Featured Research

from universities, journals, and other organizations

Zeno's Quantum Paradox Reversed: Watching A Flying Arrow Increase Its Speed

Date:
June 5, 2000
Source:
Weizmann Institute
Summary:
For over 2,500 years, scientists and philosophers have been grappling with Zeno of Elea's famous paradox. More recently, scientists believed that the counterpart of this paradox, known as the quantum Zeno paradox, is realizable in the microscopic world governed by quantum physics. Now, scientists from the Weizmann Institute of Science have shown that in most cases, the quantum Zeno paradox should not take place.

Is motion an illusion? Can"glimpses" freeze radioactive decay?

For over 2,500 years, scientists and philosophers have been grappling with Zeno of Elea's famous paradox. More recently, scientists believed that the counterpart of this paradox, known as the quantum Zeno paradox, is realizable in the microscopic world governed by quantum physics. Now, scientists from the Weizmann Institute of Science have shown that in most cases, the quantum Zeno paradox should not take place. An article describing the calculations that lead to this surprising conclusion appears in today's Nature. The article is also surveyed in the journal's News and Views section.

The Greek philosopher Zeno, who lived in the 5th Century B.C., decades before Socrates, dedicated his life's work to showing the logical paradoxes inherent to the idea of indefinite divisibility in space and time (i.e., that every line is composed of an infinite number of points). One of these paradoxes is known as the arrow paradox: if the motion of a flying arrow is divided ad infinitum, then during each of these infinitesimal moments, the arrow is at rest. The sum of an infinity of zeroes remains zero, and therefore the arrow cannot move. One can imagine how someone giving a flying arrow quick, repeated glimpses, can actually freeze it in place. Zeno inferred from this that movement cannot happen. Indeed, he was a true follower of Parmenides, his teacher and mentor, who advocated that any change in nature is but an illusion.

This philosophical view was rejected by Aristotle, as well as by scientists and philosophers of the 19th century, who resolved Zeno's paradox by showing that non-zero velocity can exist in the limit of infinitesimal divisions of a trajectory. However, the paradox was bolstered in the 1960s by the physicist Leonid A. Khalfin, working in the former USSR, and by physicists E.C.G. Sudarshan and Baidyanath Misra, working in the USA during the 1970s. Using quantum theory, they concluded that if an "observer" makes repeated quick observations of a microscopic object undergoing changes in time, it is highly probable that the object will indeed stop changing. The frequent observations divide the trajectory along which the object evolves into infinitesimal segments in which there is no change. In other words, in the quantum world an observer can freeze the evolution of an object, in accordance with Zeno's paradox.

Skeptics who doubted those calculations must have been genuinely surprised when, in 1990, Colorado University physicist John Wineland proved in an experiment that "freezing glimpses" do work in the real world (or at least in a "simple" world with only two energy levels). Ever since, physicists have been struggling to understand the implications of the experiment. Can the Zeno paradox, for example,"glimpse-freeze" radioactive nuclear decay, thus stopping radiation? The prevailing answer during the past 30 years has been that such a freeze should be possible, provided the successive observations are made frequently enough.

Prof. Gershon Kurizki and Dr. Abraham Kofman of the Weizmann Institute of Science have recently shown that, for better or for worse, such "freezing" does not take place in reality, and decay cannot actually be stopped by "bombarding" the system with glimpses. According to their calculations, the ability to "freeze" changes through quick glimpses depends on the ratio between the memory time of the decay, and the time interval between successive observations. Every process of decay has a memory time. In the case of radioactive decay, for instance, this is the period in which the radiation has not yet escaped from the atom, allowing the system to "remember" its state prior to the decay. The memory time in a radiative decay process of an excited atom (an atom occupying an unstable energy level) is less than one billionth of a billionth of a second. To "freeze" this decay, the observations would have to be at intervals of much less than a billionth of a billionth of a second.

However, a sequence of observations so close in time would cause the appearance of new particles, changing the system completely and destroying it, and thus the question of stopping the decay would become meaningless. On the other hand, if the time interval between observations is longer than the decay's memory time, the rate of decay and radiation is actually increased. Not only does Zeno's paradox not take effect in such a case but there is actually an opposite effect: the "anti-Zeno effect".

Prof. Kurizki: "In other words, if we make the analogy between an object undergoing changes in time, for example a decaying nucleus or an excited atom, and Zeno's moving arrow, the arrow will increase its speed as the rate of the 'glimpses' increases. The surprising conclusion of this research is that the anti-Zeno effect (i.e., the increase of decay through frequent observations) can occur in all processes of decay, while the original Zeno effect, which would slow down and even stop decay, requires conditions that only rarely exist in such processes."

Professor Gershon Kurizki is the holder of the George W. Dunne Chair of Chemical Physics.


Story Source:

The above story is based on materials provided by Weizmann Institute. Note: Materials may be edited for content and length.


Cite This Page:

Weizmann Institute. "Zeno's Quantum Paradox Reversed: Watching A Flying Arrow Increase Its Speed." ScienceDaily. ScienceDaily, 5 June 2000. <www.sciencedaily.com/releases/2000/06/000602074805.htm>.
Weizmann Institute. (2000, June 5). Zeno's Quantum Paradox Reversed: Watching A Flying Arrow Increase Its Speed. ScienceDaily. Retrieved September 18, 2014 from www.sciencedaily.com/releases/2000/06/000602074805.htm
Weizmann Institute. "Zeno's Quantum Paradox Reversed: Watching A Flying Arrow Increase Its Speed." ScienceDaily. www.sciencedaily.com/releases/2000/06/000602074805.htm (accessed September 18, 2014).

Share This



More Matter & Energy News

Thursday, September 18, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Virtual Reality Headsets Unveiled at Tokyo Game Show

Virtual Reality Headsets Unveiled at Tokyo Game Show

AFP (Sep. 18, 2014) Several companies unveiled virtual reality headsets at the Tokyo Game Show, Asia's largest digital entertainment exhibition. Duration: 00:48 Video provided by AFP
Powered by NewsLook.com
Stocks Hit All-Time High as Fed Holds Steady

Stocks Hit All-Time High as Fed Holds Steady

AP (Sep. 17, 2014) The Federal Reserve signaled Wednesday that it plans to keep a key interest rate at a record low because a broad range of U.S. economic measures remain subpar. Stocks hit an all-time high on the news. (Sept. 17) Video provided by AP
Powered by NewsLook.com
Space Race Pits Bezos Vs Musk

Space Race Pits Bezos Vs Musk

Reuters - Business Video Online (Sep. 16, 2014) Amazon CEO Jeff Bezos' startup will team up with Boeing and Lockheed to develop rocket engines as Elon Musk races to have his rockets certified. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
MIT's Robot Cheetah Unleashed — Can Now Run, Jump Freely

MIT's Robot Cheetah Unleashed — Can Now Run, Jump Freely

Newsy (Sep. 16, 2014) MIT developed a robot modeled after a cheetah. It can run up to speeds of 10 mph, though researchers estimate it will eventually reach 30 mph. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins