Ask a physicist anything. (7)

[Wiccan_Child]

Actually that's very helpful, thank you!

If this is true, why is not space in our own world (and our own bodies) expanding?

As pgp_protector said, gravity. While the metric expansion of space causes all points to move away from each other, actual matter can move through space due to forces and energy.

 

[Tinker Grey]

Last post?

 

[NGC 6712]

If this is true, why is not space in our own world (and our own bodies) expanding?

This is actually a very interesting question that hasn't really been looked at much.

The standard answer has been that universal scales are analysed using the FRW solution to the Einstein field equations of GR - and this necessitates it only applies on the very largest of scales.

Now the solar system - or I should say the solution for a single spherical star (forgetting about rotation/electric charge) is the Schwarzchild solution.

But in reality the universe is a patchwork of these things all added together for which there is no mathematical solution either in practice or even theory.

Now I know some people have investigated modifications to the regime applicable to Solar system scales and get numbers like the radius of the Earth's orbit would have changed by one part in 10^24 over the Earth's lifetime. This effect is dwarfed by other effects let alone being impossible to measure anyway.

For atoms the situation is even more miniscule. Just like we don't take account of gravity when doing calculations in atomic physics the effects of a universal expansion on an atom are utterly utterly negligible and immeasurable.

 

[ChrisBot]

This thread was split automatically after 1000 replies and this thread has been automatically closed.
The new thread automatically created is here: "Ask a physicist anything. (8)"