In the meantime, astronomers who have observed galaxies got to know the following facts;
(1) There are more than 100 billion galaxies in the Cosmos.
(2) Galaxies are basically forming clusters here and there; several or dozens of galaxies gather to make up a Group.
(3) Galaxies in a Group system are combined by gravity.
(4) Galaxies revolve around the whole gravitational center of a Group system.
(5) The Milky Way Galaxy is also a member of a Group called the Local Group which consists of 30-odd nearby galaxies, including the Andromeda galaxy which is about 2.5 million light-years away from us.
The Amdromeda galaxy at the opposite side of the Milky Way Galaxy in the Local Group, is nearing toward us in the course of its revolution around the whole gravitational center of the Local Group.
(6) The pure rectilinear approaching speed of the Andromeda galaxy is about 50km/sec.
The total rectilinear travelling distance of the Andromeda galaxy during its one time revolution around the Local Group may be about double the distance between it and us; that is 5 million light-years.
Consequently, you can simply figure out the revolution period of the Andromeda galaxy, through dividing 5 million light-years by 50 km/sec.
5 million light-years ÷ 50 km/sec
= (5,000,000×365d×24h×60m×60s×300,000 km) ÷ 50 km/sec
= 9.46 ×10^17sec (10^17 represents 10 to the power of 17; from now, all exponentiations will be written this way.)
When we convert 9.46×10^17 seconds into years, it makes 30 billion years.
This means the Andromeda galaxy has not yet revolved once since the beginning of Cosmic history.
It does not make sense.