I’m in a magazine!
Physics is largely a matter of finding patterns in natural processes and translating that to mathematical expression. That’s a horribly oversimplified view, of course, but there’s no question that physics (and other branches of science) seeks to find symmetries. The huge successes of modern particle physics have largely arisen from identifying symmetries — and when those symmetries break down. To cite just one: physicists understand the weak force, which governs neutrinos and processes like nuclear beta decay, using a mathematical symmetry. That symmetry isn’t perfect, however, and one outward manifestation of that imperfection is the Higgs boson.
This pattern-seeking behavior among physicists is the theme of Dave Goldberg’s book The Universe in the Rearview Mirror: How Hidden Symmetries Shape Reality. I reviewed the book for Physics World, which marks my first publication in a print magazine. (It also may be the first time The Decemberists were quoted in Physics World.) You can read my review online, though the site requires a free registration to do so. In brief, I enjoyed the book, but found a few problems with it as well.
Inevitably, Goldberg’s explanations vary in quality. I found his discussion of the Casimir and Unruh effects (weird quantum phenomena in the vacuum) to be very good introductions for non-specialists. He also provides an excellent summary of the problems facing attempts to unify the different forces of nature, and specifically the question of pro- ton decay. On the other hand, his explanation of Lagrangians and the principle of least action (both essential topics in a mathematical sense) falls short, since it requires him to define a lot of new terminology in just a few pages, most of it barely mentioned again. The book also misses an opportunity to explain how specific symmetries shaped the development of the Standard Model; while it outlines a few of the important symmetries (including parity or reflection symmetry, time-reversal, time-translation, and exchange of matter and antimatter) early on, it fails to bring them back into the picture when the Standard Model is discussed. [Read more…]
The BICEP2 telescope (foreground) with the South Pole Telescope (SPT) behind. [Credit: Steffen Richter (Harvard University)]
Today was an exciting and stimulating day: the BICEP2 collaboration announced the first measurement of the cosmic microwave background that might tell us whether or not inflation happened. Inflation is the hypothetical rapid expansion of the Universe during its first instants, which explains a lot about why the cosmos appears the way it does. However, data on inflation itself, as opposed to its side-effects, are hard to come by. This new observation could help resolve that
…assuming we can figure out why some of its aspects don’t agree with prior observations.
While they do not constitute a direct detection of either primordial gravitational waves (the distortions causing the light polarization) or inflation, the BICEP2 results could provide the best evidence for both that could not be easily explained away by other theories. This observation cannot be the end of the story, however. The measurement of polarization is significantly larger that what is seen in the results of prior observations in a way that cannot be immediately dismissed. Whether the problems are with the interpretation and analysis of the BICEP2 data, or if something more subtle is at work, remains to be seen. [Read more….]
A visual representation of the “axis of evil”: the strange alignment of temperature fluctuations on the largest scales on the sky. [Credit: Craig Copi]
On the largest scales — far bigger than any galaxy or galaxy cluster — the Universe is remarkably smooth and regular. Tiny irregularities in the early cosmos are what gave rise to all the structures we see today, including us, but there’s another irregularity covering the whole sky. The Universe appears to be ever-so-slightly lopsided, an anomaly facetiously known as the “axis of evil”. Cosmologists are concerned with trying to understand whether the anomaly is a significant challenge to our understanding of some of the laws of physics, or whether it can be understood either as a new astronomical source or a random fluke based on the fact that the whole cosmos is much larger than our observable Universe.
In my latest feature article at Ars Technica, I explored why the “axis of evil” could be a big deal and how some physicists are trying to understand it.
The lopsidedness is real, but cosmologists are divided over whether it reveals anything meaningful about the fundamental laws of physics. The fluctuations are sufficiently small that they could arise from random chance. We have just one observable Universe, but nobody sensible believes we can see all of it. With a sufficiently large cosmos beyond the reach of our telescopes, the rest of the Universe may balance the oddity that we can see, making it a minor, local variation.
However, if the asymmetry can’t be explained away so simply, it could indicate that some new physical mechanisms were at work in the early history of the Universe. [Read more….]
Astronomers measured the rotation of a black hole from halfway across the Universe.
What, I need to say more?
Astronomers have now used gravitational magnification to measure the rotation rate of a supermassive black hole in a very distant galaxy. From four separate images of the same black hole, R.C. Reis, M.T. Reynolds, J.M. Miller, and D.J. Walton found it was spinning nearly as fast as possible. That likely means it was spun up by a small number of mergers with other black holes rather than a gradual increase from eating smaller amounts of mass.
This marks the first measurement of black hole rotation outside the local Universe…. [Read more]
The Cassiopeia A supernova remnant. [Credit: NASA/CXC/SAO]
Nearly every atom of your body was forged in a supernova explosion and dispersed into space. But how do massive stars explode? The details are complicated, pushing the limits of computer simulations and our ability to observe with telescopes. In the absence of very close-by events, the best data come from supernova remnants: the still-glowing gas ejected during the explosion. A new set of observations of X-ray emissions from radioactive titanium in the Cassiopeia A supernova remnant show that it was a
lumpy space princess
highly asymmetrical explosion. That agrees with theory, but the researchers also turned up an odd disconnect between the titanium and other materials
Cassiopeia A (abbreviated Cas A) is a historical oddity. The supernova was relatively close to Earth—a mere 11,000 light-years distant—and should have been visible around CE 1671, yet no astronomers of any culture recorded it. That’s in stark contrast to famous earlier explosions: Tycho’s supernova, Kepler’s supernova, and of course the supernova that made the Crab Nebula. This mysterious absence has led some astronomers to speculate that some unknown mechanism diffused the energy from the explosion, making the supernova far less bright than expected. [Read more…]
Calvin has it right.
“Dark energy” is one of the more unfortunate names in science. You’d think it has something to do with dark matter (itself a misnomer), but it has the opposite effect: while dark matter drives the clumping-up of material that makes galaxies, dark energy pushes the expansion of the Universe to greater and greater rates. Though we should hate on the term “dark energy”, we should respect Michael Turner, the excellent cosmologist who coined the phrase. He is also my academic “grand-advisor”: he supervised Arthur Kosowsky’s PhD, and Arthur in turn supervised mine.
And of course, I worked on dark energy as a major part of my PhD research. In my latest piece for Slate, I describe a bit of my dysfunctional relationship with cosmic acceleration, and why after 16 years dark energy is still a matter of frustration for many of us.
Because dark energy doesn’t correspond easily to anything in the standard toolkit of physics, researchers have been free to be creative. The result is a wealth of ideas, some that are potentially interesting and others that are frankly nuts. Some string theorists propose that our observable universe is the result of a vast set of parallel universes, each with a different, random amount of dark energy. Other physicists think our cosmos is interacting with a parallel universe, and the force between the two drives cosmic acceleration. Still others suspect that dark energy is a sign that our currently accepted theory of gravity—Einstein’s general theory of relativity—is incomplete for the largest distances. [Read more…]
Chandra space telescope image of an X-ray binary system containing a neutron star. [Credit: X-ray: NASA/CXC/Univ. of Wisconsin-Madison/S.Heinz et al; Optical: DSS; Radio: CSIRO/ATNF/ATCA]
About 380,000 years after the Big Bang, the Universe cooled off enough for stable atoms to form out of the primordial plasma. However, sometime in the billion years or so after that, something happened to heat the gas up again, returning it to plasma form. Though we know reionization (as it is called) happened, that epoch in the history of the cosmos is hard to study, so we don’t know exactly when and how the reheating happened. If a new proposed model is correct, though, ionization happened close to the end of that era, and was driven by binary systems containing a black hole or neutron star
One new model, proposed by Anastasia Fialkov, Rennan Barkana, and Eli Visbal, suggests that energetic X-rays could have heated the primoridal gas to the point that reionization happened relatively rapidly. That’s in contrast with other hypotheses, which predict a more gradual reionization process. The X-rays in the new model were emitted by systems that include neutron stars or black holes. The nicest feature of the new proposal is that it predicts a unique pattern in light emission from the primordial gas, which could conceivably be measured by current radio telescopes. [Read more….]