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purintjp

Light properties in curved space

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I was reading an article about the properties of light and

it was stated that light does not react directly to a

gravitational field but instead reacts to the space-time

curvature associated with the field.

 

Since light from distant galaxies (or even close ones) does

not travel in a straight line from the source to our

observations and instead travels through the expanding space

of a hypersphere in a curve varying with the distance from us,

is this not a de facto curvature of space and could it have

implications for speed and wavelength (specifically the red-

shift) variations ?

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Do you think maybe the original percussions are searching for an atmosphere to slow down into and when they reach the threshold of finite "small"ness they begin to fall back on its origination in the form of energy from sound? which in turn creates the appearance of gravitationally lensed light?>:D

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Do you think maybe the original percussions are searching for an atmosphere to slow down into and when they reach the threshold of finite "small"ness they begin to fall back on its origination in the form of energy from sound? which in turn creates the appearance of gravitationally lensed light?>:D

 

O.o

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Do you think maybe the original percussions are searching for an atmosphere to slow down into and when they reach the threshold of finite "small"ness they begin to fall back on its origination in the form of energy from sound? which in turn creates the appearance of gravitationally lensed light?>:D

 

Huh ????

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My understanding is that gravitational fields ARE curved spacetime. Mass curves spacetime. Using the phrase "gravitational fields" is just another way of referencing curved spacetime. Spacetime curvature is the result of Mass. So, spacetime curvature and gravitational field are essentially the same thing. Gravity is often referred to as a "force". But this isn't strictly true according to Einstien - there is no "force" between the Earth and the Sun, for example. The Sun has lot of mass and thus curves the spacetime around it. Earth is revolving around the Sun because it is following a "straight" line in curved space. Travel in a straight line around the the Earth and you will find that you are actually traveling in a curve around the curved surface/space of the surface of the Earth.

 

So, light definitely is affected by a gravitational field - this has been confirmed by observation many, many times. But that gravitational field is simply the curvature of spacetime that massive bodies cause.

 

Light from distant galaxies (or near ones) or light from any source no matter how far away (or how close) travels in as straight a line as possible in curved spacetime. The light from a street lamp travels to your eyes in a slight (VERY slight, insignificant really) curve because it is following the curved spacetime that Earth itself causes.

 

The speed of light never changes in a uniform medium. In the empty expanding spacetime between distant galaxies, the speed of light never varies. Of course, if the space it is traveling through is expanding, then it will take longer to get through it only because it has farther to travel. Also of course, there will indeed be a red shift in this case.

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I understand all you have stated and don't disagree generally.

What I was referring to was an effect to the red shift

as it pertains to the Hubble constant. I am wondering

how we can end up with a scalar linear constant when light

has been travelling in curved space which is no where near

linear. It would seem that the light could be distorted at

varying degrees during it's journey based on varying curves

as the Universe expands since it has supposedly expanded at

different rates.

Can we really trust this constant ?

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Perhaps a visit to Wikipedia will help: http://en.wikipedia.org/wiki/Cosmological_redshift

 

The discovery of the linear relationship between redshift and distance coupled with a supposed linear relation between recessional velocity and redshift yields a straightforward mathematical expression for Hubble's Law as follows:

 

v = H_0 \, D,

 

where

 

* v is the recessional velocity, typically expressed in km/s.

* H0 is Hubble's constant and corresponds to the value of H (often termed the Hubble parameter which is a value that is time dependent) in the Friedmann equations taken at the time of observation denoted by the subscript 0. This value is the same throughout the universe for a given comoving time.

* D is the comoving proper distance from the galaxy to the observer, measured in mega parsecs (Mpc), in the 3-space defined by given cosmological time. (Recession velocity is just v = dD/dt).

 

Hubble's law is considered a fundamental relation between recessional velocity and distance. However, the relation between recessional velocity and redshift depends on the cosmological model adopted, and is not established except for small redshifts.

 

For distances D larger than the radius of the Hubble sphere rHS objects recede at a rate faster than the speed of light:[14]

 

r_{HS} = \frac{c}{H_0} \ .

 

Inasmuch as the Hubble "constant" is not constant at all, but varies with time in a manner dictated by the choice of cosmological model, the radius of the Hubble sphere may increase or decrease over various time intervals. The subscript '0' indicates the value of the Hubble constant today.

The key concept here is that the Hubble constant is not really constant. If I understand your question correctly (and there's no guarantee of that since you say I didn't answer your question with my previous post), then the variation of the Hubble constant over time and the Hubble sphere increasing or decreasing over time seems to have it covered. If I still don't understand your question, then I'm afraid I'll have to give up and admit defeat. :D

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Perhaps a visit to Wikipedia will help: http://en.wikipedia.org/wiki/Cosmological_redshift

 

The key concept here is that the Hubble constant is not really constant. If I understand your question correctly (and there's no guarantee of that since you say I didn't answer your question with my previous post), then the variation of the Hubble constant over time and the Hubble sphere increasing or decreasing over time seems to have it covered. If I still don't understand your question, then I'm afraid I'll have to give up and admit defeat. :D

 

Thanks for your time and patience. I'll need some time to digest most of this.

I did not realize that the 'constant' varied with the cosmological model.

Is that flat, closed, or open ? Why only for small redshifts ?

How would you conduct an experiment to see how vast distances through

curved space would affect wavelength or can it be extrapolated ?

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