Why can't we feel expansion?

1. Jan 20, 2008

Manicwhale

I can think of two reasons:

1. Expansion is very small, and therefore not noticeable. That is, space expands by 0.00005% in a year (which does not rule out the universe expanding by say, a million light years in a year), so we don't feel it.
2. Everything expands, so we don't notice it. But then... how did we discover it?

Perhaps I'm partially right, but can someone give a thourough explanation?

2. Jan 20, 2008

Staff: Mentor

The first is true. It is only noticeable at large distance scales.

3. Jan 20, 2008

Manicwhale

Thanks.

Also, in terms of why we'd notice it at any scale, would it be right to say that while space expands, certain forces (e.g. EM, or gravity on larger scales) keep objects (e.g. the earth, or galaxies on larger scales) together, so that the distances (as measured by the lenght of a given object) between objects increase?

4. Jan 20, 2008

marcus

did you mean to say "do not increase"?

In that case I would say that you are right. the expansion of space does not affect the size of ordinary objects, or even things as large as the solar system and our galaxy.

As long as they are held together by physical forces or form bound systems.

the expansion of distances can affect smallscale stuff like the wavelength of light, but the undulation track of a wave is not an object held together by forces like a steel rod. the undulations can get stretched out by expansion, over a long period of time

but typically I think of expansion of distances as affecting only really largescale distance like 100 million LY between galaxies that have nothing to do with each other (not part of some gravitationally bound assembly). Probably 10 million LY is far enough.

I think you have it right but just forgot to type in a couple of words
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To reinforce what Russ Watters said. the current rate of expansion is only 1/140 of a percent every million years
or one percent every 140 million years. So for small distances it would be neglible.

Last edited: Jan 20, 2008