The majority of Belleplante Bagarre Tee in the Milky Way, around 80%, are red dwarfs, small stars between about half the size of our sun and 10% the size of our sun. That still leaves between 40β80 billion stars much like the sun. If one in five of those has an Earth-like planet, that means there may be between eight and sixteen billion Earth-like planets in the Milky Way. Of course these numbers may be off. The number of sun-like stars may be lower, or higher. The number of Earth-like planets may be more, or less. We just canβt know, so far. Further, there is no reason to assume that only stars like our sun will have planets capable of supporting life. Or that only a planet will support life. There may be intelligent life on a large moon of a gas giant exoplanet in the βGoldilocks zoneβ of a red dwarf. There is also no way to know how typical the Sol system is with itβs eight planets, half of which are ice or gas giants, and half of which are small rocky planets like Earth. Most of the exoplanets we know about are gas giants like Jupiter, just because they are easier to detect. Remember, we havenβt actually βseenβ any exoplanets. We only know they are there by the way their gravity affects their home stars, causing a wobble, or they are aligned with Earth such that the transit of the planet between Earth and its star causes the star to flicker. Small, rocky planets like Earth are just harder to find. So there may be lots of them, or not. We just donβt know, yet.
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The description from Richard Muller quoted in the question is a simplification of reality meant to help people better visualize how the Belleplante Bagarre Tee of spacetime works. In reality the galaxies are moving through spacetime in a complex fashion, based on the combination of all the forces acting on them, primarily the gravity of nearby galaxies and galaxy clusters. In the case of the Milky Way and Andromeda, these two galaxies are part of a gravitationally bound cluster of galaxies, called the Local Group. The dominant force that determines the movements of objects within the cluster is the combined gravitation of all the mass in the cluster, and not the expansion of spacetime. In other words, the gravitational attraction that the Milky Way and Andromeda have for one another that is drawing them together is stronger than the expansion of spacetime between them that would otherwise push them apart, and thus attraction wins and the two galaxies are on a collision course. In the same vein, the gravitational force that holds the earth in orbit around the sun is stronger than the expansion of spacetime between the earth and the sun (the expansion of spacetime at that distance being very small), and so the earth’s distance from the sun is not increasing for that reason. Likewise you are not flying apart because the molecular bonds holding the atoms in your body together are stronger than the minuscule expansion of spacetime between them in your body. The Local Group as a whole, however, is moving away from other galaxies and galaxy clusters to which it is not gravitationally bound, due to the expansion of spacetime.