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Documentário com entrevistas a Wheeler, Bohm, Bell e Aspect.

18.02.17

 

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Physics of Information

31.01.17

 

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This is fun

09.12.16

 

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"How Do You Say “Life” in Physics?"

08.12.16

"Jeremy England is concerned about words—about what they mean, about the universes they contain. He avoids ones like “consciousness” and “information”; too loaded, he says. Too treacherous. When he’s searching for the right thing to say, his voice breaks a little, scattering across an octave or two before resuming a fluid sonority.

His caution is understandable. The 34-year-old assistant professor of physics at the Massachusetts Institute of Technology is the architect of a new theory called “dissipative adaptation,” which has helped to explain how complex, life-like function can self-organize and emerge from simpler things, including inanimate matter. This proposition has earned England a somewhat unwelcome nickname: the next Charles Darwin. But England’s story is just as much about language as it is about biology.

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As a young faculty member at MIT, he neither wanted to stop doing biology, nor thinking about theoretical physics. “When you refuse to let go of two things that are divergent in the way they cause you to talk,” he says, “it forces you in the direction of translation.”

 

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"State Space Compression, Coarse Graining, and the Averaging of Life and Mind"

13.09.16

Renormalization is a principled coarse-graining of space-time. It shows us how the small-scale details of a system may become irrelevant when looking at larger scales and lower energies. Coarse-graining is also crucial, however, for biological and cultural systems that lack a natural spatial arrangement. I introduce the notion of coarse-graining and equivalence classes, and give a brief history of attempts to tame the problem of simplifying and "averaging" things as various as algorithms and languages. I then present state-space compression, a new framework for understanding the general problem. At the end, I present recent empirical results, in an animal social system, that show evidence for the coupling of scales: the reaction of coarse-grained facts about a system "downwards" to influence the microphysics.

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"In Search of Time's Origin"

14.07.16

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Page and Wooters decided to apply the controversial concept that the universe as a whole could be treated as a giant quantum object—subject to the same physical laws as electrons, protons, and other tiny particles of the subatomic world. They imagined splicing the contents of the cosmos into two pieces. Because quantum laws prevailed, the pieces would be entangled. Scientists have found that two entangled particles measured in the lab can have equal but opposite values. If one is spinning clockwise, for instance, the other will be spinning counter-clockwise so that, when summed together, the properties cancel each other out. Page and Wooters argued that in similar fashion, each section of their divided cosmos could independently evolve, but because they were entangled, the changes in one would be counter-balanced by the changes in the other. To someone inside one of the sections, time would appear to pass. But to the outside observer, the overall universe would appear static.

While Page and Wooters had offered a theoretical sketch, based on quantum entanglement, for how the cosmos might appear to be stationary to someone peering in from the outside, there seemed to be no way to confirm or rule out their idea. But, in 2013, Genovese and his colleagues performed an experiment to test whether—at least in the lab—it is possible to create a model of the universe in miniature, with just two particles of light, or photons, generated from a laser. The aim of the experiment was to prove that it is possible to create a situation in which a quantum system, when viewed from outside, appeared unchanging, but when observed from within appeared to evolve.

To do the experiment, Genovese set out to monitor the photons’ polarizations—the directions in which they vibrated. If a polarized particle could be made to rotate at a constant rate, then its position at any moment could be used to mark out intervals in time, just like a second-hand on a clock. The team entangled the two photons together, in such a way that their polarizations took on opposing traits. For instance, if the polarization of one was measured to move up and down, the other would vibrate from side-to-side.

In order to set their photons’ “second-hands” in motion, the team passed both particles through quartz plates, causing their polarizations to rotate. The amount of rotation was related to the actual time spent within the plates, giving physicists a means of measuring the passage of time. They carried out their experiment repeatedly and in each run they stopped at a different moment and measured the polarization of one of the photons. “By measuring the first clock photon, we became entangled with it,” says Genovese. “That means we became part of that universe and can register the evolution of the second photon against our clock photon.” Vested with this ability, the team confirmed that one photon appeared to change when measured against its partner, in the same way that Wooters and Page believed one part of the universe could be seen to evolve if measured against another portion of the cosmos.

However, Genovese still had to confirm the second part of the hypothesis: that when the entire entangled system was monitored as a whole, from the outside, it would appear static. In this part of the experiment, the team took the point of view of a “super observer” standing outside the universe. This external watcher could never look at the individual state of either photon because by doing so he would become entangled with them, becoming an internal observer. Instead, the observer could only measure the joint state of the pair of photons. The team ran the test many times, stopping at different points. They looked at the two photons as a combined whole and measured their joint polarization. Each time, they ascertained that the two entangled photons were polarized in equal but opposite ways. No matter how much time passed, the two photons were always poised in exactly the same “embrace.” The mini-universe appeared to be static from the outside and completely unchanged. It turns out the so-called “problem of time,” discovered by Wheeler and DeWitt, can be resolved if time is an artifact of quantum entanglement.

 

 

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"To Understand Your Past, Look to Your Future"

04.07.16

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"When formulating explanations, most of us tend to think in terms laid down by Isaac Newton over 300 years ago. This “Newtonian Schema” takes the past as primary and uses it to solve for the future, explaining our universe one time-step at a time. Some researchers even go so far as to think of the universe as the output of a forward-running computer program, a picture that is a natural extension of this schema. Even though our view of time has changed dramatically in the last century, the Newtonian Schema has somehow endured as our most popular physics framework.

But imposing old Newtonian Schema thinking on new quantum-scale phenomena has landed us in situations with no good explanations whatsoever. If these phenomena seem inexplicable, we may just be thinking about them in the wrong way. Much better explanations become available if we are willing to take the future into account as well as the past. But Newtonian-style thinking is inherently incapable of such time-neutral explanations. Computer programs run in only one direction, and trying to combine two programs running in opposite directions leads to the paradoxical morass of poorly plotted time-travel movies. In order to treat the future as seriously as we treat the past, we clearly need an alternative to the Newtonian Schema.

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“Quantum mechanics is a law of thought.”

23.04.16

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Along with the researchers Carlton Caves and Rüdiger Schack, he interpreted the wave function’s probabilities as Bayesian probabilities — that is, as subjective degrees of belief about the system. Bayesian probabilities could be thought of as gambling attitudes for placing bets on measurement outcomes, attitudes that are updated as new data come to light. In other words, Fuchs argued, the wave function does not describe the world — it describes the observer. “Quantum mechanics,” he says, “is a law of thought.”

Quantum Bayesianism, or QBism as Fuchs now calls it, solves many of quantum theory’s deepest mysteries. Take, for instance, the infamous “collapse of the wave function,” wherein the quantum system inexplicably transitions from multiple simultaneous states to a single actuality. According to QBism, the wave function’s “collapse” is simply the observer updating his or her beliefs after making a measurement. Spooky action at a distance, wherein one observer’s measurement of a particle right here collapses the wave function of a particle way over there, turns out not to be so spooky — the measurement here simply provides information that the observer can use to bet on the state of the distant particle, should she come into contact with it. But how, we might ask, does her measurement here affect the outcome of a measurement a second observer will make over there? In fact, it doesn’t. Since the wavefunction doesn’t belong to the system itself, each observer has her own. My wavefunction doesn’t have to align with yours.

 

 

 

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"String Theory Meets Loop Quantum Gravity"

14.01.16

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Eight decades have passed since physicists realized that the theories of quantum mechanics and gravity don’t fit together, and the puzzle of how to combine the two remains unsolved. In the last few decades, researchers have pursued the problem in two separate programs — string theory and loop quantum gravity — that are widely considered incompatible by their practitioners. But now some scientists argue that joining forces is the way forward.

 

 

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A Santissima Trindade

04.06.14

 

 More than 40 years after a Soviet nuclear physicist proposed an outlandish theory that trios of particles can arrange themselves in an infinite nesting-doll configuration, experimentalists have reported strong evidence that this bizarre state of matter is real.

 

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