Is The Starry Night Turbulent?

The Starry Night
Vincent van Gogh (1889)

James Beattie, Neco Kriel
Vincent van Gogh’s painting, The Starry Night, is an iconic piece of art and cultural history. The painting portrays a night sky full of stars, with eddies (spirals) both large and small. Kolmogorov1941’s description of subsonic, incompressible turbulence gives a model for turbulence that involves eddies interacting on many length scales, and so the question has been asked: is The Starry Night turbulent? To answer this question, we calculate the azimuthally averaged power spectrum of a square region (1165×1165 pixels) of night sky in The Starry Night. We find a power spectrum, P(k), where k is the wavevector, that shares the same features as supersonic turbulence. It has a power-law P(k)∝k2.1±0.3 in the scaling range, 34≤k≤80. We identify a driving scale, kD=3, dissipation scale, kν=220 and a bottleneck. This leads us to believe that van Gogh’s depiction of the starry night closely resembles the turbulence found in real molecular clouds, the birthplace of stars in the Universe.


Lost in Math?

Lost in Math? A review of ‘Lost in Math: How Beauty Leads Physics Astray’, by Sabine Hossenfelder

Jeremy Butterfield
This is a review of Hossenfelder’s book, ‘Lost in Math: How Beauty Leads Physics Astray’. The book gives a breezy exposition of the present situation in fundamental physics, and raises important questions: both about the content of the physics, and the way physics research is organized. I first state my main disagreements. Then, I mostly praise the book: I concentrate on Hossenfelder’s discussion of supersymmetry, naturalness and the multiverse.

After primordial inflation

D. V. Nanopoulos, K. A. Olive, M. Srednicki
We consider the history of the early universe in the locally supersymmetric model we have previously discussed. We pay particular attention to the requirement of converting the quanta of the field which drives primordial inflation (inflatons) to ordinary particles which can produce the cosmological baryon asymmetry without producing too many gravitinos. An inflaton mass of about 1013 GeV (a natural value in our model) produces a completely acceptable scenario.

How does a quantum particle see the world?

Researchers at the University of Vienna study the relevance of quantum reference frames for the symmetries of the world

Quantum features, such as quantum superposition, are only defined relative to an observer. When we look at the train from the point of view of an observer standing on the platform, the train looks in a quantum superposition of different positions. (© Christian Murzek/IQOQI-Vienna)

However, an observer sitting on the train sees the observer on the platform and the ball in a quantum superposition. (© Christian Murzek/IQOQI-Vienna)

According to one of the most fundamental principles in physics, an observer on a moving train uses the same laws to describe a ball on the platform as an observer standing on the platform – physical laws are independent on the choice of a reference frame. Reference frames such as the train and the platform are physical systems and ultimately follow quantum-mechanical rules. They can be, for example, in a quantum state of superposition of different positions at once. So, what would the description of the ball look like for an observer on such a “quantum platform”? Researchers at the University of Vienna and the Austrian Academy of Sciences proved that whether an object (in our example, the ball) shows quantum features depends on the reference frame. The physical laws, however, are still independent of it. The results are published in Nature Communications.

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An optical analogue to Schrödinger’s cat

Entanglement between a rubidium-87 atom and a laser pulse leads to the creation of macroscopic superposition states.

A rubidium-87 atom (blue sphere) is entangled with a light pulse that is in two distinct superpositions of phase states. A measurement of spin collapses the atom state and leads to the odd (top) or even (bottom) superposition state of the light.

Erwin Schrödinger’s cat gedanken experiment of 1935 presented the possibility of entanglement between microscopic and macroscopic physical systems and the resulting quantum behavior of macroscopic objects. In the years since, researchers have realized analogous systems with entanglement between microscopic and macroscopic structures—for example, the entanglement between a trapped ion and the vibrational state in the trap described in David Wineland’s Nobel Prize–winning work. However, the resulting macroscopic quantum superposition states typically had limited utility because their creation had a low probability or they had short transmission distances. Now Gerhard Rempe of the Max Planck Institute of Quantum Optics in Germany and his colleagues have deterministically produced a macroscopic light pulse with a controlled superposition state.

Rempe and his colleagues used a single rubidium-87 atom trapped in an optical cavity as the microscopic object and a laser pulse as the macroscopic cat. After putting the atom into a quantum superposition of up- and down-spin states, the researchers reflected the light pulse off the optical cavity. Although the light would not gain a phase shift for an atom in the up-spin state, it would gain one for the down-spin state. Because the atom had both up and down spin, the light experienced both phase shifts and became entangled with it. After rotating the atom’s spin by 90 degrees, the researchers measured the spin state, projecting it into either the up or down state. For a spin-up measurement, the light was in an odd superposition of the phase states; for a spin-down measurement, it was in an even superposition, as shown in the figure. Rempe and his colleagues confirmed the creation of a macroscopic superposition state by measuring the probability distribution in phase space with a homodyne detector.

The experiment performed by Rempe and his colleagues offers more than the realization of a famous thought experiment. Compared with previous work, the results provide some important advantages, such as the creation of atom-light entanglement in every trial. Furthermore, because it is optical, the macroscopic object can propagate without losing its superposition state. Those features make the new technique particularly promising for quantum network applications. Schrödinger’s cat, simultaneously alive and dead, may become a new mode of information transmission. (B. Hacker et al., Nat. Photonics 13, 110, 2019.)