Does light travel forever?

Discussion in 'Physics & Math' started by drumbeat, Mar 28, 2011.

  1. siphra Registered Senior Member

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    Actually, if neutrino interaction increases with density (logical), then it could be tested in theory... Build a photon chamber with high photon density of one particular photon (and hope it is the one that the neutrinos can interact with, a negative result wouldn't be an absolute failure as the energy level of the photon may determine it) Changes in the photons would be potential neutrino/photon interactions. Using background estimations of solar neutrino production as a source...
     
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  3. OnlyMe Valued Senior Member

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    That's the ticket. Think of space like it is a 3D example of the surface of a baloon. Blow the balloon up part way and mark equal distances on the surface. Think of each as a light year. Then blow the balloon up a bit more. That is like the universe/space expanding. The distance between marks still equals a light year, so it takes light the same time from mark to mark, but the the wave length gets streached. Blue light has a shorter wave length than blue. Shorter wave lengths get stretched and move toward red.
     
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  5. Rocks Registered Member

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    This is starting to sink in as I consider the distance. As i said, I'm used to studying EM and nearby objects. I guess to me, it's a different kind of refraction, but I'm also thinking there is hella dust across several billions of LYs that could also alter the appearance of the light. Heady hurty...
     
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  7. OnlyMe Valued Senior Member

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    The problem is not with the photons. It is with the neutrino. While it is possible to generate neutrinos, even in a way that they travel in a specific direction (within limits), we cannot create enough to establish a reliable probability of interaction.

    Think about neutrino detectors. They are under ground or ice, so other cosmic radiation can be reduced. Still for every neutrino that results in an observable interaction there are trillions if not trillions of trillions that do not. And those are interactions are with ordinary matter, meaning atoms.

    I believe interaction is theoretically possible. Perhaps it would be better to say hypothetically... But designing an experiment to prove it... We have a hard time observing neutrino-atom interactions...
     
  8. OnlyMe Valued Senior Member

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    How photons from more distant sources interact with interstellar and intergalactic dust is how we know it is there and what it is. The photons that don't interact are the ones that tell us about the more distant source.
     
  9. siphra Registered Senior Member

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    This is the great thing about this experiment, you don't have to control the number of neutrinos, put this detector below another, (this way you can estimate expected events) and just keep increasing the photon density. (Now of course, the problem here is photon = energy .... so the device is going to have to be designed to handle the intensity of photons, I would say, as a good starting point, no less dense than that of the photosphere of the sun.
     
  10. RJBeery Natural Philosopher Valued Senior Member

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    Red-shift from expansion isn't much of a mystery:

    If a light source is moving away from you, Doppler effects make it appear red-shifted even though the light itself still appears to travel and reach us with a velocity of c, correct? Assuming you understand this, then expanding space is simply a way of describing ALL interstellar light sources as moving away from all observers. If all stars were making a noise which we would hear, their pitches would sound lower for the same reason that a car's engine does as it drives away from you...
     
  11. Rocks Registered Member

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    Except that the light on the front of the train doesn't change color. I do understand the Doppler effect, but sound is much slower than light, and exhibits much different behavior (eg: sound can't also be a particle, at least the way we know how to understand or observe it), which I guess is why I haven't tried to use analogies that compare the two or apply Doppler principles to light. I still don't have any new way of conceptualizing this besides a kind of refraction. I guess the Doppler effect with sound could be considered a kind of refraction in the same way???
     
  12. Motor Daddy Valued Senior Member

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    Speaking strictly of the volume of space, it is infinite. It is impossible for the volume of space to be finite. Sure, it's possible for an object to have a finite volume, but we are talking about space, not an object, or a mass, or a cluster of mass. We are talking about the volume of space, and that is impossible to be finite.
     
  13. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    Well it does, but not enough to notice.
    Any speed a train is doing is an insignificant fraction of the speed of light.
     
  14. Rocks Registered Member

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    Yes, also a reason I've been avoiding that comparison. Like I said, it's sinking in, but with some things, I get a big "ah hah!" and without others, it's a slow progression/transformation in thinking. This seems to be one of those slow things, and my training is more in Earth sciences and less in the details of physics beyond the normal year and some EM work in relation to remote sensing of the Earth.

    I don't imagine there are many experimental/lab ways to recreate this? Just mathematical, I guess? I've learned to love math (which wasn't easy, but I made it), but I do love pictures a lot more

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    And thanks, everyone, for the friendly help.
     
  15. OnlyMe Valued Senior Member

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    The velocity of the source of a photon has no affect on the photon. There are situations where a red and blue shift is observed for distant galaxies depending on where in the disk of the galaxy the light originates. In an arm rotating away or toward us. This is theorized to be due to gravitational force similar to gravitational lensing.

    The Doppler shift observed with sound was the original model. It was dismissed when it was discovered that light is not affected by the velocity of its source. Further sound is different in other ways. Sound travels faster through more dense mediums, light through less dense mediums. Sound is a concussion wave trough matter. Light a photon through vacuum and transparent materials...
     
  16. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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  17. OnlyMe Valued Senior Member

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    Not really.

    Take as an example the Michelson-Morley experiments, in the late 1800s. They used a sensitive interferometer to measure the velocity of light in the direction of the earths motion and at right angles to that motion. They were actually not measuring the velocity they were measuring any difference in the velocity. They found no difference. If the light measured in the direction of travel had been red shifted even slightly the experiment which relied in a change in the interference pattern of a beam of light split and then recombined, it would have affected the interference pattern. The wave forms of the two beams would have been different.

    The velocity of a light source has no affect on the photons emitted. In the case of galaxies mentioned previously, the gravitational force and frame dragging changes the shape of space and stretches or compresses the wave lenth of light.

    I probably messed that up some but I am posting on a portable device and it is hard to edit.
     
  18. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    Correct.
    But each successive photon is emitted increasingly closer to the observer. This causes "bunching" for that observer, no?
     
  19. Pete It's not rocket surgery Registered Senior Member

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    The velocity of sound is also not affected by the velocity of its source.

    The doppler effect for light is the same as the doppler effect for sound when the receiver is stationary with respect to the medium.
     
  20. OnlyMe Valued Senior Member

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    Could but that would either make the light brighter or dimmer depending on direction does not affect the wave lenth of individual photons.

    There are at least two other explanations for the red shift in light, but they assume conditions that are not in agreement with currently accepted theory. The effect of gravity on light is an observed phenomena, gravitational force and perhaps the frame dragging effect, fit with our current understanding.
     
  21. OnlyMe Valued Senior Member

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    This was the original idea. Doppler actually proposed this. The problem is that at the time the Luminiferous Aether was the accepted model. Today, the existance of the ether is not accepted. Light travels through vacuum, empty space.., there is no medium.

    Either way there are problems still to be explained.
     
  22. Rocks Registered Member

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    My pragmatic thinking suggests to me that space isn't all that empty, and lots of small, lightweight particles of dust still haven't been pulled into the known bodies yet, and that the many explosions since the assumed BB have continually put small particles out into space. That's why I'm not so willing to embrace the expansion ideas as absolute with redshift, although I feel like I'm, grasping that more. I am just not convinced it's the only thing when there is likely so much fine dust of who-knows-what composition millions of light years away. It seems silly assume that the whole Universe is just the way we can observe it from our fixed location, with limited tools, which aren't very old.
     
  23. OnlyMe Valued Senior Member

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    The dust or particles don't matter. Remember that the photons get to us without hitting anything. At least enough of them that we ca see that star or galaxy they came from.

    I was attempting to explain currently accepted theory. As I said there are a couple of other mechanisms that could return the same results but they are not consistent with some aspects of general relativity, so theynare not worth discussing here..., yet.
     

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