Why Doesn't Planetary Distance Change Despite Universal Expansion?
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Understanding Universal Expansion
In response to a subscriber's inquiry, we delve into a fascinating question: How does the expansion of the Universe influence objects that are gravitationally bound? Specifically, does it increase the separation between planets in our Solar System? Furthermore, do measurements like kilometers grow longer due to this expansion?
The Universe is continuously expanding as new space emerges at every location. Consequently, the farther apart objects are, the more space forms between them each second, accelerating their movement away from one another.
However, for objects that are in close proximity, the force of gravity is strong enough to keep them from drifting apart. The gravitational pull they experience overcomes the effects of cosmic expansion. Thus, many objects can actually move closer to one another, although the expansion of the Universe does influence the rate at which this convergence occurs.
Examples of such interactions include galaxies and their clusters, as well as smaller cosmic structures. For instance, even with the Universe expanding, our Milky Way galaxy is gradually approaching the Andromeda galaxy. This is due to the gravitational attraction between them outpacing the rate at which space is expanding between them.
Impact on Planetary Systems
On a planetary scale, the influence of the Universe's expansion is virtually undetectable at present. The change in distance between planets due to this expansion is minuscule—far less than what current measuring instruments can detect.
Currently, the Universe is expanding at an accelerating rate, and most cosmological models predict that this trend will continue. This means that over time, the expansion may become significant even at the scale of star systems and atomic nuclei. Eventually, this expansion could lead to the disintegration of these structures.
This theoretical outcome is known as the Big Rip. According to scientific projections, the Big Rip could occur in about 22 billion years. Prior to this event, galaxy clusters may start to disassemble roughly one billion years earlier, followed by galaxies about 60 million years before the Big Rip, and planetary systems just three months prior.
It’s worth noting that current measures of distance in physics rely on fundamental processes and constants that remain unaffected by the Universe's expansion, ensuring that they do not change over time.
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The first video title is Space DOES NOT Expand Everywhere - YouTube, which discusses the nuances of cosmic expansion and its implications.
The second video title is If the Universe is expanding, where is the centre? - YouTube, which explores the conceptual center of an expanding Universe.