Schrödinger’s Cat may be the most famous thought experiment of all time, but due to its quantum trickiness it must remain in the realm of the hypothetical for the time being. However, researchers suggest they might just be able to pull off a similar, smaller-scale experiment they call Schrödinger’s virus.
The physicist Erwin Schrödinger came up the the feline thought experiment in the 1930s, presenting it as a caution against applying quantum rules to the real, ‘classical’ world…. At its most fundamental level, quantum mechanics says that particles can only exist in discrete states. For example, researchers can measure the direction a particle spins as either ‘up’ or ‘down’, but nothing in between. Yet, as long as no one is looking, the particle exists in a combination of both states simultaneously, a strange blend known as a superposition [Nature News].
Schrödinger proposed an experiment where a cat would be put in box containing a vial of poison gas. A hammer would be suspended ready to smash down on the vial if triggered by the decay of a single atom of radioactive material. If no one looked inside the box, Schrödinger said, the radioactive atom would be in a superposition–both intact and decayed–and therefore the cat would exist in two states as well, being simultaneously alive and dead.
To take a step towards this logical impossibility, researchers propose in a paper posted on the arXiv pre-print server that they start with a much smaller living organism, a virus–although other researchers point out that there is still debate over whether viruses are truly alive. Still, the researchers say that since they think they’ve figured out a way to conduct an experiment putting a single virus in a superposition, it may as well be tried.
The proposed experiment would involve trapping a single virus in a vacuum chamber, and then gradually cooling it and slowing it down until it rests, motionless, in its lowest possible energy state. Finally a single photon, a light particle, would be beamed into the chamber, and as long as nobody peeked inside the chamber the virus would be placed in a superposition of two states: both moving and not.
Researcher Oriol Romero-Isart, one of paper’s coauthors, say the experiment would only work if the virus has certain properties: if it’s dielectric (meaning it doesn’t conduct electricity), can survive the vacuum and appears transparent to laser light, which would otherwise rip it apart. As luck would have it, Romero-Isart and co say that several viruses fit the bill. The common flu virus is known to be able to survive in a vacuum, seems to have the required dielectric properties and may well be transparent to a careful choice of laser light. The tobacco mosaic virus, to all intents and purposes a dielectric rod, looks like another good candidate [Technology Review].
Some experts say the experiment may have limited use. Physicist Martin Plenio (who’s not involved in the proposed research) says there’s no reason to think that a virus will behave differently than an inorganic molecule, but he still thinks that testing relatively large objects, whether viruses or molecules, could prove interesting. According to quantum mechanics, it should be possible for macroscopic objects like cars and people to enter superpositions, but that never appears to happen. Studying relatively large objects, says Plenio, may help physicists learn where the quantum world ends and the our macroscopic world begins [Nature News].
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Image: Wikimedia Commons
September 15th, 2009 at 3:37 pm
I think a virus may illustrate this concept better than a cat.
September 15th, 2009 at 3:54 pm
It’s peeked not peaked. You’re welcome.
September 15th, 2009 at 4:16 pm
It’s always been my opinion that a cat is perfectly capable of observing whether or not it’s alive, with or without the help of a physicist. The virus experiment, though, is a bit more ambiguous.
September 15th, 2009 at 4:46 pm
Thanks bigjohn756, typo is fixed.
September 15th, 2009 at 5:02 pm
Eliza has an excellent point. The superposition state is achieved, as far as we can tell, by its property of not being able to be observed by an “intelligence”. Once it can be measured, it is no longer in superposition. So the question that arises is; is that cat\virus intelligent enough to observe? That could also be the answer as to why we don’t find things in the macroscopic world in superposition, we are here to observe it.
One question I have is how are they going to be able to determine if the virus is in superposition? Won’t they have to observe it to tell?
September 15th, 2009 at 8:16 pm
@3: A dead cat can’t observe anything. You could argue that the cat would be aware of the smashing of the vial before it dies, but in any case, I don’t think it’s a matter of observation, just interaction, which observation involves.
September 15th, 2009 at 10:56 pm
If the observation of the cat is enough to nix the experiment, how do we know that the observation of the virus will not?
;-)
September 16th, 2009 at 9:32 am
Got another typo to fix in the last line :):
“… and the our macroscopic world begins”
September 16th, 2009 at 11:09 am
No one addressed the issue of autopsy. Because we are capable of performing autopsy, we ARE OBSERVING THE CAT CONSTANTLY. Schrodinger’s cat is a crock. (And just because we may not be able to pin down the exact second, doesn’t mean that we couldn’t in principle determine the exact second.) Also this article didn’t mention so what happens if you use a camera? Is the camera in a superposition of states? Analytic continuation is what makes Schrodinger’s cat a crock.
September 16th, 2009 at 5:56 pm
Your study is important but I question the fact of using cats as your outcome. Maybe more thought needs to be put into what excactly you will receive from using these mammmals.
Karla Meinberg
September 17th, 2009 at 9:41 am
One more typo. Sorry, Eliza. First line, second paragraph. “the the feline”.
Great article. Interesting concept. But as with others here, I can’t wrap my head around how any of this could be proved if you can’t observe it. It’s not impossible as we have found that some particles can, and do exist simultaneously in two places. But how do we prove it.
September 17th, 2009 at 1:19 pm
Yup, I have to agree – the whole point of quantum uncertainty is that once you observe something it’s probability wave function collapses – so just how exactly are we to observe the superposition? or even verify afterward whether it did or did not happen????
September 17th, 2009 at 9:36 pm
All the results of a test can be observed, which is how we know of superposition to begin with. When they noticed that light reacts as both a wave and a particle they used a method to record where the photons struck as they passed through space. If somehow they developed a similar indirect method of observing then i believe it may be possible to observe a result without disturbing the experiment.
September 24th, 2009 at 10:53 am
Except you are not at superposition to the event when you do the experiment. The Universe is debris of change in possibility.