Paging Captain Obvious: To perform a legitimate experiment, scientists must observe the results of a system in motion without influencing those results. Turns out that’s harder than it sounds. In 1927, German physicist Werner Heisenberg discovered that in the Wonderland-like subatomic realm, it is impossible to measure position and momentum simultaneously with any kind of precision. “In an attempt to observe an electron or other subatomic particle using light, very short wavelengths of light are required,” says David Cassidy, a science historian and Heisenberg expert at Hofstra University. “But when that light hits the electron, it knocks it all over the place like a billiard ball.” This can become a serious issue when you’re working with the kind of focused, high-intensity beams found in, say, particle accelerators. “The more precise the momentum of the beam particles,” Cassidy says, “the more difficult it becomes to focus the beam.” This argument is often summed up in Physics textbooks as the 'Plausibility Argument' for Uncertainty, which uses a simplification of a microscope to illustrate the idea, without appealing to quantum mechanical concepts: In a microscope, light is used to irradiate and observe a subject under examination. With large objects under the microscope, the impact that the observing light has on the subject is tiny, ompared to the mass of the object. But if the subject under examination is itself not much larger than a photon, then a single photon will disturb the object significantly compared to its state before observation.

The plausibility argument, however, glosses over what happens when quantum mechanical systems are under observation, and for this there is no classical explanation. The real problem, though, is what this so-called uncertainty principle does to reality. Do an experiment to find the fundamental unit of light and you find particles called photons. But change the conditions of the experiment and you get waves. Physicists have no problem with the cognitive dissonance of this “wave-particle duality.” But... so... what’s light made out of, really? Quantum Mechnical theory extended through Bell's inequality shows that, until the time of the measurement, the system hadn't actually decided which final state to 'collapse' into. Quantum systems (such as entangled particles) exist as a superposition of contradictory possible states, such as Left+Right, Up+Down and so on. Such systems do not actually become 'Left' or 'Right' (or any other possibilities allowed for by theory) until the measurement process, which is when the system instantaneously (and randomly) chooses one, even if the different parts of the system (such as the individual entangled photons) are on opposite sides of the universe.

The dichotomy raises the mind-boggling prospect that unless we observe an event or thing, it hasn’t really happened, that all possible futures are quantum probability functions waiting for someone to notice them - trees falling unheard in a forest. Maybe this article wasn’t even here until you turned to this page.

Elizabeth Svoboda, San Jose-based writer,

Return to Big Questions: http://www.wired.com/42

G. Emory Anderson, ex-Physicist working in London.

Isn't it the case that when dealing with very small particles, there is simply no way to observe them without physically altering them? Why is that such a mystery?

An analogy in my mind would be a blind man trying to determine the items on a table in front of him. No mystery. There's no possible way for him to know what the objects are without displacing them, by touching, and the more he manipulates the object before putting it down, the more that object will be displaced from its original state.

Maybe I'm looking at this all wrong.

contributed by Guest User on Jan 24 9:52am

<Maybe I'm looking at this all wrong.>

Yes, you are. In the blind man example, we could add a device that detects objects on the table without disturbing them, and then tells him.

In quantum superposition, there simply is no state of things independent of a measurement. Not only are there no ways of measuring without disturbing, there are no facts to measure until you measure them. So actually "disturbing" is a mischaracterization.

Hope that helps.

contributed by Guest User on Jan 24 10:37am

do not confuse the observer effect with the uncertainty principle. the uncertainty principle has nothing to do with "observing", it has to do with measuring. the observer effect is a supposed effect of observing an event and the influence of your observations on the event. no one would ever have to actually observe a particle's position to obfuscate its momentum, the mere act of using the photons to measure its position, even if nobody ever observed it, would suffice. it's the act of measuring, not actually observing that causes the uncertainty principle. richard feynman gives a good explanation on the uncertainty principle in (i think) the feynman lectures on physics. the big problem is that people often confuse observation with measurement.

contributed by Guest User on Jan 24 10:55am

What if light is made of solitons.. this solves the wave / particle problem.

contributed by Guest User on Jan 24 6:16pm

I would like to know what constitutes an "observation" and what is the minimum type of "observation" required to affect the outcome of an experiment.

Contributed by Alex Zavatone ala an edit since adding comments doesn't work in Safari. On 2007-1-25 at late o'clock GMT
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I think there's also something called "The Anderson Effect" which says something similar. -I've heard it applied all over the place, like in measuring systems, productivity, etc.

contributed by The Will on Jan 25 7:01am

<span class="nlw_phrase">&gt;</span>Maybe this article wasn’t even here until you turned to this page.

I am reminded of the scene in the 13th Floor where he drives out to Arizona and sees the end of the universe--literally. But my belief is that if there were such a thing as a simulation, it would just extend reality out as we travel, so such a thing (finding the end of the universe) couldn't happen.

Of course, it's possible that Creation--in the Judeo-Christian sense--works the same way. The world, and people with it, was created some thousands of years ago, and everything before--including the billions of years that transpired before that--that has come into being purely because we chose to observe it. Not perhaps so different from the Participatory Universe that John Archibald Wheeler talks about. And now Stephen Hawking and Thomas Hertog have taken what appears to be a similar position in their joint paper "Populating the Landscape: A Top Down Approach". (My use of the weasel-word "appears" is because I can't claim to understand their paper, or even some of the commentary on it.)

Speculation, of course...

(hmm, not sure how I "sign" this; I'll try Wikipedia's tildes: ~~~~)