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Thread: The Universe according to Puzzling Evidence....

  1. #21
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    Quote Originally Posted by Puzzling Evidence View Post
    The Speed of Light as Measured by Non-Inertial Observers
    That the speed of light depends on position when measured by a non-inertial observer is a fact routinely used by laser gyroscopes that form the core of some inertial navigation systems. These gyroscopes send light around a closed loop, and if the loop rotates, an observer riding on the loop will measure light to travel more slowly when it traverses the loop in one direction than when it traverses the loop in the opposite direction. This is known as the Sagnac Effect. The gyroscope does employ such an observer: it is the electronics that sits within the gyro. This electronic observer detects the difference in those light speeds, and attributes that difference to the gyro's not being inertial: it is accelerating within some inertial frame. That measurement of an acceleration allows the body's orientation to be calculated, which keeps it on track and in the right position as it flies.

    You will sometimes find discussions that insist the only correct way to describe the Sagnac Effect is by reference to an inertial frame: they will say that the only concept with meaning is the locally measured speed of light, which is c, and that what the non-inertial observer sitting on the loop says about the motions of two light rays has no physical meaning. Whilst the Sagnac effect is easy to calculate using an inertial frame—because then we can use the simple equations of adding velocities in special relativity—it doesn't follow that any non-inertial description of it is invalid. Those who insist that non-inertial descriptions are invalid are like the man whose house is about to be picked up by a cyclone: they will shout "Don't worry folks! The wind isn't really circulating at 300 km/h. It's really Earth that's rotating in an inertial frame, and the resulting differential motions give rise to the illusion that the wind is about to shred this house." Yes, it's certainly valid to analyse the situation using Newton's laws in an inertial frame. But you might want to hang on to your house while doing so.

    You might also find it said that the Sagnac Effect is somehow not measuring the speed of the two light beams sent around the loop, but "merely" their times of flight, as if that's somehow different to measuring their (average) speed. But the simple fact is that if you send two horses in opposite directions around the same race track, then the horse that crosses the finish line first must have run faster. The different arrival times of the two light beams have nothing to do with anything strange going on with "the geometry of spacetime": this discussion holds in the absence of any gravity, in which case spacetime can be flat, and if it's flat for one observer, it's flat for all, including those sitting on rotating loops. The observer sitting on the rotating loop concludes that the beams simply move at different speeds. And that's all right, because it's only either an inertial observer who must measure their speeds to be both c, or an observer sitting right next to the light beams. But the observer on the loop is neither inertial nor sitting right next to each beam at all times of its flight.

    Discussing non-inertial observers can be simpler if we consider not the rotating frame of a laser gyroscope, but the "uniformly accelerated" frame of someone who sits inside a rocket, far from any gravity source, accelerating at a rate that makes them measure their weight as constant. ...

    Is The Speed of Light Everywhere the Same?
    Correct.

    But the sagnac effect probably isn't the most direct example of varying c as observed from two different, non-inertial reference frames.

    One can simply take a black hole, whose radiation will never reach earth (implying c=0) from the point of view of an observer on earth. However, for an observer within the event horizon of a black hole, radiation is still travelling at the speed of light.

  2. #22
    Veteran Member Puzzling Evidence's Avatar
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    Quote Originally Posted by kingrat View Post
    Correct.

    But the sagnac effect probably isn't the most direct example of varying c as observed from two different, non-inertial reference frames.

    One can simply take a black hole, whose radiation will never reach earth (implying c=0) from the point of view of an observer on earth. However, for an observer within the event horizon of a black hole, radiation is still travelling at the speed of light.
    That's because IT IS traveling at the speed of light. All other measurables are variables. Speed of light is the common denominator that is always the same. All this nonsense about mesuring the speed of light going the opposite direction and such is a moot point.

    It's like a cop giving you a ticket for going 110 because he was passing you going 55 in the opposite direction. It's a monumental waste of time to even discuss it.

    To Kingrat and the sites other "physicist," This thread is in philosophy and religion..

    Philosophy and Religion.
    Last edited by Puzzling Evidence; 26th January 2018 at 05:35 AM.

  3. #23
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    To put this seemingly contradictory statements to its proper perspective, it is better to imagine special relativity as a 'local' scientific law -- where co-moving inertial reference frames travel through a more or less uniform space-time. Locally, the speed of light would be observed as constant in those reference frames. The sagnac effect is a quirk in special relativity because, although light is travelling at a constant speed, it does so in a curvilinear/circular motion, which by definition, is a kind of acceleration.

    General relativity however, takes into consideration non-inertial (accelerating) reference frames and one of the most common example of this type of reference frame is an observer within a gravitational field. Instead of travelling along uniform space, light travels through curved space, hence takes longer to travel from one point to the next point. But for this 'lag' (called gravitational red shift) to be noticeable, the observe should be very, very far away.

  4. #24
    Veteran Member Puzzling Evidence's Avatar
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    Quote Originally Posted by kingrat View Post
    To put this seemingly contradictory statements to its proper perspective, it is better to imagine special relativity as a 'local' scientific law -- where co-moving inertial reference frames travel through a more or less uniform space-time. Locally, the speed of light would be observed as constant in those reference frames. The sagnac effect is a quirk in special relativity because, although light is travelling at a constant speed, it does so in a curvilinear/circular motion, which by definition, is a kind of acceleration.

    General relativity however, takes into consideration non-inertial (accelerating) reference frames and one of the most common example of this type of reference frame is an observer within a gravitational field. Instead of travelling along uniform space, light travels through curved space, hence takes longer to travel from one point to the next point. But for this 'lag' (called gravitational red shift) to be noticeable, the observe should be very, very far away.
    zzzzzzzzzzzzzzzzzzzzzzzzzz

    Like I just fucking said, this thread is in Philosophy and Religion.

    Please go start your own topic where you can brag to the rest of humanity about how smart you are. Your constant harping on the same subject is tedious and mind-numbing.

    Kingrat: The worst thing that you can do online is to be boring.

    zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz zzzzzzzzzzzzzzzzzzzzzzzz

  5. #25
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    Quote Originally Posted by Puzzling Evidence View Post
    That's because IT IS traveling at the speed of light. All other measurables are variables. Speed of light is the common denominator that is always the same. All this nonsense about mesuring the speed of light going the opposite direction and such is a moot point.

    It's like a cop giving you a ticket for going 110 because he was passing you going 55 in the opposite direction. It's a monumental waste of time to even discuss it.
    Sorry but your analogy is very far away from your original topic. This is a case for galilean transformation, not lorentz transformation.

    What would be pertinent is that you and the cop would observe light, whether travelling in your direction or the cop's direction, at speed c (assuming, of course that neither of you are accelerating).

    Quote Originally Posted by Puzzling Evidence View Post
    To Kingrat and the sites other "physicist," This thread is in philosophy and religion..

    Philosophy and Religion.
    https://www.thefreedictionary.com/natural+philosophy

    natural philosophy
    n
    (Education) (now only used in Scottish universities) physical science, esp physics
    natural philosopher n

  6. #26
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    Quote Originally Posted by Puzzling Evidence View Post
    zzzzzzzzzzzzzzzzzzzzzzzzzz

    Like I just fucking said, this thread is in Philosophy and Religion.

    Please go start your own topic where you can brag to the rest of humanity about how smart you are. Your constant harping on the same subject is tedious and mind-numbing.
    And as I said, physics is a topic of natural philosophy.

    Quote Originally Posted by Puzzling Evidence View Post
    Kingrat: The worst thing that you can do online is to be boring.

    zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz zzzzzzzzzzzzzzzzzzzzzzzz
    Actually, the worst thing that you can do online is to be unaware that you are wrong.

    I mean, it is bad enough that you had to make a pun about vacuum repair shops. If you have time for that sort of nonsense in a forum on philosophy and religion, you ought have time to be a bit accurate.

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