Re: [time-nuts] NPR Story I heard this morning
Hi Tom, Based on mass and radius, a clock here on Earth ticks about 6.969e-10 slower than it would at infinity. The correction drops roughly as 1/R below sea level and 1/R² above sea level. For practical and historical reasons we define the SI second at sea level. Yes, the change in clock rate at sea level is about 1e-18 per centimeter, and the geoid is known only to about 1 centimeter uncertainty at best. The non-local gravity perturbations you speak of are 2nd or 3rd order and so you probably don't need to worry about them. Then again, if you want to get picky, it's easy to compute how much the earth recoils when you stand up vs. sit down. So it's best to avoid the notion of arbitrary precision; that's for mathematicians. For normal people, including scientists, we know that precision and accuracy have practical limits. Let me rephrase what I'm after. The geoidal uncertainty sets a hard limit on clock comparison performance on the Earth's surface (for widely-spaced clocks). At some point, as Chris Albertson noted, the clocks will measure the potential and not the other way around. (It should be possible to express this geoidal uncertainty as an Allan variance and include it in graphs with the legend Earth surface performance limit.) What I'm curious about is this: what are the limits on clocks in more benign environments? How predictable is the potential in LEO, GEO, Earth-Sun L2, solar orbit at 1.5 AU, solar orbit at 100 AU, etc.? I imagine the latter few are probably very, very good, because the tidal terms get extremely small, but how good? Suppose a clock dropped into our laps with 1e-21 performance, just to pick a number. Where would we put it to fully realize its quality (and permit comparisons with its friends)? And is the current IAU framework adequate to define things at this level (or any other arbitrarily-picked level)? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
You people are evil. Now you have me wondering where I can get a microgram level accurate scale. Simply tracking the weight of a 'constant' (anyone got a silicon sphere with exactly 1 mole of Si atoms in it? :)) over time would be an interesting experiment. As a geologist, I also have to say, that while we know the geoid to ~1cm, it is ~1cm at the time it was measured, which is constantly changing. The obvious tidal effects, as well as internal heating effects (and I suspect external heating effects), continental drift (both long term events and short term events like earthquakes), currents in the molten layers, probably magnetic effects all are going to contribute to geoid uncertainty. I really do need to spin the seismograph back up. On Tue, Nov 4, 2014 at 2:04 PM, Peter Monta pmo...@gmail.com wrote: Hi Tom, Based on mass and radius, a clock here on Earth ticks about 6.969e-10 slower than it would at infinity. The correction drops roughly as 1/R below sea level and 1/R² above sea level. For practical and historical reasons we define the SI second at sea level. Yes, the change in clock rate at sea level is about 1e-18 per centimeter, and the geoid is known only to about 1 centimeter uncertainty at best. The non-local gravity perturbations you speak of are 2nd or 3rd order and so you probably don't need to worry about them. Then again, if you want to get picky, it's easy to compute how much the earth recoils when you stand up vs. sit down. So it's best to avoid the notion of arbitrary precision; that's for mathematicians. For normal people, including scientists, we know that precision and accuracy have practical limits. Let me rephrase what I'm after. The geoidal uncertainty sets a hard limit on clock comparison performance on the Earth's surface (for widely-spaced clocks). At some point, as Chris Albertson noted, the clocks will measure the potential and not the other way around. (It should be possible to express this geoidal uncertainty as an Allan variance and include it in graphs with the legend Earth surface performance limit.) What I'm curious about is this: what are the limits on clocks in more benign environments? How predictable is the potential in LEO, GEO, Earth-Sun L2, solar orbit at 1.5 AU, solar orbit at 100 AU, etc.? I imagine the latter few are probably very, very good, because the tidal terms get extremely small, but how good? Suppose a clock dropped into our laps with 1e-21 performance, just to pick a number. Where would we put it to fully realize its quality (and permit comparisons with its friends)? And is the current IAU framework adequate to define things at this level (or any other arbitrarily-picked level)? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
pmo...@gmail.com said: Let me rephrase what I'm after. The geoidal uncertainty sets a hard limit on clock comparison performance on the Earth's surface (for widely-spaced clocks). At some point, as Chris Albertson noted, the clocks will measure the potential and not the other way around. Old news... :) Time Too Good to Be True, Daniel Kleppner Physics Today, March 2006, page 10 http://scitation.aip.org/journals/doc/PHTOAD-ft/vol_59/iss_3/10_1.shtml -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
I wish I could take the credit for being evil here, but no. What the natural consequence is that every atomic clock of this type should have a gravitational sensor that compensates for gravitational shift, as it now has become a frequency shift component. The first degree compensation should not be too shabby. Cheers, Magnus On 11/04/2014 08:27 PM, Bob Bownes wrote: You people are evil. Now you have me wondering where I can get a microgram level accurate scale. Simply tracking the weight of a 'constant' (anyone got a silicon sphere with exactly 1 mole of Si atoms in it? :)) over time would be an interesting experiment. As a geologist, I also have to say, that while we know the geoid to ~1cm, it is ~1cm at the time it was measured, which is constantly changing. The obvious tidal effects, as well as internal heating effects (and I suspect external heating effects), continental drift (both long term events and short term events like earthquakes), currents in the molten layers, probably magnetic effects all are going to contribute to geoid uncertainty. I really do need to spin the seismograph back up. On Tue, Nov 4, 2014 at 2:04 PM, Peter Monta pmo...@gmail.com wrote: Hi Tom, Based on mass and radius, a clock here on Earth ticks about 6.969e-10 slower than it would at infinity. The correction drops roughly as 1/R below sea level and 1/R² above sea level. For practical and historical reasons we define the SI second at sea level. Yes, the change in clock rate at sea level is about 1e-18 per centimeter, and the geoid is known only to about 1 centimeter uncertainty at best. The non-local gravity perturbations you speak of are 2nd or 3rd order and so you probably don't need to worry about them. Then again, if you want to get picky, it's easy to compute how much the earth recoils when you stand up vs. sit down. So it's best to avoid the notion of arbitrary precision; that's for mathematicians. For normal people, including scientists, we know that precision and accuracy have practical limits. Let me rephrase what I'm after. The geoidal uncertainty sets a hard limit on clock comparison performance on the Earth's surface (for widely-spaced clocks). At some point, as Chris Albertson noted, the clocks will measure the potential and not the other way around. (It should be possible to express this geoidal uncertainty as an Allan variance and include it in graphs with the legend Earth surface performance limit.) What I'm curious about is this: what are the limits on clocks in more benign environments? How predictable is the potential in LEO, GEO, Earth-Sun L2, solar orbit at 1.5 AU, solar orbit at 100 AU, etc.? I imagine the latter few are probably very, very good, because the tidal terms get extremely small, but how good? Suppose a clock dropped into our laps with 1e-21 performance, just to pick a number. Where would we put it to fully realize its quality (and permit comparisons with its friends)? And is the current IAU framework adequate to define things at this level (or any other arbitrarily-picked level)? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
On Mon, 3 Nov 2014 11:54:41 -0800 Peter Monta pmo...@gmail.com wrote: Sorry if this is a bit off-topic. I'd like a simple, clear explanation for the layman that drills down on exactly how the current definitional scheme can be realized to arbitrary precision. For example, assume that we must go off-earth at some point to get a better timescale. How fuzzy is the solar potential (soloid)? It will be done as usual: As soon as they can reliably measure an systematic effect that is impossible to cancel out, they will redefine or ammend the definition of the second to account for this issue. And going by the presentations given at EFTF this year, there is quite some interest in precision gravity measurements in the time/frequency community. And yes, they use the same basic phyiscs as their atomic clocks :-) (one apporach is to let Cs atoms fall down a tube and measure their acceleration using doppler shift of the hyperfine transitions line) Attila Kinali -- I pity people who can't find laughter or at least some bit of amusement in the little doings of the day. I believe I could find something ridiculous even in the saddest moment, if necessary. It has nothing to do with being superficial. It's a matter of joy in life. -- Sophie Scholl ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
But won't the doppler effect change as the Cs atoms fall down the gravity well? :) On Tue, Nov 4, 2014 at 3:14 PM, Attila Kinali att...@kinali.ch wrote: On Mon, 3 Nov 2014 11:54:41 -0800 Peter Monta pmo...@gmail.com wrote: Sorry if this is a bit off-topic. I'd like a simple, clear explanation for the layman that drills down on exactly how the current definitional scheme can be realized to arbitrary precision. For example, assume that we must go off-earth at some point to get a better timescale. How fuzzy is the solar potential (soloid)? It will be done as usual: As soon as they can reliably measure an systematic effect that is impossible to cancel out, they will redefine or ammend the definition of the second to account for this issue. And going by the presentations given at EFTF this year, there is quite some interest in precision gravity measurements in the time/frequency community. And yes, they use the same basic phyiscs as their atomic clocks :-) (one apporach is to let Cs atoms fall down a tube and measure their acceleration using doppler shift of the hyperfine transitions line) Attila Kinali -- I pity people who can't find laughter or at least some bit of amusement in the little doings of the day. I believe I could find something ridiculous even in the saddest moment, if necessary. It has nothing to do with being superficial. It's a matter of joy in life. -- Sophie Scholl ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
On Tue, 4 Nov 2014 11:04:58 -0800 Peter Monta pmo...@gmail.com wrote: Let me rephrase what I'm after. The geoidal uncertainty sets a hard limit on clock comparison performance on the Earth's surface (for widely-spaced clocks). At some point, as Chris Albertson noted, the clocks will measure the potential and not the other way around. (It should be possible to express this geoidal uncertainty as an Allan variance and include it in graphs with the legend Earth surface performance limit.) Actually, currently the limit of clock comparison is not the geoid uncertainties, but the comparison itself. Common view GPS does not cut it at all. TWSTFT might be enough, if more second/third order effects are compensated for and the orbit is measured with a higher precision [1,2]. For short distances (up to 1000km or so), temperature and delay-variation compensated fibers seem to be the way to go [3,4]. Also, frequency transfer down to very low numbers seems to be easier (depending on system and distance in the range of 1e-12 to 1e-16) than accurate time transfer (around a couple 100ps seems to be the limit for any non-trival distance, at the moment) [1] Two-way Satellite Time and Frequency Transfer:Overview, Recent Developments and Application, by Wu et al, 2014 [2] Practical Evaluation of Relativistic Effects in Two-Way Satellite Time and Frequency Transfer, by Shemar, Delva, Lamb, 2014 [3] Optical Frequency Transfer with a 1284 km Coherent Fiber Link, by Calonico et al, 2014 [4] Novel Techniques for Optical Fiber Links beyond Current Practice, by Calosso et al, 2014 And these are just a few of the presentation given at EFTF this year on that topic. Attila Kinali -- I pity people who can't find laughter or at least some bit of amusement in the little doings of the day. I believe I could find something ridiculous even in the saddest moment, if necessary. It has nothing to do with being superficial. It's a matter of joy in life. -- Sophie Scholl ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
And you can get a I climbed Mt. Washington sticker for your clock. Lester B Veenstra MØYCM K1YCM W8YCM les...@veenstras.com US Postal Address: 5 Shrine Club Drive HC84 Box 89C Keyser WV 26726 GPS: 39.336826 N 78.982287 W (Google) GPS: 39.33682 N 78.9823741 W (GPSDO) Telephones: Home: +1-304-289-6057 US cell+1-304-790-9192 UK cell+44-(0)7849-248-749 Guam Cell: +1-671-929-8141 Jamaica: +1-876-456-8898 This e-mail and any documents attached hereto contain confidential or privileged information. The information is intended to be for use only by the individual or entity to whom they are addressed. If you are not the intended recipient or the person responsible for delivering the e-mail to the intended recipient, be aware that any disclosure, copying, distribution or use of the contents of this e-mail or any documents attached hereto is prohibited. -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of David McGaw Sent: Monday, November 03, 2014 4:07 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] NPR Story I heard this morning The highest accessible peak in the Adirondacks I think would be Whiteface at 4,867 ft, though that would be by ski lift and not all the way to the top. The highest point accessible by car in the Northeast would be Mt. Washington here in New Hampshire at 6288 ft. Hmm... David On 11/3/14 1:02 PM, Hal Murray wrote: x...@darksmile.net said: I was planning a similar trip from Astoria Queens, NYC which is sea level, to Adirondack Mountains, upstate New York. You will need clocks that are better than Tom's. :) He parked at 5,000 feet. Do any roads go that high in the Adirondacks? How high can you park? What's the efficiency of the generator in a parked car compared to a portable generator? What's the right unit? kilo-watt-hours per gallon? How does a normal car compare to a hybrid? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] NPR Story I heard this morning
Lester Veenstra lester at veenstras.com Tue Nov 4 16:56:29 EST 2014 wrote: And you can get a I climbed Mt. Washington sticker for your clock. +++ It may be a little OT but I actually worked on the summit for the Mount Washington Weather Observatory for 4 winters as well as climbing the mountain both summer and winter over 70 times and I don't have one of those stickers. :-( -Arthur ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] NPR Story I heard this morning
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 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
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 x...@darksmile.net 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 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
Small correction: The numbers were 10E-16. 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 x...@darksmile.net 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 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
Have you read Tom's story about his family trip up Mount Ranier with a Cesium clock? Project GREAT: General Relativity Einstein/Essen Anniversary Test Bob From: xaos x...@darksmile.net To: time-nuts@febo.com Sent: Monday, November 3, 2014 10:17 AM Subject: Re: [time-nuts] NPR Story I heard this morning Small correction: The numbers were 10E-16. 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 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
You know, I was thinking that exact same thing as the story went on. The one (important) thing I got from Tom's story was that kids might like the idea of the trip, but the details might seem boring. Although, I'm sure, Tom had a blast. I was planning a similar trip from Astoria Queens, NYC which is sea level, to Adirondack Mountains, upstate New York. Never found enough friends to make it tho :( -GKH On 11/03/2014 11:40 AM, Bob Stewart wrote: Have you read Tom's story about his family trip up Mount Ranier with a Cesium clock? Project GREAT: General Relativity Einstein/Essen Anniversary Test Bob From: xaos x...@darksmile.net To: time-nuts@febo.com Sent: Monday, November 3, 2014 10:17 AM Subject: Re: [time-nuts] NPR Story I heard this morning Small correction: The numbers were 10E-16. 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 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
On Mon, Nov 3, 2014 at 8:17 AM, xaos x...@darksmile.net 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 x...@darksmile.net 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 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
x...@darksmile.net said: I was planning a similar trip from Astoria Queens, NYC which is sea level, to Adirondack Mountains, upstate New York. You will need clocks that are better than Tom's. :) He parked at 5,000 feet. Do any roads go that high in the Adirondacks? How high can you park? What's the efficiency of the generator in a parked car compared to a portable generator? What's the right unit? kilo-watt-hours per gallon? How does a normal car compare to a hybrid? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
In a normal car, bring a generator. Using a big 6 cyl. engine to drive a tiny 20 amp alternator is not so good. And that alternator is not designed to run 24x7 at full load.The Prius is on the other hand a very good generator and with some add on equipment can power your house. The Prius engine turns itself on and off to keep the large battery charged to you can take out lots of power with the engine off. So the engine never runs at an inefficient speed. Normal cars are very poor at this because the engine must run full time. On Mon, Nov 3, 2014 at 10:02 AM, Hal Murray hmur...@megapathdsl.net wrote: x...@darksmile.net said: I was planning a similar trip from Astoria Queens, NYC which is sea level, to Adirondack Mountains, upstate New York. You will need clocks that are better than Tom's. :) He parked at 5,000 feet. Do any roads go that high in the Adirondacks? How high can you park? What's the efficiency of the generator in a parked car compared to a portable generator? What's the right unit? kilo-watt-hours per gallon? How does a normal car compare to a hybrid? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
albertson.ch...@gmail.com said: But you are right, no two clocks will ever agree at that level because they will experience different gravitational fields. What if I adjust the elevation (aka gravity) of one of them until it matches? Or at least gets within the resolution and ADEV of the pair? Suppose you had two super-accurate clocks that were next to each other. Would they phase lock? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
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 x...@darksmile.net 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 x...@darksmile.net 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 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] NPR Story I heard this morning
It's surprisingly large. I have a scale that can measure 20g down to a microgram (and worked on one that can do a gram at nanogram resolution). Taking the microgram scale up one floor in a building was easily detectable... I don't remember the exact number but it think it was in the 1 ppm/meter range. Does anyone know how much g changes per cm of altitude? I'm to lazy to figure it out ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] NPR Story I heard this morning
Found it on page 17 of Mettler's excellent article: Adverse Influences and Their Prevention in Weighing http://us.mt.com/dam/mt_ext_files/Editorial/Generic/2/Weigh_Uncertain_Number1_0x0003d6750003db6700091746_files/adverse_influences.pdf It works out to be -0.3 ppm/meter. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
Chris Albertson writes: 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. I have a question about that. If I understand correctly, recent IAU resolutions have decoupled the definition of the SI second from the terrestrial geoid, which is too fuzzy to be used for a definition. Instead the geoid potential is held fixed by (or defined by) a constant. Potential with respect to what exactly? At infinity is all very well, but there are local gravity sources (solar, even galactic) that would seem to complicate any operational realization of this definition. Sorry if this is a bit off-topic. I'd like a simple, clear explanation for the layman that drills down on exactly how the current definitional scheme can be realized to arbitrary precision. For example, assume that we must go off-earth at some point to get a better timescale. How fuzzy is the solar potential (soloid)? Cheers, Peter ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
On Mon, Nov 3, 2014 at 10:15 AM, Hal Murray hmur...@megapathdsl.net wrote: albertson.ch...@gmail.com said: But you are right, no two clocks will ever agree at that level because they will experience different gravitational fields. What if I adjust the elevation (aka gravity) of one of them until it matches? Or at least gets within the resolution and ADEV of the pair? You adjust it but then how long does it stay adjusted. The Earth, Moon and Sun are in constant motion. The gravity field is no static. OK maybe you could compute this and place the clocks n moving platforms? They will never agree, not at the lowest level. Here is another question: Is time a continuous function? It may not be at some scale. Suppose you had two super-accurate clocks that were next to each other. Would they phase lock? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
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Re: [time-nuts] NPR Story I heard this morning
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. Hi Chris, That's correct. When it comes to frequency standards the official SI second is defined only for sea level. We know time and frequency are bent by speed or gravity; time is the integral of frequency; and frequency is a function of height (h) by approximately gh/c². It's that simple. But it's a very tiny effect. Planet gravity fields decrease quadratically over large distances (1/R²) but approximately linearly near the surface. So here on Earth, with g = ~9.8 m/s² and c = ~300,000 km/s, frequency increases by about 1e-18/cm, or 1e-16/m, or 1e-13/km. This is called gravitational time dilation, or blueshift. Now, for amateurs like us who just make things at home or buy and repair atomic clocks on eBay, numbers like 1e-18 and 1e-16 are completely out of range: that's what government labs are for. But the 1e-13 number is interesting, and approachable -- especially if you live near a tall mountain. If you take a 1e-14 stable cesium clock up 1 km, it will run fast by about 1e-13 (in frequency) and thus it will gain about 10 ± 1 ns per day (in time, or phase) compared to a clock left down at home. These days, time differences at the nanosecond level are easily measurable -- so that's what I did with http://leapsecond.com/great2005/ Of course, NIST USNO always have much better clocks than we do, so they can measure the effect of smaller elevation changes, over smaller time scales. Just amazing. Maybe we'll be able to buy an optical clock on eBay 20 years from now. Note that their clocks are not (yet) portable and consequently you can make a more accurate gravitational time dilation / general relativity measurement at home by taking vintage hp 5071A cesium beam microwave clocks up a tall mountain than they can with record-setting strontium optical clocks inside a NIST building. Essentially, if you take a clock to high altitude for a weekend you create a super-duper blueshift microscope. Instead of unimaginably small numbers like 1e-18, I went up about 1340 meters (instead of just 1 cm) and I stayed up there about 42 hours (instead of one second). Thus my cm-second magnification factor was 1340 * 100 * 42 * 3600 = 20 billion! That reduces a crazy tiny number like 1e-18 to a real, tangible, measurable, fun-with-family, DIY time dilation number like 2e-8, or 20 ns. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
OK, I am going to show my ignorance now. Being in my 70th year, I forgot an awful lot of what I learned in school. Anyway, regarding time and gravity, I certainly believe the mathematics of Einstein and others, however, I have a hard time believing that man-made instruments to measure the effects of gravity on time is valid. For example in a Cesium clock, time is a function of the transition time between two hyperfine lines of Cesium atoms. So, does gravity affect this transition time within the Cesium atoms? It may very well, but, I am not smart enough to know that. Maybe someone can help. Also, when someone mentioned moving a very sensitive scale up in elevation and noting the difference due to gravitational effects, also seems odd to me. Seems like even in the most sensitive scales, weight is measured as the difference between the weighing platform and the body of the instrument. Here again, moving the whole assembly up in elevation it would seem to me that gravity would affect both the platform and the body, and the relative weight indicated should remain the same. What am I missing besides gray matter? Thanks - Mike Mike B. Feher, EOZ Inc. 89 Arnold Blvd. Howell, NJ, 07731 732-886-5960 office 908-902-3831 cell -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Tom Van Baak Sent: Monday, November 03, 2014 3:55 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] NPR Story I heard this morning 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. Hi Chris, That's correct. When it comes to frequency standards the official SI second is defined only for sea level. We know time and frequency are bent by speed or gravity; time is the integral of frequency; and frequency is a function of height (h) by approximately gh/c². It's that simple. But it's a very tiny effect. Planet gravity fields decrease quadratically over large distances (1/R²) but approximately linearly near the surface. So here on Earth, with g = ~9.8 m/s² and c = ~300,000 km/s, frequency increases by about 1e-18/cm, or 1e-16/m, or 1e-13/km. This is called gravitational time dilation, or blueshift. Now, for amateurs like us who just make things at home or buy and repair atomic clocks on eBay, numbers like 1e-18 and 1e-16 are completely out of range: that's what government labs are for. But the 1e-13 number is interesting, and approachable -- especially if you live near a tall mountain. If you take a 1e-14 stable cesium clock up 1 km, it will run fast by about 1e-13 (in frequency) and thus it will gain about 10 ± 1 ns per day (in time, or phase) compared to a clock left down at home. These days, time differences at the nanosecond level are easily measurable -- so that's what I did with http://leapsecond.com/great2005/ Of course, NIST USNO always have much better clocks than we do, so they can measure the effect of smaller elevation changes, over smaller time scales. Just amazing. Maybe we'll be able to buy an optical clock on eBay 20 years from now. Note that their clocks are not (yet) portable and consequently you can make a more accurate gravitational time dilation / general relativity measurement at home by taking vintage hp 5071A cesium beam microwave clocks up a tall mountain than they can with record-setting strontium optical clocks inside a NIST building. Essentially, if you take a clock to high altitude for a weekend you create a super-duper blueshift microscope. Instead of unimaginably small numbers like 1e-18, I went up about 1340 meters (instead of just 1 cm) and I stayed up there about 42 hours (instead of one second). Thus my cm-second magnification factor was 1340 * 100 * 42 * 3600 = 20 billion! That reduces a crazy tiny number like 1e-18 to a real, tangible, measurable, fun-with-family, DIY time dilation number like 2e-8, or 20 ns. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
The highest accessible peak in the Adirondacks I think would be Whiteface at 4,867 ft, though that would be by ski lift and not all the way to the top. The highest point accessible by car in the Northeast would be Mt. Washington here in New Hampshire at 6288 ft. Hmm... David On 11/3/14 1:02 PM, Hal Murray wrote: x...@darksmile.net said: I was planning a similar trip from Astoria Queens, NYC which is sea level, to Adirondack Mountains, upstate New York. You will need clocks that are better than Tom's. :) He parked at 5,000 feet. Do any roads go that high in the Adirondacks? How high can you park? What's the efficiency of the generator in a parked car compared to a portable generator? What's the right unit? kilo-watt-hours per gallon? How does a normal car compare to a hybrid? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
On Mon, Nov 3, 2014 at 1:18 PM, Mike Feher mfe...@eozinc.com wrote: Anyway, regarding time and gravity, I certainly believe the mathematics of Einstein and others, however, I have a hard time believing that man-made instruments to measure the effects of gravity on time is valid. For example in a Cesium clock, time is a function of the transition time between two hyperfine lines of Cesium atoms. So, does gravity affect this transition time within the Cesium atoms? It may very well, but, I am not smart enough to know that. Maybe someone can help. This may not be a very satisfactory explanation, but in a nutshell it's not the atomic transition time that changes with gravitational potential, but *time itself*. And remember, it's a *relative* effect - you can only measure it when you compare two clocks at different heights, never just by looking at one by itself, no matter how good it is. Also, when someone mentioned moving a very sensitive scale up in elevation and noting the difference due to gravitational effects, also seems odd to me. Seems like even in the most sensitive scales, weight is measured as the difference between the weighing platform and the body of the instrument. Here again, moving the whole assembly up in elevation it would seem to me that gravity would affect both the platform and the body, and the relative weight indicated should remain the same. What am I missing besides gray matter? Thanks - Mike Weighing scales do not work by measuring the gravitational attraction between the scale and the object to be measured. They measure the attraction between the earth and the object to be measured. When you go up a hill, you move the apparatus and the object, but not the earth. Henry ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
I have a question about that. If I understand correctly, recent IAU resolutions have decoupled the definition of the SI second from the terrestrial geoid, which is too fuzzy to be used for a definition. Instead the geoid potential is held fixed by (or defined by) a constant. Potential with respect to what exactly? At infinity is all very well, but there are local gravity sources (solar, even galactic) that would seem to complicate any operational realization of this definition. Sorry if this is a bit off-topic. I'd like a simple, clear explanation for the layman that drills down on exactly how the current definitional scheme can be realized to arbitrary precision. For example, assume that we must go off-earth at some point to get a better timescale. How fuzzy is the solar potential (soloid)? Cheers, Peter Hi Peter, Based on mass and radius, a clock here on Earth ticks about 6.969e-10 slower than it would at infinity. The correction drops roughly as 1/R below sea level and 1/R² above sea level. For practical and historical reasons we define the SI second at sea level. The non-local gravity perturbations you speak of are 2nd or 3rd order and so you probably don't need to worry about them. Then again, if you want to get picky, it's easy to compute how much the earth recoils when you stand up vs. sit down. So it's best to avoid the notion of arbitrary precision; that's for mathematicians. For normal people, including scientists, we know that precision and accuracy have practical limits. The most obvious gravitational perturbation is that of the Moon. You can predict, and even measure, that g changes in the 7th decimal place as the moon orbits the earth. This is so minor it cannot as yet be measured by the best atomic clocks, but it has been measured by the best pendulum clocks (because pendulum clock make better gravimeters than atomic clocks). For details, see: http://leapsecond.com/hsn2006/ Your fuzzy question is good. When error or noise is constant one can simply use standard deviation or rms to quantify the amount of fuzz. But when the perturbations are not simple and fixed in time you want a statistic that incorporates not just accuracy, but stability. For this you need something like ADEV and its log-log plots of stability as a function of tau. As an example, here is the ADEV of Earth: http://leapsecond.com/museum/earth/ /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
David, Let's talk. It is not impossible that I could drive my clocks to the East Coast for a Mt. Washington experiment. /tvb - Original Message - From: David McGaw n1...@dartmouth.edu To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Monday, November 03, 2014 1:07 PM Subject: Re: [time-nuts] NPR Story I heard this morning The highest accessible peak in the Adirondacks I think would be Whiteface at 4,867 ft, though that would be by ski lift and not all the way to the top. The highest point accessible by car in the Northeast would be Mt. Washington here in New Hampshire at 6288 ft. Hmm... David ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
On 11/3/2014 3:54 PM, Tom Van Baak wrote: When it comes to frequency standards the official SI second is defined only for sea level. We know time and frequency are bent by speed or gravity; According to the BIPM: At its 1997 meeting the CIPM affirmed that: This definition refers to a caesium atom at rest at a temperature of 0 K. - http://www.bipm.org/en/publications/si-brochure/second.html Isn't weight equivalent to acceleration, and it's therefore not at rest when sitting on a table at sea level? I don't see anything in the BIPM definition of the second regarding sea level. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
I'd be happy to volunteer my 5061 for such an experiment! Located in Troy, N.Y., I can get it down to about 15' ASL, possibly as low as 12' if I go to the basement in a downtown building. The river is at 13' ASL iirc. Bob On Mon, Nov 3, 2014 at 4:53 PM, Tom Van Baak t...@leapsecond.com wrote: David, Let's talk. It is not impossible that I could drive my clocks to the East Coast for a Mt. Washington experiment. /tvb - Original Message - From: David McGaw n1...@dartmouth.edu To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Monday, November 03, 2014 1:07 PM Subject: Re: [time-nuts] NPR Story I heard this morning The highest accessible peak in the Adirondacks I think would be Whiteface at 4,867 ft, though that would be by ski lift and not all the way to the top. The highest point accessible by car in the Northeast would be Mt. Washington here in New Hampshire at 6288 ft. Hmm... David ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
I don't see anything in the BIPM definition of the second regarding sea level. Hi Mike, The usual wording for the definition of the SI second also includes the word unperturbed. That little word covers a host of physics and engineering effects and can keep graduate students busy for years. You either have to eliminate them from your clock or your lab, or extra carefully measure then and back-out their effects on your clock's operating frequency. For a really good example of the sort of corrections that are made inside a cesium clock see: http://tf.nist.gov/general/pdf/1497.pdf By the time you read to page 30, you'll see table 3 and 4 which summarize the perturbing corrections. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
Not to put too fine a point on it, but my practical understanding is that any two or more clocks generally do *not* agree (that is - yield identical phase/frequency information) ever, anyway. So atomic horology - and beyond - means that we continue to ?adjust? ?compensate? clocks of whatever stability and accuracy to the current, agreed upon ideal - even as the ideal may move or evolve. On Mon, Nov 3, 2014 at 4:27 PM, Tom Van Baak t...@leapsecond.com wrote: I don't see anything in the BIPM definition of the second regarding sea level. Hi Mike, The usual wording for the definition of the SI second also includes the word unperturbed. That little word covers a host of physics and engineering effects and can keep graduate students busy for years. You either have to eliminate them from your clock or your lab, or extra carefully measure then and back-out their effects on your clock's operating frequency. For a really good example of the sort of corrections that are made inside a cesium clock see: http://tf.nist.gov/general/pdf/1497.pdf By the time you read to page 30, you'll see table 3 and 4 which summarize the perturbing corrections. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
Hi Ken, That's correct. No two clocks ever agree. If they look like they do, you are not looking close enough or not waiting long enough. That's also why UTC is based on the combined stability of hundreds of clocks. The weighted average of many cesium clocks is known to be better than any one cesium clock. So a big part of the UTC infrastructure is the inter-comparison of clocks all around the world. Another part is then slowly adjusting local standards to follow the more accurate global mean. You'll notice too, that many postings to this list are not just about clocks, but also precise time measurement, and about disciplining. Whether UTC at a national lab or a GPSDO at home, there is clock, measurement, and gradual adjustment. /tvb - Original Message - From: ken hartman To: Tom Van Baak ; Discussion of precise time and frequency measurement Sent: Monday, November 03, 2014 2:52 PM Subject: Re: [time-nuts] NPR Story I heard this morning Not to put too fine a point on it, but my practical understanding is that any two or more clocks generally do *not* agree (that is - yield identical phase/frequency information) ever, anyway. So atomic horology - and beyond - means that we continue to ?adjust? ?compensate? clocks of whatever stability and accuracy to the current, agreed upon ideal - even as the ideal may move or evolve. On Mon, Nov 3, 2014 at 4:27 PM, Tom Van Baak t...@leapsecond.com wrote: I don't see anything in the BIPM definition of the second regarding sea level. Hi Mike, The usual wording for the definition of the SI second also includes the word unperturbed. That little word covers a host of physics and engineering effects and can keep graduate students busy for years. You either have to eliminate them from your clock or your lab, or extra carefully measure then and back-out their effects on your clock's operating frequency. For a really good example of the sort of corrections that are made inside a cesium clock see: http://tf.nist.gov/general/pdf/1497.pdf By the time you read to page 30, you'll see table 3 and 4 which summarize the perturbing corrections. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
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 x...@darksmile.net 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 x...@darksmile.net 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 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
(I noticed earlier in the thread, folks writing 10E-16 when I think they meant 1E-16, at least based on the Fortran notation I learned a long time ago. I am living proof, that a good Fortran programmer can write spaghetti code in any language!) On time quantization: Planck Time is 3.59E-44 seconds: http://en.wikipedia.org/wiki/Planck_time Caldirola's model gives the chronon for the electron to be 6.27E-24 seconds: http://dinamico2.unibg.it/recami/erasmo%20docs/SomeRecentSCIENTIFICpapers/Chronon(QuantumOfTime)/RRuyAIEP2010Ch2.pdf On Mon, Nov 3, 2014 at 3:05 PM, Chris Albertson albertson.ch...@gmail.com wrote: On Mon, Nov 3, 2014 at 10:15 AM, Hal Murray hmur...@megapathdsl.net wrote: albertson.ch...@gmail.com said: But you are right, no two clocks will ever agree at that level because they will experience different gravitational fields. What if I adjust the elevation (aka gravity) of one of them until it matches? Or at least gets within the resolution and ADEV of the pair? You adjust it but then how long does it stay adjusted. The Earth, Moon and Sun are in constant motion. The gravity field is no static. OK maybe you could compute this and place the clocks n moving platforms? They will never agree, not at the lowest level. Here is another question: Is time a continuous function? It may not be at some scale. Suppose you had two super-accurate clocks that were next to each other. Would they phase lock? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
On 11/3/14, 1:50 PM, Tom Van Baak wrote: I have a question about that. If I understand correctly, recent IAU resolutions have decoupled the definition of the SI second from the terrestrial geoid, which is too fuzzy to be used for a definition. Instead the geoid potential is held fixed by (or defined by) a constant. Potential with respect to what exactly? At infinity is all very well, but there are local gravity sources (solar, even galactic) that would seem to complicate any operational realization of this definition. Sorry if this is a bit off-topic. I'd like a simple, clear explanation for the layman that drills down on exactly how the current definitional scheme can be realized to arbitrary precision. For example, assume that we must go off-earth at some point to get a better timescale. How fuzzy is the solar potential (soloid)? Cheers, Peter Hi Peter, Based on mass and radius, a clock here on Earth ticks about 6.969e-10 slower than it would at infinity. The correction drops roughly as 1/R below sea level and 1/R² above sea level. For practical and historical reasons we define the SI second at sea level. The non-local gravity perturbations you speak of are 2nd or 3rd order and so you probably don't need to worry about them. Then again, if you want to get picky, it's easy to compute how much the earth recoils when you stand up vs. sit down. So it's best to avoid the notion of arbitrary precision; that's for mathematicians. For normal people, including scientists, we know that precision and accuracy have practical limits. The most obvious gravitational perturbation is that of the Moon. You can predict, and even measure, that g changes in the 7th decimal place as the moon orbits the earth. This is so minor it cannot as yet be measured by the best atomic clocks, but it has been measured by the best pendulum clocks (because pendulum clock make better gravimeters than atomic clocks). For details, see: http://leapsecond.com/hsn2006/ Sun and Moon are of about the same gravity magnitude, and, of course, you get approx one cycle/day for both. Wikipedia says about 2E-6 m/sec^2 (e.g. 7th digit, as Tom said) Wikipedia also provides some math models for variation with latitude, etc. Interestingly, they say that the variation among different cities amounts to about 0.5% (Anchorage high, Kandy low) for height.. g(h) = g(0) * (Re/(Re+h))^2 Change of 0.08% for 0 to 9000 meters Since the period of a pendulum goes as Sqrt(1/g), the sun/moon effect is about 1E-7.. Set up a 10 meter long pendulum, which will have a period a bit longer than 6 seconds.Set it swinging, and time it for 200 swings (about 20 minutes) (I think it will run that long if you've got a nice heavy bob, etc.) Accurately(!) time that 1200 second interval with 100 microsecond precision and you might *just* be able to see the effect. I started down this measurement path in the 70s in high school, but encountered several logistics problems. - big pendulums are subject to environmental effects. You might do better with a shorter pendulum in a vacuum, which would eliminate air drag and reduce temperature effects. - this kind of timing implies that you've got a counter stable to 1E-8 over the measurement period (notionally 12 hrs) And at this precision, there's all kinds of other effects one should take into account (for instance, the period is only approximately = 2*pi*sqrt(L/g).. that depends on the sin(theta)=theta small angle approximation. However, i've always wanted to set up a rig where there's one of those big Foucault pendulums and see if you can do it. I suspect the drive system on the big ones would perturb the system, but maybe you could do an off hours experiment and let it just swing down to zero. - ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] NPR Story I heard this morning
On Tue, Nov 4, 2014 at 4:28 AM, Tim Shoppa tsho...@gmail.com wrote: (I noticed earlier in the thread, folks writing 10E-16 when I think they meant 1E-16, at least based on the Fortran notation I learned a long time ago. I am living proof, that a good Fortran programmer can write spaghetti code in any language!) Or, like me, be unable to learn any other language again. Variable names starting from I to N are integers, all others are floats. How much simpler do you wish to go? -- Sanjeev Gupta +65 98551208 http://www.linkedin.com/in/ghane ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
