NoelC wrote:If the speed of light is changing (in my mind another way to think of the "expansion" of space-time - am I way off base?)...
I do think that's off base. The expansion has no connection with c, but only shifts the wavelength as the intervening space expands.
...then is it really meaningful to think in terms of distance?
There is some kind of meaning there, but perhaps it isn't so useful. Cosmologists generally look at
z, the redshift, as the fundamental unit, and it isn't usually felt necessary to convert this to a distance- except in press releases <g>.
Not to mention that the distances are virtually unimaginable anyway.
Are they? I don't find it difficult at all to think in terms of billions of light years. These seem like natural and easy units for measuring the Universe. It's no different than thinking in fractions of nanometers for many atomic scale examples. I think the problem comes when people try to tie together units that are radically different, like directly comparing the distance to the supermarket to the distance across the observable Universe. But there's no need to do that.
I like that this map is presented in % of C as opposed to trying to describe things in terms of distance.
The map is not really showing a percentage of c. That would be a velocity. The map is showing redshift, which is a ratio of the apparent recessional velocity to c- a unitless value.
[quote="NoelC"]If the speed of light is changing (in my mind another way to think of the "expansion" of space-time - am I way off base?)...[/quote]
I do think that's off base. The expansion has no connection with c, but only shifts the wavelength as the intervening space expands.
[quote]...then is it really meaningful to think in terms of distance?[/quote]
There is some kind of meaning there, but perhaps it isn't so useful. Cosmologists generally look at [i]z[/i], the redshift, as the fundamental unit, and it isn't usually felt necessary to convert this to a distance- except in press releases <g>.
[quote]Not to mention that the distances are virtually unimaginable anyway.[/quote]
Are they? I don't find it difficult at all to think in terms of billions of light years. These seem like natural and easy units for measuring the Universe. It's no different than thinking in fractions of nanometers for many atomic scale examples. I think the problem comes when people try to tie together units that are radically different, like directly comparing the distance to the supermarket to the distance across the observable Universe. But there's no need to do that.
[quote]I like that this map is presented in % of C as opposed to trying to describe things in terms of distance.[/quote]
The map is not really showing a percentage of c. That would be a velocity. The map is showing redshift, which is a ratio of the apparent recessional velocity to c- a unitless value.