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Thread: light traveling through space

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    light traveling through space

    Is it possible that light, from every point in the universe travels like a spiral of a galaxy, except over vastly greater distances. Would there be any way of testing it?
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    Quote Originally Posted by Copernicus View Post
    Is it possible that light, from every point in the universe travels like a spiral of a galaxy, except over vastly greater distances. Would there be any way of testing it?
    I think you need to clarify what you mean about how it travels, and what you imagine would be a test before there is any possibility of a meaningful answer here.
    Forming opinions as we speak

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    Geometrically, you can't have such a situation in three dimensions.

    Grant Hutchison

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    Even the spiral arms of a galaxy don't travel like the spiral arms of a galaxy.

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    Quote Originally Posted by Ken G View Post
    Even the spiral arms of a galaxy don't travel like the spiral arms of a galaxy.
    You are right. The question doesn't make sense.
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    Quote Originally Posted by Copernicus View Post
    Is it possible that light, from every point in the universe travels like a spiral of a galaxy, except over vastly greater distances. Would there be any way of testing it?
    We can model the paths of photons emitted from rotating sources that travel in straight lines to an observer locally. The most simple model is when the observer is stationary relative to the center of mass of the rotating sources, the sources are rotating in the same plane as the center of mass, there is nothing that will distort the photon path between the source(s) and the observer, and the source(s) continue to rotate and emit at the same rate during the 1 complete rotation it takes the photons to reach the observer.

    Rotations shift.jpg

    This is a breakdown of one photon path from one source over the 4 quarters of rotation.

    Rotations shift quarters.jpg

    Different planes of rotation.

    Rotations shift three.jpg

    This can be tested easily as the photon paths exist between the source and the observer at the time of the observation. i.e. test/observe at another location along a path. The only difference between the observations made on the same path should be the differences in the shift due to the direction of the source(s) wrt the observer when the photons were emitted.

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    Quote Originally Posted by LaurieAG View Post
    We can model the paths of photons emitted from rotating sources that travel in straight lines to an observer locally. The most simple model is when the observer is stationary relative to the center of mass of the rotating sources, the sources are rotating in the same plane as the center of mass, there is nothing that will distort the photon path between the source(s) and the observer, and the source(s) continue to rotate and emit at the same rate during the 1 complete rotation it takes the photons to reach the observer.

    Rotations shift.jpg

    This is a breakdown of one photon path from one source over the 4 quarters of rotation.

    Rotations shift quarters.jpg

    Different planes of rotation.

    Rotations shift three.jpg

    This can be tested easily as the photon paths exist between the source and the observer at the time of the observation. i.e. test/observe at another location along a path. The only difference between the observations made on the same path should be the differences in the shift due to the direction of the source(s) wrt the observer when the photons were emitted.
    That makes no sense. Light emitted from a rotating body will travel in straight lines; not continue to spiral after leaving the source.

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    Quote Originally Posted by LaurieAG View Post
    We can model the paths of photons emitted from rotating sources that travel in straight lines to an observer locally. The most simple model is when the observer is stationary relative to the center of mass of the rotating sources, the sources are rotating in the same plane as the center of mass, there is nothing that will distort the photon path between the source(s) and the observer, and the source(s) continue to rotate and emit at the same rate during the 1 complete rotation it takes the photons to reach the observer.

    Rotations shift.jpg

    This is a breakdown of one photon path from one source over the 4 quarters of rotation.

    Rotations shift quarters.jpg

    Different planes of rotation.

    Rotations shift three.jpg

    This can be tested easily as the photon paths exist between the source and the observer at the time of the observation. i.e. test/observe at another location along a path. The only difference between the observations made on the same path should be the differences in the shift due to the direction of the source(s) wrt the observer when the photons were emitted.

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    Quote Originally Posted by Strange View Post
    That makes no sense. Light emitted from a rotating body will travel in straight lines; not continue to spiral after leaving the source.
    I can't make head nor tail of the diagrams and accompanying text, but perhaps there's some confusion between the propagation pathway (a straight line for each photon) and the instantaneous locus of all photons emitted by a revolving radially-directed light beam (a spiral). Like this lawn sprinkler video, for instance: https://www.videoblocks.com/video/sl...a-lawn-byzajfi
    Each water jet produces a revolving spiral pattern of water drops, despite the fact all the drops are moving in "straight lines" (modified parabolic trajectories in this case).

    Grant Hutchison

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    Quote Originally Posted by Copernicus View Post
    Is it possible that light, from every point in the universe travels like a spiral of a galaxy, except over vastly greater distances.
    As far as we know, light ravels in straight lines.

    Would there be any way of testing it?
    Maybe you could suggest a way to test it: what would you expect the result of this spiralling light to be?

    I assume the result would be that we are not be able to see distant objects, just a random mush of light from all directions. As that isn't what we see, I would assume that your idea is wrong.

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    Quote Originally Posted by Strange View Post
    As far as we know, light ravels in straight lines.



    Maybe you could suggest a way to test it: what would you expect the result of this spiralling light to be?

    I assume the result would be that we are not be able to see distant objects, just a random mush of light from all directions. As that isn't what we see, I would assume that your idea is wrong.
    It looks like microlensing does not distort the image. If light is bent and the universe is spinning I would expect the CMB to be different in one direction vs another direction depending how far from the edge of the universe one is.
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    Quote Originally Posted by Strange View Post
    Maybe you could suggest a way to test it: what would you expect the result of this spiralling light to be?
    Quote Originally Posted by Copernicus View Post
    It looks like microlensing does not distort the image. If light is bent and the universe is spinning I would expect the CMB to be different in one direction vs another direction depending how far from the edge of the universe one is.
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    Quote Originally Posted by Strange View Post
    That makes no sense. Light emitted from a rotating body will travel in straight lines; not continue to spiral after leaving the source.
    The light does travel in straight lines from its emission point to the observer, it is the emitting source(s) that rotate and move, and the model is based on 1 complete rotation.

    This is basic Euclidean geometry.

    What doesn't make sense is considering that emitted photons do not exist until they are observed which is is implied through your response.

    If my post is considered ATM then please move the relevant post(s) to ATM so they can be discussed.

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    Quote Originally Posted by LaurieAG View Post
    What doesn't make sense is considering that emitted photons do not exist until they are observed which is is implied through your response.
    I don't know how that is implied in my response as I didn't mention photons and I said that light travels in straight lines (ie from source to destination).

    The light does travel in straight lines from its emission point to the observer, it is the emitting source(s) that rotate and move, and the model is based on 1 complete rotation.
    So I assume that Grant's interpretation of what you were trying to say was correct?
    If so, your diagram is (a) so misleading as to be useless and (b) irrelevant as the Copernicus was asking about light travelling in spirals, not straight lines.

    This is basic Euclidean geometry.
    And that is what I don't understand about the original question. Is Copernicus wondering if there can be so much space-time curvature (due to intervening masses) that light travels in spirals?

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    Quote Originally Posted by grant hutchison View Post
    I can't make head nor tail of the diagrams and accompanying text, but perhaps there's some confusion between the propagation pathway (a straight line for each photon) and the instantaneous locus of all photons emitted by a revolving radially-directed light beam (a spiral).
    Another issue that causes endless confusion is whether one is taking the reference frame of the sprinkler or the lawn, which also have different effects on the pattern. Sometimes it is convenient to choose a reference frame that creates a "steady state", which is a reference frame from which the flow pattern always looks the same. A stream of water seen in the lawn frame is called a "streakline" and curves because of its shared history, whereas in the sprinkler frame a snapshot of that same stream of water is called a "streamline", which is also curved but now because of the coriolis effect. Even the words sound similar, but the reasons are very different! In a reference frame where you have steady-state streamlines, the individual water droplets follow the same path as their pattern, but for streaklines, the water droplets do not follow the direction of the pattern (which is what I meant that a galaxy spiral arm doesn't follow the motion of a galaxy spiral arm). So streaklines can be misleading, and I think this is the trap the OP fell into, though galaxy spiral arms aren't quite the same thing as streaklines either, they are more like a wave phenomenon.

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    On the issue of reference frames, what makes cosmology tricky is there is such an obvious preferred reference frame that we often see language that completely ignores that a reference frame has been chosen. That obvious preferred frame is called the "comoving frame," which takes advantage of the fact that most of the matter of the universe is observed to move locally together on large enough scales (yet moving differently on even larger scales, hence cosmological redshift). So if the OP is framing their question from the perspective of this locally comoving frame, it amounts to asking if it might be necessary to enter a frame that involves rotation in order to be in the comoving frame. Such a frame would manifest itself in unexplained coordinate forces, akin to the coriolis effect and analogous to the curve in a sprinkler stream in the sprinkler reference frame. So I believe the OP question boils down to asking if there could be rotational aspects to comoving material in cosmology, and as Grant pointed out, the best way to tell that would be to look for some kind of special axis along which the behavior is very different. The only special axis we see is due to our motion through the comoving frame (we are not exactly comoving with everything else), so there isn't evidence of rotation, but people have certainly looked quite closely for it.

    Note also that there is a difference between rotation that depends on distance (so either breaks the cosmological principle, like a whorl in a stream, or involves a changing global rotation with age) and a constant rotation of the entire universe, like a solid body. The OP might be asking about either. In the case of the constant version, there is a debate as to whether or not that would actually be observable at all-- a solid body rotation of the entire universe might be as meaningless as a constant velocity for the entire universe. It all depends on how "Machian" is the universal gravity, and to my knowledge there is still debate around what general relativity says about that! But observations show no such effects, so either it is indeed meaningless, or it isn't happening.

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    Quote Originally Posted by LaurieAG View Post
    The light does travel in straight lines from its emission point to the observer, it is the emitting source(s) that rotate and move, and the model is based on 1 complete rotation.

    This is basic Euclidean geometry.

    What doesn't make sense is considering that emitted photons do not exist until they are observed which is is implied through your response.

    If my post is considered ATM then please move the relevant post(s) to ATM so they can be discussed.
    LaurieAG

    When you've already been infracted once for ATM in a Q&A thread, and a second moderator says to knock off the ATM discussion, continuing the discussion on the topic and the moderation will result in another infraction. This will also result in your suspension.

    Since the original question seems to have been dealt with, the thread will also remain closed.
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