Notices
Results 1 to 49 of 49

Thread: The Speed Of Light Might Be Wrong

  1. #1 The Speed Of Light Might Be Wrong 
    Forum Sophomore
    Join Date
    Feb 2014
    Posts
    115
    The Speed Of Light Might Be Wrong

    What do you all think?


    Reply With Quote  
     

  2.  
     

  3. #2  
    exchemist
    Join Date
    May 2013
    Location
    London
    Posts
    3,527
    Quote Originally Posted by molecool View Post
    The Speed Of Light Might Be Wrong

    What do you all think?
    Well hardly "wrong", just a tiny bit more sensitive to gravitational effects between the stars than we had thought, if this fellow is right, due to QED.

    I see only now is the article undergoing peer review, so perhaps we ought to wait a bit before hyperventilating.


    Reply With Quote  
     

  4. #3  
    New Member
    Join Date
    Jun 2014
    Posts
    2
    The speed of light depends on the permittivity and the permeability of the matter through which light travels. Maxwell's equation in regard to the speed of light shows that. The speed of light is affected by gravity; black holes are proof of that. Light also slows down when going through glass or water. Diamonds slow it down even more. Who can tell what the permeability or permittivity is somewhere far in outer space. My guess is that the speed of light in free space has been measured as accurately as it can be done.

    Molecool, When you say wrong, by how much do you think it is?
    Reply With Quote  
     

  5. #4  
    exchemist
    Join Date
    May 2013
    Location
    London
    Posts
    3,527
    Quote Originally Posted by Janitor View Post
    The speed of light depends on the permittivity and the permeability of the matter through which light travels. Maxwell's equation in regard to the speed of light shows that. The speed of light is affected by gravity; black holes are proof of that. Light also slows down when going through glass or water. Diamonds slow it down even more. Who can tell what the permeability or permittivity is somewhere far in outer space. My guess is that the speed of light in free space has been measured as accurately as it can be done.

    Molecool, When you say wrong, by how much do you think it is?
    Actually if you read the link it makes clear the alleged effect would be very small.
    Reply With Quote  
     

  6. #5  
    Moderator Moderator Markus Hanke's Avatar
    Join Date
    Nov 2011
    Location
    Ireland
    Posts
    7,302
    Quote Originally Posted by molecool View Post
    The Speed Of Light Might Be Wrong

    What do you all think?
    The headline is misleading, it is not really "wrong". The issue here is two-fold :

    1. The value of c is a purely local measurement
    2. The vacuum has a non-trivial quantum structure

    The consequences of (2) are negligible on small scales ( i.e. locally ), however, thus far no one has considered what kind of impact quantum effects such as pair production have on the large scale propagation of light. This is a surprising oversight, since now that someone has brought it to our attention it appears to be staring us squarely in the face But I do agree with exchemist in that we should wait for this to go through peer-review first before getting too excited or anxious about it. Also, contrary to what a few pop-sci articles I have seen seem to be claiming, this is not going to "break" all of our existing models on astrophysics and cosmology and send us back to the drawing board with tails between our legs. However, if this turns out to be a real effect, it will necessitate adjustments on some of our models, but the basic principles of cosmology still stand firm.

    In terms of magnitude, this effect would add approximately 1 hour to the propagation time of light for every 37,000 light years of distance.
    Reply With Quote  
     

  7. #6  
    exchemist
    Join Date
    May 2013
    Location
    London
    Posts
    3,527
    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by molecool View Post
    The Speed Of Light Might Be Wrong

    What do you all think?
    The headline is misleading, it is not really "wrong". The issue here is two-fold :

    1. The value of c is a purely local measurement
    2. The vacuum has a non-trivial quantum structure

    The consequences of (2) are negligible on small scales ( i.e. locally ), however, thus far no one has considered what kind of impact quantum effects such as pair production have on the large scale propagation of light. This is a surprising oversight, since now that someone has brought it to our attention it appears to be staring us squarely in the face But I do agree with exchemist in that we should wait for this to go through peer-review first before getting too excited or anxious about it. Also, contrary to what a few pop-sci articles I have seen seem to be claiming, this is not going to "break" all of our existing models on astrophysics and cosmology and send us back to the drawing board with tails between our legs. However, if this turns out to be a real effect, it will necessitate adjustments on some of our models, but the basic principles of cosmology still stand firm.

    In terms of magnitude, this effect would add approximately 1 hour to the propagation time of light for every 37,000 light years of distance.
    This isn't my field but I imagine a lot will turn on the incidence of pair-production events while light is in transit. I thought I had read somewhere that the probability of pair production is related to frequency and (in the context in which I was then reading) would only be significant for gamma rays. But I suppose over intergalactic distances and times of flight, even lower frequency light may undergo this process from time to time.
    Reply With Quote  
     

  8. #7  
    ox
    ox is offline
    Forum Professor
    Join Date
    Mar 2009
    Posts
    1,660
    You can trust neutrinos to go at the speed of light, but not necessarily photons over a vast expanse of space as photons can be interrupted in the vacuum forming electrons and positrons which then annihilate and form another photon, the whole process only taking a 'squillionth' of a second. I think that is what is being implied.
    Reply With Quote  
     

  9. #8  
    Suspended
    Join Date
    Feb 2013
    Posts
    1,774
    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by molecool View Post
    The Speed Of Light Might Be Wrong

    What do you all think?
    The headline is misleading, it is not really "wrong". The issue here is two-fold :

    1. The value of c is a purely local measurement
    2. The vacuum has a non-trivial quantum structure

    The consequences of (2) are negligible on small scales ( i.e. locally ), however, thus far no one has considered what kind of impact quantum effects such as pair production have on the large scale propagation of light. This is a surprising oversight, since now that someone has brought it to our attention it appears to be staring us squarely in the face But I do agree with exchemist in that we should wait for this to go through peer-review first before getting too excited or anxious about it. Also, contrary to what a few pop-sci articles I have seen seem to be claiming, this is not going to "break" all of our existing models on astrophysics and cosmology and send us back to the drawing board with tails between our legs. However, if this turns out to be a real effect, it will necessitate adjustments on some of our models, but the basic principles of cosmology still stand firm.

    In terms of magnitude, this effect would add approximately 1 hour to the propagation time of light for every 37,000 light years of distance.
    Too bad that the "Like" button doesn't work anymore. So, you get a star.
    Reply With Quote  
     

  10. #9  
    exchemist
    Join Date
    May 2013
    Location
    London
    Posts
    3,527
    Quote Originally Posted by ox View Post
    You can trust neutrinos to go at the speed of light, but not necessarily photons over a vast expanse of space as photons can be interrupted in the vacuum forming electrons and positrons which then annihilate and form another photon, the whole process only taking a 'squillionth' of a second. I think that is what is being implied.
    I thought, when I read it, that was a bit more to it, in that the pairs would be subject to gravity during their short existence.
    Reply With Quote  
     

  11. #10  
    Forum Sophomore
    Join Date
    Aug 2013
    Posts
    193
    Just a little terminological remark here, this is not really pair production in a sense, this is either called vacuum polarization or photon selfenergy. Important distinction is that in this case fermions are both virtual therefore doesnīt exist at all.

    edit: OK, Motl showed that this article is BS, shame on me for not seeing this :-D
    Last edited by Gere; July 2nd, 2014 at 04:41 PM.
    Reply With Quote  
     

  12. #11  
    exchemist
    Join Date
    May 2013
    Location
    London
    Posts
    3,527
    Quote Originally Posted by Gere View Post
    Just a little terminological remark here, this is not really pair production in a sense, this is either called vacuum polarization or photon selfenergy. Important distinction is that in this case fermions are both virtual therefore doesnīt exist at all. I fast-read the article and seems legit enough though I donīt really think that approximation used (classical gravitational potential acting on virtual quantum particles) will be sufficient for something more than rough estimate of order. For precise calculation one would indeed need theory of quantum gravity. While math holds in this approximation we need experiment.
    OK thanks for this, I am a bit out of my depth when it comes to QED.
    Reply With Quote  
     

  13. #12  
    Brassica oleracea Strange's Avatar
    Join Date
    Oct 2011
    Location
    喫茶店
    Posts
    17,036
    Luboš Motl has a rather poor opinion of this paper and is typically blunt about it:
    The Reference Frame: Franson's "breakthrough" concerning the speed of light
    ei incumbit probatio qui dicit, non qui negat
    Reply With Quote  
     

  14. #13  
    exchemist
    Join Date
    May 2013
    Location
    London
    Posts
    3,527
    Quote Originally Posted by Strange View Post
    Luboš Motl has a rather poor opinion of this paper and is typically blunt about it:
    The Reference Frame: Franson's "breakthrough" concerning the speed of light
    Interesting rant. But Motl has a bit of form, himself, doesn't he?
    Reply With Quote  
     

  15. #14  
    Brassica oleracea Strange's Avatar
    Join Date
    Oct 2011
    Location
    喫茶店
    Posts
    17,036
    Quote Originally Posted by exchemist View Post
    Interesting rant. But Motl has a bit of form, himself, doesn't he?
    Only for not suffering fools, I think. Although, his definition of a fool may include anyone who disagrees with string theory...
    ei incumbit probatio qui dicit, non qui negat
    Reply With Quote  
     

  16. #15  
    Forum Professor astromark's Avatar
    Join Date
    May 2013
    Location
    New Zealand
    Posts
    1,015
    Would the person that understands string theory please step forward.. Bang.. that's fixed, next...
    I find it concerning that how willing to use the word 'wrong' is the media..
    When a adjustment due to gravity fields is all this is about.. or am I wrong again.
    It's a little like the use of the word lie's.. Some times a shortage of testing experiment can lead to a error of conclusion.. fare.
    Reply With Quote  
     

  17. #16  
    Forum Sophomore
    Join Date
    Aug 2013
    Posts
    193
    Luboš Motl is from my university Oh god hes a legend
    Reply With Quote  
     

  18. #17  
    Forum Isotope
    Join Date
    Feb 2012
    Location
    Western US
    Posts
    2,893
    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by Strange View Post
    Luboš Motl has a rather poor opinion of this paper and is typically blunt about it:
    The Reference Frame: Franson's "breakthrough" concerning the speed of light
    Interesting rant. But Motl has a bit of form, himself, doesn't he?
    I just wish that he were less subtle. It's so hard to figure out what he really means.
    Reply With Quote  
     

  19. #18  
    Suspended
    Join Date
    Feb 2013
    Posts
    1,774
    Quote Originally Posted by molecool View Post
    The Speed Of Light Might Be Wrong

    What do you all think?
    Any "journal" that CHARGES (1950$) for publishing is a scam. Any "paper" published in such a "journal" is not worth the paper it is printed on.
    Reply With Quote  
     

  20. #19  
    Moderator Moderator Cogito Ergo Sum's Avatar
    Join Date
    Jun 2013
    Location
    Belgium
    Posts
    2,519
    Quote Originally Posted by xyzt View Post
    Quote Originally Posted by molecool View Post
    The Speed Of Light Might Be Wrong

    What do you all think?
    Any "journal" that CHARGES (1950$) for publishing is a scam. Any "paper" published in such a "journal" is not worth the paper it is printed on.

    Yet, I have not detected any signs of NJP being a scam. It is not indexed as predatory open-access journal, it has a legitimate Wikipedia article and it is indexed in scientific databases. Is the publication fee the sole reason to assume it is a scam or do you have other reasons?
    "The only safe rule is to dispute only with those of your acquaintance of whom you know that they possess sufficient intelligence and self-respect not to advance absurdities; to appeal to reason and not to authority, and to listen to reason and yield to it; and, finally, to be willing to accept reason even from an opponent, and to be just enough to bear being proved to be in the wrong."

    ~ Arthur Schopenhauer, The Art of Being Right: 38 Ways to Win an Argument (1831), Stratagem XXXVIII.
    Reply With Quote  
     

  21. #20  
    Forum Cosmic Wizard
    Join Date
    Dec 2013
    Posts
    2,408
    So exactly what does it matter if there is a very small error in the measured speed?
    Reply With Quote  
     

  22. #21  
    Suspended
    Join Date
    Feb 2013
    Posts
    1,774
    Quote Originally Posted by Cogito Ergo Sum View Post
    Quote Originally Posted by xyzt View Post
    Quote Originally Posted by molecool View Post
    The Speed Of Light Might Be Wrong

    What do you all think?
    Any "journal" that CHARGES (1950$) for publishing is a scam. Any "paper" published in such a "journal" is not worth the paper it is printed on.

    Yet, I have not detected any signs of NJP being a scam. It is not indexed as predatory open-access journal, it has a legitimate Wikipedia article and it is indexed in scientific databases. Is the publication fee the sole reason to assume it is a scam or do you have other reasons?
    The fee
    The fact that Simon Fraser Fund is bankrolling it
    The fact that none of the serious journals charges ANYTHING for publication
    Don't worry, it will show on Beall's list
    Reply With Quote  
     

  23. #22  
    ▼▼ dn ʎɐʍ sıɥʇ ▼▼ RedPanda's Avatar
    Join Date
    Aug 2012
    Location
    UK
    Posts
    2,737
    Quote Originally Posted by xyzt View Post
    The fact that Simon Fraser Fund is bankrolling it
    I hadn't heard of the Simon Fraser Fund before.
    Could you provide a link to why it is a bad thing?
    SayBigWords.com/say/3FC

    "And, behold, I come quickly;" Revelation 22:12

    "Religions are like sausages. When you know how they are made, you no longer want them."
    Reply With Quote  
     

  24. #23  
    Suspended
    Join Date
    Feb 2013
    Posts
    1,774
    Quote Originally Posted by RedPanda View Post
    Quote Originally Posted by xyzt View Post
    The fact that Simon Fraser Fund is bankrolling it
    I hadn't heard of the Simon Fraser Fund before.
    Could you provide a link to why it is a bad thing?
    I did, scroll down on the page I linked in. It is one of those "universities" that prints you a diploma (for a price).
    Last edited by Howard Roark; July 2nd, 2014 at 06:22 PM.
    Reply With Quote  
     

  25. #24  
    ▼▼ dn ʎɐʍ sıɥʇ ▼▼ RedPanda's Avatar
    Join Date
    Aug 2012
    Location
    UK
    Posts
    2,737
    Quote Originally Posted by xyzt View Post
    I did, scroll down on the page I linked in.
    Do you mean this link?
    Quote Originally Posted by xyzt View Post
    SayBigWords.com/say/3FC

    "And, behold, I come quickly;" Revelation 22:12

    "Religions are like sausages. When you know how they are made, you no longer want them."
    Reply With Quote  
     

  26. #25  
    Suspended
    Join Date
    Feb 2013
    Posts
    1,774
    Quote Originally Posted by RedPanda View Post
    Quote Originally Posted by xyzt View Post
    I did, scroll down on the page I linked in.
    Do you mean this link?
    Quote Originally Posted by xyzt View Post
    yep
    Reply With Quote  
     

  27. #26  
    ▼▼ dn ʎɐʍ sıɥʇ ▼▼ RedPanda's Avatar
    Join Date
    Aug 2012
    Location
    UK
    Posts
    2,737
    Quote Originally Posted by xyzt View Post
    Quote Originally Posted by RedPanda View Post
    Quote Originally Posted by xyzt View Post
    I did, scroll down on the page I linked in.
    Do you mean this link?
    Quote Originally Posted by xyzt View Post
    yep
    But that page doesn't say anything about why the Simon Fraser Fund is a bad thing.
    SayBigWords.com/say/3FC

    "And, behold, I come quickly;" Revelation 22:12

    "Religions are like sausages. When you know how they are made, you no longer want them."
    Reply With Quote  
     

  28. #27  
    Suspended
    Join Date
    Feb 2013
    Posts
    1,774
    Quote Originally Posted by RedPanda View Post
    Quote Originally Posted by xyzt View Post
    Quote Originally Posted by RedPanda View Post
    Quote Originally Posted by xyzt View Post
    I did, scroll down on the page I linked in.
    Do you mean this link?
    Quote Originally Posted by xyzt View Post
    yep
    But that page doesn't say anything about why the Simon Fraser Fund is a bad thing.
    It is one of those "universities" that prints you a diploma (for a price).
    Reply With Quote  
     

  29. #28  
    ▼▼ dn ʎɐʍ sıɥʇ ▼▼ RedPanda's Avatar
    Join Date
    Aug 2012
    Location
    UK
    Posts
    2,737
    Quote Originally Posted by xyzt View Post
    It is one of those "universities" that prints you a diploma (for a price).
    Are you sure?

    "SFU has been rated as Canada's best comprehensive university (in 1993, 1996, 1997, 1998, 2000, 2008, 2009, 2010, 2011 and 2012) in the annual rankings of Canadian universities in Maclean's magazine since 1991. The Higher Education Strategy Associates ranked Simon Fraser University 6th nationally in Science and Engineering and 10th nationally in Social Sciences and Humanities.[17] Research Infosource, Canada's leading provider of research intelligence evaluation, named SFU the top comprehensive university in Canada for "publication effectiveness" in 2006. Similar to most Canadian universities, SFU is a public university, with more than half of funding coming from taxpayers and the remaining from tuition fees. SFU was ranked 8th among all Canadian universities by Academic Ranking of World Universities - 2012, and Webometrics Ranking of World Universities,[18] which ranks universities on their presence on the Internet, ranks Simon Fraser University 5th in Canada, 67th in North America and 83rd in the world."

    Simon Fraser University - Wikipedia, the free encyclopedia
    SayBigWords.com/say/3FC

    "And, behold, I come quickly;" Revelation 22:12

    "Religions are like sausages. When you know how they are made, you no longer want them."
    Reply With Quote  
     

  30. #29  
    Suspended
    Join Date
    Feb 2013
    Posts
    1,774
    Quote Originally Posted by RedPanda View Post
    Quote Originally Posted by xyzt View Post
    It is one of those "universities" that prints you a diploma (for a price).
    Are you sure?

    "SFU has been rated as Canada's best comprehensive university (in 1993, 1996, 1997, 1998, 2000, 2008, 2009, 2010, 2011 and 2012) in the annual rankings of Canadian universities in Maclean's magazine since 1991. The Higher Education Strategy Associates ranked Simon Fraser University 6th nationally in Science and Engineering and 10th nationally in Social Sciences and Humanities.[17] Research Infosource, Canada's leading provider of research intelligence evaluation, named SFU the top comprehensive university in Canada for "publication effectiveness" in 2006. Similar to most Canadian universities, SFU is a public university, with more than half of funding coming from taxpayers and the remaining from tuition fees. SFU was ranked 8th among all Canadian universities by Academic Ranking of World Universities - 2012, and Webometrics Ranking of World Universities,[18] which ranks universities on their presence on the Internet, ranks Simon Fraser University 5th in Canada, 67th in North America and 83rd in the world."

    Simon Fraser University - Wikipedia, the free encyclopedia
    pretty much
    Reply With Quote  
     

  31. #30  
    Forum Cosmic Wizard
    Join Date
    Dec 2013
    Posts
    2,408
    Simon Fraser is a real university located in Vancouver, British Columbia, Canada. To suggest it is a low grade diploma mill is simply ridiculous.
    It does have a funding arrangement for graduate students to publish in open access journals.
    The journals must be ones listed in the Directory of Open Access Journals
    Directory of Open Access Journals
    Directory of Open Access Journals

    But back to the serious question.
    What does a small difference in the measured speed of light at interstellar distances through space really make?
    We already know that space is not a perfect vacuum and the theoretical speed of light is only through a perfect vacuum.
    Reply With Quote  
     

  32. #31  
    Forum Junior
    Join Date
    Mar 2014
    Location
    WA
    Posts
    287
    I believe some evidence to possibly prove this is inaccurate. Since gravity waves are similar to light waves from what I have been reading. Wouldn't this break the laws of energy? Because if a n object takes 5newtons of force to move against gravity in space on return it would have less energy on return but instead of 7 hours it would be in newtons.

    If you catch what I'm saying that would be the destruction of energy which is impossible. The only way is if light and gravity waves are affected exactly the same on the way out
    Reply With Quote  
     

  33. #32  
    Moderator Moderator Markus Hanke's Avatar
    Join Date
    Nov 2011
    Location
    Ireland
    Posts
    7,302
    Quote Originally Posted by ScienceNoob View Post
    Since gravity waves are similar to light waves from what I have been reading.
    Actually, there are some major differences, most notably that gravitational radiation is quadrupole in nature ( EM is dipole ), and in that the polarisation states of the two are different ( 45 degrees v 90 degrees ). The notion of "energy-momentum carried by a gravitational wave" is also problematic, since energy is not localisable in GR - one has to average out over several wavelengths to make this a meaningful concept, unlike in the case of EM.
    Reply With Quote  
     

  34. #33  
    Forum Junior
    Join Date
    Mar 2014
    Location
    WA
    Posts
    287
    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by ScienceNoob View Post
    Since gravity waves are similar to light waves from what I have been reading.
    Actually, there are some major differences, most notably that gravitational radiation is quadrupole in nature ( EM is dipole ), and in that the polarisation states of the two are different ( 45 degrees v 90 degrees ). The notion of "energy-momentum carried by a gravitational wave" is also problematic, since energy is not localisable in GR - one has to average out over several wavelengths to make this a meaningful concept, unlike in the case of EM.
    Thank you for the information!

    I am about to make a post in regards to this same concept in personal ideas/theories i'd love to have you take a look at it, thanks!
    Reply With Quote  
     

  35. #34  
    mvb
    mvb is offline
    Thinker Emeritus
    Join Date
    Dec 2012
    Location
    Delaware, USA
    Posts
    195
    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by molecool View Post
    The Speed Of Light Might Be Wrong

    What do you all think?
    The headline is misleading, it is not really "wrong". The issue here is two-fold :

    1. The value of c is a purely local measurement
    2. The vacuum has a non-trivial quantum structure

    The consequences of (2) are negligible on small scales ( i.e. locally ), however, thus far no one has considered what kind of impact quantum effects such as pair production have on the large scale propagation of light. This is a surprising oversight, since now that someone has brought it to our attention it appears to be staring us squarely in the face But I do agree with exchemist in that we should wait for this to go through peer-review first before getting too excited or anxious about it. Also, contrary to what a few pop-sci articles I have seen seem to be claiming, this is not going to "break" all of our existing models on astrophysics and cosmology and send us back to the drawing board with tails between our legs. However, if this turns out to be a real effect, it will necessitate adjustments on some of our models, but the basic principles of cosmology still stand firm.

    In terms of magnitude, this effect would add approximately 1 hour to the propagation time of light for every 37,000 light years of distance.
    I have read over the paper. Although I have not verified the details of the mathematical calculations, barring algebraic or numeric errors the QED parts make sense. I am not knowledgeable enough to review the General Relativity he uses. Basically he puts the GR in as a potential energy in the QED Lagrangian, which is surely an approximation and which I cannot judge the reasonableness of. If that idea is reasonable, then he has a very interesting idea. Basically he is saying that there is in Relativity a speed of "ideal" light, the speed light would have if it had no interactions of any kind. Then there is the actual speed of light which he gets analogously to the way the effective speed of light in dielectrics is obtained. The physics behind the smaller speed is that the photon can very briefly turn into an electron-positron pair, which might behave somewhat differently than the photon that gave rise to them. This could indeed be very, very wrong, but it isn't nonsense and the size of the effect he calculates is reasonable. I am very anxious to get the opinion of a General Relativist about the technique.

    I haven't yet heard any professional ideas that definitively that refute this idea, and actually nothing that indicates that the writer had actually read the paper carefully. That lack does not mean, of course, that the paper isn't wrong, but I haven't yet seen a persuasive rebuttal.

    I should perhaps mention that I am a retired particle theorist but have done no recent calculations in the field.
    Reply With Quote  
     

  36. #35  
    Moderator Moderator Markus Hanke's Avatar
    Join Date
    Nov 2011
    Location
    Ireland
    Posts
    7,302
    Quote Originally Posted by mvb View Post
    I am very anxious to get the opinion of a General Relativist about the technique.
    I would love to be able to make more technical comments on this, but my problem is that I am sitting on the opposite end of the bench - I am fairly well versed in GR, but my knowledge about QFTs is extremely limited. What we need is someone who is equally comfortable in both realms. Personally I think the paper does make sense, and I can't immediately spot any major objections either.
    Reply With Quote  
     

  37. #36  
    Forum Junior whizkid's Avatar
    Join Date
    Jan 2013
    Posts
    282
    Quote Originally Posted by ox View Post
    photons can be interrupted in the vacuum forming electrons and positrons which then annihilate and form another photon, the .
    Quote Originally Posted by ScienceNoob View Post
    Since gravity waves are similar to light waves from what I have been reading.
    Are these two proposition true, is it mainstream ascertained fact? If so can you give a link where to learn more

    Thanks
    Reply With Quote  
     

  38. #37  
    Moderator Moderator Markus Hanke's Avatar
    Join Date
    Nov 2011
    Location
    Ireland
    Posts
    7,302
    Quote Originally Posted by whizkid View Post
    Quote Originally Posted by ox View Post
    photons can be interrupted in the vacuum forming electrons and positrons which then annihilate and form another photon, the .
    Quote Originally Posted by ScienceNoob View Post
    Since gravity waves are similar to light waves from what I have been reading.
    Are these two proposition true, is it mainstream ascertained fact? If so can you give a link where to learn more
    Pair production from photons is empirical fact, so the answer to that part is yes.
    As for gravitational waves, the answer would have to be no - gravity waves and electromagnetic waves are not really similar other than in the trivial sense that both obey wave equations. Other than that, there are major differences between the two.
    Reply With Quote  
     

  39. #38  
    Forum Junior whizkid's Avatar
    Join Date
    Jan 2013
    Posts
    282
    Quote Originally Posted by Markus Hanke View Post
    Pair production from photons is empirical fact, so the answer to that part is yes.

    As for gravitational waves, the answer would have to be no - gravity waves and electromagnetic waves are not really similar other than in the trivial sense that both obey wave equations. Other than that, there are major differences between the two.
    It is a fact, but you need a nucleus or an obstacle, the post made understand that a photon travelling in vacuum undergoes such process
    What are the main differences between them? are gravitational waves EMR anyway?
    and why are they different from regular gravity?
    Reply With Quote  
     

  40. #39  
    Forum Sophomore
    Join Date
    Aug 2013
    Posts
    193
    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by mvb View Post
    I am very anxious to get the opinion of a General Relativist about the technique.
    I would love to be able to make more technical comments on this, but my problem is that I am sitting on the opposite end of the bench - I am fairly well versed in GR, but my knowledge about QFTs is extremely limited. What we need is someone who is equally comfortable in both realms. Personally I think the paper does make sense, and I can't immediately spot any major objections either.

    Take a look at this sentence: "According to general relativity [38, 39], the speed of light c as measured in a global reference frame is given by..."

    also in Figure 2 (a): " Any effect that this process may have on the velocity of light is removed using renormalization techniques to give the observed value of c0. " this doesnīt seem right.

    Also change in energy of photon would lead to change in wavelenght, he ignores that and this leads to his change in speed of light. Also he calculated this thing for one such process but in reality these processes are happening repeatedly, that would lead to extremely fast loss of photon energy.

    I think the major problem though is that speed of light is defined by measurement of the very same photons which undergo such loop processes.
    Reply With Quote  
     

  41. #40  
    mvb
    mvb is offline
    Thinker Emeritus
    Join Date
    Dec 2012
    Location
    Delaware, USA
    Posts
    195
    Quote Originally Posted by Gere View Post
    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by mvb View Post
    I am very anxious to get the opinion of a General Relativist about the technique.
    I would love to be able to make more technical comments on this, but my problem is that I am sitting on the opposite end of the bench - I am fairly well versed in GR, but my knowledge about QFTs is extremely limited. What we need is someone who is equally comfortable in both realms. Personally I think the paper does make sense, and I can't immediately spot any major objections either.

    Take a look at this sentence: "According to general relativity [38, 39], the speed of light c as measured in a global reference frame is given by..."

    also in Figure 2 (a): " Any effect that this process may have on the velocity of light is removed using renormalization techniques to give the observed value of c0. " this doesnīt seem right.

    Also change in energy of photon would lead to change in wavelenght, he ignores that and this leads to his change in speed of light. Also he calculated this thing for one such process but in reality these processes are happening repeatedly, that would lead to extremely fast loss of photon energy.

    I think the major problem though is that speed of light is defined by measurement of the very same photons which undergo such loop processes.
    I agree that the first of your quotations raises some concern. Your comment that he seems to have kept the wavelength of the photon constant rather than using it to compensate for the change of energy looks very cogent. This looks to be a significant problem.

    On your second point, I assume he is using standard techniques here. The problem is that diagram (a) gives an infinite result. His result would still be interesting if the difference between (a) and (b) would be finite, as the infinity would be absorbed into value of c in the Lagrangian. If the rest of the work makes sense a check that this renormalization works properly should be checked formally, and it would be by somebody even if he didn't. Also, both parts of Figure 2 would conserve energy in normal QFT since no new free particles are created by the diagram.

    On your third point, one effect of his argument, if valid, would seem to be the replacement of the "speed of light" in Special Relativity by a "maximum possible speed" not directly attached to the photon. This is another place where justification would be needed.

    Clearly Franson's paper would be only a beginning, if (and only if) it makes sense at all. The wavelength business seems to me to be a point that is very damaging. It makes me worry about whether his method of putting gravitational effect into QFT for the photon is indeed justified.
    Last edited by mvb; July 8th, 2014 at 08:37 AM.
    Reply With Quote  
     

  42. #41  
    Suspended
    Join Date
    Feb 2013
    Posts
    1,774
    Quote Originally Posted by Gere View Post
    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by mvb View Post
    I am very anxious to get the opinion of a General Relativist about the technique.
    I would love to be able to make more technical comments on this, but my problem is that I am sitting on the opposite end of the bench - I am fairly well versed in GR, but my knowledge about QFTs is extremely limited. What we need is someone who is equally comfortable in both realms. Personally I think the paper does make sense, and I can't immediately spot any major objections either.

    Take a look at this sentence: "According to general relativity [38, 39], the speed of light c as measured in a global reference frame is given by..."

    also in Figure 2 (a): " Any effect that this process may have on the velocity of light is removed using renormalization techniques to give the observed value of c0. " this doesnīt seem right.

    Also change in energy of photon would lead to change in wavelenght, he ignores that and this leads to his change in speed of light. Also he calculated this thing for one such process but in reality these processes are happening repeatedly, that would lead to extremely fast loss of photon energy.

    I think the major problem though is that speed of light is defined by measurement of the very same photons which undergo such loop processes.
    Yes, Franson makes a (classical) rookie mistake, there are NO global frames in GR. There is NO such thing as "speed of light c measured in a global frame". Franson takes the COORDINATE light speed as light speed.
    Reply With Quote  
     

  43. #42  
    Forum Sophomore
    Join Date
    Aug 2013
    Posts
    193
    Quote Originally Posted by mvb View Post
    On your second point, I assume he is using standard techniques here. The problem is that diagram (a) gives an infinite result. His result would still be interesting if the difference between (a) and (b) would be finite, as the infinity would be absorbed into value of c in the Lagrangian. If the rest of the work makes sense a check that this renormalization works properly should be checked formally, and it would be by somebody even if he didn't. Also, both parts of Figure 2 would conserve energy in normal QFT since no new free particles are created by the diagram.
    So instead of renormalizing charge he renormalized speed of light? Could you elaborate? I am not overly familiar with renormalization group. My understanding is this:

    we want to find full Feynman propagator for photon. Using simple Dyson equation we can "upgrade" unperturbed propagator



    to full propagator



    where is one particle irreducible diagram.

    Since this can work as internal line between two fermion lines then in some basic Feynman graph one gets a factor of (electrical charge) from both vertexes at the ends of propagator. Therefore internal photon propagator can be written like this



    where is renormalization parameter. We can "easily" calculate that irreducible diagram and get to divergent integral, then use dimensional regularization, split it to finite contribution and divergent term and that divergence is then hidden in renormalized charge and/or renormalized field. This results in modifying lagrangian with corresponding counterterms. That is my understanding.

    I donīt know how to renormalize speed of light using this standard technique. Perhaps you could explain some more. My take on renormalization is very naive and simplistic so any deeper knowledge would be appreciated.
    Reply With Quote  
     

  44. #43  
    mvb
    mvb is offline
    Thinker Emeritus
    Join Date
    Dec 2012
    Location
    Delaware, USA
    Posts
    195
    Quote Originally Posted by Gere View Post
    Quote Originally Posted by mvb View Post
    On your second point, I assume he is using standard techniques here. The problem is that diagram (a) gives an infinite result. His result would still be interesting if the difference between (a) and (b) would be finite, as the infinity would be absorbed into value of c in the Lagrangian. If the rest of the work makes sense a check that this renormalization works properly should be checked formally, and it would be by somebody even if he didn't. Also, both parts of Figure 2 would conserve energy in normal QFT since no new free particles are created by the diagram.
    So instead of renormalizing charge he renormalized speed of light? Could you elaborate? I am not overly familiar with renormalization group. My understanding is this:

    we want to find full Feynman propagator for photon. Using simple Dyson equation we can "upgrade" unperturbed propagator



    to full propagator



    where is one particle irreducible diagram.

    Since this can work as internal line between two fermion lines then in some basic Feynman graph one gets a factor of (electrical charge) from both vertexes at the ends of propagator. Therefore internal photon propagator can be written like this



    where is renormalization parameter. We can "easily" calculate that irreducible diagram and get to divergent integral, then use dimensional regularization, split it to finite contribution and divergent term and that divergence is then hidden in renormalized charge and/or renormalized field. This results in modifying lagrangian with corresponding counterterms. That is my understanding.

    I donīt know how to renormalize speed of light using this standard technique. Perhaps you could explain some more. My take on renormalization is very naive and simplistic so any deeper knowledge would be appreciated.
    I haven't figured out if he actually did any renormalization or not, and it isn't normally necessary to renormalize velocities, at least explicitly. I am worried that he may simply have assumed E = h f is valid and used that relation to get the speed of light. If so, I need to see a justification for putting a potential energy for the photon into E = h f. I now think that this may be the weak point of the paper.

    However, in any event I would like to know rigorously that virtual pair-production does or does not effect properties that depend on a particle's moving at the speed of light. I haven't seen it done, and I suspect that no one thinks about the possibility. After all, this process is much like the progress of a photon through a dielectric, which in fact does affect the effective speed of the light. Moreover, neutrinos can move faster than "effective photons" in a dielectric.
    Reply With Quote  
     

  45. #44  
    Forum Sophomore
    Join Date
    Aug 2013
    Posts
    193
    He doesnīt do any renormalization in his paper. He actually says that in standard renormalization procedure the effect of selfenergy on speed of light is removed. Figure 2 (a): "...Any effect that this process may haveon the velocity of light is removed using renormalization techniques to give the observed value of c0.... " This doesnīt seem right to me.
    Reply With Quote  
     

  46. #45  
    mvb
    mvb is offline
    Thinker Emeritus
    Join Date
    Dec 2012
    Location
    Delaware, USA
    Posts
    195
    Quote Originally Posted by Gere View Post
    He doesnīt do any renormalization in his paper. He actually says that in standard renormalization procedure the effect of selfenergy on speed of light is removed. Figure 2 (a): "...Any effect that this process may haveon the velocity of light is removed using renormalization techniques to give the observed value of c0.... " This doesnīt seem right to me.
    What he is saying is that the infinite parts of the renormalization are not changed, and the additional terms are finite. I read past that originally, and I don't especially like it now that you have pointed it out. Skimming section 3 again I see that he really hasn't checked the finiteness of the process, and he assumes E=h f to get the speed. So, as you are pointing out, he hasn't really proved anything.

    So I think where we are is that he has a rough calculation with the intriguing result that he roughly matches the delay time between arrival of the photons and the neutrinos from the supernova of 1987, and no proof that his calculation is likely to be correct. I hope (I think) that someone will try to do the calculation better. It has been 50 years more or less since I worked through a real renormalization calculation, and I don't really want to dig out the old books and try it again, especially since a negative result would likely get no attention whatsoever.
    Reply With Quote  
     

  47. #46  
    Moderator Moderator Markus Hanke's Avatar
    Join Date
    Nov 2011
    Location
    Ireland
    Posts
    7,302
    Quote Originally Posted by whizkid View Post
    but you need a nucleus or an obstacle
    Not necessarily. There is a non-zero probability for this to happen spontaneously in vacuum. That's the main idea behind the paper.

    What are the main differences between them?
    The two main differences are :

    1. Gravitational waves are quadrupole in nature, whereas EM radiation is dipole
    2. The polarisation modes for gravitational waves are offset by 45 degrees, whereas the EM ones are 90 degrees

    are gravitational waves EMR anyway?
    No, gravitational waves are periodic oscillations in the metric of space-time, whereas EM radiation are excitations of the electromagnetic field.

    and why are they different from regular gravity?
    I am not sure how you define "regular gravity". Under normal circumstances gravity is static, in the sense that the coefficients of the metric don't depend on time. Gravitational waves on the other hand are described by a time-dependent metric.
    Last edited by Markus Hanke; July 10th, 2014 at 01:20 AM.
    Reply With Quote  
     

  48. #47  
    Forum Junior whizkid's Avatar
    Join Date
    Jan 2013
    Posts
    282
    Excellent, and clear as usual, Marcus, thanks a lot. You are a great tutor!
    Reply With Quote  
     

  49. #48  
    Moderator Moderator Markus Hanke's Avatar
    Join Date
    Nov 2011
    Location
    Ireland
    Posts
    7,302
    Quote Originally Posted by whizkid View Post
    Excellent, and clear as usual, Marcus, thanks a lot. You are a great tutor!
    Reply With Quote  
     

  50. #49  
    mvb
    mvb is offline
    Thinker Emeritus
    Join Date
    Dec 2012
    Location
    Delaware, USA
    Posts
    195
    I just ran into another piece of data that is relevant to the Franson paper, because it provides another possible mechanism for later arrival of photons relative to neutrinos from supernova 1987a. In a note about recent scientific results it was reported that evidence had recently been found for the passage of photons from an astronomical object through an ionized plasma, with a resulting change in the frequency of the photons. The plasma acts like a dielectric for the photons going through; this means that the effective speed of the light will be lowered while it is passing through the plasma. It wouldn't take much of this to produce the time difference between the neutrinos that are believed to have come from the supernova and the light seen in ordinary telescopes. This means that there is a possible conventional explanation for the neutrinos arriving first, preventing a proof that the photons were delayed by virtual pair production.

    I still think that the idea is fascinating, but I don't see how it will be quickly made plausible that the idea is correct.
    Reply With Quote  
     

Similar Threads

  1. Replies: 20
    Last Post: April 9th, 2014, 09:05 PM
  2. Speed of data traveling in relation to speed of light
    By Polarbear1981 in forum Physics
    Replies: 8
    Last Post: February 21st, 2014, 04:17 AM
  3. Speed of light
    By gene4452 in forum General Discussion
    Replies: 1
    Last Post: June 7th, 2012, 04:13 PM
  4. Is it the speed of light the max speed
    By MadeinRo in forum Physics
    Replies: 17
    Last Post: August 14th, 2011, 07:00 PM
Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •