string

Testing the string theory with astronomy

Il “Sacro Graal” della fisica potrebbe venire alla luce. E’ oggi quello che un gruppo di fisici del Department of Physics, Astronomy and Geosciences presso la Towson University (TU) sperano di aver trovato dopo quasi mezzo secolo di ricerche: verificare sperimentalmente una delle teorie più elusive e più complicate da capire, la teoria delle stringhe, osservando il moto dei pianeti, della Luna e degli asteroidi in una sorta di reminiscenza di uno dei più famosi test realizzati da Galileo sulla caduta dei gravi dalla Torre di Pisa.

Scientists have joked about how string theory is promising…and always will be promising, for lack of being able to test it”, says James Overduin, professor in Towson’s Department of Physics, Astronomy and Geosciences and lead author on a paper about the test TU scientists are developing. The paper was presented at the 223rd Meeting of the American Astronomical Society in Washington.

String theory posits an explanation for the connection between all the forces in the Universe. If it sounds overly broad, it is; string theory is nicknamed “the theory of everything.”

Scientific theories need tests in order to be truly valid, and string theory hasn’t been testable because the energy level and size to see its effects are just too big. “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”, Overduin explains. For most people, the understanding of string theory goes about as far as CBS’s “The Big Bang Theory” can convey it. The very basic explanation of the complex concept is that all matter and energy in the Universe is made of one-dimensional strings, a quintillion times smaller than the extremely tiny hydrogen atom. That means the strings are too small to detect indirectly, and finding signs of them in an instrument like a particle accelerator would require millions of times more energy than what was used to uncover, for example, the Higgs boson, a particle pivotal to the explanation and further proof of particle theory. The Higgs boson was posited in the 1960s, around the same time as string theory’s introduction; the boson’s identification was announced in 2012. The TU team’s string theory test borrows from Galilean and Newtonian laws of gravity. History holds that Galileo tested rates of acceleration by simultaneously dropping balls of two different weights off the Tower of Pisa to demonstrate that, despite the weight difference, they would hit the ground at the same time. Newton later found that Jupiter and its moons, in their orbits, “fall” at the same rate of acceleration toward the Sun. Much later, Einstein developed the theory of relativity when he recognized that gravity pulls all masses with precisely the same amount of strength, regardless of size.

Overduin and his team use those understandings for their test because string theory posits violations of Einstein’s relativity. It asserts that there are other fields that couple with objects differently, depending on the objects’ composition. That makes them accelerate differently, even within the same gravitational field.

But why does it matter? According to Overduin, the answer is nothing short of revolution. “Every time physicists have succeeded in unifying two different branches of physics, society has been transformed”, Overduin says. The Scientific Revolution was born of Newton’s unification of physics and astronomy. The Industrial Revolution, steam engines leading to train and boat transportation, began after physicists unified mechanics and heat. Electrification came when James Clerk Maxwell unified electricity and magnetism. Einstein’s relativity ushered in the Atomic Age, and then the Information Age, when relativity entered the quantum mechanics. That leaves two parts of physics still unconnected: gravitation and everything else. Physicists believe unifying them, as a test of string theory could do, would spark yet another revolution. But for all this time, they couldn’t do it. Towson University scientists might.

TU: TU scientists may spark revolution with string theory test

arXiv: Expanded solar-system limits on violations of the equivalence principle