ER = EPR

Einstein is known for reshaping our conception of space and time and showing that this involved a re-imagining of gravity. This set the stage for the field of General Relativity, a field of physics that is still vigorously researched today. This only scratches the surface as to his contributions. He, for example, was the first person to successfully prove the existence of atoms by deriving Avogadro’s number; he was the first person to understand diffusion; and he was the first person to successfully predict the existence of a new kind of matter, Bose-Einstein condensates. Not to mention he also won a Nobel Prize in 1920 for helping invent the field of quantum physics, a subject that has boggled minds since its inception.

Ok, so he is the most profound physicist since Newton – and one might think that we can pay our dues to him and move on as we have largely done with every other physicist. The amazing thing is that we have been unable to move forward and will likely not be able to in the near future because he produced some of the most perplexing and deepest insights in physics to date. This story regards the melding of two fundamental concepts that Einstein introduced in two separate fields, entanglement, and wormholes, that might well prove to be fundamental in understanding the very foundations of the laws of physics. Even after his death, his ideas are still a well-spring of inspiration.

EPR (Einstein, Poldosky, and Rosen)

Having laid the groundwork for quantum physics, the great departure that it demanded from the realms of classical physics (the world of Newton) was too great for Einstein to bear. Not surprisingly, while his contemporaries were quite willing to move ahead and use quantum physics to understand the world around them.  It was Einstein who deeply understood that which he had helped create demanded a great departure from our conventional notions of reality. To demonstrate this struggle between classical and quantum physics, he and two other authors, Poldosky and Rosen, (EPR for short), explored an idea now called entanglement.


Entanglement can best describe with an example. Consider a coin, not just a regular coin, but a quantum coin. Quantum physics says this special coin can be in a state in which it is meaningless to ask whether it is heads up or tails up. This uncertainty has nothing to do with the observer but rather represents a legitimate state of the coin. The lingo is that it is in a superposition of heads and tails. But upon observation, it randomly selects which state to show so that the observer always sees heads or tails with some probability. The big leap forward that Einstein made was the following: suppose we have two such quantum coins each in a superposition state and they interacted (i.e., literally touched each other for example). Then imagine that Alice takes one coin on Mars and Bob takes the other somewhere in the Andromeda galaxy.  There exists some state so that if Alice sees his coin in the heads up position, he will know with 100% certainty that the second observer’s coin is in the heads up position whether or not the second observer has done any observation. The same thing applies if the Alice sees tails. If this does not spook you out, remember that the coins held by each Alice and Bob are in a superposition state and Alice or Bob randomly see heads or tails when they each see their coin.

This action at distance, Einstein argued, violated special relativity because the action seemed to require faster than light communication. He thought he had proved quantum mechanics to be incomplete. We now know that entanglement can’t be used to send messages so we are not violating special relativity. However, this leaves us in a very awkward position where one experiment instantaneously affects the other with no known mechanism as to how this happens.

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New York Times headline reporting Einsteins’ claims. Source: Wikimedia Commons

….and now for something completely different: ER (Einstein and Rosen)

Most people are familiar with black holes, as a staple of science fiction. What is less known is their brothers, white holes. While black holes eat up everything in their neighborhood, white holes spit out everything.  Einstein and Rosen, in 1935 (sound familiar?) described the possibility for traversing between two points in space using a combination of black holes and white holes. We call this geometric structure in space-time, a “wormhole” or Einstein Rosen bridges.

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Entrance into a wormhole. Source: Wikimedia Commons

 

ER = EPR

In a previous article, I explained the central drama of black holes and quantum mechanics, the black hole information paradox. Briefly, Stephen Hawking showed that black holes can radiate by removing entangled pairs of particles from the vacuum. One particle goes into the black hole while the other escapes. This slowly shrinks the black hole because of the equivalence of energy and mass.  Now imagine a universe in which only the black hole existed, then at some point, it would shrink and disappear. But then what would happen to all the particles that went into the black hole? We have lost information! This violates quantum mechanics because Quantum Mechanics predicts the situation should be reversible. It turns out the best attempts at a solution to save quantum mechanics, black hole complementarity, would also violate General Relativity because it involves a tearing of space-time.  A radical idea introduced in 2013 by Juan Maldacena and Leonard Susskind was that space-time can be saved if it can be glued together by entanglement. Each pair of entangled particles is connected by a microscopic wormhole.  Skepticism abounds, but this is a tantalizing connection between the two 1935 papers by Albert Einstein. Could he have thought of this? Chances are no, but who among us is willing to bet?

About the author:

amara Amara Katabarwa is a PhD candidate in the Physics and Astronomy Department at the University of Georgia studying His research focus is understanding Decoherence in Quantum Circuits and near term application of first generation Quantum Computers. In his free time he likes to read or guiltlessly laze about. He can be contacted at akataba@uga.edu