[magnat]

> Or the machine language expression of the most advanced expert systems, though by then the notch might be small enough that Planck’s constant got in the way.

With Planck's length being roughly 10^-35m, I'd say you'd hit the limit trying to store more than 15 bytes.

[Tepix]

Also depends on the length of the metal rod, doesn't it?

[OscarCunningham]

The observable universe is 2^205.5 Planck lengths across, so you can store at most 205 bits, or 25 bytes.

[soVeryTired]

And at that length your latency gets reeeeeeal bad.

[hamilyon2]

This is insightful. 15 bytes is not a lot. I wonder what are other narural limits on information density? For example, magnetic field. Is there a least measurable difference?

[AmericanChopper]

The limit on information density is called the Bekenstein Bound, the point after which adding more information to the volume would create a black hole.

https://en.m.wikipedia.org/wiki/Bekenstein_bound

[jtrip]

How are you calculating a value of simply 15 bytes? The proposal is that the mathematical value of the ratio of the lengths of rod and the notch will deliver a value on the number line, which in effect can be of any desired length. You actually could find a number that can represent the complete contemporary knowledge of Humanity.

The limitations mentioned in the above comment relate to the fact that to know you'd arrived at the number designed into the Notch and the Rod, you'd have to have agreed to beforehand the tolerance limits on measurement of this 'device' so that the uncertainty in measurement can be ignored and the ratio derived.

To maybe get the right number you would have to expand your possible number of ratios (at a certain measurement sensitivity you would have a certain number of lengths you could use, and thus certain number of ratios would be available to you) and to get just the right number to describe your whole "machine language expression of the most advanced expert systems" you would have to delve into tolerances of the Plank length.

Or adjust the size of your rod length and notch, make them bigger, to get that sweet number with a 'poorer' level of sensitivity.

.. Or find a number with enough usable number sequences to serve the purpose and program in the numbers surrounding gibberish as markers/jump points to the next sequence of usable numbers. I suppose you could find enough usable sequences in the full expression of pi (as it's rational expression is without end) to write a program that can decode the full linux kernel out of it.

[rcxdude]

Assuming the length of the rod is 1m, and you have a resolution of one plank length, there are 10e35 possible ratios you can express (because that's the number of possible locations of the notch). that's about 2^113, which is a number which fits in 15 bytes of information. As discussed below, if you also allow for the bar to be the size of the observable universe, this doesn't increase by much. A notch or ratio is linear, information and combinatorics grows a lot lot faster than that.

[jtrip]

How would you say a rod to notch ratio of 22/7 compares? How much information would you say that has?

[rcxdude]

Meaningless on its own. What matters is how many distinct ratios are possible.

[stevenhuang]

> Meaningless on its own.

That's the crux. What we're saying is that, of these set of ratios, there exists one whose infinite decimal representation contains our intended data. Yes we'd be limited to Planck length resolution, but the idea is that we would determine such a ratio and construct the notch and bar in such a way that it yields the decimal sequence desired; the # of particular ratios is not relevant.

I wouldn't be surprised if it can be proven this can't be done, but then that would be proper question to ask.

[utopcell]

you can loosely think of it as writing down a number in unary where each "digit" takes 1.6 x 10^-35 m space to draw.

[jtrip]

But what does that have to do with the emergent ratio between the notch and the rod? There may be 10^35 possible steps, but that does not mean that the answer, the ratio of the notch and the rod, will be limited by that. The answer will come from the number line, where any irrational number can have however many trailing numbers. If the ratio of the rod and the notch is 22/7, how much information would you say that is?

[utopcell]

If 'x' marks the notch of a rod of length "1", [0---------x------------1], then the implied ratio is not x/(1-x), but x/1 (so the ratio is always < 1.) Even so, your question could be "what is the information content of 1/7" (the presumed implication being that 1/7, while periodic, has an infinite decimal representation.)

But that is not the direction we are interested in. We would like, given a message, such as "l-o-v-e", or 12-15-22-05, or 0.12152205, to figure out what is the ratio that uniquely specifies it. As we can only mark one notch, we can create "only" h ~= 10^35 ratios, or represent h unique messages. We know how to distinguish between h unique elements with log(h) bits (we just enumerate them from 1 to h and write that number down in binary.)

[jtrip]

Let's assume that the rod is 1 m in length, and say I wrote a book that is perfectly represented by the number 0.abcdefg...yz. If that number is perfectly represented by one of the ratios in set 'h', then have I not stored more infromation than 15 bytes?

As for x/(1-x), why not? And why limit ourselves to a 1 m rod? Why not a 22 m rod with a 7 m notch? I could then define the method of decoding the information via (Rod length)/(notch length). The I'd have 'infinite' information in the form of expression of pi.

My main issue with the parent comment is that they imply only 15 bytes of data could be stored via this method. I think that's prespoterous as the number of ratios my be only 15 bytes, the ratios themselves can have any possible size.

It becomes more a game of probability rather than that of exact numbers. Will you find the right number, from set 'h', that matches exactly what you wanted to say?

    0.abcd...xyz = [(notch length=alpha*plank length)/(rod length=beta*plank length)]

where alpha and beta are just any variables that you play with until you solve the equation.

[utopcell]

A 22m rod with a 7m notch is perfectly ok. You'd then be encoding 7/22. As others have pointed out, the rod could span the known universe and it would still not matter.

Say you found a great message in the representation of 1/7. Weird, since it is a rational so if its representation is infinite, its periodic (you can't write down 1/π or 1/e for example, as these are irrationals.)

Excited you found that message, you want to put your notch exactly at 1/7 on the rod to celebrate it.

But you can't. Your desired notch position will fall between two possible notches, spaced one planck distance apart, and you'll have to pick one of the two.

And when you do, you truncate your message to 15 bytes worth of information.

[rcxdude]

Not really. You have stored something which has a representation of more than 15 bytes, but you will struggle to find a way to store most things longer than 15 bytes in this way. (everything can be transformed into a representation which is infinite in size anyway, for example by using an irrational base). Information really comes down to the number of possible values you can distinguish.

If you do the ratio thing you have described you will find that alpha and beta are many, many times the size of the observable universe for something like a book. If you allow the length of the rod itself to also contribute to the information, you have added another symbol so you can store more than 15 bytes, but this doesn't even double the amount of bytes you can store.