What is the use of General Relativity

Discussion in 'Pseudoscience' started by The God, Dec 25, 2016.

  1. The God Valued Senior Member

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    Let me skip the intro on GR, but how useful is GR?

    1. The extreme approximate calculations gave a result which roughly matched with the Mercury Precession. I am not sure, I will cross check and revert, but why there is no news about precession of other planets or systems? GR figures do not match there ? Precession of Mercury some few arc seconds in a century, is not of much use for us.

    2. Deflection of light by an Object : This also matches with some uncertainty with observed deflection around Sun. But there are still some issues with Gravitational Lensing Images in certain cases. Mass and mass profile of many galaxies or big objects is not known to a very accurate level, so these deflections figures are a kind of you-help-me-I-help-you.

    3. GPS : Everyone is fed that GR plays a massive role in GPS calculations. There are two questions, Does it really play any role or every one is blindly taken for ride? The second question is no other alternative to GR can help in GR calculations.

    Is it really desirable to keep the GR in such high esteem with Black holes, Dark Energy and dark matter around it, the problem list contents much more than 3 points, so what is the truth? Should we embark on a journey to find the truth about GR?
     
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  3. Xelasnave.1947 Valued Senior Member

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    Yes indeed we should.
    First we need to understand what the theory says and what it does not say.
    Second we need to be able to do the maths.
    I can't do either step one or two so I am out.
    I guess one would need to read a text book or two maybe take a course on GR and certainly learn the maths involved.
    Then we could know the truth but I think there are professionals who know the truth what do they say.
    Well they seem to say its the best theory on gravity and I expect that is the truth.
    You don't like GR so will you be happy to accept that truth as a starting point?
    You understand GR better than I do I expect where do you think we should start to find the truth?

    Alex
     
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  5. Michael 345 Valued Senior Member

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    Humpty hasn't got any relatives who are Generals.

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    So am I no use?
     
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  7. The God Valued Senior Member

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    Deeper meaning is you too have doubts about GR.

    Not necessarily, this may bias. we need to understand the observations, we need to understand the gravitational influence. But still if you feel what the theory says, post it.

    Again not necessary. You may like to know that even till today we do not have analytical solution in GR for multi body problem. Einstein himself did not offer any exact solution when he suggested those equations. I am not saying that we should be maths-less.

    That should not make you a blind follower. More important is you know the influence of Gravity, so can you appreciate what GR says about Gravity without scratching your head.

    Not necessary.

    Who are they? and what truth they know?

    These are Cat-II professionals. They expect the GR, the truth of the fact that accepting GR may keep them fruitfully busy for this life, opposing GR and they will be branded crankies.

    GR is bad IMO.

    Start from basics.
     
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  8. paddoboy Valued Senior Member

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    Newtonian could not explain or account for the orbit's eccentricity and its precession around the sun. It was of course an indication of the sun dragging the fabric of space-time around with it, and obviously that effect is felt the greatest at the planet which is closest to the Sun.
    Why hasn't it been tested on other planets? Firstly because the Newtonian system explained those orbits with accepted precision, secondly, neither you nor I know if it has been done or not.
    No, we have no issues with gravitational lensing at all, and this was shown to you in a past thread where you also tried to fabricate similar non existent issues.
    http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html
    Real-World Relativity: The GPS Navigation System

    People often ask me "What good is Relativity?" It is a commonplace to think of Relativity as an abstract and highly arcane mathematical theory that has no consequences for everyday life. This is in fact far from the truth.

    Consider for a moment that when you are riding in a commercial airliner, the pilot and crew are navigating to your destination with the aid of the Global Positioning System (GPS). Further, many luxury cars now come with built-in navigation systems that include GPS receivers with digital maps, and you can purchase hand-held GPS navigation units that will give you your position on the Earth (latitude, longitude, and altitude) to an accuracy of 5 to 10 meters that weigh only a few ounces and cost around $100.

    GPS was developed by the United States Department of Defense to provide a satellite-based navigation system for the U.S. military. It was later put under joint DoD and Department of Transportation control to provide for both military and civilian navigation uses.

    The nominal GPS configuration consists of a network of 24 satellites in high orbits around the Earth, but up to 30 or so satellites may be on station at any given time. Each satellite in the GPS constellation orbits at an altitude of about 20,000 km from the ground, and has an orbital speed of about 14,000 km/hour (the orbital period is roughly 12 hours - contrary to popular belief, GPS satellites are not in geosynchronous or geostationary orbits). The satellite orbits are distributed so that at least 4 satellites are always visible from any point on the Earth at any given instant (with up to 12 visible at one time). Each satellite carries with it an atomic clock that "ticks" with an accuracy of 1 nanosecond (1 billionth of a second). A GPS receiver in an airplane determines its current position and course by comparing the time signals it receives from a number of the GPS satellites (usually 6 to 12) and trilaterating on the known positions of each satellite[1]. The precision achieved is remarkable: even a simple hand-held GPS receiver can determine your absolute position on the surface of the Earth to within 5 to 10 meters in only a few seconds. A GPS receiver in a car can give accurate readings of position, speed, and course in real-time!

    More sophisticated techniques, like Differential GPS (DGPS) and Real-Time Kinematic (RTK) methods, can deliver centimeter-level positions with a few minutes of measurement. Such methods allow GPS and related satellite navigation system data to be used in precision surveying, autodrive systems, and other applications requiring greater position accuracy than achieved with standard GPS receivers.

    To achieve this level of precision, the clock ticks from the GPS satellites must be known to an accuracy of 20-30 nanoseconds. However, because the satellites are constantly moving relative to observers on the Earth, effects predicted by the Special and General theories of Relativity must be taken into account to achieve the desired 20-30 nanosecond accuracy.

    Because an observer on the ground sees the satellites in motion relative to them, Special Relativity predicts that we should see their clocks ticking more slowly (see the Special Relativity lecture). Special Relativity predicts that the on-board atomic clocks on the satellites should fall behind clocks on the ground by about 7 microseconds per day because of the slower ticking rate due to the time dilation effect of their relative motion [2].

    Further, the satellites are in orbits high above the Earth, where the curvature of spacetime due to the Earth's mass is less than it is at the Earth's surface. A prediction of General Relativity is that clocks closer to a massive object will seem to tick more slowly than those located further away (see the Black Holes lecture). As such, when viewed from the surface of the Earth, the clocks on the satellites appear to be ticking faster than identical clocks on the ground. A calculation using General Relativity predicts that the clocks in each GPS satellite should get ahead of ground-based clocks by 45 microseconds per day.

    The combination of these two relativitic effects means that the clocks on-board each satellite should tick faster than identical clocks on the ground by about 38 microseconds per day (45-7=38)! This sounds small, but the high-precision required of the GPS system requires nanosecond accuracy, and 38 microseconds is 38,000 nanoseconds. If these effects were not properly taken into account, a navigational fix based on the GPS constellation would be false after only 2 minutes, and errors in global positions would continue to accumulate at a rate of about 10 kilometers each day! The whole system would be utterly worthless for navigation in a very short time. This kind of accumulated error is akin to measuring my location while standing on my front porch in Columbus, Ohio one day, and then making the same measurement a week later and having my GPS receiver tell me that my porch and I are currently somewhere up in the air many kilometers away.

    The engineers who designed the GPS system included these relativistic effects when they designed and deployed the system. For example, to counteract the General Relativistic effect once on orbit, they slowed down the ticking frequency of the atomic clocks before they were launched so that once they were in their proper orbit stations their clocks would appear to tick at the correct rate as compared to the reference atomic clocks at the GPS ground stations. Further, each GPS receiver has built into it a microcomputer that, in addition to performing the calculation of position using 3D trilateration, will also compute any additional special relativistic timing calculations required [3].

    Relativity is not just some abstract mathematical theory: understanding it is absolutely essential for our global navigation system to work properly!
    We already know this truth you talk about: GR is the overwhelming accepted and evidenced theory of gravity that we have.
    It is constantly being tested, [just as it should be and as the scientific method dictates] as many reputable links and articles that are posted on this forum shows, plus of course with regards to other aspects that most on this forum are probably unaware of.
    Of course GR has limitations, and while this constant testing is being undertaken, scientists are also trying to formulate a validated QGT that may extend beyond those paraemters of GR.
     
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  9. paddoboy Valued Senior Member

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    Why is Einstein’s general relativity such a popular target for cranks?

    http://theconversation.com/why-is-e...tivity-such-a-popular-target-for-cranks-49661

    Scientists may be celebrating the 100th anniversary of Albert Einstein’s general theory of relativity, but there was also a death in 1915. It was one of the many deaths of simple and intuitive physics that has happened over the past four centuries.

    Today the concepts and mathematics of physics are often removed from everyday experience. Consequently, cutting edge physics is largely the domain of professional physicists, with years of university education.

    But there are people who hanker for a simpler physics, toiling away on their own cosmologies. Rightly or wrongly, these people are often labelled cranks, but their endeavours tell us much about misconceptions of science, its history and what it should be.

    I regularly browse open access website arxiv.org to look for the latest astrophysics research. Real astrophysics, that is. But if I want to take a look at what pseudoscientists are up to, I can browse vixra.org. That’s right, “arxiv” backwards. The vixra.org website was founded by “scientists who find they are unable to submit their articles to arXiv.org” because that website’s owners filter material they “consider inappropriate”.

    There are more than 1,800 articles on vixra.org discussing relativity and cosmology, and many don’t like relativity at all. Perhaps one reason why cranks particularly dislike relativity is because it is so unlike our everyday experiences.

    Einstein predicted that the passage of time is not absolute, and can slow for speeding objects and near very massive bodies such as planets, stars and black holes. Over the past century, this bizarre predication has been measured with planes, satellites, and speeding muons.

    But the varying passage of time is nothing like our everyday experience, which isn’t surprising as we don’t swing by black holes on our way to the shops. Everyday experience is often central to cranky ideas, with the most extreme example being flat earthers.

    Thus many crank theories postulate that time is absolute, because that matches everyday experience. Of course, these crank theories are overlooking experimental data, or at least most of it.

    History and linearity
    One of the most curious aspects of pseudoscience is an oddly linear approach to science. To be fair, this can result from an overly literal approach to popular histories of science, which emphasise pioneering work over replication.

    A pivotal moment in relativity’s history is Albert Michelson and Edward Morley’s demonstration that the speed of light didn’t depend on its direction of travel nor the motion of the Earth.

    Of course, since 1887 the Michelson-Morley experiment has been confirmed many times. Modern measurements have a precision orders of magnitude better than the original 1887 Michelson-Morley experiment, but these don’t feature prominently in popular histories of science.

    Interestingly many pseudoscientists are fixated on the original Michelson-Morley experiment, and how it could be in error. This fixation assumes science is so linear that the downfall a 19th century experiment will rewrite 21st century physics. This overlooks how key theories are tested (and retested) with a myriad of experiments with greater precision and different methodologies.

    Another consequence of the pseudoscientific approach to history is that debunked results from decades past are often used by buttress pseudoscientific ideas. For example, many pseudoscientists claim Dayton Miller detected “aether drift” in the 1930s. But Miller probably underestimated his errors, as far more precise studies in subsequent decades did not confirm his findings.

    Unfortunately this linear and selective approach to science isn’t limited to relativity. It turns up in cranky theories ranging from evolution to climate.

    Climate scientist Michael E Mann is still dealing with cranky accusations about his seminal 1998 paper on the Earth’s temperature history, despite the fact it has been superseded by more recent studies that achieve comparable results. Indeed, it devoured so much of Mann’s time he has literally written a book about his experience.

    What about the maths?
    During the birth of physics, one could gain insights with relatively simple (and beautiful) mathematics. My favourite example is Johannes Kepler’s charting of the orbit of Mars via triangulation.

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    In the 17th century, Johannes Kepler used elegantly simple mathematics to chart the motion of Mars. Johannes Kepler / University of Sydney

    Over subsequent centuries, the mathematics required for new physical insights has become more complex, as illustrated by Newton’s use of calculus and Einstein’s use of tensors. This level of mathematics is rarely in the domain of the enthusiastic but untrained amateur. So what do they do?

    One option is to hark back to an earlier era. For example, trying to disprove general relativity by using the assumptions of special relativity or even Newtonian physics (again, despite the experiments to the contrary). Occasionally even numerology makes an appearance.

    Another option is arguments by analogy. Analogies are useful when explaining science to a broad audience, but they aren’t the be-all and end-all of science.

    In pseudoscience, the analogy is taken to the point of absurdity, with sprawling articles (or blog posts) weighed down with laboured analogies rather than meaningful analyses.

    Desiring simplicity but getting complexity
    Perhaps the most fascinating aspect of pseudoscientific theories is they hark for simplicity, but really just displace complexity.

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    A desire for naively simple science can produce bizarrely complex conclusions, like the moon landing hoax conspiracy theories. NASA/flickr

    Ardents of the most simplistic pseudoscientific theories often project complexity onto the motives of professional scientists. How else can one explain scientists ignoring their brilliant theories? Claims of hoaxes and scams are commonplace. Although, to be honest, even I laughed out loud the first time I saw someone describe dark matter as a “modelling scam”.

    Again, this isn’t limited to those who don’t believe in relativity. Simple misunderstandings about photography, lighting and perspective are the launch pad for moon landing conspiracy theories. Naively simple approaches to science can lead to complex conspiracy theories.

    Changing intuition
    Some have suggested that pseudoscience is becoming more popular and the internet certainly aids the transmission of nonsense. But when I look at history I wonder if pseudoscience will decay.

    In the 19th century, Samuel Rowbotham promoted Flat Earthism to large audiences via lectures that combined wit and fierce debating skills. Perhaps in the 19th century a spherical world orbiting a sun millions of kilometres away didn’t seem intuitive.

    But today we can fly around the globe, navigate with GPS and Skype friends in different timezones. Today, a spherical Earth is far more intuitive than it once was, and Flat Earthism is the exemplar of absurd beliefs.

    Could history repeat with relativity? Already GPS utilises general relativity to achieve its amazing precision. A key plot device in the movie Interstellar was relativistic time dilation.

    Perhaps with time, a greater exposure to general relativity will make it more intuitive. And if this happens, a key motivation of crank theories will be diminished.
     
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  10. Xelasnave.1947 Valued Senior Member

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    I would suggest that if I do not understand the subject it is not wise for me to criticize.

    The fact is GR is certainly accepted by mainstream and I doubt if someone with little knowledge such as me can really said to be in a position to comment.

    Take the positioning system how can one criticize if one does not understand the maths or indeed after rejecting GR offer a system that delivers the same accuracy that is apparently delivered using GR.

    You asked in your op of what use is GR well the answer must be the global positioning system.
    If you can deliver such a system without using GR then you knock out a very practical application.

    I must admit I have never understood frame dragging or why it was important but clearly I may be missing something.
    Ask why would they go to such trouble and expence if it was not important.
    Just because I don't understand something does not mean there is not someone who does understand.
    Alex
     
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  11. paddoboy Valued Senior Member

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    Frame Dragging, or the "Lense Thirring" effect, is annalogous to stirring a cup of syrup, or anything for that matter [coffee, tea] and watch how the strirring drags the mixture around with it.
     
  12. Xelasnave.1947 Valued Senior Member

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    Thanks Paddoboy.
    What I guess I should have said was..I can't understand why folk find it so interesting it would seem a very natural expectation of behaviour.
    I am probably just too clever.

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    Mmmmm Xmas feast take two...not sick of ham yet.

    Alex
     
  13. paddoboy Valued Senior Member

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    Same here...Seems I'm in line for ham for the next week...sliced ham, ham rissoles, ham fritters and whatever else the better half can dream up!

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  14. The God Valued Senior Member

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    But its wise for you to accept it, even if you do not understand?

    Your stand is to support it, without knowing it. Isn't it?
     
  15. James R Just this guy, you know? Staff Member

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    No, not roughly. The matching is phenomenally accurate, and moreover cannot be accounted for by Newtonian mechanics.

    Yes, they do match there too. Mercury is used because, being the closest planet to the Sun, the effect is largest there.

    That 43 arcseconds per century is the amount left over once you factor out all other causes of precession due to the Newtonian gravity effects of the other planets in the solar system. It cannot be accounted for by Newtonian gravity alone. So, GR is a lot of use for us here.

    Gravitational lensing is now a fairly mature method in astronomy. There is no doubt at all that gravitational lensing occurs.

    See paddoboy's helpful posts above for how the GPS system has to take GR into account, and what would happen if it didn't.

    There is no doubt that black holes exist.
    Dark matter does not necessarily have anything to do with GR.
    As for dark energy, we're not sure what that is yet, or even whether it is a real effect yet. We know the effect can be modelled as a cosmological constant in GR, but we don't have a complete theory of dark matter. Nor does GR attempt in any way to provide such a theory.
     
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  16. The God Valued Senior Member

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    James R,

    1. Mercury Precession: We can't do maths without considering Mercury as point. We also completely ignore effects of other objects and very high motion of our solar system while doing GR maths on this precession. The very small magnitude of left over precession, requires exact calculations considering these effects too. Thats why I said approximate. Almost all GR calculations are approximate. You know that our solar system is orbiting around GC, this motion surely can cause additionsl 43 arc seconds in a century or at least a few arc seconds to bump the accurate claim of hours.

    2. Gravitational Lensing is there. Paddoboy copy paste is pop science, he does not understand the niceties. There are certain observation which cannot be accommodated under GR. Moreover we know the solar mass, so we can calculate the deflection and compare it with observed, but for all other lensing objects, these parameters (mass and mass distribution) cannot be accurate, so its you help me I help you.

    3. Give one more planet example where GR calculated precession matches with observed.

    4. GPS is fed information. Everyone is fed that GR plays significant role in GPS. Have you seen the maths? Can you organize the algorithm here for GPS calculations which can prove this fed story?

    5. Some system which creates the motion attributed to Black Holes certainly exists, but Black Hole Singularities are GR babies, they do not exist. GR fails.

    6. Absence of DM: then GR fails.

    7. Absence of DE : then also GR fails.

    You cannot say that some cosmogical constant explains DE and expansion thereof, it has to have physical significance. Playing with maths is not done.
     
    Last edited: Dec 26, 2016
  17. danshawen Valued Senior Member

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    No one should forget the prediction of gravitational waves and their recent discovery as another huge vote in favor of the formulation of GR.

    Remember also that it took even someone as brilliant as Einstein more than one attempt and many years to get GR correct. His correspondence with Hilbert during the process reveal how stressful it was. Possibly the most stressful thing he ever experienced, and basically we have Hilbert to thank also for driving Einstein through competition to produce his best estimate of how it should work.

    Like Einstein's Special Relativity, General Relativity relies heavily on the calculus developed by Newton and chiefly Leibniz. The postulated integral / differential relationship of the calculus applied to a study of physics to derive GR's field equations actually runs afoul of the clock postulate, not completely formulated until the 1990s. What this basically says is that nature herself PLACES LIMITATIONS ON THE FUNDAMENTAL THEOREM OF CALCULUS. That is to say, "acceleration' is not as important to nature as instantaneous velocity. And there is a good reason why this is the case. dt is the basic error element. Space and bound energy do not behave as a Euclidean solid. Time and energy in bound and unbound forms, the enranglement and time dilation that makes bound forms of energy possible, and energy transfer events are all that exists in the natural universe we inhabit. Living in a mathematical dream reality where division by zero is somehow a divine limitation, or believing that the speed of light is its ultimate physical embodiment, is sheer fantasy. The only choices for mathematical or any other symbolic systems of reasoning here are incomplete or inconsistent. Welcome to incomplete. If light continues to propagate in any frame, time itself has not 'stopped'. What has seized up is most likely your brain.

    The PROPRTIONAL relationship that gives Special Relativity its veracity is the same proportional relationship that fails if you try to apply it to understanding the nature of time sans entanglement faster than c. Time as conceived by relativity math is a velocity, and if you ignore limitations imposed by not understanding what really is the fastest velocity in the universe, the chances of you understanding what is happening physically is the same as dividing by zero and getting anything other than nonsense out of the math you are using.

    The ONLY reason GR works as well as it does is because it operates for the most part closer to the low speed limit of the rest frame for large gravitating objects. Not a total loss because the rest frame is also defined by +/- c. I believe only a minor modification may yet be needed to render the model an exact one.
     
    Last edited: Dec 26, 2016
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  18. Xelasnave.1947 Valued Senior Member

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    My support is more to following scientific method really.
    I do not feel compelled to attack or support the theory.
    It is there I know it has support I recognise that it has support.
    I also recognise there are folk who don't think it is right.
    Alex
     
  19. paddoboy Valued Senior Member

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    You obfuscate rather amateurishly my friend. Simply put, the 43 arc seconds that Newtonian mechanics is unable to account for, is accounted for by GR.

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    We have discussed gravitational lensing before and many arxiv papers were linked to by myself, supporting the legitimacy of gravitational lensing and the many reasons. Your constant denial of such once again reflects on your agenda that I have mentioned before, particularly when coupled with the fact that you seem to have a problem with all answers given by 21st century cosmology...I smell a "god of the gaps" again.

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    And of course that is supported by your rather silly attempt to write off all reputable links as "pop science"
    As I and James have already informed you, the effects are small, and obviously most noticable with Mercury for obvious reasons, and less, far less noticable with other planets.

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    It seems to me that its you trying to force feed others with an even more fanciful force fed theory.

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    GR does not fail. That is ignorance. GR has limitations like all models.
    Rubbish. GR accommadates those without any problems.
    Of course if you are able to show otherwise, then go ahead..or better still why not write up a paper for professional review?

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    At this stage, this to me seems like just an anti GR rant that you have conducted before. We do have sections for that.
     
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  20. Boris2 Valued Senior Member

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    Yet Verlinde doesn't seem to be worried about that. Didn't worry Barry Marshall and his discovery of what caused stomach ulcers. Sure some theorists might be put off but new stuff is where the Nobels are not in saying "me too".
     
  21. The God Valued Senior Member

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    Verlinde is bringing back ether without naming it directly! Secondly the guy is careful not to chuck the term spacetime away. He is focusing on eliminating the need of DM.
     
  22. paddoboy Valued Senior Member

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    And both admirably show your conspiracy theory to be nonsense.

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  23. The God Valued Senior Member

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    For you support means, support of those who matters.
     

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