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Adrian07
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Is it possible to explain simply what a Theory of Quantum Gravity is supposed to achieve/explain and why it is needed.
Perihelion precession of mercury, light deflection by the sun, gravitational redshift on Earth (at lab scale and with satellites) and for stars, gravitational time dilation (again at lab scale and with satellites), gravitational lensing from individual stars and galaxies, Shapiro delay, Frame-dragging of earth, spectroscopy of black hole accretion disks, energy loss in binary pulsars, cosmology. It is not so bad I think.Jolb said:We still have very few "experiments" that test general relativity (and these experiments are often just astronomical phenomena we have no control over)
Sure., so any sort of experiment that tests the quantum gravity regime is even further out of reach, and it will stay that way for quite a while
That's how most particles were predicted, too. Symmetries in the theory and Lorentz covariance.it seems like whoever invented GR didn't mind that there was close to zero observational/experimental evidence, and instead he was very fond of "Philosophical Principles" (e.g. the principle of locality, the principle of causality, the principle of general covariance) and mathematical beauty as his basis for the theory.
mfb said:Well, particle physics is easier to test in the lab. Sure, compared to particle physics the list of tests of GR is short, and the tests have larger error bars.
That's how most particles were predicted, too. Symmetries in the theory and Lorentz covariance.
Suppose you have a spherically symmetric quantum state and a spherical detector array. The gravitational field of this system is spherically symmetric. Suppose the quantum state decays into several particles which are registered on the detector array. Via this measurement the symmetry of the original system is broken, therefore after the measurement the gravitational field is no longer spherically symmetric.Adrian07 said:Why is Theory of Quantum Gravity needed?
mfb said:@audioloop: There are hundreds, probably thousands of particle physics measurements, including measurements with a precision of 10 significant digits. It is nice to see an extension of the GR list, but that does not change my statement.
Adrian07 said:Is it possible to explain simply what a Theory of Quantum Gravity is supposed to achieve/explain and why it is needed.
The Theory of Quantum Gravity is needed because it aims to unify two of the most successful theories in physics - quantum mechanics and general relativity. These two theories have been extremely successful in explaining the behavior of the universe on a small scale (quantum mechanics) and a large scale (general relativity), but they are fundamentally incompatible with each other. By developing a Theory of Quantum Gravity, scientists hope to bridge this gap and create a more complete understanding of the universe.
The Theory of Quantum Gravity is different from other theories of gravity because it takes into account the principles of quantum mechanics. This means that it considers the behavior of particles on a subatomic level, rather than just the macroscopic behavior of objects in space. Other theories of gravity, such as Newton's theory of gravity and Einstein's theory of general relativity, do not incorporate quantum mechanics.
The potential applications of the Theory of Quantum Gravity are vast and varied. By unifying the theories of quantum mechanics and general relativity, it could help us better understand the behavior of the universe on a larger scale, such as the behavior of black holes and the origin of the universe. It could also have practical applications, such as improving our understanding of time and space and potentially leading to new technologies.
Developing the Theory of Quantum Gravity is a daunting task and scientists have been facing numerous challenges. One of the biggest challenges is the fact that quantum mechanics and general relativity are fundamentally different and merging them into a single theory is not an easy feat. Additionally, the theory is incredibly complex and requires advanced mathematical and computational techniques to be fully understood.
At this point in time, scientists have not yet developed a complete Theory of Quantum Gravity. There are several promising theories and models that have been proposed, such as string theory and loop quantum gravity, but none have been widely accepted as the definitive theory. However, advancements in technology and computational power have allowed scientists to make progress in this field, and many believe that a complete Theory of Quantum Gravity may be within reach in the near future.