ONE of the grandest visions of physics could be a mirage. Conventional thinking has it that all the fundamental forces of nature diverged from one single force soon after the big bang. Now it seems that quantum effects may make it impossible to prove if this idea is correct.
In the 1970s, data from the Large Electron Positron Collider at CERN near Geneva hinted that the strong, weak and electromagnetic forces were beginning to converge at the energies created during particle collisions. By extrapolating this convergence to much higher energies, physicists speculated that the forces would become indistinguishable at around 1016 gigaelectronvolts. The universe was in this energy state soon after the big bang, which suggests that all the forces may once have been unified.
Now Xavier Calmet of the Catholic University of Louvain in Belgium and his colleagues argue that it may be impossible to prove if this theory is right via any conceivable experiment in a particle accelerator.
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The problem is that the high energy levels at which unification of all the forces is thought to occur is close to the 鈥淧lanck scale鈥�, at which quantum fluctuations in space-time become strong. These fluctuations may create huge uncertainties in the strengths of the forces at this scale, says Calmet. If true, it would mean that all bets are off as to how the forces will actually behave at high energies 鈥� no matter what the data from particle accelerators might suggest in the future.
The researchers鈥� calculations explored whether the existence of 鈥渟upersymmetric鈥� particles would make a difference to the Planck scale. Supersymmetry models, devised to tackle inherent problems with standard theories of unification, suggest that every particle has a high-energy partner. The existence of all these extra supersymmetric particles reduces the Planck scale, causing enough uncertainty to make it impossible to tell if unification does occur at higher energies. The results will appear in Physical Review Letters ().
Calmet admits all this is 鈥渁 bit depressing鈥�, because it dashes hopes of a grand unified theory emerging from the relatively low-energy measurements made at the Large Hadron Collider at CERN. 鈥淲e have shown that this is virtually impossible,鈥� he says. 鈥淲e鈥檒l never find out whether unification happens by doing low-energy measurements.鈥�
鈥淲e will never find out whether unification of all the forces happens by doing measurements at the Large Hadron Collider鈥�
Frank Wilczek of the Massachusetts Institute of Technology says the paper provides a 鈥渟alutary warning鈥� but thinks that there is no reason to panic just yet. Calculating quantum effects at high energies is mainly guesswork, he says, and they may turn out not to be as strong as expected. Results from the LHC will put us in a better position to judge, he adds.
