Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userWhat if Time Really Exists?
243
0
0.0
(
0
)
Authors
Sean M. Carroll
Ask ChatGPT about the research
No Arabic abstract
Despite the obvious utility of the concept, it has often been argued that time does not exist. I take the opposite perspective: lets imagine that time does exist, and the universe is described by a quantum state obeying ordinary time-dependent quantum mechanics. Reconciling this simple picture with the known facts about our universe turns out to be a non-trivial task, but by taking it seriously we can infer deep facts about the fundamental nature of reality. The arrow of time finds a plausible explanation in a Heraclitean universe, described by a quantum state eternally evolving in an infinite-dimensional Hilbert space.
rate research
Read More
We analyze various possible interpretations of the narrow state $D_{sJ}^+(2632)$ observed by SELEX Collaboration recently, which lies above threshold and has abnormal decay pattern. These interpretations include: (1) sever
In the system of a gravitating Q-ball, there is a maximum charge $Q_{{rm max}}$ inevitably, while in flat spacetime there is no upper bound on $Q$ in typical models such as the Affleck-Dine model. Theoretically the charge $Q$ is a free parameter, and phenomenologically it could increase by charge accumulation. We address a question of what happens to Q-balls if $Q$ is close to $Q_{{rm max}}$. First, without specifying a model, we show analytically that inflation cannot take place in the core of a Q-ball, contrary to the claim of previous work. Next, for the Affleck-Dine model, we analyze perturbation of equilibrium solutions with $Qapprox Q_{{rm max}}$ by numerical analysis of dynamical field equations. We find that the extremal solution with $Q=Q_{{rm max}}$ and unstable solutions around it are critical solutions, which means the threshold of black-hole formation.
The concept of boundary plays an important role in several branches of general relativity, e.g., the variational principle for the Einstein equations, the event horizon and the apparent horizon of black holes, the formation of trapped surfaces. On the other hand, in a branch of mathematics known as geometric measure theory, the usefulness has been discovered long ago of yet another concept, i.e., the reduced boundary of a finite-perimeter set. This paper proposes therefore a definition of finite-perimeter sets and their reduced boundary in general relativity. Moreover, a basic integral formula of geometric measure theory is evaluated explicitly in the relevant case of Euclidean Schwarzschild geometry, for the first time in the literature. This research prepares the ground for a measure-theoretic approach to several concepts in gravitational physics, supplemented by geometric insight. Moreover, such an investigation suggests considering the possibility that the in-out amplitude for Euclidean quantum gravity should be evaluated over finite-perimeter Riemannian geometries that match the assigned data on their reduced boundary. As a possible application, an analysis is performed of the basic formulae leading eventually to the corrections of the intrinsic quantum mechanical entropy of a black hole.
Combining insights from both the effective field theory of quantum gravity and black hole thermodynamics, we derive two novel consistency relations to be satisfied by any quantum theory of gravity. First, we show that a particular combination of the number of massless (light) fields in the theory must take integer values. Second, we show that, once the massless spectrum is fixed, the Wilson coefficient of the Kretschmann scalar in the low-energy effective theory is fully determined by the logarithm of a single natural number.
We study the emission of large-scales wavelength space-time waves during the inflationary expansion of the universe, produced by back-reaction effects. As an example, we study an inflationary model with variable time scale, where the scale factor of the universe grows as a power of time. The coarse-grained field to describe space-time waves is defined by using the Levy distribution, on the wavenumber space. The evolution for the norm of these waves on cosmological scales is calculated, and it is shown that decreases with time.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
