Archivi tag: unification of physics

The potential of string theory as an elegant unified description of physics

Nell’Agosto del 1984 due fisici arrivarono ad elaborare una formula che aprì una nuova finestra verso la comprensione della teoria delle stringhe. Lo scorso mese di Dicembre, Michael Green dell’Università di Cambridge e John Schwarz del California Institute of Technology sono stati insigniti del Fundamental Physics Prize 2014, uno dei premi della serie “Breakthrough Prizes” che riguarda le scienze fisiche e biologiche. La citazione del premio, che ammonta a 3 milioni di dollari, dice “per aver introdotto nuove prospettive sulla gravità quantistica e l’unificazione delle forze“.

Green and Schwarz are known for their pioneering work in string theory, postulated as a way of explaining the fundamental constituents of the Universe as tiny vibrating strings. Different types of elementary particles arise in this theory as different vibrational harmonics (or ‘notes’). The scope of string theory has broadened over the past few years and is currently being applied to a far wider field than that for which it was first devised, which has taken those who research into it in unexpected directions. Although the term ‘string theory’ was not coined till 1971, it had its genesis in a paper by the Italian physicist Gabriele Veneziano in 1968, published when Green was a research student in Cambridge. Green was rapidly impressed by its potential and began working seriously on it in the early 1970s. As he explains in the accompanying film, he stuck with string theory during a period when it was overshadowed by other developments in elementary particle physics. As a result of a chance meeting at the CERN accelerator laboratory in Switzerland in the summer of 1979, Green (then a researcher at Queen Mary, London) began to work on string theory with Schwarz. Green says that the relative absence of interest in string theory during the 1970s and early 1980s was actually helpful: it allowed him and a small number of colleagues to focus on their research well away from the limelight. “Initially we were not sure that the theory would be consistent, but as we understood it better we became more and more convinced that the theory had something valuable to say about the fundamental particles and their forces”, he says. In August 1984 the two researchers, while working at the Aspen Center for Physics in Colorado, famously understood how string theory avoids certain inconsistencies (known as ‘anomalies’) that plague more conventional theories in which the fundamental particles are points rather than strings. This convinced other researchers of the potential of string theory as an elegant unified description of fundamental physics. “Suddenly our world changed – and we were called on to give lectures and attend meetings and workshops”, remembers Green. String theory was back on track as a construct that offered a compelling explanation for the fundamental building blocks of the Universe: many researchers shifted the focus of their work into this newly-promising field and, as a result of this upturn in interest, developments in string theory began to take new and unexpected directions. Ideas formulated in the past few years, indicate that string theory has an overarching mathematical structure that may be useful for understanding a much wider variety of problems in theoretical physics that the theory was originally supposed to explain, this includes problems in condensed matter, superconductivity, plasma physics and the physics of fluids. Green is a passionate believer in the exchange of ideas and he values immensely his interaction with the latest generation of researchers to be tackling some of the knottiest problems in particle physics and associated fields. “The best ideas come from the young people entering the field and we need to make sure we continue to attract them into research. It is particularly evident that at present we fail to encourage sufficient numbers of young women to think about careers in physics”, he says. “Scientific research is by its nature competitive and there are, of course, professional jealousies – but there’s also a strong tradition of collaboration in theoretical physics and advances in the subject feel like a communal activity.” In 2009 Green was appointed Lucasian Professor of Mathematics at Cambridge. It comes with a legacy that Green describes as daunting: his immediate predecessor was Professor Stephen Hawking and in its 350-year history the chair has been held by a series of formidable names in the history of mathematical sciences.

The challenges of pushing forward the boundaries in a field that demands thinking in not three dimensions but as many as 11 are tremendous. The explanation of the basic building blocks of nature as different harmonics of a string is only a small part of string theory, and is the feature that is easiest to put across to the general public as it is relatively straightforward to visualise.

Far harder to articulate in words are concepts to do with explaining how time and space might emerge from the theory”, says Green. “Sometimes you hit a problem that you just can’t get out of your head and carry round with you wherever you are. It’s almost a cliché that it’s often when you’re relaxing that a solution will spontaneously present itself”. Like his colleagues Green is motivated by wonderment at the world and the excitement of being part of a close community grappling with fundamental questions. He is often asked to justify the cost of research that can seem so remote from everyday life, and that cannot be tested in any conventional sense. In response he gives the example of the way in which quantum mechanics has revolutionised the way in which many of us live. In terms of developments that may come from advances in string theory, he says: “We can’t predict what the eventual outcomes of our research will be. But, if we are successful, they will certainly be huge and in the meantime, string theory provides a constant stream of unexpected surprises.”

Michael Green will be giving a lecture, ‘The pointless Universe’, as part of Cambridge Science Festival on Thursday 13 March, 5pm-6pm, at Lady Mitchell Hall, Sidgwick Site, Cambridge. The event is free but requires pre-booking.

University of Cambridge: Strings that surprise: how a theory scaled up

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