# Quantum Physics

### Commerial quantum

Are Many Worlds and the Multiverse the Same Idea? | Cosmic Variance. When physicists are asked about “parallel worlds” or ideas along those lines, they have to be careful to distinguish among different interpretations of that idea.

There is the “multiverse” of inflationary cosmology, the “many worlds” or “branches of the wave function” of quantum mechanics, and “parallel branes” of string theory. Increasingly, however, people are wondering whether the first two concepts might actually represent the same underlying idea. Experiment. Experiment - Multimedia. How Cosmic Inflation Creates an Infinity of Universes [Video] Arovas_Stern_2007. World line. In physics, the world line of an object is the unique path of that object as it travels through 4-dimensional spacetime.

The concept of "world line" is distinguished from the concept of "orbit" or "trajectory" (such as an orbit in space or a trajectory of a truck on a road map) by the time dimension, and typically encompasses a large area of spacetime wherein perceptually straight paths are recalculated to show their (relatively) more absolute position states — to reveal the nature of special relativity or gravitational interactions. The idea of world lines originates in physics and was pioneered by Hermann Minkowski. The term is now most often used in relativity theories (i.e., special relativity and general relativity). However, world lines are a general way of representing the course of events. The use of it is not bound to any specific theory. Diffraction of water waves (opening)

<em>From Eternity to Here:</em> Book Club | Cosmic Variance. From Eternity to Book Club: Chapter Eleven | Cosmic Variance. Welcome to this week’s installment of the From Eternity to Here book club.

Part Three of the book concludes with Chapter Eleven, “Quantum Time.” Excerpt: This distinction between “incomplete knowledge” and “intrinsic quantum indeterminacy” is worth dwelling on. If the wave function tells us there is a 75 percent chance of observing the cat under the table and a 25 percent chance of observing her on the sofa, that does not mean there is a 75 percent chance that the cat is under the table and a 25 percent chance that she is on the sofa. There is no such thing as “where the cat is.” Density matrix. Explicitly, suppose a quantum system may be found in state with probability p1, or it may be found in state with probability p2, or it may be found in state.

Einselection. In quantum mechanics, einselection, short for environment - induced superselection, is a name coined by Wojciech H.

Zurek[1] for a process which explains the phenomenon of wavefunction collapse and the emergence of classical descriptions of reality from quantum descriptions. Classicality is an emergent property induced in open quantum systems by their environments. Due to the interaction with the environment, the vast majority of states in the Hilbert space of a quantum open system become highly unstable to entangling interaction with the environment, which in effect monitors selected observables of the system. From Eternity to Book Club: Chapter Twelve | Cosmic Variance. Welcome to this week’s installment of the From Eternity to Here book club.

Part Four opens with Chapter Twelve, “Black Holes: The Ends of Time.” Excerpt: