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March 28, 2007

Relativity on the World-Wide Web

Posted by John Baez

Chris Hillman is back! — with a new, improved guide to online resources on general relativity:

Popular science sites, web tutorials, undergraduate and graduate-level course material online, and a detailed survey of books — everything you need to learn general relativity, no matter where you’re starting!

There are even lots of nice visualization websites, packed with eye candy like this…

This picture, part of Michael Cramer Andersen’s website on the geometry around black holes, shows a beam of photons getting blue-shifted as they get pulled towards — and sometimes into — a black hole.

Posted at March 28, 2007 9:07 PM UTC

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11 Comments & 1 Trackback

Re: Relativity on the World-Wide Web

I like the Misinformation Concerning Cosmology and Relativity page, although I must admit the warning about Wikipedia left me feeling rather depressed. It fairly accurately reflects how I feel on my more pessimistic days (and after seven thousand Wikipedia edits, shouldn’t I know what’s going on?), but one thing my life does not need is injections of extra pessimism! :-/

Quoting the conclusion of Chris Hillman’s warning:

In other words, the principle value of the Wikipedia may be that it can suggest an almost unlimited number of search terms which a sufficiently Google-savvy reader can use to find more reliable sources of information. Unfortunately, the Google-Wikipedia synergy sketched above may be undermining even this limited utility, and perhaps even undermining the effectiveness of Google itself. Fortunately, many still have a much older alternative: their local public library.

I should note that Firefox users can employ the CustomizeGoogle extension along with a list of mirror sites to remove Wikipedian echoes from their search results. Having just found out about this, I don’t know how well it works, but I figure I should mention it.

Posted by: Blake Stacey on March 28, 2007 10:04 PM | Permalink | Reply to this

Re: Relativity on the World-Wide Web

It’s interesting that you’d promptly glom on to the most controversial of Chris Hillman’s pages, less than an hour after I advertised them.

I don’t agree with the dark tone of his assessment of Wikipedia. I think the Wikipedia is a wonderful thing. I think it will keep getting better. I use it a lot — and I correct errors in it whenever I find them. But, I think it’s worthwhile warning gullible youths that the Wikipedia is fallible. And, I think there could be reforms of Wikipedia policy that could make it more reliable over time.

Posted by: John Baez on March 28, 2007 10:19 PM | Permalink | Reply to this

Re: Relativity on the World-Wide Web

Controversy is no fun if we can’t get started talking about it right away!

Notice that I said “how I feel on my more pessimistic days”. When the sun is shining on Cambridge, Mass., I think of all the pseudophysics which got found and deleted, and I tend more towards your assessment.

I wholeheartedly agree that “gullible youths” should be warned that Wikipedia is fallible. In fact, I think this is what the folks in the education biz call a “teachable moment”: the flaws in Wikipedia are the specific cases of more general theorems about the difficulties of education and discourse. The mutable nature of WP articles and the issues the project has with citations are an excellent way for a savvy teacher to make a point: “Now, class, this is why bibliographies matter!”

If I’d had WP (and the Blagnet) when I was twelve or thirteen, I would have understood many things about writing much faster.

And, I think there could be reforms of Wikipedia policy that could make it more reliable over time.

For example?

Just for fun, it’s interesting to note that the page on the Bogdanov Affair was nominated for Featured Article status back in December. (I’d put some work into cleaning and expanding the article — I was studying in France and, you know, wondering how hard it would be to get a degree — but I had nothing to do with the nomination.) The biggest reason it didn’t succeed was not because of the content, which most people seemed happy about, but because of the continual sockpuppet pressure. Looks like it’ll be a couple more years before that fades away.

Posted by: Blake Stacey on March 28, 2007 10:52 PM | Permalink | Reply to this


I wrote:

And, I think there could be reforms of Wikipedia policy that could make it more reliable over time.

Blake Stacey wrote:

For example?

Sorry to take a while to reply! It seems that Citizendium is trying some interesting policies:

Apparently Citizendium was first envisioned as being an offshoot of Wikipedia, but then they decided to go it alone. That seems unfortunate to me, though I’m not aware of all the issues involved (besides possibly some friction between Jimmy Wales and Larry Sanger).

Posted by: John Baez on April 9, 2007 5:32 PM | Permalink | Reply to this

Re: Relativity on the World-Wide Web

I think Hillman is way too pessimistic about Wiki. In terms of depth and breadth of mathematics articles alone, my experience is that Wiki completely dwarfs the Britannica; for example, last night I needed to look up stuff on Verma modules, and found good, useful, and as far as I could judge, accurate information. This kind of depth, which I have seen time and again in Wikipedia, is simply unthinkable in a traditional encyclopedia.

I cannot concur that “the Wikipedia is on balance untrustworthy”. I would say that most articles I read in the sciences are compiled by reasonable and reasonably well-informed individuals with good intentions. Authoritative? Not like the Britannica – as with anything, use your own judgment. Encyclopedic? And how!

It’s like this blog: messy in places, but exuberant, exciting, alive, real!

Posted by: Todd Trimble on March 29, 2007 3:32 PM | Permalink | Reply to this

Re: Relativity on the World-Wide Web

I also find the assessment of Wikipedia too pessimistic, although there’s a lot of truth to it. I agree completely with what Chris Hillman considers Wikipedia’s best use: a starting point from which to find further information.

However, I use Wikipedia primarily to investigate unfamiliar terms in pure math, which is less prone than physics (and most other topics) to financially motivated manipulation and other problems Chris Hillman cites.

Posted by: Mark on March 28, 2007 10:45 PM | Permalink | Reply to this

Re: Relativity on the World-Wide Web

Just now I finished writing week248 of This Week’s Finds.

I was about to add a link to Wikipedia on the topic of magnetic reconnection, a fascinating topological phenomenon shown vividly in this movie — dramatized by a flash of white light behind the Earth. Then I noticed that the otherwise reasonable-sounding Wikipedia article ended like this:

Magnetic reconnection is the phenomena that occurs in the flow of magnetic energy of the human body that follows a “Chiropractic Treatment” which changes the justa position” of one spinal segment to another. The resultant changes in the flow of magnetic energy alters the cellular’s DNA responses to the cellular environment at the speed of light.

Whoops! I deleted it, but decided to add a different link. The process was good for me, since this other link delved far deeper into the topology of magnetic reconnection.

Posted by: John Baez on March 29, 2007 3:53 AM | Permalink | Reply to this
Read the post Chris Hillman is back!
Weblog: Science After Sunclipse
Excerpt: Chris Hillman, physics and math expositor since the ancient of days, has returned with a new and improved guide to educational resources on general relativity: Chris Hillman, Relativity on the World-Wide Web. This new site provides a panoply of links...
Tracked: March 29, 2007 5:51 PM

Re: Relativity on the World-Wide Web

As a mathematics student, I am very pleased to see a serious review of technical resources. Guys, don’t worry too much - as far as I can tell, serious students are still attracted to rigorous and influential works rather than fly-by-night presentations. Would the contributors please discuss the undergraduate and early graduate experience with regard to reasonable portions of mathematics/physics to include (as independent study) outside of the standard course offerings? Also, toward productively probing the depths of the standard courses themselves?

Posted by: tdstephens3 on April 1, 2007 4:14 AM | Permalink | Reply to this

Supplementing the math/science curriculum

The standard course offerings, at least in math, are not especially standard. For example, here is a partial list of topics that might be covered in a “standard” undergraduate real analysis course:

Basic set theory, cardinality
Construction of the real numbers
Point-set topology of metric spaces
Point-set topology of general topological spaces
Rigorous development of differential calculus in one dimension
Rigorous development of Riemann integration
Classical analysis of the elementary functions
Differential and integral calculus in n dimensions
Calculus on submanifolds of Rn
Lebesgue integration
Basic Fourier analysis
Hilbert spaces and Banach spaces

No one-year course can cover all of these topics in any reasonable way, nor does anyone I know try to. But everyone author or teacher makes a different selection. In my experience, this causes much less difficulty than one might expect when students get to first-year graduate courses. This is in part because the most central topics do get covered in any reasonable undergraduate course, and no one minds that some of the less central or more advanced topics get covered twice for many students. Learning the same material again from a different perspective is good for you.

Based on those observations, here’s one suggestion for tdstephens3: find out what other textbooks might also be used the classes you’re taking or have taken. (One way to do this is find the corresponding graduate texts and see if they list, in the introduction or preface, which undergraduate texts include the necessary background to read them.) Read those books, and do the problems, both from chapters on topics your class doesn’t cover, but also for another perspective on the topics you’ve already seen.

Posted by: Mark on April 1, 2007 4:00 PM | Permalink | Reply to this

Re: Supplementing the math/science curriculum

The class I took (18.100B) went in almost exactly that order, stopping after differential and integral calculus in n dimensions, with a little bit of Lebesgue integration.

Posted by: Blake Stacey on April 2, 2007 3:32 PM | Permalink | Reply to this

Re: Relativity on the World-Wide Web

You might add my Schwarzschild metric simulator to your list. It’s fairly unique. As far as I know, it’s the only simulation on the web that has all the following features:

(a) Multiple test masses.
(b) Both Schwarzschild and Painleve coordinates.
(c) Does massive, massless, and tachyons.

It uses equations of motion derived directly from the metric. The differential equations are in coordinate time, not an affine , no use of Christoffel symbols.

The equations of motion were found by applying the Euler-Lagrange equations to extremize:

s = \int (ds/dt) dt.

The calculus was a mess, so I used MAXIMA to factor and reduce the equations. But the result is 3 DEs in t instead of 4 DEs in s, very efficient.

AND to add spice, Chris Hillman looked at my work, rejected it, and suggested I publish a retraction on the calculations, and then got my thread locked at Physics Forums.

Posted by: Carl Brannen on May 6, 2007 5:45 AM | Permalink | Reply to this

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