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Registered Senior Member
Distinguishing Cosmological Expansion frame from SR frame.
In a recent discussion there were assertions regarding what if any effective difference there was between said frames when a detector measures redshift of a photon from a cosmologically distant source and no actual separation of SR and Cosmological Expansion causation components is even attempted let alone considered pertinent to better understanding of space-time expansion theory and its real implications on the photon itself and the frames involved at emission, in-transit and at absorption. This thread is an attempt to discuss how it may be possible to, at least in theory if not in practice, to ascertain whether or not there are any differences between the Cosmological Expansion frame and the Special Relativity frame, which two frames are at present effectively lumped in together in theory and in analysis methods and measurements. To start this discussion, I have composed a thought experiment to highlight both theoretical and logical possible differences between the Cosmological and SR frames, and the effective implications for the photon at emission, in-transit and absorption.
Thought Experiment in Two Parts
Part One: Non-expanding space-time context:
Two transceivers, co-moving in free space far from significant GE effects from any massive feature, and identical in all respects as to their set frequency of emission and absorption. They send a photon between them and it arrives traveling at light speed at moment of impact (beginning of absorption process). The detectors being co-moving in Non-expanding space-time have no SR Doppler attenuation effect on photon wavelength/frequency, so photons at reception are identical as to wavelength/frequency as at emission.
Now apply transient identical but oppositely directed rocket acceleration to both transceivers such that they now separate with a constant proper motion in SR-Doppler terms. The photons will be equally redshifted; that total redshift being composed of motion related shift during the emission process and then the motion related shift during the absorption process.
NB In this Non-expanding space-time scenario, all increasing space-time distance between the two transceivers is solely due to the proper motions of the transceivers; with no cosmological expansion component whatsoever. This is important to note; because the next part of the experiment involves Expanding Space-time context which will involve space-time distance increase due to OTHER THAN PROPER motion separation in space-time as in this first part
Part Two: Expanding space-time context:
Same two transceivers as above, initially co-moving such that no distance increase is discernible between them. Unlike in the first scenario, no rocket accelerations are imparted to change in any way their initial proper co-moving motional states. We now allow cosmological expansion to increase the space-time distance between them according to the theory; which theory states that no proper motion relativity arises between the two initially co-moving transceivers; only that the space-time distance between them is now increasing in some unidentified manner such that they are separating along with the space-time locations they started in.
NB In this Expanding space-time scenario, the two transceivers did not experience any acceleration through space via rocket impulse, hence there is no proper motion related separation speed to give rise to SR-Doppler effect as in part one scenario. So, if any redshift to photons is detected during absorption process at either end, then that shift cannot logically or effectively be attributed to proper motional relativity SR-Doppler mechanism, since there is no actual proper motional change related increase in space-time distance over time between the two transceivers in this second scenario, as only the cosmological expansion related increase in space-time distance is active as per this thought experiment's design to distinguish between expansion and and non-expansion scenarios.
NB A further observation: When the photons are being emitted and absorbed, both the photons and their respective transceivers are effectively in the same frame irrespective of the scenario being expanding space-time or non-expanding. This is because at instant of photon's departure and instant of photon's approach, the photon and transceiver are BOTH in the same frame state! Be it the SR-Doppler frame state determined by solely by the transceivers proper-motion-ONLY relativity (in part one: non-expanding context); OR be it the Cosmological Expansion frame state determined solely by the increasing 'space-time distance over time' according to theory (which theory does NOT depend on any actual proper motion component as part of the cosmological expansion phenomena and interpretations as such).
That is the thought experiment, thankyou.
If any member wishes to participate in discussing this OP and its implications according to the Thought Experiment as set up and described, I only ask that they first read and understand thoroughly what has been posed by way of illustrative example of how we can, at least logically if not practically, have a perspective on the TWO frames which are indicated to exist in fact even if not currently discerned in theory and practice. Only if we can do that can we then tackle the question of the Mechanism for either frame effects on the photon and transceiver wavelength/frequency in space-time terms and somehow find a way to analytically separate the proper motion SR and Cosmological Expansion contribution to the total redshift which currently lumps the two components together in equations treating them via the mathematically convenient "SR-Doppler" perspective, thus conflating both the respective components, the respective mechanisms and the respective frames. I feel this is what has led to all the confusion which persists; and will persist as long as no effort is made to actually separate and understand effectively the two very different frames, components and mechanisms which must be at play in whatever space-time terms one wishes to couch them in.
Thank you for your patient and kind indulgence. The floor is open to all, laypersons and learned members, with the reasonable expectation that anyone wishing to participate in the discussion will have made every effort to properly and thoroughly understand the above as intended (and hopefully not as expediently interpreted in order to just say anything for its own sake and without due regard to what was described and intended for the purposes of the OP).
I will leave this OP to stand without any further comment from me until there has been sufficient interest and comment from members for me to make pertinent interactive clarifications or etc as necessary. Thank you, fellow members.
In a recent discussion there were assertions regarding what if any effective difference there was between said frames when a detector measures redshift of a photon from a cosmologically distant source and no actual separation of SR and Cosmological Expansion causation components is even attempted let alone considered pertinent to better understanding of space-time expansion theory and its real implications on the photon itself and the frames involved at emission, in-transit and at absorption. This thread is an attempt to discuss how it may be possible to, at least in theory if not in practice, to ascertain whether or not there are any differences between the Cosmological Expansion frame and the Special Relativity frame, which two frames are at present effectively lumped in together in theory and in analysis methods and measurements. To start this discussion, I have composed a thought experiment to highlight both theoretical and logical possible differences between the Cosmological and SR frames, and the effective implications for the photon at emission, in-transit and absorption.
Thought Experiment in Two Parts
Part One: Non-expanding space-time context:
Two transceivers, co-moving in free space far from significant GE effects from any massive feature, and identical in all respects as to their set frequency of emission and absorption. They send a photon between them and it arrives traveling at light speed at moment of impact (beginning of absorption process). The detectors being co-moving in Non-expanding space-time have no SR Doppler attenuation effect on photon wavelength/frequency, so photons at reception are identical as to wavelength/frequency as at emission.
Now apply transient identical but oppositely directed rocket acceleration to both transceivers such that they now separate with a constant proper motion in SR-Doppler terms. The photons will be equally redshifted; that total redshift being composed of motion related shift during the emission process and then the motion related shift during the absorption process.
NB In this Non-expanding space-time scenario, all increasing space-time distance between the two transceivers is solely due to the proper motions of the transceivers; with no cosmological expansion component whatsoever. This is important to note; because the next part of the experiment involves Expanding Space-time context which will involve space-time distance increase due to OTHER THAN PROPER motion separation in space-time as in this first part
Part Two: Expanding space-time context:
Same two transceivers as above, initially co-moving such that no distance increase is discernible between them. Unlike in the first scenario, no rocket accelerations are imparted to change in any way their initial proper co-moving motional states. We now allow cosmological expansion to increase the space-time distance between them according to the theory; which theory states that no proper motion relativity arises between the two initially co-moving transceivers; only that the space-time distance between them is now increasing in some unidentified manner such that they are separating along with the space-time locations they started in.
NB In this Expanding space-time scenario, the two transceivers did not experience any acceleration through space via rocket impulse, hence there is no proper motion related separation speed to give rise to SR-Doppler effect as in part one scenario. So, if any redshift to photons is detected during absorption process at either end, then that shift cannot logically or effectively be attributed to proper motional relativity SR-Doppler mechanism, since there is no actual proper motional change related increase in space-time distance over time between the two transceivers in this second scenario, as only the cosmological expansion related increase in space-time distance is active as per this thought experiment's design to distinguish between expansion and and non-expansion scenarios.
NB A further observation: When the photons are being emitted and absorbed, both the photons and their respective transceivers are effectively in the same frame irrespective of the scenario being expanding space-time or non-expanding. This is because at instant of photon's departure and instant of photon's approach, the photon and transceiver are BOTH in the same frame state! Be it the SR-Doppler frame state determined by solely by the transceivers proper-motion-ONLY relativity (in part one: non-expanding context); OR be it the Cosmological Expansion frame state determined solely by the increasing 'space-time distance over time' according to theory (which theory does NOT depend on any actual proper motion component as part of the cosmological expansion phenomena and interpretations as such).
That is the thought experiment, thankyou.
If any member wishes to participate in discussing this OP and its implications according to the Thought Experiment as set up and described, I only ask that they first read and understand thoroughly what has been posed by way of illustrative example of how we can, at least logically if not practically, have a perspective on the TWO frames which are indicated to exist in fact even if not currently discerned in theory and practice. Only if we can do that can we then tackle the question of the Mechanism for either frame effects on the photon and transceiver wavelength/frequency in space-time terms and somehow find a way to analytically separate the proper motion SR and Cosmological Expansion contribution to the total redshift which currently lumps the two components together in equations treating them via the mathematically convenient "SR-Doppler" perspective, thus conflating both the respective components, the respective mechanisms and the respective frames. I feel this is what has led to all the confusion which persists; and will persist as long as no effort is made to actually separate and understand effectively the two very different frames, components and mechanisms which must be at play in whatever space-time terms one wishes to couch them in.
Thank you for your patient and kind indulgence. The floor is open to all, laypersons and learned members, with the reasonable expectation that anyone wishing to participate in the discussion will have made every effort to properly and thoroughly understand the above as intended (and hopefully not as expediently interpreted in order to just say anything for its own sake and without due regard to what was described and intended for the purposes of the OP).
I will leave this OP to stand without any further comment from me until there has been sufficient interest and comment from members for me to make pertinent interactive clarifications or etc as necessary. Thank you, fellow members.
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