Letter to Dan’s Data

Attentive readers to the journal will know about my affinity for the Clock of The Long Now project. Being a card-carrying member of the Long Now Foundation I am constantly thinking in the long-term. Art in the long term, therefore, is important to me.

Paleoanthropology is, sadly, imprecise when it comes to the lifestyle of ancient humans/hominids. All of our beliefs about the humanity of our distant ancestors is myth at worst and theory at best therefore it worries me what our 10,000 year descendants will think of us. And to think I was recently accused of caring too much what other people think about me…

But I digress.

I asked the venerable Dan Rutter of Dan’s Data a question about an ultra-long-term storage tank that I’d like to build for daguerreotypes.

Dan,

Suppose I wanted to maintain a vacuum in a standard bell-jar / vacuum plate setup for around 10 millenia (give or take) without interruption or maintenance? What, other than “comical,” would be my options?

These thoughts occur:

Short-term thinking would assume an electric vacuum pump but I’m assuming that is preposterous due to the mechanical degradation of the components. Powering the electric device bumps into the same hurdles: solar and wind are out due to mechanical degradation, right? What about radioactivity? Is there any reasonably sized undeadly hunk of radioactive ore that could be used to provide electric power to the pump while simultaneously requiring zero maintenance?

Maybe I could even use the heat from a radioactive source to more directly drive a steam pump in a sealed engine to maintain vacuum… thoughts?

I should mention that the vacuum is only for purposes of removing contaminants from the air (most specifically sulfur) so it doesn’t need to be very strong.

Thanks!
Jon

The reply, under the header of “This boy worries me” was this.

I presume shooting the vessel into high Earth orbit is also not possible.

You can forget about any kind of mechanical pump. It’s barely possible that some jewel-like device with glass cylinders and graphite pistons and diamond bearings could do the job, but it’s not as if you’d be able to demand a refund from the maker’s descendants in 150 years if it wore out. I bet, eventually, it would.

Actually, I wouldn’t be surprised if a pretty ordinary refrigerator compressor – easily convertible into a vacuum pump – would last a hundred years if run on a relatively short duty cycle (see also The Secret Life Of Machines, episode two). Even one thousand years is well over the odds for any mechanical pump, though.

Power sources aren’t entirely impossible if you only need a little power – perhaps some kind of expanding-metal-driven ratchet spring-winder that clicks the spring a few times every noon and midnight, or a granite cistern feeding a waterwheel that’s lubricated by its own water – but all mechanical vacuum pumps require close tolerances, by definition, and close tolerances invariably get less and less close over the span of years, not centuries.

There are, however, several kinds of vacuum pump – or related device – that have no moving parts at all.

The only one that I think would be feasible over really long periods, especially if the only job you want it to do is police up impurities in an evacuated vessel, is a great big metallic “getter“.

It’d just sit there passively in the vessel – which could be vacuum-filled, or possibly even filled with an atmospheric-pressure noble gas if that’s workable – and it soaks up the unwanted molecules. Easy.

Getters can also be helped along by an ion pump, but I don’t know how you’d make one of those that’d last for a very long time. Yes, a radioisotope thermoelectric generator could power one for a long time, but the ion pump itself would degrade, and RTGs by definition have to be based on the kind of excitable isotopes which, to quote Dr Emmett Brown, are not available at every corner drugstore.

The other no-moving-parts options, like cryopumps and sorption pumps, are out of the question on account of how you’d need to set up an unusually durable religion based around supplying your vacuum bottle with liquid nitrogen.

Dan

Thanks, Dan. I really appreciate the thought that you put into that! The getter seems like a reasonable avenue to explore.

Jon

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