Expanding people in an expanding universe?

[vera]

Help me please!
do'nt know if I'm right here, but any hint leading to a simple answer of the following question would be appreciated:

if the universe is expanding, are we expanding as well?
does my hand expand at the moment?
what about a center of expansion?
what about our point of view?

and how to explain it in a few simple but profound sentences to my physics professor on monday?

 

[UltraPi1]

In an expanding universe it is necessary that something not expand in order to detect it. Apparently we don't expand. Well shiver me timbers! My personal opinion is that current acceptance of the model so closely held to the chest by those in the establishment will be proven wrong.

 

[selfAdjoint]

Notice that atomic forces and such are not dependent on fixed distances but have variable strengths at variable distances. Same with gravitation. So physics will have the scale determined by the strengths of the forces, which don't change (at least in theories that don't have a changing fine structure constant). And the scale of out world is fixed by the scale of physics. So your hand won't change size.

But fixed wavelengths will. The wavelength of a particular batch of radiation is a fixed length, and hence will expand with the universe. hence the CMB. In the far future our broadcasts of "I Love Lucy" will be stretched to kilometer waves.

 

[vera]

finally got it by the "raisins in an unbaked dough"-metaphor.

 

[Phobos]

Welcome to Physics Forums, vera!

Just to help clarify...The expansion of space only becomes significant at HUGE (intergalactic) distances. Within a solar system or galaxy (or even a galaxy cluster), gravity is strong enough to keep matter together against the expansion force. Similarly the structures of your body, atomic forces, etc. are much stronger than the expansion force and keep you together.

As you may have gathered from the raison bread analogy, there is no center or edge to 3D space (guess you need to consider an infinitely large hunk of raison bread). The expansion of space (dough) occurs throughout in all directions, thereby separating all the galaxies (raisons) from each other without a specific center. The further away a galaxy is from ours, the faster it APPEARS to be receding even though the expansion rate is consistent throughout (appears faster because there is more expanding space between you and it as compared to closer galaxies).

Our point of view is relative to us, but not an absolute reference frame that applies elsewhere in the universe. We may see Galaxy A moving away from us, but an inhabitant of Galaxy A would see us moving away from him/her/it.

 

[rdt2]

By a weird coincidence - I've not been to this forum for months and hadn't read all the current threads - I've just asked the same question in a different format:

'If space is expanding, aren't all our measuring sticks expanding with it. Hence, is it not the same _measured_ size as it always was? Although perhaps getting more lumpy?'

Is self-Adjoint's point that you can attribute a 'scale' to each of the (reducing number of) different forces? Does that mean that the ratio of the different force strengths is changing as the Universe expands? What happens when someone comes up with a TOE?

Cheers,

Ron.

 

[Phobos]

helpful explanation by marcus here...
https://www.physicsforums.com/showthread.php?s=&threadid=13011

 

[rdt2]

Thanks, Marcus - is that because there's an elastic aspect to electromagnetism (or electroweak-ism?) force that doesn't apply to gravity?

Does that have any implications for the relative strengths of the forces over time - or does it present problems in the attempt to unify all of the forces?

Cheers,

Ron.