New Uncertainty About the Uncertainty Principle

One of the most often quoted, yet least understood, tenets of physics is the uncertainty principle.


Formulated by German physicist Werner Heisenberg in 1927, the rule states that the more precisely you measure a particle's position, the less precisely you will be able to determine its momentum, and vice versa.


The principle is often invoked outside the realm of physics to describe how the act of observing something changes the thing being observed, or to point out that there's a limit to how well we can ever really understand the universe.


While the subtleties of the uncertainty principle are often lost on nonphysicists, it turns out the idea is frequently misunderstood by experts, too. But a recent experiment shed new light on the maxim and led to a novel formula describing how the uncertainty principle really works.




The uncertainty principle only applies in the quantum mechanical realm of the very small, on scales of subatomic particles. Its logic is perplexing to the human mind, which is acclimated to the macroscopic world, where measurements are only limited by the quality of our instruments.


But in the microscopic world, there truly is a limit to how much information we can ever glean about an object.


For example, if you make a measurement to find out exactly where an electron is, you will only be able to get a hazy idea of how fast it's moving. Or you might choose to determine an electron's momentum fairly precisely, but then you will have only a vague idea of its location.  [Graphic: Nature's Tiniest Particles Explained]


Heisenberg originally explained the limitation using a thought experiment. Imagine shining light at a moving electron. When a photon, or particle of light, hits the electron, it will bounce back and record its position, yet in the process of doing so, it has given the electron a kick, thereby changing its speed.


The wavelength of the light determines how precisely the measurement can be made. The smallest wavelength of light, called gamma-ray light, can make the most precise measurements, but it also carries the most energy, so an impacting gamma-ray photon will deliver a stronger kick to the electron, thereby disturbing its momentum the most.


Though not imparting as much disruption to the electron's momentum, a longer wavelength of light wouldn't allow as precise a measurement.




Marbles and billiard balls


"In the early days of quantum mechanics, people interpreted the uncertainty relation in terms of such back-reactions of the measurement process," said physicist Georg Sulyok of the Institute of Atomic and Subatomic Physics in Austria. "But this explanation is not 100 percent correct."


Sulyok worked with a research team, led by physicists Masanao Ozawa of Japan's Nagoya University and Yuji Hasegawa of Vienna University of Technology in Austria, to calculate and experimentally demonstrate how much of the uncertainty principle is due to the effects of measurement, and how much is simply due to the basic quantum uncertainty of all particles.


In quantum mechanics, particles can't be thought of as marbles or billiard balls — tiny, physically distinct objects that travel along a straight course from point A to point B. Instead, particles can behave like waves, and can only be described in terms of the probability that they are at point A or point B or somewhere in between.


This is also true of a particle's other properties, such as its momentum, energy and spin.


This probabilistic nature of particles means there will always be imprecision in any quantum measurement, no matter how little that measurement disturbs the system it is measuring.


"This has nothing to do with error or disturbances due to a measurement process, but is a basic fundamental property that every quantum mechanical particle has," Sulyok told LiveScience. "In order to describe the basic uncertainty together with measurement errors and disturbances, both particle and measurement device in a successive measurement have to be treated in the framework of quantum theory."


Calculating the uncertainty


To test how much this fundamental property contributes to the overall uncertainty, the researchers devised an experimental setup to measure the spin of a neutron in two perpendicular directions. These quantities are related, just as position and momentum are, so that the more precise a measurement is made of one, the less precise a measurement can be made of the other.


The physicists used magnetic fields to manipulate and measure the neutrons' spin, and conducted a series of measurements where they systematically changed the parameters of the measuring device.  


"You have this basic uncertainty, and then by measuring you add an additional uncertainty," Sulyok said. "But with an apparatus performing two successive measurements, you can identify the different contributions."


Using their data, the physicists were able to calculate just how the different types of uncertainty add together and influence each other. Their new formula doesn't change the conclusion of the Heisenberg uncertainty principle, but it does tweak the reasoning behind it.


"The explanation that Heisenberg gave is very intuitive," Sulyok said. "On a popular science level it is hardly ever distinguished at all, and sometimes it's even not correctly explained in university textbooks. The quantum-mechanically correct calculation reinforced by our experimental data is a valuable step in achieving a more consistent view on the uncertainty principle."


The results of the study were published in January 2012 in the journal Nature Physics

Planck All-Sky Images Show Cold Gas and Strange Haze

New images from the Planck mission show previously undiscovered islands of star formation and a mysterious haze of microwave emissions in our Milky Way galaxy. The views give scientists new treasures to mine and take them closer to understanding the secrets of our galaxy.

Planck is a European Space Agency mission with significant NASA participation.

"The images reveal two exciting aspects of the galaxy in which we live," said Planck scientist Krzysztof M. Gorski from NASA's Jet Propulsion Laboratory in Pasadena, Calif., and Warsaw University Observatory in Poland. "They show a haze around the center of the galaxy, and cold gas where we never saw it before."

The new images show the entire sky, dominated by the murky band of our Milky Way galaxy. One of them shows the unexplained haze of microwave light previously hinted at in measurements by NASA's Wilkinson Microwave Anisotropy Probe (WMAP).

"The haze comes from the region surrounding the center of our galaxy and looks like a form of light energy produced when electrons accelerate through magnetic fields," said Davide Pietrobon, another JPL Planck scientist. 

"We're puzzled though, because this haze is brighter at shorter wavelengths than similar light emitted elsewhere in the galaxy," added Gorski. 

Several explanations have been proposed for this unusual behaviour. 

"Theories include higher numbers of supernovae, galactic winds and even the annihilation of dark-matter particles," said Greg Dobler, a Planck collaborator from the University of California in Santa Barbara, Calif. Dark matter makes up about a quarter of our universe, but scientists don't know exactly what it is.

The second all-sky image is the first map to show carbon monoxide over the whole sky. Cold clouds with forming stars are predominantly made of hydrogen molecules, difficult to detect because they do not readily emit radiation. Carbon monoxide forms under similar conditions, and though it is rarer, the gas emits more light. Astronomers can use carbon monoxide to identify the clouds of hydrogen where stars are born. 

Surveys of carbon monoxide undertaken with radio telescopes on the ground are time-consuming, so they are limited to portions of the sky where clouds of molecules are already known or expected to exist. Planck scans the whole sky, allowing astronomers to detect the gas where they weren't expecting to find it. 

Planck's primary goal is to observe the Cosmic Microwave Background, the relic radiation from the Big Bang, and to extract its encoded information about what our universe is made of, and the origin of its structure.

This relic radiation can only be reached once all sources of foreground emission, such as the galactic haze and the carbon monoxide signals, have been identified and removed.

"The lengthy and delicate task of foreground removal provides us with prime datasets that are shedding new light on hot topics in galactic and extragalactic astronomy alike," said Jan Tauber, Planck project scientist at the European Space Agency

Spirit Lander and Bonneville Crater in Color

Near the lower left corner of this view is the three-petal lander platform that NASA's Mars Exploration Rover Spirit drove off in January 2004. The lander is still bright, but with a reddish color, probably due to accumulation of Martian dust.

The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter recorded this view on Jan. 29, 2012, providing the first image from orbit to show Spirit's lander platform in color. The view covers an area about 2,000 feet (about 600 meters) wide, dominated by Bonneveille Crater. North is up. A bright spot on the northern edge of Bonneville Crater is a remnant of Spirit's heat shield.

Spirit spent most of its six-year working life in a range of hills about two miles east of its landing site. An image of the lander platform taken by Spirit's Panoramic Camera (Pancam) after the rover had driven off is at PIA05117. The bright heat shield remnant can be seen in a panorama the same camera took of Bonneville Crater, at PIA05591.

This image is one product from HiRISE observation ESP_025815_1655. Other products from the same observation can be found at http://hirise.lpl.arizona.edu/ESP_025815_1655 

Habitable Zones Around Alien Suns May Depend on Chemistry

This diagram compares our own solar system to Kepler-22, a star system containing the first "habitable zone" planet discovered by NASA's Kepler mission.

Trace elements in stars may influence the evolution of habitable zones around them where life as we know it might dwell, scientists now find.

Stars are made nearly entirely from hydrogen and helium gas. Still, traces of heavier elements — which astronomers call metals, even if they are not what one normally think of as metals — can be found in stars as well, either inherited from the remains of older stars or forged via nuclear fusion.

Scientists can detect what elements a star possesses by looking at its light, which comes in a wide variety of wavelengths, some visible, many invisible. The wavelengths of light that matter emits often comes in specific clumps or lines, which can act like a fingerprint, revealing the identity of the material in question.

By looking at the wavelengths or spectra of light from nearby dwarf stars as part of searches for alien worlds, or exoplanets, researchers have with high precision determined the abundance of certain elements for more than a hundred of these stars, with more to come. Now researchers suggest variations in the compositions of these stars could impact the habitable zones around them.

Finding the habitable zone

Normally scientists figure out the habitable zones of stars by seeing how hot the stars are. This involves looking at their brightness and color. Computer models now suggest that variations in a star's elemental composition might alter its long-term behavior, significantly affecting the location and lifetime of its habitable zone.

"I was expecting some subtle changes in our stellar evolution models in terms of the surface temperature and brightness — I was not looking for such a dramatic change in the lifetimes of the stars," said study lead author Patrick Young, a theoretical astrophysicist and astrobiologist at Arizona State University.

Scientists typically measure the abundance of heavy elements in a star relative to the iron content in its atmosphere, as iron is a common element and its spectrum is relatively easy to measure. Past research found that abundances of various heavy elements could vary by more than a factor of two given otherwise similar star types


Young and his colleagues generated computer models for how variations in levels of eight elements — carbon, oxygen, sodium, aluminum, magnesium, silicon, calcium and titanium — might affect the behavior of F, G and K stars, those most similar to our sun. Metals in a star can alter its evolution by affecting how opaque its plasma is.

"The persistence of stars as stable objects relies on the heating of plasma in the star by nuclear fusion to produce pressure that counteracts the inward force of gravity," Young explained. "A higher opacity traps the energy of fusion more efficiently and results in a larger radius, cooler star. More efficient use of energy also means that nuclear burning can proceed more slowly, resulting in a longer lifetime for the star."

Elements of stars

The scientists found that calcium, sodium, magnesium, aluminum and silicon had small but significant effects on a star's evolution. Higher levels of these elements resulted in cooler, redder stars.

Oxygen also proved especially important because it could dramatically alter the lifetime of a star's habitable zone.

"The habitable lifetime of an orbit the size of Earth's around a one-solar-mass star is only 3.5 billion years for oxygen-depleted compositions but 8.5 billion years for oxygen-rich stars," Young said. "For comparison, we expect the Earth to remain habitable for another billion years or so, for about 5.5 billion years total, before the sun becomes too luminous. Complex life on Earth arose some 3.9 billion years after its formation, so if Earth is at all representative, low-oxygen stars are perhaps less than ideal targets."

Moreover, the presence of oxygen was linked with ultraviolet radiation, which is known to damage cells. "A star that is otherwise like the sun in iron abundance and mass but relatively scarce in oxygen could produce twice as much of the cell-damaging radiation that causes skin cancer and is sometimes used for sterilization," Young said.

Young did note that habitable zones are a rather nebulous concept, since they depend on the atmosphere and geological evolution of a planet, making it tricky to draw any conclusions about the lifetime or extent of habitable zones.

"This is why we concentrate on the stellar modeling," Young said. "We can provide input to any climate model other researchers wish to use. For illustrative purposes we have chosen a simple, conservative prescription, not too optimistic or pessimistic."

A better knowledge of where a star's habitable zone really lies could influence which exoplanets astrobiologists end up studying more and which they end up ignoring because they lie outside habitable zones.

"Kepler has already detected worlds in the current habitable zones of their stars and planets smaller than Earth, and there are dozens more candidates that await confirmation," Young said. "Detecting a planet with life will be a difficult proposition at best, requiring too many resources to observe indiscriminately. With this information we can narrow down our search to planets that are not only currently in their habitable zones, but have been and will remain there for long enough to potentially develop complex life."

The composition of a star can also influence the composition of its planets. Two important considerations are the carbon-oxygen and magnesium-silicon ratios of stars, which can affect whether a planet has certain magnesium- or silicon-loaded clay minerals such as magnesium silicate (MgSiO3), silicon dioxide (SiO2), magnesium orthosilicate (Mg2SiO4), and magnesium oxide (MgO). Clay minerals seem to be a good surface to create key components of life, such as the lipid membranes of cells.

"This is why one of the targets of the Mars Science Laboratory will be phyllosilicate clays in Gale Crater," Young said. "Some clays are better than others, and the magnesium-silicon ratio in part determines the type of clay formed."

Variety of cosmic elements

Variations in the compositions of stars could also lead to planets that have different elemental combinations dominating, such as a planet with mostly carbon-based rock as opposed to our silicon-based Earth. "We'd expect tectonics and volcanism to be very different on a planet whose crust is dominated by graphite and silicon carbide than on Earth."

Certain elements within a star also strongly line up with the abundance of radioactive elements such as uranium and thorium, which are key in determining how molten the interior of planets are, Young said. Molten planetary interiors are key to plate tectonics, which in turn may be important to the evolution of life on Earth.

Young noted that some of the elements they would like to look at are very difficult to observe. For instance, "we want to find trace elements that are important to terrestrial-style life like molybdenum and phosphorus," he said. "I am conducting other research to find abundant elements that we could use as proxies for finding enhancements in those trace elements because they are produced in the same conditions inside stars or stellar explosions."

The researchers are now analyzing the elemental abundances seen in 600 stars that are targets of exoplanet searches.   They are also producing a much larger set of stellar evolution models for different mass stars and compositions.

"We will be producing a list of what we consider the best 100 targets for habitable planet searches based on a number of criteria including those presented in this work," Young said.

NASA's Kepler Announces 11 New Planetary Systems

NASA's Kepler mission has discovered 11 new planetary systems hosting 26 confirmed planets. These discoveries nearly double the number of verified Kepler planets and triple the number of stars known to have more than one planet that transits, or passes in front of, the star. Such systems will help astronomers better understand how planets form. 

The planets orbit close to their host stars and range in size from 1.5 times the radius of Earth to larger than Jupiter. Fifteen are between Earth and Neptune in size. Further observations will be required to determine which are rocky like Earth and which have thick gaseous atmospheres like Neptune. The planets orbit their host star once every six to 143 days. All are closer to their host star than Venus is to our sun. 

"Prior to the Kepler mission, we knew of perhaps 500 exoplanets across the whole sky," said Doug Hudgins, Kepler program scientist at NASA Headquarters in Washington. "Now, in just two years staring at a patch of sky not much bigger than your fist, Kepler has discovered more than 60 planets and more than 2,300 planet candidates. This tells us that our galaxy is positively loaded with planets of all sizes and orbits." 

Kepler identifies planet candidates by repeatedly measuring the change in brightness of more than 150,000 stars to detect when a planet passes in front of the star. That passage casts a small shadow toward Earth and the Kepler spacecraft. 

"Confirming that the small decrease in the star's brightness is due to a planet requires additional observations and time-consuming analysis," said Eric Ford, associate professor of astronomy at the University of Florida and lead author of the paper confirming Kepler-23 and Kepler-24. "We verified these planets using new techniques that dramatically accelerated their discovery." 

Each of the newly confirmed planetary systems contains two to five closely spaced transiting planets. In tightly packed planetary systems, the gravitational pull of the planets on each other causes some planets to accelerate and some to decelerate along their orbits. The acceleration causes the orbital period of each planet to change. Kepler detects this effect by measuring the changes, or so-called Transit Timing Variations. 

Planetary systems with Transit Timing Variations can be verified without requiring extensive ground-based observations, accelerating confirmation of planet candidates. This detection technique also increases Kepler's ability to confirm planetary systems around fainter and more distant stars. 

"By precisely timing when each planet transits its star, Kepler detected the gravitational tug of the planets on each other, clinching the case for 10 of the newly announced planetary systems," said Dan Fabrycky, Hubble Fellow at the University of California, Santa Cruz, and lead author for a paper confirming Kepler-29, 30, 31 and 32. 

Five of the systems (Kepler-25, Kepler-27, Kepler-30, Kepler-31 and Kepler-33) contain a pair of planets where the inner planet orbits the star twice during each orbit of the outer planet. Four of the systems (Kepler-23, Kepler-24, Kepler-28 and Kepler-32) contain a pairing where the outer planet circles the star twice for every three times the inner planet orbits its star. 

"These configurations help to amplify the gravitational interactions between the planets, similar to how my sons kick their legs on a swing at the right time to go higher," said Jason Steffen, the Brinson postdoctoral fellow at Fermilab Center for Particle Astrophysics in Batavia, Ill., and lead author of a paper confirming Kepler-25, 26, 27 and 28. 

Kepler-33, a star that is older and more massive than our sun, had the most planets. The system hosts five planets, ranging in size from 1.5 to 5 times that of Earth. All of the planets are located closer to their star than any planet is to our sun. 

The properties of a star provide clues for planet detection. The decrease in the star's brightness and duration of a planet transit combined with the properties of its host star present a recognizable signature. When astronomers detect planet candidates that exhibit similar signatures around the same star, the likelihood of any of these planet candidates being a false positive is very low. 

"The approach used to verify the Kepler-33 planets shows the overall reliability is quite high," said Jack Lissauer, planetary scientist at NASA Ames Research Center at Moffett Field, Calif., and lead author of the paper on Kepler-33. "This is a validation by multiplicity."

Primordial Galaxy Cluster is Farthest Ever Seen

The composite image at left, taken in visible and near-infrared light, reveals the location of five tiny galaxies clustered together 13.1 billion light-years away. The circles pinpoint the galaxies

NASA Probe Data Show Liquid Water Evidence on Europa

PASADENA, Calif. -- Data from a NASA planetary mission have provided scientists evidence of what appears to be a body of liquid water, equal in volume to the North American Great Lakes, beneath the icy surface of Jupiter's moon, Europa. 

The data suggest there is significant exchange between Europa's icy shell and the ocean beneath. This information could bolster arguments that Europa's global subsurface ocean represents a potential habitat for life elsewhere in our solar system. The findings are published in the scientific journal Nature.

"The data open up some compelling possibilities," said Mary Voytek, director of NASA's Astrobiology Program at agency headquarters in Washington. "However, scientists worldwide will want to take a close look at this analysis and review the data before we can fully appreciate the implication of these results."  

NASA's Galileo spacecraft, launched by the space shuttle Atlantis in 1989 to Jupiter, produced numerous discoveries and provided scientists decades of data to analyze. Galileo studied Jupiter, which is the most massive planet in our solar system, and some of its many moons.

One of the most significant discoveries was the inference of a global saltwater ocean below the surface of Europa. This ocean is deep enough to cover the whole surface of Europa and contains more liquid water than all of Earth's oceans combined. However, being far from the sun, the ocean surface is completely frozen. Most scientists think this ice crust is tens of miles thick.

"One opinion in the scientific community has been if the ice shell is thick, that's bad for biology. That might mean the surface isn't communicating with the underlying ocean," said Britney Schmidt, lead author of the paper and postdoctoral fellow at the Institute for Geophysics, University of Texas at Austin. "Now, we see evidence that it's a thick ice shell that can mix vigorously and new evidence for giant shallow lakes. That could make Europa and its ocean more habitable."

Schmidt and her team focused on Galileo images of two roughly circular, bumpy features on Europa's surface called chaos terrains. Based on similar processes seen on Earth -- on ice shelves and under glaciers overlying volcanoes -- they developed a four-step model to explain how the features form. The model resolves several conflicting observations. Some seemed to suggest the ice shell is thick. Others suggest it is thin. 

This recent analysis shows the chaos features on Europa's surface may be formed by mechanisms that involve significant exchange between the icy shell and the underlying lake. This provides a mechanism or model for transferring nutrients and energy between the surface and the vast global ocean already inferred to exist below the thick ice shell. This is thought to increase the potential for life there.

The study authors have good reason to believe their model is correct, based on observations of Europa from Galileo and of Earth. Still, because the inferred lakes are several miles below the surface, the only true confirmation of their presence would come from a future spacecraft mission designed to probe the ice shell. Such a mission was rated as the second highest priority flagship mission by the National Research Council's recent Planetary Science Decadal Survey and is being studied by NASA. 

"This new understanding of processes on Europa would not have been possible without the foundation of the last 20 years of observations over Earth's ice sheets and floating ice shelves," said Don Blankenship, a co-author and senior research scientist at the Institute for Geophysics, where he leads airborne radar studies of the planet's ice sheets.