Keysh

10 ms·

91.
by Keysh 4y ago
It’s not really a Big Bang “alternative” at all. It is possibly an explanation of how the early Big Bang got going.
92.
by Keysh 4y ago
In Anthony Grafton's The Footnote: A Curious History , he claims that citations practices in the field of history have the tendency to use "cf." -- which normally means something like "compare with this reference&quot
93.
by Keysh 4y ago
Written Arabic and Hebrew often omit vowels; the actual spoken languages do not, of course.
94.
by Keysh 5y ago
Not “way” less, because most stars are lower mass than the Sun and thus have longer lifetimes (~ trillions of years in the case of red dwarfs).
95.
by Keysh 5y ago
It’s actually no problem mathematically to have toroidal topology and flat geometry. (The classic Asteroids video game, where your ship can go off the top of the screen and come in at the bottom, or similarly with the left and right edges
96.
by Keysh 5y ago
That’s Olber’s Paradox, of course, and it relies on three assumptions: 1. The universe is infinitely large and 2. The universe is filled with stars and 3. The universe has been this way forever . It turns out #3 is wrong, so it’s st
97.
by Keysh 5y ago
Uh, no. 1. You're way overestimating the wealth of the Near East in the time period we're talking about. If you look at Maddison's estimates of historical GDP (e.g., https://en.wikipedia.org/wiki/List_of_
98.
by Keysh 5y ago
The Ottomans did not get a monopoly on eastern routes until they conquered Mameluke Egypt in the early 1500s. Western European (particularly Portuguese) attempts to go "the other direction" started in the 1400s.
99.
by Keysh 5y ago
Note that the oldest version of that story is due to a Christian Arab writing centuries later, complaining about all the bad things Muslims have done. There's no credible evidence from a non-axe-grinding source that anything like tha
100.
by Keysh 5y ago
Uh, no. The Enlightenment -- which was a phenomenon of Western and Central Europe, not the Mediterranean -- was in no way affected by Turkish naval control of the (Eastern) Mediterranean.
101.
by Keysh 5y ago
Medieval Christians weren’t nearly as hostile to pagan works as you imply. Julius Caesar, Cicero, and Virgil were regularly copied and read. (And the enthusiasm with which Arabic translations of pagan Greeks like Aristotle and Ptolemy — and
102.
by Keysh 5y ago
The reported angular resolution (in the main paper: https://arxiv.org/abs/2201.10541 ) is 4 arcseconds. This is radio interferometry, which makes for better resolution, but it’s at a very low frequency (centered around
103.
by Keysh 5y ago
OK, you're really not making much sense. I mentioned exoplanets because that was a (barely) plausible interpretation of something that was a "hot field in modern astronomy but was barely a thing when JWST began", since the pr
104.
by Keysh 5y ago
Of course JWST is an instrument for studying exoplanets (among other things). Something like 24% of the first year’s approved observing proposals are for doing just that. There are coronagraphs in two of the main instruments, all specifical
105.
by Keysh 5y ago
This is known as the “tired light” hypothesis, and there are a number of problems with it; see https://www.astro.ucla.edu/~wright/tiredlit.htm .
106.
by Keysh 5y ago
The observations in the 1930s you allude to were of the motions of galaxies in galaxy clusters . The rotation-curve measurements for individual galaxies started in the 1970s and really took off in the 1980s. "Tidal effects" are a
107.
by Keysh 5y ago
Kaiser's presentation doesn't suggest you can do the measurement for individual clusters; the example analysis is from Wojtak et al. (2011), which is similar to Mpetha et al. in using thousands of galaxies and thousands of cluster
108.
by Keysh 5y ago
It wasn't clear to my why you said what you did. (Good to know it was just an editing failure.) Sometimes people get confused and think "dark matter halo" means all the dark matter is outside the main body of the galaxy, so I
109.
by Keysh 5y ago
The reddening is because of the additional mass of the dark-matter-containing structures, and also because the distribution of the dark matter into halos allows for slower orbits of stars and gas clouds, thus suppressing their non-gravitat
110.
by Keysh 5y ago
One important caveat to all this is that the gravitational redshift for a galaxy or galaxy cluster is an incredibly tiny effect. For example, the mean gravitational redshift for massive galaxy clusters has been measured (e.g., link below)
111.
by Keysh 5y ago
The paper in question is by people from a variety of institutions (none of them being Veritas International University). Early in the paper there is this comment: "After eleven seasons of excavations, the site excavators [i.e., the fol
112.
by Keysh 5y ago
The suggestion in the article is that the bolide impact (or airburst) was well outside the city, to the SW, since a lot of the evidence suggests a blast moving from SW to NE through the city.
113.
by Keysh 5y ago
And screw the people who actually live there, right? A better way to think about this is to consider the case of Saint Pierre et Miquelon, which are two islands off the coast of Canada -- literally 19 km away, and so much closer than the Fa
114.
by Keysh 5y ago
From the video, the question is, in effect, “Why don’t they make movies like they did in the 1990s any more?”
115.
by Keysh 5y ago
The “leaders in editing software” are arguably Avid’s Media Composer, Adobe Premiere pro, and Apple’s Final Cut Pro X, none of which have free versions. The free version of Da Vinci Resolve was released back when it was still a color-correc
116.
by Keysh 5y ago
Dyson spheres would glow in the mid- and far-infrared (re-radiating energy absorbed from the enclosed star), and so would not be "dark".
117.
by Keysh 5y ago
Friction in this context refers to "dynamical friction", where massive objects -- e.g., dense cluster cores -- moving through a medium of many small masses -- e.g., DM particles -- will experience gravitational drag and slow down.
118.
by Keysh 5y ago
This is rather overstated (especially the "incredibly unlikely" bit). The best attempt I've seen to summarize this is in this paper https://arxiv.org/abs/1412.7719 which argues that there's rough
119.
by Keysh 5y ago
On the other hand, the center of a star is much hotter than the periphery, so there are potentially more accessible states in phase space for the particles in the former location (it's "can be in N positions in phase space",
120.
by Keysh 5y ago
In fact, assuming extra undetected mass to explain the anomalous motions of galaxies in clusters (as originally noted by Fritz Zwicky in the 1930s) was at least partly correct, because we now know that galaxy clusters contain rarified, extr

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