- #36
OscarCP
Care to explain? Reading argued comments about it was the whole point of putting the URL here.
That is correct. In a universe with anisotropic speed of light the age of the universe is also anisotropic due to anisotropic time dilation. From the “fast direction” we receive immediate light from a very young part of the universe as it is now. From the “slow direction” we receive delayed light from a currently old part of the universe back when it was much younger. Thus we currently receive light from the early universe in all directions.OscarCP said:Becase if the light sources' positions change with their coordinates and their distances to us and between themselves change, all of it so the redshifts stay the same if light is stipulated to be different in different directions, those things, distances and age of the universe, it seems to me, won't stay the same.
Thanks for this answer. A very interesting concept that helps me understand this fact never encountered before that the one-way speed of light is impossible to measure.Dale said:That is correct. In a universe with anisotropic speed of light the age of the universe is also anisotropic due to anisotropic time dilation. From the “fast direction” we receive immediate light from a very young part of the universe as it is now. From the “slow direction” we receive delayed light from a currently old part of the universe back when it was much younger. Thus we currently receive light from the early universe in all directions.
Why would it be “without knowing first … what it is in any given direction”. Since the one way speed of light is a convention, it cannot be an unknown. We know it as soon as we choose it. We don’t have to wait to know.OscarCP said:Thanks for this answer. A very interesting concept that helps me understand this fact never encountered before that the one-way speed of light is impossible to measure.
But I wonder now, how would one know that what is seeing are "now" and "long ago" parts of the same earlier universe and not parts of the universe of different ages, without knowing first that the speed of light is not the same in all directions and what is it in any given direction?
Well, confused again, I'm afraid. You seem to be saying, keeping your most recent statement in mind, that by changing our choice of one-way speed of light convention we change how the universe looks like to us: some old parts as they are now, some as they were then. I really doubt you meant to say that. Do you mean: "We know as we choose it, based on the two-way measured speed of light?" (And on the assumption that this speed, in a given direction, is the same anywhere and anywhen in this direction?)Dale said:Why would it be “without knowing first … what it is in any given direction”. Since the one way speed of light is a convention, it cannot be an unknown. We know it as soon as we choose it. We don’t have to wait to know.
No. We see the young side of the universe as it is now (because the light is fast on that side) and the old side of the universe as it was long ago (because the light is slow on that side).OscarCP said:some old parts as they are now, some as they were then
We don’t choose the two way speed. That is measured and not a convention. We only choose the convention for the one way speedOscarCP said:Do you mean: "We know as we choose it, based on the two-way measured speed of light?"
Hmmm ... And why couldn't it be the other way around? Or some other way that is neither?Dale said:No. We see the young side of the universe as it is now (because the light is fast on that side) and the old side of the universe as it was long ago (because the light is slow on that side).
Because the other way around wouldn’t fit observations.OscarCP said:Hmmm ... And why couldn't be the other way around?
For example ... Or, because it would result also in some kind of causality violation?Dale said:Because the other way around wouldn’t fit observations.
They're both coordinate dependent, not invariants. (It is actually possible to define an invariant "age of the universe", but it takes some care.)OscarCP said:You don't mean to say that the distance to stars and galaxies and the age of the universe are irrelevant, do you?
That's correct, all of these things are coordinate dependent and will change if you change coordinates.OscarCP said:Becase if the light sources' positions change with their coordinates and their distances to us and between themselves change, all of it so the redshifts stay the same if light is stipulated to be different in different directions, those things, distances and age of the universe, it seems to me, won't stay the same.
You can start here:OscarCP said:rather than a repeated blanket statement about "invariants", I would prefer an explanation or a reference that actually explains things beyond technicisms.