# Measuring the curvature of spacetime

Discussion in 'Physics & Math' started by Plazma Inferno!, Dec 28, 2015.

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3. ### brucepValued Senior Member

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5. ### danshawenValued Senior Member

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The Lagrangian describing the nutation and precession of a spinning top or a gyroscope under the influence of gravity, including precession and nutation is something I derived from scratch on my theoretical classical dynamics final exam, and received a grade of "A".

This example demonstrates only the conservation of angular momentum, NOT "curvature of space", the same as a Foucault pendulum, and for the same reasons.

The same dynamics of gyroscopes apply to motion of the Earth around the Sun, and the Sun around the galaxy. It doesn't demonstrate space curvature. If it could, the motion would be much more complex than shown, nor would it be possible to track down all of the contributions.

Apparatus such as this (laser gyroscopes) are however quite useful for developing maps of mass concentrations of the Earth from orbiting spacecraft. I'm only disputing what this article claims it is measuring. It isn't "space". It's "mass". If curvature of space were this easy to measure, we would have constructed functional gravity wave detectors and actually observed them a very long time ago.

7. ### CheezleHab SoSlI' Quch!Registered Senior Member

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Leonard Susskind does a very nice job of simply explaining how you measure the curvature of space in this lecture:

Einstein's General Theory of Relativity | Lecture 6

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Thanks Plasma...we need more threads illustrating the accepted mainstream theories and how they do stand up to scrutiny, particularly in light of the rash of cranks we have at this time, that for invalid various reasons, continue to rant and rave about which they mostly know nothing about.

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9. ### Q-reeusValued Senior Member

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A fair guess said 'influence of gravity' was that applying to a gyro perched at an angle on say a bench top:
http://ocw.mit.edu/courses/aeronaut...fall-2009/lecture-notes/MIT16_07F09_Lec30.pdf
Totally different scenario to that of OP article. You think not?
See above.
Supporting citations please (I expect none).
Gyros used were of the old fashioned variety - actual spinning spheres - not laser gyros: https://einstein.stanford.edu/TECH/technology1.html
Didn't pick that much up?
Denying there is any connection between mass (spinning or not) and spacetime curvature. Might as well argue electric charge has nothing to do with electric field.
Interesting logic: 'if not A, then not B' - regardless of how disparate A and B are conceptually and regardless of the expected orders of magnitude difference in required sensitivities.

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While many of our crank friends continue to try and pull GR apart, the real world continues as is and in appreciation of the greatest of them all and the theories that changed the universe.......

http://www.isgrg.org/GR100events.php

GR100 Events around the World

The year 2015 marks the 100th anniversary of Albert Einstein's presentation of the complete Theory of General Relativity to the Prussian Academy. We list here conferences and other events in honor of this centenary from colleagues throughout the world. If you are aware of an appropriate event not listed here, please send a link to the event's website to beverlyberger@me.com.

A Century of General Relativity, Berlin, Germany, 30 Nov 2015 - 5 Dec 2015. ISGRG has declared this event to be our official centenary conference due to its proximity in location and time of the year to Einstein's presentation.

General Relativity & Gravitation: a Centennial Perspective, Pennsylvania State University, 8-12 June 2015. This conference will take place under the auspices of ISGRG and of the American Physical Society's Topical Group in Gravitation. ISGRG sponsored student travel awards, deadline 1 March 2015

Other events:
32nd Winter School in Theoretical Physics: 100 years to General Relativity: From Theory to Experiment and Back, Jerusalem, 29 Dec 2014 - 8 Jan 2015.

junior scientist Andrejewski Days: 100 years of General Relativity, Begegnungsstatte Schloss Gollwitz, Brandenburg an der Havel, Germany, 22 March - 4 April 2015.

The Next Detectors for Gravitational Wave Astronomy, Kavli Institute for Theoretical Physics China, Beijing, 6 Apr - 8 May 2015.

GR100 in Rio, Rio de Janeiro, Brazil, 27 - 31 July 2015.

APS April Meeting, Baltimore, MD, USA, 11 - 14 April 2015.

Gravitation 2015, including exhibits and a workshop: 100 years of curved space time, Austrian Academy of Sciences, Vienna, October 2015. Contact: elisabeth.eder@oeaw.ac.at.

20th International Summer School on Global Analysis and its Applications - General Relativity: 100 years after Hilbert , Stará Lesná, Slovakia, 17th - 21st August 2015.

The 2015 Penn State Lectures on the Frontiers of Science, held in January and February 2015 at Penn State, celebrate the 100-year anniversary of Einstein's discovery of general relativity, a theory recognized as Einstein's greatest discovery.

GR100: Centennial of General Relativity, held at the Serbian Academy of Sciences and Arts, Belgrade, 22 or 23 June 2015. For further details contact Dr. Marko Vojinovic (vmarko@ipb.ac.rs).

Instant Expert - Einstein's Universe is a public event sponsored by New Scientist magazine. It will be held at the British Library in London, 23 May 2015.

The International Conference on Gravitation and Cosmology/The Fourth Galileo-Xu Guangqi Meeting celebrates the 100th anniversary of general relativity. It was held at the Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing, 4-8 May 2015.

International Conference on General Relativity (ICGR-2015) will be held to celebrate the centennial of general relativity. It will be held at SantGadge Baba Amravati University (India) on 25-28 November 2015.

The IoP Gravitational Physics Group announces a conference, Einstein's Legacy: Celebrating 100 Years of General Relativity, to be held 28-29 November 2015 at Queen Mary University of London. See the linked website for additional details.

The 2nd conference of the Polish Society on Relativity: 100 years of General Relativity will take place in Warsaw, Poland, on November 23-28, 2015. A registration form, a list of invited speakers, and all other details can be found at http://potor.fuw.edu.pl/.

The Second LeCosPA International Symposium under the auspices of AAPPS-DACG, Everything about Gravity: Celebrating the Centenary of Einstein's General Relativity, will be held at National Taiwan University, Tapei, Taiwan, 14-18 December 2015.

A conference, General Relativity at 100, sponsored by the Institute for Advanced Studies and Princeton University, will be held at the Institute for Advanced Studies, Princeton, NJ, USA, 5-6 November 2015.

The conference Strings 2015 included a special session 100 Years of General Relativity. The conference was held at ICTS-TIFR, Bengaluru, India, 22 - 26 June 2015. Lecture videos and slides are available from the linked website.

The I UNIFESP Cosmology and Astrophysics Workshop, will be held in December 2015 at the Federal University of Sao Paulo (UNIFESP). It celebrates the 100-year anniversary of Einstein's general relativity theory. Detais are available athttps://wcaunifesp.wordpress.com.

NOVA "Inside Einstein's Mind" Premieres Wednesday, November 25, 2015 at 9pm ET/8C on PBS: Retrace Einstein’s thought experiments as NOVA reveals the simple but powerful ideas that reshaped our understanding of gravity, illuminating the theory of general relativity—and Einstein’s brilliance—as never before.

The international conference GR 100 Years in Lisbon will be held at the Instituto Superior Tecnico (University of Lisbon, Portugal) on Dec 18th-19th, 2015.Additional information may be found on the linked website.

Books commemorating GR100:
The International Society on General Relativity and Gravitation (ISGRG) has commissioned the book “General Relativity and Gravitation: A Centennial Perspective.” It will be published by Cambridge University Press later this spring. The editors are Ashtekar, Berger, Isenberg, and MacCallum, and the table of contents can be found at http://event.gravity.psu.edu/book_toc.shtml. This book provides a comprehensive overview of the current state of gravitational physics. Cambridge University Press is offering a 50% discount to members of ISGRG who pre-order the book. Orders must be placed by June 7, 2015. After this date the book will be available at a 20% discount to ISGRG members, just like all other Physics and Astronomy books published by Cambridge University Press.

General Relativity: The most beautiful of theories - Applications and trends after 100 years, Carlo Rovelli (Ed.), De Gruyter Studies in Mathematical Physics 28.

Public lectures by ISGRG members related to GR100:
USA: Gary Horowitz, "Einstein and his Theory of General Relativity", Goleta (California) Public Library, 25 January 2015.

India: Abhay Ashtekar, "Gravitation and the Cosmos: 100 Years After Einstein's Discovery of General Relativity", 102nd Indian Science Congress, Mumbai, January 2015.

Ireland: Cormac O' Raifeartaigh, "Einstein's Universe: Relativity and the Big Bang", School of Theoretical Physics, Dublin Institute for Advanced Studies , 10 Burlington Road, Nov 9th at 7.00 p.m. Admission is free but advance booking is required: click here.

Ireland: Professor Mike Cruise (University of Birmingham), "One Hundred Years of Einstein’s Gravity - but where are the Waves?", 25 November 2015, Heaney lecture theatre, St Patrick’s College, Drumcondra at 7:30 p.m. Admission is free but advance booking is required: click here.
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11. ### Q-reeusValued Senior Member

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Steady on there - actually it has not 'changed the universe' one iota, except in some over enthusiastic head spaces. No doubt you meant 'changed perceptions of...'. As for AE being 'the greatest of them all', that is debatable, but for sure he has undoubtedly had by far the greatest PR machine pumping him as 'Numero Uno'. It tends to be overlooked how many others were involved in the painful formulation of what eventuated as 1915/1916 GR.
Very good question! Super-sensitive ALIGO now running since July, with first 'data run?' Sept: https://www.advancedligo.mit.edu/
You can be real sure, disclaimers notwithstanding, that any tentative, cross-correlated GW detection would have been enthusiastically leaked to the press ASAP. Probably not even needing cross-correlation from two detectors first off. The pressure to confirm AE as a mortal god this GR 100th anniversary year is just so great.
Nature seems not be so accommodating however. Fingers crossed though - all you devotees out there. The 100th anniversary of publishing of GR is still around the corner - still time for that faint first glimmer of GW's to triumphantly crown the event!

12. ### danshawenValued Senior Member

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If "spacetime curvature" were in the equations (ANYWHERE) for a simple conservation of angular momentum of a gyroscope in the presence of a gravitational field, I think I would have noticed. It isn't.

You could equally claim that Newton's description of gravitation is proof of curvature of spacetime or of general relativity. It isn't either.

General relativity is a fantastic piece of work with many different types of experimental evidence to support it, but part of that work included simplifications made possible by Minkowski and Hilbert's mangled versions of spacetime geometry, and the only reason they work at all is because the bound energy that is matter and that exerts and is influenced by gravitational fields will almost by definition be closer to "at rest" locally than they are to relativistic speeds traveling near the speed of light in a vacuum. Even Euclidean geometry works fine for matter at rest. It doesn't mean it emerged from the mind of a mathematician directly into G-d's countenence, or anyone else's.

Space is light travel time in every direction. Time dilates with relative motion or with the virtual acceleration that is gravity. Space doesn't curve; matter and the spaces between particles of bound energy that is matter Doppler shifts the same as any other form of energy does, either with relative motion or with the virtual acceleration that is gravity.

Quantum entanglement travels faster than light because no bulk transport of energy or matter is involved, and because the same inertialess quantum field mechanism works the same whether it is a pair of electrons in the same shell of an atom, or entangled photons scattered across cosmological light travel times. For photons, the Big Bang and inflation JUST HAPPENED. It doesn't matter how far they have traveled or how much time has passed in a rest frame that is comprised of the vector addition of +c to -c everywhere. It's as simple as that.

And there is literally nothing like 'space' to curve. But time, including light travel time, does dilate. If your mathematical constructs work well at rest, then by all means stay at rest. Anchor the origins of your coordinate system's geometry in inertialess space if you wish. I don't care.

The only absolute space in a universe comprised of energy transfer events is at the geometric centers of bound particles of energy that is matter. The only absolute time is quantum entanglement's instant of "now", which is the same instant everywhere. An instant is not a time interval. Time INTERVALS are different anywhere and everywhere time may dilate.

Simultaneity does not even exist the way Minkowski thought of it, other than for the same event viewed from different perspectives, or for entangled energy events, which amount to the same thing. Because Minkowski referenced simultaneity to the bulk propagation of energy, it isn't going to render consistent answers to questions about distances between spacetime events involving entanglement using his 19th century formulation of a relativistic / Euclidean geometric universe using intervals instead of the much stronger invariant speed of light in a vacuum that was the basis for E=mc^2.

Last edited: Dec 30, 2015
13. ### Q-reeusValued Senior Member

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Maybe not looking particularly hard:
https://en.wikipedia.org/wiki/Geodetic_effect
https://en.wikipedia.org/wiki/Frame-dragging
Gravity probe-B results are consistent with those GR-based calcs. Weak field conditions prevailed and distinguished GR from Newtonian gravity but not certain other gravity theories.
See above.
Passing over the rest there, I note you have used that G_d term a lot. It's afaik typically associated with orthodox/ultra-orthodox Jews, as a 'sacred name' substitute. Just wondering then....
So simple I have very little idea still just what kind of grand picture of gravity/QM synthesis is in your head. But that's ok - just row your own boat as the Diamond/Lulu song encourages.

14. ### danshawenValued Senior Member

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I began conversion to Judaism (reform, not orthodox) about eight years ago. Does that make any difference?

15. ### danshawenValued Senior Member

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I do not dispute this. GR time dilation calculations work just fine, and are a considerable improvement over Newton's. But they are not consistent with quantum theory. There are good reasons for that, and this needs to change. They won't change when there is a Higgs field that imparts inertial mass to matter from an inertialess medium that is the foundation of the Standard Model. The anchors into inertialess space by Euclidean geometric systems have to go. No how massive the object, it will move with respect to other massive objects. When it moves, time will dilate and another correction term will be needed to compensate.

Sooner or later, someone will need to handle the inconsistency between GR and SM or there is no hope at reconciliation. This usually means that some concept that is in error needs to be rejected. And this is a function that math, if it is done properly, is supposed to do at each and every step of a calculation. It isn't even a question of arriving at a consensus.

Last edited: Dec 30, 2015
16. ### Q-reeusValued Senior Member

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Not particularly but thanks for clarifying. Always had difficulty deciphering various comments of yours that could be taken any number of ways. But....

17. ### Q-reeusValued Senior Member

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Then we have common ground - fantastic!

18. ### PhysBangValued Senior Member

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It's perfectly fine for you to believe in a preferred, perfect reference frame that is in principle undetectable. You can't just say that it is a fact that this exists.
But you clearly do care, since you are making grand metaphysical pronouncements about what exists and you are denying what many people take to be the most straightforward metaphysical interpretation of General Relativity. You provide no argument for your position, you merely take an insulting tone against those who have done work or provided arguments that you don't like.

19. ### danshawenValued Senior Member

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Why not? Gigantic turtles carrying the Earth on their backs don't exist. I can't prove that they don't. obviously. I can explore the consequences of that idea. Someone would need to feed them.

What other tone would I take with respect to lots of discussion about the care and feeding of the turtles?

When the turtles change direction, angular momentum is conserved. Sure it is.

You can't "prove" that space is curved, either. A parabolic trajectory of a projectile in a gravitational field doesn't prove it. Neither does the conservation of angular momentum of a gyroscope, even fancier ones. I can however prove that time dilates for GPS satellites orbiting the Earth. That is about the ONLY thing that can be proved about the situation. Geometry has little to do with it, other than the approximate shape and mass of the Earth, NOT the shape and mass (or curvature) of space.

If "space" really curved, then orbiting spacecraft would be left behind in Earth's orbit. They aren't, only because they share the inertia of the planet they were launched from. The same as the space from which the Higgs mechanism imparted inertial mass to electrons at the core of the Earth. That is the "cause" of "frame dragging", if there is one, not a geometry of space anchored in something that has no means of getting (or giving) inertia. Compared to this idea, "space curvature" is just a wacked out idea that belongs in the 19th century, along with the luminiferous aether, absolute space and time.

Last edited: Dec 30, 2015
20. ### PhysBangValued Senior Member

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Sure. But you give your metaphysical additions to GR as if they are fact. That is misleading.
You might want to read a little about the idea of geometry as convention.

You might want to reread some GR textbook.

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21. ### brucepValued Senior Member

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The likelihood he's read a GR text is nil.

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I'll accept that correction. I was of course being overly enthusiastic at the numbers of anti relativists that this forum now appears to have: Although of course as I often say, these forums are the only outlet that they have to broadcast their tripe and attempted conversion of adherents.

I'll accept that correction too, except of course for your little conspiracy jibe.
And yes there were a number of other greats involved and which I have in various threads given cudos to.
Irrespective, he is undoubtedly up there. very near the top in any one's language I'm sure you'll agree.

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