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Category: physics

Scientists believe that time is continuous, not discrete—roughly speaking, they believe that it does not progress in “chunks,” but rather “flows,” smoothly and continuously. So they often model the dynamics of physical systems as continuous-time “Markov processes,” named after mathematician Andrey Markov. Indeed, scientists have used these processes to investigate a range of real-world processes from folding proteins, to evolving ecosystems, to shifting financial markets, with astonishing success.

However, invariably a scientist can only observe the state of a system at discrete times, separated by some gap, rather than continually. For example, a stock market analyst might repeatedly observe how the state of the market at the beginning of one day is related to the state of the market at the beginning of the next day, building up a conditional probability distribution of what the state of the second day is given the state at the first day.

In a pair of papers, one appearing in this week’s Nature Communications and one appearing recently in the New Journal of Physics, physicists at the Santa Fe Institute and MIT have shown that in order for such two– dynamics over a set of “visible states” to arise from a continuous-time Markov process, that Markov process must actually unfold over a larger space, one that includes hidden states in addition to the visible ones. They further prove that the evolution between such a pair of times must proceed in a finite number of “hidden timesteps”, subdividing the interval between those two times. (Strictly speaking, this proof holds whenever that evolution from the earlier time to the later time is noise-free—see paper for technical details.)

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A Harvard physicist has shown that wormholes can exist: tunnels in curved space-time, connecting two distant places, through which travel is possible.

But don’t pack your bags for a trip to other side of the galaxy yet; although it’s theoretically possible, it’s not useful for humans to through, said the author of the study, Daniel Jafferis, from Harvard University, written in collaboration with Ping Gao, also from Harvard and Aron Wall from Stanford University.

“It takes longer to get through these wormholes than to go directly, so they are not very useful for ,” Jafferis said. He will present his findings at the 2019 American Physical Society April Meeting in Denver.

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One of the ultimate goals of modern physics is to unlock the power of superconductivity, where electricity flows with zero resistance at room temperature.

Progress has been slow, but in 2018, physicists have made an unexpected breakthrough. They discovered a superconductor that works in a way no one’s ever seen before — and it opens the door to a whole world of possibilities not considered until now.

In other words, they identified a brand new type of superconductivity.

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We already recover power from the wheels of some cars when slowing. Kinetic energy recovery systems (KERS) have been used in Formula One racing to store energy in a flywheel when braking, and then push it back to the wheels later for a boost in speed. Electric cars often use regenerative braking, which converts the speed of the wheels into electrical power to recharge the battery. These systems are a great way to increase efficiency, but like everything in the Universe, they are not 100 per cent efficient. Sadly, the laws of physics prohibit the existence of true perpetual motion, so it’s the best we can do.

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Today our middle-aged Universe looks eerily smooth. Too smooth, in fact.

While a rapid growth spurt in space-time would explain what we see, science needs more than nice ideas. It needs evidence that whittles away contending arguments. We might finally know where to look for some.

A team of physicists from the Centre for Astrophysics | Harvard & Smithsonian (CfA) and Harvard University went back to the drawing board on the early Universe’s evolution to give us a way to help those inflation models stand out from the crowd.

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If there is one thing Twitter has taught us, it’s that the world loves a question that sounds stupid but actually has a profound and interesting answer. For instance, what would happen if the world suddenly turned into blueberries, as answered by physics recently. Or what color is that dress?

In a similar way, perception scientists have recently been fighting it out on Twitter to answer the seemingly trivial question of: “Which is the best sense and why?” The debate has opened up some surprisingly deep questions — like what actually makes a sense more or less valuable? And, are some senses fundamentally more important in making us human?

The question was also put to a poll. While most people would probably assume the obvious winner is vision, “somatosensation” — which we normally refer to as touch but technically incorporates all sensations from our body — took the day. But does this vote hold up when you take a closer look at the scientific evidence?

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The hunt for gravitational waves is back on. After a series of upgrades, the National Science Foundation’s Laser Interferometer Gravitational-Wave Observatory (LIGO) will resume its search for ripples in space and time on Monday, April 1.

LIGO is famous for making the first direct detection of gravitational waves in 2015, for which the observatory’s founders were awarded the Nobel Prize. The observatory was able to detect gravity waves generated by two colliding black holes which were located 1.3 billion light-years away from Earth, and since then has observed nine more black hole mergers and one collision of two neutron stars.

Gravitational waves are ripples in the fabric of spacetime, caused by massive bodies which bend it like a bowling ball placed on a rubber sheet. They were predicted by Einstein as part of his general theory of relativity in 1916, but it took nearly a century for physicists to observe them because the effects are so small. Since these waves have been detected, they can be used to investigate cosmic objects as an alternative to light-based telescopes.

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