by Bart Verberck, Nature Physics 13, 623 (2017) doi:10.1038/nphys4207 (sci-hub)
Your Earthly carpet sweeper won’t do the job in the low-pressure, CO2
-dominant atmosphere on Mars. But Catalin Ticoş and colleagues
have now shown how to build a Mars-proof dirt broom, which can be used for removing sand and dust from equipment stationed on the Martian surface.
The authors’ experimental setup involved a coaxial plasma gun, capable of producing dense pulsed plasma jets, directed perpendicularly to the area to be cleaned. As a test surface, they used an array of photovoltaic cells, covered with a powder retrieved from volcanic ash, which mimicked Martian surface soil.
Ticoş et al.
measured the efficiency of their cleaning method in terms of how the voltage delivered by the cells increased during operation. An analysis of the plasma jets in a CO2
environment at the same pressure as that on Mars’s surface revealed an average plasma plume speed several orders larger than the planet’s typical wind speeds — implying that the plasma broom would indeed succeed in the Martian environment.
Causality is a concept deeply rooted in our understanding of the world and lies at the basis of the very notion of time. It plays an essential role in our cognition — enabling us to make predictions, determine the causes of certain events, and choose the appropriate actions to achieve our goals. But even in quantum mechanics, for which countless measurements and preparations have been rethought, the assumption of pre-existing causal structure has never been challenged — until now.
Giulia Rubino and colleagues have designed an experiment to show that causal order can be genuinely indefinite. By creating wires between a pair of operating gates whose geometry is controlled by a quantum switch — the state of single photon — they realized a superposition of gate orders. From the output, they measured the so-called causal witness, which specifies whether a given process is causally ordered or not. The result brings a new set of questions to the fore — namely, where does causal order come from, and is it a necessary property of nature?
via Nature Physics (sci-hub)