divided by D. Rational structures are either circularly symmetric with respect to the center point or bilaterally symmetric. Secondly spiral galaxy arms are neither circularly symmetric nor bilaterally symmetric. Therefore arms are not rational structure. Arm patterns exist only in spiral galaxies and they are weak compared with the main disk structure of spiral galaxies. Therefore the presence of arm structure is the disturbance to the rational structure. Because arm patterns exist only in spiral galaxies and only spiral galaxies present dust Dr. He comes to the critical answer to the above question: any disturbance to rational structure produces cosmic dust! From now on we call the disturbance to rational structure the cosmic impulse. Therefore the universe is originated not only rationally but also impulsively!