If the universe is expanding, then why does the distance between the planets not change?


Again, we answer the question sent by the subscriber:

Our universe is rapidly expanding due to the constant appearance of new space, at every point of the universe. Thus, the further objects are from each other, the more space is formed between them every second and the faster they are from each other as a result of this move away.

However, objects located at relatively small distances are attracted to each other strongly enough not to scatter: the acceleration given to them by gravity turns out to be greater than the acceleration from the expansion of the universe, so most objects may well approach each other, although the expansion of the universe and affects the speed of this convergence.

These objects include galaxies and their clusters, as well as all the smaller structures in the universe. So, for example, despite the expansion of the universe, our galaxy is approaching the Andromeda galaxy. This is because our galaxy and Andromeda are attracted to each other faster than the space between them can expand.

On the scale of planetary systems, the expansion of the universe in our time is practically imperceptible and the distance between the planets because of it changes by an amount many orders of magnitude less than any equipment can register.

Now our universe is expanding with acceleration and, according to most cosmological forecasts, this will not change, which means that over time the expansion will become significant both on the scale of stellar systems and even on the scale of atomic nuclei, at some point all these structures will simply be torn apart by the expansion of the universe ,

This cosmological scenario is called the Big Rip (BR). At the same time, according to the calculations of scientists, a Big Rip will happen in about 22 billion years. Clusters of galaxies will decay about a billion years before BR, galaxies 60 million years before BR, and planetary systems just 3 months before BR.

As for the measures of distance in modern physics, they are determined through physical processes and constants that do not depend on the expansion of the universe, so they do not change.