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 by Staff Writers Hoboken NJ (SPX) Aug 23, 2019
Quantum mechanics boasts all sorts of strange features, one being quantum superposition - the peculiar circumstance in which particles seem to be in two or more places or states at once. Now, an international group of physicists led by Stevens Institute of Technology, University of Vienna and University of Queensland flip that description on its head, showing that particles are not the only objects that can exist in a state of superposition - so can time itself. "The sequence of events can become quantum mechanical," said co-author Igor Pikovski, a physicist at the Center for Quantum Science and Engineering at Stevens Institute of Technology. " We looked at quantum temporal order where there is no distinction between one event causing the other or vice versa." The work, reported in the August 22 issue of Nature Communications, is among the first to reveal the quantum properties of time, whereby the flow of time doesn't observe a straight arrow forward, but one where cause and effect can co-exist both in the forward and backward direction. In the upcoming era of quantum computers, the work holds particular promise: quantum computers that exploit the quantum order of performing operations might beat devices that operate using only fixed sequences. To show this scenario, Pikovski and colleagues merged two seemingly conflicting theories - quantum mechanics and general relativity - to conduct a Gedanken experiment, a way of using the imagination to investigate the nature of things. The team, consisting of Pikovski, Magdalena Zych, Fabio Costa and Caslav Brukner, started by asking the question, "what would a clock measure if it was influenced by a massive object in a quantum superposition state, i.e. both near and far at the same time?" According to general relativity, the presence of a massive object slows down the flow of time, such that a clock placed close to a massive object will run slower compared to an identical one that is farther away. To illustrate what happens, imagine a pair of starships training for a mission. They are asked to fire at each other at a specified time and dodge the fire at another time, whereby each ship knows the exact time when to fire and when to dodge. If either ship fires too early, it will destroy the other, and this establishes an unmistakable time order between the firing events. However, if a powerful agent could place a sufficiently massive object, say a planet, closer to one ship it would slow down its flow of time. As a result, the ship would dodge the fire too late and would be destroyed. Quantum mechanics complicates the matter. When placing the planet in a state of superposition near one ship or the other, both can be destroyed or survive at the same time. The sequence of events exists in a state of superposition, such that each starship simultaneously destroys the other. The authors illustrate for the first time how this quantum scenario can occur and how it can be verified. "Moving planets around is hard," said Pikovski. "But imagining it helped us examine a quantum aspect of time that was previously unknown."
University of Vienna However, the rules of quantum theory allow for any object to be prepared in a superposition state. A superposition state of two locations is different to placing an object in one or the other location randomly - it is another way for an object to exist, allowed by the laws of quantum physics. One of the open questions in physics is: What happens when an object massive enough to influence the flow of time is placed in a quantum superposition state? This is a controversial topic: some physicists claim that such scenarios are fundamentally impossible - some new mechanism must block the superposition from forming in the first place - while others develop entire theories based on the assumption that this is possible. "We started by tackling a question: what would a clock measure if it was influenced by a massive object in a quantum superposition state?" explains Magdalena Zych from the University of Queensland. The scientists were expecting to face the roadblocks making the scenario impossible, but surprisingly, using standard textbook physics they were able to exactly describe what happens. They so discovered that when a massive object is placed in a quantum superposition in the vicinity of a set of clocks, their time order can become genuinely quantum, defying any classical description. Caslav Brukner, coauthor from the University of Vienna and the Austrian Academy of Sciences added that the regime where quantum time order could arise is quite remote from our everyday experience, "but the most important insight from our work is that quantum time order is at all possible, and that it results in new physical effects." To illustrate what happens, imagine a pair of starships training for a mission. They are asked to fire at each other at a specified time, and immediately start their engines in order to dodge each other's attack. If either of the ships fires too early, it will destroy the other, and this establishes an unmistakable time order between the firing events. If a powerful agent could place a sufficiently massive object, say a planet, closer to one ship it would slow down its counting of time. As a result, the ship farther away from the mass will fire too early for the first one to escape. The laws of quantum physics and gravity predict that by manipulating a quantum superposition state of the planet, the ships can end up in a superposition of either of them being destroyed. Such a superposition state, involving two systems, is called entangled. The new work shows that the temporal order among events can exhibit superposition and entanglement - genuinely quantum features of particular importance for testing quantum theory against alternatives. The result can now be used as a theoretical testing ground for frameworks for quantum gravity, and thus help to move forward in formulating the correct theory of quantum gravity. The study will also be relevant for future quantum technologies. Quantum computers that exploit quantum order of performing operations might beat devices that operate using only fixed sequences. Practical implementations of quantum temporal order do not require extreme conditions--such as planets in superposition--and can be simulated without the use of gravity. The discovery of quantum properties of time can lead to better quantum devices in the upcoming era of quantum computers.
Research Report: "Bell's theorem for temporal order"
NASA selects proposals to further study the fundamental nature of space Washington DC (SPX) Aug 14, 2019 NASA has selected two proposals for concept studies that could help us better understand the fundamental nature of space and how it changes in response to planetary atmospheres, radiation from the Sun, and interstellar particles. The proposals will advance NASA's heliophysics program and could lead to better protection for both technology and humans as we travel farther from home. Each of these Heliophysics Science Mission of Opportunity proposals will receive $400,000 to conduct a nine-month miss ... read more
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