Science & Technology Q&A for Kids (and others) [May 13, 2022]

Stephen Wolfram answers general questions from his viewers about science and technology as part of an unscripted livestream series, also available on YouTube here: https://wolfr.am/youtube-sw-qa Questions include: What's the densest thing in the universe? I've heard that black holes don't count—why? - The entire mass of the Earth at neutron star density would fit into a sphere of 305 m in diameter (the size of the Arecibo Telescope). - What if black holes are like visible branchings in the multiway system? Consider the existence of white holes. So if there is "another universe" on the other side, that universe is causally... - AFAIK, fractal-like patterns are the best method to receive signals, but we now have cellular automata—which can maybe do it even better? - ​I lived in a 16th-floor apartment across from a field of transmission towers for an AM station. There were 5–6 radio towers, the closest about 200 yards away. So the AM station could be heard on lots of electronic devices in our house: telephones, answering machine, recording devices, etc. (The AM station towers were powerful.) - Can it be that one day we will be able to see into Earth's past, finding an object in space that mirrors light left by Earth a long time ago? ​- I can imagine future humans, having forgotten we sent such a signal on a long round-trip journey, receiving our message and jumping to all sorts of funny conclusions, depending on what we sent.