Impressionen von der Nacht des Wissens 2025 #ndwgoe

Knapp 6000 Gäste erlebten am 21. Juni 2025 die Nacht des Wissens am MPS. In der verlinkten Bildergalerie findet ihr einige unserer schönsten Fotos aus der Nacht https://www.mps.mpg.de/8463489/nacht-des-wissens-2025

@ndw_goe @thegoecampus @unigoettingen

#ndwgoemps #mpsgoettingen #goettingen #maxplanck

For reasons I will once explain, I am becoming a conoisseur of Michael #Faraday life and correspondance.

These are his (not too flattering) feelings about the people he met in #France (mostly in Paris), during his first trip abroad following his master, Sir. Humphry Davy, in 1814 (he was 23 at the time), in a letter he sent to his friend Abbott.

#science #physics #astronomy

New on 'Stuff': Book Review - Logic Beach, Part 1 \n
https://stuff.graves.cl/posts/2025-06-29_12_05-book-review-logic-beach,-part-1.html

#science-fiction
#philosophy
#physics
#ontology
#cs
#⭐️⭐️⭐️⭐️
#book-review
#english

The main idea of HoTT/UF is to narrow the gap between equality and isomorphism. The problem is that (set-thoretic) equality is a yes/no proposition, whereas there could be many different isomorphisms between two objects. So if we want to merge the two notions, we have to extend equality to allow for multiple witnesses. Thus in MLTT, (propositional) equality is a type whose elements are witnesses.

Set-theoretic isomorphism is itself defined using equality (two compositions must be equal to identities). So if we modify equality, we should replace isomorphism with a more general type of equivalence.

The final step is to identify the new equality with the new equivalence in the axiom of univalence, which states that equality is equivalent to equivalence.

If you're the kind of person who follows me, you may know about the Kessler Syndrome.

That's when collisions between satellites and space junk create enough debris to cause *more* collisions, leading to a runaway chain reaction. This could render certain regions of near-Earth space unusable!

It's one of nature's ways of containing stupid civilizations, sort of like how inflammation contains infections. So don't be surprised:

A new study by Lewis and Kessler argues that we've hit the "runaway threshold" - the point where a chain reaction is expected - at nearly all altitudes between 520 and 1000 kilometers.

Below that, or above that, space could remain usable. So we could still get out and ruin other layers of space - or go to other planets and mess up those. Luckily, planned deployments of large satellite constellations like Starlink, Amazon's Project Kuiper, etc. will reduce the risk of such a breakout.

Yes, I'm joking - we can differ on whether the expansion of stupidity into the cosmos would be a good or bad thing compared to a mostly dead cosmos, and I don't really have an opinion on that. But the study is for real, and worth checking out:

• Hugh G. Lewis and Donald J. Kessler, Critical number of spacecraft in low Earth orbit: a new assessment of the stability of the orbital debris environment, https://conference.sdo.esoc.esa.int/proceedings/sdc9/paper/305/SDC9-paper305.pdf

Thanks to @michael_w_busch for pointing this out.

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I'm under the impression that liquid does not exist in space. The boiling point of a substance is proportional to the pressure it's under, so if pressure is near zero, then so is the boiling point.

But Wikipedia https://en.wikipedia.org/wiki/Melting_point tells me that the *melting* point is also dependent on pressure.

How, then, is it possible for solids under negligible gravitational pressure (like asteroids) to exist in space?

#physics