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> Not possible. Redshift is not the only observation we have. The totality of all the observations we have cannot be explained in any other way than an expandin

> Not possible. Redshift is not the only observation we have. The totality of all the observations we have cannot be explained in any other way than an expanding universe. Well..? What are those other observations that point to expansion?

pdonis 2y ago
> What are those other observations that point to expansion? The apparent brightness and apparent angular size of distant galaxies, and more importantly, the relationship between the three observables of redshift, apparent brightness, and apparent angular size. No known model other than the expanding universe predicts the actually measured relationship between those three observations.
- handsclean 2y ago
  That’s just redshift. Redshift alone wouldn’t be evidence of expansion, just relative speed, when people say redshift evidence they mean the relationship between redshift and brightness of a standard candle. And regardless of whether you call it redshift or the relationship between redshift and something else, it would be impacted by a change to redshift.
  - pdonis 2y ago
    > That’s just redshift. No, it isn't. I explicitly described two other direct observations that are not redshift. > when people say redshift evidence they mean the relationship between redshift and brightness of a standard candle. No, they don't. Redshifts of distant objects are directly observed. We don't need a "standard candle" to measure them. Observations of apparent brightness are used to estimate distances to objects by comparing apparent brightness to the absolute brightness of a "standard candle" that is the same kind of object. However, such distance estimates are model-dependent; before they can even be made, the model parameters first have to be estimated using the observed relationship between redshift, apparent brightness, and apparent angular size. > And regardless of whether you call it redshift or the relationship between redshift and something else, it would be impacted by a change to redshift. I have no idea what you mean here.
    - stoperaticless 2y ago
      > Redshifts of distant objects are directly observed How do you know the object is distant? (notion being challenged “more redshift -> more distance”) Please answer. Thanks for the patience.
  - eigenket 2y ago
    Its not just redshift. If you look at very distant galaxies you see their apparent angular size is larger than you expect. https://en.wikipedia.org/wiki/Angular_diameter_distance https://en.wikipedia.org/wiki/Angular_diameter_distance You know how distant objects appear smaller, well in an expanding universe that isn't completely true, very distant objects start looking bigger again. Roughly speaking this happens because the distance between paths different photons take to get to us gets stretched by the expansion. Theres also the very obvious observation of the cosmic microwave background, which isn't explained by any non-expanding universe model.
    - rachofsunshine 2y ago
      To expand on the CMBR bit here for readers who aren't as familiar with cosmology: the current temperature of the CMBR is a result of redshift, but that's not what establishes the need for expansion. No, the problem is that the CMBR seems to be in thermal equilibrium (or more properly to have been in thermal equilibrium at the time of its emission a few hundred thousand years after the Big Bang). The problem with that is that, if the Universe had remained the same size and has the finite age it appears to have, there would not have been time for information from the "north" side of our observable Universe to reach the "south" side. After all, the "north" side's light is only just now reaching us, at the center of our observable Universe, and would have to travel a very long way again to reach the south side. In cosmological/relativity terms, we say they're not causally connected. The obvious explanation for this is that the early Universe expanded from a very small region that was causally connected for long enough to reach thermal equilibrium, and then expanded. So while the "north" side of the observable Universe and the "south" side of the observable Universe cannot communicate from their current positions (and in an expanding Universe will never be able to do so again), they were able to communicate in the past for long enough to establish equilibrium. Without expansion, you need a way for two patches of sky that have never been able to communicate with one another to somehow "agree" to be the same temperature. And that's pretty hard to do.
      - twinsun 2y ago
        Couldn't this be explained by suggesting that the speed of light was faster in the past?
ForOldHack 2y ago
Sit Fredrick Hoyles wimper theory and Joe Halddmens sawtooth theory.

pdonis 2y ago

> What are those other observations that point to expansion? The apparent brightness and apparent angular size of distant galaxies, and more importantly, the relationship between the three observables of redshift, apparent brightness, and apparent angular size. No known model other than the expanding universe predicts the actually measured relationship between those three observations.

handsclean 2y ago
That’s just redshift. Redshift alone wouldn’t be evidence of expansion, just relative speed, when people say redshift evidence they mean the relationship between redshift and brightness of a standard candle. And regardless of whether you call it redshift or the relationship between redshift and something else, it would be impacted by a change to redshift.
- pdonis 2y ago
  > That’s just redshift. No, it isn't. I explicitly described two other direct observations that are not redshift. > when people say redshift evidence they mean the relationship between redshift and brightness of a standard candle. No, they don't. Redshifts of distant objects are directly observed. We don't need a "standard candle" to measure them. Observations of apparent brightness are used to estimate distances to objects by comparing apparent brightness to the absolute brightness of a "standard candle" that is the same kind of object. However, such distance estimates are model-dependent; before they can even be made, the model parameters first have to be estimated using the observed relationship between redshift, apparent brightness, and apparent angular size. > And regardless of whether you call it redshift or the relationship between redshift and something else, it would be impacted by a change to redshift. I have no idea what you mean here.
  - stoperaticless 2y ago
    > Redshifts of distant objects are directly observed How do you know the object is distant? (notion being challenged “more redshift -> more distance”) Please answer. Thanks for the patience.
- eigenket 2y ago
  Its not just redshift. If you look at very distant galaxies you see their apparent angular size is larger than you expect. https://en.wikipedia.org/wiki/Angular_diameter_distance https://en.wikipedia.org/wiki/Angular_diameter_distance You know how distant objects appear smaller, well in an expanding universe that isn't completely true, very distant objects start looking bigger again. Roughly speaking this happens because the distance between paths different photons take to get to us gets stretched by the expansion. Theres also the very obvious observation of the cosmic microwave background, which isn't explained by any non-expanding universe model.
  - rachofsunshine 2y ago
    To expand on the CMBR bit here for readers who aren't as familiar with cosmology: the current temperature of the CMBR is a result of redshift, but that's not what establishes the need for expansion. No, the problem is that the CMBR seems to be in thermal equilibrium (or more properly to have been in thermal equilibrium at the time of its emission a few hundred thousand years after the Big Bang). The problem with that is that, if the Universe had remained the same size and has the finite age it appears to have, there would not have been time for information from the "north" side of our observable Universe to reach the "south" side. After all, the "north" side's light is only just now reaching us, at the center of our observable Universe, and would have to travel a very long way again to reach the south side. In cosmological/relativity terms, we say they're not causally connected. The obvious explanation for this is that the early Universe expanded from a very small region that was causally connected for long enough to reach thermal equilibrium, and then expanded. So while the "north" side of the observable Universe and the "south" side of the observable Universe cannot communicate from their current positions (and in an expanding Universe will never be able to do so again), they were able to communicate in the past for long enough to establish equilibrium. Without expansion, you need a way for two patches of sky that have never been able to communicate with one another to somehow "agree" to be the same temperature. And that's pretty hard to do.
    - twinsun 2y ago
      Couldn't this be explained by suggesting that the speed of light was faster in the past?

ForOldHack 2y ago

Sit Fredrick Hoyles wimper theory and Joe Halddmens sawtooth theory.