Cosmological Red Shift

Discussion in 'Astronomy, Exobiology, & Cosmology' started by The God, Apr 3, 2016.

  1. The God Valued Senior Member

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    https://en.wikipedia.org/wiki/Redshift...says

    ........As a result, photons propagating through the expanding space are stretched, creating the cosmological redshift.......


    Now from a remote Galaxy, we hardly get few photons, the question is how do you stretch a single photon ??
     
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  3. Russ_Watters Not a Trump supporter... Valued Senior Member

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    I'm not following - you answered the question in the sentence before you asked it. What is the problem?
     
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  5. paddoboy Valued Senior Member

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    Why do you need to ask such questions if you are god?

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    But as your pretentious and arrogant nature is now well known on this forum, let me try and help anyway.
    With cosmological redshift the wave length is lengthened due to the expanding intervening space.
    Lengthening the wavelength of any single photon needs to be considered in light of the duel nature of light.
    Although it must be said that your inquiry, like your other inquiries, including the one's shifted to the fringes, do not appear genuine in nature and merely a means of pushing your well known agenda.


    Here's a couple of proper links anyway.......

    http://astronomy.swin.edu.au/cosmos/c/cosmological redshift


    Cosmological Redshift
    Laboratory experiments here on Earth have determined that each element in the periodic table emits photons only at certain wavelengths (determined by the excitation state of the atoms). These photons are manifest as either emission or absorption lines in the spectrum of an astronomical object, and by measuring the position of these spectral lines, we can determine which elements are present in the object itself or along the line of sight.

    However, when astronomers perform this analysis, they note that for most astronomical objects, the observed spectral lines are all shifted to longer (redder) wavelengths. This is known as ‘cosmological redshift’ (or more commonly just ‘redshift’) and is given by:

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    for relatively nearby objects, where z is the cosmological redshift, λobs is the observed wavelengthand λrest is the emitted/absorbed wavelength.

    Caused solely by the expansion of the Universe, the value of the cosmological redshift indicates the recession velocity of the object, or its distance. For small velocities (much less than thespeed of light), cosmological redshift is related to recession velocity ( v ) through:

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    where c the speed of light. At larger distances (higher redshifts), using the theory of general relativity gives a more accurate relation for recession velocities, which can be greater than the speed of light. Note this doesn’t break the ultimate speed limit of c in Special Relativity as nothing is actually moving at that speed, rather the entire distance between the receding object and us is increasing. This is a complex formula requiring knowledge of the overall expansion history of the universe to calculate correctly but a simple recession velocity is given by multiplying the comoving distance (D) of the object by the Hubble parameter at that redshift (H) as:

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    Doppler Shift: the wavelength of the radiation detected depends on the motion of the object at the instant the photon was emitted.
    Credit: NASA/JPL-Caltech


    Although cosmological redshift at first appears to be a similar effect to the more familiar Doppler shift, there is a distinction. In Doppler Shift, the wavelength of the emitted radiation depends on the motion of the object at the instant the photons are emitted. If the object is travelling towards us, the wavelength is shifted towards the blue end of the spectrum, if the object is travelling away from us, the wavelength is shifted towards the red end. In cosmological redshift, the wavelength at which the radiation is originally emitted is lengthened as it travels through (expanding) space. Cosmological redshift results from the expansion of space itself and not from the motion of an individual body.

    For example, in a distant binary system it is theoretically possible to measure both a Doppler shift and a cosmological redshift. The Doppler shift would be determined by the motions of the individual stars in the binary – whether they were approaching or receding at the time the photons were emitted. The cosmological redshift would be determined by how far away the system was when the photons were emitted. The larger the distance to the system, the longer the emitted photons have travelled through expanding space and the higher the measured cosmological redshift.



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    Cosmological Redshift: the wavelength of the emitted radiation is lengthened due to the expansion of the Universe. In this animation, the galaxy on the left was formed a long time ago, while the galaxy on the right was formed more recently. Although each galaxy emits the same wavelength of the light, the light from the left hand galaxy has spent longer travelling through the expanding Universe, and has therefore experienced a greater ‘stretching’ (redshift). Astronomers are able to determine how far away distant objects are by measuring this wavelength expansion.
     
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  7. paddoboy Valued Senior Member

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  8. The God Valued Senior Member

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    How does the spacetime expansion stretch a photon ? Try this it will take you to deeper understanding of the subject.
     
  9. The God Valued Senior Member

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    Paddoboy,

    Your copy paste is the definition part/just the statements, it does not answer the question...see my above post.
     
  10. Daecon Kiwi fruit Valued Senior Member

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    How do you think an expansion of space might stretch a wave travelling through it?
     
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  11. The God Valued Senior Member

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    I don't think, it can......So you tell me how a photon can be stretched as given in wiki article or accept that you follow what mainstream says without understanding..
     
  12. Daecon Kiwi fruit Valued Senior Member

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    Okay, enough with the cryptic bullshit.

    If you have something to say, then say it.

    Enlighten us, instead of waiting for us to come up with whatever answer you're thinking of.
     
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  13. The God Valued Senior Member

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    I dont know, I am just asking how a photon, repeat a solitary photon, gets stretched ?
     
  14. Russ_Watters Not a Trump supporter... Valued Senior Member

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    Redshift is caused by relative motion between source and receiver. This is all described in your link and your own quote of it. I don't see how you can just keep asking "how" as if you didn't read your own source. This is very confusing.
     
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  15. Russ_Watters Not a Trump supporter... Valued Senior Member

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    Why do you think saying "solitary photon" changes anything? Do you otherwise understand how redshift works? Describe it.
     
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  16. Farsight Valued Senior Member

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    I don't know.

    People say a photon is redshifted when it climbs out of a gravitational well, but it isn't. It's emitted at a lower frequency. You can see Einstein saying that here: "An atom absorbs or emits light at a frequency which is dependent on the potential of the gravitational field in which it is situated". Once the ascending photon is emitted, it doesn't lose any E=hf energy. In similar vein the descending photon doesn't gain any energy. It looks blueshifted, because you and your clocks go slower when you're lower and you lose energy in line with the mass deficit. If you sent a 511keV photon into a black hole, the black hole mass increases by 511keV/c², not by some other amount. The photon energy doesn't change in a gravitational field. Conservation of energy applies.

    I know of no experiments where energy is not conserved. And I'm afraid I'm not satisfied by the rather glib non-explanation of photon energy loss in cosmology.
     
  17. The God Valued Senior Member

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    Oh my ! you need to read/learn more..

    You are talking about doppler Red Shift, I am talking about cosmological Red Shift, both are different animals...
     
  18. The God Valued Senior Member

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    Your post # 11 (as responded by me in post #14) shows and confirms that you do not have much idea about the subject...and the worst part is that you are putting no efforts to learn either....Yes a solitary photon has a meaning in the context, but first learn the basics please.
     
  19. The God Valued Senior Member

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    Even I do not know, Such a well known point in cosmology, cosmological red shift (z) and still.......
     
  20. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    I'll try to answer the god's question (how expanding space makes a red shirt):

    Imagine a fine Cartesian xy plain holds both a photon and a steel rod parallel to the x-axis. At T=0 the ends of both are at the origin (0,0) and at (1000,0). At some time T=1 later the right end of the photon is still at (1000,0) but the steel rod's right end is at (980,0) as it does not stretch with space expansion as does the grid. The length of the steel rod is the sum of all the spacing between its atoms, and that is determined by their equilibrium positions in their mutual force fields. These forces are determined by the outer shell electron interaction, which don't change; no part of chemistry, also determined by outer shell electrons, changes with the expansion of space.

    The photon does not have any internal length determining forces. The distance between two adjacent wavelength peaks can change, and does. For example, that spacing between adjacent peaks of the wave becomes much less if the photon enters glass from the air or slightly more if the photon passes from air into vacuum. Lacking any internal length determining forces, the photon flexibly responds to its environment.

    If you could make the space between the molecules in glass 10 times larger than normal, the index of refraction would decrease and both the speed and space between the peaks would increase – I. e. the photon's environment is becoming more "vacuum like." As the photon has a fixed number of cycles, each longer, the length of the photon increases - it is "red shifted."

    Just as "expanding glass" produces a red shift, so does expanding space. This analogy is defective (I think, but am not sure) as the index of refraction of space (vacuum), which by definition is always unity, possibly does not change slowly with time - get to be a "lesser unity." For that to happen the magnetic and / or dielectric properties of space / vacuum would need to be changing. I don't know any proof, either way, so they may be. Perhaps these properties of space do change as space becomes "more dilute," much like the properties of glass do as it becomes more dilute.

    An alternate way to understand the red shift of an EM wave long time traveling thru expanding space, is just to accept that unlike the steel rod, the head and tail of the photon are fixed to their postulated positions on the grid. So as it expands the photo grows longer. I. e. "red shifts" as it has no internal forces to hold its length constant, like the steel rod does, and we know photon lengths are determined by the properties of their environment.
     
    Last edited: Apr 4, 2016
  21. Russ_Watters Not a Trump supporter... Valued Senior Member

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    The effect works the same. All that is different is the mechanism that creates the relative speed between source and receiver. But hey, if you already understand it, why are you asking - why don't you just explain it?
    I'm quite certain I understand this better than you, but if you have an idea, please share it.
     
  22. Russ_Watters Not a Trump supporter... Valued Senior Member

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    Nobody who understands it would say there is energy loss, so I don't know who you are arguing against. Like kinetic energy, photon energy is frame dependent, that's all.
     
  23. The God Valued Senior Member

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    The photon does not have any internal length determining forces, if so then how do you fix a photon between (0,0) and (1000, 0) ?

    What you are talking here is the wave nature of the photon, so what is the meaning of a solitary photon wave, how many peaks, rather how many wavelengths would be there in a single photon pulse ? Is it not incorrect to talk about photon stretching as such ?

    Secondly, we can stretch something if it is tied on one end, how do we stretch a photon wave if it is not tied ?

    In glass media it is absorption and re emission, so it is ok if the re-emitted photon has a different parameters, but a photon travelling in vacum, how does it get stretched....I do not think mainstream explanation is stretching the way we understand..the general understanding is like that HR particle - anti particle kind misunderstanding.


    Can we say that expanding spacetime will not have interstellar dust ? So will the distance between these dust particles will go up ? Surely it should as they are not bound like the stick of your example.....extending this argument if we talk of longitudinal wave which requires medium, fine the spacetime expansion can sretch the wave, as medium particle may be stretched, but transverse wave which requires no medium, how can that be stretched ?
     
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