Quantum weirdness reaches new heights, now implies parallel universes.

Einstein's theory of general relativity states that nothing in the universe can travel faster than light. As usual, quantum mechanics disagrees. In special cases, a pair of particles can be connected in such a way that by measuring the state of one, the state of the other can be instantaneously known, even if the two particles are separated by a large distance. Einstein famously poked fun at the idea, sarcastically nicknaming it "spooky action at a distance." Many physicists today still have trouble accepting this so-called quantum entanglement, despite experimental evidence that implores them to think otherwise. In a recent paper, Dr. Frank J. Tipler, a mathematician and physicist at Tulane University, has developed a model that links alleged quantum nonlocality with the Many Worlds interpretation of quantum mechanics. He claims that his theory solves the paradox of faster-than-light travel, but only if we are prepared to accept the fact that we live in a multiverse, a wacky version of the cosmos in which parallel universes are born every time a decision is made.


Einstein's famous gibe, paired with the mathematical notation for "spin-up."
Image courtesy of Matt Mechtley.

The most oft-cited example of quantum entanglement is a system in which two electrons exist in a singlet state; that is, they must have opposite spins. Spin is a property that measures the angular momentum of a particle. When measured in the vertical direction, the spin of a particle can either be "up" or "down." In a singlet state, if one electron is spin up, the other must be spin down; this holds true even if the electrons are separated by hundreds of thousands of lightyears. The problem with such systems is that electrons should not be able to communicate with each other any faster than light can travel. For instance, if they are positioned 100,000 lightyears away from each other, it should take no less than 100,000 years for the news of one electron's chosen spin to reach the other so that it can choose the opposite spin; however, experiments indicate that such information seems to travel instantly.

How can this be? According to Tipler, we should embrace the Many Worlds interpretation of quantum mechanics in order to make sense of this seeming paradox. In the Many Worlds interpretation, every possible set of circumstances exists in a separate universe. Every time one choice is made over another, the universe splits. In my current universe, I am writing this article at a coffee shop in downtown Boulder. In a separate but equally real parallel universe, I am writing from home, successfully resisting the lure of overpriced tea. In yet another universe, I have horrible command of the English language and am instead spending my afternoon pondering the financial merits of becoming a stripper. Regardless of circumstance, each of these alternate universes is just as real as the one in which I sit, fully clothed, diligently pounding out a wordy and rambling piece of science writing.


Image courtesy of anomalous4.

Back to Tipler. In his model, there are four distinct universes that are born of such an experiment: one in which electron #1 is spin up, one in which electron #1 is spin down, one in which electron #2 is spin up, and one in which electron #2 is spin down. But because the two electrons exist in a singlet state, there are only two possible combinations of these worlds. Either electron #1 is spin up and electron #2 is spin down, or electron #1 is spin down and electron #2 is spin up. When an observer measures the state of electron #1 here on Earth, two universes result, each one containing an observer that detects an opposite spin. Thus, the resulting spin of electron #2 has nothing to do with any kind of faster-than-light communication by its counterpart. It is simply a consequence of the particular universe the observer happens to find himself in. Measurement of one electron does not determine the spin of the other; instead, it selects for one universe over another, one in which the two electron spins have been predetermined.

Confused yet? Don't worry, in another universe you know exactly what's going on. I promise.

A tiny mistake.

The proton is one of nature's most famous elementary particles. Solid, stable and always positive, this subatomic celebrity is, quite literally, at the center of everything in the universe. But new research suggests that the proton may actually be smaller than previously thought. If this turns out to be true, the laws of physics will definitely need some rehabilitation.

Excepting dark matter and dark energy, the entire universe is made up of atoms. In the center of each is a small positively-charged core called a nucleus, which is made up of protons and neutrons held together by the strong force. Like a swarm of bees, electrons buzz around the nucleus in different "shells", or energy states. Hydrogen, the lightest and most abundant element, has been exploited by scientists for centuries due to its extraordinarily simple structure: one proton orbited by one electron.


Ionized clouds of hydrogen. Image courtesy of UC Astronomy Dept.

Most recently, researchers at the Max Planck Institute used our atomic minimalist to probe some choice principles of Quantum Electrodynamics (QED), a theory that merges Einstein's theory of special relativity with quantum mechanics. According to QED, an electron orbiting the hydrogen nucleus in the 2S shell will have a different energy than it would if it were orbiting in the 2P shell. This difference is called the Lamb shift, and it contradicts Paul Dirac's original prediction that the 2S and 2P shells should have the same energy. In order to learn more about the Lamb shift, the team at Max Planck replaced the electron in hydrogen with its cousin the muon, a particle that is 200 times as massive and far less stable. When researchers observed the newly created muonic hydrogen, they found that the massive muon orbited the central proton far more closely than the electron did, and was therefore far more sensitive to its size. The team's calculations assign the proton a radius of 0.84184 femtometers (0.00000000000000084184 meters), a number that is 4% smaller than its previously accepted value of 0.8768 femtometers.

4% may not seem like a whole lot, but this tiny miscalculation could have enormous implications for particle physics. If this new result turns out to be accurate, QED and the Standard Model will have to be completely rewritten. No easy task for the most relied-upon theory in modern physics. Quite frankly, scientists may have a revolution on their hands.