Wednesday, January 28, 2015

Charles Townes

As reported almost everywhere, we lost Nobel Laureate Charles Townes at the age of 99. Oh how we we all are standing on the shoulder of this giant in physics.


Wednesday, January 21, 2015

GUTs and TOEs

Another informative video, for the general public, from Don Lincoln and Fermilab.

Of course, if you had read my take on the so-called "Theory of Everything", you would know my stand on this when we consider emergent phenomena.


Tuesday, January 20, 2015

Macrorealism Violated By Cs Atoms

It is another example where the more they test QM, the more convincing it becomes.

This latest experiment is to test whether superposition truly exist via a very stringent test and applying the Leggett-Garg criteria.

In comparison with these earlier experiments, the atoms studied in the experiments by Robens et al.’s are the largest quantum objects with which the Leggett-Garg inequality has been tested using what is called a null measurement—a “noninvasive” measurement that allows the inequality to be confirmed in the most convincing way possible. In the researchers’ experiment, a cesium atom moves in one of two standing optical waves that have opposite electric-field polarizations, and the atom’s position is measured at various times. The two standing waves can be pictured as a tiny pair of overlapping one-dimensional egg-carton strips—one red, one blue (Fig. 1). The experiment consists of measuring correlation between the atom’s position at different times. Robens et al. first put the atom into a superposition of two internal hyperfine spin states; this corresponds to being in both cartons simultaneously. Next, the team slid the two optical waves past each other, which causes the atom to smear out over a distance of up to about 2 micrometers in a motion known as a quantum walk. Finally, the authors optically excited the atom, causing it to fluoresce and reveal its location at a single site. Knowing where the atom began allows them to calculate, on average, whether the atom moved left or right from its starting position. By repeating this experiment, they can obtain correlations between the atom’s position at different times, which are the inputs into the Leggett-Garg inequality.

You may read the result they got in the report. Also note that you also get free access to the actual paper.

But don't miss the importance of this work, as stated in this review.

Almost a century after the quantum revolution in science, it’s perhaps surprising that physicists are still trying to prove the existence of superpositions. The real motivation lies in the future of theoretical physics. Fledgling theories of macrorealism may well form the basis of the next generation “upgrade” to quantum theory by setting the scale of the quantum-classical boundary. Thanks to the results of this experiment, we can be sure that the boundary cannot lie below the scale at which the cesium atom has been shown to behave like a wave. How high is this scale? A theoretical measure of macroscopicity [8] (see 18 April 2013 Synopsis) gives the cesium atom a modest ranking of 6.8, above the only other object tested with null measurements [5], but far below where most suspect the boundary lies. (Schrödinger’s cat is a 57.) In fact, matter-wave interferometry experiments have already shown interference fringes with Buckminsterfullerene molecules [9], boasting a rating as high as 12. In my opinion, however, we can be surer of the demonstration of the quantumness of the cesium atom because of the authors’ exclusion of macrorealism via null result measurements. The next step is to try these experiments with atoms of larger mass, superposed over longer time scales and separated by greater distances. This will push the envelope of macroscopicity further and reveal yet more about the nature of the relationship between the quantum and the macroworld.


Monday, January 19, 2015

I Win The Nobel Prize And All I Got Was A Parking Space

I'm sure it is a slight exaggeration, but it is still amusing to read Shuji Nakamura's response on the benefits he got from UCSB after winning the physics Nobel Prize. On the benefits of winning a Nobel Prize:

 "I don't have to teach anymore and I get a parking space. That's all I got from the University of California." 


Wednesday, January 14, 2015

Superstrings For Dummies

Here's another educational video by Don Lincoln out of Fermilab. This time, it is on the basic idea (and the emphasis here is on BASIC) of String/Superstrings.


Thursday, January 08, 2015

Arrow Of Time Due To Gravity?

I just got back from vacation and an unexpected trip out of the country, so I'm still catching up. But when I came across a news article on physics in Business Insider, I had to read it, and you should to. It is on another model to explain the nature of the arrow of time in our universe.

Tentative new work from Julian Barbour of the University of Oxford, Tim Koslowski of the University of New Brunswick and Flavio Mercati of the Perimeter Institute for Theoretical Physics suggests that perhaps the arrow of time doesn’t really require a fine-tuned, low-entropy initial state at all but is instead the inevitable product of the fundamental laws of physics. Barbour and his colleagues argue that it is gravity, rather than thermodynamics, that draws the bowstring to let time’s arrow fly. Their findings were published in October in Physical Review Letters.

The team’s conclusions come from studying an exceedingly simple proxy for our universe, a computer simulation of 1,000 pointlike particles interacting under the influence of Newtonian gravity. They investigated the dynamic behavior of the system using a measure of its "complexity," which corresponds to the ratio of the distance between the system’s closest pair of particles and the distance between the most widely separated particle pair. The system’s complexity is at its lowest when all the particles come together in a densely packed cloud, a state of minimum size and maximum uniformity roughly analogous to the big bang. The team’s analysis showed that essentially every configuration of particles, regardless of their number and scale, would evolve into this low-complexity state. Thus, the sheer force of gravity sets the stage for the system’s expansion and the origin of time’s arrow, all without any delicate fine-tuning to first establish a low-entropy initial condition.