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Name: Jordan
Status: student
Grade: other
Country: United Kingdom
Date: Fall 2012


Question:
I've heard that the universe's expansion results in every point in space moving away from every other point with a recessional velocity... does this apply on the scale of molecules, atoms and the subatomic as well? If so; does that mean that all substances are moving away from each other? Doesn't this have some affect on chemical reactions and things?

Replies:
Jordan, the answer to this question depends on the time scale you are concerned with. Chemical reactions happen a lot faster than universe expansion. So if you are talking In very short time scales, like "millions of years", then you can safely ignore universe expansion in chemistry. However, in larger time scales (e.g. billions of years), yes, chemicals are moving apart due to the universe expanding, and eventually the energy (and mass) associated with the universe will spread out enough that chemistry ceases to exist. This is a concept known as "heat death" -- you can read more about "heat death" by doing an Internet search.

Hope this helps, Burr Zimmereman


For now, the recessional rate is quite slow at the scale of molecules or even galaxies. Things move away from each other only if other forces are too weak to keep them in proximity. For molecules and galaxies, their inherent attractions easily overwhelm cosmic expansion.

Richard E. Barrans Jr., Ph.D., M.Ed. Department of Physics and Astronomy University of Wyoming


The expansion of the Universe only results in objects moving away from each other on very large distance scales. Consider that fact that the Moon is in a stabile orbit around the Earth and is not moving away. In fact, the nearest large galaxy, M31, to ours is not moving away from us. In fact, M31 and our galaxy are moving toward each other. This is because the force of gravity between M31 and our galaxy is larger than the effect of the expanding Universe. On larger scales, e.g., clusters of galaxies, objects are moving apart from each other due to the expansion of the Universe. Thus, the expansion of the Universe does not have a measurable effect on atomic and subatomic scales, nor on chemical reactions.

Joseph Bernstein


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