Is Gravity Faster than Light?

Discussion in 'General Science & Technology' started by Bowser, Jan 18, 2018.

  1. nebel Registered Senior Member

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    736
    I

    was not thinking in terms of gravitons at an eclipse, but, if gravity was an exchange of particles, there would have been a traffic jam between Earth, and Moon and Sun. all going at only c.
    surely, "gravitons" would be affected by the combined gravity of Sun, Moon and Earth the same as photons?
     
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  3. Write4U Valued Senior Member

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    5,589
    OK. I know very little about gravity except that it stretches spacetime.
    I do have another question about that, to hopefully gain a better perspective.

    I read that a photon may spend a thousand years inside the sun, always moving @ c and always in a straight line, but encountering so many other photon (electrons) that it is bounced back and forth always trying to follow a straight line, but unable to find a free path. Then, when it finally manages to escape the interior, it only takes 8 minutes for that now unobstructed photon to reach earth.

    If your example represents a room "filled" with photons, would our photon also be obstructed on occasion and take longer to traverse the room than if the room had no other photons to get in the way?

    I realize one could never attain the density of photons in the sun, but light waves do seem to interfere in the double slit experiment (for one). Does this wave- interference cause the photon to have to travel further (not in a straight line, but at an angle), thereby taking more time to traverse the light filled room? Obviously any minute increase in time may not be measurable, but the illustrations of the double slit experiment, clearly show that the spread of the interference patterns do cause some photons to have to travel further in order to register on the receiving plate. Seems that these differences in travel lengths could be measured?
     
    Last edited: Feb 4, 2018
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  5. Michael 345 Next mythical choc bunnies for mystic who died Valued Senior Member

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    Check this out

    Good information

    *****

    As Jupiter moved between Earth and the quasar, the gravitational bending of Jupiter allowed us to measure the speed of gravity, ruling out an infinite speed and determining that the speed of gravity was between 2.55 × 10^8 and 3.81 × 10^8 meters-per-second, completely consistent with Einstein's predictions.Jan 15, 2014

    https://medium.com/starts-with-a-bang/what-is-the-speed-of-gravity-8ada2eb08430

    *****

    Speed of light 299,792,458 metres per second

    Speed of gravity was estimated to be between 2.55 × 10^8 and 3.81 × 10^8 meters per second

    Of which the average works out to be 3.18 X 10^8 slightly above light speed

    Not being in the Scientists field I have no idea what pluses and minuses come into play but I'm sure as equipment and measurements improve the gravity range will shrink

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    Last edited: Feb 4, 2018
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  7. DaveC426913 Valued Senior Member

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    An excellent question.

    TLDR: No.


    Atoms - electrons, protons neutrons - are fermions - the stuff that makes up the physical matter of the universe. They obey the Pauli Exclusion Principle, which means (simplistically) they cannot occupy the same space. This is what causes electrons to form shells around a nucleus. Once a shell is "filled", no more electrons can occupy that same shell ,so it occupies the next outer shell (again, simplistically). It is also what causes atoms to take up space and forms (almost) all physical matter of our universe.

    Photons are bosons - they have no such restrictions. All EMR is photons, therefore bosons. You can have as many photons in a space as you want, and they do not fill space. In fact (with a few exceptions), they do not even interact - they just fly around past each other until they encounter some fermions, where they will likely get absorbed.

    Essentially, yes. It whizzes right past all the other photons, but it does interact with any atoms, nucleii and electrons it encounters (which it does a lot).

    The reason it takes so long is because the sun is not the usual kind of matter we encounter. It is so hot that it's a plasma - every atom has had its electrons stripped away, leaving just +ive nucleii ion and -ive electron ions all over the place. i.e. there pretty much aren't any plan ol' neutral atoms in the sun (at least, for very long). So the sun is a sea of charged ions, and it is these ions that photons interact with.

    (There was an epoch shortly after the BB where the entire universe was so hot that no stable atoms could form - no electrons could drop into shells to make atoms without being bashed apart again. The universe was dark during this period because photons could not go more than a step or two before encountering an ion. So the universe did not shine.)
     
    Last edited: Feb 4, 2018
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  8. Write4U Valued Senior Member

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    5,589
    @ Dave,

    Thank you for that clear and concise summation. This clears up many other related questions....

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  9. ajanta Registered Senior Member

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    And honestly; I know that I don't know everything.
     
  10. Q-reeus Valued Senior Member

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    2,703
    Actually the quoted range is anywhere between ca 5,000 to 500,000 years: https://sciencing.com/long-photons-emerge-suns-core-outside-10063.html
    But it's misleading, because as admitted near the start of the article, the actual process is not one 'bouncing off' but of of continual absorption (photon annihilation) and emission (photon creation).
    Which is the QED picture. There is therefore no such thing as *a* photon taking X thousands of years to travel from core to surface and finally escaping.
    And that has to be true because to go from gamma ray to light ray frequencies, only two processes allow a single photon to do so. Gravitational redshift. Which is negligible for the sun. Or SR Doppler shift - also negligible for the sun. Hence what emerges as light could not possibly be the same photon as a gamma ray initially way down and way back in the core.
    Completely negligible. Only if centre-of-energy photon-photon collisions approach the so-called Schwinger limit would significant scattering occur: https://en.wikipedia.org/wiki/Schwinger_limit
    At sun's core, that will practically never happen. Even less likely further out.
    More confusion. Are you still not aware that single-photon-at-a-time double slit experiments have been performed for a long time?:
    http://www.animations.physics.unsw.edu.au/jw/light/youngs-experiment-single-photons.html
    Same deal with Fermionic electrons etc. btw. It can be shown that photons do mutually interfere, but that is not the same as mutually scattering. FAPP, they just pass through each other as though not there.
     
    Last edited: Feb 6, 2018
  11. Write4U Valued Senior Member

    Messages:
    5,589
    I am getting the picture.
    OK, I accept "interference". But that does not quite answer my question about the difference in distances photons must traverse in order to create the interference pattern on the receiving plate.

    I know, this may be negligible as far as time is concerned but it should be possible to triangulate the distances which the photons must travel from the slit to the plate.
     
  12. Q-reeus Valued Senior Member

    Messages:
    2,703
    Again - the fact that a single photon evidently interferes with itself ala one-at-a-time double-slit interference pattern, should be telling you something. It cannot be treated as a particle re 'triangulation'. There is a clear angular dependence wrt long-time, averaged interference intensity at the screen. One you get from classical optics.
     
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  13. Write4U Valued Senior Member

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    5,589
    Question: If the wave of the first paricle has collapsed, how then can it interfere with the wave function of the second particle?

    The problem would be much simpler if we recognized Bohm's model of the Pilot Wave, which persists even as in mainstream science the wave functions of particles collapse at time of explication.
     
    Last edited: Feb 8, 2018
  14. Q-reeus Valued Senior Member

    Messages:
    2,703
    A non sequitur question. In the standard Feynman path-integral approach, a single particle interferes with itself in taking all possible paths from slits to screen. Any individual screen hit is more or less random but on average, the path(s) generating the least mutual destructive interference are most likely and will correspond to the interference fringes actually observed to build up over a long run of such individual events.
     
  15. Write4U Valued Senior Member

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    5,589
    OK, but then one cannot say that the first particle interferes with the second.
     
  16. Q-reeus Valued Senior Member

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    2,703
    If you mean the second particle is delayed beyond the time it takes the previous one to have gone through and made a screen hit, well obviously so. Which is btw taken as proof that each particle interferes with itself. But....Dirac's famous dictum: "Every photon then interferes only with itself. Interference between two different photons never occurs."
    Investigating whether that actually holds true in general leads to some interesting conclusions. One article: http://arxiv.org/abs/nucl-th/0604021

    I was able to show years ago that some quite pedestrian classical physics absolutely requires mutual interference between photons. But this is getting well away from the OP topic. Agreed?
     
  17. Write4U Valued Senior Member

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    5,589
    One more question: Would we know the difference between Bohm's Guiding Pilot Wave experiencing wave interference and the accepted notion that the wave function of a particle interferes with itself?
     
  18. Q-reeus Valued Senior Member

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    2,703
    I could point you to some articles where one author claims to have found a discrepancy that distinguishes BM from standard QM. And reply articles by the BM advocate claiming the anti-BM article(s) was flawed for such-and-such reasons. But it's deeply technical so why bother unless you have graduated with QM under your belt?
    The consensus view is BM was constructed from the start so as to always reproduce standard QM. So only the interpretation of results not results themselves differ.
     
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  19. Write4U Valued Senior Member

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    5,589
    I can agree with that, but it does not necessarily describe the function which produces the results.

    I found this presentation very interesting;
     
  20. Q-reeus Valued Senior Member

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    2,703
    I did decide to watch. Pretty decent and balanced in that the 'warts' aspects of BM were spelled out. If you are comfortable with those bizarre warts, fine.
    The OP question has been adequately dealt with, so.....END.
     
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  21. Michael 345 Next mythical choc bunnies for mystic who died Valued Senior Member

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  22. Q-reeus Valued Senior Member

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    2,703
    From first linked article:
    "This device can be used as a measure of gravity at a specific site due to a phenomenon described by Einstein’s theory of relativity. Specifically, a clock in a strong gravity field will run slow compared with a clock in a less strong gravity field."
    Wrong but various SF members and others keep making above journalist's mistake. Clock-rate varies with the gravitational potential, not it's gradient i.e. 'strength'. The big deal there is portability i.e. miniaturization of atomic clock, otherwise nothing new at all.

    The topic of 2nd linked article has been discussed here before: http://www.sciforums.com/posts/3488867/
    but I additionally include there a link to evidence against Verlinde's theory of 'entropic gravity'. Which was also brought up prior to that.
     
  23. Write4U Valued Senior Member

    Messages:
    5,589
    For some reason, when speaking of dark energy, dark mass, and gravity, the image of the Higgs field comes to mind. This little excerpt from a knowledgeable scientist just reinforces this intuitive image;
    http://www.fnal.gov/pub/science/inquiring/questions/higgs_boson.html

    This is due to the density of water.

    OK, assumption; Dark matter is result of the Higgs field, a sea which gives mass to particles and determines the speed of that particle by it's acquired mass.
    "c" (SOL) is caused by the restriction of a photon's acquiring mass which imposes a speed limit as the photon swims through the Higgs field.

    As the quote mentions, there are massless particles so small that they are unaffected by the Higgs field and theoretically will be able to exceed "c", because they do not interact with the field at all, which, if they did would impart mass. Could this account for the "spooky action" at a distance, i.e. "c" is not a factor in restrictng the speed of this subquantum particle?

    However, just as a large body of water imposes a speed limit on a boat when it reaches it maximum "hull speed"
    https://en.wikipedia.org/wiki/Hull_speed

    I can see a similar phenomena happening in the "sea" of the Higgs field. The more mass (size) a particle acquires, the slower it must move, due to its becoming trapped by its own displacement mode (hull speed) in the Higgs field. Which, IMO, would nicely explain the restriction of a photon inability to exceed SOL and might confirm the proposition of "gravitational waves" surrounding a massive object, the extend of which is directly proportional to the mass (displacement) within the sea of the Higgs field.

    Coming to "gravity"; Is it possible that a very large and massive moving object creates a dense Higgs field
    "bow wave", increasing in density the closer we get to the large (relatively slow moving) massive object and gravity is somehow a result of this denser Higgs field surrounding the massive object.

    This would cause all smaller massive objects within the bow wave to slow down until stops moving relative to the original massive object ( say, a star), at which point it begins to "fall" towards the star or more simply put "meets" the star and is absorbed.

    I always found the rings around Saturn to be indicative of a wave like function around the star, where objects of specific masses and speed are caught and must travel in the throughs of the surrounding gravitational waves. If they slow down, they fall into a through closer to the star, if they somehow speed up they escape the troughs by riding the crests and eventually escaping the compressed gravitational wave and assume their own naturally allowed speed within the Higgs Field.

    This is completely speculative, but does it merit an analysis?
     

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