Measurement
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I have long wanted to know the answer to this.
Nowadays time (or distance) is defined and measured by atomic clocks. A caesium(?) atom vibrates something like 86 thousand or million or billion(?) of times per second. That's what you need to count to 100% precision to move the second hand one tick forward.
How do you measure these vibrations in an atom. And vitally how do you design something and know when the 86,000,000,000'th vibration has just happened and it's not the 85,999 or 86,001'th?
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@mzimmers
OK, thank you for that. I suspect that is about as good an explanation as I am going to get.But I still have a couple of observations/queries:
How do you fit this into your wristwatch?
well-separated cesium atoms that travel without collisions at about 250 m/s, through a vacuum maintained by the vacuum pump
And what happens when (as we know) it's not a perfect vacuum and they bump into the very rare air atoms which are still there?
spins at 9 192 631 770 rotations per second
Yep, I knew it was a big number!
Simple electronics counts the output cycles of the quartz oscillator, and issues a pulse every 10 million cycles - exactly 1 second apart.
This is the crux. I understand nothing about electronics. What "simple" electronics do the counting? This doesn't appear to be the 9 billion number above, but nonetheless how come you know when it's exactly 10 million and not 9,999,999 or 10,000,001?
All in all, I think I don't buy it. They tell us this all works and is incredibly accurate, I wonder if that's hogwash and they won't admit it's probably all very approximate....
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@JonB Maybe the „How it works“ section will answer your questions?
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@JonB said in Measurement:
How do you fit this into your wristwatch?
You don't. Those time standards, besides being huge, are insanely expensive and have to be kept in laboratory conditions.
I thought most of the pre-smart-device era wristwatches used quartz clocks, which work on an entirely different principle (pushing a light beam (or maybe just an electron array) around the inside of a properly cut quartz element, and it always bounces a known number of times before exiting).
Thinking about stuff like this makes me happy I'm a programmer...
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@DerReisende said in Measurement:
@JonB Maybe the „How it works“ section will answer your questions?
Thanks. Read it. Still don't really get how all this electronics is accurate to 1 in 10 million or 10 billion counts. Since none of us sits there and count-checks, the manufacturers probably don't care much if they're not accurate ;-)
and it always bounces a known number of times before exiting
Just the sort of thing where I don't really believe that's accurate/consistent to 1 in 10 million/billion bounces, sorry....
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@JonB the quartz explanation is easier to understand/believe, IMO. Imagine a room with a bunch of mirrors, set at angles to receive a beam of light and pass it on to another mirror, until the last one points at some kind of receiver.
Now imagine this room being less than 1mm across and having many, many mirrors (which are really just facets in the quartz). That’s my understanding of how quartz clocks work.
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@mzimmers
The mirrors must be so close together and the angles so accurate to achieve 1/10 million/billion precision, seems likely to me some photons occasionally skip a mirror or re-use the same one twice. If anyone wants my opinion that is :)Everything in math seems OK to me. Everything in physics seems to be just... dodgy....
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@JonB remember, they don't have to be perfect -- they just have to be better than anything else. According to one of the articles I read, the pre-cesium definition of a second was based on a solar day. When they invented the cesium clock, they found that it's measurement was so close to the previous definition that the error was below any consumable measurement.
For some reason, this discussion reminds me of a story my mom told me about when she was in high school. One of the teachers that no one liked wore a shiny round brooch. My mom and her friends would catch the sunlight on their wristwatches, and deflect it toward the brooch so that it would hit the teacher in the eye.
I guess this was the sort of thing that teenage girls in parochial schools did for fun in the 1950s....
