New answers tagged quantum-gravity
3
I wouldn't say that "holographic theories are non-local by definition". On the contrary, in AdS/CFT the CFT is completely local and satisfies cluster decomposition.
The cluster decomposition property in AdS can be proved using the CFT bootstrap for all CFTs in $d > 2$ (see http://arxiv.org/abs/arXiv:1212.3616, the proof only requires CFT `axioms', ...
0
I wouldn't describe Nesvizhevsky's work as groundbreaking. It's a refinement on a type of experiment that was first carried out 38 years ago (Colella 1975). For a recent review article, see Abele 2012.
It also isn't a probe of quantum gravity. By the equivalence principle, this type of experiment is equivalent to simply accelerating the apparatus in a ...
-2
All this time, the field of physics did not seriously consider the possibility of existence of negative mass (energy) in a general state. The standard explanation of negative mass is that the state of low energy is stable when a negative energy level exists and that the lowest state of energy is minus infinity. Thus, this means that all positive mass emits ...
7
One shouldn't imagine the T-duality between the two heterotic strings to be a $Z_2$ group, like in the case of type II string theories' T-duality. In type II string theory, there is only one relevant scalar field, the radius of the circle producing T-duality, and it gets reverted $R\to 1/R$ under T-duality.
In the heterotic case, it's more complicated ...
0
Decoherence is more than anything a matter of what you define to be the "environment". The environment is supposed to be external to the system of interest and entangling interaction with it produces decoherence. If the environment in question is a part of the adS space then the subsystem can certainly decohere. If what you are asking is whether the space as ...
2
The natural diversity of energy levels at which matter organizes itself tends to isolate related phenomena in interesting and often confusing ways.
Consequently, physics has found that phenomena that seemed inexplicable often began to unravel and start to show revealing internal structure when energy levels are raised high enough to overcome those internal ...
1
Approaches to Quantum Gravity: Toward a New Understanding of Space, Time and Matter by Daniele Oriti.
3
Here is a link to the equations whose solutions lead to the model of the expanding universe from an initial discontinuity called Big Bang.
The Friedmann equations are a set of equations in physical cosmology that govern the expansion of space in homogeneous and isotropic models of the universe within the context of general relativity.
The article ...
4
The short answer to this question is that there is no answer because the question makes invalid (classical) assumptions. "Things" start to get blurry. They stop having a definite position, size, and boundary.
Take an electron for example. The electric field extends to infinity and the mass appears, to the best we can measure, to be a point in the center.
...
1
I like previous answer but:
1) I believe that in the provided formula the mass of the electron should have a power of one (not two)
2) It is valid for electrons only, because it uses their Compton wavelength.
By the way, there is such a thing as "Caianiello’s maximal acceleration". In his 1985 paper Caianiello demonstrated the existence of a maximal ...
0
On space-time, the useful notion of points are events. Only events that are separated by time-like curves are causally connected. Causal connectedness implies that fields happening at one of the events can influence fields happening at the other. Events that are separated by space-like curves are not causally connected, they might be still connected ...
1
All points in the observable universe are "connected" in the sense that they can be acted upon by forces that have an infinite range (gravity and electromagnetism).
However, points that are outside of our cosmological horizon (due to the expansion of the universe) are no longer causally connected with points in our local vicinity, since they are receding ...
0
The Nyquist-Shannon sampling theorem is about continuously sampling a waveform. This really matters when a waveform is a mix of many different frequencies. The theorem says you must sample at a rate double the highest frequency. With light you only need to take one "sample" (the energy of the photon or its momentum) to fully know its frequency:
$E = ...
3
I remember attending a seminar by Unruh a few months ago and the same question arised. As far as I remember, he enfasized that in these hydrodynamic analogs of black holes, the flow is not quantized, it is a classical fluid, and everything is classical and that the dumb hole behaves like a quantum amplifier emitting quantum noise from the Horizon. ...
4
Spectral geometry is one of the many ways mathematicians think about geometry. The general idea is that if you have some manifold equipped with a metric, you can cook up some canonical differential operators. These operators can be thought of as linear operators, acting on (infinite-dimensional) vector spaces of functions, tensors, spinors, and the like. ...
2
First off, props for even knowing the proper use of the terminology. I dare say most middle-schoolers probably think classical field theory is about listening to Mozart in a meadow.
Now, if I may start at the beginning...
You seem to know this already, but I'll restate it for pedagogical reasons. When someone says they have a classical field theory they ...
-2
foamy space is nothing but quantization of spacetime, ie discrete spacetime. Using the concept of discrete spacetime all the open questions in phyics right from general relativity to quantum mechanics can be solved.
http://www.scribd.com/doc/138077520/Space-Time-2013
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Mendel Sachs may have been blacklisted, which would certainly be wrong. But his theory has a fatal error. His derivation depends on the assumption that certain 2x2 complex matrices, standing for quaternions, approach the Pauli spin matrices in the limit of zero curvature. This is impossible; the Pauli matrices are not quaternions and the argument collapses.
8
A few developments since 2001:
There is the new field of loop quantum cosmology, which shows some promising signs of being able to actually calculate things that might conceivably be testable by observation.
The LHC hasn't found any evidence of supersymmetry, which may reduce the appeal of string theory.
There have been some high-precision tests of ...
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