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   XPost: alt.alien.research, alt.alien.visitors, alt.astronomy   
   XPost: alt.atheism, sci.physics   
   From: papa@vatican.va   
      
   In alt.atheism, HVAC said...   
      
   >   
   > Pulsars are rotating neutron stars that produce highly periodic bursts   
   > of radio waves. So accurate are pulsar signals that when they were   
   > discovered, astronomers gave serious credence to the idea that they   
   > were evidence of intelligent life elsewhere in the Universe because   
   > they were unmatched by anything physicists could make on Earth. This   
   > has lead to the widespread belief that pulsars are the most accurate   
   > clocks in the Universe.   
   >   
   > 40 years later, astronomers have yet to work out exactly how pulsars   
   > generate such accurate signals. But physicists on the other hand, have   
   > been working hard to find their own ways to better the performance of   
   > pulsars.   
   >   
   > Today, John Hartnett and Andre Luiten at the University of Western   
   > Australia ask whether Earth-bound time pieces have usurped their   
   > astrophysical rivals as the best clocks in the Universe.   
   >   
   > On the face of it, the answer is pretty clear cut to anybody who has   
   > followed the amazing advances in quantum optics in the last few years.   
   >   
   > "The accuracy and stability of terrestrial clocks have improved more   
   > than an order of magnitude, on average, in each decade over the last   
   > 60 years," say Hartnett and Luiten. Today, the best optical lattice   
   > neutral atom clocks and trapped ion clocks have a frequency stability   
   > approaching one part in 10^17.   
   >   
   > By contrast, as more pulsars have been discovered, their timing   
   > stability has improved by less than an order of magnitude in the last   
   > 20 years. The best millisecond pulsars have a stability of only one   
   > part in 10^15 at best.   
   >   
   > That means that terrestrial clocks can rightly be crowned the best   
   > clocks in the Universe, say Hartnett and Luiten.   
   >   
   > That's impressive but there is one other issue to consider before   
   > physicists in quantum optics labs can start popping champagne corks.   
   > This is the question of long term stability.   
   >   
   > It's all very well to build a clock that can outperform pulsars for a   
   > few months or years but try it for a significantly longer period of   
   > time, say centuries or millennia, and a whole host of other issues   
   > raise their heads. The makers of the Clock of the Long Now have   
   > already studied this issue. They've asked how you can guarantee a   
   > stable power supply over such a period? How do you store spare parts   
   > or ensure that the knowledge to effect a repair survives? Can you even   
   > rely on the survival of the human race over these periods?   
   >   
   > The answers to these questions suggest that it will be very difficult   
   > to run a wristwatch let alone a trapped ion clock over this time-   
   > scale. And yet in thousands of years pulsars will still be producing   
   > their regular heart beat.   
   >   
   > Earth-bound clocks may be able to outperform pulsars over human time-   
   > scales but to do it over significantly longer time-scales is another   
   > challenge altogether. Terrestrial clocks may have stolen the crown for   
   > now. Keeping it will be much harder.   
      
   I kinda like my cheap bedside GE digital clock. I've had it for years - I got   
   it at   
   Walt-Mart for about $8. The alarm never fails as long as I remember to set the   
   switch after setting the time.   
      
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