Perfectly accurate clocks may be impossible

The ideal clock is a myth, according to researchers who have shown that in systems with very large accelerations no clock will actually be able to show the real passage of time, known as "proper time".
Researchers from the University of Warsaw in Poland and University of Nottingham in UK showed that in systems moving with enormous accelerations, building a clock that would precisely measure the passage of time is impossible for fundamental reasons.
"In both theories of relativity, special and general, it is tacitly assumed that it is always possible to construct an ideal clock - one that will accurately measure the time elapsed in the system, regardless of whether the system is at rest, moving at a uniform speed, or accelerating," said Andrzej Dragan from the Faculty of Physics, University of Warsaw.

"It turns out, however, that when we talk about really fast accelerations, this postulate simply cannot apply," said Dragan.
The simplest clocks are unstable elementary particles, for example muons (particles with similar properties to electrons but 200 times more massive).
By measuring the decay times and averaging the results for muons moving slowly and those moving at nearly the speed of light, we can observe slowing down of the passage of time.

The faster the muons are moving, the less likely the experimenter is to see them decay. Velocity therefore affects the clocks' observed tempo.
Researchers were looking at the description of unstable particles moving in accelerating motion in a straight line.

According to an effect predicted in 1976 by physicist William Unruh, the number of particles visible within a quantum field varies depending on the acceleration experienced by an observer - the greater the acceleration, the more of them there are.
The unstable particles which the researchers treated as fundamental clocks in their analysis decay as a result of interactions with other quantum fields.
The theory says that if such a particle remains in a space filled with a vacuum it decays at a different pace than when in the vicinity of many other particles interacting with it.
Thus if in a system of extreme acceleration more particles can be seen as a result of the Unruh effect, the average decay times of particles such as muons should change.

"Our calculations showed that above certain very large accelerations there simply must be time disorders in the decay of elementary particles," said Dragan.
If the disturbances affect fundamental clocks such as muons, then any other device built on the principles of quantum field theory will also be disrupted, he said.
"Therefore, perfectly precise measurements of proper time are no longer possible," said Dragan.
The study was published in the journal Classical and Quantum Gravity.