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I’m an economist and the owner of Graukaue.


Graukaue (Gray Coe) is my podcast studio at the Fürst Leopold Coal Mine in Hervest-Dorsten.


The pits. There's Graukaue 2 and Graukaue 1.

Graukaue 2

This is the English-language pit.

Underground with Michael Holtkamp

Under the roof of the Gray Coe there are countless microphones, with each microphone being suspended from the ceiling just like a clothes hook. At the beginning of a shift, each miner lowers his microphone, like the announcer in a boxing ring did in the past. When the bell rings three times, the crew goes down into the mine. Glückauf!

Graukaue 1

This is the German-language pit; see

Audio podcasts

All shows' audio versions are available at You can subscribe to the podcasts via their feeds as well as on the platforms listed below.

Podcast feeds
Listen on Apple Podcasts
Apple Podcasts

Apple Podcasts

Listen on YouTube Music
YouTube Music

YouTube Music

Video podcasts

All shows' video versions are available on Graukaue's YouTube channel at You can subscribe to the channel as well as to the podcasts.


Born in 1984, I initially grew up in Dorsten, Germany. After stays in the USA and Chile, each as a high school exchange student, I got my high school diploma (Abitur) from a school in Bottrop, Germany. Subsequently, I studied International Economics at Kiel University (Kiel, Germany) and Jönköping University (Sweden). After traveling around the world for six months, I returned to Kiel University for my doctoral studies. There I was employed as a research/teaching assistant for over seven years. My fields of interest are urban/regional/international economics or economic geography, and transport economics. In 2019, I returned to Dorsten and am now self-employed.


The Wider Impacts of Transport Infrastructure Investments
Agglomeration and Imperfect Competition in General Equilibrium

The wider impacts of transport infrastructure investments are pecuniary externalities that are commonly alleged to be positive. At least when inferred from partial equilibrium analysis, this can be viewed as reasonable. Though, for an economy with limited resources, it might be reasonable to presume that positive wider impacts are redistributive effects rather than self-contained benefits. If they are, what is the sign of the net wider impact? To study this sign and its determinants, I set up various general equilibrium models of spatial economies in which the costs of transportation are brought down by means of some tax-funded scheme. Applying two separate classes of models, I study the wider impacts both from imperfectly competitive markets in the wider economy and from the agglomeration of economic activity. The former comprehends monopolistic, duopolistic and monopolistically competitive markets, including one with endogenous firm entry. The latter is a New Economic Geography model that is devised as to allow for a welfare analysis. The signs of the wider impacts are found to be highly ambiguous.


The bell system. This is how I communicate with the outside world.