Does the future affect the PAST? Physicists demonstrate how time can seem to run backwards
Source: dailymail.co.uk
In a standard double slit experiment, photons can be seen behaving like particles when they pass through a single slit, shown by the dappled pattern on the top image, but when a second slit is introduced it creates an interference band that is typical of photons travelling in a wave, as seen on the bottom image
It has been one of the central planks of modern physics – time can only run in one direction, meaning the past can influence the future but not the other way around.
But now a new experiment has thrown the concept of what is possible and what is not into disarray after showing that at a quantum level this seems not to be true.
Researchers have shown that an event in the future may indeed influence something in the past - in other words time can run backwards as well as forwards.
The research centres around the strange behaviour of particles in quantum mechanics.
In the quantum world it is possible for a moving object to exist in two states at once – a particle and a wave – but it is impossible to see it in both states at once.
This is because when scientists attempt to look at light photon or fast moving atom, for example, it can either appear as a particle or as a wave.
In the new experiment, however, scientists found an action that occurred after they attempted to observe an atom seemed to determine whether they saw it as a wave or a particle.
Dr Andrew Trustcott, a physicist at the Australian National University who led the work, said: 'At the quantum level, reality does not exist if you are not looking at it.
'The atoms did not travel from A to B. It was only when they were measured at the end of the journey that their wave-like or particle-like behaviour was brought into existence,'
The research, which is published in the journal Nature Physics, built on a thought experiment proposed by John Wheeler in 1978.
He suggested what is known as the 'delayed choice thought experiment', which is a variation on the double slit experiment where light is shone through narrow slits in a screen.
When shone through one slit a single glow on the wall behind appears as if the photons are behaving as particles, when a second slit is introduced, this changes to an interference band as if the photons are behaving as waves.
Wheeler suggested introducing a second screen behind the first the light has passed through the first slits.
By placing a second screen in behind it, the idea was to see if the state of the photons would remain consistent when passing through both screens.
Until now it has not been possible to conduct this experiment, but the researchers behind the latest study altered it slightly to make it possible.
Instead of photons they used helium atoms and passed these through a grate created by laser light instead of a physical screen.
This allowed them to precisely measure what happened to the speeding atom when it passed through the second gate, which was introduced at random.
They found that without the second grate, the atom travelled on a single path like a particle. When both grates were present, the atom travelled on many paths rather like a wave.
As the researchers measured the path of the atom through the first grate before the second grate was introduced, it suggests the potential introduction of the second grate influenced the particles state.
This suggests that if the atom really did take a particular path or paths, then future measurement is affecting the atom's path, explained Dr Trustcott.
Roman Khakimov, a PhD student at the Australian National University's research school of physics and engineering, added: 'Quantum physics' predictions about interference seem odd enough when applied to light, which seems more like a wave, but to have done the experiment with atoms, which are complicated things that have mass and interact with electric fields and so on, adds to the weirdness.'
Source: dailymail.co.uk
