reference frame

An MRI scanner is a big magnet that aligns hydrogen atoms in the body and then picks up their response signal. Such machines usually take up an entire room and cost as much as a nice house. Engineers from several labs decided to build a scanner that fits in a suitcase and released all the plans as open source.

Researchers took 16 everyday activities — from washing dishes to squatting — and broke the movements down into elementary components, much like a spectroscope splits light into a spectrum. Comparing three approaches, they found an unexpected key to recognition: a single averaged snapshot is enough. Only nine joints out of dozens carried the crucial information — the rest hardly mattered.

According to Einstein's general theory of relativity Albert Einstein, a massive rotating body drags the fabric of spacetime along with it, much like a spoon twirled in a jar sets thick honey flowing.

Seismologists catch every underground tremor the way a doctor listens to a heart. But small earthquakes have weak and fuzzy signals: it's hard to tell exactly where the rock shifted. Usually, scientists look at the first wave motions: compression or dilation. But if the tremor starts gently, without a sharp snap, the picture gets blurred.

There's no tool to measure distances to faraway galaxies, but nature left a clue: after the Big Bang, sound waves created rhythmic clumps of matter. Today, this is noticeable as a slight preference for galaxies to be at a certain distance from each other — a built-in ruler.

According to physicist Hugh Everett, every observation splits the universe into parallel branches. Normally, your memory of the outcome locks you into one branch, like a key keeping a door shut. A new protocol, reality steering, shows you can pick that lock: erase the memory, and the barrier fades, letting you slide into another reality.

For centuries, three branches of physics (cosmology, particle physics, and nuclear physics) worked like isolated shores.