Robotic swordsmanship helps humans get exercise; A cell phone app that can pick your lock by listening to you use your key; YouTube discussion of the idea that the universe is a hologram; Geologists date the beginning of plate tectonics to 3.2 billion years ago; and the IEEE Spectrum weekly selection of awesome robot videos

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Foam Sword Fencing With a PR2 Is the Best Kind of Exercise - Most human robotic interaction tasks have collaboration as their goal. Sometimes, though, a bit of good ol' competition is called for. Research has shown that humans get better exercise when it requires competitive effort and it has also shown that robots can be effective exercise coaches. Enter the PR2 robot, armed with a foam sword. Here is a video:

Listen to Your Key: Towards Acoustics-based Physical Key Inference - Researchers propose SpiKey, a cell phone app that can create a key to open your lock by listening to you use your house key. Right now, it only works under tightly controlled conditions.

Related: Smartphones Can Hear the Shape of Your Door Keys (Scientific American Podcast), Phone app can figure out the shape of your house key by listening to you use it (Boing Boing), and Copying a Key by Listening to It in Action (August 2020 coverage). -h/t Bruce Schneier

Is the universe REALLY a hologram? - Physicist, Sabine Hossenfellder discusses the idea that we might live in a hologram. The video and transcript can be found here. In the talk, she starts by describing common 2D holograms on things like bank cards and driver's licenses, then mentions that these are not "real holograms". Real holograms, she says, actually encode a 3D object on a 2D surface using a technique known as "interference", but as-of yet there is not much market demand for this capability. With that background, she explains that when string theorists talk about the universe as a hologram, they are referring to the cosmological constant. It is believed that our universe has a positive-valued cosmological constant. However, universes with a negative cosmological constants (anti-De Sitter spaces) are easier to manipulate mathematically. For that reason, string theorists often construct anti-De Sitter spaces that are mathematically equivalent to our universe. Here is her conclusion:
First, an optical hologram is not actually captured in two dimensions; the holographic film has a thickness, and you need that thickness to store the information. The holographic principle, on the other hand, is a mathematical abstraction, and the encoding really occurs in one dimension less.

Second, as we saw earlier, in a real hologram, each part contains information about the whole object. But in the mathematics of the holographic universe, this is not the case. If you take only a piece of the boundary, that will not allow you to reproduce what goes on in the entire universe.

This is why I don’t think referring to this idea from string theory as holography is a good analogy. But now you know just exactly what the two types of holography do, and do not have in common.

And here is the video:

Scientists Pin Down When Earth’s Crust Cracked, Then Came to Life - Short answer: 3.2 billion years ago. Geochemists Jonas Tusch and Carsten Münker were able to determine this by performing calculations on a thousand pounds of rock from the Australian outback. The work was published in Convective isolation of Hadean mantle reservoirs through Archean time, and Australian geologist, Alan Collins says it, "captured 'a snapshot' of the advent of plate tectonics". This is important because plate tectonics are more than a mere curiosity. Plate tectonics can provide insight into the emergence of life and the ways that climate changes. According to Oxford petrologist, Richard Palin, this is consistent with other emerging evidence establishing plate tectonics as somewhere between 3 and 3.2 billion years in age. The method used to date the rocks was devised in 2015, and it exploited the decay rate of the tungsten-182 isotope.

Video Friday: Shadow Plays Jenga, and More - IEEE Spectrum's weekly selection of awesome robot videos includes a shadow robot that plays Jenga; Grassy field navigation by Digit, a biped from Agility Robotics; A robotic magic show by Mario the Magician; Drones from Georgia Tech that collaborate on hauling and delivery; a robotic arm from Flexiv uses force sensing and control to balance a ball; and more...

Here is NASA's Honey Astrobee robot in a conversation with Vice President Kamala Harris:

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