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Innovation

Measuring the galaxies, one centimetre at a time

My colleague Karen 'Hive Mother' Friar, community editor and not-so-closet geek, has an interesting post about another improvement in quantum key distribution, which is cool and geeky. No question of that.
Written by Rupert Goodwins, Contributor on

My colleague Karen 'Hive Mother' Friar, community editor and not-so-closet geek, has an interesting post about another improvement in quantum key distribution, which is cool and geeky. No question of that.

But it's not geeky enough. We can do better than that.

This is cooler. It's a prize talk from a meeting of the American Physical Society's Division of Atomic, Molecular and Optical Physics, which was going on last week in Alberta, Canada.

In it, Jun Ye of (among other places) the National Institute of Standards and Technology - the same American outfit that pumped Karen's photons - talks about yet more laser-based wonders, in particular frequency comb lasers.

Frequency comb lasers produce lots of emissions at lots of frequencies -- if you look at the light output on a graph of frequency against power, it resembles a comb - but in this case, with exceptional stability and accuracy. In fact, exceptional is far too small a word: the exact relationship between components of the spectra is so well known and controlled that the device can be used as a ruler to measure the frequency of any light to almost one part in ten to the eighteen.

That number may not mean too much. It is, however, extraordinary.

If I understand this correctly, this is the sort of accuracy that will let us measure the relative velocity of galaxies at the edge of observable space to within a few centimetres a second, meaning we can directly observe cosmological expansion.

It will let us check the doppler shift of the light from stars caused by planets practically down to asteroid size.

It lets us check the time variation of the fine-structure constant, a number at the heart of physics which directly defines how electromagnetism works, which is seemingly unrelated to any other physical constant, and which I understand even less than I understand why people like The Archers. That's like asking God for a DNA sample.

I'm just going to repeat myself: we now have the tools to look back in time and space billions of years, to close to the creation of the Universe, and measure the speeds of objects there with resolutions of centimetres per second.

You can see why I don't get that excited about help-desk applications.

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