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By hellowalkman · Posted
The quantum search for Time's origin had an equally mind-boggling conclusion by Sayan Sen Image by Steve Johnson via Pexels A theoretical study from researchers at the University of Surrey suggested that the direction of time may not be fundamentally fixed in certain quantum systems. The work, published in Scientific Reports, examined how the “arrow of time” could emerge from microscopic physics and found that time-reversal symmetry can remain intact even in models used to describe processes such as energy loss and thermalisation. The arrow of time refers to the observed one-way direction from past to future in everyday life. In macroscopic processes, this is easy to see. Spilled milk spreads across a table and does not gather back into a glass, and heat flows from hotter objects to colder ones. These processes shape the common sense idea that time moves in a single direction. However, at the level of fundamental physics, many equations do not prefer a direction of time. Time-reversal symmetry means that the same physical laws can describe a system whether time moves forward or backward. This has made it difficult to explain why irreversible behaviour appears in the large-scale world even when the underlying rules do not require it. Dr Andrea Rocco, Associate Professor in Physics and Mathematical Biology at the University of Surrey, described this contrast: "One way to explain this is when you look at a process like spilt milk spreading across a table, it's clear that time is moving forward. But if you were to play that in reverse, like a movie, you'd immediately know something was wrong – it would be hard to believe milk could just gather back into a glass. However, there are processes, such as the motion of a pendulum, that look just as believable in reverse. The puzzle is that, at the most fundamental level, the laws of physics resemble the pendulum; they do not account for irreversible processes. Our findings suggest that while our common experience tells us that time only moves one way, we are just unaware that the opposite direction would have been equally possible." The study focused on open quantum systems, which are quantum systems that interact with a surrounding environment. This environment, often described as a heat bath, can exchange energy and information with the system. The researchers used this framework to study how a direction of time might appear even when the underlying physics does not enforce one. A key part of the analysis involved the Markov approximation. This is a simplification used in many models where the system is assumed not to retain memory of its past states. The idea is that changes depend only on the current state, not on earlier history. This is commonly used when studying thermalisation, which is the process where a system settles into equilibrium with its environment. The study also used concepts such as master equations, including the Lindblad and Pauli equations, which describe how probabilities of different quantum states change over time. Another related model discussed was quantum Brownian motion, which describes the random-like movement of a quantum particle interacting continuously with its environment. In these descriptions, a “memory kernel” can appear, which is a mathematical term that accounts for how past states influence current behaviour. The researchers found that applying the Markov approximation did not break time-reversal symmetry. Even when the system interacted with an effectively infinite heat bath, the resulting equations of motion remained symmetric in time. This meant that the same mathematical description could, in principle, run forward or backward in time without contradiction. The study further showed that standard frameworks used in open quantum systems, including quantum Brownian motion and master equations like the Lindblad and Pauli forms, could be written in a time-symmetric way. These equations are typically used to describe processes that look irreversible, such as dissipation and thermalisation, but the results suggested they can also be interpreted as allowing evolution in both time directions. Thomas Guff, Research Fellow in Quantum Thermodynamics, said: "The surprising part of this project was that even after making the standard simplifying assumption to our equations describing open quantum systems, the equations still behaved the same way whether the system was moving forwards or backwards in time. When we carefully worked through the maths, we found that this behaviour had to be the case because a key part of the equation, the "memory kernel," is symmetrical in time. We also found a small but important detail which is usually overlooked – a time discontinuous factor emerged that kept the time-symmetry property intact. It’s unusual to see such a mathematical mechanism in a physics equation because it's not continuous, and it was very surprising to see it appear so naturally." The researchers also noted that deriving a one-way arrow of time from time-reversal symmetric microscopic dynamics remains an open problem across fields such as thermodynamics, statistical mechanics, particle physics, and cosmology. Their results suggested that some standard descriptions of irreversible behaviour in open quantum systems may be better understood using a time-symmetric formulation of Markovianity. According to the study, processes such as thermalisation, which are usually treated as irreversible, could in theory be described in a way that allows evolution in either time direction under the same rules. This does not imply that time reversal occurs in everyday life, but rather that the underlying equations do not strictly enforce a single direction. Overall, the findings suggested that the perceived direction of time may emerge from how physical systems are modelled and approximated, rather than from a fundamental asymmetry in the laws themselves. The researchers noted that this perspective could have implications for ongoing work in quantum mechanics, thermodynamics, and cosmology on the origin of time’s arrow. Source: University of Surrey, Nature This article was generated with some help from AI and reviewed by an editor. Under Section 107 of the Copyright Act 1976, this material is used for the purpose of news reporting. Fair use is a use permitted by copyright statute that might otherwise be infringing -
By WaltC · Posted
A bit premature... 100% Marketing. Bizarre. -
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Question
jordan.
I found the following snippet of javascript (uses jQuery) that would allow me to centre a menu/nav that is set to float:left. It seems to work in IE and Opera OK. But in FF and Safari, it works sometimes and other times trips out (keep refreshing the page and it will eventually work/fail). In Chrome it doesn't work at all.
Here is the code:
$(function() { var menu_width = $('#nav').css('float', 'left').width(); $('#nav').css({float : 'none', width : menu_width, margin : '0 auto'}); });I don't know js so I can't figure out what the problem is. If anyone can help it would be much appreciated.
Here is the page running the code:
http://www.islandrobot.com/vanessa/
Cheers,
Jordan
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https://www.neowin.net/forum/topic/894492-js-center-a-menu-that-is-floated-left/Share on other sites
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