Because for optical clocks Strontium is better suited than Caesium.
Caesium was at one time judged as the best suited for atomic beam
designs, but is not considered the best for fountain clocks, since
caesium has larger cross-section than rubidium, so the effect of
collisions becomes larger. For optical clocks strontium and aluminium is
among several possible choices.
There is nothing magic about caesium, it was just the chosen reference
at one time. There where actually a better choice from certain aspects,
but for several reasons judged as harder to design a clock from.
Cheers,
Magnus
On 11/03/2014 07:16 PM, xaos wrote:
Why Strontium over Caesium?
Is it because it just sounds more hi-tech ? LOL
Maybe stupid question to most here, but I do
not know the answer.
-GKH
On 11/03/2014 12:59 PM, Chris Albertson wrote:
On Mon, Nov 3, 2014 at 8:17 AM, xaos <[email protected]> wrote:
Small correction: The numbers were 10E-16.
No I think it was "one part in 10E16" ;) But the interesting thing was
they used numbers rather then saying something like "really super ultra
tiny".
But you are right, no two clocks will ever agree at that level because they
will experience different gravitational fields. At this level the reason
to have a clock is no longer to tell time. It is to measure the
gravitational field. With an array of many clocks like these we might be
able to map the density of the interior of the earth or detect black holes
or who knows what. I think it opens up a new area of observation. When
ever this happens we discover things we never would have thought of. Maybe
in 40 years these Strontium oscillators will be mass produced for $2 each.
Does anyone know how much "g" changes per cm of altitude? I'm to lazy to
figure it out.
One important concept that was discussed was this:
If the next generation clock was even more accurate
(maybe by an order or two), then no two clocks
can ever agree on the time.
Minute changes in gravity and other factors will
always make each clock completely different.
So, to that I said: WOW! Wait just a damn minute.
I got into this so I can tell time precisely. Now I'm back
to to the beginning.
I know I am exaggerating a bit here but still.
-GKH
On 11/03/2014 11:09 AM, Chris Albertson wrote:
Yes, A story about time and frequency standards. They actually used
numbers like 10E16 in the story. Apparently at that level your clock can
measure a change in elevation of a few centimeters because of the
relativistic effects of the reduced gravity field in just a few cm.
On Mon, Nov 3, 2014 at 6:28 AM, xaos <[email protected]> wrote:
This morning, as I was driving to work,
I heard this really cool story on NPR radio here in NYC.
This is the link to the story:
http://www.npr.org/2014/11/03/361069820/what-time-is-it-it-depends-where-you-are-in-the-universe
What a nice way to start the week.
Past stories with similar headlines.
http://www.npr.org/2014/01/24/265247930/tickety-tock-an-even-more-accurate-atomic-clock
Cheers,
George Hrysanthopoulos, N2FGX
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