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## Main Question or Discussion Point

Hello,

While riding home today, I started to wonder what was the definition of a second in the context of time. I looked it up and found out that the definition has changed somewhat over the years and it is now defined as (paraphrased) 9,192,631,770 periods of the cesium atom.

A meter is defined as the distance light travels in a vacuum in 1 over 299,792,458 seconds.

Since we are arbitrarily defining our units, why not make them a rounded value? We have changed the definition a few times before, and I imagine the new definitions are more exact approximations of what our old definitions "meant". When the meter was proposed, they wanted to use 10 million meters from pole to equator and while they got close, it was ultimately wrong. We now have the capability to map the surface in rather fine detail, so why not go back to the original definition? Or perhaps use 1 over 300,000,000 and call it close enough?

I notice that there are no zeros in the light definition and only the least significant place in the time definition is a zero. Is this significant?

I guess my problem is that 9,192,631,770 periods seems so random. Perhaps at the scale of atoms everything seems random but we could have easily forced some "order" into these definitions.

The period of cesium seems to be a great source of something that won't change over time, but we have tied that to something that will change over time: our day.

Anyway, any thoughts and perspectives would be appreciated.

Jack

While riding home today, I started to wonder what was the definition of a second in the context of time. I looked it up and found out that the definition has changed somewhat over the years and it is now defined as (paraphrased) 9,192,631,770 periods of the cesium atom.

A meter is defined as the distance light travels in a vacuum in 1 over 299,792,458 seconds.

Since we are arbitrarily defining our units, why not make them a rounded value? We have changed the definition a few times before, and I imagine the new definitions are more exact approximations of what our old definitions "meant". When the meter was proposed, they wanted to use 10 million meters from pole to equator and while they got close, it was ultimately wrong. We now have the capability to map the surface in rather fine detail, so why not go back to the original definition? Or perhaps use 1 over 300,000,000 and call it close enough?

I notice that there are no zeros in the light definition and only the least significant place in the time definition is a zero. Is this significant?

I guess my problem is that 9,192,631,770 periods seems so random. Perhaps at the scale of atoms everything seems random but we could have easily forced some "order" into these definitions.

The period of cesium seems to be a great source of something that won't change over time, but we have tied that to something that will change over time: our day.

Anyway, any thoughts and perspectives would be appreciated.

Jack