Tweaking Einstein on the Nature of Light

It makes sense to this former Midwesterner that Alan Kostelecky can compare light to waves propagating across a field of grain. After all, Kostelecky works at Indiana University, in a state where fields of grain are not so far from view. The theoretical physicist argues in research published online today in Physical Review D that we could consider light as the result of small violations of relativity, which compare not only to waving wheat but to “…a shimmering of ever-present vectors in empty space.”

Having seen my share of winds rippling across wheat fields, I know one thing: a propagating wave in a nearby crop comes with a sense of directionality. You know which way the wind is coming from, and how it’s affecting the local environment. Thinking of light in such terms is a far cry from a view with a much longer pedigree, that light depends upon an an underlying symmetry that is built into nature itself.

Waving wheat in the windThink of symmetry this way: Spacetime in the Einstein model has no preferred or distinguishable direction; this proposition is known as Lorentz invariance. A break from the Einsteinian view would occur if, for example, an underlying energy field permeated the universe, allowing interactions with particles that created directionality, just as a magnetic field favors a particular orientation in spacetime. Another possibility: finding subtle differences in the behavior of matter and antimatter could undermine the presumed symmetry and suggest a deeper solution.

Kostelecky and co-author Robert Bluhm of Colby College say that light may indeed break such symmetry. “Nature’s beauty is more subtle than perfect symmetry,” Kostelecky said. “The underlying origin of light may be another example of this subtlety.” What relativity may provide is a highly accurate approximation of how the universe works, but perhaps not the final answer. Variations in relativity could be clues in the attempt to build a true unified theory.

If light is somehow creating tiny violations of Einsteinian relativity, how could such effects be tested? The authors answer that equipment from particle accelerators to atomic clocks may be able to tell us that there are asymmetries between some particles and antiparticles, and perhaps cyclic variations in their behavior dependent on the Earth’s rotation. Much experimental work lies ahead, and you can get details galore in a FAQ at Kostelecky’s Web site.

So is relativity wrong? Not any more than Newtonian physics is ‘wrong,’ the point being that each is valid within the parameters of the tests that have been devised to measure it. But studying odd effects around the edges can expand our view, just as oddities in the way stars shifted behind a solar eclipse in 1919 helped us to confirm an Einsteinian understanding of a previously Newtonian view of orbital mechanics. An article called “Is Special Relativity Wrong?” on the American Institute of Physics news site offers useful background.

A preprint of the paper “Spontaneous Lorentz Violation, Nambu-Goldstone Modes, and Gravity” can be found at the ArXiv site. See Kostelecky’s site for a useful page containing animations on the topic of breaking spacetime symmetries. A University of Indiana press release on Kostelecky and Bluhm’s recent work is here.

Puzzling Stars in Omega Centauri

Globular clusters are vast cities of tens of thousands of stars, traditionally thought to have been formed from a single interstellar cloud at roughly the same time. But Omega Centauri is different. As viewed by Hubble, this southern cluster (15,000 light years away in the direction of the constellation Centaurus) contains two separate stellar populations. Its blue stars, about one quarter of the total, are well outnumbered by a second hydrogen-burning population of redder stars.

Now the European Southern Observatory’s Very Large Telescope has collected data that show the blue stars, contrary to expectation, are metal-rich when compared to their red counterparts, meaning they include elements heavier than hydrogen and helium. Astronomers call elements heavier than helium ‘metals’ — the Sun, for example, is made up of 70 percent hydrogen and 28 percent helium, with the remaining two percent being classed as metals.

Omega Centauri clusterCurrent theories of star formation suggest that as metallicity increases, stars become redder. According to the ESO team, the only way to explain the oddity of metal-rich blue stars is to assume that they have a far higher helium content than their red counterparts. That would make them the most helium-rich stars ever found, and raises a major question: with the present abundance of helium in the Milky Way at 28 percent, how did this globular cluster produce stars with a 39 percent abundance?

Image: Omega Centauri, largest of the 160 globular clusters in the Mily Way. In the center of such a cluster, stars are packed more than 10,000 times more closely than in the neighborhood of our Sun. Credit: P. Seitzer (U. Michigan).

ESO’s Luigi Bedin has a possible solution:

“The scenario we presently favour is one in which the high helium content originates from material ejected during the supernovae explosions of massive stars. It is possible that the total mass of Omega Centauri was just right to allow the material expelled by high-mass supernovae to escape, while the matter from explosions of stars with about 10-12 times the mass of the Sun was retained.”

Omega Centauri, then, would have seen two generations of stars. The first produced the redder stars, whose most massive members exploded as supernovae within tens of millions of years. The second population of blue stars then formed from this helium-rich environment. But the real issue raised by Omega Centauri is broader: why did this globular cluster produce extremely helium-rich stars, whereas all other known clusters did not?

Centauri Dreams take: another suggestion that globular cluster star formation is poorly understood comes from a Hubble study that scanned the globular star cluster 47 Tucanae (located 15,000 light-years away in the southern constellation Tucana) using the transit method to search for planets. As reported in 2000, the team expected to find about 17 hot Jupiter-class planets, but they found none at all. Is the deficiency of heavier elements found in most globular clusters an indication that planets can only form in a metal-rich universe? And if so, what does this imply about Omega Centauri?

For more on the Omega Centauri conundrum, see Piotto, G., Villanova, S. Begin, L. et al., “Metallicities on the Double Main Sequence of omega Centauri Imply Large Helium Enhancement,” now available on the ArXiv site and also in the March 10 issue of the Astrophysical Journal, Vol. 621, p. 777. ESO’s press release is here.

Surprise at Enceladus

How does a moon that would fit within the state boundaries of Arizona manage to hold an atmosphere? That’s the question following Cassini’s most recent flyby of Enceladus. The spacecraft found magnetic field oscillations that scientists now attribute to ionized water vapor. The odd magnetic field signature has shown up on both Cassini flybys, the second of which, on March 9, came to within 500 kilometers of the Saturnian moon’s surface.

Atmosphere of Enceladus diagrammed

Image: This artist conception shows the detection of an atmosphere on Saturn’s icy moon Enceladus. The Cassini magnetometer instrument is designed to measure the magnitude and direction of the magnetic fields of Saturn and its moons. During Cassini’s two close flybys of Enceladus — Feb. 17 and March 9 — the instrument detected a bending of the magnetic field around Enceladus. Credit: NASA/JPL.

Because Enceladus is too small to hold an atmosphere for long, a continuous source of replenishment is suspected. The most likely candidate: volcanoes or geysers, which have been found elsewhere in the Solar System on Jupiter’s moon Io and Neptune’s moon Triton. “Enceladus,” says Dr. Fritz Neubauer, co-investigator for the Cassini magnetometer, and a professor at the University of Cologne in Germany, “could be Saturn’s more benign counterpart to Jupiter’s dramatic Io.” And ‘ice volcanoes’ could explain the remarkably high reflectivity of the moon as ice particles are continuously deposited on the surface. Enceladus reflects 90 percent of the light that hits it.

More on the Enceladus findings in this JPL news release.

On Propulsion, Dark Energy, and Humility

Exotic forms of propulsion like warp drives or journeys through wormholes often seem like pure fantasy. It was Harvard’s Edward Purcell, no stranger to the study of the cosmos through his work as a radio astronomer, who made the classic negative case: “All this stuff about traveling around the universe in space suits — except for local exploration which I have not discussed — belongs back where it came from, on the cereal box.”

But then humility returns and we realize how little we know. It would have astounded Purcell, as it astounds Centauri Dreams, to think that 70 percent of the universe is now considered to be ‘dark energy,’ the exact nature of which mystifies our greatest thinkers other than to say that without it, the universe would not be continuing to expand — and accelerating its expansion, at that. And, of course, another 25 percent of the universe is equally bizarre, the so-called ‘dark matter’ that seems to pervade the cosmos.

Computer view of dark energySo our notions of interstellar flight have to take into account the fact that we have a sound working knowledge of only five percent of the universe, the ordinary matter we are all made of. We recently looked at Fabio Governato’s work on dark energy and a computer model his team used to model galaxy formation. As shown in the illustration, Governato views the universe as a sea of dark energy out of which galaxies emerge.

Image: A supercomputer-produced cross-section of part of the universe shows galaxies as brighter dots along filaments of matter, with a sea of dark energy filling in between the galactic islands. Credit: James Wadsley, McMaster University, Hamilton, Ontario.

Further information on Governato’s work can be found in this University of Washington press release. It’s fascinating stuff, and leads this writer to suppose that a universe aswarm with unknown energies might be one with serious prospects for advanced propulsion.

But not everyone is convinced about dark energy. A paper submitted to Physical Review Letters now argues there is no such thing; instead, the observed acceleration of the universe is the result of cosmological inflation. The authors, Edward W. Kolb (Fermi National Accelerator Laboratory, Chicago), Sabino Matarrese (University of Padova), Alessio Notari (University of Montreal), and Antonio Riotto of (Istituto Nazionale di Fisica Nucleare, Italy) are disturbed by the lack of a sound theoretical model to explain dark energy.

“If dark energy were the size that theories predict, the universe would have expanded with such a fantastic velocity that it would have prevented the existence of everything we know in our cosmos,” says Antonio Riotto.

Perhaps we need to return to the standard cosmological model. Inflationary theory posits that immediately following the Big Bang, the universe underwent a huge expansion, one that explains the apparent homogeneity of the cosmos. Such an expansion would cause ripples in spacetime that stretch beyond the boundaries of the visible universe. The development of these ripples over time, the authors believe, may account for the observed acceleration and does away with the need for dark energy.

“We realized that you simply need to add this new key ingredient, the ripples of spacetime generated during the epoch of inflation, to Einstein’s General Relativity to explain why the universe is accelerating today,” Riotto says. “It seems that the solution to the puzzle of acceleration involves the universe beyond our cosmic horizon. No mysterious dark energy is required.”

You can read more in a press release from the Istituto Nazionale di Fisica Nucleare. These are serious issues, yet the reader can be pardoned a certain sense of whimsy. What we are seriously discussing is whether seventy percent of the universe is made up of a bizarre force we cannot understand or is explicable by more ‘conventional’ models like inflation (which itself only emerged in 1981, and has now been confirmed by observations from the WMAP satellite).

Humility, anyone? No matter how these issues are ultimately resolved, Centauri Dreams opts for the notion that even the back of a cereal box may contain its share of mysteries. We are dwarfed by a universe we are only beginning to comprehend. Pushing into the bewildering world of dark energy is one more reminder that the final word is never spoken on any technology.

New Exoplanet Findings Promised for Next Week

NASA will announce “… major findings about planets outside our solar system…” in a press conference to be held at 1 PM EST on Wednesday March 23. NASA TV is planning to cover the event live. The new data come from the Spitzer Space Telescope, which works in the infrared and most recently made the news with its findings of remarkably bright galaxies hidden by dust some 11 billion light years away. The NASA press release can be read here.