# Naked Science Forum

## Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: guest39538 on 21/07/2016 10:42:59

Title: How long is one second?
Post by: guest39538 on 21/07/2016 10:42:59
Time moves regardless of velocity, an observer in a ''stationary'' inertial reference frame experiences time whether they move or stand still.   However the act of measurement always needs two points of comparison and we define the distance between two points the measurement length such as centimetres or an increment of time by a degree of motion or the repetition of cycles.

So my question is , what length between two points do we define a second is and must the length remain constant?

added- if we change the length of a second are we not in affect changing the speed of measurement?

Title: Re: How long is one second?
Post by: alancalverd on 21/07/2016 12:11:47
One second is the time that elapses during 9,192,631,770 (9.192631770 x 10^9 ) cycles of the radiation produced by the transition between two levels of the cesium 133 atom.
Title: Re: How long is one second?
Post by: evan_au on 21/07/2016 12:15:08
Quote from: TheBox
what length between two points do we define a second is and must the length remain constant?
We define the second in terms of the period of oscillation of cesium atoms.

Specifically: "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom"

So you measure the start and end of one cycle, then repeat 9,192,631,769 more times.
The interval between the start and end of this measurement is 1 second.

And since you mention the effects of velocity, to be a valid and constant second (in your frame of reference), the cesium atoms also have to be in your frame of reference.

See: https://en.wikipedia.org/wiki/Second

PS: Mr Box, I know that you are familiar with this definition. So why do you keep asking?

Oops: Crossover with alancalverd
Title: Re: How long is one second?
Post by: guest39538 on 21/07/2016 12:39:10
Quote from: TheBox
what length between two points do we define a second is and must the length remain constant?
We define the second in terms of the period of oscillation of cesium atoms.

Specifically: "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom"

So you measure the start and end of one cycle, then repeat 9,192,631,769 more times.
The interval between the start and end of this measurement is 1 second.

And since you mention the effects of velocity, to be a valid and constant second (in your frame of reference), the cesium atoms also have to be in your frame of reference.

See: https://en.wikipedia.org/wiki/Second

PS: Mr Box, I know that you are familiar with this definition. So why do you keep asking?

Oops: Crossover with alancalverd

I ask and keep asking because my discussion always ends without a conclusion to my question.

You mention you measure a start and end of this cycle, so what is the length of distance of your two points of start and end reference?

Title: Re: How long is one second?
Post by: jeffreyH on 21/07/2016 12:53:58
The interval isn't a length it is a period of time. Metres and seconds are quite distinct units that cannot be directly interchanged. They can however be applied in combination. To give velocity for instance.
Title: Re: How long is one second?
Post by: guest39538 on 21/07/2016 13:33:31
The interval isn't a length it is a period of time. Metres and seconds are quite distinct units that cannot be directly interchanged. They can however be applied in combination. To give velocity for instance.

Hmmm, so you are saying it is a period of time equal to the speed of cycles per what?

Title: Re: How long is one second?
Post by: PhysBang on 21/07/2016 15:15:18
PS: Mr Box, I know that you are familiar with this definition. So why do you keep asking?

I ask and keep asking because my discussion always ends without a conclusion to my question.

I think that I would all that a lie. I am pretty sure that Thebox asks these questions because Thebox has his own, special answer independent from any scientific work ever done on the question and Thebox wants to try to share this special answer with people.
Title: Re: How long is one second?
Post by: IAMREALITY on 21/07/2016 15:44:37
PS: Mr Box, I know that you are familiar with this definition. So why do you keep asking?

I ask and keep asking because my discussion always ends without a conclusion to my question.

I think that I would all that a lie. I am pretty sure that Thebox asks these questions because Thebox has his own, special answer independent from any scientific work ever done on the question and Thebox wants to try to share this special answer with people.

Indeed.

It's always one big mindcluck.
Title: Re: How long is one second?
Post by: guest39538 on 21/07/2016 22:44:33

I think that I would all that a lie. I am pretty sure that Thebox asks these questions because Thebox has his own, special answer independent from any scientific work ever done on the question and Thebox wants to try to share this special answer with people.

I have no special answer to how long a second is, I can only go off history and what we know.

Jeff said this

''The interval isn't a length it is a period of time.''

So what on earth as length contraction got to do with time dilation?

I dont get it, to me ''you'' are saying that if we record 1 cycle a second instead of 2 cycles a second that time is slowing down, yet the second remains a second , because of 1 cycle or two cycles per second.

1 cycle being half a second if there is 2 cycles per second.

So in the Keating experiment, time doesnt slow down, the measurement is less than a second or the speed of cycles slows down?

9,192,631,770 =1s

9,192,631,760 =<1s

Added question - How do you measure the caesium cycles?

I presume the caesium beam is received by something that counts, I assume the beam travels a length of space before it reaches the counter?

The length between counter and atom is the answer I am after!

Added - I have now looked up the atomic clock and how it works, there is a fixed length of mechanism but it was not what I thought, however when the clock is in motion it gains more kE in the magnets that then gain more permitivity in the magnetic  field that slows down the caesium beam ?

Because tell me if I am wrong, if the magnetic field of the magnets fluctuates, then so will the result of measurement of the beam.

added-  wouldn't the magnetic field ''turn'' like a compass needle because of the earths magnetic field and distort its field form?

Title: Re: How long is one second?
Post by: evan_au on 22/07/2016 11:51:33
Quote from: TheBox
How do you measure the caesium cycles?
You expose them to microwave radiation.
If the microwave radiation is at the right frequency, you will flip the state of the cesium atom; if the frequency is wrong, you won't flip the atomic state.
So the microwave frequency is continually adjusted so that it remains at the right frequency to trigger the atomic transition.
The you just use an electronic circuit which can count microwave oscillations - it only needs to count up to 9 billion or so before it emits a pulse representing 1 second.

Quote
I assume the beam travels a length of space before it reaches the counter?
You are thinking of the older cesium beam (http://) standard, where the cesium atoms fly down a tube. These have gone out of fashion because they aren't so accurate.

Quote
The length between counter and atom is the answer I am after!
The current best design for use on Earth is called the cesium fountain (https://en.wikipedia.org/wiki/Atomic_clock#Fountain_standard), where the cesium atoms flow upwards against Earth's gravity, stop, and fall back to where they started. So overall the atom has not travelled anywhere since the beginning of the measurement (although its velocity has changed direction).

The clock will be more accurate and stable if the cesium atoms don't move; such a design may be possible for an atomic clock in space (eg in the GPS satellites).

In fact some of the newer experimental atomic clocks actually hold the atoms in an ion trap (https://en.wikipedia.org/wiki/Atomic_clock#Ion_trap_standard) so they don't move.

Quote
So what on earth as length contraction got to do with time dilation?
Objects travelling at a significant fraction of the speed of light appear to suffer time dilation and length contraction, as well as mass increase. These are independent effects, but they have the same relationship to the observer's relative velocity: The Lorentz Factor (https://en.wikipedia.org/wiki/Lorentz_factor).

But this does not affect you measuring 1 second in your lab. The cesium atoms are gently heated so they drift at a speed of meters per second (or less, with the fountain method), for which relativistic effects are negligible.
Title: Re: How long is one second?
Post by: guest39538 on 23/07/2016 07:37:59

Objects travelling at a significant fraction of the speed of light appear to suffer time dilation and length contraction, as well as mass increase. These are independent effects, but they have the same relationship to the observer's relative velocity: The Lorentz Factor (https://en.wikipedia.org/wiki/Lorentz_factor).

But in reality relativistic mass is just a replacement explanation for more speed and force of impact.  The length contraction is just a visual thing involving light and time dilation is poorly worded when the effect of time dilation is simply a change in rate of entropy gain and loss and not really a change of real time.

It is wrong of us to change time by disregarding the precedence for a constant of time and a constant length/increment to represent 1 second.  In the Keating experiment it is wrong of us to overlook the magnetic field distortions of the magnets inside the clock that in affect could have tighter field lines increasing the permitivity slowing down the Caesium beam. The magnetic field of the the magnets inside the Caesium clock, acting like a gyroscope and being subjective to the Earths magnetic field influence, a compass needle points north.

Title: Re: How long is one second?
Post by: PhysBang on 23/07/2016 13:59:02

But in reality relativistic mass is just a replacement explanation for more speed and force of impact.  The length contraction is just a visual thing involving light and time dilation is poorly worded when the effect of time dilation is simply a change in rate of entropy gain and loss and not really a change of real time.
You have an amazing grasp of reality for someone who continually demonstrates the inability to produce correct statements on the contents of actual scientific theory.
Title: Re: How long is one second?
Post by: dlorde on 25/07/2016 16:28:45
... The magnetic field of the the magnets inside the Caesium clock, acting like a gyroscope and being subjective to the Earths magnetic field influence, a compass needle points north.
One would hope that if Earth's magnetic field was considered likely to affect the clock's accuracy, they would shield it.
Title: Re: How long is one second?
Post by: chris on 25/07/2016 19:59:51
This is an article I wrote recently about a new generation of clocks capable of being many times more accurate than the present generation of caesium clocks (http://www.thenakedscientists.com/HTML/science-news/news/1000875/).
Title: Re: How long is one second?
Post by: guest39538 on 25/07/2016 21:56:10
This is an article I wrote recently about a new generation of clocks capable of being many times more accurate than the present generation of caesium clocks (http://www.thenakedscientists.com/HTML/science-news/news/1000875/).

Thank you for sharing your article , I do feel it was incomplete in some points. I feel you should of explained that the Caesium cycles were ''counted'' to match the original old second that was based on relative Sun/Earth motion in affect keeping the ''length'' of the second the same period increment.

My feeling were towards this part-

''The "second" as we know it today actually dates from 1967 when, rather than being based on the Earth's movement around the Sun as it had been previously, a caesium-based atomic clock, invented by Englishman Louis Essen, was used instead.''

Title: Re: How long is one second?
Post by: evan_au on 25/07/2016 22:09:32
Here is a detailed description of Galileo (http://omegataupodcast.net/209-satellite-development-at-ohb/) (European civilian equivalent of the US military GPS).

Each satellite carries 4 atomic clocks: 2 Rubidium and 2 Hydrogen masers (30 satellites are planned).