Ruxandra's Blog

New Blog

2012-02-01T07:13:00.000-08:00

I have started a new blog today about my brilliant science reading. So far I just posted titles and authors of papers I find interesting on the arXiv. In the future, I will read some of them and explain what I understand from them. Eventually, I might organize them by topic and not by date and maybe expand to books I read, and then I'll have to switch to a wiki. For now, the point is to get in the habit to read more and understand what I read better (and sometimes why I read on a given topic). Once this is accomplished, the means of communicating is relevant only if enough other people read the information. At this point, I am not convinced that my readings and thoughts will be interesting enough for the real world and so the documentation is mostly for myself.

The link is below:
Ruxandra's Science Reading

Why a new blog? Because I did not want to clutter this one with 20 to 30 papers a week. I want to keep this blog for more important posts or at least important for me.

The Sultanate of Oman?

2012-02-01T07:04:00.000-08:00

Mihai went for an interview in Dublin for a position at a military college in the Sultanate of Oman. This is a country I did not hear of before he received this job interview. Its neighbors are Saudi Arabia, the United Arab Emirates and Yemen. My brother is the ideal person to hang out with if you want to have an exciting life!

We do not know any of the details yet, but it appears that he will get the job - or at least this is what he understood from the interview. He would be department head in physics at an university in Muscat, the capital of Oman. Once/IF he receives an offer, we will try to understand the contract and the region better. I am curious and hopeful that such a position will come with the freedom to build a good physics department, but Mihai seemed very worried and afraid to go to a 'military institution'.

The Physics of the Far Future

2012-01-09T07:11:00.000-08:00


www.phenomenica.com (I took the image from this website)

Since we are the beginning of 2012, the year the Mayan calendar ends, Andy, Mihai, and I wrote a paper about the cosmological future of our universe and submitted it to Physical Review Letters (PRL). Well...ok... I do not actually believe that the world will end this year, but it is tantalizing to think of the 'far future'. Our paper can be found on the arXiv: http://arxiv.org/abs/1201.1298. Most of the statements below are also in the manuscript.

The far future is surprisingly simple and yet very interesting from a scientific perspective. In due time, all the matter and radiation of the universe will be absorbed by the cosmological horizon, which grows in response. Nothing will be left other than slowly evaporating supermassive black holes. Black holes are believed to be the densest and most lasting objects in the universe. We study the thermodynamics of our local universe in this future. The local group is expected to collapse to a supermassive black hole that will slowly evaporate in an empty universe dominated by a cosmological constant. In our paper we look at the dynamics between the extremely cold cosmological horizon and the hotter black hole horizon. We discuss how heat and entropy produced by black hole are absorbed by the cosmological horizon and find that even though the presence of the black hole initially depressed the total entropy, the total entropy increases as the black hole evaporates and, of course, heat flows from the hotter black hole horizon to the colder cosmological horizon.

So, what is the end state of the universe? If the cosmological constant is a true constant, then the universe will reach its final thermodynamics equilibrium state in empty deSitter, i.e., empty space that expands forever. However, if a slow rolling scalar field mimics the cosmological constant, this scalar field could eventually reach the bottom of its potential and then the universe would stop expanding becoming flat. Stephen Hawking states that since flat space has no horizon, it also has zero entropy. We argue that it has divergent entropy because it could be indistinguishable from a space with a very small cosmological constant; the entropy of deSitter depends on the inverse of the cosmological constant. With this assumption, flat space would have a infinitely large entropy, which would be consistent with the second law of thermodynamics; if flat space could be the final state of our universe at the end of the slow roll period, it should have higher entropy than deSitter.

We also discuss the Weyl curvature hypothesis of Roger Penrose who states that the difference in entropy between the initial and final state of the universe is related to the growth of the Weyl curvature. The Weyl curvature is small at the beginning of the universe, but grows with the production of singularities. However, empty deSitter has zero Weyl curvature. Empty deSitter is the thermodynamics equilibrium (final state) of our universe for a true cosmological constant. We modify the conjecture by stating that the entropy does not come directly from the Weyl tensor, but from a coarse-graining over the states of the Weyl tensor. The cosmological constant limits the wavelength of the gravitational wave modes. When a black hole evaporates, the cosmological horizon grows allowing more gravitational wave modes. This increases the number of available microstates in the Weyl tensor and hence the entropy of the space. We emphasize that the cosmological constant is not just an energy scale, but an entropy scale as well. It plays a very important role in black hole thermodynamics that still has to be understood.

The Right Pitch to Shatter a Neutron Star

2012-01-09T05:46:00.000-08:00

From David Tsang, Caltech

The paper with Dave et al. was spotlighted by PRL and given a synopsis by a science writer

http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.108.011102

It was later picked up in the news! This is the New Scientist article. Another article about it is in ArsTechnica.

Here is Dave's Summary: "Can neutron stars, dead stars composed of exotic material trillions of times more dense than a normal star, shatter like an ordinary wine glass? Our new research shows that indeed they can. As a neutron star spirals in towards another neutron star or black hole due to emission of gravitational waves, tidal forces act on the star with increasing frequency. When this frequency matches the resonance frequency of the neutron star crust -- just like an opera singer hitting the right note for a wine glass -- the crust shatters. The shattering crust may excite high-energy emission, explaining gamma-ray flares seen just prior to short gamma-ray bursts. Just as the note at which a wineglass shatters tells you about the composition and shape of that wineglass, studying the timing of these flares could allow physicists to learn about the properties of dense matter in neutron star crusts, material that cannot be probed by ordinary terrestrial experiments."

An opera singer and a broken glass can be seen below:

Disclaimer: Unfortunately, I do not know who are the authors of either of these two pictures or who the opera singer is.

Welcome 2012! Happy new year everyone!

2012-01-05T16:09:00.000-08:00

Since I am most thankful for the happy children in my house, I am writing this post about them.

Edward and his legos

Edward will be 1 year and 5 months old next week. He admires his cousin David with his whole heart and imitates him as much as he can. This year was the first Christmas when Edward was old enough to run and play. He can put together legos now and his favorite toys are cars, which he calls "masina". Some other words he says are: mama (with different intonations), apa (water), bomboana (candy; maybe not so good for his diet), cheese, papu (shoes), DeDe or David (depending on his mood), tata or daddy, pita (bread), Titzi (either the guest cat to be explained later or my breast; he is still nursing at night), knock-knock (which he can accompany by knocking), poc, buff, mu-mu (most animals including sheep), ham-ham (usually dogs), up, brate (arms in Romanian when he wants to be picked up).

David in the livingroom-to-kitchen window

David at 4 years and 10 months has a rich imagination and likes to exaggerate. He could not give a paper plane to Edward the other day because it was really a rocket that would explode if not handled properly and, of course, he is the only one who has the expertise to use this rocket. So, sometimes discipline becomes harder to enforce, and I have never been too good at enforcing discipline in the first place. He also thinks that he became the richest David in the whole world when my brother brought him a suitcase of books and that almost every cake that my mom makes is the best cake ever. The latter is a reasonably good habit to cultivate. In 20 years from now his girlfriend or wife will enjoy this type of compliments. And David's opinion is that fireworks should be called atomic bombs because it's just a more suitable word that would be easier to say for Edward. I did explain to him how dangerous an atomic bomb is, but he does not understand bad things well yet. In the end, I guess that all words are a just a name for things that could change and do change some times in different languages/cultures and as adults we tend to forget that.

The Guest Cat

Who was the guest cat? We found a cat a few days before Christmas. She followed the children and my mother home and entered the house on her own. She clearly loved children and various kinds of meat including fish. Edward would sometimes pull her tail, and she never even once hissed and did not run away from him. I put flyers at the bus station and, eventually, her rightful owner showed up to claim her on the 31st of December. We found out that she had been a barn cat belonging to the brother of her current owner only 5 weeks ago and that she was let into the house when she followed the children of the guy in. We received champagne, candy and martipan in return for the cat, but we still miss her sometimes.

Luke-warm dark matter: Bose-condensation of ultra-light particles

2011-12-16T06:03:00.000-08:00

My brother, Mihai, gave an informal ITP seminar today on Our 2010 Astrophysical Journal Letter. I was surprised at how much I forgot about this project. He gave really good talk that was followed by an interesting discussion. Since this discussion could result in potential collaborations, I thought I would summarize my own work to remind myself of what we learned and why we did it and of the work that has been done on this topic since 2010. With this relatively grandiose goal in mind, it will take me some time to complete this post.

What are ultra-light scalar particles?
Scientists have yet to find fundamental spin zero particles, but theory predicts that they exist. Particle physicists have almost detected the Higgs boson. The Higgs is a scalar (spin zero) particle that weighs 120some GeV (more than 120 times heavier than a proton) and is expected to be produced by colliding particle beams at energies of several trillion electron volts in the largest particle accelerator on Earth. However, there has been little exploration of the light side of the spectrum. The ultra-light scalar particles that I study should be comparable in size to a dwarf galaxy and have really light masses of about 10^(-23) eV. This is about 10^(-29) times lighter than an electron!

Why are ultralight scalar fields interesting in cosmology?

How could we study such particles?

LHC press conference: Have they found the Higgs particle?

2011-12-13T08:02:00.000-08:00

There was a press conference today at 2 p.m. The range in which the Higgs particle could exist is narrowed to 115 to 130 GeV with 95% confidence. The mass of the Higgs appears to be around 125-126 GeV, but more data needs to be taken to declare a detection.

What is the Higgs boson?
The Higgs boson is a spin zero, scalar particle that is necessary to explain how most elementary particles obtain their mass in the Standard Model. The Higgs mechanism gives mass to every elementary particle that couples with the Higgs boson including the Higgs itself.

The Most Massive Black Holes

2011-12-08T07:53:00.000-08:00

Two ten billion solar mass black holes were found. The first one is in the brightest galaxy cluster at a distance of 98 Mpc from Earth, NGC 3842. It weighs about 9.7 billion solar masses. The second supermassive black hole is at the center of NGC 4889 at a distance of 104 Mpc from us. It weighs about 21 billion solar masses. Until now the record for the most massive black hole was held by a black hole in the center of the M87 galaxy that weighs 6.3 billion solar masses. This post is mainly a summary of the Nature article.

How do scientists estimate black hole masses?
Empirical scaling relations between the black hole mass, galaxy bulge dispersion and luminosity are used to estimate the black hole masses in galaxies where a direct measurement is not possible due to large distance from Earth or low central stellar density. These two black holes are special because scientists were able to directly measure their masses, i.e., they measured the stellar velocities of the central regions of the host galaxy accurately enough to determine the black hole mass. The two black hole masses did not agree with the predictions, which were off by several standard deviations (about a factor of 10 in both cases).

What instruments did they use?
The line of sight stellar velocities were measured using the Gemini North and Keck 2 telescopes, in Hawaii. The stellar luminosity distribution of each galaxy is provided by surface photometry from Hubble and ground based telescopes.

Possible conclusions?
The most massive black holes appear to be in the brightest cluster elliptical galaxies and not in brightest field elliptical galaxies. Clusters contain more objects and so more mergers are likely to occur. Many predictions are contradictory. Direct measurements of more black holes masses will help revise these relations. So far it appears that the mass vs. velocity dispersion relation either disappears or steepens at high masses. The steepening can occur due to the accretion of residual gas after star formation stops, which is likely in these very massive galaxies.

What are the progenitors of these black holes?
Black holes heavier than 10 billion solar masses are observed as quasars in the early universe (a few billion years after the big bag). Quasars contain young, rapidly accreting black holes. However, as time passes, the accretion slows down and they become regular galaxies. Quasars are still not well understood. Much more research needs to be done.

Kepler Confirms Its First Planet in a Habitable Zone

2011-12-06T05:36:00.000-08:00

The Kepler mission confirmed the first Earth-like planet in its habitable zone. See the NASA briefing. Its name is Kepler-22b and it is located about 600 light years away from us. This planet orbits a solar mass star (mass 0.97 times the mass of our sun) every 290 days. Its radii is 2.4 times bigger than the radius of our Earth. This means that the gravity on it will be stronger than on Earth. They say the near surface temperature of this planet is about 22 Celsius. The Kepler data so far resulted in over 2, 300 planet candidates. Out of these planets about 48 are believed to be in the habitable zone of their star.

How Does the Kepler Satellite Work?
The Kepler Satellite monitors the brightness of more than 100,000 stars for the life of the mission, which is expected to be extended beyond its current 3.5 years. The satellite was launched in March 2009. It observes the changes in brightness of these stars when planets pass in front of them. The size of a transiting planet is found from the size of its star and 'the deepness of the transit', which is the decrease in brightness of a star when a planet passes in front of it. Since Earth-like planets create 'small' dips in brightness, i.e., close to the noise level of the instrument, the Kepler mission requires three transits to declare a detection. This, of course, takes time and it is why we have to wait before even smaller Earth-like planets will be reported.

David's Green Science

2011-12-02T02:45:00.000-08:00

My nephew, David, is 4 years old. He and my brother powered a clock using an apple, two wires connected to the clock and two electrodes. The clock was still working 24 hours later and showed the correct time. The electrodes in the potato battery kit can be replaced by other metals such as a nail and a coin. That's right! There is a kit for kids for building this type of battery for potatoes, but it works with most other fruits and vegetables.

Warning: The apples should not be eaten after they are used in this type of battery. They will contain zinc, which is toxic.

How does it work? The zinc ions and copper ions are separated by the apple. Otherwise they would interact with each other and produce a little bit of heat. The electron transfer takes place over the copper wire, which powers our clock. Chemical energy is converted into electric energy by electron transfer. The electricity produced is not much (definitely not enough for a person to feel), but clocks need very little energy to run and this makes them ideal for this project.

The not-so-Elusive Neutrinos

2011-11-30T05:21:00.000-08:00

I typically attend the Particle and Astrophysics Seminar at the ITP. It is held in a room on the same floor as my office and that sometimes plays a role in influencing me to go. Some of these seminars have been about neutrino experiments. We had a speaker from the T2K (Tokai to Kamioka) collaboration and one from the Majorana demonstrator. The message of the talks was largely that there has been a lot of progress made in this area and that we have the technology to learn even more about neutrinos and so many new experiments are being built. Both talks were really good, but I wish they had spent a few slides talking about the broader impacts of their research vs. only the facts and details of their experiment and its results.

What we know about neutrinos, what do we want to find out, and why do we care?

These small, neutral particles (neutrino does mean the small, neutral one in Italian) have three flavors: electron, muon and tau neutrino. We know mass differences between flavors and that neutrinos can oscillate between the three available flavors as they travel through space. The probability of measuring a particular flavor for a neutrino varies periodically as the particle propagates. What we do not know is the actual masses of the neutrinos or if the neutrinos can be their own anti-particle. Some experiments such as the T2K will measure neutrino oscillations more accurately and others such as the Majorana experiment constrain the neutrino mass. The cool thing about neutrinos is that they interact very weakly with other particles and fields. They can carry information from supernovae remnants, the core of the sun or the Galactic center allowing us to learn about objects produced in messy environments that we could not study otherwise.

The Large Hadron Collider and the Origin of Mass

2011-11-28T08:35:00.000-08:00

This grandiose title is for an inaugural lecture across town that is targeted at a general audience. The speaker is a young professor at ITP, Stefano Pozzorini. Once a person receives a professorship at the University of Zurich, which does not have to be a permanent position, they have to sustain this type of public lecture. It's dark out already. The talk starts at 6:15 p.m. and is followed by a small reception. I hope I will find the building and the room.

Update: I did find the building. It is one of the most beautiful buildings on campus with columns, writing in latin and majestic horse statues at the entrance. The auditorium was equally impressive. The ceiling is tens of meters high and the walls are covered with imitations of sculptures from thousands of years ago.

The seminar was interesting. It often happens that general audience seminars end up at a low enough level so that I understand some part of what they say, but not low enough for the targeted audience. The talk was about detecting the Higgs boson. The Higgs boson is a spin zero, scalar particle that is necessary to explain how most elementary particles obtain their mass in the Standard Model. It would give mass to every elementary particle that couples with it including the Higgs itself. The data from Large Hadron Collider (LHC) has excluded heavy and mid-mass Higgs bosons. The hope is that the Higgs is light (around 120 GeV) and will be discovered soon.

The LHC is a detector that collides high energy protons or lead nuclei. The term hardon means it collides particles made of quarks. The protons and neutrons are heavy and made out of quarks, while the electron is still believed to be an elementary particle. It shuts down for the winter and will be operating for another 8 months starting in February. Afterwards, it shuts down for 2 years for upgrades. The proton beams have only reached half their design energy and are expected to reach the full 7 TeV per beam after this upgrade. The University of Zurich designed/built the inner track system of one of the detectors within the LHC, which determines the resolution with which the charged particles are detected.

The expectation was that they would find a new family of particles with the Higgs as a certain detection. So far they have not detected any new particles. If they do not find the Higgs, then the Standard Model is incorrect. One of the most minor modifications of the Standard Model is that there is a "invisible" sector of Higgs particles. This would mean that there are fewer "visible" Higgs particles than previously thought and hence harder to detect. The consensus from this talk was that we will find out very soon if there is a Higgs boson in the mass range they search and that we should just wait for data vs. speculate wildly. Speculation is fun, though...

I arrived home at almost 9 p.m. after I missed one of the buses. These long days at work do have a price and sometimes I wonder if this price is worth paying. I guess there must be some balance between activities and, in general, some balance in life that I still have to find.

The first post

2011-11-28T08:24:00.000-08:00

I have started this blog to practice writing. I am not committing to writing every day. I will write when I feel that I have learned something important or when I want to share my thoughts. Sometimes I may give too much information and sometimes too little. I apologize for that in advance. I do not have a target audience in mind. The purpose of this blog is to document some of my own personal growth over the period of a few months. If I find it meaningful or fun, I will continue posting.

I also created this blog in hope for some permanency of my thoughts. I started writing a diary at 14 in a plain text file and later I continued to write in various files that I later deleted and on random sheets of paper that I eventually recycled. I still love to look at letters written by my grandparents and my parents and maybe my children will enjoy reading what I write someday.