How many snowflakes?

06:00 pm March 12th, 2013




			Cheerfully Demented - How many snowflakes?

frankwu


	How many snowflakes?
	A question for all you physics/astronomy types. I am re-watching "Cosmos" and in episode 10, Carl Sagan is commenting on those huge radio telescopes and he says that they detect extraordinarily small amounts of energy. A distant quasar, he says, is a quadrillionth of a watt. In fact, the total energy picked up by all the radio telescopes on the entire planet in all of history is less than the energy of "a single snowflake hitting the ground". Sagan said that in 1980. That was 33 years ago. How many snowflakes do you think we are up to now? Do you think Earth is maybe a two snowflake planet by now? And how many snowflakes do we have to be before we're technologically interesting enough for aliens to come and visit? FOLLOW-ON: Beamjockey went and asked Frank Drake his thoughts on this question. Drake's answer was that "we might be up to two snowflakes. He cautiously allows that it might even be three." Yeah! We're a two snowflake planet, maybe even three! Come on, you sweet aliens, come see about us! Aren't we awesome?

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	From: beamjockey	Date: March 13th, 2013 02:20 am (UTC)		(Link)

Might just be a bigger snowflake. What was the mass of his snowflake, and how fast was it falling? Sagan probably did the calculation, or lifted it from a pal who did the calculation, but scrubbed away the assumptions before presenting the colorfully-phrased result to a TV audience.

Post-hypertext, he could have put the calculation in a link. Oh, well.

What you really want to know is: Do radio astronomers have a piece of folklore about how much energy has been collected by all the world's radio telescopes? Here's hoping some radio astronomers will answer. (Have you thought about writing to Green Bank?)

When I was in school, Prof. Darwin Mead taught me that one erg was "the energy used by an ant when he expectorates." Never worked it out for myself, but the image always stuck with me. Barely enough to impinge on the macroscopic world.

When I came to Fermilab, I was thrilled to work out that a proton coursing through the Tevatron had more than one erg of energy. A fantastically small thing with energy enough, I thought, to make an ant stumble.

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	From: frankwu	Date: March 13th, 2013 02:26 am (UTC)		(Link)

Being an armchair entomologist, I LOVE that definition of an erg. That's awesome.

Good point about the snowflake - we don't know the size or speed Sagan is assuming.

But I was wondering... could we approximate by figuring out how many telescope-years of radio astronomy had existed by 1980 (how many radio telescopes in operation for how many years), and assume that that is 1 Sagan snowflake, and then compare it to the number of telescope-years of radio telescopes since then? Assuming, of course, that the amount of energy gathered per telescope per year is the same pre and post-1980. Or is that a bad assumption? Do newer radio telescopes gather more energy than older ones? Are/were there any in space or other locations that might absorb more energy than those in the desert?

Any thoughts on any of those factors?

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	From: beamjockey	Date: March 14th, 2013 12:28 pm (UTC)		(Link)

I went and did some legwork for you on this question.

You're welcome.

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	From: frankwu	Date: March 14th, 2013 01:28 pm (UTC)		(Link)

Who da man? You da man! That is awesome!

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	From: mike_van_pelt	Date: March 16th, 2013 06:38 am (UTC)		(Link)

Is that like being promoted from "Harmless" to "Mostly Harmless"?

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	From: frankwu	Date: March 16th, 2013 01:23 pm (UTC)		(Link)

That's very funny, Mike. Very funny!

(Complete tangent: I read a review, that I thought was quite accurate, of the last Hitchhiker's book that called it "Mostly Charmless".)

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	From: mike_van_pelt	Date: March 17th, 2013 07:46 am (UTC)		(Link)

I never read the last (fifth?) book in the trilogy. It seemed to me it was kind of running out of steam in the previous book. ("Infinite Improbability Drive", I thought was great. "Bistromatic"... fell off the "too silly" edge of what humor works for me.)

I think the original old TV show was my favorite version of the story. I haven't heard the radio show, though, and I have heard good things about it.

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