EPR, Bell & Aspect: The Original References (in PDF Format)
By David R. Schneider


NOTE: Please feel free to link to this page or the PDF files. I will leave them up permanently for this purpose.

This page contains references to the key original papers on the longstanding debate about the completeness of Quantum Mechanics (QM), particularly Bell's Theorem. It is not intended to be a definitive collection or exposition on the matter. Quite the opposite, it is limited to the 3 essential papers in the series, which were written over a nearly 50 year time span. These amazing papers lay out a complex line of reasoning involving our fundamental understanding of reality in the physical sense. Each is brilliant and ground-breaking in its own right, building to a powerful conclusion regarding the matter.

What do they say? Relativistic Quantum Mechanics is the foundation of our understanding of physical reality. Einstein felt the statistical nature of QM indicated that it was an incomplete theory. He believed that particles had distinct properties which had definite values, even when they were not observed. Certainly a reasonable idea, akin to asking "whether a tree falling in the woods makes a noise if no-one hears it." However, this idea led to conflict with the predictions of QM, and Bell exploited those differences to create his famous theorem. Aspect performed the experiment which proved QM to be accurate. The result: there is no deeper level of reality in which all effects have specific causes. Determinism fails if the speed of light is respected.

Does this settle the matter? Not really, because the debate continues. There have been more experiments performed - all confirming the original results - but attempting to eliminate criticisms. And there has been a lot of discussion about theoretical issues as well. But one thing is certain: the predictions of QM have succeeded. Recent experiments have improved the accuracy to stunning levels, and newer versions of key experiments are being performed on the tabletop in undergraduate labs!

Seeing the originals of these three papers is - to me - very exciting as they expose the power of human ideas. These are the original source documents representing some truly amazing minds. You need the free Adobe Acrobat Reader to view them. Enjoy!

1. A. Einstein, B. Podolsky, N. Rosen: "Can quantum-mechanical description of physical reality be considered complete?" Physical Review 41, 777 (15 May 1935).

The first was the paper written in 1935 by Albert Einstein and two others, Rosen and Podolsky. It is known by their collective initials as EPR. This is the paper that set out the original challenge to the Quantum Mechanical school to that QM was incomplete as a theory.

As per usual, Einstein cut to the heart of the matter. "God does not play dice" was his famous quote. However, this time he finally met his match: himself. In the end, his statement about dice is only true if the speed of light (c) is not the absolute speed limit Einstein envisioned. Quantum theory proved to be correct regardless, but Einstein never knew. He died in 1955, and it would take Bell and others to prove him wrong years later.

• For the complete EPR paper in PDF (Acrobat Reader) format: EPR.pdf (4 pages, 300k)

2. J.S. Bell: "On the Einstein Podolsky Rosen paradox" Physics 1 #3, 195 (1964).

The second was the paper written in 1964 by J.S. Bell. It is known as Bell's Theorem. This is the paper that showed how to exclude an entire class of "hidden variable" theories from the realm of possibility via experiment. In a brilliant (and relatively straight-forward) mathematical proof, he showed that there existed certain settings for physical experiments that contradicted "common sense" views of reality. The Bell test related to so-called "entangled" pairs of light particles (photons), and measurement of their polarity relative to an apparatus set at specified angles. The relative angles were picked to exaggerate and highlight the desired effect, leading to apparently impossible measurements. After all, the likelihood of any event must be between 0 and 100%, right? Well, just don't forget that Quantum Mechanics sometimes ventures beyond the weird...

• For the complete Bell paper in PDF (Acrobat Reader) format: Bell_Compact.pdf (6 pages, 500k)
Or download a larger file, but containing better resolution: Bell.pdf (6 pages, 5 megabytes)

3. A. Aspect, Dalibard, G. Roger: "Experimental test of Bell's inequalities using time-varying analyzers" Physical Review Letters 49 #25, 1804 (20 Dec 1982).

The last was the paper written in 1982 by Alain Aspect and two others. It is known as Aspect. This is the paper that experimentally answered the original challenge in a definitive manner. The actual results confirmed the statistical predictions of Quantum Mechanics - as formulated in the late 1920's - and ruled out Einstein's view of a more complete specification of reality. To paraphrase, a particle falling in the woods does NOT make a sound if there is no one to hear it. Strange - but true!

• For the complete Aspect paper in PDF (Acrobat Reader) format: Aspect.pdf (4 pages, 300k)

Other helpful links on the EPR Paradox:

• Summary from John Baez:
Does Bell's Inequality Principle rule out local theories of quantum mechanics?

• And perhaps the best recap of the current "state of the debate", by Alain Aspect himself:
Bell's inequality test: more ideal than ever (PDF)

• The 1998 Innsbruck Experiment (EPR with 1 kilometer of separation):
Violation of Bell's inequality under strict Einstein locality conditions (PDF), by Weihs, Jennewein, Simon, Weinfurter and Zeilinger

• Using an EPR setup to demonstrate the particle nature of light in a relatively inexpensive tabletop setup (repeating an experiment performed by Aspect and others):
Observing the quantum behavior of light in an undergraduate laboratory (PDF), by Thorn, Neel, Donato, Bergreen, Davies and Beck

• My own humble derivation of Bell's Theorem in relatively simple terms (it must be simple because I did it!):
Bell's Theorem: An Overview with Lotsa Links
Bell's Theorem with Easy Math
Bell's Theorem and Negative Probabilities

(c) 2003-2014 David Schneider.