# What is the fastest event (shortest time duration) that can be measured with today's technology, and how is this done?

Scott Diddams and Tom O'Brian of the Time and Frequency Division of the National Institute of Standards and Technology, explain.

Just how fast an event is depends somewhat on your point of view. In nature around us there are various physical events that occur on time scales from the yoctosecond (10-24 second) to the exasecond (1018 second). In the time it just took your heart to beat once, the computer on the desk next to you completed about one billion clock cycles, whereas the electron of a hydrogen atom could have circled its proton about 1 quadrillion (1015) times. On the other hand, that very slow heart beat is actually quite fast and fleeting if one considers it relative to the 500 quadrillion (500 x 1015) second lifetime of our universe. Within this tremendous range of time scales, science and technology, which are constantly improving, determine how accurately different events can be measured or inferred.

For example, in the late 19th century, the best scientists and technologists struggled to measure time intervals on the order of a hundredth or thousandth of a second. In a well-known (and often mythologized) story, photography pioneer Eadweard Muybridge, on commission from Leland Stanford, took several years to develop a system of rapid-sequence photography to conclusively prove that a galloping or trotting horse briefly has all four feet aloft simultaneously--an event too fast for the human eye to follow. Muybridge was able to perfect his system to record events on the scale of about 0.001 second in 1877.

But this story also points out a challenge in answering the original question: The answer depends on how one interprets the word "measured." This might sound like a pedantic dodge, but at the National Institute of Standards and Technology (NIST) we spend a lot of time trying to understand and apply the subtleties of measurement. Muybridge's photography was a record of short duration events--possibly the best such record of its time--but was not a measurement of time interval in the strict sense. Both the recording or inference of short duration events and accurate measurements of such events are of interest, so we suggest rephrasing the original question into two new questions: "What are the shortest time durations that can be measured with a particular accuracy?" and "What are the shortest duration events that can be recorded or inferred in experiments?"

To best answer the first question about measurement with a particular accuracy, let us agree to define measurement as a comparison to a generally accepted standard. By international treaty the standard for the second, the unit of time, is defined as exactly 9,192,631,770 cycles of a particular electron transition in cesium 133 atoms. So a time measurement is a direct or indirect comparison to this defined standard.

Currently, the best technical approach to measuring time against this standard is to use laser-cooled cesium atomic fountain frequency standards, known as cesium atomic fountain clocks. The handful of these cesium atomic fountain devices operating around the world are actually frequency standards rather than clocks (timekeeping devices), and they are used to realize the defined cesium standard frequency with exceptional accuracy of about 1 part in 1015. The best reported uncertainty at the time of this writing is about 6 x 10-16 for the NIST-F1 fountain standard. Because 86,400 seconds make up one day, this relative uncertainty means the standard is accurate to about 50 picoseconds (50 x 10-12 second) per day. Put another way, if the frequency standard could be operated indefinitely as a clock it would neither gain nor lose more than a second in 50 million years compared to a perfect clock.

Cesium atomic fountain standards are the world's most accurate primary standards of any kind. No other standard--including ones used for length, mass and electrical current--has an accuracy within even a factor of 1,000 of the cesium atomic fountain clock. The atomic fountain standard uncertainty of about 1 x 10-15 might seem to imply that these "clocks" could be used to measure events on the order of femtoseconds (10-15 second), but in fact fountain standards are not generally useful for directly measuring short duration events.

Rights & Permissions

View
1. 1. phayez 11:59 PM 12/26/08

Before the blogs were canceled here on Sci Am I had a blog under the username "PHAYEZ" which dealt with, among other things, time and measurement. I put forward that time only exists as a feature of three dimensional existence. Time is the "velocity/distance of 3D matter relative to the velocity/distance of other 3D matter". Outside of three dimensions "TIME" as such does not exist and infinity is equal to zero "time". Also outside of three dimensions measurements cannot be made of anything which makes mathematics, with all due respect, irrelevant since the language of mathematics has, as a syntax, products of measurement. The existence and non-existence of time is a spatial relationship oxymoron which is difficult to grasp when you are an entity who is wholly dependent on being made up of atoms which are moving through space.
One final comment, if I may, on the speed limit of light and the fact that even information cannot exceed the speed of light. At the speed of light time is zero, in other words for the light there is no time that passes so that regardless of where it arrives, it arrives instantaneously. Nothing can move faster than instantaneously, even information...
Pierre

2. 2. phayez 02:19 PM 5/31/09

"Time" as we know it by our clocks and knotted burning strings and sun dials are merely disconnected events which we use to relate to other events such as cellular changes in our bodies which we perceive as aging. "Time" as a universal constant simply does not exist at all. Eternity is equal to zero "time". Change in the universe occurs and continues to occur at different rates. The mystery of slowing clocks with increases in speed is just that a mystery. If one considers that "time" does not exist the mystery of slowing clocks becomes a simple search for a physical explanation of some kind of change affecting the apparatus in question. When a person is riding along with the slowing clock the person can be considered to be an apparatus as well and experiences the same changes as the slowing clock.

3. 3. robert schmidt 12:41 PM 1/23/10

@phayez, "If one considers that 'time' does not exist ", I think it is difficult to claim that something that can be measured does not exist. I may agree that it does not exist in the way we have interpreted based on the measurements, i.e. that time moves in one direction at a constant rate within an inertial frame. It is a bit like the blind men discovering the elephant, each has a very different interpretation based on the body part they are touching. I personally believe that time has no inherent direction and is just another dimension like the three spatial dimensions and that it is the 2nd law of thermodynamics that gives us the impression of a linear-unidirectional, flowing time.

For me the big question is; if time is a product of the universe, then what was the dimensional environment like prior to the creation of time? I realize that using the word "before" creates a number of issues. I can envision the primordial universe being one large black hole that evaporated (Hawking’s Evaporation) but that implies that there was an Event Horizon which implies space beyond the horizon, which implies time, so I guess that doesn't quite work. If all the matter in the universe collapsed into a black hole, would the black hole become something else? Is their another threshold where given a certain amount of mass you have a new object that not only no longer occupies space but completely collapses all dimensions?

I guess I am impatiently waiting for the LHC to start generating answers!

4. 4. phayez 05:10 PM 2/17/10

*

phayez at 12:23 AM on 12/27/08

Before the blogs were canceled here on Sci Am I had a blog under the username "PHAYEZ" which dealt with, among other things, time and measurement. I put forward that time only exists as a feature of three dimensional existence. Time is the "velocity/distance of 3D matter relative to the velocity/distance of other 3D matter". Outside of three dimensions "TIME" as such does not exist and infinity is equal to zero "time". Also outside of three dimensions measurements cannot be made of anything which makes mathematics, with all due respect, irrelevant since the language of mathematics has, as a syntax, products of measurement. The existence and non-existence of time is a spatial relationship oxymoron which is difficult to grasp when you are an entity who is wholly dependent on being made up of atoms which are moving through space.
One final comment, if I may, on the speed limit of light and the fact that even information cannot exceed the speed of light. At the speed of light time is zero, in other words for the light there is no time that passes so that regardless of where it arrives, it arrives instantaneously. Nothing can move faster than instantaneously, even information...
Pierre

*

phayez at 02:26 PM on 05/31/09

I have a simple explanation for "time". Time does not exist. "Time" as we know it by our clocks and knotted burning strings and sun dials are merely disconnected events which we use to relate to other events such as cellular changes in our bodies which we perceive as aging. "Time" as a universal constant simply does not exist at all. Eternity is equal to zero "time". Change in the universe occurs and continues to occur at different rates. The mystery of slowing clocks with increases in speed is just that a mystery. If one considers that "time" does not exist the mystery of slowing clocks becomes a simple search for a physical explanation of some kind of change affecting the apparatus in question. When a person is riding along with the slowing clock the person can be considered to be an apparatus as well and experiences the same changes as the slowing clock.

*

phayez at 02:41 PM on 05/31/09

The question redclay poses above is easily answered when one accepts that time does not exist. Time is a mental construct with memory being the main component of the "past" and the intent to change something being the prediction of the "future". When a person is deciding whether to do something or not do something in the "future" there is no determined event in the "future".

*

phayez at 11:40 AM on 06/03/09

I do not accept that "time" is a fourth dimension. I accept that "time" is a dimension but I postulate that "time" is the third of the three dimensions. The dimension of length contracts as 3D matter approaches the speed of light and "time" slows. This shows that what we perceive to be "time" is actually the dimension of length.

*

phayez at 11:59 AM on 06/03/09

Having postulated that "time" is actually the dimension of length this shows that a universal "time" constant does not exist. There are many dimensions starting with matter having zero dimensions through 1,2,3,4,5 etc. dimensions. The three dimensions which we experience comprise a bandwidth of dimensions which involve movement. The lower limit of the bandwidth is zero movement which is found at a temperature of absolute zero where all movement ceases. The upper limit of the bandwidth is 3D matter moving at the speed of light where the dimension of length ("time") contracts and reaches zero. Outside of this bandwidth (3D existence) the effects we perceive as "time" do not exist. This shows that "time" as we perceive it does not exist.

*

phayez at 03:24 PM on 06/04/09

The answers to the original two questions, "Is time quantized? In other words, is there a fundamental unit of time that could not be divided into a briefer unit? " , are yes "time" is quantized and no there is not a fundamental unit of "time" that can be divided into a briefer unit. Firstly, the dimension of length ("time") as a single entity is a quantum dimension and therefore quantized. Secondly, there is no fundamental unit of time that can not be divided into a briefer unit because "time" as a universal constant does not exist and is equal to zero. The effects of "time" are only evident in the reality of three dimensions. The three dimensions emerge from the quantum state (where "time" does not exist) as sub-atomic particles into the three dimensional reality where "time" effects can then be observed. The sub-division of "time" into units can continue forever because "time" is a theoretical mental construct and as such is not subject to real limits.

*

phayez at 07:25 PM on 06/12/09

The term "quantized"< http://en.wikipedia.org/wiki/Quantization_(physics) > should be distinguished from the term "quantified"< http://en.wikipedia.org/wiki/Universal_quantification > . In the question above, " Is time quantized?", the term "quantized" should have been "quantified" given the second qualifying question " In other words, is there a fundamental unit of time that could not be divided into a briefer unit? " Quantized refers to quantum mechanics and quantify refers to a measured quantity.

*

phayez at 07:31 PM on 06/12/09

The answer to the question "Is time quantified?" becomes no, given all that is written above.

*

phayez at 08:51 AM on 07/20/09

What determines which of the three dimensions is the dimension of length? The concept of three dimensions is a stick figure representation of existence which is convenient for human speech and interpersonal communication. There are multiple dimensions emanating from every point in space creating an unimaginably complex matrix of dimensions which we know as " three dimensions". The dimension of length is given priority amongst all other dimensions by the special property of movement. Moving matter has, as a property, the dimension of length in the direction of travel. As matter moves it is constantly being renewed so that in a curved path the dimension of length constantly reorients itself to the direction of travel. I stated in previous writings that "time is the velocity distance of 3D matter relative to the velocity/distance of other 3D matter" so that this allows for changes in the direction of travel. For example when two bits of matter are traveling together the time relation between the two is 1:1. As soon as there is a divergence in the direction and/or the velocity of the two bits of matter relative to each other the time relationship between the two changes to some ratio which is not 1:1.

1-10 | 11-11 |
2,573 characters remaining
You will be asked to sign in or register as a SciAm.com member when you click submit.

Email me when someone responds to this discussion.

5. 5. phayez 05:19 PM 2/17/10

The comments above may seem a little jumbled because I copied them from another blog. Refer to... October 21, 1999 | 11 comments
Is time quantized? In other words, is there a fundamental unit of time that could not be divided into a briefer unit?

You must sign in or register as a ScientificAmerican.com member to submit a comment.
Click one of the buttons below to register using an existing Social Account.

## More from Scientific American

• Scientific American Magazine | 21 hours ago

### Teenage Flu Scientist Shares His Recipe for Prizewinning Research

• Scientific American Magazine | 21 hours ago

• @ScientificAmerican | Dec 6, 2013

### Can We Harness Disruption to Improve Our World's Future?

• News | Dec 6, 2013

### Federal Flood Maps Left New York Unprepared for Sandy, and FEMA Knew It

• News | Dec 6, 2013

More »

## Latest from SA Blog Network

• ### Stream of Thought Description of Teaching James's "Stream of Thought": A Work of Faction

Cross-Check | 18 hours ago
• ### Wonderful Things: The Pugnacious, Alien-esque Skeleton Shrimp

The Artful Amoeba | Dec 6, 2013
• ### Can We Harness Disruption to Improve Our World's Future?

STAFF
@ScientificAmerican | Dec 6, 2013
• ### British Storm Brings Up History's First Work of Social Media

Plugged In | Dec 6, 2013
• ### Rolling on Wheels That Aren t Round

Observations | Dec 6, 2013

## Science Jobs of the Week

What is the fastest event (shortest time duration) that can be measured with today's technology, and how is this done?

X

Give a 1 year subscription as low as \$14.99

X

X

###### Welcome, . Do you have an existing ScientificAmerican.com account?

No, I would like to create a new account with my profile information.

X

Are you sure?

X