Weekend Argus (Saturday Edition)
Unification theory still eludes world’s scientists
LIKE Albert Einstein, the late Stephen Hawking had an ambition that was never realised. They both wanted to do what physicists the world over have been trying to do – find the great unification theory of physics.
This would explain the contradictions between Einstein’s theory of general relativity and more recent quantum mechanics theories.
What are some of the principles of quantum mechanics? They sound weird but have been proved.
A particle can be a wave and a wave can be a particle.
Probability is all-important. For example, given an experiment in which an electron can end up in one of two places, you could say there is a 20% probability of finding it at point A and an 80% probability of finding it at point B. You can never say definitely what the outcome of the experiment will be.
Measurement is everything – the exact state of a quantum particle is indeterminate until it has been measured. This is often called the observer effect. To anyone new to quantum mechanics this principle is one of its most fascinating elements.
There are many simple examples of the observer effect in everyday life (the principle that the act of observation makes changes on the phenom- enon being observed).
The original experiment in the observer effect was called a “thought experiment” because it had not yet been proved. Here it is. An electron is fired at a plate with two closely spaced slits in it. Behind the plate is a sensitive screen which can detect the electron.
Remember, a particle can also act as a wave. So, that the electron can act in a wave-like manner by going through both slits at once and meet again on the other side of the plate. This phenomenon is called interference.
Interference can only occur when no one (or no instrument) is watching. Once an observer begins to watch the particle going through the plate, the picture changes very basically.
If a particle can be seen going through one slit, then it can’t be going through the other slit. In other words, when they are being observed, the electron is in effect being made to act like a particle and not a wave.
The Weizmann Institute proved this by demonstration. in 1978. John Wheeler published what he called the “delayed thought experiment”. A moving object is given a “choice” to act like a particle or a wave. Quantum physics predicts whether you observe behaviour that is like a wave (interference) or like a particle ( non- interference) depends only on the way it is measured at the end of its journey.
The Australian National University conducted a practical experiment proving Wheeler’s “delayed choice thought experiment”.
They trapped some helium atoms in a suspended state, then ejected them till there was only one left. This atom was dropped through laser beams that made a grate pattern.
A second laser grating was added randomly to recombine the paths. This led to interference, as if the atom had travelled by both paths. When the second grating was not added, no interference was observed, as if the atom had “chosen” to use only one path.
But the random number that determined whether the grating was added or not, was only generated after the atom had passed through the “crossroads”.
In other words, it was only when the atom was measured at the end of its journey that its wave-like or particle-like behaviour took place and was observed.
Some have said that this suggests particles can see into the future.
Whether the unified theory of physics has been found or not, for those of us for who science presents something of a challenge, following its progress remains a fascinating pastime.