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Clocks

Entry 1376, on 2012-04-05 at 14:12:07 (Rating 1, Science)

Clocks don't sound like a very interesting topic for a blog post, do they? I mean who cares about clocks? We just have them and they work. They perform a simple function well (hopefully) and what interesting new developments could possibly occur? Well quite a lot, actually.

My interest in horology began when I read a book by Dava Sobel called "Longitude". Actually I read a few pages of it when I found it in a client's office while I was waiting for an install to finish. It was so good that I bought a copy myself. It was a real paper book because this was a few years back before I started reading on the iPad.

So what's the connection between longitude (which is the measure, usually in degrees, of a position around the Earth) and clocks? It goes back to the time of sailing ships when measuring longitude (and getting an accurate position) was impossible. The problem was that the Earth rotates on its axis so that unless you know the time accurately the observed location of the stars was useless as a measure of your position on Earth.

But clocks were notoriously difficult to keep accurate on a ship which was being tossed around at sea as well as experiencing extremes of temperature.

So the British Parliament offered a huge prize for solving this problem and the obvious way to do that was to build an accurate clock (there were other ways as well). A brilliant inventor and clock builder, John Harrison, built a series of increasingly accurate and compact clocks which were remarkably accurate even in the most difficult conditions.

They incorporated incredibly clever and complex mechanical mechanisms to compensate for the movement of the ship and changes in temperature. For example, bimetal strips would expand and contract and alter the balance of the clock's timing just enough to keep it accurate. What he achieved was almost unbelievable.

His clocks (or copies of them) were used on famous voyages such as Captain Cook's and on the Bounty. His most successful design, a large "watch" called H4 lost only 5 seconds after a two month journey at sea. But even though the clocks were admired by the sailors who used them he still had a lot of trouble extracting the full payment from the prize.

As I said, mechanical clocks are capable of impressive accuracy. In fact, according to a recent podcast (which was the reason for writing this post), the best pendulum clocks are actually more accurate than modern quartz electronic clocks. This probably only applies to standard modern models without accurate calibration and temperature control, I suspect. And also remember that modern quartz clocks are extremely cheap, compact, and reliable.

But that aside, mechanical clocks which achieved an accuracy of one hundredth of a second per day are very impressive. It's also an example of genuine progress because the first pendulum clocks were only accurate to 15 seconds per day (but even that was almost one hundred times better than other technologies at the time).

So where have we gone from there? Modern atomic clocks are accurate to one second in about 50 million years. That is a hundred million times more accurate than the mechanical clocks I mentioned above.

And a new technology, which has been suggested by a team at an Australian university, is accurate to less than a second for the entire age of the Universe (about 14 billion years). As far as I know no one has yet built one of these "nuclear clocks" (which use neutron oscillation instead of the electrons used in conventional atomic clocks) but they would be another 300 thousand times more accurate than even atomic clocks.

But what's the point? After all, if you are a billionth of a second late meeting your friend at the coffee shop it's not really a big deal, is it? Obviously not, but picosecond timing can be useful for physics experiments involving precise measurements of events.

The recent controversy over the so-called faster than light neutrinos illustrates this issue. The neutrinos were travelling over 700 kilometers through the solid crust of the Earth and arriving at their target 0.0024 seconds later. But the timing revealed some arriving 0.00000006 seconds (or 60 billionths of a second) sooner than expected.

In that case the timing system was correct but the error was probably due to a faulty piece of cabling. However it does show the sort of accuracy required in modern experiments.

Incredibly precise measurements of time might lead to truly fundamental discoveries concerning the most basic laws of physics. They could tell us just how accurate theories like relativity and quantum theory really are (so far they have passed every test we have thrown at them) and even reveal if fundamental laws and "constants" are changing with time.

So something as simple as a clock is important and maybe just as critical as a far more spectacular bit of equipment like the Hubble Space Telescope, the Large Hadron Collider, or the (yet to be built) Square Kilometer Array.

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Comment 1 (3008) by Rob on 2012-04-08 at 11:13:56:

Please... 60 nanoseconds. You failed to mention the current standard that time is now based; caesium 133 (note the IUPAC spelling and not the ACS; we can discuss aluminum another time). It also appears that the si unit of length, the meter, is based on time. TIL.

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Comment 2 (3010) by OJB on 2012-04-09 at 12:41:39:

Oh no, I appear to have been spelling cesium the wrong way all these years. On the other had, I did get aluminium right! Regarding the relationship between time and distance, you are right but that's not really relevant in the FTL neutrino issue.

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Comment 3 (3011) by Rob on 2012-04-10 at 10:36:47:

True, time and distance are not relevant to the FTL neutrino since the distance remains constant. Although, the length of a meter must change if a different standard was used for time.

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