Absolutely Awesome Accuracy:
The Cosmic Constancy of the Latest Laser-locked Clock
01/11/2015
The other day in my car I listened to a New Zealand's National Radio podcast of an episode from the series "Our Changing World". The episode, entitled "Ultra-fast lasers" was an interesting look at the development of lasers which can produce ultra-short pulses of light. They are currently known as femtosecond lasers.
(femto- (symbol f) is a unit prefix in the metric system denoting a factor of 10−15 or 0.000000000000001.)
Amazing enough is the quote "A single one of these short pulses lasts just hundreds of femtoseconds, and one femtosecond is to one second what one second is to 32 million years,” says Miro. “Basically these pulses are the shortest things that humans have ever created."
However, what struck me as most amazing was a reference to the application of these lasers to the science of timekeeping. I have already written a piece "Who Knows Where the Time Comes From" on how a device gets the time off the Internet, and how inaccurate the timekeeping is on the average computer (up to a hundred times worse than a typical quartz watch).
What I heard on the program just staggered me: a reference to "optical atomic clocks, which are so precise they won’t gain or lose a second, even over billions of years."
I was so intrigued by this stunning fact I was driven (ha-ha) when I got to work, to do some searching on the Internet to get some detail about it.
The killer fact I found is this: -
(femto- (symbol f) is a unit prefix in the metric system denoting a factor of 10−15 or 0.000000000000001.)
Amazing enough is the quote "A single one of these short pulses lasts just hundreds of femtoseconds, and one femtosecond is to one second what one second is to 32 million years,” says Miro. “Basically these pulses are the shortest things that humans have ever created."
However, what struck me as most amazing was a reference to the application of these lasers to the science of timekeeping. I have already written a piece "Who Knows Where the Time Comes From" on how a device gets the time off the Internet, and how inaccurate the timekeeping is on the average computer (up to a hundred times worse than a typical quartz watch).
What I heard on the program just staggered me: a reference to "optical atomic clocks, which are so precise they won’t gain or lose a second, even over billions of years."
I was so intrigued by this stunning fact I was driven (ha-ha) when I got to work, to do some searching on the Internet to get some detail about it.
The killer fact I found is this: -
The latest in atomic clocks would neither gain nor lose one second in some 15 billion years—roughly the age of the universe.
Now, after taking in the almost incomprehensible accuracy this represents, one could be forgiven for thinking "Yes, but who needs clocks that accurate? What could they possibly be used for?"
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One second in 15 billion years is 1 part in 1000,000,000 x 15 x 365.25 x 24 x 60 x 60 = 473,364,000,000,000,000 = 4.73 x 10^17
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Well, it turns out that they can be made useful by studying what makes them INACCURATE. Once you have this steady pulse, gravity, magnetic fields, electrical fields, force, motion, temperature and other things can introduce tiny but measurable variations, such measurements becoming a proxy for measuring the actual gravity or force etc.
For example, as Einstein predicted, a gravitational field causes time to pass more and more slowly as gravity increases. A clock which is higher is further from Earth, experiences less gravity, and thus runs faster. The new clock is sensitive enough to detect the time shift caused by a rise of only two centimeters! It can thus serve as an extremely accurate measure of height for mapping, and of gravity variations caused by the earth's composition and shape. (Note that gravity's effect on time is NOT relevant to GPS satellites)
A reader interested in a fuller description of the intricacies involved and the influences which must be accounted for to achieve this accuracy should click here for the article "About time: New record for atomic clock accuracy", April 21, 2015 at phys.org.
For example, as Einstein predicted, a gravitational field causes time to pass more and more slowly as gravity increases. A clock which is higher is further from Earth, experiences less gravity, and thus runs faster. The new clock is sensitive enough to detect the time shift caused by a rise of only two centimeters! It can thus serve as an extremely accurate measure of height for mapping, and of gravity variations caused by the earth's composition and shape. (Note that gravity's effect on time is NOT relevant to GPS satellites)
A reader interested in a fuller description of the intricacies involved and the influences which must be accounted for to achieve this accuracy should click here for the article "About time: New record for atomic clock accuracy", April 21, 2015 at phys.org.
Update 3/10/23 - Ultra-fast lasers just got more ultrafast, and there was a Nobel Prize in it.
What are attoseconds? Nobel-winning physics explained
What are attoseconds? Nobel-winning physics explained