Random Linkiness

It's been a while since I've done one of these...

My bookmarks folder wasn't backed up when my laptop was stolen in March, so I lost a bunch of links, but I remembered some of the really cool stuff from before:

♦  It turns out that if you expose a synthetic diamond to radioactivity, it generates an electrical current.  Diamond is also pretty good at shielding certain kinds of radioactive rays.  So scientists at the University of Bristol are proposing to convert radioactive waste into diamond batteries, as shown in this video.  The batteries generate a very small amount of power, but would last for thousands of years, and would be safe to use e.g. inside of humans as pacemakers.  So apparently that sci-fi trope about using diamonds to generate power will be right after all!

♦  A searchable database of classical oaths, which I found from the author Jo Walton's website.

♦  Why Our Children Don't Think There Are Moral Facts.

I've thought for a long time that the curriculum about Facts vs. Opinions harms critical thinking far more than it hurts it.  Is something a "fact" (rather than an "opinion") because it is objectively true?  Or decisively proven?  Because it is uncontroversial to a certain community, or can be used in an essay (aimed at a particular audience) as ammunition to support a conclusion?  Because it has to do with tangible, physical reality, rather than being a normative judgement like morality or aesthetics?

(For example, the Resurrection of Jesus is a fact in the sense that it is claimed to be about objective physical reality, it is a fact in the sense that it actually occurred, but it is certainly not an opinion shared by everybody and when talking to people outside of the Church, it is indeed the sort of opinion which requires backing up with other, less controversial, facts.  Admittedly, as St. N.T. Wright says [pdf lecture], this is kind of a category-bending "fact", but there are plenty of other examples I could have used as well.)

"Well, you can't expect elementary school students to understand subtle distinctions like the ones you've just distinguished!"  But these are completely different meanings of the word, related only by metaphorical similarity!  That's like saying that you shouldn't expect children to understand the fine distinction between breaking a glass and breaking the law.

And now for some bookmarks on the new laptop:

♦  Math with Bad Drawings, a blog by a math teacher sharing math [facts?/opinions?]

♦  Did you know that the world's richest dog inherited his wealth from another dog?

♦  Meet St. John Mitchell, the clergyman who in addition to many other scientific accomplishments wrote the first paper about black holes, entitled by the impressively long title:

"On the Means of Discovering the Distance, Magnitude, &c. of the Fixed Stars, in Consequence of the Diminution of the Velocity of Their Light, in Case Such a Diminution Should be Found to Take Place in any of Them, and Such Other Data Should be Procured from Observations, as Would be Farther Necessary for That Purpose. By the Rev. John Michell, B. D. F. R. S. In a Letter to Henry Cavendish, Esq. F. R. S. and A. S."

♦  A blog post about some recent developments in black hole information theory, which happens to mention my work with some guys at Harvard about how to make a traversable wormhole!

♦ If you want to make your own black hole, check out this astonishingly black paint, which you can buy for a reasonable price.

♦  I've also been profiled by a journalist at HubPages (St. Joel Furches).  Oh, and I won a prize a while back.

♦  The fake history of Giordano Bruno, martyr for "Science!"?

♦  A sermon by a Coptic priest with a more legitimate claim than Cosmos to speak for martyrs.

♦  Speaking of dealing with grief over death, here is a tearjerking interview with a woman about coping with life after her son committed suicide.  I listened to it on Good Friday this year.  (Note: this is a Catholic radio show, so Protestant viewers may need to screen out all the remarks about how being Catholic is so very Catholic and have we mentioned that we're Catholic?)

Blog post on the same site: A Meditation On The Shocking Idea That Maybe Were Actually Not Just Lazy Whiners.

♦  Deconstructing the Documentary Hypothesis.  (Again, Roman Catholic site with various other polemics I don't endorse, but we're pretty much on the same team when it comes to the Old Testament having a basis in historical reality.)

♦  As for the New Testament, here's your periodic reminder that there are really easy ways to distinguish the historically authentic texts about Jesus from the rest.

♦  My Bionic Quest for Boléro, a story about what it takes to get a deaf person able to appreciate classical music again.  I highly recommend you listen to the musical piece in question while reading the article.

♦  Here is what a low-trust society looks like: Poor Russian Families Berate a Store Owner for Handing Out Free Bread.  It's also an image or an icon of how human beings treat God.  So now you know what it looks like from the other side.

About Aron Wall

I am a Lecturer in Theoretical Physics at the University of Cambridge. Before that, I read Great Books at St. John's College (Santa Fe), got my physics Ph.D. from U Maryland, and did my postdocs at UC Santa Barbara, the Institute for Advanced Study in Princeton, and Stanford. The views expressed on this blog are my own, and should not be attributed to any of these fine institutions.
This entry was posted in Links. Bookmark the permalink.

10 Responses to Random Linkiness

  1. Philip Wainwright says:

    The link above 'really easy ways to distinguish' appears to be broken

  2. Bob Kurland says:

    Those are interesting. I thank your for including the Catholic ones.

  3. Aron Wall says:

    Should work now!

    You're welcome... I think it's important not to be too insular.

  4. TY says:

    Interesting articles. Please allow me refer to one and make some comments for more comments.
    1. I like the article “Why do we pay pure mathematicians?” from Math with Bad Drawings. I totally agree with the writer's opinion because I experienced it, albeit indirectly in previous life. I knew an acquaintance from the maths department for many years. He was just brilliant and he wrote and published numerous and highly abstract articles in his area. But in all the many years I have known him (and we were good pals), not one of those many papers found its way into a practical application. And yet I’m convinced that someday, one overlooked part of his work would be applied.
    2. In the same article was the reference to Gödel’s Theorem, which has far-reaching implications for human knowledge. (Aside: The Reverend at mass today made a quick reference to axioms and my ears perked up right away because I had been thinking about Herr Gödel!). Scott (Church) wrote two interesting pieces on the wave function that drew many comments. Given that maths is the essential tool of physics, which in turn inspires mathematical advances, is understanding about the universe outside the reach of science? I wonder what he and all commentators think.
    3. Do you "believe" that there is an absolute limit to human knowledge? Is this "opinion" also a "fact"? See "Why Our Children Don't Think There Are Moral Facts".


  5. Miloš says:

    Dear Aron,

    I just want to congratulate on your prize! I hope that your health is fine and that you are back to blogging!

  6. Thank you for the mention. And for the cool links. Oddly, I want the black paint ...

    And congratulations.

    Take care & God bless

  7. Mike Rathbone says:

    Dear Dr. Wall,

    Based on your new paper, is it possible for traversable work holes to exist? I seem to remember you writing that the Generalized Second Law of Thermodynamics means that traversable wormholes can't exist. I am sure I am missing something, but I would like to hear your thoughts. Glad you are back to blogging.

  8. Aron Wall says:

    The new work exploits a loophole in my previous proof, which allows it to evade my result without violating the GSL. However, the resulting traversable wormholes cannot be used for FTL travel or time travel.

    In GR, an eternally existing black hole (not one that forms from collapse) would have an "Einstein-Rosen bridge" which is a wormhole connecting it to a black hole in another universe. However, this wormhole is (just barely) not traversable; if you jump in, you fall into the singularity and die. In order to make it traversable, you need to add some negative energy. However, ordinary matter has positive energy, and even quantum matter satisfies something called the "Average Null Energy Condition" (ANEC) that prevents you from making a traversable wormhole.

    In arXiv:1608.05687, we considered the case where the Einstein-Rosen bridge connects black holes living in Anti-de Sitter* (AdS) spacetimes---this is a spacetime which is distorted at large distance scales in such a way that it is possible to reach infinity and bounce back in a finite amount of time (as measured by somebody who waits in the middle).

    *I should really say "asymptotically AdS" since the black holes distort the geometry in the middle, so it only looks like AdS far away from the black holes.

    We then---and this was a bit of a cheap trick, but mathematically it is allowed---considered laws of physics in which at some moment of time you turn on a direct interaction between fields living at infinity on one side of the wormhole, and fields living at infinity on the other side. This allows particles to go directly from one "boundary at infinity" to the other. But don't worry, such a direct jump which avoids the black holes entirely is not what we mean by a traversable wormhole---that would be too cheap! Instead, the point is that once we turn on our interaction, we found that the ANEC would be violated by quantum effects, in such a way that the wormhole also becomes slightly traversable. Then we showed that if you jump in early enough before the interaction is turned on, you can get through the wormhole without any problems.

    Normally, such a trversable wormhole would violate the GSL for the following reason. Let W be the wordline of a particle successfully traversing the wormhole (from the "left" side to the "right") and then departing at the speed of light. Let H be the "causal horizon", the boundary of the region where signals can eventually reach W. There will be a last moment of time on the left "boundary at infinity", such that if you depart after that time, you can never catch up with W. In other words, H intersects the "boundary at infinity". But this means it has infinite area there. Whereas it has finite area when it is passing through the (finite sized) wormhole. Hence the area goes down infinitely. Since the entropy of the horizon H is proportional to its area, this violates the GSL.

    However, when we turn on the direct interaction between the two boundaries at infinity, there is another way for somebody on the left to catch up with W. And that is to use the direct coupling between the two boundaries to "teleport" directly to the right side, and ambush W on the other side. Because of this change in the causal structure of the spacetime, H is cut off so that it no longer hits the left hand boundary at infinity. As a result, the GSL is no longer violated.

    If you want more details, they are in our paper, including figures (if you know how to interpret Penrose diagrams).

  9. Scott Church says:

    Aron, congratulations on your prize! You da' man! :-) The bio at that link says you've accepted a postdoc at Stanford beginning next month. Are you and Nicole are moving back to the West Coast then, and if so, does that mean you'll be getting up my way more often?

Leave a Reply

Your email address will not be published. Required fields are marked *


You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>

My comment policy, including help with leaving LaTeX equations. Place these between double dollar signs, for example: $$\hbar = 1.05 \times 10^{-34} \text{J s}$$. Avoid using > or < since these may be misinterpreted as html tags.
If your comment fails to appear do NOT submit it again.  Instead, email me so I can rescue it from the spam filter.  You can find my email by clicking on "webpage".