Astronomy Question: Cosmic Expansion and Inter-Atomic Distances?
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A graphical representation of cosmic expansion. Image Credit: NASA/WMAP Science Team
It’s time for another featured question! This week’s featured question is from Gianmario in Finland. If you have a question about Astronomy, feel free to send it in via the contact form , my Google+ page, or even the “Dear Astronomer” Facebook page.
Gianmario asks,
I know that space is expanding at a rate of 2.3*10^-18 cm/s/cm. I figured that means the milky way’s diameter increases by about 2.3 km/s. Fine. Does this also mean that also inter-atomic distances increase, albeit by zepto-meters per second?
Great question Gianmario!
Essentially the forces behind cosmic expansion manifest themselves over large distances. Secondly, the forces that govern intermolecular and submolecular bonds are much, stronger than the forces responsible for said expansion, so no… inter-atomic distances won’t increase, just the distances between large groups of molecules. e.g the distances between galaxies will increase, but individual masses won’t lose density (same mass, larger volume).
Consider cosmic expansion more an issue of geometry than one of stretched taffy. Essentially the expansion causes the distance between two fixed points ( or galaxies separated by vast distances) to increase. The rate of expansion increases at a rate proportional to the distance between the two distant points. Simply put, the farther apart two points, the more the effect of cosmic expansion is noticed.
Edwin Hubble is one of the first astronomers to notice this phenomenon – hence “Hubble’s Law“, which has been measured to be about 74 kilometers per second, per megaparsec. (1 parsec is a bit over 3 light-years)
The effect of cosmic expansion isn’t perceived until you look at things, such as distant galaxies. Ordinary matter, like you, Earth, even solar systems and individual galaxies. are bound together. When you start considering galaxy clusters, separated by many mega-parsecs, cosmic expansion is the more domninant effect between them.
I actually discussed your question with a few other people I know. An interesting way of looking at the situation was explained as such”:
“Take a steel girder and hang it from the ceiling so it’s suspended by one end and supporting its own weight. Climb onto the bottom of the girder, kind of like a clock pendulum. The force you are exerting on the steel girder is trillions more than the force cosmic expansion would have on said girder.“
So there you have it. Based on current theories, the forces of cosmic expansion aren’t strong enough to overcome the forces that bind atoms together. I wouldn’t say there’s absolutely zero effect, just infinitely close to zero.
Ray Sanders is a Sci-Fi geek, astronomer and blogger. Currently researching variable stars at Arizona State University, he writes for Universe Today, The Planetary Society blog, and his own blog, Dear Astronomer
2012-12-04 08:06:34
Source: http://www.dearastronomer.com/2011/08/22/cosmic-expansion-and-inter-atomic-distances/
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