Notoriously, the theory of quantum mechanics reveals a fundamental weirdness in the way the world works. Commonsense notions at the very heart of our everyday perceptions of reality turn out to be violated: contradictory alternatives can coexist, such as an object following two different paths at the same time; objects do not simultaneously have precise positions and velocities; and the properties of objects and events we observe can be subject to an ineradicable randomness that has nothing to do with the imperfection of our tools or our eyesight.

Gone is the reliable world in which atoms and other particles travel around like well-behaved billiard balls on the green baize of reality. Instead they behave (sometimes) like waves, becoming dispersed over a region and capable of crisscrossing to form interference patterns.

This article was originally published with the title A Do-It-Yourself Quantum Eraser.

8 Comments

1. 1. Tom Adams MD 09:38 PM 11/26/07

   Because light has properties of both mass and wave function, then should light below the event horizon of a black hole go faster than C. If not then does light as we know it exist below the event horizon of a BH?

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2. 2. CristianAntiba 08:04 PM 9/7/08

   ...in video: http://grupocaos2007.brinkster.net/0lomas/lomas1.htm
   Stm. CristiᮠAntiba

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3. 3. shiekh 10:27 AM 6/9/09

   So it is not really an eraser experiment at all, since it just filters in an interference pattern that was present all along, but hidden by being mixed in with an anti-interference pattern.

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4. 4. gjwilkie 04:30 PM 12/3/09

   The "punchline" is invalid because light of different polarization doesn't interfere even in classical E&M.

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5. 5. bartoleme 06:39 AM 2/2/10

   The implied time paradox is an invalid one, as, under special relativity, all events occuring to a photon are simultaneous within its frame of reference. Since the two photons are traveling in the same reference frame, all of their events share simultaneity.

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6. 6. jayanayana0@gmail.com 09:05 AM 2/24/10

   very good explanation

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7. 7. hca5900 06:44 AM 9/1/11

   Note that this experiment actually does not require a quantum explanation. Classical electromagnetic theory can explain the result by reminding us that there is a real interaction of the fields with electrons in the polarizing filter . See e.g. the reference below:
   
   http://van.physics.illinois.edu/qa/listing.php?id=16544
   
   Moreover, the 3-polarizers effect can be reproduced with microwaves (i.e. 'light' of long wavelength) using the appropriate experimental set-up. Once more, no quantum explanation is really necessary for this experiment...

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8. 8. James Dunn 10:20 AM 11/17/12

   Tom Adams MD:
   
   I wonder if there are other feasibilities regarding the apparent behavior of light and black holes. Light can be potentially transformed into other non-observable artifacts "like" Bremsstrahlung. Bremsstrahlung is where a photon passes near an electron shell and evolves the electron shell into a higher energy state and the photon is absorbed.
   
   http://en.wikipedia.org/wiki/Bremsstrahlung
   
   Does high density gravity fields make matter absorb photons? Perhaps what we are looking at is simply the mass where low temperature absorption is taking place.
   
   I've wondered why x-rays are allowed to escape from black holes. Bremsstrahlung is frequency sensitive.
   
   To test this theory, I'm wondering if there is another feature in the Universe that has different gradients of high gravity fields and photons escape at different frequencies other than just x-rays?
   
   Perhaps Bremsstrahlung has a gravity (space-time curvature) component not yet part of its equations.
   
   ===
   
   This would seem to imply that a black hole may be near some extreme, absolute zero because if all light is absorbed and the mass structure is transformed to some extremely stable state. An absolute high temperature state where a stable system of energy transformations are bound and perpetual. Or, systems of interactive extremes that support the observed characteristics.
   
   One feature I find particularly interesting is that when a black hole is observed, that it can be observed. The movements of the galaxies and the gravitational lensing near a black hole should completely obscure its presence at our distance, unless there is fundemental causality (relativity) that connects the observer to the sources of the photons beyond the black hole.
   

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