El Universo vuelve a temblar.

Los detectores de ondas gravitatorias, LIGO, han vuelto a sentir un estremecimiento en el espacio-tiempo. La fusion de dos agujeros negros ha emitido tanta energía en un segundo como el resto del universo.

Por segunda vez en tres meses, los detectores LIGO (en USA) han detectado ondas gravitatorias, provenientes de la fusion de dos agujeros negros. Estos exóticos objetos astronómicos, en un acelerado baile, rotando el uno alrededor del otro a un ritmo de unas 55 vueltas por segundo, se han fusionado en un agujero negro final de 21 masas solares. En este proceso han emitido una enorme cantidad de energia. En un solo segundo han emitido tanta energia como si toda la masa del Sol se transformase en energia en esa fracción de tiempo, o lo que es equivalente, la energia que emiten toda las estrellas del universo en ese segundo.

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Gravitational Waves, Relativity & Photonics

We have already detected gravitational waves. The rumors of the news were in the air for a few weeks and finally the researchers (from the MIT, Caltech and the LIGO project) have announced their finding

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Michelson interferometer (from scienceclarified.com).

​Special Relativity: one century of interferometry

One of the most common ways to introduce special relativity is by describing the interferometry experiment of Michelson and Morley from the late 19th Century. Their negative result was pointing to a fundamental problem in the interpretation of space and time. Even though Albert Einstein didn’t use their result to present his special theory of relativity, the experiment was one of the most precise experiments of all times, and it is a pedagogical tool.

Michelson designed an interferometer to measure the drag of the “luminiferous aether” on the speed of light. This aether was a supposed fluid that filled all space and was introduced in order to explain the wave nature of light.

In his experiment, Michelson first and with Morley later, compared the time that light needed to travel along two perpendicular paths, as in the figure. The light was coming from the left (see figure). A beam splitter divided the beam of light into two. One half going to Mirror 2 and the other half to Mirror 1. Then those beams were reflected. They interfered at the beam splitter again and recombined, being sent to the detector. Depending on the difference in time the interference pattern can be different, and from this we can extract the difference in velocity, if any.

As light has undulatory behavior the interference between two pulses or beams of light depends on their relative phases. This phase will depend on the difference of path taken by each beam.

The problem shown in this experiment was that, contrary to the general belief, there was no aether, and the way to explain some contradictory results was to assume that space and time are distorted as seen from different observers that move one with respect to the other: if a traveler flies at very high speeds (comparable to that of light), time for the traveler passes much slowly than for an observer at rest. Also, space seen by the traveler  gets contracted. This is a direct implication of two principles:

– The speed of light is constant (has an absolute value). It is the same for all observers, independently of the velocity of the observer with respect to the source that emitted the light.
– All inertial reference frames (those with constant velocity but no acceleration) are equivalent. We can not design an experiment to tell us if our reference frame is at rest or it moves with uniform motion (constant velocity in magnitude and direction). All the laws of physics are the same for all observers.


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General Relativity

But the Special Theory of Relativity of 1905 didn’t account for gravity. After almost a decade later 9in 1915), Albert Einstein presented his general theory of relativity, which described gravity. This theory introduced the idea of curved space-time. Einstein introduced a geometric description of space and time in 1905 and he showed that space and time formed a continuum four dimensional tissue where all matter in the universe is immersed. Matter deforms the space-time fabric and the distortion of space-time shows the matter and light how/where they have to move.

The Universe is full of matter that gravitates and distorts space-time as it flies by. It is like playing bowling in a green that is not uniform, but also, it changes shape as the bowls roll by.


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But an indirect observation of gravitational waves had already been made in the late 1990s. General Relativity predicts that a fast spinning neutron star will emit energy in for of gravitational waves. This lost of energy will be reflected is the rotational energy of the star. Detailed observations through thirty years confirmed that the rotational energy lost was exactly the one predicted by General Relativity to be emitted as gravitational waves.Gravitational waves

All the predictions of general relativity have been confirmed. Gravitational lensing, or how gravity changes the straight lines and makes light travel in curved trajectories. gravitational time dilation, or how gravity makes clocks travel slower, so that a person in a intense gravity field will experience less time lapse than a person far from an intense gravity field. Gravitational redshift, or how light looses energy due to gravity by changing its wavelength.

Gravitational waves was the last prediction to be directly observed. This waves are created when cataclysmic phenomena  happen in the universe, such as collision of black holes or coalescence of neutron stars. Even though the energy released in these phenomena are huge (about two solar masses in the  gravitational waves observed by LIGO), when we detect them (so far away, luckily) they are really tiny.


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Interferometry to the rescue.

​But to measure the Gravitational Waves we need to measure tiny, very tiny variations in the distance between atoms, as the waves traverse them. It is like measuring the distance from the Sun to Proxima Centaury (~4light years) with a resolution of one human hair!

To do this, physicists form the LIGO project have used a Michelson interferometer (yes, again the same experiment Michaelson did in 1887). In this case, though, it was not a tabletop experiment. The two arms of the interferometer were four kilometers long. This has to be this way so that the distance of the mirrors are change enough to be detected (one thousandth of the size of the proton).

In order to be sure that what was measured were really Gravitational Waves, the experiment counted with two different interferometers, one in the state of Washington and the other in the state of Louisiana. They are far enough so that any local perturbation measured in one of them is not detected by the other. Also, the time difference between detections can hive hints on the origin of such waves. In September, 14th, 2015, both interferometers detected the same signal, almost simultaneously. The signal had the specific frequency pattern predicted by General Relativity for two merging black holes, and could not be attributed to any other phenomena.  The first ever Gravitational Wave had been observed.

This detection technique, not only confirms once more Einstein’s Relativity, but opens a new window to the Universe. We can now observe it not only with electromagnetic waves, but also with gravity waves.

​In Terrassa (Spain) the Association Planeta da Vinci, together with the Astronomical Association of Terrassa, are organizing the 9th Dissemination Day on Relativity. They have been creating a meeting point between Scientists, Science Communicators and Society since 2008.

Water on Mars. So what?

NASA has just confirmed that there were lakes of salty liquid water on Mars billions of years ago, but magnetic activity from the sun affected Mars such that it began to loose its atmosphere. That is a great peace of a new from the scientific perspective but, does that affect our daily lives? Yes, for sure!sara_haravifard

Dr. Sara Haravifard, from Duke University, with the six-circle diffraction stage in the 4-ID-D experiment station (image from phys.org).

NASA has just confirmed that there were lakes of salty liquid water on Mars billions of years ago, but magnetic activity from the sun affected Mars such that it began to loose its atmosphere. That is a great peace of a new from the scientific perspective but, does that affect our daily lives? Yes, for sure!

Last week, in the Physics Research Seminar course that I coordinate at Duke University, Dr. Sara Haravifard came to talk about her research in the field of the magnetic properties of crystals at very low temperatures and very high pressures. She creates specific types of crystals, to which she then applies those extreme conditions to understand how they behave, and how their structure is affected when different phases emerge, such as superconductivity.

Superconductivity is the lack of resistance to an electrical current that some materials have at very low temperature (lower than -100C approx., but some at lower than -200C). Although there are a couple of models that describe this phenomenon for some of the superconducting materials, it is not well understood how or why some others are superconductors. Understanding it, could help researchers to design superconductors at room temperature, for our use, giving our society a great tool for telecommunications, transport industry, and energy.

To investigate their properties, Dr. Haravifard needs to submit her samples to many different measurement, as X-rays or neutron scattering. Those measurements imply complex and big instruments, most of them huge facilities such as synchrotron accelerator or Spallation Neutron and Pressure Diffractometer (SNAP). These big facilities are huge instruments that most research centers or universities can not acquire or maintain. That is why there are just a few in the U.S. and in other countries around the world. The budgets to build and maintain them are big, although smaller than yearly budget of most soccer teams in Europe.

Sometimes it is difficult for newspapers to explain why we need a new synchrotron, for example, but without it we might not have that useful medicine you need, or that synthetic molecule to reduce cars pollution, or that light and resistant material that can be used in some prothesis.

It is good to have in mind that, when you use your laptop, or send a text massage to your loving ones, or watch the Super Bowl on cable TV, or have a medical diagnosis, you are having it due to people like Dr. Haravifard, doing basic research to understand Nature. Discoveries such as that of water on Mars, which a priori could seem not directly related to you, are present in your daily life.

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Congratulations!

​100 years ago today, on Thursday, November 25th, 1915, Albert Einstein presented his General Theory of Relativity. After having been working on it for eight years he finished one of the most beautiful and robust scientific theories.

In these 100 years, the theory has passed from not being accepted at first, to not having found any deviation from the observations and experimental tests.

In 1905 Einstein presented his special theory of relativity, that unified space and time, matter and energy. This first theory showed us how these values depended on the observer and changed our view of space and time as non being rigid, but deformable. At that time, many scientists were about to find it: Poincare, Lorentz, Fitzerald. Indeed, these scientists had already found the equations that Einstein presented in his theory. But they didn’t understand their meaning. They though those mathematical expressions weren’t but artifacts to get to the right numbers to agree with experiments. They believed they didn’t have any physical significance, though. Einstein, in a very elegant manner, presented those same equations from simple principles and gave them physical meaning. Conceptually, he had to work on the theory for ten years to understand it, and only three weeks to develop the mathematics to describe the phenomena.

The General Theory of Relativity went the other way round. He visualized the physical theory with one thought experiment, but he needed eight years to develop the mathematical description. The Special theory was on the air in science at the time Einstein came through it. If it hadn’t been him, another would have presented and understood it in a few years. The General theory was much more complex to envision, and Einstein had the great vision of a bright mind that could have taken decades to others at that time.

It was not a straightforward work, Einstein went back and forth and had to learn mathematical concepts he didn’t know. Due to the geometric aspect of the theory, it soon attracted the attention of many mathematicians.

The first test to the new theory was the total eclipse of the Sun in 1919 (Einstein had preciously calculated the orbit of Mercury, where Newton’s theory had a little discrepancy, Einstein’s theory hadn’t). At that time, the equipment was not very precise and the pictures taken by Eddington in that eclipse wouldn’t have been published today [1]. But he was right. Since then, the theory of relativity has been tested in many different ways, showing always to be a correct theory [2, 34, 5, 6,  7, 8, 9, 10].

But we have not yet managed to reconcile General Relativity with Quantum Mechanics. The fact that the first rules physics when huge masses are in play, and the latter rules physics of elementary particles makes it difficult to observe or design experiments where both aspects are into play. Masses of elementary particles don’t have enough mass to create a detectable gravitational field. There are many theories that try to unify both of them.  The most relevant are string theory and quantum loop gravity. Both approaches introduce new perspectives to our view of the universe and matter, but their predictions are far from being tested, which makes it almost impossible to verify whether one of them is correct. Physics final goal is to describe Nature and we need to test theories. If one theory doesn’t describe Nature, it doesn’t matter how beautiful it is, we can not consider it as a real physical theory.

Also, the dark matter and dark energy conundrums we are dealing with in the latest years, have pushed some physicists to think that, maybe, General Relativity has to be reconsidered and it needs some modifications to account for the Universe as a whole. In any case, up to date, none of this alternative gravity theories has better success than relativity to describe the universe with or without the dark sector.

But, besides the unification with quantum mechanics, and the understanding of dark matter and dark energy, the last 100 years have given us great success of General Relativity. We understand much better the universe, stars, galaxy formation that we did one century ago. And we also have General Relativity in our pockets.  Due to the difference in speed and in gravitational field between us and the GPS satellites, our clocks don’t run at the same pace as those in the satellites. There is a difference of 43 nanoseconds in one whole day. This difference is predicted by relativity and it might seem small, but if we don’t consider it in the GPS protocol, our devices would be wring by 11 kilometers after 24 hours, making this positioning system useless.

So, we should be very happy and thankful to Einstein and his General Relativity for letting us understand better our Universe, and for helping us drive our way to where we are going to have our turkey this Thanksgiving Day.


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Read here the post at the Duke Research Blog by Anika Ayyar talking about my class of Science and Fiction at OLLI (Osher Lifelong Learning Institute at Duke).

PictureDr. Sara Haravifard with the six-circle diffraction stage in the 4-ID-D experiment station (image from phys.org).

NASA has just confirmed that there were lakes of salty liquid water on Mars billions of years ago, but magnetic activity from the sun affected Mars such that it began to loose its atmosphere. That is a great peace of a new from the scientific perspective but, does that affect our daily lives? Yes, for sure!

Human beings are a particular species on Earth. Since the dawns of time, humankind has being making questions on her place in the universe. Science has been working to answer those questions in the last few centuries, generating many new more questions for each answered one. Maybe that is the main reason why we scientists do research. But our experience has shown us that lots of technological advances for our society come out thanks to basic science. As Richard Feynman said once “Science is like sex, it may give some practical results, but that’s is not why we do it“.

Last week, in the Physics Research Seminar course that I coordinate at Duke University, Dr. Sara Haravifard came to talk about her research in the field of the magnetic properties of crystals at very low temperatures and very high pressures. She creates specific types of crystals, to which she then applies those extreme conditions to understand how they behave, and how their structure is affected when different phases emerge, such as superconductivity.

Superconductivity is the lack of resistance to an electrical current that some materials have at very low temperature (lower than -100C approx., but some at lower than -200C). Although there are a couple of models that describe this phenomenon for some of the superconducting materials, it is not well understood how or why some others are superconductors. Understanding it, could help researchers to design superconductors at room temperature, for our use, giving our society a great tool for telecommunications, transport industry, and energy.

To investigate their properties, Dr. Haravifard needs to submit her samples to many different measurement, as X-rays or neutron scattering. Those measurements imply complex and big instruments, most of them huge facilities such as synchrotron accelerator or Spallation Neutron and Pressure Diffractometer (SNAP). These big facilities are huge instruments that most research centers or universities can not acquire or maintain. That is why there are just a few in the U.S. and in other countries around the world. The budgets to build and maintain them are big, although smaller than yearly budget of most soccer teams in Europe.

Sometimes it is difficult for newspapers to explain why we need a new synchrotron, for example, but without it we might not have that useful medicine you need, or that synthetic molecule to reduce cars pollution, or that light and resistant material that can be used in some prothesis.

It is good to have in mind that, when you use your laptop, or send a text massage to your loving ones, or watch the Super Bowl on cable TV, or have a medical diagnosis, you are having it due to people like Dr. Haravifard, doing basic research to understand Nature. Discoveries such as that of water on Mars, which a priori could seem not directly related to you, are present in your daily life.

We’re back to the future!

Thirty years after the release of the film “Back to the future“, we finally reach October, 21st, 2015. This is the day when Marty McFly, with Doc. Emmet Brown, come to visit from the year 1985. Most of us have been waiting for this day, and have wondered how similar the real 2015 will be with respect to the 2015 in the movie. Now we can compare.

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Breakfast in America: Nobel laureate on campus.

One of the great things of doing research in one of the best Universities in the U.S. is that you can wake up one morning and, while watching the news during breakfast, you realize that the university you work at has a brand new Nobel laureate.

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When working at Duke, you already know that there are great scientists in its labs. You meet them in talks, conferences, you work with them and you learn a lot from them. That is extremely rewarding, as that improves yourself as a scientist, making you enjoy even more of your work.

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Breakfast in America: relojes, malaria y cerveza.

Este semestre coordino una asignatura de doctorado en la Duke University. En esta asignatura, Physics Research Seminar, he de coordinar que dos profesores cada miércoles, de 7:30 a 9:30 de la tarde-noche, vengan a explicar a los estudiantes de doctorado en qué están investigando. De momento ya hemos escuchado apasionantes ponencias sobre de técnicas de medida y diagnostico mé dico no invasivas mediante diferentes técnicas ópticas, sobre plasmas de quarks y gluones (la sopa liquida que formaba el universo original), hemos visitado el láser de electrones libres y conocido numerosas aplicaciones, o sobre sistema granulares, que dan información desde
terremotos a como se comporta una multitud ante una situación de pánico.
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Photo by Anyi Mazo-Vargas from Dr. Buchler’s group

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