Kurt Gödel: A postcard from Vienna

Kurt Gödel was one of the greatest mathematicians of the 20th century. He made many important contributions to mathematical logic and philosophy, but is best known for his incompleteness theorems. Loosely speaking, the theorem states that the dream of phrasing all of mathematics in terms of a formal system, based on a set of axioms and the rules of logic, is bound to fail: there will always be statements that are true but whose truth cannot be proved within the axiomatic system itself. This abruptly ended a longstanding quest by some mathematicians to construct a set of axioms sufficient for all of mathematics.

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I’m staying in a little village called Lackenberg, to do some hiking in the area. After arriving, I walked around a bit in and around the village, and then watched a beautiful sunset from the balcony of my hotel room.

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A Partial Lunar Eclipse

On Tuesday 16 July, 2019, there was a partial lunar eclipse visible from most of Europe. I decided to spend the night in a hut halfway up a mountain near Vienna to watch this eclipse, and invited some colleagues to come along. We were lucky that it was a mostly clear sky that evening, making for excellent viewing from just over 1200m up.

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Beating the Avatar Blues

When the movie Avatar was released in late 2009, a strange thing happened with many people who saw it. They got depressed, even suicidal. It wasn’t because they disliked the movie, but because they liked it so much, they wanted to live in a gorgeous, almost utopian, world like Pandora, rather than on planet Earth. Pandora, the fictitious alien moon portrayed in the movie, has an amazing natural beauty, and human-like inhabitants (the Na’vi) living in peaceful harmony with it.

Read the full piece on ORBITER magazine

The February 2019 Supermoon

A “supermoon” happens when a full moon occurs around the same time that the moon is at its closest point to the earth (perigee) in its elliptical orbit around our planet. This means that the full moon will appear extra large and bright. In fact, it can appear up to 30% larger and brighter compared to the opposite, a “micro-moon”, when the full moon occurs around the same time that it is furthest away from the earth (apogee). Last night happened to be the brightest supermoon of 2019.

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The Chat Noir Cabaret

My good friend Charles Tichenor has been playing the piano since he was a little kid. And he’s still going at it tirelessly at his weekly Chat Noir Cabaret show at the Los Magueyes Mexican restaurant on Burro Alley in Santa Fe, NM, USA. Here’s a short slide show to give an impression of his performances.

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A Home for Complex Systems Science

In complex systems science, the notion of complexity is often summarized with the phrase “the whole is more than the sum of its parts“. This expression can be traced all the way back to the early Greek philosopher Aristotle (Metaphysics, Book VIII, 1045a.8-10) and mathematician Euclid (Elements, Book I, Common Notion 8). It was therefore appropriate to have a conference on complex systems in Greece. As part of a delegation from the Institute for Advanced Study of the University of Amsterdam, I attended this conference to learn more about recent advances in complex systems science, and about some ancient Greek history. Read more

La Cathedrale de Strasbourg

I spent a morning strolling around the old town of Strasbourg, France, with as main goal a visit to its impressive cathedral. Unfortunately it was a completely overcast day, so the sky was white instead of blue. But in some way it actually made the whole experience even more mystical!

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A Chalk Walk

Among scientists, a “chalk talk” means a lecture without a laptop and beamer to display fancy graphics, but simply using a blackboard and a piece of chalk to draw diagrams and formulas while you speak. It’s sort of going back to the basics to force you to explain your topic clearly. Last week I also went back to the basics, leaving my laptop behind to go on a 5-day walking trip through Zuid-Limburg, the southernmost area of The Netherlands. This region is well known for its extensive layers of limestone, and the 90km walking path I followed is appropriately called Krijtlandpad, or chalkland path. It was indeed a beautiful “chalk walk”, also highlighting many of the other things the region is famous for, including the country’s highest point.

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Lunar Eclipse over Amsterdam

Last night there was a (complete) lunar eclipse which was visible from Amsterdam. Many thanks to Jo & Piet for sharing their 9th-floor apartment balcony with me, from where the views were just wonderful! Here are some impressions. Click any of the pics for a full-size view…

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Impressions of Amsterdam

I’ll admit it straight away: it’s not my city, and it never will be. But on one of those rare blue-sky days it’s actually not so bad (if you can manage to dodge the hordes of tourists, that is). Here are some impressions from around the old town of Amsterdam, in the area where I currently live and work.

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Tracing the Roots of my Family Name

It’s quite fun when your family name originates from a specific place that still exists and can be visited. As had already been known for a long time, my family name comes from a street, the Hordijk, in a neighborhood that is now in the southern part of the city of Rotterdam. So, on a sunny Saturday afternoon, I decided to go and pay a visit to this place where my ancestors once lived…

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Marvellous Mallorca: Hiking the Ruta de Pedra en Sec

I just spent two weeks in Mallorca (Spain), with as main goal hiking the Ruta de Pedra en Sec (GR221), a long-distance trail that crosses the entire Serra de Tramuntana, Mallorca’s beautiful mountain range. Eight days on the trail (plus one rest day in between), and sleeping most nights in “refugis” (mountain huts). But I also had some extra days to explore in and around Palma de Mallorca, including a visit to some amazing limestone caves and a bike ride along the bay of Palma. All-in-all a fantastic trip that was well worth it. Here are some brief impressions. Click any of the pics for a full-size view, or any of the links throughout the story for more images.

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A Perfect View from Mount Le Grammont

Le Grammont is a mountain in the Chablais Alps in Western Switzerland situated at the south-east end of Lake Geneva, close to the Swiss-French border where the Rhône River flows into the lake. With a height of 2,172 m (7,126 ft), Le Grammont is not the highest mountain in the Chablais Alps (highest point Dents du Midi 3,257m/10,686 ft), but because of its prominent location right next to Lake Geneva at the lower end of the Rhône valley in the Canton Valais, it is a popular hiking destination that offers wonderful all-round views from the top.

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Vienna by Night

Last night I took advantage of a temporary break in the extreme cold weather we’re experiencing this month, and went for a walk along the Ringstrasse in Vienna to take some shots of the various beautiful buildings located along it. This was a bit of a spontaneous experiment, but I’m actually quite pleased with how some shots came out. So here’s a nice impression of Vienna by night. Click any pic for a full-size view.

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Castles, Canyons, and Caves

The historic city of Graz, in south-eastern Austria, was designated a UNESCO world cultural heritage site in 1999 for having “the best preserved city center of Central Europe”. It combines renaissance, gothic, baroque, and also modern architecture, and has some wonderful natural beauty nearby as well. I recently spent four days exploring this fascinating city and its surroundings, combining culture and nature with a lot of walking.

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Summer Solstice Full Moon

Last night a rare event happened: the summer solstice and a full moon at the same time. So I went up Kahlenberg, a hill above the city of Vienna, to have a good view of this special full moonrise. Unfortunately my cheap little point-n-shoot camera is almost useless in low-light conditions, but I got a few halfway decent shots anyway. Click each pic to see a larger version.

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Sunset in Santiago

I’m in Santiago, Chile, for two weeks to provide some computing support for a colleague. Unfortunately this city is often covered in a blanket of smog (especially during the summer). As a consequence the Andes mountains, which are pretty much right next to the city, are rarely visible in their full glory. But occasionally the smog lifts, revealing beautiful mountain views, especially during sunset. Here are some impressions (click on any pic for a full-sized view).

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Watching the Perseid Meteor Shower

On the night of 12-13 August, I took some friends up to the top of a small mountain to watch the annual Perseid meteor shower. This year was predicted to be particularly good, largely due to the peak of the shower being just a few days before a new moon, making for optimal (i.e., dark) viewing conditions. The weather forecast called for a clear night sky, so we were all excited to watch this show (with an expected 50-100 meteors per hour) from a high and dry vantage point away from the city lights. Read more