# Can the size of an atom change?

1. Dec 6, 2011

### dumdedo

The big bang theory, leaves me with the impression that atoms can change size.

Is this true?

Can gravitational forces compress, can atoms become smaller?

What regulates an atom's size?

Can adjusting the space/time fabric change the size of an atom?

Thank you for your time. I'm really wondering how all the atoms can fit into the space of a green pea, as computer models suggest.

2. Dec 6, 2011

### mathman

As far as I know gravitation does not effect the size of atoms. Size for atoms is a difficult concept, but the simplest way to look at it is in terms of energy. Increasing the energy of an atom means the electrons are in more energetic levels which take up more room.

3. Dec 6, 2011

### dumdedo

Then forget gravity.

If there is space inside each atom, would it not also have to obey the expansion of space?

http://en.wikipedia.org/wiki/Metric_expansion_of_space

Last edited: Dec 6, 2011
4. Dec 6, 2011

### HallsofIvy

Staff Emeritus
Why would you say "The big bang theory leaves me with the impression that atoms can change size"?

5. Dec 6, 2011

### dumdedo

Because if expansion of space is true, wouldn't the size atoms be related to the size of the Universe?

6. Dec 6, 2011

### phinds

Not at all. The expansion of space has no effect on gravitationally bound objects, such as clusters of galaxies, galaxies, solar systems, planets, you, atoms, etc.

7. Dec 6, 2011

### dumdedo

So, space inside each atom is not effected by the inflation of space? Is that space inside an atom special?

8. Dec 6, 2011

### phinds

Has nothing to do with space, it's the presence of a force that binds the objects together. For macro objects, it's gravity, for micro objects, it's sub-atomic forces.

9. Dec 6, 2011

### dumdedo

Okay. I was just under the impression that if gravity caused macro objects to be pulled towards each other, the galaxies would not be getting farther apart, like they are doing.

10. Dec 6, 2011

### DaveC426913

They are getting farther apart precisely in the empty gaps where gravity is too weak to pull them together.

11. Dec 7, 2011

### dumdedo

12. Dec 7, 2011