Scientists find a practical test for string theory

Two-minute lectures by Towson University faculty. James Overduin (Department of Physics, Astronomy and Geosciences) explains why a single theory of physics is needed to restore the "house of physics" and enable humans to progress in science and technology.

Scientists at Towson University in Towson, Maryland, have identified a practical, yet overlooked, test of string theory based on the motions of planets, moons and asteroids, reminiscent of Galileo's famed test of gravity by dropping balls from the Tower of Pisa.

String theory is infamous as an eloquent theoretical framework to understand all forces in the universe —- a so-called "theory of everything" —- that can't be tested with current instrumentation because the energy level and size scale to see the effects of string theory are too extreme.

Yet inspired by Galileo Galilei and Isaac Newton, Towson University scientists say that precise measurements of the positions of solar-system bodies could reveal very slight discrepancies in what is predicted by the theory of general relativity and the equivalence principle, or establish new upper limits for measuring the effects of string theory.

The Towson-based team presents its finding today, January 6, 2014, between 10 a.m. and 11:30 a.m., at the 223rd meeting of the American Astronomical Society, in Washington, D.C.

The work also appears in the journal Classical and Quantum Gravity.

This is an image of a two-dimensional hypersurface of the quintic Calabi-Yau three-fold. 

Credit: Jbourjai/Wikipedia.

String theory hopes to provide a bridge between two well-tested yet incompatible theories that describe all known physics: Einstein's general relativity, our reigning theory of gravity; and the standard model of particle physics, or quantum field theory, which explains all the forces other than gravity.

String theory posits that all matter and energy in the universe is composed of one-dimensional strings.

These strings are thought to be a quintillion times smaller than the already infinitesimal hydrogen atom and thus too minute to detect indirectly.

Similarly, finding signs of strings in a particle accelerator would require millions of times more energy than what has been needed to identify the famous Higgs boson.

"Scientists have joked about how string theory is promising...and always will be promising, for the lack of being able to test it," said Dr. James Overduin of the Department of Physics, Astronomy and Geosciences at Towson University, first author on the paper.

"What we have identified is a straightforward method to detect cracks in general relativity that could be explained by string theory, with almost no strings attached."

More information: "Expanded Solar-System Limits on Violations of the Equivalence Principle," m.iopscience.iop.org/0264-9381/31/1/015001

Einstein's General Relativity Theory Fights Off Challengers

Two new and independent studies have put Einstein's General Theory of Relativity to the test like never before. These results, made using NASA's Chandra X-ray Observatory, show Einstein's theory is still the best game in town.

Each team of scientists took advantage of extensive Chandra observations of galaxy clusters, the largest objects in the Universe bound together by gravity. One result undercuts a rival gravity model to General Relativity, while the other shows that Einstein's theory works over a vast range of times and distances across the cosmos.

The first finding significantly weakens a competitor to General Relativity known as "f(R) gravity".

"If General Relativity were the heavyweight boxing champion, this other theory was hoping to be the upstart contender," said Fabian Schmidt of the California Institute of Technology in Pasadena, who led the study. "Our work shows that the chances of its upsetting the champ are very slim."

In recent years, physicists have turned their attention to competing theories to General Relativity as a possible explanation for the accelerated expansion of the universe. Currently, the most popular explanation for the acceleration is the so-called cosmological constant, which can be understood as energy that exists in empty space. This energy is referred to as dark energy to emphasize that it cannot be directly detected.

In the f(R) theory, the cosmic acceleration comes not from an exotic form of energy but from a modification of the gravitational force. The modified force also affects the rate at which small enhancements of matter can grow over the eons to become massive clusters of galaxies, opening up the possibility of a sensitive test of the theory.

Schmidt and colleagues used mass estimates of 49 galaxy clusters in the local universe from Chandra observations, compared them with theoretical model predictions and studies of supernovas, the cosmic microwave background, and the large-scale distribution of galaxies.

They found no evidence that gravity is different from General Relativity on scales larger than 130 million light years. This limit corresponds to a hundred-fold improvement on the bounds of the modified gravitational force's range that can be set without using the cluster data.

"This is the strongest ever constraint set on an alternative to General Relativity on such large distance scales," said Schmidt. "Our results show that we can probe gravity stringently on cosmological scales by using observations of galaxy clusters."

The reason for this dramatic improvement in constraints can be traced to the greatly enhanced gravitational forces acting in clusters as opposed to the universal background expansion of the universe. The cluster-growth technique also promises to be a good probe of other modified gravity scenarios, such as models motivated by higher- dimensional theories and string theory.

For the full article click here on this link to NASA

Explained: The 10 Dimensions that make up our Universe

This is an excellent, clear and concise description of the 10 Dimensions that make up our perceived Universe. To connect with the 10 Dimensions CLICK HERE

String Theory tied into Multiverses

BRIAN GREENE spent a good part of the last decade extolling the virtues of string theory. He dreamed that one day it would provide physicists with a theory of everything that would describe our universe - ours and ours alone. His bestselling book The Elegant Universe eloquently captured the quest for this ultimate theory.

"But the fly in the ointment was that string theory allowed for, in principle, many universes," says Greene, who is a theoretical physicist at Columbia University in New York. In other words, string theory seems equally capable of describing universes very different from ours. Greene hoped that something in the theory would eventually rule out most of the possibilities and single out one of these universes as the real one: ours.

So far, it hasn't - though not for any lack of trying. As a result, string theorists are beginning to accept that their ambitions for the theory may have been misguided. Perhaps our universe is not the only one after all. Maybe string theory has been right all along.

Greene, certainly, has had a change of heart. "You walk along a number of pathways in physics far enough and you bang into the possibility that we are one universe of many," he says. "So what do you do? You smack yourself in the head and say, 'Ah, maybe the universe is trying to tell me something.' I have personally undergone a sort of transformation, where I am very warm to this possibility of there being many universes, and that we are in the one where we can survive."

We keep banging into the possibility that we are one universe of many. Maybe that's telling us something