Been meaning to get back to alkemical's map of the Universe's redshift and two fallacies of redshift.
Q: What's redshift and the accompanying blueshift?
When light travels through space, if that space is expanding (Universal expansion) the wavelength is stretched and turns redder. If the space is not expanding or not much, the light largely keeps its originating wavelength - notice the purple on the map's legend is zero expansion, not contraction.
Redshift is not caused by a star moving away from us or blueshift if it's traveling toward us, as in the Doppler effect. ie; If a car driving towards you honks it's horn and flashes it's lights, the sound will be at a higher pitch due to the forward velocity, but the light will be the same wavelength as when the car is parked. This is because sound's velocity is dependent on density while light is a constant.
Fallacy #1 - Gravitational Red/Blueshift
It has been theorized that as light enters a gravitational well, like reaching the surface of Earth, it blueshifts because time moves slower the deeper you go into a gravitational well (ie; a clock on Mercury would tick slower because it's proximity to the Sun). The problem with that theory is frequency, like the speed of light, is dependent on the rate of time aka as time slows, so does the speed of light and frequency, linearly. The only way for light to actually blueshift is if space itself is contracting and squeezing the wavelengths together into a higher frequency.
In the theory I earlier proposed of mass/gravity affecting the expansion of space, therefore determining the shape and expansion of the Universe, gravity would slow expansion and, if strong enough, begin contracting space around it. This would be shown in two ways; 1) light passing through a gravitational well would be diverted by the contraction, or inflow, of space 2) light observed contracting from this inflow would blueshift. So while localized lensing and blueshift of light is currently defined as an effect of gravity, I'd submit it's actually an effect of the contraction of space due to gravity. A technicality, but important.
Gravitational redshift is currently theorized as light expanding leaving a gravitational well, but the light would actually be blueshifted by the contracting space within the well. The only way light could appear redshifted coming from a gravitational well is when it's directly around blackholes and space is being stretched enough to overcome the blueshift encountered in contracting space outside the immediate vincinity.
Fallacy #2 - Redshift is an accurate means of cosmologic measurement
The current theory that all the Universe expands at the same rate, regardless which direction you look, implies that the farther away a star, galaxy, ect is, the more expanding space the light has traveled through. Therefore, the more light is redshifted, the farther away its source is. But if the Universe is not expanding uniformly, redshift cannot be used to measure distance.
- If light is emitted from an area high in gravity, it will be blueshifted from the contracting space. It may then travel across space where expansion has halted due to local gravity and neither redshift or blueshift during that time. It may then travel through gravitationally 'clean' space and begin redshifting on its way to Earth.
- If light is emitted from an area low in gravity and travels here through gravitationally 'clean' space, it will arrive soley redshifted.
If the light in the above two examples traveled the same distance to Earth, the first one may not be, or only slightly be redshifted and the second highly redshifted. The current theory of redshift = distance would interpret the second source of light as originating from much farther away. Likewise, the first light source could originate billions of lightyears farther away, but have the same redshift as the second light source by the time it reaches Earth.