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Physics

  • The Universe Waved and We Heard It

    More than 100 years ago Einstein predicted the existence of gravitational waves—ripples in spacetime, where space is stretched in one direction and compressed in the other. The prediction is a consequence of his theory of general relativity, fitting nicely with his mathematical model. It wasn’t until September 14, 2015 that anyone observed a gravitational wave. It’s not that the Earth hasn’t been hit by them. We haven’t had a way to detect them. Gravitational waves are very tiny. Really tiny. Like 1/1000 the diameter of a proton. To measure something like that, you need a very special instrument—an interferometer, and not just an off-the-shelf model. 

    The Laser Interferometer Gravitational-Wave Observatory (LIGO) is designed specifically to detect these waves. The project is a collaboration of many scientists, technicians, colleges, and universities. LIGO uses two interferometers, one located in Hanford, Washington and the other in Livingston, Louisiana. Each is identical, even in its orientation.  They are very large instruments, as you can see in these images (courtesy of LIGO CalTech). This is the Hanford site. The next image is the Livingston site.

    When a gravitational wave encounters the Earth, it will reach one of the locations first. This gives scientists clues to the origin of the wave. When the wave arrived on September 14, it was seen at both locations, but with a 7 millisecond difference—the time it took for the wave to travel from one location to the other. 

    The wave is so tiny that you might wonder if LIGO really detected a gravitational wave. They weren’t sure either, which is why they did not announce their finding until February 11, 2016. This gave scientists a chance to complete various verification protocols that gave the confidence of almost 100% that they did indeed observe a gravitational wave. 

    It is an extraordinary observation considering that footsteps, storms, traffic, ambient temperature, and just about anything else you can think of that causes motion can be detected by LIGO. It is an incredibly sensitive instrument. So sensitive, it can detect the motion of ocean waves during a storm. The scientists use a variety of techniques to tease out the signal of a gravitational wave from the noise of everything else. For example, to subtract out the ground vibrations contributed at each location, they place an array of 100 seismic detectors at each interferometer site. Using the seismic signals and machine learning techniques (statistics) scientists can figure out which vibrational “squiggles” are from the site and which are not. They have to use a different technique for each type of unwanted noise source. 

    What is actual signal like? It’s a short chirp. 

    This is relatively old news, so why am I writing about it? Barry Barish is speaking at STARMUS 2016 on “Einstein, Black Holes and a Cosmic Chirp.” I will be attending STARMUS and decided to find out what role Barry Barish had in the discovery.  

    The National Science Foundation first funded exploratory studies in 1980. By 1989 the project started in in full force, more or less.  An experiment of this magnitude requires a special person to run the project. It’s a big budget, with personnel and instruments spread over several locations. It’s cutting edge science. It had to be precisely executed. The people in charge, though extremely smart and well meaning, weren’t able to make sufficient progress. It wasn’t until Barry Barish was appointed laboratory director in 1994 that LIGO took off. One person can make a difference. I look forward to his talk.

  • Good Vibrations: Brian Greene and String Theory

    At STARMUS 2016 Brian Greene will tell us about String Theory and the Nature of Reality. He will do this in just 20 minutes. So I’ll try to explain it to you in just a few paragraphs but from the perspective of a non-physicist.

    String theory rose from the quest to explain inconsistencies in existing theories in physics. Gravity seems to be the bad boy that doesn’t fall in line with quantum physics and general relativity. If scientists could reconcile that, they might even have the holy grail—one theory that explains everything in the physical universe. 

    The idea of unifying explanations of the universe is laudable, but the “stringicists” have given rise to even more theories—strings, superstrings, supersymmetry, branes, m-branes, and more. They  generated so many types of string theories—Type 1, Type IIA, Type IIB, Type HO, Type HE, and so on—that they themselves had to devise a unified theory of string theory call M-Theory (the mother of all string theories). 

    So what’s it all about? Strings are tiny, one-dimensional vibrating entities. The vibrational state of the string manifests itself as different physical particles. We don’t see a string, but we can observe ordinary particles and measure the particle’s mass and charge. But under the hood, that particle is just vibrations. The apple in the image is, ultimately, good vibrations! (Image courtesy of Wikimedia Commons.)

    Scientific theories are supposed to have predictive power—you should be able to predict a consequence of the theory and then measure those consequences in the real world. So far nothing has panned out for string theory, which is why some people refer to it as a “theoretical framework.” There are some elegant mathematics behind strings, which is the primary reason why this area of study has survived from 1960’s until now. That and the fact it has cool jargon.

    For more information, see Brian Greene's TED Talk on string theory. 

  • Asymptotic Freedom: David Gross

    The STARMUS Festival in the Canary Islands claims to make “the most universal science and art accessible to the public.” The speakers are some of the best in their field and include physicists, astrophysicists, chemists, biochemists, biologists, neuroscientists, and economists. Many of them are nobel laureates. Although the festival claims to be aimed at the “public”, I suspect that many of those brainy nobel laureates don’t have a good idea of where the intellect of the pubic lays. That’s why I am looking at the conference program now to investigate some of the conference speakers’ areas of expertise. I hope that by knowing a bit more about some of the speakers’ interests, I’ll get more out of the conference.

    On the first day David Gross, who won the Nobel Prize in Physics in 2004, will discuss the great challenges faced by physics. One of his challenges was explaining the behavior of quarks by introducing the property of asymptotic freedom, an explanation for which he (and two others) received the Nobel prize. 

    What exactly is asymptotic freedom, or AF as I’ll call it? It doesn’t sound too daunting. I know what freedom is—being free to do or think what you want without being constrained. I know what an asymptote is—a line that approaches a curve but does not meet is. How does that relate to physics? Why would someone get a nobel prize for that?

    To understand AF, you need to have a basic understanding of atoms, those tiny things that make up matter. Atoms in turn are made up of subatomic particles—protons, neutrons, and electrons. While most of us are worried about how to keep our lives togethers, people like David Gross are concerned with how an atom keeps itself together. Physicists know there is a strong nuclear force that holds protons and neutrons in place in an atom, but they wanted to know more about that force, as it is one of the four fundamental forces in the universe. (The other forces are electromagnetic, weak, and gravitational.) 

    How strong is the strong force? Over very tiny distances—atomic nucleus sized—the strong force is 100 times stronger than the electromagnetic force that repels positively charged protons. That’s why an atomic nucleus stays together under normal circumstances.

    Both protons and neutrons are themselves made up of quarks—precisely three quarks. These days, quarks are assigned “colors”, either red, green or blue. This might see like an homage to the pixel, but using color as a metaphor in physics helps to explain a lot of subatomic particle interactions that I’m not going to explain in this discussion. (I’ll also ignore quark “flavors.”) Suffice it to say that subatomic particle interactions have to result in white. Red, green, and blue combine to white.  (Image from Wiki Commons.)

    So far you know that the quarks are held in place by a strong force. The theory behind this strong force is named quantum chromodynamics (QCD) because of the arbitrary use of color. That finally brings us to AF.

    AF is important because it explains some baffling behavior of quarks. You can’t see quarks, which indicates they are trapped in matter by the strong force. If they weren’t confined, you’d be able to see them, right?  Yet a big smash up at the linear accelerator down the road from me—Stanford Linear Accelerator (SLAC)—showed that in a high-energy reaction  the force between the quarks weakens and the distance between them decreases asymptotically. That is, they get closer and closer, but don’t run into each other.

    What  it boils down to is that quarks have two phases—confinement and AF. Much like water and steam, the phases depend on temperature. In the case of quarks, temperature (which is really energy) is measured in Mega electron Volts, or MeV. The phase change occurs at 160 MeV. Quarks are mostly confined below that energy level, and mostly have asymptotic freedom above that level.

    So what’s the lesson for the lay person? Although your personal life may seem to be falling apart, take comfort in the fact that the atoms around you are quite stable. You might need to expend a lot of energy to keep things together, but atoms are just the opposite.  

    AF isn’t all that Dr. Gross is known for. He is one of the signers of the Humanist Manifesto.

  • Who’s Got the Most Talent—CERN or Berkeley Physicists?

    The European Organization for Nuclear Research (aka CERN) made news after the Large Hadron Collider (LHC) Rap hit YouTube. I was impressed that physicists could be smart and entertaining. Who would have thought? After a few listenings, uniqueness wore off and I began to question whether they really had talent. Now that I've seen what Berkeley physicists can do, I think it's time for CERN to update their video.

    I'll let you judge which one is more talented.

    The Nano Song

    Large Hadron Collider Rap