The traditional way to savour scotch whisky is to add a dribble of water before sipping. Pub lore says that it makes the flavour pop, and experiments confirmed it and told us why. Now, chemists have duplicated that result without resorting to complicated apparatus, and their findings could tell us how certain types of drugs move through the body.

and at Linnaeus University in Sweden used a computer simulation to model how the ethanol molecules in whisky interact with water. To capture the molecular motion precisely, they simulated the mixing using tiny time steps, equivalent to half a trillion frames per second.

Then, they added a single molecule called guaiacol, which provides some of scotch’s distinctive smoky and bitter flavour.

They found that when liquor is at or above 40 percent alcohol by volume, guaiacol molecules tend to stay in the body of the liquid, away from the surface. But when the researchers diluted the simulated whisky to about 25 percent alcohol, the guaiacol floated to the top and wafted its smoky scent and taste front and center.

“We found a result that supports the claims for diluting whisky,” says Karlsson. The researchers now hope to figure out how drugs containing a similar mix of molecules behave inside the body. Some cough medicine, for instance, contains guaiacol, water and glycerol, another alcohol molecule.

To the casual sipper, 25 percent may seem watery. “There’s quite a lot of snobbery about this,” says at Oregon State University, who researches alcoholic beverages.

But the professionals who mix single-malt whiskies to make blended ones taste samples diluted to about 20 per cent.

Previous experiments showed that flavour compounds like guaiacol tend to stick to ethanol. Before dilution, when the alcohol concentration is high, ethanol molecules tend to hover in clusters in the middle of the liquid, which keeps the guaiacol molecules from rising to the surface.

As water dilutes the whisky, the ethanol spreads more uniformly, allowing more of the guaiacol to reach the surface. “It all comes back to the strange behaviour of alcohol in water,” says Hughes.

The fact that this vastly simplified simulation backed up earlier experiments indicates that even in liquids as complex as whisky, it may be enough just to understand how the alcohol mixes with the water.

However, Hughes points out that the mixing behaviour changes depending on the shape of the container. The simulation used a box-shaped vessel, and it’s hard to say whether guaiacol would behave the same way in a flask, a mug or an antique crystal decanter.

Of course, how you take your whisky is a matter of taste, whatever science may have to say. “Sometimes I add water, and sometimes I don’t. I can do what I like,” Hughes says.

Fine-tuning

IF YOU find the quantum world confusing you’re not alone. A recent survey shows that physicists disagree over the picture of reality that quantum mechanics describes – and that many of them don’t even care.

There was no consensus among the 149 survey participants. While 39 per cent supported the so-called Copenhagen interpretation, the conventional picture of quantum mechanics, 25 per cent supported alternatives and 36 per cent had no preference at all. In addition, many weren’t sure they understood what certain interpretations described.

“I don’t think the debate will resolve soon,” says Sujeevan Sivasundaram, a recent graduate of Aarhus University in Denmark who conducted the survey. “I could see us still discussing this 100 years from now.”

The conventional interpretation, which is often the first and only one a physicist is taught, may have been the most popular in the survey, but that doesn’t indicate it’s right, says Charles Sebens at the University of California, San Diego. “It’s what physicists go on believing because it’s the first way they’re introduced to the theory,” he says. “But it’s a disservice to only learn one interpretation.”

This interpretation uses the Schrödinger equation to accurately predict the results of quantum experiments. But it includes a problem: if you measure or observe a particle, you abruptly change its trajectory in defiance of this equation.

Critics point out that nothing else we know of makes such a weird instant switch, and it seems to be inconsistent with other established laws of nature. In addition, making “measurements” is poorly defined, says Aephraim Steinberg at the University of Toronto, Canada. “If a fly looks at it, if a bacteria interacts with it, if a dog looks at it – what constitutes a measurement?” he says.

“In a survey, 32 per cent of respondents didn’t understand enough to have an opinion”

Alternatives approach things differently. For example, the many interacting worlds interpretation, published by Howard Wiseman at Australia’s Griffith University and colleagues in 2014, says quantum phenomena arise from multiple universes interacting with each other under consistent physical laws. “It’s very strange, I admit,” says Wiseman. But to him, parallel universes that consistently obey a set of laws are far less strange than a single universe with exceptions to the rules, as with Copenhagen.

Despite some enthusiasm for alternatives, 32 per cent of respondents didn’t understand the interpretations enough to have an opinion, and 23 per cent thought interpretations were irrelevant. “One physicist wrote in the comments that he found the survey a complete and utter waste of time,” says Sivasundaram. Furthermore, some thought that certain interpretations couldn’t be experimentally verified, and thus belonged more in philosophy than physics.

The number of diverging ideas suggests that maybe all of them are off the mark, says Sabine Hossenfelder of Germany’s Frankfurt Institute for Advanced Studies. “There doesn’t seem to be two people who can come to any agreement on anything,” she says. “It seems to me that they’re just discussing the wrong things or in the wrong way.”

This article appeared in print under the headline “Physicists cannot agree about quantum world”

Generation gap?

We know what we’d like to use for the innards of future quantum computers: exotic things like pink diamonds and cold atoms. But getting these components to talk to each other has been a challenge. Now, researchers have come up with a way to allow one component to efficiently transmit information to another, without losing its quantum character.

Quantum computers are theoretically capable of running calculations exponentially faster than classical computers, and can be made by exploiting atoms, superconductors, and more. Each of these has its own strengths: atoms are better at storing information, while superconductors are better at processing it. A device linking these diverse systems together would combine their strengths and compensate for their weaknesses.

Once linked, these systems would talk to each other by sending and receiving photons. The photons would encode quantum states but, unlike the voltages and currents interpreted by a classical computer chip, they cannot be transmitted via copper wires.

Matching spreads

What’s more, quantum rules require that a single photon must essentially carry a spread of frequencies, rather than a single frequency. For different components to talk to each other using photons, the spread of the sender’s photons must therefore be converted to the spread that the receiver can handle. That requires a device in the middle that can convert photons from one spread of frequencies to another, while still preserving their delicate quantum state.

Christine Silberhorn of the University of Paderborn in Germany and her colleagues have designed such a system. It includes a converter that “translates” photons emitted from one component into the infrared. That infrared photon is then transmitted over a fibre optic cable connected to a second component. Finally, the photon is translated into another frequency that the receiving component can read.

Only part of the system has been built so far: the researchers have managed to convert infrared photons to a visible wavelength – while leaving their quantum state intact – with a success rate of about 75 per cent. But the technique could be adapted to build the full system, Silberhorn says.

Once that is done, the next step would be to figure out how to fit the device on a chip that could be manufactured easily and cheaply in large quantities, says of the University of Washington in Seattle. “The science works,” he says. “But scalability is the biggest problem. Making the same device 1000 times is extremely difficult.”

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