* Astronomy

Richard Feynman called the fine structure constant, alpha, "one of the greatest damn mysteries of physics: a magic number". One puzzle is whether this constant of nature has always had the same value. A signal from the early universe could answer that.
Alpha determines the strength of the electromagnetic force. Its value can be calculated by studying the so-called 21-cm line in the spectrum of neutral hydrogen atoms in the universe. The spectrum has a blip at a wavelength of 21 centimetres because the atoms absorb light at this wavelength in a manner that depends on alpha.
To find out if alpha has always been the same, Ben Wandelt and Rishi Khatri at the University of Illinois at Urbana-Champaign suggest measuring the 21-cm line from about 400,000 years after the big bang, when neutral hydrogen formed, to about 150 million years later when the first stars flared up.
As you go back in time the intensity of the 21-cm spectrum should follow an expected pattern that mirrors the varying amounts of neutral hydrogen at different times. Deviations from this would mean alpha had other values in the past.
So far, physicists have only studied alpha using the cosmic microwave background - the radiation left over from about 400,000 years after the big bang - but the 21-cm radiation can see variations at different times.

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A group of US physicists funded by the US Department of Energy have made a material capable of making light travel backwards, at speeds "that appear faster than the speed of light", at the smallest wavelength ever.

The work, led by Costas Soukoulis at Iowa State University, could pave the way for a "perfect lens", and could even have implications for the basic laws of physics.

"Snell's law on the refraction of light is going to be different; a number of other laws will be different" - Costas Soukoulis.

No natural material is capable of refracting light negatively, so scientists working in this area have to use so-called metamaterials, which can be engineered to have a negative refractive index. Normal materials have positive refractive indices, meaning that light bends to the right of an incident beam. Metamaterials can have a negative index, bending light backwards, to the left of the incident beam.

The ultimate goal is to make one that works at visible wavelengths, which would make it possible to build a perfect, flat lens. This is some way off, and in the meantime researchers must learn to build materials capable of refracting light at shorter and shorter wavelengths. So far, the best researchers have been able to manage is microwave or far-infrared radiation.
Soukoulis' material can negatively refract electromagnetic radiation at 1.5 micrometres, or in the near-infrared part of the spectrum. This makes it potentially useful for telecommunications.

"When we have a metamaterial with a negative index of refraction at 1.5 micrometers that can disperse, or separate a wave into spectral components with different wavelengths, we can tune our lasers to play a lot of games with light. We can have a wavepacket hit a slab of negative index material, appear on the right-hand side of the material and begin to flow backward before the original pulse enters the negative index medium" - Costas Soukoulis.

The pulse flowing backward also releases a forward pulse out the end of the medium. Thus, the pulse entering the front of the material appears to move out the back almost instantly.

"In this way, one can argue that that the wave packet travels with velocities much higher than the velocities of light. This is due to the dispersion of the negative index of refraction; there is nothing wrong with Einstein's theory of relativity" - Costas Soukoulis.

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An international team of astronomers has looked at something very big -- a distant galaxy -- to study the behaviour of things very small -- atoms and molecules -- to gain vital clues about the fundamental nature of our entire Universe. The team used the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT) to test whether the laws of nature have changed over vast spans of cosmic time.

"The fundamental constants of physics are expected to remain fixed across space and time; that's why they're called constants! Now, however, new theoretical models for the basic structure of matter indicate that they may change. We're testing these predictions" - Nissim Kanekar, an astronomer at the National Radio Astronomy Observatory (NRAO), in Socorro, New Mexico.

So far, the scientists' measurements show no change in the constants.

"We've put the most stringent limits yet on some changes in these constants, but that's not the end of the story. This is the exciting frontier where astronomy meets particle physics" - Christopher Carilli, NRAO astronomer.

The research can help answer fundamental questions about whether the basic components of matter are tiny particles or tiny vibrating strings, how many dimensions the Universe has, and the nature of "dark energy."

The astronomers were looking for changes in two quantities: the ratio of the masses of the electron and the proton, and a number physicists call the fine structure constant, a combination of the electron charge, the speed of light and the Planck constant, (alpha = 1/137.03599958).

These values, considered fundamental physical constants, once were "taken as time independent, with values given once and forever".
However, with ideas such as superstring theory and extra dimensions in space-time calling for the "constants" to change over time

"the viewpoint of modern particle theory has changed in recent years," - Christof Wetterich, German particle physicist.


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CREDIT: NRAO/AUI/NSF
The GBT is the world's largest fully steerable radio telescope. It is located in Green Bank, West Virginia. The GBT achieved "first light" in August 2000. The GBT stands 485 feet tall. Its dish measures 100 by 110 meters. Unlike conventional radio telescopes, which have a series of supports in the middle of the surface, the GBT's aperture is unblocked so incoming radiation meets the surface directly. This design increases the useful area of the telescope and eliminates reflection and diffraction that ordinarily complicate a telescope's pattern of response. The GBT weighs 7.3 million kg, and can be pointed with an accuracy of one arcsecond, or the equivalent to the width of a single human hair seen 2 m away. Composed of 2,004 metal panels, the telescope's surface covers almost 8,000 m2. The telescope is designed to handle a great range of wavelengths, from 3 m long down to 3 mm.

The astronomers used the Green Bank Telescope to detect and study radio emissions at four specific frequencies between 1612 MHz and 1720 MHz coming from hydroxyl (OH) molecules in a galaxy more than 6 billion light-years from Earth, seen as it was at roughly half the Universe's current age. Each of the four frequencies represents a specific change in the energy level of the molecule.

The exact frequency emitted or absorbed when the molecule undergoes a transition from one energy level to another depends on the values of the fundamental physical constants. However, each of the four frequencies studied in the OH molecule will react differently to a change in the constants. That difference is what the astronomers sought to detect using the GBT, which, is the ideal telescope for this work because of its technical capabilities and its location in the National Radio Quiet Zone, where radio interference is at a minimum.

"We can place very tight limits on changes in the physical constants by studying the behaviour of these OH molecules at a time when the Universe was only about half its current age, and comparing this result to how the molecules behave today in the laboratory" - Karl Menten, Max-Planck Institute for Radio astronomy in Germany.

Wetterich, a theorist, welcomes the new capability, saying the observational method "seems very promising to obtain perhaps the most accurate values for such possible time changes of the constants." He pointed out that, while some theoretical models call for the constants to change only in the early moments after the Big Bang, models of the recently-discovered, mysterious "dark energy" that seems to be accelerating the Universe's expansion call for changes "even in the last couple of billion years."

"Only observations can tell" - Christof Wetterich.

This research ties together the theoretical and observational work of Wetterich and Carilli, this year's winners of the prestigious Max Planck Research Award of the Alexander von Humboldt Foundation and the Max Planck Society in Germany. Menten and Carilli have collaborated on research in this area for years, and Kanekar has pioneered the OH molecular technique.

Kanekar, Carilli and Menten worked with Glen Langston of NRAO, Graca Rocha of the Cavendish Laboratory in the UK, Francoise Combes of the Paris Observatory, Ravi Subrahmanyan of the Australia Telescope National Facility (ATNF), John Stocke of the University of Colorado, Frank Briggs of the ATNF and the Australian National University, and Tommy Wiklind of the Space Telescope Science Institute in Sweden. The scientists reported their findings in the December 31 edition of the scientific journal Physical Review Letters.

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Scientists are debating clues that suggest the laws of physics change over time. University of California scientists are among the major players on both sides of the debate, which threatens to shake up our basic notions of reality.
At stake is one of the fundamental values in physics: the arcane-sounding "fine structure constant," which measures how subatomic particles interact with light and with each other.



Some astrophysicists have proposed that the value of the fine structure constant, a.k.a. "alpha," has changed subtly over billions of years. They base this proposal on their work -- using telescopes like the giant Keck telescope, which sits atop a dormant Hawaiian volcano -- analyzing light from interstellar gas and galaxy-gobbling super-furnaces called quasars on the outskirts of the universe.
If they're right, then our theories of the cosmos might be due for an overhaul. One speculation is that alpha is changing over time because of now- unknown alternate dimensions. As these hidden dimensions change shape, they change the fine structure constant.
But sceptics, citing observations that contradict the claim that alpha is changing, are plentiful -- and even the pro-change claimants are being cautious, partly because there's so much at risk. The notion that the laws of physics are eternal and unchanging is one of the ground-floor assumptions of everyday life -- when you drop a ball, for example, you expect it to fall, not to rise -- and no one wants to abandon that assumption unless they've got compelling reasons.
"We are claiming something extraordinary here," acknowledged astrophysicist Michael Murphy of Cambridge University in England, one of the scientists who reported possible evidence of a change in the fine structure constant at a scientific conference earlier this year. "And the evidence, though strong, is not yet extraordinary enough."
At another science conference, a group of Berkeley scientists reported that alpha is not changing, based on their independent analysis of light from galaxies.
Observational techniques
Murphy defends his observational technique as more precise than that of critics. As he reported recently, his latest observations have "a precision of 1 in a million. So it's about a factor of 30 better" than the technique deployed by critics.

The critics disagree. They say that their observational technique is relatively simple and, thus, yields pretty unambiguous results, whereas Murphy's technique is an especially complex one that is vulnerable to all kinds of "systematic errors," in scientific lingo.
In short, what's brewing is a dandy little scientific controversy. It's one in which, paradoxically, very much depends on very little -- that is, in which unimaginably slight variations in measurements could alter our understanding of the whole universe.
The idea that nature's laws change over time was proposed in the 1930s by one of the titans in the history of physics, Paul Dirac of England. According to Dirac's large numbers hypothesis, the force of gravity changed over time. Others modified his thesis to argue that the fine structure constant is, in fact, inconstant.
Twenty-one years after Dirac's death, his theory still hasn't been proved.
"These are very adventurous ideas -- and it's always healthy to challenge the things that 'everybody knows,' " says one of the nation's most distinguished astronomers, Robert Kirshner of Harvard. "I would be very surprised if there are measurable changes in the fine structure constant."

But, referring to the 1990s discovery of dark energy, a mysterious cosmic force that counteracts the force of gravity and causes the universe to expand faster over time, he added: "I was also very surprised that the 'cosmological constant' isn't zero! In any case, the burden of proof is on the person making an extraordinary claim. The rest of us are skeptical, but our minds are open to convincing evidence."

In mid-April, noted physicist-author Lee Smolin of the Perimeter Institute in Waterloo, Ontario, heard Murphy present his latest findings.
It is too soon to tell if the fine structure constant is changing.
"It is a very hard measurement, and there are many possible sources of error. ....I would not be surprised if the measurement is right. ... (I have) a nervous feeling that we have become too complacent (in cosmology), having gone too long without a shocking new experimental discovery."

Murphy, who has since moved to England, was part of an Australian scientific team led by astronomer John K. Webb that started the debate rolling again in 2001 with a report in the journal Physical Review Letters. Using the Keck telescope, they said, they had observed subtle anomalies in light from quasars.
Specifically, they reported puzzling shifts in the position of thin dark lines in the quasars' spectra, the rainbow-like bands of light produced when the light passes through a prism; just as the keys on a piano produce different frequencies of sound, the colours in the spectra correspond to different frequencies of light.
The dark spectral lines are absorption lines, which reveal how light is absorbed by different types of atoms in outer space, while thin bright emission lines reveal light emitted by atoms.
Here was the surprise: The faraway quasars' dark spectral lines occupied slightly different positions from those occupied by related lines in the spectra of light from laboratory instruments. It was, very roughly speaking, like discovering a new alphabet in which X comes before W.
The quasars are 12 billion light years away; the Australian scientists were literally looking back in time and seeing what the cosmos looked like 12 billion years ago.
They proposed an explanation for the anomaly in the position of the quasars' absorption lines: namely, the fine structure constant was very slightly weaker 12 billion years ago. Since the fine structure constant controls the strength of electromagnetism -- of which light is the visible manifestation -- it "therefore controls the way light and matter interact," Murphy says. Hence the anomalous absorption lines are signatures of a weaker constant long, long ago -- just after the Big Bang and more than 7 billion years before the formation of Earth.
Others conduct studies
Since then, scientists around the world have jumped into the debate. Some support the idea of long-term change in alpha, others contradict it, and yet others say it's too soon to decide. For example:
-- Astronomer Jeffrey Newman of Lawrence Berkeley National Laboratory reported at the American Physical Society meeting in Tampa in April that he had analyzed emission lines of light from galaxies up to 7 billion light years away. He detected no evidence of a long-term change in alpha, he said. Newman's results are pretty definitive, says his associate, astronomer Marc Davis of UC Berkeley.
-- Physicist Steve Lamoreaux of Los Alamos National Laboratory and his colleagues have analyzed data from a so-called natural nuclear reactor near Oklo in Gabon, Africa, where a large geological deposit of uranium has radioactively decayed over the last 2 billion years. In theory, a long-term variation in the fine structure constant should modify the concentration of radioactive waste products from the natural reactor -- and indeed, the Lamoreaux team has calculated that the fine structure constant has varied slightly.
"No one's published a counter-calculation to what we did, and I think it's pretty unlikely that (our claim is) going to change."
-- UC Berkeley physicist Dmitry Budker and colleagues are using sensitive lab instruments to check for changes in alpha over a period of a few years. So far, they have collected four months of measurements of the fine structure constant -- too little to suggest any conclusions one way or another.
Until more decisive evidence comes in, most astronomers are playing it safe. For now, they're assuming that Mother Nature is what she has always seemed to be: constant, not fickle.
"Until we have independent studies that converge on a single answer," says astronomer Stephen P. Maran, press officer for the American Astronomical Society and author of "Astronomy for Dummies," "the doubters will prevail, and the fine structure constant will continue to be regarded as well, constant."

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-- Edited by Blobrana at 01:27, 2005-05-10