Would 'sacrilegious' experiment require rewrite of physics textbooks? Probably not

Scientists are set to carry out an experiment they claim would mean textbooks on nuclear physics have to be rewritten. The international team of researchers has said the internal structure of protons could change inside the nucleus of an atom, under certain conditions, and that they can test the theory.

If they are right, they say, this would change everything we know about one of the basic building blocks of the universe. Anthony Thomas, professor of physics at the University of Adelaide, said in a statement: "Atoms contain protons and electrons, but they also have their own internal structure comprised of quarks and gluons – these are what we consider to be the basic building blocks of matter. For many scientists, the idea that the internal structure of protons might change under certain circumstances can seem absurd, even sacrilegious. To others like myself, evidence of this internal change is highly sought after and would help to explain some inconsistencies in theoretical physics."

The paper by researchers from the US, Japan and Australia has been published in the Physical Review Letters. It predicts that the structure of protons could change – and that they have designed a way to test this. "By firing a beam of electrons at an atomic nucleus you can measure the difference in energy of the outgoing electrons, representing the changed state," Thomas said. The experiment is taking place at the Thomas Jefferson National Accelerator facility in the US.

Thomas said the principle of the experiment itself is "relatively simple", but making sure the measurements are reliable and accurate would be extremely demanding. "The ramifications for the scientific world are significant," he added. "This is about as high-stakes as it gets in science. It could represent a new paradigm for nuclear physics."

However, a number of physicists have told IBTimes UK that claims of textbooks needing to be rewritten are a bit of an overstatement. Protons consist of quarks, and the experiment relates to the idea that we should be using the appropriate theory for the behaviour of quarks to determine the behaviour of protons within an atomic nucleus. The experiment sets out to resolve this.

Tony Weidberg, Professor of Particle Physics at the University of Oxford, said our current understanding of the strong nuclear force is based on the theory of Quantum Chromodynamics (QCD). This has been successfully tested in high energy experiments, including those taking place at Cern's Large Hadron Collider.

"While the theory has been used very successfully at high energy it turns out to be very difficult to use the theory to make predictions at low energy, such as the nuclear physics experiments discussed in this paper," he said. "This doesn't imply that there is a fundamental problem with the theory, just that the calculations at low energy are much more difficult than at low energy.

Difficulties in calculations mean most theories in nuclear physics are based on ad-hoc models rather than QCD, he explained. "This paper is interesting because it attempts to perform QCD calculations in this difficult regime. However it has to make some assumptions about nuclear matter, so that if it turns out not to agree with data, it will not be used to reject the theory of QCD but merely to question the other assumptions.

"Therefore in my opinion this is an interesting paper but to say that it could re-write physics textbooks is hype."

David Sloan, also from the University of Oxford's Department of Physics, added: "We should hold off on rewriting any textbooks until the experiment is run. This behaviour would certainly change our understanding of the nature of protons and the theoretic work is valuable, but it remains unverified until the data comes in."