Einstein's General Relativity Confirmed

Proof Is in the Cosmos: Einstein's General Relativity Confirmed

Composite image of the galaxy cluster Abell 2744, also known as Pandora's Cluster, taken by the Hubble and Chandra space telescopes and the Very Large Telescope in Chile. Hot intracluster gas is shown in pink, and the blue overlay maps the location of dark matter. CREDIT: NASA, ESA, ESO, CXC, and D. Coe (STScI)/J. Merten (Heidelberg/Bologna) View full size image

Albert Einstein wins again. His general theory of relativity has proved accurate in predicting how light travels from some of the most distant galaxy clusters in the universe, according to new measurements.

However, the findings still do not disprove an alternative theory of gravity invented to undo the need for dark energy, which is thought to be causing the accelerated expansion of the universe.

The new findings come from a study of light from hundreds of thousands of distant galaxies. General relativity predicts that the wavelength of this light will be shifted by a small amount due to the galaxies' mass, in an effect called gravitational redshift.

The effect is very difficult to measure, because it is the smallest of the three types of redshift, with redshift also being caused by the movement of the galaxies and the expansion of the universe as a whole. To disentangle the three sources of redshift, the researchers relied on the vast number of galaxies in the Sloan Digital Sky Survey sample, which allowed them to perform a statistical analysis. [Twisted Physics: 7 Mind-Blowing Findings]

The amount of redshift they found that appeared to be caused by gravity agreed exactly with the predictions of general relativity.

"We have independent measurements of the cluster masses, so we can calculate what the expectation for gravitational redshift based on general relativity is," said University of Copenhagen astrophysicist Rados?aw Wojtak. "It agrees exactly with the measurements of this effect."

Wojtak is lead author of a paper reporting the results in tomorrow's (Sept. 29) issue of the journal Nature.

Warped space-time

General relativity, proposed by Einstein in 1916, revolutionized the way physicists think about space and time. Specifically, it united the two concepts, which were thought to be independent, into one entity. And mass, Einstein showed, affects space-time profoundly, by warping it.

Where you have a large mass like a galaxy cluster, there is strong gravity and space-time is severely warped, causing time to move more quickly. Light emitted in this environment will have a certain frequency, which is related to the time scale (or the gravity strength) of the environment. When that light travels to a new environment, say to a telescope on Earth, where there is comparatively lower gravity, and time moves more slowly, the light's frequency will decrease. A decreased frequency is equivalent to a longer, or redder, wavelength. This is gravitational redshift.

It took physicists 43 years to detect evidence of gravitational redshift. This discovery came in 1959, when researchers measured the gravitational redshift in gamma-ray light emitted in a lab here on Earth.

"This was a groundbreaking experiment," Wojtak said.

Other studies confirmed the effect in the sun and in small nearby stars called white dwarfs. Yet no one had managed to detect a proof of this prediction of general relativity on the cosmic scale, until now.

"In our work we present for the first time the same effect but on a scale which is many orders of magnitude larger," Wojtak told LiveScience. "This is the only general relativistic effect which has been observed and confirmed locally on the Earth and on the scale corresponding to the universe. We have a link between our local scale of the Earth and galaxy clusters."

Alternative theories

The findings further support the already well-entrenched general theory of relativity, which has been successful in predicting many cosmic phenomena observed throughout the universe.

Yet there are still competing theories that have been proposed in recent years to accommodate the strange discovery that the universe seems to contain much more mass than simply the visible matter we can see, and that the cosmos seems to be accelerating in its expansion, propelled by an unknown force.

Within the framework of general relativity, scientists have invented concepts called dark matter and dark energy, respectively, to deal with these problems. But some researchers say these bizarre inventions aren't necessary if we simply tweak general relativity itself.

One such competing theory is called the f(R) theory. This model, too, agrees with Wojtak and his colleagues' new measurements. However, another alternative theory, called Tensor–vector–scalar gravity (TeVeS), does conflict with the new findings. To preserve the theory, physicists would have to make some changes. [Video: Dark Matter in 3-D]

Ultimately, as more data is gathered about distant galaxies, such cosmic measurements should become even more accurate, and physicists may be able to distinguish better between the competing models.

"Discussions of gravity's properties will continue, but Wojtak and colleagues' pioneering work gives a glimpse of the potential of new cosmological tests for achieving higher precision when millions of galaxy redshifts, from which gravitational redshifts can be extracted, become available in the future," physicist Gary Wegner of Dartmouth College in New Hampshire, who was not involved in the new research, wrote in an accompanying essay in the same issue of Nature.

Article from Livescience.

Hillary Maruwa; September 29th, 2011

Life's Little Mysteries

Could NASA Launch a Secret Moon Mission?

If NASA were to launch a secret moon mission, setting off at night, as Apollo 17 is shown doing here, might be a good start. CREDIT: NASA

The new film "Apollo 18" is like "The Blair Witch Project" of space travel flicks, couched as found footage shot by NASA astronauts during a secret mission to the moon in 1973. In the story, the astronauts encounter unfriendly lunar aliens, chaos ensues and NASA forever hushes the whole thing up.

It's science fiction, of course: History has it that Apollo 18, along with 19 and 20, was canceled — Apollo 17 was NASA's final lunar mission. But the new film will surely stoke conspiratorial fires about the agency's secret activities. Might NASA really have launched a secret human spaceflight during the Apollo era, without anyone noticing it?

Almost definitely not.

Too many eyes and ears

"Developing the entire manned program involved 400,000 people, so to cover up the whole thing you'd have to keep them all quiet," Craig Nelson, a space historian and author of "Rocket Men: The Epic Story of the First Men on the Moon" (Viking 2009), told Life's Little Mysteries. "Just to send astronauts up in the air required a crew of 300 people. Not only did you have all of them working as part of NASA, but a huge percentage worked for other contractors, so you'd have to have hundreds of people keeping a secret forever."

According to archival records, the number of NASA employees had, in fact, dropped to around 200,000 by 1973, the year Apollo 18 was originally scheduled to take off. That's half the peak employment of 1965, but still a huge number of people to keep silent, had NASA carried out a lunar mission in secret. [What If NASA Hadn't Canceled the Apollo Program?]

Furthermore, Nelson pointed out that the space agency would have somehow had to quiet the millions  of people who saw each liftoff of the Saturn V rocket (which delivered Apollo's lunar capsules into space) as it left the launch pad at Kennedy Space Center in Florida. "There's no way [NASA] could cover up a launch. They could claim that the Air Force was doing it, but even then they would have to completely disguise an Apollo mission as an Air Force satellite mission, and that would be extremely difficult," Nelson said.

If NASA were to attempt a secret launch in today's world, in which there are more watchful eyes and more avenues for information sharing, he thinks the space agency would be even less able to hide a launch from the public.

That's not to say that it couldn't be done at all, though.

Military secrecy

The "Apollo 18" trailer includes a snippet in which the astronauts are communicating with the Department of Defense (DoD), suggesting that it is involved in the secret mission. (The astronauts, however, are decked out in NASA gear and communicate with personnel in Houston, the location of NASA's mission control center.) Filmmakers might be playing off of the fact that the DoD's space program is much more secretive than NASA's, making the premise slightly more conceivable (though more confusing, too).

"The space budget at the Pentagon is much bigger than NASA's budget," Nelson said. "They launch missions all the time and they don't reveal hardly any of it. They have their own launch pad next to NASA's in Florida, and another launch pad in California." [7 Things That Create Convincing UFO Sightings]

The Department of Defense's space budget currently stands at $26 billion; by comparison, NASA's budget is $18 billion. The bulk of the DoD funds, according to Gregory Schulte, the deputy assistant secretary of defense for space policy, pay for satellites that aid in ground navigation, missile launch detection and smart bomb precision. The military satellite network also helps to relay unmanned aerial vehicle feeds to troops, and to track space junk, which can collide with satellites.

Satellites aren't the whole story when it comes to the military's space operations, though. Last year, the Pentagon sent a spacecraft called X-37B, which looks like a miniature space shuttle, into low-Earth orbit. The launch wasn't secret — the Pentagon has said that it couldn't hide a launch even if it tried — but everything else about the mission, including what it accomplished and why, is classified.

Nelson says there's no way of knowing whether the Pentagon has launched a manned mission, to the moon or otherwise. However, when reached for comment, DoD spokeswoman April Cunningham wrote in an email: "The Department of Defense has not launched a manned mission to space."

Article from Livescience.

Hillary Maruwa September 07, 2011