Wave away the material world

A single molecule can be shown to exist in two places at once, according to new experiments in quantum mechanics. Could the same be true of living creatures? Andrew Watson reports

We live in a world of comforting solidity in which everything has its place and nothing can be in two places at once. Yet a series of experiments carried out in France, Russia, and the US last year is undermining our perceptions of the way the world is. Some things can indeed be in two places at once - possibly even living creatures - and the reassuring solidity of our material world appears to be illusory.

Matter, the rigid "stuff" we see all around us, isn't really hard little pellets all stuck together but is mostly waves and empty space. It certainly seems as if matter is pretty hard stuff. For instance, salt crystals are so hard that it takes a grinder to reduce chunky ones to a more palatable size. Salt is an assembly of sodium and chlorine atoms. As such it is reasonably typical of the way atoms stick together, the building blocks of bulk material.

But sodium atoms can do some fancy things, according to David Pritchard of the Massachusetts Institute of Technology in the United States. In his laboratory at MIT, Professor Pritchard sent a beam of sodium atoms towards a thin foil, just a few millionths of a metre thick and placed edge-on. The beam split in two and passed on opposite sides of the foil. But when a detector at the far end started to register the atoms coming through, it showed a remarkable banded pattern, "bright" bands where many atoms were detected separated by "dark" bands where few were arrived.

The pattern is distinctive and well known: it is an interference pattern, the signature not of solid particles but of ethereal waves. The pattern arises typically with "real" waves such as water waves and sound. The crests of two waves reinforce each other to give bright patches, while crests of one wave cancel out troughs in the other to give no waves, resulting in dark patches. The inescapable conclusion is that sodium atoms behave like waves.

That is surprising enough, but what is really difficult to comprehend is that "each atom interferes only with itself", according to Professor Pritchard. He explained that each incoming sodium atom was spaced about a metre apart from the others, so that there was little chance of two atoms overlapping.

In other words, a single atom passed both sides of the foil simultaneously. What emerged then recombined to give an interference pattern. Each atom passed on both sides of an impenetrable barrier. The same thing would happen with lots of spaced sheets of foil, or equivalently a barrier with slits cut in it. It's as though when confronted by a row of supermarket check-outs a shopper passes through all of them at once. It's that bizarre.

This is the quantum nature of our universe revealed. And the reason it happens is that nature is like that: there is no deeper explanation. "Objects really propagate according to a wave-like equation that agrees with classical predictions only if you do not look carefully enough," said Professor Pritchard. "Your intuitive notion that the atom has to have a location at all times is incorrect."

The first MIT sodium atom interference experiment was reported in 1991. In the same journal issue appeared details of a similar experiment by Oliver Carnal and Jurgen Mlynek at the University of Konstanz in Germany using helium. Scientists were pleased but not surprised: they had expected it, based on earlier work with tiny fundamental "particles" that also displayed wave-like properties. But early in 1995, Professor Pritchard's group went one step further, showing that molecules of two sodium atoms also show wave-like properties.

"Our experiments have shown that even 'large' objects like molecules behave like waves," said Professor Pritchard. Christian Borde and his collaborators at the Universite Paris-Nord in France have shown interference effects in experiments using iodine molecules, and a Russian group has done similar experiments with even heavier molecules such as osmium tetrafluoride.

How big can we go? "This is clearly an underlying theme of our research; to push quantum mechanics and the observation of quantum effects toward macroscopic objects. It's just a question of developing gentle technique as far as I can see," said Professor Pritchard.

Recently they have published results on an experiment so difficult the great American physicist Richard Feynman proposed it only as a "thought" experiment, one that demonstrates a principle but which is too hard to do in practice.

What Professor Pritchard's group has done is to watch for sodium atoms as they emerge from above or below the foil divider, using single particles of light called photons. When they do this, they find that the results show each atom suddenly spoils the game by going above or below the divider, and the interference vanishes. Atoms no longer behave like waves.

If quantum mechanics is correct it had to be this way. Quantum mechanics says that as soon as the experimenter has a way of determining where an atom or some other particle has gone, then the wave-like aspect vanishes. In terms of the quantum supermarket, the reality of having to pay a cashier means that the shopper is effectively tracked, and a quantum shopper wouldn't show wave-like behaviour after all.

So there is a limit to how strange the quantum world is. "We showed that shining a single photon of light on a system will destroy its quantum interference," he said. "We also showed that quantum coherence is easier to destroy in bigger systems. Thus suggestions that quantum coherence explains ESP or other strange correlations over large distances fly in the face of our results."

Quantum mechanics as a way of explaining ESP may be dead, but Professor Pritchard has done a simple calculation that should make philosophers sit up and take notice. Imagine if a living organism could show wave-like properties. Then passing it both sides of a thin foil to give an interference pattern would mean that in some sense this living organism is in two places at once.

"I calculated that we could see interference of large bacteria if we could let them spend about a year in our interferometer, and could keep it from vibrating during this time," said Professor Pritchard. There is a catch, however: "Unfortunately they wouldn't really be living - we would have to cool them almost to absolute zero to keep the heat photons they radiate spontaneously from messing up the interference pattern." So philosophers are safe - for the moment.

News
scienceExcitement from alien hunters at 'evidence' of extraterrestrial life
Life and Style
Customers can get their caffeine fix on the move
food + drink
Sport
sport
Sport
David Moyes gets soaked
sport Moyes becomes latest manager to take part in the ALS challenge
PROMOTED VIDEO
Life and Style
techCould new invention save millions in healthcare bills?
News
peopleEnglishman managed quintessential Hollywood restaurant Chasen's
Life and Style
food + drinkHarrods launches gourmet food qualification for staff
Voices
Mosul dam was retaken with the help of the US
voicesRobert Fisk: Barack Obama is following the jihadists’ script
Arts and Entertainment
Michael Flatley prepares to bid farewell to the West End stage
danceMichael Flatley hits West End for last time alongside Team GB World champion Alice Upcott
News
Members and supporters of the lesbian, gay, bisexual, transgender (LGBT) community walk with a rainbow flag during a rally in July
i100
News
ebooksAn evocation of the conflict through the eyes of those who lived through it
Life and Style
Black Ivory Coffee is made using beans plucked from elephants' waste after ingested by the animals
food + drinkFirm says it has created the "rarest" coffee in the world
Arts and Entertainment
Loaded weapon: drugs have surprise side effects for Scarlett Johansson in Luc Besson’s ‘Lucy’
filmReview: Lucy, Luc Besson's complex thriller
Arts and Entertainment
Jamie T plays live in 2007 before going on hiatus from 2010
arts + entsSinger-songwriter will perform on the Festival Republic Stage
Life and Style
food + drinkThese simple recipes will have you refreshed within minutes
News
Jermain Defoe got loads of custard
i100
Independent
Travel Shop
the manor
Up to 70% off luxury travel
on city breaks Find out more
santorini
Up to 70% off luxury travel
on chic beach resorts Find out more
sardina foodie
Up to 70% off luxury travel
on country retreats Find out more
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Business Analyst - Banking - London - £550 - £650

£550 - £650 per day: Orgtel: Business Analyst - Traded Credit Risk - Investmen...

Data Insight Manager - Marketing

£32000 - £35000 Per Annum: Clearwater People Solutions Ltd: Our client based o...

Data Centre Engineer - Linux, Redhat, Solaris, SAN, Puppet

£55000 per annum: Harrington Starr: A financial software vendor at the forefro...

.NET Developer

£600 per day: Harrington Starr: .NET Developer C#, WPF,BLL, MSMQ, SQL, GIT, SQ...

Day In a Page

Air strikes? Talk of God? Obama is following the jihadists’ script

Air strikes? Talk of God? Obama is following the jihadists’ script

The President came the nearest he has come yet to rivalling George W Bush’s gormless reaction to 9/11 , says Robert Fisk
Ebola outbreak: Billy Graham’s son declares righteous war on the virus

Billy Graham’s son declares righteous war on Ebola

A Christian charity’s efforts to save missionaries trapped in Africa by the crisis have been justifiably praised. But doubts remain about its evangelical motives
Jeremy Clarkson 'does not see a problem' with his racist language on Top Gear, says BBC

Not even Jeremy Clarkson is bigger than the BBC, says TV boss

Corporation’s head of television confirms ‘Top Gear’ host was warned about racist language
Nick Clegg the movie: Channel 4 to air Coalition drama showing Lib Dem leader's rise

Nick Clegg the movie

Channel 4 to air Coalition drama showing Lib Dem leader's rise
Philip Larkin: Misogynist, racist, miserable? Or caring, playful man who lived for others?

Philip Larkin: What will survive of him?

Larkin's reputation has taken a knocking. But a new book by James Booth argues that the poet was affectionate, witty, entertaining and kind, as hitherto unseen letters, sketches and 'selfies' reveal
Madame Tussauds has shown off its Beyoncé waxwork in Regent's Park - but why is the tourist attraction still pulling in the crowds?

Waxing lyrical

Madame Tussauds has shown off its Beyoncé waxwork in Regent's Park - but why is the tourist attraction still pulling in the crowds?
Texas forensic astronomer finally pinpoints the exact birth of impressionism

Revealed (to the minute)

The precise time when impressionism was born
From slow-roasted to sugar-cured: how to make the most of the British tomato season

Make the most of British tomatoes

The British crop is at its tastiest and most abundant. Sudi Pigott shares her favourite recipes
10 best men's skincare products

Face it: 10 best men's skincare products

Oscar Quine cleanses, tones and moisturises to find skin-savers blokes will be proud to display on the bathroom shelf
Malky Mackay allegations: Malky Mackay, Iain Moody and another grim day for English football

Mackay, Moody and another grim day for English football

The latest shocking claims do nothing to dispel the image that some in the game on these shores exist in a time warp, laments Sam Wallace
La Liga analysis: Will Barcelona's hopes go out of the window?

Will Barcelona's hopes go out of the window?

Pete Jenson starts his preview of the Spanish season, which begins on Saturday, by explaining how Fifa’s transfer ban will affect the Catalans
Middle East crisis: We know all too much about the cruelty of Isis – but all too little about who they are

We know all too much about the cruelty of Isis – but all too little about who they are

Now Obama has seen the next US reporter to be threatened with beheading, will he blink, asks Robert Fisk
Neanderthals lived alongside humans for centuries, latest study shows

Final resting place of our Neanderthal neighbours revealed

Bones dated to 40,000 years ago show species may have died out in Belgium species co-existed
Scottish independence: The new Scots who hold fate of the UK in their hands

The new Scots who hold fate of the UK in their hands

Scotland’s immigrants are as passionate about the future of their adopted nation as anyone else
Britain's ugliest buildings: Which monstrosities should be nominated for the Dead Prize?

Blight club: Britain's ugliest buildings

Following the architect Cameron Sinclair's introduction of the Dead Prize, an award for ugly buildings, John Rentoul reflects on some of the biggest blots on the UK landscape