btrettel

Karma: 621

btrettel Apr 12, 2017, 9:45 PM
2 points
on: Requesting Questions For A 2017 LessWrong Survey
I’d be interested in a question about aerobic fitness. My impression is that most rationalists severely underrate aerobic physical activity compared against anaerobic, which is surprising because anaerobic doesn’t help cardiovascular capacity much. Presumably given the interest in cryonics and whatnot here, rationalists are interested in living longer. Cardiovascular capacity (VO2max, typically) is strongly correlated with longevity, and it’s easy to see the direction of causation.

Possible question: “Over the past month, have you typically met the US federal guidelines for aerobic physical activity? This means at least 150 minutes (2 hours and 30 minutes) a week of moderate-intensity, or 75 minutes (1 hour and 15 minutes) a week of vigorous-intensity aerobic physical activity, or an equivalent combination of moderate- and vigorous-intensity aerobic activity. See health.gov for more information.”

There’s a lot of data on this question, so it will be easy to compare LessWrongers against other groups.

btrettel Jan 17, 2017, 1:55 AM
2 points
in reply to: JamesFaville’s comment on: Open thread, Jan. 16 - Jan. 22, 2016
If you think in terms of QALYs, that could be one reason to prefer interventions targeted at children. Your average child has more life to live than your average adult, so if you permanently improve their quality of life from 0.8 QALYs per year to 0.95 QALYs per year, that would result in a larger QALY change than the same intervention on the adult.

This argument has numerous flaws. One which comes to mind immediately are that many interventions are not so long lasting, so both adults and children would presumably gain the same. It also is tied to particular forms of utilitarianism one might not subscribe to.

btrettel Jan 8, 2017, 11:06 PM
0 points
in reply to: Flipnash’s comment on: Open thread, Jan. 02 - Jan. 08, 2017
Omnilibrium was nominally supposed to be a rationalist political discussion website, but it seems to have died.

I have been too busy to participate much, but I did find my brief time there to be valuable, and would be interested in seeing the website become more active again.

btrettel Dec 19, 2016, 3:43 AM
2 points
in reply to: arundelo’s comment on: Diseased thinking: dissolving questions about disease
I spidered his site with wget at one point. I’d be happy to provide a copy to anyone who wants it, but I’m afraid wget did not get everything, e.g., the image in question here would probably not have been found by wget.

btrettel Dec 17, 2016, 12:45 AM
1 point
in reply to: Eneasz’s comment on: Diseased thinking: dissolving questions about disease
A copy is available from the Internet Archive.

btrettel Dec 15, 2016, 10:33 PM
2 points
in reply to: [deleted]’s comment on: Which areas of rationality are underexplored? - Discussion Thread
Romashka, I appreciate the reply.

Yes, I remember that post. It was ‘almost interesting’ to me, because it is beyond my actual knowledge. So, if you could just maybe make it less scary, we landlubbers would love you to bits. If you’d like.

If you don’t mind, could you highlight which parts you thought were too difficult?

Aside from adding more details, examples, and illustrations, I’m not sure what I could change. I will have to think about this more.

re: errors. I mean that it seemed to me (probably wrongly) that if you measure a bunch of variables, and try to make a model from them, then realise you only want a few and the others can be screwed together into a dimensionless ‘thing’, then how do you know the, well, ‘bounds of correctness’ of the dimensionless thing? It was built from imperfect measurements that carried errors in them; where do the errors go when you combine variables into something new? (I mean, it is a silly question, but i haz it.)

This is an important question to ask. After non-dimensionalizing the data and plotting it, if there aren’t large gaps in the coverage of any dimensionless independent variable, then you can just use the ranges of the dimensionless independent variables.

I could add some plots showing this more obviously in a discussion post.

Here are some example correlations from heat transfer. Engineers did heat transfer experiments in pipes and measured the heat flux as a function of different velocities. They then converted heat flux into the Nusselt number and the velocity/pipe diameter/viscosity into the Reynolds number, and had another term called the Prandtl number. There are plots of these experiments in the literature and you can see where the data for the correlation starts and ends. As you do not always have a clear idea of what happens outside the data (unless you have a theory), this usually is where the limits come from.

btrettel Dec 12, 2016, 9:16 PM
2 points
in reply to: [deleted]’s comment on: Which areas of rationality are underexplored? - Discussion Thread
Sure, I’d be interested in writing an article on dimensional analysis and scaling in general. I might have time over my winter break. It’s also worth noting that I posted on dimensional analysis before. Dimensional analysis is not as popular as principal components analysis, despite being much easier, and I think this is unfortunate.

I don’t know what a “ribbon-shaped population” is, but I imagine that fern spores are blown off by wind and then dispersed by a combination of wind and turbulence. Turbulent dispersion of particles is essentially an entire field by itself. I have some experience in it from modeling water droplet trajectories for fire suppression, so I might be able to help you more, assuming I understand your problem correctly. Feel free to send me a message on here if you’d like help.

And even worse, I had a weird feeling like ‘oh this has to be so noisy, how do they even know how the errors are combined in these new parameters? Surely they don’t just sum.’

Could you explain this a little more? I’m not exactly following.

Because dimensional homogeneity is a requirement for physical models, any series of independent dimensionless variables you construct should be “correct” in a strict sense, but they are not unique, and consequently you might not naively pick “useful” variables. If this doesn’t make sense, then I could explain in more detail or differently.

btrettel Dec 11, 2016, 4:54 PM
0 points
in reply to: RowanE’s comment on: Take the Rationality Test to determine your rational thinking style
The test labeled me as a “rationalist”.

btrettel Dec 10, 2016, 9:49 PM
0 points
in reply to: sen’s comment on: Which areas of rationality are underexplored? - Discussion Thread
Glad to help. I’ll go through your recommendations later this month when I have more time.

btrettel Dec 10, 2016, 1:26 AM
5 points
in reply to: sen’s comment on: Which areas of rationality are underexplored? - Discussion Thread
Thanks for the detailed reply, sen. I don’t follow everything you said, but I’ll take a look at your recommendations and see after that.

I can probably give a better answer if I know more precisely what you’re referring to. Do you have examples of fluid dynamicists simplifying equations and citing group theory as the justification?

Unfortunately, the subject is rather disjoint. Most fluid dynamicists would have no idea that group theory is relevant. My impression is that some mathematicians have interpreted what fluid dynamicists have done for a long time in terms of group theory, and extended their methods. Fluid dynamicists call the approach “dimensional analysis” if you reduce the number of input parameters or “similarity analysis” if you reduce the number independent variables of a differential equation (more on the latter later)

The goal generally is dimension reduction. For example, if you are to perform a simple factorial experiment with 3 variables and you want to sample 8 different values of each variable, you have 8^3 = 512 samples to make, and that’s not even considering doing multiple trials. But, if you can determine a coordinate transformation which reduces those 3 variables to 1, then you only have 8 samples to make.

The Buckingham Pi theorem allows you to determine how many dimensionless variables are needed to fully specify the problem if you start with dimensional quantities. (If everything is dimensionless to begin with, there’s no benefit from this technique, but other techniques might have benefit.)

For a long list of examples of the dimensionless quantities, see Wikipedia. The Reynolds number is the most well known of these. (Also, contrary to common understanding, the Reynolds number doesn’t really say anything about “how turbulent” a flow is, rather, it would be better thought of as a way to characterize instability of a flow. There are multiple ways to measure “how turbulent” a flow is.)

For a “similarity variable”, I’m not sure what the best place to point them out would be. Here’s one example, though: If you take the 1D unbounded heat equation and change coordinates to \eta = x / \sqrt{\alpha t} (\alpha is the thermal diffusivity), you’ll find the PDE is reduced to an ODE, and solution should be much easier now. The derivation of the reduction to an ODE is not on Wikipedia, but it is very straightforward.

Dimensional analysis is really only taught to engineers working on fluid mechanics and heat transfer. I am continually surprised by how few people are aware of it. It should be part of the undergraduate curriculum for any degree in physics. Statisticians, particularly those who work in experimental design, also should know it. Here’s an interesting video of a talk with an application of dimensional analysis to experimental design. As I recall, one of the questions asked after the talk related the approach to Lie groups.

For an engineering viewpoint, I’d recommend Langhaar’s book. This book does not discuss similarity variables, however. For something bridging the more mathematical and engineering viewpoints I have one recommendation. I haven’t looked at this book, but it’s one of the few I could find which discusses both the Buckingham Pi theorem and Lie groups. For something purely on the group theory side, see Olver’s book.

Anyhow, I asked about this because I get the impression from some physicists that there’s more to applications of group theory to building models than what I’ve seen.

Consider that the !∘sqrt∘ln of a dimensionless quantity is also technically a dimensionless quantity while also being almost-certainly useless and uninterpretable.

This is an important realization. The Buckingham Pi theorem doesn’t tell you which dimensionless variables are “valid” or “useful”, just the number of them needed to fully specify the problem. Whether or not a dimensionless number is “valid” or “useful” depends on what you are interested in.

Edit: Fixed some typos.

btrettel Dec 8, 2016, 5:25 AM
0 points
in reply to: RomeoStevens’s comment on: Which areas of rationality are underexplored? - Discussion Thread
Creativity is another big area that seems neglected. I’ve read a fair amount on the subject, but feel I have barely touched the surface.

I also feel it probably is relevant to AI, so I’m somewhat surprised to see so little discussion of it here. (By “AI” I mean a number of things here. Might be easiest to see it as application of computers to solve problems.) At the moment, AI works when the actions one can take are clear (e.g., small number of valid moves in a game). When the possible actions are not precisely specified, the specification becomes the issue. Generating these possibilities is not trivial, and frequently this is what creativity is.

btrettel Dec 8, 2016, 5:22 AM
2 points
in reply to: sen’s comment on: Which areas of rationality are underexplored? - Discussion Thread
Is there a single book or resource you would recommend for learning how group theory/symmetry can be used to develop theories and models?

I work in fluid dynamics, and I’ve mainly seen group theory/symmetry mentioned when forming simplifying coordinate transformations. Fluid dynamicists call these “dimensionless parameters” or “similarity variables”. I am certain other fields use different terminology.

btrettel Dec 8, 2016, 2:07 AM
2 points
in reply to: biker19’s comment on: LessWrong Help Desk—free paper downloads and more (2014)
The Library of Congress does not have these proceedings, unfortunately.

btrettel Dec 7, 2016, 8:50 PM
4 points
in reply to: biker19’s comment on: LessWrong Help Desk—free paper downloads and more (2014)
As a cyclist, I’d be interested in seeing these articles as well.

Unfortunately my university doesn’t have any of these. I could request them by interlibrary loan, but I suspect I’d be on break by the time they come in.

I usually visit the Library of Congress when visiting my parents on breaks, and I’ll check their catalog to see if they have these proceedings later. Their online catalog is not working at the moment. I’ll make a new reply to your comment when I do.

btrettel Dec 7, 2016, 1:29 AM
0 points
in reply to: sarahconstantin’s comment on: Open thread, Dec. 05 - Dec. 11, 2016
I’ve had good experience with MyFitnessPal with respect to speed, and find the features sufficient for my purposes. I manually enter my exercise data, so I can not comment on automatic exercise tracking.

I found FitDay to be annoyingly slow, but I used the site for years before MyFitnessPal.

btrettel Dec 6, 2016, 1:09 AM
5 points
in reply to: hamnox’s comment on: Fact Posts: How and Why
Learning of the reputation of the journal from someone knowledgeable about its field is the most reliable way I can think of for someone outside the field of interest.

Impact factors seem inappropriate to me, as they can vary wildly between fields and even wildly among subfields. A more specialized, but still high quality, journal could have a much lower impact factor than a more general journal, even if the two are at roughly the same average quality. Also, some foreign language journals can be excellent despite having low impact factors for the field of the journal. This unfortunately is true even for cover-to-cover or partial translations of those foreign language journals.

You also could learn what signs to avoid. Some journals publish nonsense, and that’s usually pretty obvious after looking at a few articles. (Though, in some fields it can be hard to separate nonsense from parody.)

Beyond the previous recommendations, it’s probably better to focus on the merits of the article rather than the journal. I can immediately think of one article in particular which has a non-obvious major flaw that is published in a small journal that I consider excellent. This error should have been caught in review, but it was not, probably because catching the error requires redoing math the authors skipped over in the article. (In intend to eventually publish a paper on this error after I finish my correction to it.)

btrettel Dec 6, 2016, 12:27 AM
0 points
in reply to: turchin’s comment on: Which areas of rationality are underexplored? - Discussion Thread

I want to show that fighting aging is underestimated from effective altruistic point of view. I would name it second most effective way to prevent sufferings after x-risks prevention.

I’d be very interested in seeing this.

btrettel Dec 6, 2016, 12:26 AM
5 points
in reply to: turchin’s comment on: Which areas of rationality are underexplored? - Discussion Thread
I think life extension should be discussed more here.

Many rationalists disappointment me with respect to life extension. Too many of them seem to recognize that physical conditioning is important, yet very few seem to do the right things. Most rationalists who understand that physical conditioning is important think they should do something, but that something tends to be almost exclusively lifting weights with little to no cardiovascular exercise. (I consider walking to barely qualify as cardiovascular exercise, by the way.) I think both are important, but if you only could do one, I’d pick cardio because it’s much easier to improve your cardiovascular capacity that way. (Cardiovascular capacity/VO2max correlates well with longevity, as discussed here.) I’m not alone in the belief that cardio is much more important; similar things have been said for a long time. I’d recommend Ken Cooper’s first book for more on this perspective.

The inability for rationalists to regularly do cardiovascular exercise probably stems from similar problems that cause cryocrastination. I’d like to see more on actually implementing cardiovascular exercise routines. I have some notes on this which could help. Off the top of my head I can remember that there’s evidence morning runners tend to maintain the habit better and that there’s evidence that exercising in a group helps with compliance. I personally find Beeminder to help a little bit, but not much.

btrettel Dec 6, 2016, 12:08 AM
3 points
on: Which areas of rationality are underexplored? - Discussion Thread
A big gap I see is memory. Having read a few books on learning and memory, I think what’s been posted on LessWrong has been fragmented and incomplete, and we’re in need of a good summary/review of the entire literature. There’s a lot of confusion on the subject here too, e.g., this article seems to think spaced repetition and mnemonics are mutually exclusive techniques, but they’re not at all. When I used Anki I frequently used mnemonics as well. The article seems to be an argument against bad flash cards, not spaced repetition in general. Probably over a year ago I did start writing a sequence on memory enhancement, but it is a low priority task for me it and do not anticipate completing it any time soon.

btrettel Nov 30, 2016, 4:31 PM
6 points
in reply to: casebash’s comment on: On the importance of Less Wrong, or another single conversational locus
Some sort of emoticon could work, like what Facebook does.

Personally, I find the lack of feedback from an upvote or downvote to be discouraging. I understand that many people don’t want to take the time to provide a quick comment, but personally I think that’s silly as a 10 second comment could help a lot in many cases. If there is a possibility for a 1 second feedback method to allow a little more information than up or down, I think it’s worth trying.