Hacker News: ultrafilter

New comment by ultrafilter in "If gravity isn't a force, then why does it "need" a boson?"

ultrafilter — Wed, 20 Mar 2024 19:18:57 +0000

Your charge-based g-meter would also measure zero acceleration in free fall.

https://en.wikipedia.org/wiki/Paradox_of_radiation_of_charge...

New comment by ultrafilter in "A scalar triple product identity"

ultrafilter — Sat, 26 Aug 2023 04:22:17 +0000

Near the end, the author claims that if a,b,c form a basis of R3, then the cross products a x b, b x c, and c x a are orthogonal.

This is false. E.g., a=(1,1,0), b=(0,1,1), c=(1,0,1) implies

a x b = (+1,-1,+1), b x c = (+1,+1,-1), c x a = (-1,+1,+1).

However, this "dual basis" still serves its claimed purpose, which essentially is to precompute part of Cramer's rule.

New comment by ultrafilter in "Show HN: SpicyPass – A free and open-source minimalist password manager"

ultrafilter — Sat, 28 Mar 2020 23:27:53 +0000

If I have a keyboard, then for a relatively small dataset, such as my saved passwords, I prefer a text file over any database. Lookup workflow: decrypt file (with, say, gpg), find what I want (with, say, grep), delete decrypted file. (Not safe if you don't use disk encryption!) Update workflow: decrypt file, edit file, encrypt file, commit encrypted file to local git repo, git push to backup storage.

New comment by ultrafilter in "The field of “useful reals” between rational and real numbers (2019)"

ultrafilter — Tue, 24 Mar 2020 21:23:13 +0000

Set theorists have located the "end" for all practical and most impractical purposes. Let M be the minimal countable transitive model of ZFC. Declare a real to be useful if and only if it is in M.

New comment by ultrafilter in "Get Your Book, Make It Free"

ultrafilter — Fri, 17 May 2019 16:18:08 +0000

If you're giving the book away, why not release the source (LaTeX, Word, whatever) in addition to your favorite subset of {PDF,EPUB,...}? Then readers who want a different format have a better chance of being able to produce it themselves.

New comment by ultrafilter in "The Tyranny of the Clock (2012) [pdf]"

ultrafilter — Sat, 21 Jul 2018 16:49:12 +0000

The author's more recent work is here:

http://arc.cecs.pdx.edu/publications

Surface codes: Towards practical large-scale quantum computation (2012)

ultrafilter — Thu, 11 Jan 2018 20:55:10 +0000

Article URL: https://arxiv.org/abs/1208.0928

Comments URL: https://news.ycombinator.com/item?id=16127749

Points: 1

# Comments: 0

New comment by ultrafilter in "The Foundations of Mathematics (2007) [pdf]"

ultrafilter — Fri, 05 Jan 2018 23:25:33 +0000

You're right. I should have written "halts last among its peers" or similar.

New comment by ultrafilter in "The Foundations of Mathematics (2007) [pdf]"

ultrafilter — Fri, 05 Jan 2018 16:56:30 +0000

Every formal axiom system, whether about sets or anything else, can only prove that N of Busy Beavers halt, for some (not-too-large in practice) finite number N. If you just want to maximize N, right now your best bet is set theory plus a very strong large cardinal axiom, like I0.

http://cantorsattic.info/L_of_V_lambda%2B1

Perhaps simply because it is older, set theory is way ahead of its competitors in developing a hierarchy of extremely strong (but apparently consistent) axioms to supplement its base theory ZFC.

New comment by ultrafilter in "Cryptocurrency Analysis with Python – Log Returns"

ultrafilter — Fri, 29 Dec 2017 21:40:11 +0000

Nice overall; my only complaint is that you raised the question "Are LTC log returns normally distributed?" but only gave an uninterpreted graphical comparsion. I was hoping for a test statistic...

https://en.wikipedia.org/wiki/Normality_test

The choiceless cardinals are inconsistent

ultrafilter — Fri, 29 Dec 2017 19:59:57 +0000

Article URL: https://arxiv.org/abs/1712.09678

Comments URL: https://news.ycombinator.com/item?id=16031601

Points: 1

# Comments: 0

New comment by ultrafilter in "Microsoft Adds an OpenSSH Client to Windows 10"

ultrafilter — Tue, 12 Dec 2017 16:23:46 +0000

I put a copy of putty at a short but private url at my own domain so that I can get it over https.

New comment by ultrafilter in "Show HN: Effects of House and Senate Bill on California Residents"

ultrafilter — Wed, 06 Dec 2017 23:32:33 +0000

Indeed, the source code only considers tax brackets, the personal exemption, and the standard deduction. I've read of an increase of $650 in the per-child tax credit combined with the loss of the per-dependent personal exemption and an increase in the standard deduction. If your last $4333 of annual income is going to be taxed at rate of 15%, then a $650 credit is just as valuable as a $4333 deduction or exemption and thus slightly more valuable than the current $4050 personal exemption. Thus, contrary to this calculator, middle-class families with lots of kids will not get big tax increases.

New comment by ultrafilter in "Quadratic voting (2014)"

ultrafilter — Sat, 09 Sep 2017 18:15:39 +0000

Yes. Perhaps the voting currency should be hours, not dollars. Make the first vote free. But N-1 more votes costs you N^2-1 hours from your "registered community service" account maintained by the government. No overdrafts allowed: the hours must be credited before they can be debited.

New comment by ultrafilter in "American energy use"

ultrafilter — Mon, 08 May 2017 20:29:36 +0000

The Carnot cycle is a poor model for steam turbine electric power plants. Rankine cycle efficiency of ~40% is the more relevant theoretical upper limit.

https://en.wikipedia.org/wiki/Rankine_cycle

New comment by ultrafilter in "A program that accepts exactly any desired finite set, in the right universe"

ultrafilter — Sun, 07 May 2017 22:40:09 +0000

In the real world, Hamkins' program would search forever, never outputting anything. In the context of a "nonstandard" version of the line of natural numbers, "finite" no longer means what you think it means. In this context, Hamkin's program does output something after a "finite" number of steps, and Hamkins can make the program output whatever he wants by changing the meaning of "finite" instead of changing the program.

New comment by ultrafilter in "Data diversity: Preserving variety in data sets should aid machine learning"

ultrafilter — Sun, 18 Dec 2016 22:17:42 +0000

The article has a link in a sidebar:

https://arxiv.org/abs/1608.01008v2

New comment by ultrafilter in "The Space Doctor’s Big Idea"

ultrafilter — Thu, 19 Nov 2015 06:10:53 +0000

I think your watch is slow and you think mine is slow in the following sense. For each of many events, I record their time t and position x while you, moving relative to me at constant velocity, observe a different time T and position X. Between two events with the same X-value, such as ticks of your pocket watch, the difference in t-times is larger than the difference in T-times by a factor gamma. Conversely, between two events with the same x-position, such as ticks of my pocket watch, the difference in T-times is larger than the difference in t-times by that same factor gamma.

There is no contradiction because events with identical x-positions do not have identical X-positions.

If you already know what a partial derivative is, see the first paragraph of this: http://mathpages.com/rr/s4-07/4-07.htm

New comment by ultrafilter in "Homeschooled with MIT courses at 5, accepted to MIT at 15"

ultrafilter — Wed, 18 Nov 2015 18:28:58 +0000

In contrast (but not contradiction) with your experience, as an MIT undergraduate math major applying for PhD programs, my advisor warned me that the math dept. doesn't admit their own graduates. I applied anyway and indeed was not admitted (which was fine since I was admitted to UW-Madison, where I most wanted to go).

New comment by ultrafilter in "Polynomial-Time Hierarchy Is Infinite Under a Random Oracle"

ultrafilter — Wed, 22 Apr 2015 04:39:06 +0000

Theorems 1 and 3 are finitary and easier to physically interpret. As for Theorem 2, "With probably p a random foo has property bar" intends no interpretation of "random foo"; it merely claims that the set of foo's with property bar has measure p with respect to some probability measure. In this case, the probability measure is the Bernoulli measure.

http://www.encyclopediaofmath.org/index.php/Bernoulli_measur...