Question of the Month

How does a lightning bolt find its target?

 Question of the Month, Vol.9 issue 2 2019  Comments Off on How does a lightning bolt find its target?
May 222019

Once, thunderstorms with thunder and lightning were interpreted as signs of the god’s wrath; nowadays, we are taught the mechanics behind a thunderstorm in school. You are probably already thinking about ice crystals that are smashed together by strong winds inside clouds, creating static charges in the process. How does a lightning bolt, though, find its way from the cloud to the ground? This question still keeps scientists awake at night – and there is still not a clear answer to how exactly the formation and movement of a lightning bolt work. This Question of the Month will give a brief summary on how a lightning bolt selects its target.

Lightning [1,2] occurs always when a large thunderstorm cloud with strong winds generates sufficient electrostatic charge that it must discharge towards the ground. The discharge itself occurs (simplified) in a twostep process, consisting of a main lightning bold and a preflash: The preflash travels as comparably weak (but still dangerous!) current downwards from the cloud. This usually happens in little jumps, which have been investigated with high-speed cameras. They show that the current path is apparently selected randomly by slowing down at a given position and then randomly selecting the next to jump to. This random selection appears to happen within a sphere of a few tens of meters in diameter around the tip of the growing lightning bolt. The process also involves growing many tendrils with individual tips and thus covers a large area (see also Fig. 1). With this procedure, the lightning bold eventually “feels” its way to the ground until it reaches it either directly or via a structure connected to it.

Figure 1: Lightning bolts are branching off into many tendrils. [3]

Therefore, if a conductive object reaches into such a sphere, the bolt will immediately jump to it and use it as a low-resistance shortcut to the ground – as a result, if possible, shortening the path for the discharge. This behavior leads to the curious effect of exclusion areas around structures that are protected with lightning rods, in which practically no ground strike will occur, and a person will not be hit directly. Unfortunately, this will not completely protect the person, as the electricity can still be dangerous within the ground.

Now that the preflash has found a path to the ground, the second phase starts, and the majority of the charge starts to flow with up to 20 000 A along the path found by the preflash. This is also the portion of the discharge that is visible by bare eye. It can consist of several distinct discharges that all follow the path of ionized air of the previous one, creating the characteristic flickering of a lightning bolt.

How the entire process from preflash to main discharge works is still not completely understood today and much of the presented insights were simply gathered phenomenologically by camera imaging. Additionally, there are many more types of and effects related to lightning bolts, which are relevant for our understanding of a variety of weather phenomena. All in all, thunderstorms are still something magical today, even if only figuratively.

— Kai Litzius

Further reading:




[4] Chem. Unserer Zeit, 2019, 53. DOI: 10.1002/ciuz.201980045

Will it be possible to revive species that have gone extinct?

 Question of the Month  Comments Off on Will it be possible to revive species that have gone extinct?
Mar 012019

Just a few years before Dolly was born as the first surviving clone of a sheep in 1996, the movie Jurassic Park was launched, based on the same-named novel by Michael Crichton.[1,2] In this story scientists insert genetic material derived from fossils into amphibious eggs to bring all sorts of dinosaurs back to life. The actual cloning of animals follows a quite similar approach called somatic cell nuclear transfer or SCNT (fig 1): a nucleus with the desired DNA is isolated from a somatic (body) cell and introduced into an emptied ovum of the same species. Several electrical impulses excite the cell and stimulate proliferation in a nutritional medium. The most stable cell clusters, called blastomeres, can then be transferred to a host mother and grow into an embryo.[1] Dolly managed to fully develop into a lamb and lived 13 years until she died of an infection. She even gave birth to a lamb, proving the viability of cloned creatures.[3] Blastomeres that are dissected instead of implanted can be used to treat diseases or might enable the growth of tissue. Maybe in the future we will be even able to grow a whole surrogate organ ‒ an approach that is highly controversial since human somatic cells are mostly derived from embryotic tissue.[4]

Fig 1: Schematic depiction of the SCNT process: The nucleus with the desired genetic material is inserted into an empty egg cell which is growing into a blastomere.[5]

According to a report from the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) about one million species of an estimated number of around 8 million species (only counting eukaryotes) on earth are currently endangered or threatened with loss of habitat.[6,7] In the history of Earth extinction has mostly been a consequence of natural disasters like climate change, volcanic eruptions, or meteorite impacts until human population started to expand.[8,9] The IPBES report demonstrates the present impact of human behaviour on biodiversity and it seems that we are facing many more extinctions caused by anthropogenic reasons in the next decades. It has become a growing interest to not only preserve existing species but also to revive those that have already died out.

One attempt is currently being made to revive Quaggas, a subspecies of the living plain zebra that has died out in the 1880s (fig 2), by selective breeding. Due to their close genetic relation some plain zebras that resemble the characteristic pattern of the quaggas have been selected in the hope to one day give birth to a zebra that looks just like them and shows similar genetic information.[10,11,12]

Fig 2: Taxidermied Quagga foal in the Museum of Natural History in Mainz, Germany. (© Tatjana Dänzer)

More demanding is the CRISPR Cas9 method: the DNA that can be extracted from most fossils like the woolly mammoth could be much too old to produce a healthy individuum. But their DNA might be partially recovered by replacing some sequences in the DNA of their closest living relative, the elephant, with extracted mammoth DNA. The genome will not be the same as it was millions of years ago and no one really knows how this will influence the livability of the animals.[13]

But most of the extinct species do not have such close relatives anymore. Interspecies nuclear transfer like in Jurassic Park can be another possibility for de-extinction, that means to revive species that have gone extinct or are on the verge of extinction. The San Diego Zoo Institute for Conservation Research maintains a large collection of cells and embryos called Frozen Zoo®.[14] By using reproductive technologies they develop methods to prevent endangered species like the northern white rhino or the Przewalski horse from extinction or inbreeding.[ 15] The first animal of an endangered species that was successfully cloned was a gaur (bos gaurus), an Asian ox, in 2001 by Advanced Cell Technology using genetic material from the San Diego Zoo. DNA from the skin cells of a male gaur were implanted into empty cow egg cells, grown into blastomeres that were then transferred into the wombs of domestic cows. One of eight embryos developed to a full-grown calf. Unfortunately, after being born, the gaur did not live for more than two days. However, the cause of death is considered to be an infection and not the fact that it is a trans-species clone.[16] The second clone that was created with the very same method had a higher life expectance. It was a banteng (bos javanicus), another endangered Asian cattle. Also remarkable is, that the used fibroblasts were taken and frozen 25 years before, in 1978.[17] An attempt to clone a species that has already gone extinct, the Pyrenean ibex (capra pyrenaica pyrenaica) failed since the kid was born with a deformed lung.[18]

The fact that cloned cells do in principle develop to embryos and even prolific adult animals (like Dolly) gives hope that one day species that have recently been wiped out could come back to life. But besides the challenging and time-consuming scientific research these plans also evoke a lot of critical questions in the society:

How is decided which species will be revived and which stays extinct?

It is clearly difficult to revive every species that we know has ever lived on this planet. There would just not be enough space and food and we might soon experience another wave of mass extinction. Since DNA from fossils might be too old, mammoths and dinosaurs are still out of question. This is shifting the focus on species of the recent past. But how can we select which species can live again and which won’t? We surely must consider the preservation of still existing species as a priority.

Where should they live?

If it is possible to clone many animals of one kind that can even mate, there must be a safe and nourishing environment, most likely captivity. Who knows how an entire species that has been created in captivity will develop? And the knowledge about the behaviour and needs of most of those animals is very little.[13]

Who is going to pay?

The scientist’s motivation might surely be an idealistic one but somehow all the research and maintenance must be financed. Innovations will always attract temporizers that try to exploit it financially. Zoos and wildlife parks that exhibit animals are the lesser problem. Some worry that wealthy poachers and “gourmets” who don’t withhold from hunting and eating endangered species now will just as much be attracted by the thought of getting hold of a cloned specimen. Paying to hunt an endangered species to support the protection financially is already practised in southern Africa and raises a lot of ethical issues.[19,20]

To see living “fossils” like dinosaurs, mammoths, dodos and all the others is surely an exciting thought. But if mankind proceeds like this, in just a few decades there might be much less animals on earth than there are now. Let’s hope that combined common sense, technical progress, and less vanity will lead to a preserved and healthy nature in our future.

‒Tatjana Dänzer

Read more:

[1] I. Wilmut, A. E. Schnieke, J. McWhir, A. J. Kind, K. H. S. Campbell, Nature 1997, 385, 810–813.

[2] M. Crichton, Jurassic Park, Alfred A. Knopf, Inc., 1990.


[4] S. Lü, Y. Li, S. Gao, S. Liu, H. Wang, W. He, J. Zhou, Z. Liu, Y. Zhang, Q. Lin, C. Duan, X. Yang, C. Wang, J. Cell. Mol. Med. 2010, 14, 2771‒2779.

[5] By en: converted to SVG by Belkorin, modified and translated by Wikibob – derived from image drawn by / de: Quelle: Zeichner: Schorschski / Dr. Jürgen Groth, with text translated, CC BY-SA 3.0,


[7] C. Mora, D. P. Tittensor, S. Adl, A. g. B. Simpson, B. Worm, PLoS Biology, 2011, 9, 1‒8.

[8] D. B. Weishampel, P. Dodson, H. Osmólksa, The Dinosauria, 2nd ed., University of California, 2004.

[9] D. P. G. Bond, P. B. Wignall, Geological Society of America Special Papers, 2014, 505, 29–55.



[12] J. A. Leonard, N. Rohland, S. Glaberman, R. C. Fleischer, A. Caccone, M. Hofreiter, Biol. Lett., 2005, 1, 291‒295.

[13] B. Shapiro, Genome Biology, 2015, 16, 1‒3.

[14], [15]


[17] D. L. Janssen, A. L. Edwards, J. A. Koster, R. P. Lanza, O. A. Ryder, Reproduction, Fertility and Development, 2004, 16, 224‒224.




Which way is up?

 Question of the Month  Comments Off on Which way is up?
Feb 052019

Imagine you are on an airplane, ten thousand meters up in the sky. Now, if you close your eyes you know exactly which way the airplane has started moving, whether it has begun to manoeuvre to the right or to descend. This ability we owe to our inner ear as a part the humans’ vestibular system.

The vestibular system is designed to send information about the position of the head to the brain’s movement control centre, that is the cerebellum. It is made up of three semi-circular canals and two pockets called the otolith organs (Fig. 1), which together provide constant feedback to the cerebellum about head movement. Each of the semi-circular canals is orthogonal to the two others so that they detect the variety of movements in three independent directions: rotation around the neck (horizontal canal), nodding (superior canal) and tilting to the sides (posterior canal). Movement of fluid inside these canals due to the head movement stimulates tiny hairs that send signals via the vestibular nerve to the cerebellum. The two otolith organs (called the saccule and utricle) signal to the brain about linear movements (backwards/forwards or upwards/downwards) and also about where the head is in relation to gravity. These organs contain small crystals that are displaced during linear movements and stimulate tiny hairs communicating via the vestibular, or balance nerve to the cerebellum.

So why is that, even equipped with such a tool, sometimes we get a feeling sitting on an airplane that it is falling down when in fact it is not? Why is that some people, particularly underwater divers, may lose direction and no longer know which way is up?[1] Surely, typical divers should still have the inner ear, unless a shark has bitten their heads off. Is it all caused by stress? Actually, there is much more to it!

Humans have evolved to maintain spatial orientation on the ground, whereas the three-dimensional environment of flight or underwater is unfamiliar to the human body, creating sensory conflicts and illusions that make spatial orientation difficult. Normally, changes in linear and angular accelerations and gravity, detected by the vestibular system, and the relative position of parts of our own bodies, provided by muscles and joints to the proprioceptive system, are compared in the brain with visual information. In unusual conditions, these sensory stimuli vary in magnitude, direction, and frequency. Any differences or discrepancies between visual, vestibular, and proprioceptive sensory inputs result in a sensory mismatch that can produce illusions. Often the result of these various visual and nonvisual illusions is spatial disorientation.

For example, fighter pilots who turn and climb at the same time (they call it “bank and yank”), feel a strong sensation of heaviness. That feeling, caused by their acceleration, surpasses the pull of gravity. Now, if you asked them while blindfolded to tell which way was down using only their vestibular organ, they would point to the cues provided by the turn, not to the cues provided by the earth’s gravity. [2]

Furthermore, the vestibular system detects only changes in acceleration, thus a prolonged rotation of 15-20 seconds [3] results in a cessation of semi-circular output. As a result, the brain adjusts and does not feel the acceleration anymore which can even result in the perception of motion in the opposite direction. In other words, it is possible to gradually climb or descend without a noticeable change in pressure against the seat. Moreover, in some airplanes, it is even possible to execute a loop without exerting negative G-forces so that, without visual reference, the pilot could be upside down without being aware of it.

Another interesting example is the phenomenon of loopy walking. When lost in a desert or a thick forest terrain without landmarks people tend to walk in circles. Recent studies performed by researchers of Max Planck Institute for Biological Cybernetics, Germany, revealed that blindfolded people show the same tendency. Lacking external reference points, they curve around in loops as tight as 20 meters in diameter while believing they are walking in straight lines. [4]

Seemingly the vestibular system is quite easy to trick by eliminating other sensory inputs. However, even when visual information is accessible, e.g. underwater, spatial disorientation can still occur [any scuba diving forum – for the reference]. The obvious fact that water changes visual and proprioceptive perception is crucial here: humans move slower, see differently and let’s not forget the Archimedes’ principle. It happened a lot, that a confused diver thought that the surface was down, especially when the bottom seemed brighter because of reflections. This can be a dangerous mirage in such an unusual gravity. On top of it, water can affect the vestibular system directly through the outer ear. When the cold water penetrates and reaches the vestibular system, it can cause thermal effects on the walls of the semi-circular canals, leading to slight movements of the fluid inside, which are enough to be detected by the brain.[5] Just like in the situations described before this causes the symptoms of spatial disorientation and dizziness.

Fig. 1. Schematic structure of a humans’ inner ear [6].

The vestibular system is indeed frightfully complicated. We can trick it for fun riding roller coasters in an adventure park, but when incorrect interpretation of the signals coming from the vestibular system occurs at the wrong moment this can lead to serious consequences. Luckily, nowadays the airplanes and even divers are equipped with precise instruments used to complement the awareness of the situation and thus avert dangerous situations.

P.S. If you are interested, try riding an elevator while seated on a bike.

— Mariia Filianina


  1. The Editors of Encyclopaedia Britannica, (2012). Spatial disorientation, Encyclopædia Britannica, inc.,
  2. L. King, (2017). The science of psychology: An appreciative view. (4th. ed.) McGraw-Hill, New York.
  3. Previc, F. H., & Ercoline, W. R. (2004). Spatial disorientation in aviation. Reston, VA: American Institute of Astronautics and Aeronautics.
  4. J. L. Souman, I. Frissen, M. N. Sreenivasa and M. O. Ernst,Walking straight into circles, Current Biology 19, 1538 (2009).

The Spaghetti Turn

 Question of the Month  Comments Off on The Spaghetti Turn
Jan 052019

Certainly, most of us enjoy an occasional nice bowl of spaghetti. Some of us use a spoon along with the fork, some don’t. Doesn’t matter, as long as you enjoy and don’t make a mess. But have you ever wondered whether there is a preferred direction to turn the fork? And is it related to where you live? We did!

In our last issue (Vol 2, 2018), we launched a survey asking our readers exactly this question (Figure 1).

Figure 1: The Spaghetti Turn survey as it appeared on the webpage.

Our survey was advertised in social media (Facebook, LinkedIn, Twitter, ResearchGate) and via QR codes on flyers. The survey reached a total number of n=160 readers, 132 of them found their way directly to our website. The results are shown in Table 1 and Figure 2.

Table 1: Results of the survey “The Spaghetti Turn”.

Northern hemisphere Southern hemisphere worldwide
n % n % n %
right-handed clockwise 117 75.5 3 60 120 75.0
right-handed counter clockwise 12 7.7 1 20 13 8.1
left-handed clockwise 10 6.5 0 0 10 6.3
left-handed counter clockwise 10 6.5 0 0 10 6.3
both-handed clockwise 0 0 0 0 0 0
both-handed counter clockwise 1 0.6 0 0 1 0.6
shovel 4 2.6 1 20 5 3.1
other 1 0.6 0 0 1 0.6
sum 155 96.9 5 3.1 160 100

Figure 2: Worldwide percentage of the preferred direction to turn the fork when eating spaghetti related to the handedness (values in %).

The option „no preferred direction” remained unanswered. One single participant chose “I am right-handed and turn clockwise” and “I am right-handed and turn counter clockwise”, depicted as “other”. Assuming that this is no miss-click one out of a total number of 160 participants has no preferred direction when using the fork with their right hand. This underlines that most people on earth indeed have a favourite direction to screw the fork.

Although there is no clear definition to determine handedness, some publications claim that 70–95 % of human population worldwide are right-handed, 5–30% are left-handed and a small minority is ambidextrous.[1] This is consistent with our findings: the survey was answered by 133 right-handed people, which is 86.9% of all 154 participants who revealed their handedness. 20 participants are left-handed (13.1% of all 154 participants who revealed their handedness). One participant (<1%) is ambidextrous and turns the fork counter clockwise with both hands.

75.0% of all participants are right handed and turn the fork in clockwise direction. Only 8.1% turn it counter clockwise. Surprisingly, there seems to be no preference about the turning direction among left-handed people. Their numbers equal (each ten or 6.3%), while 90.2% of all right-handed people turn clockwise. Fortunately (or shockingly?), 3.1% of spaghetti eaters worldwide shovel.

Unfortunately, we did not reach a significant number of readers from the southern hemisphere. Four participants out of five are right-handed, one shovels. 60% of the right-handed southerners turn the fork clockwise, 20% turn it counter clockwise. Considered that only five participants (3.1% of all) do not represent the whole ~10% of the human population living on the southern hemisphere,[2] the preference of turning counter clockwise shows the same tendency for both hemispheres. There is therefore supposedly no relation to where you live on this planet.

But why is the clockwise direction so obviously favoured?

Time and therefore clocks have a powerful influence in our daily lives. Also, in a lot of cultures texts are written from left to right (as the clockhand moves). Moving and looking to the right is very often linked to the future and openness. An experiment from Sascha Topolinski and Peggy Sparenberg from 2012 suggests, that the preferred direction to turn objects could be determined by one’s conservative or open personality.[3] Or is it just for handling reasons only and it is a little easier to apply force on the edge of the fork while turning it clockwise?

With a simple survey like our’s it is impossible to determine whether the habit to turn the fork left or right is a matter of education, subconsciousness or technique.

Throughout the active survey it was possible to answer the poll via the Facebook “Surveys for Pages” and our webpage. Hence, we cannot entirely assure the integrity of the results. Also, we hope our readers understand humour but also answer the survey genuinely. We simply trust in the scientific spirit of our readers. We also did not consider that for cultural habits in certain cultures spaghetti dishes might not be available or forks might not be part of the traditional cutlery. Although it is very often a cause for heavy crossfires during meals, the use of a spoon along with the fork is discounted in the evaluation of the results too. With this survey we just aim to give a picture about the general turning behaviour of spaghetti eaters. To the best of our knowledge there has not been a similar survey until now.

We are now smarter than before but still missing the details of the big picture. Let’s see what the new year brings…

Tatjana Dänzer, Mariia Filianina, Alexander Kronenberg, Kai Litzius, Adrien Thurotte

The editorial team of the Journal of Unsolved Questions thanks all 160 participants of the survey and wishes Bon Appetit and a very happy start into the year 2019!

Read more:

[1] [ (last access 31.12.18, 15:20).

[2] (last access 31.12.18, 15:40).

[3] Sascha Topolinski, Peggy Sparenberg, Social Psychological and Personality Science, 2012, 3, 308–314.

How many colours are needed for a map? And for a plane?

 Question of the Month  Comments Off on How many colours are needed for a map? And for a plane?
Dec 042018


When Francis Guthrie took on the task to colour a map of England in 1852 he needed four colours to ensure that no neighbouring shires had the same colour. Is this the case for any map imaginable, he wondered.

As it turns out, five colours do suffice, as mathematically proven in 1890 in the five-colour theorem [1]. That indeed four colours are enough to colour a map if every country is a connected region took until 1967 to prove [2] and required computer assistance. It abstracted the idea to geometric graph theory where regions are represented by vertices connected by an edge if they share a border (see fig. 1).

Fig 1: Illustration of the abstraction of the map colouring problem to graph theory.

The four-colour theorem was then proven by demonstrating the absence of a map with the smallest number of regions requiring at least five colours. In its long history the theorem attracted numerous false proofs and disproofs. The simplest versions of counterexamples focus on painting extensive regions that bordering many others, thereby forcing the other regions to be painted with only three colours. The focus on the large region might cause people’s inability to see that colouring the remaining regions with three colours is actually possible.

Even before the four-colour theorem was proven, the abstraction to graph theory evoked the question as to how many colours would be needed to colour a plane so that no two points on that plane with distance 1 do have the same colour. This is also known as the Hadwiger–Nelson problem. Note that we are not colouring continuous areas in this case, but instead each individual point of the plane, rendering it extremely more complex. In the 1950s it was known that this sought number, the chromatic number of the plane, had to be between four and seven.

The upper border is known from the existing tessellation of a plane by regular hexagons that can be seven-coloured [4] (fig. 2). The maximal distance within one hexagon, the diameter, needs to be smaller than one to comply with the requirement. Additionally one needs to ensure that the distance to the next hexagon of the same colour is larger than one. These constraints imply that the hexagon edge length a has to be between 0.5 and $\sqrt(7)/2$ for an allowed colouring of the plane, where no two points with distance one have the same colour.

Fig. 2: Colouring of a plane in a seven colour tessellation pattern of regular hexagons.

As to the lower border for the chromatic number of the plane, it is obvious that two colours will not suffice to colour even the simple unit-distance path of an equilateral triangle (see fig. 3 a). To demonstrate that three colours do not suffice either and therefore at least four colours a needed, we take a look at the Moser spindle shown in fig. 3 b. The seven vertices (all eleven edges / connections have unit-distance) cannot be coloured with three colours, say green, blue, and yellow. Assigning green to vertex A, its neighbours B and C need to be blue and yellow, respectively, or vice versa, enforcing D to be green again. A’s other neighbouring vertices E and F analogously are assigned blue and yellow, or vice versa, enforcing in turn G to be green. This conflicts with G’s neighbour D to be green, too, thus demonstrating that arbitrary unit-distance graphs require at least four colours.

Fig 3: a) An equilateral triangle as a simple example for a unit-distance graph. b) The Moser spindle is a four-colourable unit distance graph [3].

After many years of intractability only this year there was some significant progress in closing in on the Hadwiger–Nelson problem. It was demonstrated that “the chromatic number of the plane is at least 5” [5], by finding two non-four-colourable unit-distance graphs (with 20425 and 1581 vertices). The smallest unit-distance graph with chromatic number five found this year has 553 vertices [6] and is shown in fig. 4. Whether the chromatic number of the plane is five, six, or seven still remains to be shown.

Fig 4: Five-colourable unit distance graph with 533 vertices. The fifth colour (white) is only used in the centre. [6]


— Alexander Kronenberg

[1] Heawood, (1890), “Map-Colour Theorems”, Quarterly Journal of Mathematics 24, pp. 332–338

[2] Appel, Haken, (1989), “Every Planar Map is Four-Colorable”, Contemporary Mathematics 98, With the collaboration of J. Koch., doi:10.1090/conm/098

[3] Soifer, (2009) “The Mathematical Coloring Book”, Springer

[4] Hadwiger, (1945), “?berdeckung des euklidischen Raumes durch kongruente Mengen”, Portugal. Math. 4 ,pp. 238–242

[5] de Grey, (2018), “The chromatic number of the plane is at least 5”, arXiv:1804.02385

[6] Heule, (2018), “Computing Small Unit-Distance Graphs with Chromatic Number 5”, arXiv:1805.12181

Why do alkali metals actually explode in water?

 Question of the Month  Comments Off on Why do alkali metals actually explode in water?
Nov 222018

It is one of the most common educational experiments in school and straight from the books: The reaction of an alkali metal with water. During this reaction significant amounts of hydrogen gas are produced, which can ignite and thus explode due to the strongly exothermic reaction – at least that is the explanation one finds pretty much everywhere. However, there is something odd about this reasoning. On the one hand, a complete immersion of the metal within water should then prevent the explosion from happening as no oxygen is present to ignite the hydrogen gas. On the other hand, it is surprising that the solid-liquid interface of this heterogeneous reaction creates enough physical contact to drive the reaction. Additionally, the produced gas tends to separate the educts and therefore stop the reaction. Overall, there are quite a few unclear details in this proposed reaction mechanism.

A study of the Czech Academy of Sciences in Prague and the Technical University of Braunschweig, however, showed that even in presumably clear textbook reactions a lot of surprises may be found sometimes. [1,2] The scientists used drops of sodium-potassium alloy that is liquid at room temperature and filmed the reaction with high speed cameras. They could show that the explosive reaction also happens under water when the metal is completely immersed, thus ruling out the ignition of the hydrogen gas as the main driving mechanism for the explosion. Supported by molecular dynamics simulations, they instead showed what mechanism actually drives the reaction: A Coulomb explosion! During the reaction of a clean metal surface with the adjacent water molecules, electrons move quickly from the metal atoms into the water. This also explains why a solid piece of an alkali metal does not always explode in water: it needs a clean interface without significant oxidation. After the electrons left the metal surface and moved into the water, a strongly charged surface is left. On this surface, the ionized atoms strongly repel each other, and thus open up a path to more inner atoms that have not taken part in the reaction yet. On a time scale of about 0.1 ms, metal dendrites shoot into the water (see figure) and suddenly increase the surface area of the metal. [1-3] This happens extremely fast with giant charge currents flowing in the interface region. The surface tension is pretty much nullified in this case [2,3] and the expanding surface provides more reactive area. As a result, large amounts of hydrogen gas are suddenly produced. Together, these effects drive the explosion, while the ignition of the gas is not directly necessary for the explosion to occur. Instead, the hydrogen gas can also burn off later. [2]

Further results of the study could lead to approaches to avoid metal-water explosions and thus gain application relevance in industry. What is however most unusual about this study is that parts of it got funded by the YouTube science channel of the lead author of the paper, which he explicitly acknowledges. In this exciting case, science and media are really in a close relationship.

As soon as a drop of NaK-alloy gets in contact with water (top left), fine metal fingers are protruding into the water (middle). These are driven by the Coulomb explosion that massively increases the surface area and therefore the reactive interface. As a result, a fast production of hydrogen becomes possible, which further drives the explosion (bottom left). The right column depicts the impact of a water droplet for reference. [1,3]

— Kai Litzius


[1] P. E. Mason et al., Nature Chemistry 7, 250–254 (2015).




The Spaghetti Turn

 Question of the Month  Comments Off on The Spaghetti Turn
Sep 282018

Certainly, most of us enjoy an occasional nice bowl of spaghetti. Some of us use a spoon along with the fork, some don’t. Doesn’t matter, as long as you enjoy and don’t make a mess ?

But have you ever wondered if there is a preferred direction to turn the screw? And is it related to where you live? We did!

Please take a minute of your time and participate in our survey to enlighten the world.


If you are both-handed, please choose your preferred direction for right- and left-handed.

It is irrelevant whether you use a spoon in addition or not.

Please don’t shovel. That’s rude

The results will be published on Spaghetti Day (Jan 4th, 2019) on

The Spaghetti Turn

How does a candle burn in zero gravity?

 Question of the Month, Uncategorized  Comments Off on How does a candle burn in zero gravity?
Jul 172018

We are all familiar with the appearance of a candle flame. Warm, bright yellow, and formed like a teardrop it nestles up the wick just to reach far out into the empty above it. This behavior can be easily explained by the rise – the convection – of the less dense air that is heated by the combustion around the wick. While colder, more dense air floats inward, the buoyancy of the warm air lets it move upward and away from the combustion zone. However, this process requires buoyancy, which only exists in an environment with gravity. But what would then happen to a flame in zero gravity?

In so-called microgravity, that is an environment with very little gravity like it is present in the Earth’s orbit, there is no convection since there is no definition of a classical “up and down”. The flame therefore looks significantly different and forms a light blue, spherical shape instead of the familiar teardrops. To understand this behavior, one has to consider the chemistry of the combustion as well as the physics of the gas exchange.

In case of the “normal” candle flame, the bright yellow color stems from soot particles that originate in the (non-perfect) combustion. They rise with the hot air and glow yellow in the upper region on the flame. The lower blue-ish region on the other hand is fed by the stream of fresh oxygen-rich air from below. In case of the flame in microgravity, there is no preference for up and down and therefore it assumes a spherical shape. Due to the lack of conversion, the combustion is fed only by (slow) diffusion of the oxygen into and the fuel out of the central combustion zone. This means that the zero-gravity flame burns much slower and does not produce equally distributed soot particles. Thus it is blue, spherical, and produces much more CO and formaldehyde than CO2, soot, and water.

This behavior, and how to extinguish a flame in microgravity, is under investigation aboard on the International Space Station (ISS) in the so-called FLame Extinguishment Experiment (FLEX). It is carried out on small heptane bubbles that are ignited in a controlled atmosphere. The experiment found that such small flame bubbles are not just exotic to look at, but also can pose a threat to space exploration since they can be much more difficult to extinguish. In this way, research on small bubbly flames can thus help making space exploration a bit safer.

A candle on Earth (left) and in microgravity (right): The different combustion patterns are clearly visible. [3, NASA]


— Kai Litzius






What is the Cause of Sonoluminescence?

 Question of the Month  Comments Off on What is the Cause of Sonoluminescence?
May 292018

Sonoluminescence is a fascinating, mysterious physical phenomenon, that combines the principles of light and sound.

In the year 1934 H. Frenzel and H. Schultes discovered a luminous effect by ultrasonication of water.[1] The defining moment that leads to sonoluminescence is the emergence of a cavitation in the liquid (figure 1). The high frequency ultrasound leads to the formation of bubbles, that are filled with gas and expand and collapse rapidly like a shock wave. Shortly after the collapse, the energy is released in form of sound and a short lightning, which is barely observable with the bare eye and reaches temperatures up to 10,000 K.[2,3]

Figure 1. Schematic illustration of the formation of sonoluminescence (f.l.t.r.): Growth of a gas bubble in a liquid, collapse or implosion of the bubble and emission of light.[4]

In the 1990s, the causes and impacts that lead to sonoluminescence have been intensively investigated but the real cause of this phenomenon remains unresolved even nearly 85 years after its discovery.[5,6] There are different quantum mechanical approaches, but they are highly controversial.[7,8]

Sonoluminescence is not only a physical phenomenon, it does indeed show capability for an academic application, at least in chemistry: in 1991 Grinstaff et al. were able to generate nearly pure amorphous iron by ultrasonication of an iron pentacarbonyl solution in decane. Compared to crystalline iron this compound shows enhanced catalytic activity when used in the Fischer-Tropsch process.[3]

Sonoluminescence also occurs in wildlife: by snapping their claws, pistol shrimp create a sharp stream of water that does not only kill prey but generates a cavitation bubble and thus a short lightning. Scientists call this special phenomenon “shrimpoluminescence”.[9]


— Tatjana Daenzer



[1] H. Frenzel, H. Schultes, Z. Phys. Chem. 1934, 27, 421–424.

[2] B. P. Barber, S. J. Putterman, Nature, 1991, 352, 318–320.

[3] K. Suslick, S.-B. Choe, A. A. Cichowias, M. Grinstaff, Nature, 1991, 353, 414–416.

[4] „Creative Commons“ from Dake CC BY-SA 3.0. ( last access: 15.05.2018.

[5] B. P. Barber, C.-C. Wu, R. L?fstedt, P. H. Roberts, S. J. Puttermann, Phys. Rev. Lett. 1994, 72, 1380–1383.

[6] R. Hiller, K. Weninger, S. J. Puttermann, Science, 1994, 266, 248–250.

[7] C. Eberlein, Phys, Rev. Lett. 1996, 76, 3842–3845.

[8] R. P. Taleyerkhan, C. D. West, J. S. Cho, R. T. Lahey Jr., R. I. Nigmatulin, R. C. Block, Science, 2002, 295, 1868–1873.

[9] D. Lohse, B Schmitz, M. Versluis, Nature, 2001, 413, 477–478.

Apr 012018

“Dr.” Martin Luther plagiarized in his dissertation

LutherPlag checks

Theology professor Kim Lee-jung of Luther University in Giheung-gu, Yongin, South Korea, reports that he found the doctoral thesis of Martin Luther. The title: Iocorum Encomium (In Praise of Jokes). This discovery is in itself an epochal event. The sensation beyond that: up to 80 percent of the work is plagiarized.

Martin Luther’s is one of the best-researched lives in German history. So far it has been assumed that the reformer never submitted a dissertation, since he never mentioned such an endeavor in his writings, his letters or his diaries.

According to the trilingual press release of South Korean Luther University (see below), theology professor Kim has discovered and examined the dissertation of Martin Luther. The amazing thing is that Martin Luther apparently plagiarized massively in his dissertation. Whole passages are believed to come from a text by his humanist colleague, the Dutch theologian Erasmus of Rotterdam, says Kim.

On his spectacular find and on the content of Luther’s dissertation professor Kim will publish an article in the American Journal of Protestant Theology. In his article he will also address the question: How could such an upright man as Martin Luther do such a thing?

The Korean professor of theology has noticed that countless monuments in Germany refer to the reformer as “Dr. Martin Luther”, whereas in America the academic title is completely absent in his naming. As a reason for this, Kim suspects a cultural preference that arose in Germany during Luther’s lifetime.

“A doctor’s degree seems to be very important to Germans,” he supposes. Even Martin Luther, perhaps the most German of all Germans, may not have resisted this temptation. His example was later followed, among others, by Doktor Faustus, Doktor Allwissend, Dr. h. c. Erich Honecker, Dr. Karl-Theodor zu Guttenberg.

The news has attracted a lot of attention worldwide. Internet activists have set up LutherPlag and run the text through the plagiarism software. Already, it has been said, up to 80 percent of the text consists of plagiarism.

Meanwhile, at Martin Luther University in Halle-Wittenberg, there are unofficial debates going on whether or not to strip Luther of his academic title. This university is the successor of the University of Wittenberg, where Luther submitted his doctoral thesis on 19 October 1512. What would the divestiture mean? Should the title at the dozens of Luther statues in Germany be removed and all the publications on “Dr. Martin Luther” have an erratum attached?


Professor Kim Lee-jung had no idea what consequences his discovery would have. In a telephone conversation with JUnQ, he said: “It is about time, however, that thinking about Martin Luther enters into a postheroic and postmonumental, even into a postdoctoral phase. That’s what I stand for as a scientist, I can do no other.”

Dr. Antje Käßmann for Journal of Unsolved Questions

Mainz, April 1st; 2018



For further information please click here: website.


War der Reformator ein Plagiator?

Dr.” Martin Luther hat in seiner Dissertation abgeschrieben – LutherPlag prüft

Der Theologieprofessor Kim Lee-jung von der Luther University in Giheung-gu, Yongin, Südkorea, berichtet, er habe die Doktorarbeit Martin Luthers gefunden. Der Titel: Iocorum encomium (Lob der Scherze). Diese Entdeckung ist an sich ein Jahrhundertereignis. Die Sensation darüberhinaus: bis zu 80 Prozent der Arbeit sollen abgeschrieben sein.

Die Biographie Martin Luthers gehört zu den am besten recherchierten Leben in der deutschen Geschichte. Bisher ist man davon ausgegangen, der Reformator habe nie eine Dissertation vorgelegt, da er weder in seinen Schriften, noch in Briefen oder Tagebüchern ein solches Bemühen erwähnt habe.

Laut der dreisprachigen Pressemitteilung der südkoreanischen Luther University (siehe unten) hat der Theologieprofessor Kim Lee-jung die Dissertation Martin Luthers entdeckt und untersucht. Das Erstaunliche ist, dass Martin Luther in seiner Dissertation anscheinend massiv plagiiert habe. Ganze Textpassagen sollen aus einer Schrift seines humanistischen Kollegen, dem holländischen Theologen Erasmus von Rotterdam stammen, behauptet Kim.

Über den spektakulären Fund und über den Inhalt der Lutherschen Dissertation wird Professor Kim einen Aufsatz im American Journal of Protestant Theology publizieren. Darin wird er sich auch der Frage widmen: Wie konnte ein so geradrückiger Mensch wie Martin Luther so etwas tun?

Dem koreanischen Theologieprofessor ist aufgefallen, dass die unzähligen Denkmale in Deutschland den Reformator stets als „Dr. Martin Luther” ausweisen, wohingegen man in Amerika auf den akademischen Titel bei der Namensnennung komplett verzichtet. Kim vermutet als Grund eine kulturelle Vorliebe, die in Deutschland zu Luthers Lebzeiten aufkam.

„Die Doktorwürde scheint den Deutschen sehr wichtig zu sein”, schätzt er. Selbst Martin Luther als vielleicht Deutschester aller Deutschen habe wohl der Versuchung nicht widerstehen können. Seinem Beispiel folgten später u.a. Doktor Faustus, Doktor Allwissend, Dr. h. c. Erich Honecker, Dr. Karl-Theodor zu Guttenberg.

Die Nachricht hat weltweit große Aufmerksamkeit erregt. Internet-Aktivisten haben LutherPlag eingerichtet und jagen den Text durch die Plagiatssoftware. Schon jetzt wird von einem bis zu 80-prozentigen Plagiat gesprochen.

Inzwischen wird an der Martin-Luther-Universität zu Halle-Wittenberg inoffiziell diskutiert, ob man Luther den akademischen Grad aberkennen müsse. Diese Universität ist die Nachfolgerin der Universität Wittenberg, wo Luther am 19. Oktober 1512 seine Doktorarbeit eingereicht hat. Was würde die Aberkennung bedeuten? Müsste der Titel von den Dutzenden Lutherdenkmälern in Deutschland mechanisch getilgt werden und all den Publikationen über „Dr. Martin Luther” ein Erratum beigefügt werden?

Professor Kim habe nicht geahnt, welche Konsequenzen seine Entdeckung nach sich ziehen würde. In einem Telefonat mit JUnQ sagte er: „Es ist aber an der Zeit, dass der Umgang mit Martin Luther in eine postheroische und postmonumentale, ja sogar in eine postdoktorale Phase eintritt. Dafür stehe ich als Wissenschaftler, ich kann nicht anders.”


Dr. Antje Käßmann für Journal of Unsolved Questions

Mainz, 01. April 2018



Für weitere Informationen klicken sie bitte hier: website.


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