Gravitational redshift
or Honey I just shrunk the Universe!
Gravitational redshift appears at first to be an interesting aside to the whole Dark Energy and Dark Matter story. However once you understand what is really happening the whole universe story becomes so much simpler, much more plausible.
Later we will look at the Big Bang and Inflation Theory where some extremely ingenious mathematics are required just because they started from the wrong assumptions.
But first we will look at a simple explanation of the current version of redshifts.
"The Doppler effect can happen for light waves too (though it can't be properly understood without knowing special relativity). It turns out that just like for sound waves, the wavelength of light emitted by an object that is moving away from you is longer when you measure it than it is when measured in the rest frame of the emitting object.
In the case of distant objects where the expansion of the universe becomes an important factor, the redshift is referred to as the "cosmological redshift" and it is due to an entirely different effect. According to general relativity, the expansion of the universe does not consist of objects actually moving away from each other - rather, the space between these objects stretches. Any light moving through that space will also be stretched, and its wavelength will increase - i.e. be redshifted.
This is a special case of a more general phenomenon known as the "gravitational redshift" which describes how gravity's effect on spacetime changes the wavelength of light moving through that spacetime. The classic example of the gravitational redshift has been observed on the earth; if you shine a light up to a tower and measure its wavelength when it is received as compared to its wavelength when emitted, you find that the wavelength has increased, and this is due to the fact that the gravitational field of the earth is stronger the closer you get to its surface, causing time to pass slower - or, if you like, to be "stretched" - near the surface and thereby affecting the frequency and hence the wavelength of the light.)
Practically speaking, the difference between the two (Doppler redshift and cosmological redshift) is this: in the case of a Doppler shift, the only thing that matters is the relative velocity of the emitting object when the light is emitted compared to that of the receiving object when the light is received. After the light is emitted, it doesn't matter what happens to the emitting object - it won't affect the wavelength of the light that is received. In the case of the cosmological redshift, however, the emitting object is expanding along with the rest of the universe, and if the rate of expansion changes between the time the light is emitted and the time it is received, that will affect the received wavelength. Basically, the cosmological redshift is a measure of the total "stretching" that the universe has undergone between the time the light was emitted and the time it was received."
Thanks to Dave Rothstein for this extract.
Doppler we all know. Gravitational redshift is just the Doppler of radiation. That is, is goes red when moving away and blue coming towards you. The weird one is Cosmological redshift which it is said to be caused by the expansion of the universe. "the expansion of the universe does not consist of objects actually moving away from each other - rather, the space between these objects stretches". Oh really!
Cosmic gravity aka Dark Energy
So let's take another look from the vantage of the Cosmic Gravity theory.
Our 'universe' is only a small part of a much bigger cosmos.
Dark Energy, the force 'pushing' our galaxies out into the void is actually just normal gravity from the cosmos 'pulling' our galaxies towards the large dark mass of the cosmos where the cycle of matter will complete. More of Dark Matter later.
The universe is not expanding.
There is no need for a mysterious and unexplainable expansion of space. No need to rope in General Relativity and Spacetime to give credence to the theory.
The movement of our galaxies is under the influence of nothing more complicated than good old gravity.
However when the redshifts of the furthest galaxies are measured the high redshift value is put down to Cosmological redshift, the expansion of space.
No need for this additional concept, no need for Cosmological redshift.
It is just Gravitational redshift.
Gravitational redshift is simple. It has even been measured on Earth. Shine a light up and it has a different wavelength than if you shine it down. The difference is tiny but measurable, amazing isn’t it.
The gravitational pull from the cosmos also redshifts the light coming to us from the stars and galaxies, particularly the outer galaxies.
Now the light which reaches us from those far flung galaxies has been going against the flow of gravity for billions of years. The redshift effect is small but over billions of years it mounts up.
I can’t do the maths and the people who can, don’t reply; their loss!
So no Cosmological redshift, it’s just gravity. Just like Dark Energy; it’s just gravity.
Another outcome of this relates to the size of the universe.
Those galaxies far out there are not travelling as fast as reported. Yes they are accelerating away from the attraction of cosmic gravity. Speed at these distances is measured as redshift. Some of the measured speed, or redshift, is gravitational redshift.
They are not really moving away so fast.
They are therefore not as far away.
The observable universe is smaller than we think.
‘Honey I shrunk the Universe’.