MadSci Network: Astronomy
Query:

Re: Are the spaces between particles that make up atoms getting larger?

Date: Mon Mar 8 21:59:22 2004
Posted By: Suzanne Willis, professor,Northern Illinois University
Area of science: Astronomy
ID: 1077064920.As
Message:

Hello, Carl -

Well, I think the best response comes from Ask the Astronomer: 
 http://www.astronomycafe.net/qadir/acosmexp.html

"Am I being stretched along with the expansion of the universe?"

"No. The 'stretching' of space in Big Bang cosmology only happens on very 
large scales in the universe of millions of light years or greater. It is 
not something we can detect at our scale because local space-time is 
determined not by cosmology, but by the fact the Earth and Sun are nearby; 
and their gravitational fields do not produce a constantly dilating 
background space."

So the spaces between particles would not be stretched either.

Here are some more questions and answers from the same site:

"Wouldn't the expansion of space show up inside the solar system in the 
predicted positions of the planets?"

"No, and for a variety of reasons. The most significant reason is that the 
gravitational field of the Sun and the Milky Way are stronger than the 
local gravitational field of the universe. This means that the dynamics of 
spacetime in our solar system and Milky Way are dominated by the curvature 
produced by these local masses. As an example, if the cosmological 
expansion could be detected in our solar system, its 60 
kilometers/sec/megaparsecs would translate into a space dilation rate of 6 
centimeters per second per parsec, or for a scale inside our solar system, 
0.0002 centimeters/sec per billion kilometers. In 100 years this 
stretching would amount to 6.2 kilometers at the solar system scale, and 
186,000 kilometers at the interstellar scale. Neither of these are 
measurable, nor is there any physical reason from general relativity why 
they should even be present given the strength of the local sources of 
gravity which completely overpower the effect."


"Why don't the distances between stars also 'expand' with the universe?"

"A good question. The answer is that general relativity eventually joins 
smoothly with ordinary Newtonian physics, just as special relativity does 
for low enough velocities. By the time you get to scales comparable in 
size to individual galaxies, the character of space-time is controlled not 
by the comparatively weak gravitational fields of the cosmos, but by the 
stronger gravitational fields of individual stars, star clusters and the 
rest of the contents inside a galaxy. These fields are strong enough to 
maintain the dynamical integrity of a galaxy against the expansion of the 
rest of the universe. Clusters of galaxies, however, are in some cases so 
large that they do not remain cohesive against the so-called Hubble Flow, 
and so the physics of these vast systems can require a 'cosmological 
correction' due to the expansion of space. Stellar distances, however, are 
controlled by the gravitational physics of their immediate environment, 
and there are no cosmological corrections of any significance. 
Interstellar space, therefore, does not stretch the same way that 
intergalactic space does under cosmic expansion."





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