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The quantum fluctuations that pervade empty space spontaneously give birth to pairs of particles and antiparticles. Ordinarily, these pairs annihilate so promptly that their existence is virtual. But a powerful field can pull a pair’s members apart for long enough that their existence becomes real. In 1951 Julian Schwinger calculated how strong an electric field needs to be to beget electron–positron pairs. Now Michael Wondrak and his colleagues of Radboud University in the Netherlands have proposed that particle pairs can be brought into existence by the immense gravitational tidal forces around a black hole [1].

Wondrak and his colleagues considered all the paths a pair of virtual particles could take during their brief existence. If the vacuum is stable, all pairs that are created are also destroyed. But a strong field destabilizes the vacuum, makes some paths more likely than others, and leads to a deficit of pairs that recombine. The deficit is balanced by a net outflow of real particles, which, in the case of a black hole’s gravitational field, leads to the black hole’s eventual evaporation.

The theorists’ approach is sufficiently general that it could reproduce not only Schwinger’s effect but also Stephen Hawking’s 1974 proposal that if a particle–antiparticle pair springs into virtual existence near a black hole’s event horizon, one member could fall in while the other escapes. What’s more, the researchers found that Hawking’s effect is a special case of a more general phenomenon. Pulling virtual particles into existence depends only on the stretching of spacetime wrought by a curved gravitational field and does not require an event horizon as Hawking originally suggested. One intriguing implication is that a neutron star, whose Schwarzschild radius lies beneath the stellar surface, can also beget particle pairs and decay.

Year 2021 😗😁

They were indeed correct that lead could be turned into gold — even if they were dead wrong about how it could be done. Now, modern science routinely takes us far beyond even the wildest dreams of the alchemists.

One of the most famous stories of nuclear transmutation comes from the 1970s, when nuclear chemist and Nobel laureate Glenn Seaborg worked at the Lawrence Berkeley National Laboratory alongside colleague Walt Loveland and then-graduate student Dave Morrissey. The scientists were using a super-heavy ion linear accelerator to bombard atoms with ions as heavy as uranium at relativistic speeds. “Among the ones we bombarded was lead-208,” Loveland says.

Continue reading “Turning Lead Into Gold” »

A new demonstration involving hundreds of entangled atoms tests Schrödinger’s interpretation of Einstein, Rosen, and Podolsky’s classic thought experiment.

In 1935, Einstein, Podolsky, and Rosen (EPR) presented an argument that they claimed implies that quantum mechanics provides an incomplete description of reality [1]. The argument rests on two assumptions. First, if the value of a physical property of a system can be predicted with certainty, without disturbance to the system, then there is an “element of reality” to that property, meaning it has a value even if it isn’t measured. Second, physical processes have effects that act locally rather than instantaneously over a distance. John Bell subsequently proposed a way to experimentally test these “local realism” assumptions [2], and so-called Bell tests have since invalidated them for systems of a few small particles, such as electrons or photons [3].

An unusual kind of superconductor harbors magnetic vortices that researchers predict should be readily observable thanks to the striped configurations they adopt.

In a nematic superconductor, electron pairs are bound more strongly in one, spontaneously chosen, lattice direction than in the others. This rotational symmetry breaking of the pairs’ wave function is just one of this type of superconductor’s unusual properties. A leading candidate to exhibit nematic superconductivity, copper-doped bismuth selenide, is also predicted to sustain surface charge-carrying quasiparticles known as Majorana fermions, which researchers think could be used for superconducting quantum technologies. What’s more, nematic superconductors harbor topological solitons known as skyrmions, whose complexity gives them many ways to arrange themselves and whose small size and low energy have attracted interest for data storage technologies. Now Thomas Winyard of the University of Edinburgh, UK, and colleagues have calculated the various skyrmion configurations that could arise in a nematic superconductor [1, 2].

The physicist Tony Skyrme came up with the concept of a skyrmion in 1961 when working on a particle physics problem. In the 2000s, the quasiparticle was then linked to condensed-matter systems when it was discovered that quasiparticles could also be used to explain magnetic vortices in certain thin films.

“” This achievement connects synchrotron X-rays with quantum tunneling process to detect X-ray signature of an individual atom and opens many exciting research directions including the research on quantum and spin (magnetic) properties of just one atom using synchrotron X-rays,” Hla said.”

A team of scientists from Ohio University, Argonne National Laboratory, the University of Illinois-Chicago, and others, led by Ohio University Professor of Physics, and Argonne National Laboratory scientist, Saw Wai Hla, have taken the world’s first X-ray SIGNAL (or SIGNATURE) of just one atom. This groundbreaking achievement could revolutionize the way scientists detect the materials.

There is a lot of speculation about the end of the universe. Humans love a good ending after all. We know that the universe started with the Big Bang and it has been going for almost 14 billion years. But how the curtain call of the cosmos occurs is not certain yet. There are, of course, hypothetical scenarios: the universe might continue to expand and cool down until it reaches absolute zero, or it might collapse back onto itself in the so-called Big Crunch. Among the alternatives to these two leading theories is “vacuum decay”, and it is spectacular – in an end-of-everything kind of way.

While the heat death hypothesis has the end slowly coming and the Big Crunch sees a reversal of the universe’s expansion at some point in the future, the vacuum decay requires that one spot of the universe suddenly transforms into something else. And that would be very bad news.

There is a field that spreads across the universe called the Higgs field. Interaction between this field and particles is what gives the particles mass. A quantum field is said to be in its vacuum state if it can’t lose any energy but we do not know if that’s true for the Higgs field, so it’s possible that the field is in a false vacuum at some point in the future. Picture the energy like a mountain. The lowest possible energy is a valley but as the field rolled down the slopes it might have encountered a small valley on the side of that mountain and got stuck there.

Neil Gershenfeld is the director of the MIT Center for Bits and Atoms. Please support this podcast by checking out our sponsors:
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EPISODE LINKS:
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MIT Center for Bits and Atoms: https://cba.mit.edu/
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Continue reading “Neil Gershenfeld: Self-Replicating Robots and the Future of Fabrication | Lex Fridman Podcast #380” »

Physicist Sean Carroll explains the discovery of Higgs Boson in simple terms. Credit-ICE at Dartmouth.

Particle-like quantum states called non-abelian anyons remember being swapped and could be useful for protecting information in quantum computers.