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Astrophysicists Put All Objects in Universe into One Pedagogical Plot (sci.news)
46 points by bell-cot on Oct 22, 2023 | hide | past | favorite | 19 comments


Units of mass used: gigaelectronvolts (implicitly times c²), solar masses

Units of length used: centimetres, megaparsecs

When measuring the whole universe it's hard to pick a scale. Anyway astrophysicists are the worst for this. The rest of science is happy with SI(, or sometimes naturalized units when you're doing theory and dealing with integer qualities and numbers that you don't care about). But in astrophysics brightness is measured on a scale set by one of the Ptolemys looking at stars and literally eyeballing it. They'll measure mass in terms of energy, energy in "ergs" and do some godawful mix of imperial, metric and miscellaneous that makes electric charge something comparable to square root of energy times length.


Their car gets 40 rods to the hogshead, and that's the way they like it.


s/cars/container ships/

40 rods to the hogshead is 0.00198 miles per gallon (or 504 gallons per mile). Actually that is low even for a container ship but it is at least in the same ballpark.

I prefer to give fuel efficiency in fuel used for a given distance rather than distance for a given amount of fuel.

My car's fuel efficiency is 23 picoacres or 9.3 picohectares.


Useful XKCD here regarding weird units: https://what-if.xkcd.com/11/

TLDR; "If you took all the gas you burned on a trip and stretched it out into a thin tube along your route, 0.1 square millimeters would be the cross-sectional area of that tube."


Point of order, neither acres nor hectares are a measure of distance.


Pardon me, but I believe this would be a "point of information" (aka request) rather than a "point of order" which should refer to a procedural matter rather than factual.

For reference of course I would refer you to Robert's Rules of Order: https://www.youtube.com/watch?v=xO1zxPRRf4g


gallons/mile or liters/km are volume/length. Volume units are length^3. Thus we end up with length^2.


For more human-friendly numbers, 20 miles per gallon = 0.14 mm^2. 30 mpg = 0.09 mm^2.


And I guess the realistic interpretation of this is the cross section of a tube of gasoline that was laid down the road that could keep your engine fed without a tank.


Even better you can replace your fuel injector with a scoop at the front of the car and drive forward along the fuel tube for a sort of JIT fuelling option.


I stand happily corrected!


"Everything" in the universe, ever, on a lovely Size vs. Mass log-log plot. Sci News' article is quite brief - check the American Journal of Physics article, linked at the end, for more.



“Humans are represented by a mass of 70 kg and a radius of 50 cm (we assume sphericity)” - classic assumption!


Humans are growing generally more spherical, so the assumption is becoming more reasonable over time.


I studied physics (I wasn’t very smart) but it surprised me that the charge radius of protons and neutrons are smaller than that of electrons! Cool plot.

Also the paper this is from is linked at the bottom of the article but here’s a link: https://pubs.aip.org/aapt/ajp/article/91/10/819/2911822/All-...


Very nice. There was a gorgeous visualisation of the universe in terms of distance scale on Kottke a few days ago.

https://www.pablocarlosbudassi.com/2021/02/the-infographic-a...


Why is it "Forbidden by Gravity" but the "sub-Plankian unknown"? I thought that the Plank length was a hard limit like the speed of light. Is that not true, and there theoretically are unknown features smaller than that?


Plank length is not a hard limit the same way speed of light is. Plank length is where we expect our current models to start producing nonsense, though we fully expect that 'things can happen at smaller than plank length'. The expectation is that there exists some future model that produces meaningful predictions at sub-plank length.

Whereas for speed of light, we currently expect no future models to produce meaningful faster than light predictions, and we fully expect to never find evidence of faster than light predictions.




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