Time Measures

[Ygrene Imref]

SI defines a "second" as 9,192,631,770 cycles of the radiation produced by the transition between two levels of the cesium 133 atom.

Obviously that measure wasn't chosen for its ease and accessibility. As I understand it, cesium was chosen because of its stability, i.e. the repeatability of using that as a measure. If I'm wrong, please correct me.

I have two questions, then. First, if ease and accessibility was not a concern, but rather maximum repeatability of the measure, is cesium better for some reason than using the speed of light to define "second".

Because these are hyperfine transitions in the Cs-133 atom from ground, atomic clock make for better measurements of time than the speed of light. The idea behind it is that the speed of light travels different speed in different media (Cherenkov Effect, tachyons, bradyons, etc.) So, we would have to account for every single type of medium for which photons travel in order to determine the amount of time it takes a photon to travel 1 meter.

Radioactivity (consequence of Weak Force) is based on fundamental force, not action or transformation.

Next, do we know why cesium is so predictable and the decay of other radioactive elements is not as predictable?

We don't. There may be an explanation, but there really isn't a good explanation. Generally, Cs has valency that supports stability. The radiation emitted by Cs is more or less constant. Of the radioactive elements, Cs has been taken to be the best choice to measure emission spectra continuity/probability.

Time, by this or any other definition is, therefore, necessarily arbitrary.

 

[Radagast]

OK. What other particles have no rest mass?

Gluons. But they only exist inside nuclei. And gravitons, if they exist.

So, isn't the cesium transition affected by the medium as well?

Not really, because we're talking about an electron that never leaves the atom (although for practical reasons we do need a vacuum inside the caesium clock).

 

[Radagast]

Of the radioactive elements, Cs has been taken to be the best choice to measure emission spectra continuity/probability.

Caesium isn't radioactive. Reasons for choosing caesium include having only one outer electron (hence 1st column of periodic table) and having only one stable isotope (so all atoms have the same mass).

 

[essentialsaltes]

OK. What other particles have no rest mass? And what distinguishes them from photons?

In addition to gluons, gravitons are theoretically massless. Although they have not been experimentally verified, the recent discovery of gravity waves coinciding with a light signal from colliding black holes would seem to indicate that gravity travels at the speed of light (and if it is carried by gravitons, then the gravitons are massless).

So, isn't the cesium transition affected by the medium as well?

Atomic clocks (at least the best ones) have the cesium in very very very good vacuums.

"The cesium atoms are kept in a very good vacuum of about 10 trillionths of an atmosphere"

Although that will contribute some uncertainty to the measurement, it is not the greatest source of error.

 

[Ygrene Imref]

Caesium isn't radioactive. Reasons for choosing caesium include having only one outer electron (hence 1st column of periodic table) and having only one stable isotope (so all atoms have the same mass).

On the surface, Cesium is the most stable isotope, yes - but it is still radioactive. Even though on the QM level Cs-133 is considered stable, that is because the probability of primary, secondary and/or tertiary radiation is, on average, trivial. But, this isn't the case in reality, and there is actually a problem with Cs-133 accuracy precisely because of the belief that it is "stable." Cs-133 emits tertiary electromagnetic radiation - it is part of the emission spectrum we use to capture a dispersion to extrapolate into time. And, there is an energy shift associated with the transitional energies in the Cs-133 atom.

In nature, it has been observed as a stable isotope (like other "stable" atoms,) but that is a sort of oxymoron in nuclear/quantum physics. All atoms are a measure unstable (and, certain fields go into depth of what that means for the chemistry/physics of an atom.) This is especially true when hyperfine splitting occurs, and even more so when an external field is applied (precisely because of what hyperfine splitting implies.) Even hydrogen, which has a halflife of 10^34 years, is not always stable. It can undergo transmutations. The probability that Cs-133 will emit a dispersion comparable to electron/beta capture is negligible in practice. However, the very fact that Cs-133 has such a nuclear mass alone makes it stable. Each particle in the atom has its own carrier-particle-associated field which interacts with the entire system. The net effect of the Cs-133 atom is stable.

There are many factors that affect the radioactivity of an atom, and science is (finally) catching up. Keep in mind decay rate "constants" are not constant, and can be affected by the electroweak force. This is why, in general, time does not matter, and can actually be considered a pseudo-dimension, or nonexistent altogether (dependent on evolution of measurable events, as opposed to a random amount of hyperfine transitions in a particular atom.)

 

[essentialsaltes]

On the surface, Cesium is the most stable isotope, yes - but it is still radioactive.

Evidence please. (Also, please note that it makes no sense to say that cesium is an isotope... oh never mind)

 

[Ygrene Imref]

Evidence please. (Also, please note that it makes no sense to say that cesium is an isotope... oh never mind)

Cs-133 is an isotope even if you count neutron number as constant. All elements with differing neutrons are called isotopes of the same elements. In reality, it is a very precise measure of field interactions between boson and fermion field carriers, and occasionally "mass" potentials. Stability is relative to the reference we choose.

Evidence of radioactivity? Only the average radioactivity is stable; the number itself is based on axioms and postulated constants. Cs-133 is known to undergo a "trace" release/change in delta and epsilon radiation. The resultant carrier is a fermion.

Do you want me to refer you to a text?

 

[Ygrene Imref]

Hint: the fine structure constant is NOT constant, and each fundamental force has an associated fine structure constant - including weak force.

 

[Radagast]

On the surface, Cesium is the most stable isotope, yes - but it is still radioactive. ...

I can't make head or tail of this nonsensical post. I can't even parse the sentences.

Among other things, Caesium is an element, Caesium-133 is an isotope and, yes, Caesium-133 is stable.

And there is no evidence of variability in the fine structure constant, with the best estimate of the annual rate of change being 0 +/- 4 × 10^-17.

science is (finally) catching up

Really?

 

[Radagast]

Here, by the way, is a chart of caesium-133 electron energy levels. We are dealing with a single electron, and the lower electron shells (up to 4d and 5p) are all full.

One factor in the use of caesium is that electrons stay in the F=4 state for a long time (the probability of dropping down to F=3 is low). Consequently, there is a large time uncertainty associated with the state and hence (by the Heisenberg uncertainty principle) a low energy uncertainty (i.e. the transition is almost exactly the same energy each time). This helps to make caesium a good time reference.

 

[Resha Caner]

There are many factors that affect the radioactivity of an atom, and science is (finally) catching up. Keep in mind decay rate "constants" are not constant, and can be affected by the electroweak force. This is why, in general, time does not matter, and can actually be considered a pseudo-dimension, or nonexistent altogether (dependent on evolution of measurable events, as opposed to a random amount of hyperfine transitions in a particular atom.)

Very cool. Thanks. It's been quite a while since I thought of time as a "dimension" or a "thing" that exists independently of our measures of it. Hence my curiosity with respect to how solid those measures are. As I expected, for any practical use time can be treated as an independent dimension. But on large enough scales it appears there may be some intriguing nonlinearities.

 

[Resha Caner]

Do you want me to refer you to a text?

Please do. Not that I'd be able to grasp it all, but it might help facilitate the disagreement between you, @essentialsaltes , and @Radagast .

 

[Ygrene Imref]

Here, by the way, is a chart of caesium-133 electron energy levels. We are dealing with a single electron, and the lower electron shells (up to 4d and 5p) are all full.

One factor in the use of caesium is that electrons stay in the F=4 state for a long time (the probability of dropping down to F=3 is low). Consequently, there is a large time uncertainty associated with the state and hence (by the Heisenberg uncertainty principle) a low energy uncertainty (i.e. the transition is almost exactly the same energy each time). This helps to make caesium a good time reference.

Cesium, on average, is stable.

However, cesium-133 emits delta and epsilon radiation - the result is a fermion. The dispersion observed is consistent enough in practice to postulate Cs-133 as stabel (2 million years or so.)

 

[Ygrene Imref]

Very cool. Thanks. It's been quite a while since I thought of time as a "dimension" or a "thing" that exists independently of our measures of it. Hence my curiosity with respect to how solid those measures are. As I expected, for any practical use time can be treated as an independent dimension. But on large enough scales it appears there may be some intriguing nonlinearities.

Nonlinearity, and nonlocality.

Part of QTFT is showing that field interactions are non-local - that, for example, an electron in the atmosphere of Neptune can affect the electron in a banana in Iceland. This is a very crude way of explaining it, but non-locality actually answer curious problems in QM and relativity (e.g. Spooky Action at a Distance.)

 

[essentialsaltes]

Cesium, on average, is stable.

As usual, what you're saying doesn't make sense. Either Cs-133 decays or it doesn't. It can't be stable 'on average' and also decay somehow.

The dispersion observed is consistent enough in practice to postulate Cs-133 as stabel (2 million years or so.)

If Cs-133 had a half life on the order of millions of years, we would know. Potassium-40 (used in potassium argon dating) has a half life of more than billion years. We do not 'postulate it as stabel'.

 

[Ygrene Imref]

As usual, what you're saying doesn't make sense. Either Cs-133 decays or it doesn't. It can't be stable 'on average' and also decay somehow.



If Cs-133 had a half life on the order of millions of years, we would know. Potassium-40 (used in potassium argon dating) has a half life of more than billion years. We do not 'postulate it as stabel'.

ok

 

[Radagast]

However, cesium-133 emits delta and epsilon radiation - the result is a fermion.

Delta and epsilon radiation have nothing to do with radioactive decay. And most particles are fermions, so "fermion" doesn't say much.

I think you've been reading things that you haven't quite understood.

 

[Ygrene Imref]

Delta and epsilon radiation have nothing to do with radioactive decay. And most particles are fermions, so "fermion" doesn't say much.

I think you've been reading things that you haven't quite understood.

Ok.

 

[FrumiousBandersnatch]

Delta and epsilon radiation have nothing to do with radioactive decay. And most particles are fermions, so "fermion" doesn't say much.

I think you've been reading things that you haven't quite understood.

As I hear it, they're not emitted by radioactive decay, but you could get delta and epsilon radiation (both electrons?) as indirect results of energetic radioactive decay (secondary and tertiary ionisation products), but also from other processes too.

 

[Kylie]

I have two questions, then. First, if ease and accessibility was not a concern, but rather maximum repeatability of the measure, is cesium better for some reason than using the speed of light to define "second".

Perhaps because, if we define the second as, "The time it takes for light to travel 299792458 meters," then we need some accurate way of measuring out that rather large distance. Measuring the vibrations of a particulr kind of atom seems much more convenient.