pdonis

18,074 karmajoined 16 jaar geleden

Email me at peterdonis {at} alum {dot} mit {dot} edu

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4 uur geledendiscuss

> I thought neutron stars generally had a shell or crust of iron, which generates a magnetic field (as metals do) if the neutron star is spinning.

They do, but the neutrons themselves also have magnetic properties. (The simplest heuristic way to think of it is that neutrons are made of three quarks, and the magnetic moment is due to the quarks moving around inside the neutron. But that's a highly heuristic picture and leaves out a lot of complications.)

23 uur geledendiscuss

> The intuitive meaning is that a day is 24 hours

Ok so far.

> and you can divide that by 60 twice

I'm not so sure. The concept of 24 hours in a day originates in civil timekeeping, yes, but not minutes and seconds. Those originally came from astronomy, and corresponded to angles, not times, and those angles are constants; they don't change as the Earth's rotation slows down or as its speed in orbit around the Sun changes over the course of a year. I don't think people's intuitive concept of minutes and seconds is that they vary according to the time of year or the tidal effects on the Earth.

24 uur geledendiscuss

> The intuitive meaning is that a day is 24 hours and you can divide that by 60 twice.

And that's exactly why the SI second has the length that it has--to be as close as possible in terms of how atomic clocks work to 1/86400 of an Earth mean solar day at a chosen epoch. (Note that the actual definition before the atomic clock one was adopted was in terms of the Earth's tropical year at that epoch--but the fraction of the tropical year that was chosen was to line up the second with 1/86400 of an epoch day.) If we didn't care about "relatability", nobody would have gone to all the trouble of trying to determine how many cesium clock oscillations there were in 1/86400 of an epoch day.

24 uur geledendiscuss

> we nailed down the second to make the technical side easier at the expense of relatability.

Would you also say that getting rid of leap seconds and allowing UTC to gradually drift away from the sun is making the technical side easier at the expense of relatability?

gisterendiscuss

> The definitions of hours minutes and seconds have changed before, and in recent history.

In terms of what physical process we use to set the standard, yes. But those very changes were made to try to preserve the same time periods that were important to humans. In other words, to not change what hours, minutes, and seconds mean intuitively to us humans as we go about our daily lives.

eergisterendiscuss

> If you think about it, they must have a lot of protons to generate a field so strong

Not necessarily. Neutrons have a magnetic moment. As I understand it, there is a magnetohydrodynamic model of how a magnetar's field gets generated, which would require protons, but it's not the only model and we don't have enough data to be able to rule out other models.

eergisterendiscuss

> the 10-15 seconds I mentioned is the daily variation in solar noon.

Yes, but averaged over an entire year, it still comes out to zero. The difference between mean solar and atomic time does not. It accumulates over the years.

> we just reversed that decision

We paused it for 100 years after 2035. That doesn't change the physical fact that the Earth's rotation will continue to slow over the long term. We might eventually decide to just not care about that when it comes to civil timekeeping, but that's not what the decision you're referring to did. It just said we can afford to let the difference between UTC and TAI accumulate from 2035 to 2135 (by which time it is predicted to be about a minute) while we figure out what we want to do over the longer term.

eergisterendiscuss

> Why?

Um, because it's the prime meridian and that's how UTC is defined?

> It's nearly impossible to have your local time match your local solar noon.

Which is why I specified on the prime meridian, which is the particular local meridian that UTC is defined as corresponding to.

> solar noon varies from day to day by 10-20 seconds.

Which is why I was careful to specify mean solar noon.

I'm not quite sure what your issue is. Yes, we have time zones tied to specific meridians, and the actual sun's speed in the sky varies (which I mentioned in my post, so I'm not sure why you seem to think I'm unaware of it) so in most places local time by the clock doesn't match local time by the sun. Yes, a leap second adjustment to UTC is quite a bit smaller, taken in isolation, than the annual variation in actual solar time vs. mean solar time.

But over time, if we didn't have leap seconds, the difference would accumulate. The accumulated difference now between UTC and TAI is 37 seconds--which is almost twice the maximum variation in actual solar noon from mean solar noon that you refer to. We humans have collectively decided that we don't want that, and that it's better to do the adjustments a little at a time rather than in bigger lumps.

eergisterendiscuss

> This means the atomic clock is behind the solar clock by 37 seconds?

If anything, it's the other way around.

A UTC day is defined as exactly 86400 SI seconds. But an actual mean solar day is a few milliseconds longer (although the difference is not constant due to irregularities in the Earth's rotation--but the average difference is expected to slowly increase over time). SI seconds are counted by atomic clocks, so UTC advances its day by one every 86400 atomic clock seconds.

But a solar clock that advances its day by one every time the mean sun reaches noon (it has to be the mean sun because the rate at which the actual sun moves across the sky varies over the course of a year, we need to look at the average) will advance its day a few milliseconds later than UTC does. Or, to put it another way, each time period that the solar clock says is exactly 86400 seconds, is a few milliseconds longer according to the atomic clock.

As this happens day after day, the difference accumulates, and when it gets close to being a full second, a leap second gets inserted into UTC, so that one of its days is 86401 seconds long instead of 86400. The reason for this is that UTC is not just counting atomic clock time; it also has to stay in sync with where the sun is in the sky since so many human activities are tied to that. And we humans have defined "in sync with the sun" to be "within a second of the average sun". In other words, we want UTC noon to be within a second of mean solar noon on the prime meridian.

So the 37 seconds is how far mean solar noon would be behind UTC noon, if we didn't use leap seconds--at UTC noon, the mean sun would be 37 seconds short of actually crossing the prime meridian in the sky.

12 dagen geledendiscuss

Hm, yes, laziness is also a powerful force... :-)

13 dagen geledendiscuss

> Is 99.9% of all websites.

Not at all. You named eleven. Even if I'm generous and raise that by a couple of orders of magnitude, it's still a miniscule fraction of all websites.

Of course it's close to all big tech platforms, but that's not the same thing. And if one of the results of this whole kerfluffle is to make more people realize that the big tech platforms are not the same as "the Internet" or "the Web", that would be a good thing.

> Websites like HN are the exception, not the norm.

Which makes it even more important to ask the question of whether "exception" websites like this one can continue to survive if this bill becomes law. Sure, HN users are a tiny fraction of all Internet users. But that's supposed to be one of the things the Internet is for--to give even very small communities a place where they can be a community, and not have to worry about all the other crap that's out there, and not have to be micromanaged by politicians and lobbyists and tech giants.

> It's also disingenuous to say "a personal blog" would be exempt from this when most people don't have blogs in first place since they start microblogging instead

Not all blogging platforms use targeted ads. And if this gives more of them an incentive not to, that would be a good thing.

13 dagen geledendiscuss

You're assuming that platforms that tried age verification in order to show people targeted ads would lose enough users to make that business model no longer viable. While I would fervently like to believe that's true, I'm not so sure it is. I think there might well be enough people who will hand over their personal identifying info without a second thought in order to continue to use targeted ad-supported platforms, to keep them in business. I hope I'm wrong.

13 dagen geledendiscuss

You're looking at section 102 of the bill, which is a different part than the one I was looking at (and that the EFF article is referring to). The bill is a mismash of several different proposed bills all squashed together into one. Title I, which is what you're looking at, is more restrictive about what platforms it applies to than Title II, which contains the section I quoted.

13 dagen geledendiscuss

But there are also other requirements in section 201 for a "covered platform", which advertising-funded sites that aren't "social media" most likely don't meet. For example, a typical personal blog, even if it shows ads, doesn't meet subsection (C), because its primary purpose is not to share user-generated content (e.g., comments by readers)--it's to share the blog author's content.

(HN itself doesn't meet at least one other requirement besides subsection (E): subsection (D), "Uses a design feature to promote user engagement on the platform".)

13 dagen geledendiscuss

That's true, but the bank also already knows my age.

Also, a bank would not satisfy section 201 (B), (C), or (D), so it wouldn't be a covered platform anyway. (I should have left "bank" out of my original post, I was really thinking more about discussion sites like this one, blogs, etc.)

13 dagen geledendiscuss

Would this website (HN) be a "covered platform" according to the bill?

As far as I can tell, the answer is no, because it doesn't do what's described in Section 201 (E):

"Uses the personal information of the user to advertise, market, or make content recommendations."

Neither does, for example, my bank's website, or someone's personal blog, or many other discussion sites like this one. So from what I can see, while the set of covered platforms is certainly not negligible, it's still a lot smaller than "basically every website on the Internet that anyone cares about". So the title of the EFF article is overstating the case; the thing the bill would require age checks for (in effect, if not by the explicit language of the bill) is not "get online" but something more like "get on social media".

14 dagen geledendiscuss

> in that scenario, our standard model would say there was one electroweak particle

No, it wouldn't. There would still be four; they would just be called W1, W2, W3, and B. The electroweak vector space doesn't change when the electroweak symmetry is broken; it has 4 basis vectors before, and 4 basis vectors after. All that changes is which basis is the most "natural" to use in describing physics at the given energy scale.

(And there would still be eight gluons as well--what I say below about those applies just as well above the electroweak symmetry breaking energy scale as below.)

> There's no corresponding thing to contain gluons to individual particles

If you mean that there is no "natural" choice of basis for the gluon vector space, that's not quite true either. The Gell-Mann matrices are a natural choice of basis for the adjoint representation of SU(3) (or, equivalently, the defining representation of the Lie Algebra of SU(3)), which is the gluon representation. Those eight matrices are what physicists typically are referring to when they refer to the eight gluons.

14 dagen geledendiscuss

And then they reversed course with Wickard v. Filburn and said it was perfectly OK for Congress to regulate, not just commerce within a single state, but farmers growing their own food on their own land for their own use. So FDR ended up getting what he wanted anyway.

14 dagen geledendiscuss

> W and Z bosons, photons, etc have fixed masses, charges, interaction strengths with other particles.

But you can form a continuous set of linear combinations of these things, just as you can with gluons. Indeed, what the article calls W and Z bosons (and photons) are just such linear combinations--the ones that appear in the low energy limit after the electroweak phase transition occurs. Before that phase transition, different linear combinations (i.e., a different basis of the electroweak vector space) are the ones that naturally appear. So saying that there are two W, one Z, and one photon is really counting basis vectors in the electroweak vector space, just as saying there are 8 gluons is really counting basis vectors in the gluon sector of the strong interaction vector space.

18 dagen geledendiscuss

Yes, because it's lower in the sky so more of the UV in it gets absorbed by the atmosphere before reaching the ground.

For example, in Florida in the summer, the sun is close to directly overhead at noon. In Scandinavia in the summer, the sun is only about halfway up the sky from the horizon at noon.