Archive for August 1st, 2007

William brought tears to my eyes

August 1, 2007

An inspiring and elevating experience of an interview with William Kambkwamba: it is communication that transcends language!

PS: There are three more talks on Africa by others here.

A tribute to David Turnbull

August 1, 2007

Franz Spaepen and Michael Aziz pay their tributes to David Turnbull in the latest issue of Nature Materials:

David Harker’s challenge to David Turnbull, his colleague at the General Electric Research Laboratory, was clear: “If you can undercool molten copper by more than a few degrees, I’ll eat my hat!” Turnbull had just told his audience at a 1948 dinner meeting of the Science of Metals Club in Schenectady, New York, that he had undercooled liquid mercury several tens of degrees below its thermodynamic crystallization temperature by dispersing it into small droplets, and thereby isolating into individual droplets the small bits of ‘dirt’ that ordinarily cause crystal nucleation. At the end of the talk he had speculated that, if similarly treated, not just mercury, but also metals that crystallized into simpler structures would exhibit such large liquid undercoolings. After the meeting, Turnbull quickly showed with a hot-stage microscope that small droplets of copper, silver, gold and many other metals could be cooled to temperatures far below their crystallization points. Harker graciously accepted the results: he appeared at the next meeting with a hat made of Swiss cheese.

The tribute, though short, describes contributions of Turnbull in a lucid fashion with specific reference to crystallisation and glass transition; along the way, it also mentions the contributions of others (Frank, Bernal, Pol Duwez, and Greer) who built on his ideas. The awe and reverence in which Turnbull is held by his colleagues is clear from this sentence:

David Turnbull is one in a line of distinguished physical chemists, going back to J. W. Gibbs, who have profoundly influenced materials science.

Finally, the piece ends with a tribute to the human being behind the scientist:

But even with all his scientific distinction, David Turnbull, who died on 28 April 2007, will probably be remembered most as a remarkable human being who touched the lives of all who had the good fortune to know him. His modesty and understatement were legendary, as were his wisdom, generosity and breadth of knowledge. He was unsurpassed at recognizing and bringing out the individual strengths of his associates at General Electric and, after 1962, of his students and postdocs at Harvard. In his autobiography, available on the Materials Research Society website, David relates how he would have liked to continue to work the family farm in western Illinois. A childhood asthmatic condition put him on his way to Monmouth College and the University of Illinois to become the scientist many of us are deeply grateful to have had among us.

The autobiography referred to is available at this MRS David Turnbull page.

Wednesday morning link fest

August 1, 2007

Happy reading!

Measuring the acceleration of the universe

August 1, 2007

Rob Knop at Galactic Interactions has posted the transcript of his 15 minute talk on the measurement of the the acceleration of the expansion of the universe:

Many of you have probably heard of redshift — probably because of the Doppler shift. Something that is moving away from us will show a redshift — light (or sound) emitted by it will be shifted to longer wavelengths. Often, the redshift from the expansion of the Universe is described this way, but in fact that’s not really what it is. In fact, the dynamics of the Universe as described by Einstein’s General Relativity tell us that as the Universe expands, wavelengths of light expand at *exactly the same rate*. This is called the “cosmological redshift”.

Rob goes on to explain how to measure this cosmological redshift and hence the expansion of the universe. Further, he also tells about the implications of the acceleration of the expanding universe:

For the Universe’s expansion to be accelerating, there must be *something else* in the Universe. It turns out that Einstein’s General Relativity *does* allow for a very exotic material which will have (effectively) a negative gravitational effect. Today we call that Dark Energy. From the fact that the Universe’s expansion is accelerating, we know that Dark Energy makes up 2/3 to 3/4 of the total energy density of the Universe.

Wacky stuff.

Rob was part of one of the two teams which announced the the acceleration of the expansion of the universe; and, apparently, not many believed these results in the beginning:

A lot of people didn’t believe this at first. One prominent theorist, Rocky Kolb, apparently said in one talk that “the Supernova people had better figure out what is wrong with their data, or somebody is going to get hurt.” However, there were two independent teams that came up with the same result, so people took it seriously. Now, almost a decade later, independent methods have confirmed that it seems that the accelerating Universe measurement is correct.

A very nice talk with plenty of interesting material presented in an easy to follow fashion. What is more, Rob is also willing to answer questions:

At any rate, I’ll stop there — that’s the whirlwind tour of just how one goes about measuring the expansion history of the Universe.

For the rest of the time we have, I’d be happy to answer questions about any of this, or about the discovery.

Take a look!


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