It’s my understanding that in astronomical distances, things can be moving further apart by the space between them expanding, *not* simply by motion.
For example, say you have star A, 1 million light years from star B, both completely motionless for argument. These stars have a relative motion because the space between them expands, correct? So 1 million light years becomes 1,000,007 light years after 1 year of time.
If all that is true, does this affect smaller scale measurements? Does a mile of road technically become 1.000007 miles? Please let me know what I’m not understanding.
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[This article](https://www.newscientist.com/lastword/mg25033411-300-does-the-expansion-of-the-universe-apply-to-atoms-and-objects-like-me/) nicely answers your question, but to summarise there’s two factors:
1. This effect is observable over vast distances and times so over human distances it is negligible even for the lifetime of the universe
2. The forces holding us together be it gravity, electrostatic or even forces holding protons and neutrons together, are far stronger than the expanding force caused by dark matter/energy. Should this force increase above these, then yes I guess everything would be ripped apart.
In interstellar space, it would. But in the environments we live in, the gravity of nearby objects is enough to prevent the expansion (which is trying to pull things apart). So the expansion only takes over at very very large distance scales, on the order of tens of millions of light-years, where the expansion can win out against the thinly-distributed galaxies scattered across the Universe.
Matter itself doesn’t expand. Matter held together by gravity or molecular bonds isn’t ripped apart because those forces are way, way stronger than the expansion of space itself. If this expansion keeps accelerating without end, eventually the space between the Sun and Earth will expand faster than gravity can keep them together, and eventually eventually the space between molecules, atoms and particles will expand faster than their forces can keep them together. Fortunately for our descendants 100 billion years in the future, what little evidence we have tells is that the [Big Rip](https://en.m.wikipedia.org/wiki/Big_Rip) isn’t the fate of the universe.
By the sounds of it you’ve confused two different things – time dilation and length contraction. Neither have anything to do with the expansion of the universe.
Time dilation is where time slows down, relative to an outside observer, the more gravity you’re in or the faster you go.
Length contraction is where the faster you go the more the universe shrinks in the direction of travel from the point of view of the travelling object but the more the object shrinks in the direction of travel for outside observers.
What you’re talking about is the expansion of the universe.
I like the balloon analogy. Draw two dots on a partially inflated balloon and inflate it more. The dots move away from each other. Tape a straw at both ends to the balloon and inflate it again. The straws not going to get longer because it has forces keeping it together.
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