Dennis, a biology Ph.D. who works for an aerospace company in "mostly analysis and some software and human interface design," was originally on track to become a physicist. "I started out as a physics major at Caltech, way back in 1957," he writes. "Alas, this was before Feynmann took over the freshman course. It was also a time in which I had more freedom than ever before in my life... and my studies suffered (though I was having lots of fun, including being in the pitcrew of a formula III car). I dropped out of college at the end of '59." Well, Dennis, you've redeemed yourself in our eyes.

What is aerogel, anyway? Another QD reader writes that it's "a silicon-based substance and the world's lowest-density solid composed of 99.8% air and is a stiff foam with a typical density of 3 mg per cm3 nicknamed frozen smoke or blue smoke." It's used in the Belle experiment at KEK in Japan, where Shohei works.

We also asked for creative guesses, and this QD reader didn't disappoint: "It's a slab of 'that' new meta-material, in which light travels so slowly that what we actually see in the picture is the state of the lab as it was a few days ago, when it was presumably much more in order than it presently is (2nd law of thermodynamics). It's a very useful thing to have as well, for example, you can use a slightly thinner version to take your own portrait, as you will have just enough time to walk around the table and capture the image when it arrives."

Stay tuned for the next mystery photo and another chance to win!

Who discovered the top quark?
Who gets credit for discovering the top quark? A decade later, the debate continues on Quantum Diaries when Gordon Watts reads an article that gives all of the credit to the CDF Collaboration at Fermilab. A member of the DZERO Collaboration, Gordon writes, "There is one problem... it was discovered by both CDF and DZERO -- they submitted their papers minutes apart from each other. I scanned down to see who authored this paper. A fellow I've known for years -- and a member of CDF."

Tommaso Dorigo, a CDF member, responds with his version of the story: "As you well know, CDF did observe in 1994 a small sample of ttbar events, and from it measured a mass of the top quark which is dead-on the most precise measurements to date. This was published in April 1994, one year before the official 'discovery' papers by CDF and DZERO, back to back on PRL... I think I am not in my political correct mood today, and I believe that once the story is told fully, few would disagree that CDF did observe top quark production one year before DZERO did."

Gordon and Tommaso are not the only people still interested in this debate -- the comments section of his post grows longer and longer with contributions from readers, other physicists, and several Quantum Diarists. "I wonder how many comments this post will end up getting," Gordon writes.