Questions of Week

Jul 242017

Put a raw egg on a flat table, and give it a good spin with two fingers. The egg spins, however, rather slowly because the liquid inside poorly exchanges momentum with the outside shell. Thus, when you spin the egg by applying force to the shell, most of the inside resists the motion and the friction forces between the inside (immobile) and the shell (mobile) will be slowing down the egg’s speed. But if you consider a cooked egg, proteins contained inside the egg are now forming a solid phase that is tightly joint to the shell. In that case, there are no friction forces in the “egg system” and the movement is not slowed down.


In this case now, the only existing friction forces are those between egg and the support (the table) and the air (which can be reasonably neglected). If your initial momentum transfer is strong enough, you observe a strange phenomenon: the spinning egg starts to rotate upright.

The physical concept used to explain this phenomenon is inertia. Spinning ice skaters can reduce their moment of inertia by pulling in their arms, allowing them to spin faster. You can also sit on a swivel chair and spin on yourself. Extend your arms horizontally and you will slow down.  The same is happening with the egg. Friction forces tend to slow down the egg, and decrease overall energy. To save energy, like the skater, the egg stands up and the momentum of inertia consequently decreases.

To spin upright, the egg needs some energy, exactly as one needs some energy to get up in the morning, fighting against gravity. The necessary energy is provided by the rotation itself, and the change of orientation of the egg will only happen if the spinning is fast enough.




Video movement of interia

Bou-Rabee, N. M., J. E. Marsden, and L. N. Romero, A geometric treatment of Jellett’s egg, Angew. Math. Mech. (ZAMM) 85, (2005), 618-642

Jul 102017

Ordinary glass as it is used for windows can exhibit exceptional behaviors and even shred a riffle bullet to pieces, furthermore it can help to make car windows safer and to understand the inner processes in volcanos.

Key to all these fascinating properties are the so-called Prince Rupert’s Drops. These structures are solidified drops of glass, which are produced by letting a drop of molten glass fall into a bucket of water. The sudden shock caused by the massive temperature drop on the surface of the glass basically locks in the outer shape of the drop, preserving main body and tail. (Fig. 1) [1,2,3].

Fig. 1: Prince Rupert’s Drops. The thick main body with the long, thin tail is well visible (Copyright: public domain). [1]

This object has now very unique properties: If the main body of the droplet is hit by a hammer, it practically never breaks. It even withstands a direct hit of a riffle bullet, whereas the bullet can be completely shred to pieces. All this the main body of the glass droplet can stand without breaking. However, if there is too much force applied to the fragile tail of the Prince Rupert’s Drop, or if it is even just nicked, the whole drop explodes into tiny pieces of glass that can spread over several meters. [4,5]

To understand how this fascinating behavior is created, we have to have a closer look at how the drop is created. Everything starts with a drop of hot, molten glass, suddenly getting in contact with water. As mentioned, the outer layer of the drop immediately solidifies and locks in the characteristic drop or tear shape. The thin tail is created when the drop detaches from its origin (e.g. the glass rod) and starts falling and also gets locked into its shape when touching the water for the first time. While the outer layers are now already solid glass, the interior of the drop is still a hot liquid (Fig. 2 top). Consequently, this glass contracts while cooling down and starts pulling the solid outer layers inward, stressing them just like an arch bridge is stressed (compressive strain) and thereby stabilizes the structure. Along the axis of the drop, however, the strain is not compressive but tensile, because the shrinking material tries to pull along the tail.

Fig.2: Mechanism of creation of a Prince Rupert’s Drop. The hot, liquid interior of the drop compresses against the already hardened outer shell. The result is a highly strained structure (Copyright: CC-BY JUnQ). [4,5]

These stresses make the round shaped main body of the drop extremely resistant to external disruptions, whereas the tail constitutes a weak spot (Fig. 2 bottom). If the latter is now damaged in any way, the energy stored in the mechanical stress can be released and a mechanical failure front runs through the material, destroying more and more of it until the main body is shredded into dust. This process can happen with a speed of around 1600m/s, just like an explosion, and it usually only ends with the pulverization of the whole drop. Thus, this is the secret of the Prince Rupert’s Drop; it is always experiencing extreme internal stress that makes the convex part so extremely stable (like an arch bridge) that even riffle bullets shatter on them.

Finally, in its cooled state, the drop represents a system that exhibits extreme internal stresses. These stresses make the round shaped main body of the drop extremely resistant to external disruptions, whereas the tail constitutes a weak spot (Fig. 2 bottom). If the latter is now damaged in any way, the energy stored in the mechanical stress can be released and a mechanical failure front runs through the material, destroying more and more of it until the main body is shred to dust. This process can happen with a speed of around 1600m/s, just like an explosion, and it usually only ends with the pulverization of the whole drop. Thus, this is the secret of the Prince Rupert’s Drop; it is always experiencing extreme internal stress that makes the convex part so extremely stable (like an arch bridge) that even riffle bullets shatter on them.

So, we can ask whether this effect can be useful for anything. The answer is yes, indeed. Exactly the same principle is used in tempered glass like it is used e.g. in car windows. This glass does not shatter into sharp shards, but instead produces relatively smooth and small pieces and therefore is less harmful for the passengers of the car in case of an accident. Currently, Prince Robert’s Drops are even researched to understand better the quick cooling of volcanic lava under certain circumstances and therefore the inner processes within a volcano. Thus, all in all, these fascinating objects are full of wonders.

— Kai Litzius

Jan 162017

Have you ever wondered why rubbing alcohol, i.e. isopropyl alcohol, which is used to disinfect cuts burns so much when applied to the wound? As my mother always said: “As long as it burns, it helps”. This didn’t help me much as a kid, anyway. But why does it burn in the first place? Do you feel the bacteria die? Do some of your cells get killed, too, and you feel that?

Feel the burn.

Feel the burn.

In fact, neither is true. Interestingly, the pain you feel is due to a heat reaction. But wait, doesn’t alcohol usually give you a cool sensation when applied to the skin? True, but when the alcohol is able to penetrate your skin, e.g. when you have a cut, it gets in contact with your vanilloid receptors-1 (VR1). These are heat-gated receptors that normally get activated when the temperature rises above 42 °C, sending a painful sensation to prevent tissue damage by overheating. But why do your VR1 send a pain signal, even though the temperature does not rise above 42 °C? A study, a few years back, showed that alcohol has a similar effect on VR1 as capsaicin, the substance from chilies responsible for the hot taste.[1] Alcohol and capsaicin “trick” the VR1 by lowering the switch temperature from the above mentioned 42 °C to roughly 34 °C. Accordingly, your body temperature is high enough to induce an alert signal of VR1, giving you a burning (heat) pain even though your tissue isn’t nearly hot enough.

Maybe it helps you in the future when disinfecting wounds (or eating hot food) when you think that the pain is not real but rather a trick by played due to your heat receptors.

–Andreas Neidlinger

[1] M. Trevisani, D. Smart, M. J. Gunthorpe, M. Tognetto, M. Barbieri, B. Campi, S. Amadesi, J. Gray, J. C. Jerman, S. J. Brough, D. Owen, G. D. Smith, A. D. Randall, S. Harrison, A. Bianchi, J. B. Davis, P. Geppetti, Nat. Neurosci. 2002, 5, 546-551.

Jan 082017

According to media reports, the Italian neurosurgeon Dr. Sergio Canavero will attempt the first transplant of a human head (cephalosomatic anastomosis) in the end of 2017.[1] Valery Spiridonow is volunteering for this project since he suffers from spinal muscular atrophy (SMA) and believes the surgery will offer a chance to escape from this fatal disease.[2]

Similar experiments have already been performed more or less successfully on animals. In some cases, the animals survived but they remained paraplegic and their cardiovascular and respiratory systems had to be supported. Also they did not survive quite long after the surgery.[3,4] In fact, many experts are strongly doubting the success of this highly expensive transplant too.

Head Transplant : Fact or Fiction ?

Head Transplant : Fact or Fiction ?

Even if it might become a 100 % success, there remain a lot of serious questions:
– Will the patient (the head) be mentally and emotionally the same person as before?
– Will the brain be able to cope with a completely strange body and vice-versa?

Of course, Spiridonow will first have to find a donor for the body. He needs the body of a physically healthy man suffering from cerebral death and the consent of his relatives. Spiridonow’s new body will have the genome of the donor, so what are the legal consequences for any offspring regardless of whether they were conceived before or after the transplant?

So once again we are confronted with the problem of how far mankind can go to explore the possibilities of science and consider ethics at the same time. I think we should be excited and enthusiastic for the outcome of this dramatic surgery if it is going to happen anyway.

— Tatjana Daenzer

Read more:
[3] Canavero, Surg Neurol Int. 2013, 4, 335.
[4] Canavero, Surg Neurol Int. 2015, 6, 18.

Nov 162016

Touchscreens are getting more and more important for modern media. The most striking advantage of this technology is the combination of intuitive in- and out-put devices, which allow the user to directly interact with the system and vice-versa. But how does such a screen work, which types are available, and why do certain type of touchscreens react to fingers, but not to a normal pen? These questions we will answer in this week’s featured question.

How a resistive screen works?

How a resistive screen works?

One of the first touchscreen technologies (that is still in use nowadays) is the so-called resistive screen. This specific screen type is composed of two conductive, relatively transparent layers (usually indium-tin-oxide (ITO)), which are held separated at a small distance by spacer dots. To the bottom layer, a small voltage is alternatingly applied in x- and y-direction, while the top layer connects to the second half of the circuit. They are capped by a stiff, but bendable layer and directly sit on the actual display. Touching the screen with a little bit of pressure bends the conductive layer on top and closes the circuit. The resulting currents along the x- and y-circuits can be measured and provide information about where the circuits are closed. The idea is that the longer the current path , the higher becomes the electrical resistance. This technology is still commonly found in cheaper devices and in devices meant to be operated with gloves and can yield high accuracy. However, due to the mechanical deformation the screen has a finite lifetime.

How a capacitive screen works?

How a capacitive screen works?

The second, and probably most common, technology is used in “projected capacitive screens”. Those screens are composed of two grids, rotated at 90° to each other, of very fine conductive wires (usually ITO deposited on glass) with spacers in between. In contrast to the resistive screens, they do not form a continuous layer. Instead, the ITO grids create a large amount of crossings, which act like little capacitors whose capacity changes whenever a conductive or dielectric object (like a finger) approaches the grid. A digital controller measures now the capacity of all grid points one by one and if a certain deviation from the saved standard value is reached, a touch is registered. This technology allows multi-touch applications since all grid-points are measured separately and the image quality is enhanced due to the lower amount of ITO between the user’s eye and the actual display. However, these touchscreens need specific materials to be able to detect a signal and barely work with thick gloves or normal pens due to the fact that the capacity does not change if a standard insulator (like plastic) is brought close to it.

There are far more types of touchscreens based on, e.g. infrared light, inductive coils, sound and the piezoelectric effect. However, the two types, mentioned here, are the most commonly found ones nowadays. In the future, there might exist even more sophisticated types of human-interface-devices (HIDs), but at the current time, touchscreens still are one of the most successful HIDs and were able to widely repress the simple push-buttons.

–Kai Litzius

Further reading:

Nov 062016

There have been already two Questions of the Week about the weather: “Can we control the weather?” ( by Nicola Reusch and “Is accurate weather forecast possible?” ( by myself. Today, I do not want to go into detail about the meteorological work, but demonstrate a mathematical theorem by the means of weather.

You certainly heard about antipodes, i.e. points that lie on diametrically opposite sides on the earth’s surface. If you’d like to have a look where your antipode is at the moment, check refs. [1] and [2]. Now, these two parts of the earth are the farthest apart from each other as you can get, while staying on the ground; with the exemption that they are a little closer, when you are at sea level on both ends than they are when you are on top of Mount Everest on one side. Think about how different the climatic conditions must be between those two antipodal points. What if I told you that at any moment there are at least two antipodal points on earth’s surface which share the same temperature and air pressure. Would you believe me?

No? So too what I thought at first. But let me reveal that it’s true. Take a look at Fig. 1(left). There you see the two antipodes A and B. If we measure the temperature of both points and they are identical, fine, we did our job. But most likely this won’t happen. If we move from the original point A to point B on any path while keeping A and B antipodal points (Fig. 1, middle), the temperatures of the two points will swap (Fig. 1, right). Therefore, there must be at least one set of antipodal points, where the temperature of A and B is identical, since swapping would be impossible otherwise.

Fig. 1: Two antipodal points A and B (left), antipodal paths from A to B (middle), and swapped points A and B (right).

Fig. 1: Two antipodal points A and B (left), antipodal paths from A to B (middle), and swapped points A and B (right).

Since swapping will occur on one set of points on a given antipodal path, you can imagine a line separating hemisphere A from hemisphere B on which any pair of antipodes will have equal temperature (Fig. 2). If we check air pressure on one set of antipodal points, we most likely won’t find matching values. But we can also be certain that both values will swap, if we move from one point to the other, while staying on the equal temperature path from Fig. 2.

Fig. 2: Antipodal points on earth’s surface with equal temperature.

Fig. 2: Antipodal points on earth’s surface with equal temperature.

Therefore, we must find one pair of antipodes with equal temperature and equal air pressure on earth’s surface at any given moment. Fascinating, isn’t it? This is called the Borsuk-Ulam Theorem.[3] It is a mathematical theorem which remarkably illustrates that results which seem impossible can in fact be true, if you keep investigating in a scientific manner.

–Andreas Neidlinger


Oct 092016

What is the most useful invention of humans? Sure, most people will answer this question with “The Wheel!” Indeed, today almost any machine runs with some kind of wheel. But do we know whom to thank for this gift? Let’s take a little journey back through time.

Rewind to our greatest invention.

Rewind to our greatest invention.

Of course there was a time before the wheel, around 5000 BC. People used slides and logs of timber to transport goods. During the Bronze Age (ca. 3500 BC), wheels of clay and of wood were being attached to carts. Records of those first wheels are found in different cultures of the same age. For a long time, it was believed that the Sumerians from Mesopotamia were the inventors of the wheel. But new findings prove that other cultures from Western and Eastern Europe of the same age built something similar. The main difference of those earliest constructions were in the suspension – some were rotating with the axis, some were rotating around it.

Over the ages, this technology spread all over the world. The wheels became lighter and more stable. The development of trade, technology and (even) warfare, is due to the wheel. The wheel has made it possible for us to wonder at all the modern engineering marvels.

Still it is unlikely to identify a group of people – not to mention a single person – as the inventors of the wheel. To imagine what fortune one would amass today from such an invention…

– Tatjana Daenzer

Read more:

Oct 032016

The story of music and human cognition is intricate and intertwined from the beginning. Since close to fifty millennia, music has remained an integral part of being human.[1]

Music has always aroused feelings of rapture and desire, even though it is intangible. And now science has unlocked the mechanism. As the reward center in the brain gets primed with the anticipation of listening to familiar music, there is a flood of dopamine, the “happiness” neurotransmitter.[2] Things can get discordant too. If one listens to unpleasant music, there is a reduced production of serotonin, our mood-regulator.[3]

Music for peace of mind.

Music for peace of mind.

It is quite natural to ask, if the audience is experiencing euphoria, what is the artist feeling ? Well, scientists have looked into that aspect as well.

The brains of musicians light up like a celebration of fireworks when they play.[4] The left and right hemispheres enter in a harmonious exercise when an artist performs on their musical instrument.

But can music improve how we interact with life ? And the answer is a resounding “YES”.

Learning an instrument with structured and disciplined practice, has an array of benefits.[5] It can enable us to find more creative solutions to problems in social as well as academic settings. Playing music makes for a greater neural plasticity in the brain which can better help with retrieving and indexing information – in short, a better functioning memory.

Even though we know what neurotransmitters are responsible and the neural pathways they seem to take in the brain when we hear music, still there is so much more that we do not know. For instance, the auditory cortex is still quite unknown to us in its organization and functions. Only recently, there was a discovery of two separate populations of neurons, sensitive to how we process music and human speech, different from ambient sound in the environment.[6] Though, it is still a question of speculation – are we born with it or is it developed through experience.

Four hundred years have passed since William Congreve remarked, “Musick has Charms to sooth a savage Breast”. Music, has indeed, displayed the ability to heal. It has shown promise to improve the lives of those affected with schizophrenia.[7] As music also helps in better connecting our episodic memory, it can have a positive influence in individuals suffering from Alzheimer’s or PTSD.

So let’s tune in to some nectar for the brain and turn those frowns upside down.

– Soham Roy

[2] Salimpoor, VN et al. Nature Neuroscience, 14, 257–262 (2011).
[3] Evers, S et al. Eur Arch Psychiatry Clin Neurosci., 250, 144–7 (2000).
[5] Miendlarzewska, EA et al. Front Neurosci., 7, 1–18 (2013).
[6] Norman-Haignere, S et al. Neuron, 88, 1281–1296 (2015).
[7] Talwar, N et al. BJP, 189, 405–409 (2006).

Aug 162016

You certainly know the game little kids play where they have a cube, a sphere and a pyramid, and they have to put them through holes of the corresponding shape. In the beginning, this might be difficult, but it becomes quite easy and dull after some time. Now, it is simple for most people, but how difficult is the same task for blind people? i.e., Can people who have been blind for their entire life and are familiar with different shapes by their tactile sense, recognize the same shapes when they gain the ability to “see”?

This question, referred to as the Molyneux Problem, was first asked by William Molyneux, an Irish philosopher and politician, in 1688.[1] Of course, answers that could verify this question were not easy to find in the 17th century due to the impossibility of highly complex surgeries at that time. Nevertheless, a lot of discussions arose about the co-operation between our senses. For instance: Is the eye able to understand the geometry of objects or is the visual recognition just possible by a learned collaboration with the tactile sense?[2] Or the other way around: How do blind people understand shape; how do they “look” for them?

Just recently, in 2011, five children, who were born blind, became able to see after surgery at the ages between 8 and 17. They were familiar with several shapes by examining them with their hands. Interestingly, they were not able to relate this tactile information with the visual input from these objects, but they learned to connect both senses quite fast.[3] However, discussions are still not at an end, to unequivocally explain the outcomes.

The Molyneux Problem once again shows that even simple questions can result in long-lasting discussions and unexpected outcomes. Never stop asking questions and dig through the JUnQ to find the hidden treasures!

— Andreas Neidlinger

[1] W. Molyneux: Letter to John Locke, 7 July 1688, in: The Correspondence of John Locke (9 vols.), E.S. de Beer (ed.), Oxford: Clarendon Press, 1978, vol. 3, no. 1064.
[2] S. Pasewalk: „Die fuenffingrige Hand“: Die Bedeutung der sinnlichen Wahrnehmung beim spaeten Rilke, De Gruyter; Auflage: 1., 2002, pp. 106.
[3] R. Held, Y. Ostrovsky, B. de Gelder, T. Gandhi, S. Ganesh, U. Mathur, P. Sinha, Nat. Neurosci. 2011, 14, 551–553.

Aug 072016

Lying on the grass and looking into a sparkling star-filled summer sky. Can there possibly be anything more beautiful? But it also makes me think about how small we really are and are we truly alone in the universe. This question has bothered humans since the beginning of our existence.

In the observable universe, there are at least 100 billion galaxies containing 100-1000 billion stars each. Not to mention the gigantic number of existing planets surrounding those stars including trillions of habitable ones. Consequently, there must be plenty of opportunities for alien life to develop.

But is the contact with extraterrestrial life really that likely? It has to be mentioned, that a huge number of existing galaxies are completely out of reach because of the expansion of the universe. Only the ones being part of our local group come into consideration for a theoretical alien contact. Anyways, if life had developed only on 1% of all planets in habitable zones in the Milky Way, there would be millions of planets inhabited by aliens. Since life on earth emerged rather late compared to the age of the Milky Way, potential super-intelligent and technologically advanced aliens would have had much time to build powerful space ships and to make a trip to our blue planet. In fact, if those guys would have been able to build generation space ships, they could colonize the Milky Way in a few million years. And that is not a long time when we think that life on earth exists since 4 billion years and the fact that other planets might have had developed life long before earth did. So if only one of those theoretical alien races would have developed into a super-technological civilization, shouldn’t we know by now?

So where are all the aliens? Why did they not contact or – in a bad scenario – attack us so far? This lack of proof for aliens despite its apparently high probability is called the Fermi Paradox, named after the physicist Enrico Fermi.

There are different scenarios which can resolve the Fermi Paradox and some of them are quite amusing and imaginative. Here is a small selection:
1. In spite of the apparent high probability, we are alone in the universe. We might always have been and always will be. The condition for the emergence of life could be much harder and complicated than we assume.
2. There were intelligent aliens long before humans came into existence. They could have gone extinct before someone on earth ever thought about extraterrestrial life at all. Indeed, we do not know everything concerning different thresholds life has to overcome in order to survive. We might just be lucky that we do not yet have encountered one really tough barrier, like the dinosaurs obviously did. Or maybe at some point, every sophisticated culture will destroy itself by inventing a highly destructive super-weapon.
3. Our extraterrestrial friends want to observe us in order to do psychological studies or maybe we are just part of some “galactic zoo” for aliens. They also might just wait until we are a threat to them and then kill us. This has also been a topic in various science fiction books.
4. Life forms from outer space are already among us and we do not notice.
5. The aliens are simply not interested in having communication or imperialistic wars with anyone else and stay peacefully and happy on their home planet.
6. The universe is full of extraterrestrial signals but we are not advanced enough to detect them.

Maybe there will be a day in the future when we get a more definite answer to the Fermi Paradox. Let’s just hope it will be a salubrious one!

– Jennifer Heidrich

Read and watch more:
— M. H. Hart: Explanation for the Absence of Extraterrestrials on Earth. Quarterly Journal of the Royal Astronomical Society. 1975, 16, 128.
— A. Frank and W.T. Sullivan: A New Empirical Constraint on the Prevalence of Technological Species in the Universe. Astrobiology. 2016, 16, 359.
The Fermi Paradox — Where Are All The Aliens? (1/2)
Drake’s Equation – A Deep Dive | Answers With Joe