There's a very specific existing case study of nearly this exact question.
In the 1970s, the US Department of Energy began investigating what is now known as the Waste Isolation Pilot Plant as a means of safely storing radioactive waste for the next 10,000 years.
Considerable thought was put into the topic of signage: how to indicate to future generations, for whom the very concept or science of radioactive waste may be lost, that the materials buried in this location remain harmful in a very literal sense.
There are some interesting papers from researchers at Sandia on the topic. You can read some excerpts as well.
Do we mark it at all?
I know this wasn't specifically what you asked, but it calls into question the very premise of the exercise. Recorded history goes back only about 6,000 years. The earliest known permanent human settlements go back less than 9,000. So communicating to humans 10,000 years (or, as you posed, 50,000) in the future may simply be impossible.
One alternative (in the case of the WIPP) is simply to bury the material in as inaccessible a place as possible, and assume that any civilization able to discover and uncover it will also be able to detect the danger posed.
The Sandia panel rejected this on legal and (I would say) moral grounds.
How do you ensure the message is physically durable?
This seems to be most related to the core of your question, and the answer is fairly mundane. The final proposal calls for the use "granite monuments, 25 feet high" carrying etched messages, an information center and two storage rooms with similar granite markings, and, buried throughout the complex, the same messages etched on "nine-inch-diameter discs… made of granite, aluminum oxide, and fired clay."
In addition, the same information will be placed in various archives around the world.
How do you ensure the message is intelligible?
The plan calls for the message to be translated into the six official languages of the UN (English, Spanish, Russian, French, Chinese, Arabic) as well as Navajo, the ancestral language of the region.
But come on, how do you really ensure the message is intelligible? How do you ensure that future generations don't destroy the markers? How do you ensure that people take this seriously, anyway?
This is, to my mind, the true crux of the matter. The obvious (and somewhat pulp) analogy is to curses on Egyptian tombs – an Egyptologist might properly translate the text, but he is unlikely to take seriously a warning threatening bodily harm due to vague invisible forces.
Worse yet, the presence of the tomb encourages desecration for motives both historically minded (archeological investigation) and crassly economic (as with reuse of building materials from Roman or Egyptian edifices for more modern constructions).
The WIPP panel was quite aware of such risks, and made a number of suggestions which I will simply quote verbatim:
Each component of the marking system should be made of material(s) with little intrinsic value. The destructive (or recycling) nature of people will pose a serious threat to the marking system.
We decided against simple "Keep Out" messages with scary faces. Museums and private collections abound with such guardian figures removed from burial sites. These earlier warning messages did not work because the intruder knew that the burial goods were valuable. We did decide to include faces portraying horror and sickness (see Sections 3.3 and 4.5.1). Such faces would relate to the potential intruder wishing to protect himself or herself, rather than to protect a valued resource from thievery.
While the below messages differ from the final design, I found a certain sense of Lovecraftian poetry in their directness:
This place is a message… and part of a system of messages… pay attention to it!
Sending this message was important to us. We considered ourselves to be a powerful culture.
This place is not a place of honor… no highly esteemed deed is commemorated here… nothing valued is here.
What is here is dangerous and repulsive to us. This message is a warning about danger.
The danger is in a particular location… it increases toward a center… the center of danger is here… of a particular size and shape, and below us.
The danger is still present, in your time, as it was in ours.
The danger is to the body, and it can kill.
The form of the danger is an emanation of energy.
The danger is unleashed only if you substantially disturb this place physically.
This place is best shunned and left uninhabited.
As a final aside, the suggestions made by a poll conducted by the Zeitschrift für Semiotik and Bechtel's "Human Interference Task Force" are quite interesting in their more far-ranging conceptions – suggestions include the creation of artificial satellites that can circle the earth for millennia, genetic coding of messages into cats, and the creation of an "atomic priesthood" to keep the knowledge sacrosanct.
Save it on a Nokia 3310. – Jon Story – 2014-12-12T11:07:32.820
1
This is the subject of an in-depth book, Deep Time: How Humanity Communicates Across Millennia by Gregory Benford. I believe he said he's planning an updated re-issue.
– JDługosz – 2015-01-01T05:08:42.570Do you want the message to be communicated in exactly 50,000 years, or can it be hidden for an unpredictable time? For example, if you buried something where erosion or glacier-calving would begin to reveal it in 50-100,000 years, would that be good enough? – arboviral – 2017-02-14T08:28:53.003
3
The real problem is a semantic one. See for example the "Voyager Golden Record" - visual, haptic, representational, scale, similarity; what and how do you communicate with a species of who's sensory and cognitive abilities you haven't the slightest clue, and what assumptions you base those on?
– kontur – 2015-01-29T11:27:02.293@MooingDuck ... and what we do know about the hieroglyphics on the pyramids is that a lot of what is left (after the officially exposed surfaces have been stolen or eroded away) is grafitti (Just how drunk is the pharoah?) – pojo-guy – 2018-02-14T20:03:36.287
Interestingly, this question was addressed in the The Three Body Problem series. In the end, their solution was insufficient due to the nature of how Earth civilization was destroyed. I won't say any more to avoid spoilers.
– Draco18s no longer trusts SE – 2018-03-01T22:02:50.2602@PeterMasiar - The question posed was "how", I'm looking forward to someone asking "what" the message should be, separately, maybe? – Mikey – 2015-04-18T20:03:07.297
45Hasn't this problem been considered in real life in the context of marking nuclear waste disposal sites? Not exactly the same but certainly similar. – mu is too short – 2014-11-01T04:48:28.863
12
Take a look at projects by The Long Now foundation: http://longnow.org/
– Neil Slater – 2014-11-01T11:03:46.66726You could always carve it into the moon. – superluminary – 2014-11-01T20:44:53.337
If we perfect superconductivity for household use, then one day we might be able to preserve electronic signals in simple conducting materials which would theoretically last forever!
– Renae Lider – 2014-11-02T12:44:19.5201
I don't think this fully answers the question, but if you want a lot of ideas on how others have tackled this problem, definitely check out the 99% Invisible episode on the topic: http://99percentinvisible.org/episode/ten-thousand-years/
– Brownbat – 2014-11-02T16:18:50.5102
I don't know how I landed here, but as I started reading, I found the topic interesting enough to quickly share my thoughts with you. A message for our future beings about 50.000 years from now? Considering technological revolutions (http://en.wikipedia.org/wiki/Technological_revolution) and Prof. Michio Kaku's research (http://en.wikipedia.org/wiki/Physics_of_the_Future), I tend to believe that the concept of sending/leaving behind a 'message' will be obsolete. Beings (as we might then be considered) would be omnipotent.
– None – 2014-11-01T11:56:50.997Maybe something like this.
– nwellnhof – 2014-11-02T20:02:26.2504Eazy, behave like we currently do. The message to our future will read: Fuck You – Jens Schauder – 2014-11-03T13:06:46.013
1I think the message itself will make a huge difference in determining how it's left behind for future Archaeologists to find. Today's archaeologists seem to love attributing religious significance to everything they find; if your message is not religious in nature you'd need to overcome that. – NotMe – 2014-11-03T15:49:45.217
24Funny that accepted answer solves easy part - leaving the message but does not even attempt to solve hard part communicating what we wanted to say. Pyramids is such persistent message. What does it say? – Peter M. - stands for Monica – 2014-11-03T19:06:21.473
4Bury a monolith on the moon. – gerrit – 2014-11-03T20:31:07.663
8Our scientists have only some idea of what the glyphs on the pyramids say, and that's only four thousand years ago. – Mooing Duck – 2014-11-04T00:34:03.613
Throw 1,000 of these into an orbit that will not decay into the atmosphere for 50,000 years or more. Add solar panels that power beacons which transmit in the visible light, radio, and microwave frequencies.
– None – 2014-11-04T04:36:59.277Also, it might happen that a big asteroid will impact the Earth in 50000 years, so simple redundancy won't be enough. You need to send copies elsewhere and perhaps use some kind of active protection. – dtldarek – 2014-11-04T09:04:00.623
@kenny yes, a lot like how we today view the civilizations that left the cave paintings and even pyramids. What can we possibly say that would be relevant to them? How could we possibly know with surety that there is information we have that they will need or desire? The nuclear memorials are assuming the future civilization will be equal or worse than we are. Certainly any civilization surpassing ours would be aware of radiation if it affects them negatively. – Adam Davis – 2014-11-04T20:39:50.420
@muistooshort I guess they won't need instructions, i.e. the people "currently in charge" should know "what to do" along the way. – o0'. – 2014-11-07T21:51:43.910