# Most Long-Lasting Lightsource?



## Olumin (Nov 13, 2020)

Now this might be an interesting discussion. 

Imagine a time capsule, which is sealed away for a million years. Within is to be found a elongated cuboid cut out of synthetic sapphire. Embedded within this cube are hundreds, perhaps thousands of tiny images, lasered into the sapphire behind one another in a row and somehow colored. These images can be projected onto a surface using a light focusing mechanism made of a Platinum-iridium alloy with sapphire or fused quartz optics which is already set up and ready to use. Instructions are engraved onto several surfaces and the capsule stored in a secure location, perhaps in orbit or the antarctic, and filled with a inert gas like xenon. It will last for millions of years if undisturbed. The only thing missing is the light source.

There is no telling is a civilization thousands or millions of years from now will have the ability to craft a light source to the exact specifications needed, or if such complex instructions can even be reliably delivered. The most simple solution is to provide the light source needed for the projection. This way however finds it would only have to provide the electricity, which any civilization advanced enough to locate the time capsule to beginn with would be easily capable off. 

Now the question is, what possible light source could last such a long time? Even when stored under the most ideal of conditions, I doubt any complex electrical or electronic devices could last for this long. 
Perhaps a simple laser is the answer? A mere incandescent bulb? It is simple after all. 

What light source could still function after a million years?


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## Katherine Alicia (Nov 14, 2020)

well if you`re having fused quartz optics then how about a simple magnifying glass to capture the suns rays? that`s a light source that should still be here in a million years (I hope! LOL).


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## Olumin (Nov 14, 2020)

This is a really good suggestion and just what I was looking for. The bright sunlight would make it difficult so see the projected images in any clarity, since a projector works best in a dark location. This means there would have to be a sort of light-proof room constructed arround the projector, but leaving the magnifying glas out in the open. The projector would still have to be accessible to manually focus the images.


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## Katherine Alicia (Nov 14, 2020)

well either way, if you`re commited to having it as a projector you`ll still need a light-proof room anyway, but something like a reversed wide angle TIR as a collector with a light pipe (like fiber optics) would let you put the collector outside, bringing the raw concentrated light into your room and focus it.

Edited to add: if you didn`t want to go the quartz TIR collector route, then a polished metal parabola (like a mirrored satelite dish) with a fibre optic bundle / light pipe at the focal point would do the same thing 

Or.... make a modified platinum version of one of these with your saphire slides


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## Olumin (Nov 14, 2020)

I suppose a Glasfiber-cable made of a bundle of fibers consisting of two tubes of pure silica with no additives assembled in the traditional construction of a high-refractive-index core and low-refractive-index cladding and with a dense, protective wrapping of platinum wire, could well last for such long time. The question is if it would still remain flexible without fracturing after 1 million years. I dont know enough of material sciences to make that determination. Even low ammounts of ambient radiation and radioactive particles trapped in the material itself could weaken the crystalline structure over such a long period enough to make it fragile.


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## Katherine Alicia (Nov 14, 2020)

ok, so ignoring the sun for a bit, how about a chamber whose walls are TIR collectors merging to a single light pipe, the inside of this chanber is a phosphor, Then all it needs is a Beta emitter to be inserted for instant lght!
the beta emitter can be set up a pile to form a slow breeder reactor where the outer layers daughter products are beta emitters and the inner layers are the moderators and the very core is the actual starter fuel with a long half life, a million year decay chain is quite doable in a breeder setup


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## Olumin (Nov 14, 2020)

Making use of radio-luminescence by using a radio-phosphor-emitter is certainly an interesting idea, however the resulting light would not have a continuous spectrum, and therefore it would be difficult to accurately represent the true colors of the projected images. The emitted light would also not be very powerful, especially after a million years (or longer). Using radioactive elements would also inherently limit the lifespan of the light source. It is also a quite complicated and potentially dangerous setup, especially compared to using focused sunlight or a tungsten-filament, xenon bulb.


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## Katherine Alicia (Nov 14, 2020)

well, about 7-8 years ago I had the pleasure of working with Sotira Trifourki of Atemis Space ( https://www.spaceartemis.com/about/ ), she presented me with a problem of generating power in deep space for a couple of thousand years (obviously conventional methods are out) so I designed her a small betavoltaic reactor (thermal not optical as in this case) and she was perfectly happy with it as a solution. I must admit a Million years is a bit different and a Thermal reactor wouldn`t work for that it would have to be optical as that allows for a slower less powerful reaction that would last longer. the phosphor material is just a mixture of simple inorganic molecules that would remain the same even after a million or more years barring radiation or chemical damage, that`s why the source would be inserted when it was needed and not left running. also the phosphors would be no worse than the phosphors we use today in our LEDs they can have a good spectral spread (you could even pick your tint! LOL 
I agree that there is a potential danger there though, these thngs aren`t toys but you`re talking a Million of years here, so you need something with a bit of a kick to it!


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## Olumin (Nov 14, 2020)

I suppose I was thinking about the radio luminescent paint and tritium vials used on instrument and watch dials, which are always that iconic green color, or multiple colors in case of the tritium vials. I am no expert in that field. I have never seen radioluminescence emit white light. Are there any examples of this? A light source which functions independently of electricity would certainly be ideal in any case.


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## Katherine Alicia (Nov 14, 2020)

not sure I can help there, it`s not really an area I`v had too much experience in and there`s many different types of luminescence as well, I suspect a Fluorescent material like that in LEDs or fluorescent tubes would be best, perhaps fired up by a UV emitting layer first (like they do with YAG crystals in green lasers to change to a more suitable activation energy/wavelength).
So a double layered emulsion would probably be required, but really you`de need someone trained in this area to say exactly what you`de need.


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## Katherine Alicia (Nov 14, 2020)

OK I had another idea (this is fun!) before I just hand you a ZPM and be done with, how about going with your fillament bulb idea and having a water activated battery? something like a Silver Chloride Magnesium battery they use in torpedos? the sea water activates it, so you could always add a spoonfull of salt to the battery chamber and have a "just add water" battery.
it would only work once, but it would certainly last many millions of years if kept dry.


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## Olumin (Nov 14, 2020)

Yes, that is a great idea actually. A battery of sorts could work as well. I wonder however if the inert-gas filling of the bulb would not escape through the glas or metal and eventually some oxygen might make it inside, at which point the bulb would just burn out once turned it, would it not? A million years is a long time for this gas to stay perfectly contained.


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## Katherine Alicia (Nov 14, 2020)

I did wonder about that myself but with an equal pressure bulb 101Kpa inside (same as outside) there`s no compelling pressure difference to make it want to migrate anywhere. My main concern is the glass of the bulb itself, with it being an amorphous solid, what would the effects of gravity have on it over a million years!? so you`de need to use pure quartz to make it (that stuff retains its shape (and has done) for many millions of years)) so you`de be good using that. then fill it with Argon (or any group 8 element) to one atmoshere pressure (the Ar atoms are too big to migrate through quartz anyway) and you`ve got a million year light bulb!


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## bigburly912 (Nov 14, 2020)

The Centennial Light. [emoji16]


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## Olumin (Nov 14, 2020)

Yes, it would have to be a pure silica or sapphire bulb. I suppose another simple way to provide power would be to include a kind of hand-cranked electric generator connected to a capacitor or battery. Once a sufficiently high charge is build up, it could power the light source. Since permanent magnets would likely not stay magnetized to a sufficient level for a million or more years, a electrostatic generator could provide power, and in theory could last indefinitely. Electrical connections are simple metal-pieces and wires made out of gold or gold-plated silver or copper, and would also not degrade. Now I dont know anything about capacitors or batteries, then the question is if any kind of simple Battery or capacitor could feasibly last this long.

Edit: Electrostatic is perhaps the wrong term, as static electricity is not what is needed. What I mean is a electric generator that functions independently of permanent magnets. I dont know if such a generator exists that is capable of efficiently powering a incandescent bulb.


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## brickbat (Nov 25, 2020)

I'm stuck at the hundreds or thousands of images, behind one another. 

Setting that aside, I'd vote for View-Master technology...


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## Ken_McE (Jan 23, 2021)

Put the whole thing deep under the Moon, either North pole or South.* set up a tunnel pointed at the sun. Someone comes along, unblocks the tunnel, and it lights up an image. That image shows how to change to the next image. If the moon has processed they can see that and dig a new tunnel. Instructions engraved in the walls, all pictures, no words. No corrosive O2, no corrosive H2O, no destructive plants or animals, no earthquakes, no continental drift, hardly any metal thieves. *Better yet, both.


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## broadgage (Feb 11, 2021)

Tritium vials certainly wont work, they only last about one lifetime, and are MUCH dimmer after only 50 years.

Incandescent bulbs keep well, but I doubt that standard types would keep for a million years. A specially constructed incandescent MIGHT store for that long. A very thick glass bulb to reduce gas diffusion and an inert gas filling at atmospheric pressure. Glass base, with gold contacts. Store the lamps in an outer and sealed glass container containing inert gas at atmospheric pressure.

More realistic would be to expect the end user to provide a light source. Any future civilization able to make use of the stored images would surely have light sources.


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## Ken_McE (Apr 12, 2021)

broadgage said:


> Tritium vials certainly wont work, they only last about one lifetime, and are MUCH dimmer after only 50 years.



Trits dim fast because Tritium has a twelve year half life. There are other Beta emitters that have longer half lives. We mostly use Tritium because the others are all more dangerous to have around. Carbon 14 has a half life of 5,730 years, but that still isn't enough for this project.


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## jtr1962 (Apr 15, 2021)

A bigger problem is getting whatever you bury to last a million years. The Earth has weather and is geologically active. For all we know, maybe we had a technological civilization on this planet millions of years ago but all traces of them would be gone now.

If I wanted to preserve bits and pieces of our civilization, I would bury them fairly deeply on the moon, then maybe alter the surface above into something which appears artificial so some future race would know to maybe start digging there. I would do the same thing in a bunch of other spots. The moon has no weather or major geological activity but meteor strikes still gradually change its surface.

It's going to be very interesting when we start exploring Mars to see if maybe some intelligent race there left us clues.


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