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Thread: Why are General Relativity's real limits never discussed?

  1. #1 Why are General Relativity's real limits never discussed? 
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    General Relativity's limits are always discussed with respect to quantum physics but GR has limits outside black holes.

    PSR B1913+16
    PSR B1534 +12
    PSR B2127+11C
    PSR J1756-2251
    PSR J0737-3039A
    PSR J1518+4904
    B2303+46
    V541 Cygni
    DI Herculies
    AS Camelopardalis

    General Relativity does not describe the motion of the last 7 and there is nothing on the first 3. They mainly talk about Gravitational Waves but when GR was developed they talked about precession.


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    Could you elaborate, or give me some seeds to research from? This is very interesting, but as you might understand ..... these examples aren't the first ones you hear about in a physics class.


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    Sorry for the late reply. The fact the you do not here about these systems in a physics class does not suprise me.

    On a high school level it is understood. Maybe even on an undergraduate level but this exclusion exist at higher levels. If you were doing research on DI Herculis which is the most famous and cited you might get the article below.

    arXiv:0909.2861v1 (Link added by moderator)

    This is a recent article by a group of physicist from MIT. I contacted Simon Abrecht one of the authors because the introduction infers that DI Herculis presents the only problem. That title works best for the planet Mercury with respect to Newton's Universal law of Gravity and remember Einstein solved Mercury to prove he was on the right track with a new theory of gravity.

    Assume the inference has no merit, I also asked Simon Abrecht was their solution to the DI Herculis problem being applied to some of the other binary stars listed. This is a very important question because a solution in astronomy cannot just work for one system. Einstein proved precession exist in all planetary motion. Mercury's precession effects are the most detectable.

    Google any of the stars listed and you will find scholarly reports on the data rather the interpretation of the data. A three body system has also been used to explain DI Herculis strange motion but the third body has yet to be found.
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    I do not understand, why you think that these objects contradict the current understanding of the physics of gravity and mechanics. The cited article is a good example of scientific progress on the basis of already established physics. To me, the article is a very valid explanation of the observed phenomenon of precession speeds.

    From the information given in the caption of Figure 1, I assume that the observing time needed to attain those data is quite big. More and more smaller observatories are closing down with the preference of big telescopes for "more sexy" astronomy. The precious time at those powerful instruments is rarely "wasted" for such dull experiments. So, programmes that repeatedly need much time, can nowadays only be carried out at rather small observatories. And DI Her seems quite bright to me (visual magnitude of 8.5), so that optical spectra can be obtained in a reasonable amount of time. In comparison:

    V541 Cyg: V=10.35 mag
    AS Cam: V = 8 mag

    I expect that other binary systems will be observed and analysed in the same way in the near future.

    This example teaches us that we should not question fundamental physics each time the results do not follow our predictions. In most cases, the assumptions on which the predictions are based are incorrect because of the limited amount of information that can be drawn from individual observations.
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    Dear Dishmaster,

    Our current understanding of gravity and mechanics is largely if not all really based on General Relativity. The links below are scholarly reports on General Relativity's predictions with respect to V541 Cyg and AS Cam.

    http://www.iop.org/EJ/article/1538-3...0293.text.html
    http://www.springerlink.com/content/v6116758k5464k13/

    The observations are clear as well as General Relativity's predications.

    Most scholarly reports on PSR 1518 +4904 and B2303 +46 do not cite the General Relativity prediction but we know the prediction is wrong.

    PSR J0737-3039A is the fastest system and I have never seen the General Relativity predication so I can say if it is wrong or not. My guess is if the prediction was correct it would have been cited.

    Based on the observational data, I good reason to question our theoretical understanding of gravity and mechanics.


    I DEFEND ASTRONOMY as an observation science which ensures our theoretical models grow to explain the unexplained. If the MIT groups assessment of DI Herculis is to say we have found something unique in DI Herculis orbital configurations that might point to why it precession slower than other systems then I applaud that as astronomy as an observation science attempting to explain and unexplained phenomena. If the MIT groups assessment of DI Herculis is an attempt to defend General Relativity then I say their conclusion is premature because they will have to defend it with that analysis in each case where General Relativity is wrong.

    Astronomy as an observational science should not be questioned theories should. Newton was considered the greatest but when the motion of Uranus was not consistent with what he said.

    Astronomers said,"There is either another planet in the area or Newton is wrong" The astronomers discovery Neptune as Newton's theory pointed to where the planet should be. That is the purest relationship between Astronomers and Theoreticians.

    Mercury's motion put Newton to the test again. Astronomers said,"There is either another planet in the area or Newton is wrong". Newton was wrong and a new era in Gravitational theory began with Einstein. Astronomers tried to come to Netwon's defense with the planet Vulcan but it was never detected because it did not exist. I love astronomy because it is hard work making observations just like it is hard work coming up with theories but Astronomy has no obligation to support any theory that nature puts in question by question itself. Astronomers are responsible for building better tools so we can get the most accurate observations and theoretical physicist are responsible for building better models that accurate explain those observations. Astronomers instrumentation has gotten better since Hubble and now it is time for theoreticians to get better because they have shown little success since Einstein

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    Unification123
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    Quote Originally Posted by Unification123
    The links below are scholarly reports on General Relativity's predictions with respect to V541 Cyg and AS Cam.

    http://www.iop.org/EJ/article/1538-3...0293.text.html
    http://www.springerlink.com/content/v6116758k5464k13/

    The observations are clear as well as General Relativity's predications.
    First, can you please enlighten us, what you call "scholarly reports"? To me, it sounds like you question those publications. The publications you cite are the results of the research of professional scientists.

    I cannot comment on the results and the implications of those studies, but it is clear that every scientific result can only be as good as the technique employed to derive them. Therefore, any scientific result must be regarded preliminary until new techniques and technologies lead to more precise results. This also holds for any predictions made on the basis of previous results. So, if a prediction is wrong, the reason most likely a lack of observational data strongly affected by measurement uncertainties and not the theory on which the model calculation is based.
    Quote Originally Posted by Unification123
    Most scholarly reports on PSR 1518 +4904 and B2303 +46 do not cite the General Relativity prediction but we know the prediction is wrong.
    You don't know what the predictions are, but you know they are wrong? Very strange!
    Quote Originally Posted by Unification123
    PSR J0737-3039A is the fastest system and I have never seen the General Relativity predication so I can say if it is wrong or not. My guess is if the prediction was correct it would have been cited.
    My guess is that the measurements available to date are not sufficient to draw any conclusions.
    Quote Originally Posted by Unification123
    I DEFEND ASTRONOMY as an observation science which ensures our theoretical models grow to explain the unexplained. If the MIT groups assessment of DI Herculis is to say we have found something unique in DI Herculis orbital configurations that might point to why it precession slower than other systems then I applaud that as astronomy as an observation science attempting to explain and unexplained phenomena. If the MIT groups assessment of DI Herculis is an attempt to defend General Relativity then I say their conclusion is premature because they will have to defend it with that analysis in each case where General Relativity is wrong.

    Astronomy as an observational science should not be questioned theories should.
    But the result and conclusion of their work is strongly based on the validity of General Relativity. The only difference to earlier studies is that the observations are now much more precise than anything before. This allowed them to correct and sophisticate the previous inaccurate model predictions. It is not the fundamental physics that had to be modified - it was the assumptions of physical properties that were too inaccurate that lead to the reassessment.

    Observations are useless without a proper theory. They are used as a tool to test theories. But every measurement is affected by uncertainties that can lead to misinterpretations.
    Quote Originally Posted by Unification123
    Mercury's motion put Newton to the test again. Astronomers said,"There is either another planet in the area or Newton is wrong". Newton was wrong and a new era in Gravitational theory began with Einstein. Astronomers tried to come to Netwon's defense with the planet Vulcan but it was never detected because it did not exist.
    If I recall correctly, General Relativity was not "invented" to explain the orbit of Mercury - it was derived independently. Later, it was successfully applied to explain the precession of Mercury's orbit.
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  8. #7  
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    Dear Dishmaster,

    I use the term scholarly report to let the reader know that the observations were done by professionals that everyone respects.

    PSR 1518+4904 and B2303+46 General Relativity predictions are wrong because I have other sources. Scholarly sources are not the only sources. Their just the best sources for ending a debate which theoreticians like to do.

    I tried to get the General Relativity predictions for PSR J0737-3039A and I got nothing so it was my guess this was wrong too. That's a logical guess but I might be wrong. CAN YOU TELL ME THE PREDICTION BECAUSE I WOULD LOVE TO KNOW? Another guess is that the binary star was so resently discoverd that they do not have perameters measured to test against relativity. I think that might be the case.

    DI Herculis precession measurement has changed? The first measurement was approximately 1 degree/100 years and the later prediction was approximately 1.4 degree/100 years. This brought it closer to Einstein's approximately 4.3 degrees/100 years. These are just measurement and to my knowledge can be make without theory. Mercury's precession was know and measurement was made before Einstein.

    Authur Eddingtion asked Einstein what did his theory have to say about Mercury. It was the first test of General Relativity. Mercury's precession is not a prediction of General Relativity it is an explanation. The deflection of Sunlight by 1.75 arc seconds is a prediction. But that measurement can be made with General Relativity.

    A measurement in some case can be made without a theory. Theory's attement to explain that observation and then if that pattern is consistent in the theory, the theory can make testable predictions.

    Take care,

    Unification123
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  9. #8  
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    Quote Originally Posted by Unification123
    DI Herculis precession measurement has changed? The first measurement was approximately 1 degree/100 years and the later prediction was approximately 1.4 degree/100 years. This brought it closer to Einstein's approximately 4.3 degrees/100 years.
    Thanks for the clarifications. I suppose the other predictions are not available, because nobody cared to calculate them yet. But that's just a guess. As I already pointed out, it is quite difficult to get observing time to make the necessary studies.

    No, the measured value of the precession has not changed considerably. But the accuracy of its measurement has been improved. This obviously reduced the uncertainties of the models to be applied and consequently the parameter space of the model calculations that still agree with the measurements.

    You still seem to believe that the higher value is the one predicted by General Relativity and the measured is not, but that's only true for aligned spins. As far as I understand, the group of scientists managed to derive a model calculation, where the spins are not alinged with the orbits - still assuming General Relativity.

    This is what I am pointing to. The old prediction was made under false assumptions, namely that the rotation axis and orbits are aligned. But apparently, this is not true. If you assume other configurations, General Relativity works just fine. The same may be true for the other examples.
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    Dear Dishmaster,

    My knowledge of the details of how measurements are made is not good enough for me to defend all the measurements made by Astronomers.

    I do respect Astronomy as an observational science which as developed quite a bit since. Eddington and Hubble.

    Theoretical physics with respect to astronomy has not developed as fast and this is the difference between theory and observation.

    Powerful theories make testable predictions and General Relativity works very well in many cases but when it does not work we must look at the theory as partly flawed too. It is not wrong, if Einstein were alive he would be unifiying General Relativity with Electromagnetics. Remember these binary star systems have some of the strongest electromagnetic fields known in the universe. Einstein was not afraid to make changes to his theory. Hubble showed him the universe was expanding and he removed the Cosmological Constant. If Astronomers had not discovered the universe was accelerating Einstein's biggest blunder would have remained so. I like the way theoretician's become authorities on things they should have predicted if their models were so powerful and beyond question. The fundemental laws of physics already exist, it is the theoretician's job to discover the relationships and make broader generalizations that can accommedate our understanding of natural phenomena.

    Any theory can be tweaked to fit a discovery but it is always better when a theory is able to make the prediction first.

    Theoreticians did not predict.

    The Accelerating Universe
    Dark Matter
    Dark Energy
    Uneven Distributions in the back ground radiation
    Dark Flow *Maybe*

    All these major additions to our understanding of the universe were made by the fact that Astronomy as a more exact science is becoming a reality. If any current theory based on General Relativity or Quantum Gravity had made these predictions this discussion would not be taking place. Measurement quality is an issue for debate but the fact that theoreticans miss the ball on a number of major discoveries points to a bigger issue and it really is not about General Relativity. It points to the fact that no real major testable contributions to the development of General Relativity has been made since Einstein's death. Hubble and Eddingtion would have been proud of today's Astronomers even if they don't have the most exact measurements. I don't think Einstein would have the same opinion of theoretical physicst with respect to astronomy. We defend Einstein by making his theory better not by avoiding its flaws.

    Take care,

    Unification123
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  11. #10  
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    Quote Originally Posted by Unification123
    Theoreticians did not predict.

    The Accelerating Universe
    Dark Matter
    Dark Energy
    Uneven Distributions in the back ground radiation
    Dark Flow *Maybe*
    Dear Uni,
    I think, you are mistaken in this point. None of these phenomena have been directly verified by observation or experiment. They are inferred indirectly from observations interpreting the results based on a certain model. The models themselves are based on certain assumptions that are combined with an underlying theory. The reason, why e.g. the accelerating universe (or even initially the expanding universe) was not predicted, is that it is only one of the many possible solutions to the same set of equations. And the acceleration is a result of certain observations and assumptions how to interpret them - although I believe that it is currently the most probable explanation. But, yes, I agree that observational astrophysics are vital to the understanding of the nature of the universe.

    Just one example: Dark Matter
    It has never been observed directly. There are only indirect indications that such an exotic matter exists. Many of the phenomena that are assigned to it can also be explained in a different way. Ironically, I personally tend to think that much of the reported phenomena could be related to an incomplete understanding of gravity. I am trying to keep an open mind here and not to exclude any possibilities. I also think, in this case it is well justified, because up to now, nobody has yet detected the smallest grain of Dark Matter.

    It is important to distinguish between observation and its interpretation. Another example here: Are you familiar with the images of the Hubble Deep Fields? They are full of very distant objects of different colour. Pick the red ones, and you can interpret their colour in different ways.
    a) cosmological redshift
    b) proper motion (Doppler shift)
    c) colour excess and light extinction by dense dust and gas
    d) cool objects emitting a Black Body spectrum with their peak emission in the red part of the visual spectrum

    Now, what is the correct interpretation? All of those alternatives are absolutely valid and agree with established theories. But without any further investigation, you just cannot tell. So, in essence, without further scrutiny it is dangerous to say that certain observations have demonstrated anything.
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    Dear Dishmaster,

    An incomplete understanding of gravity may be the problem. We agree that there is a problem. Einstein showed that Newton gave us an incomplete understanding of gravity so it's possible. Personally, I do not believe it is an incomplete understanding of gravity. I believe it's an incomplete understanding of how gravitational forces interact with electromagnetic forces in stars and galaxies. This was suppose to be the next step, not by Einstein but by the generations that followed. Oh and the reason Dark Matter has not been detected as a particle is, maybe it's not a particle. Looking at the problem different is really what makes one generation's way of approaching a problem different from another. And I am not familiar the Hubble Deep Field observational analysis.

    Take care,

    Unification123
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