Random thoughts about random subjects… From science to literature and between manga and watercolours, passing by data science and rugby; including film, physics and fiction, programming, pictures and puns.
I could not help smiling widely as I was leaving that shop earlier on today… Why? Well, I was there to buy some bits and pieces. I arrived listening to some music and once inside the shop I hang my headphones around my neck. When I approached the counter the following conversation happened:
– “Is that all, love? Have you got a loyalty card?” – She asked
– “That’s all, thanks. No, I don’t have a loyalty card” – I replied
– “Oh, are you a doctor?” – She said
– “Ehhh?!” – I muttered, wondering how she knew… then realising she had mistaken my headphones by a stethoscope. – “Oh, well, no…” – I continued – “… well yes, I’m a doctor, just not a medical one” – I eventually replied.
– “Mmm, so what sort of doctor are you then?” – she queried
– “I’m a physicist…” – I shyly responded.
– “Oh really” – said the customer next to me – “have you watched ‘The Big Bang Theory’? It’s very funny”.
– “Yes, I have…” – I said – “very funny, yes… sometimes too close to home” – I confided.
– “Really?” – exclaimed both of them at the same time, with the customer adding “oh how exciting!!”.
– “Yes… oh well, thanks. Catch you later” – I said as I was leaving the place.
Continuing with the tradition of celebrating scientists birthdays, Google has marked Erwin Schrödinger’s anniversary with a Schrödinger Cat doodle.
Erwing Schrödinger was born on August 12th, 1887 in Vienna, Austria. He developed fundamental results in early quantum theory providing the basis to the so-called wave mechanics, formulating the eponymous equation at the heart of quantum mechanics. His famous cat paradox came up as a way to highlight contradictions with common sense brought up by the interpretation of quantum mechanics.
The Schrödinger cat is a gedanken experiment applied to macroscopic systems which draws our attention to discrepancies generated by the Copenhagen interpretation. Imagine that we put a cat into a sealed container together with a contraption that has a lethal poison which can be released if a radioactive substance in the device undergoes radioactive decay. If a single atoms decays, an alpha particle is detected and the poison is released, therefore killing the cat. The question is thus, before opening the box, can the observer tell whether the cat is alive or dead? Since the fate of the cat is tied to the quantum mechanical wave function of the atom then the question can be answered by knowing the state of the latter. Nonetheless, according to quantum mechanics the atom is in a superposition of decayed and undecayed states which would mean that the cat is itself in a superposition of dead and alive states! When the observer finally opens the container, the cat is “observed” and thus the wave function is “collapsed” into one of the two states.
Time flies, time is money, time is a wise counsellor, time is relative, time is… very hard to define. Paraphrasing St Augustine I can say that I know what time is if no one asks me, but if I try to explain it I simply do not know. It seems to be very natural to acknowledge the passing of time, however when we take a moment to think about its meaning, we quickly find ourselves with a few problems.
We start by arguing that time can be defined by the interval between two successive events and thus we need a ruler to measure that interval. This is indeed a quest that us humans have pursued since the dawn of civilisation; it is very easy to see how the definition of day comes about: it is the interval between two successive sunrises. Once we have this in place a lot follows effortlessly: on the one hand we can start taking smaller intervals and define hours, minutes, seconds, and on the other, it is now possible to refer to events taking place in the past, the present and even the future. The ordering of these three concepts is intuitive as time flows from the past to the future, and we even see it manifested in the objects around us. We can imagine that we go to a museum where a film installation is being shown. The film starts with a large red stain in an otherwise immaculately white carpet. The camera spans and we see some pieces of glass strangely being attracted to each other while the red stain starts to shrink. The next thing we see is a wine glass appear before our eyes and wine droplets jump into it as if by magic. It is immediately obvious that the film was played in reverse as there seems to be a natural “forward direction”. This directionality is often referred to as the arrow of time and whenever it is discussed the subject of causality arises, and even time travel.
When I mention causality I am referring to the relationship between causes and effects; in the case of the film I used as an example, the cause of the spill is shown to us as artist hits the wine glass. When the film is shown in reverse, we tangibly notice that there is something missing: the glass cannot “unbreak” out of its own accord. What does physics have to say about this? If we were to analyse the film using the laws of motion described by Newton, we would find that there is no difference between the forward and backward directions. In other words, time reversal is not prohibited anywhere in Newtonian mechanics. This means that, given a present state under specific conditions, we are therefore able to predict the future, but also retrodict the past, as there is no distinction between the two. This sounds surprising as this sort of thing does not happen in our daily lives.
Scientists have come up with their own versions of the wine glass film described above. In one case, they have taken two particles of light, known as photons, with certain energies and mashed them together; after the collision they observed a pion and a deuteron as a result of the collision. Do not be too concerned about what these two new particles are, this will not affect the discussion. When the film is reversed, it shows a pion and a deuteron colliding and producing as a result two photons. This new experiment has been realised and lo and behold the physicists observed the generation of the two photons as predicted, giving them a confirmation that the laws that govern these phenomena do not change when time is reversed. As you may have noticed, we have blatantly ignored the present, and this is because we think of it as a transitory state between the past and the future. In other words, the past is gone while the future has not arrived, and the ephemeral present expires as soon as we try thinking of it.
From this point of view, the result of these experiments seems to indicate that the arrow of time is embedded in our perception. It has been argued that the arrow of time is a psychological effect, and that this feeling that time flows mercilessly from the past to the future is all subjective. Let us take these arguments a step further, if indeed there is no difference between past and future, then there is nothing stopping us from travelling to the future (as we imminently do) or to the past (as we clearly are not). Believe it or not, but physics has something to tell us about this. I mentioned above that time reversal is allowed by Newtonian mechanics, so why can we not put together again the wine glass by time reversing the process, rather than supergluing the broken pieces? The answer is not in the realm of mechanics, but in that of thermodynamics, in other words the study of how energy converts between heat and other forms of energy. In that manner, physicists also talk about a thermodynamic arrow of time, in the sense that a given physical system invariably becomes ever more disordered, and since disorder is therefore important we quantify it with a quantity called entropy. This rule that tells us that entropy increases with time is known as the second law of thermodynamics. Following this line of thought, we are not allowed to fix our broken wine glass by running time backwards because it would imply going from a more disordered state to a more ordered one without using any extra energy, and so travelling to the past is not an easy task to achieve. What about travelling to the future, or in the direction pointed by entropy? Well, in that case there is certainly nothing that stops us in our tracks. In fact, as I pointed out earlier on, we are already travelling to the future, and we do that at a pace of sixty minutes an hour. However, if we wanted to travel to the future at a different rate, Einstein’s theory of relativity gives us a recipe to achieve this. In the so-called special theory of relativity the world has four dimensions: the usual three space dimensions that we know and love, i.e.. length, width and height; and one dimension that is related to time. In other words, when you walk from one place to another in the gallery where the wine glass video is being shown, you automatically change your position on the time coordinate, even if you don’t notice. Einstein tells us that if we were to travel at the speed of light, time expands from the perspective of a stationary observer, whereas space contracts from the point of view of the moving person. This brings into question the notion of simultaneity, as two events that seem to happen at the same time for the stationary person, could in principle happen at different times from the point of view of the moving person. It is fascinating to compare Einstein’s efforts to unravel the secrets of simultaneity in time, with Picasso’s cubism to depict simultaneity in space. The effect of time dilation has been experimentally confirmed with very precise caesium clocks. Unfortunately, it is completely outside of human experience, because we have not yet devised a way of travelling at speeds where relativistic effects become noticeable. Even if we were to spend our entire lives in a plane that moves at supersonic speed, we would barely win a second over our contemporaries on the ground.
So, time travel as presented to us in sci-fi films is not yet possible but that has not stopped us from imagining its consequences. As for the definition of time, I am sure that there are many other things that can be said on the subject. Unfortunately, time is a merciless master, and that is all the time and space I have for now.
Dr Jesús Rogel-Salazar
(originally appeared in Artesian : Issue Three : Time : 2011)
It turns out that in an effort to keep their recent building cool, the Vdara hotel in Las Vegas has come up with the idea of “energy-efficient” windows. ‘How do they work?’ do I hear you scream? Well, they are mirrored windows. The idea being that the desert Sun light is reflected out keeping the heat down inside the building… That would all be fine except that they have made the building curved and as such the entire 57-foot curved mirror is working as lens concentrating the light… The solar reflection is so strong that it has been dubbed the “Death Ray” hotel as it has already caused severe burns…
After posting this, I got to hear about a parody trailer for “Fryline”…
I have been meaning to write this post for a while, but for one reason or another (or rather many reasons…) I had not been able to. Right, so what has triggered this post? Well, I was having a look at a the BFI website as they usually have some very good films and event to attend and I happened to come across some news about Film Nation’s new programme on film education. You can have a look at the website here. Did you click on the link? Have you seen the title of the news item? If not, please take a look at the screenshot I include in this post.
That is right! They describe the new programme as a “quantum leap for film education”. I believe they want to imply that the programme is a great advancement, but I am not sure that describing it as a “quantum leap” conveys what they want. It is rather sad to see this sort of misuses and that is why I am writing this post.
So, a quantum is indeed a unit: it is the smallest amount of energy that a system can gain or lose, and this actually contradicts the message they want to communicate. The term “quantum” started being used in the early 1900s by Max Plank as part of a theory to explain the physics of the sub-atomic world. As such, light was thought as a tiny packet of energy (as well as a wave…) that could be emitted or absorbed by an electron in an atom for instance. As such a quantum leap is the smallest possible change in the energy level of that electron, and one that can take place at random.
So, who knows, perhaps the BFI (as well as others out there) do mean indeed to use “quantum leap” to describe these achievement… Or what do you think? Let me know and if you have any similar terms that get misused get in touch.
Materials that respond to the application of a magnetic field are described as magnetic materials. Magnetism can be attractive (paramagnetism) or repulsive (diamagnetism). Some materials are permanent magnets, this mess that their magnetic fields are persistent and they are caused by ferromagnetism.
Magnetic phenomena are closely related to electricity: a magnetic field can be created by moving electric charges. Electromagnetic radiation, such as light, is a form of energy emitted and absorbed by charged particles. It can exhibit a wave-like behaviour as it propagated through space.
It is possible to map the magnetic field of an object by measuring the strength and direction of the field at various locations. By following the arrows drawn you end up with field lines for the field. A map of this sort can be visualised, for instance, by doing a very simple experiment involving a magnet bar and some iron filings (see image above).
CERN has called for a press conference today (July 4th) for an important announcement. It turns out that they are reporting the claim of the discovery of a new particle “consistent” with the Higgs boson. It has been a search of 45 years for an explanation of how matter acquires mass. And the search is not yet over with this announcement: more work is needed to be certain that this is indeed the Higgs boson.
Peter Higgs was present in the audience in the conference theatre at CERN, Geneva. He was prompt to congratulate the team for their achievement. The famous boson is named after him and this was really a momentous event for him.
The CMS team, at the Large Hadron Collider (LHC), report that they have seen a signature in the data for a particle weighing 125.3 GeV, which is about 133 times heavier than the proton. If actually confirmed, this will be one of the biggest scientific discoveries in my lifetime, but even more exciting is the fact that this does not close the chapter, it may even open other avenues of research and understanding. And as such, the physicists at CERN say that, currently, the data they have is compatible with the Standard Model Higgs boson…
Yes, indeed this post is about repulsive polarons, but that does not mean that they are repulsive because they cause revulsion or anything of the sort. We are talking about quasiparticles which are predicted to occur when ‘impurity’ fermionic particles interact repulsively with a fermionic environment. And it turns out that these quasiparticles have now been detected.
Ok, “what is a quasiparticle?” I hear you say. Well, a quasiparticleis a perturbation or disturbance in a medium, whose behaviour is that of a particle and thus for all intent and purposes can be regarded as one. Their study is important in relationship to solid-state physics, condenses matter and nuclear physics as they help us in determining the properties of matter.
Rudolf Grimm (Innsbruck) and a team of physicists have experimentally realised the observation of a repulsive polaron in an ultracold quantum gas. The results have been publised in Nature.
Varios phenomena from condensed matter physics can be experimentally simulated using ultracold quantum gases. In these system, the control that can be achieved over the many-body interactions is grater and this is always helpful.
In order to observe repulsive polarons the physicists used an ultracold quantum gas of lithium and potassium atoms and they control the atomic interactions using electromagnetic fields and RF pulses. The potassium atoms are dirven into a state where they repulse the surrounding lithium atoms. This interaction can be seen as a particle with modified properties – a quasiparticel. Once the researchers analyse the energy spectrum of the system, they were able to demonstrate repulsive polarons.
The observation of these polarons is important as it demonstrates that they can indeed be observed. In condensed matter quasiparticles decay very quickly and this poses the problemof studying them. In this experiments, the researchers say, the polarons showed an almost ten times increased lifetime compared to earlier experiments in similar systems. This opens up the possibility of having a platform for a more detailed analysis of many-body systems that rely on repulsive interactions.