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This paper offers a Nobel laureate perspective on the history, status and future of GR in the astrophysical regime - https://arxiv.org/abs/1609.09781, General Relativity and Cosmology: Unsolved Questions and Future Directions.
I'm slightly annoyed that they claim that General Relativity can't explain cosmological observations without dark energy, as the cosmological constant has always been a component of the theory.Chronos said:This paper offers a Nobel laureate perspective on the history, status and future of GR in the astrophysical regime - https://arxiv.org/abs/1609.09781, General Relativity and Cosmology: Unsolved Questions and Future Directions.
Why there should be such symmetries?vanhees71 said:Indeed, the cosmological constant is a natural ingredient. Everything not forbidden by the symmetries nature has chosen to realize will happen. The only problem is that (perhaps) we don't know which symmetries these are ;-)).
To me, the history of what people thought of the cosmological constant is far less important than the math itself. It was always just assumed to be zero because its value in dimensionless units would have had to be so incredibly small for any structure in the universe to form.Chronos said:Not to split hairs, but, the cosmological constant was not a part of the original field equations paper by Einstein in 1915. He added the lambda term [CC] in 1917 because he realized the universe would otherwise be prone to collapse, in contradiction to the prevailing view of a static universe. He withdrew his support for lamda after Hubble discovered the universe was expanding in 1929. While It can be argued lamba technically belonged in the field equations from the beginning as it naturally arises as a constant of integration, the argument is historically inaccurate. Under the assumption that lambda is zero, the point was rendered moot until lambda was resurrected with the discovery of accelerated expansion by Reiss/Permutter in 1998.
Feynman summed it up as follows here: http://www.feynmanlectures.caltech.edu/I_52.html "So our problem is to explain where symmetry comes from. Why is nature so nearly symmetrical? No one has any idea why." Humans are naturally gifted in the art of pattern recognition and symmetry is one of those patterns we have recognized in the laws of nature. While it is true that symmetry is essentially nothing more than a human abstraction, we might gain a deeper understanding by exploring the question of 'why not?' as opposed to 'why?' We might ultimately realize the universe cannot evolve into what it is without symmetry.MathematicalPhysicist said:Why there should be such symmetries?
I think symmetries are a good deal more important and fundamental than that. In particular, due to Noether's Theorem, we know that all conservation laws are a result of symmetries. Furthermore, the electromagnetic, weak, and strong nuclear forces are primarily defined by the symmetries they follow.Chronos said:Humans are naturally gifted in the art of pattern recognition and symmetry is one of those patterns we have recognized in the laws of nature.
I wasn't asking about the symmetries we already know of, but of the symmetries we haven't found yet, why should they exist?Chronos said:Feynman summed it up as follows here: http://www.feynmanlectures.caltech.edu/I_52.html "So our problem is to explain where symmetry comes from. Why is nature so nearly symmetrical? No one has any idea why." Humans are naturally gifted in the art of pattern recognition and symmetry is one of those patterns we have recognized in the laws of nature. While it is true that symmetry is essentially nothing more than a human abstraction, we might gain a deeper understanding by exploring the question of 'why not?' as opposed to 'why?' We might ultimately realize the universe cannot evolve into what it is without symmetry.
If we don't know which symmetries nature has chosen to realize how do we know that it even decided on such symmetries?Everything not forbidden by the symmetries nature has chosen to realize will happen. The only problem is that (perhaps) we don't know which symmetries these are ;-)).
Well, of course it could be that there are no further symmetries than the already known at all.MathematicalPhysicist said:Well, I quoted @vanhees71
If we don't know which symmetries nature has chosen to realize how do we know that it even decided on such symmetries?
It also depends if we define new physical quantities to measure in the future, they might be invariant or not.vanhees71 said:Well, of course it could be that there are no further symmetries than the already known at all.
MathematicalPhysicist said:of the symmetries we haven't found yet, why should they exist?
MathematicalPhysicist said:If we don't know which symmetries nature has chosen to realize how do we know that it even decided on such symmetries?
vanhees71 said:Well, of course it could be that there are no further symmetries than the already known at all.
No. Here's one "proof": rotational symmetry, implemented as unitary operators on a Hilbert space, implies that quantum angular momentum comes in half-integral steps. That's crucial to the structure of all matter and fields. Add a little more symmetry details (Poincare + causality) and one gets the Pauli exclusion principle for fermions, without which atomic shell structure would not be what it is (and hence "we" wouldn't exist at all).houlahound said:Totally above my pay scale but could symmetries have an anthropomorphic basis cos that's just how we see things and how we have assembled the pieces?
Jimster41 said:is there a solution to the GR theory that can support Bell pair correlations?
PeterDonis said:can a quantum theory which predicts violations of the Bell inequalities be formulated with a dynamic spacetime geometry, i.e., one which depends on the distribution of gravitating sources, which would include the gravitational effects of any quantum objects which are present? Or does such a theory require that the background geometry of spacetime be fixed?
PeterDonis said:allow the dynamics of the spacetime geometry to be treated using the same quantum framework as everything else.
Jimster41 said:QM is not derived from GR (is that what you mean?).
Jimster41 said:Does it go too far (logically) to then say that a theory of dynamic of space-time geometry if it supports such a formulation of QM has to support non-locality?
GR stands for General Relativity, which is a theory of gravitation proposed by Albert Einstein in 1915. It is significant because it revolutionized our understanding of gravity and space-time, and has been proven to be accurate through numerous experiments and observations.
Some notable Nobel laureates in the field of GR include Albert Einstein, who received the Nobel Prize in Physics in 1921 for his work on the photoelectric effect and not specifically for GR, and Sir Roger Penrose and Reinhard Genzel, who received the Nobel Prize in Physics in 2020 for their work on black holes and confirming predictions of GR.
GR is currently considered to be one of the most successful and well-tested theories in physics. It has been confirmed through numerous experiments and observations, and is used to make precise predictions in fields such as astrophysics and cosmology.
One of the major challenges in the history of GR was the development of a mathematical framework that could describe the theory. Another controversy was the debate between Einstein and physicist Niels Bohr over the implications of GR for quantum mechanics.
The future of GR is likely to involve further testing and refinement of the theory, as well as potential connections with other areas of physics such as quantum mechanics. It may also play a crucial role in understanding the nature of dark matter and dark energy and the ultimate fate of the universe.