New 'Double Slit' Experiment Skirts Uncertainty Principle

[n2doc]

By Edwin Cartlidge of Nature magazine

An international group of physicists has found a way of measuring both the position and the momentum of photons passing through the double-slit experiment, upending the idea that it is impossible to measure both properties in the lab at the same time.

In the classic double-slit experiment, first done more than 200 years ago, light waves passing through two parallel slits create a characteristic pattern of light and dark patches on a screen positioned behind the slits. The patches correspond to the points on the screen where the peaks and troughs of the waves diffracting out from the two slits combine with one another either constructively or destructively.

In the early twentieth century, physicists showed that this interference pattern was evident even when the intensity of the light was so low that photons pass through the apparatus one at a time. In other words, individual photons seem to interfere with themselves, so light exhibits both particle-like and wave-like properties.

However, placing detectors at the slits to determine which one a particle is passing through destroys the interference pattern on the screen behind. This is a manifestation of Werner Heisenberg's uncertainty principle, which states that it is not possible to precisely measure both the position (which of the two slits has been traversed) and the momentum (represented by the interference pattern) of a photon.


more
http://www.scientificamerican.com/article.cfm?id=new-double-slit-experiment-skirts-uncertainty-principle

[stevedeshazer]

1. Fascinating.

The uncertainty principle is now uncertain?

BTW, I appreciate your science posts, n2doc.

:)

[laconicsax]

2. Nope, uncertainty is still certain.

Steinberg stresses that his group's work does not challenge the uncertainty principle, pointing out that the results could, in principle, be predicted with standard quantum mechanics. But, he says, "it is not necessary to interpret the uncertainty principle as rigidly as we are often taught to do", arguing that other interpretations of quantum mechanics, such as the pilot-wave theory, might "help us to think in new ways".

[intaglio]

3. "Approximate information about momentum"

and tracing out "the average trajectories of the photons"

Doesn't smell like it breaks uncertainty.

[rug]

4. Rec for the headline.

I don't know what the hell he's talking about but it's a great headline.

[jobendorfer]

6. it's one of the core principles of quantum mechanics

There's a fundamental limit as to how much information you can measure about very small particles.
If you measure its position with high precision, then you have a large uncertainty about where the particle is going ( its "momentum" ).
And vice versa. If you measure its momentum precisely, then you have uncertainty about where the particle is.
You can know one or the other with high precision, but not both at the same time.

At first blush it looks like this uncertainty results from examining objects so small that virtually anything you do to probe them
changes their behavior. But it's actually worse than that -- there is an uncertainty that is an inescapable artifact of the pilot
wave that guides the particle.

This was one of the nails in the coffin of the "clockwork universe" model of classical (pre-20th-century) physics.

The uncertainty principle was first articulated by Werner Heisenberg in the mid to late 1920s.

J.

[rug]

9. Thanks for the explanation.

:thumbsup:

[montanto]

5. "Precise speed" and "approximate momentum" =

uncertainty.

[Codeine]

7. Most misleading use of the terms "skirts" and "double slit" EVER!

:mad:

[Hawkowl]

8. HA!