# Wacky Physics: New Uncertainty About the Uncertainty Principle

One of the most often quoted, yet least understood, tenets of physics is the uncertainty principle.

Formulated by German physicist Werner Heisenberg in 1927, the rule states that the more precisely you measure a particle's position, the less precisely you will be able to determine its momentum, and vice versa.

The principle is often invoked outside the realm of physics to describe how the act of observing something changes the thing being observed, or to point out that there's a limit to how well we can ever really understand the universe.

While the subtleties of the uncertainty principle are often lost on nonphysicists, it turns out the idea is frequently misunderstood by experts, too. But a recent experiment shed new light on the maxim and led to a novel formula describing how the uncertainty principle really works.

Perplexing logic

The uncertainty principle only applies in the quantum mechanical realm of the very small, on scales of subatomic particles. Its logic is perplexing to the human mind, which is acclimated to the macroscopic world, where measurements are only limited by the quality of our instruments.

But in the microscopic world, there truly is a limit to how much information we can ever glean about an object.

For example, if you make a measurement to find out exactly where an electron is, you will only be able to get a hazy idea of how fast it's moving. Or you might choose to determine an electron's momentum fairly precisely, but then you will have only a vague idea of its location.  [Graphic: Nature's Tiniest Particles Explained]

Heisenberg originally explained the limitation using a thought experiment. Imagine shining light at a moving electron. When a photon, or particle of light, hits the electron, it will bounce back and record its position, yet in the process of doing so, it has given the electron a kick, thereby changing its speed.

The wavelength of the light determines how precisely the measurement can be made. The smallest wavelength of light, called gamma-ray light, can make the most precise measurements, but it also carries the most energy, so an impacting gamma-ray photon will deliver a stronger kick to the electron, thereby disturbing its momentum the most.

Though not imparting as much disruption to the electron's momentum, a longer wavelength of light wouldn't allow as precise a measurement.

Marbles and billiard balls

"In the early days of quantum mechanics, people interpreted the uncertainty relation in terms of such back-reactions of the measurement process," said physicist Georg Sulyok of the Institute of Atomic and Subatomic Physics in Austria. "But this explanation is not 100 percent correct."

Sulyok worked with a research team, led by physicists Masanao Ozawa of Japan's Nagoya University and Yuji Hasegawa of Vienna University of Technology in Austria, to calculate and experimentally demonstrate how much of the uncertainty principle is due to the effects of measurement, and how much is simply due to the basic quantum uncertainty of all particles.

In quantum mechanics, particles can't be thought of as marbles or billiard balls — tiny, physically distinct objects that travel along a straight course from point A to point B. Instead, particles can behave like waves, and can only be described in terms of the probability that they are at point A or point B or somewhere in between.

This is also true of a particle's other properties, such as its momentum, energy and spin.

This probabilistic nature of particles means there will always be imprecision in any quantum measurement, no matter how little that measurement disturbs the system it is measuring.

"This has nothing to do with error or disturbances due to a measurement process, but is a basic fundamental property that every quantum mechanical particle has," Sulyok told LiveScience. "In order to describe the basic uncertainty together with measurement errors and disturbances, both particle and measurement device in a successive measurement have to be treated in the framework of quantum theory."

Calculating the uncertainty

To test how much this fundamental property contributes to the overall uncertainty, the researchers devised an experimental setup to measure the spin of a neutron in two perpendicular directions. These quantities are related, just as position and momentum are, so that the more precise a measurement is made of one, the less precise a measurement can be made of the other.

The physicists used magnetic fields to manipulate and measure the neutrons' spin, and conducted a series of measurements where they systematically changed the parameters of the measuring device.

"You have this basic uncertainty, and then by measuring you add an additional uncertainty," Sulyok said. "But with an apparatus performing two successive measurements, you can identify the different contributions."

Using their data, the physicists were able to calculate just how the different types of uncertainty add together and influence each other. Their new formula doesn't change the conclusion of the Heisenberg uncertainty principle, but it does tweak the reasoning behind it.

"The explanation that Heisenberg gave is very intuitive," Sulyok said. "On a popular science level it is hardly ever distinguished at all, and sometimes it's even not correctly explained in university textbooks. The quantum-mechanically correct calculation reinforced by our experimental data is a valuable step in achieving a more consistent view on the uncertainty principle."

The results of the study were published in January 2012 in the journal Nature Physics.

## Recommended for You

• ### Numbers drawn for \$636M Mega Millions jackpot

DES MOINES, Iowa (AP) — The numbers for the \$636 million Mega Millions jackpot were drawn Tuesday night. Now, the country waits to see if there's a winner of the second largest lottery jackpot in U.S. history.

Associated Press
• ### Mortgage Rates Hit 2.75% (2.86% APR)

Mortgage rates are back down this month to 2.75% (2.86% APR). Get a great rate and start saving money today. Calculate your payment.

• ### Husband On Gender Journey Wants His Wife To Go Along

DEAR ABBY: A couple of years ago, my husband informed me that he likes to dress in women's clothing. (Shipping and handling are included in the price.)

Dear Abby
• ### Kim Jong-un's Aunt Now Missing From Photo

North Korea Leadership Portrait Does Not Include Wife of Purged Mentor

ABC News
• Play

### Exclusive: Suspect to be charged with "Knockout" assaults

N.J. Burkett reports from Long Island

WABC – NY
• ### Bryant Scores 21 as Lakers Beat Grizzlies 96-92

Kobe Bryant scores 21 points in leading Lakers to 2nd win in 3 games, beating Memphis 96-92

ABC News
• ### India removes U.S. Embassy security barriers in spat

By Shyamantha Asokan and Chris Francescani NEW DELHI/NEW YORK (Reuters) - Indian police removed concrete security barriers outside the U.S. Embassy in New Delhi on Tuesday in apparent retaliation for the treatment of an Indian diplomat who was strip-searched after her arrest in New York last week.…

Reuters
• ### Case Is Closed: Multivitamins Are a Waste of Money, Doctors Say

People should stop wasting their money on dietary supplements, some physicians said today, in response to three large new studies that showed most multivitamin supplements are ineffective at reducing the risk of disease, and may even cause harm. The new studies, published today (Dec. 16) in the…

LiveScience.com
• ### US backs Philippines, warns China over air zone

US Secretary of State John Kerry warned China Tuesday against any move to declare an air defence zone in the South China Sea, as he affirmed defence ties with long-time ally the Philippines. Kerry, in Manila for a two-day visit, criticised China for its declaration last month of an Air Defence…

AFP
• ### Merle Haggard calls Ray Price 'the first outlaw'

NASHVILLE, Tenn. (AP) — Merle Haggard can still remember the first time he heard Ray Price's voice come out of the radio, fronting Lefty Frizzell's band on "If You're Ever Lonely Darling" in 1951. And the memory of hearing "I'll Be There" for the first time in 1954 still makes him break out into…

Associated Press
• ### High school named after KKK 'grand wizard' to be renamed

A Florida high school named after a founding member of the Ku Klux Klan is getting a new name after a campaign to change it went viral.

Yahoo News
• ### Special Report: How China's weapon snatchers are penetrating U.S. defenses

By John Shiffman and Duff Wilson OAKLAND, California (Reuters) - Agents from Homeland Security sneaked into a tiny office in Oakland's Chinatown before sunrise on December 4, 2011. The agents had allowed a Colorado manufacturer to ship He a type of technology that China covets but cannot…

Reuters
• ### Support mounts for Jewish prayer at key holy site

JERUSALEM (AP) — For decades, the religious Jews who bucked a rabbinic ban and visited a Muslim holy site in Jerusalem where the ancient Jewish temple once stood were seen by many as a fanatic fringe.

Associated Press
• Play

### Marijuana crop was target of Fresno County home invasion robbery

Just before 2 a.m. Tuesday, Fresno County Sheriff Deputies foiled a home invasion robbery, as the suspects tried to get away.

KFSN – Fresno
• ### Credit Cards Are Now Offering 0% APR Through 2015

Consumers can now get rid of high interest rates and get 0% APR for 18 months. Compare these leading 2013 credit card offers and find your best offer.

• ### Bidding soars for painting by Trayvon Martin shooter

Bidding for a painting by George Zimmerman, whose 2012 killing of black youth Trayvon Martin sparked national outrage, neared \$100,000 on Tuesday in an online auction that ends Sunday. The signed patriotic blue-hued portrayal of the Stars and Stripes flag is overlayed with the words "God, One…

AFP
• ### More snow, frigid temps take aim at Northeast

CONCORD, N.H. (AP) — More snow and frigid temperatures trudged into the Northeast on Tuesday even as crews continued to clean up from a weekend storm.

Associated Press
• ### Your cat does not love you

It appears humans’ love and reverence for cats is a touch one-sided.

Odd News
• ### Long-Lost Nazi Diary Transferred to Holocaust Museum

Missing for decades, the rediscovered diary of Alfred Rosenberg — a chief Nazi ideologue and one of Adolf Hitler's closest confidants — was officially turned over to the U.S. Holocaust Memorial Museum in Washington, D.C., Tuesday (Dec. 17). Under Hitler, Rosenberg led the Nazi party's foreign…

LiveScience.com
• ### SAfrica: Fake signer says he interpreted for years

JOHANNESBURG (AP) — The bogus sign language interpreter at Nelson Mandela's memorial said Tuesday he had translated for years at big events for the South African ruling party and government, which is investigating how a self-described schizophrenic said to have been involved in mob killings got…

Associated Press
• ### Ind. family trying to get back dog lost in tornado

MELLOTT, Ind. (AP) — An Indiana woman whose dog vanished when a tornado struck her family's home last month says a person who adopted the dog from an animal shelter six days later refuses to return him.

Associated Press
• ### Row grows after US Marshals strip-search Indian diplomat

US officials admitted that they strip-searched a female Indian diplomat after she was arrested in New York in a new twist to a growing row that has seen India hit back with reprisals such as removing security barriers around the US embassy. The State Department sought to calm tensions saying…

AFP