Why not use the chain with the most coins at stake? In PoW, one would use the chain with most amount of work.

HeRetiK: yes, this idea as described above only applies to PoS.

There is a variation of the idea for PoW that allows to "duty-cycle" PoW (the motivation being a "greener" PoW or one suitable for energy-limited IoT devices). Imagine this protocol:
- everyone is in standby mode, waiting for a global random event to happen
- random events happens, producing the outcome "5".
- everyone starts searching for the nonce of the next block. The trick is that instead of finding the "normal" nonce such that starts with enough zeros, they look for a nonce that  such that has the right property - with "5" being the number from previous step.
- someone finds the right nonce
- information about the winner is distributed in the network and everyone stops mining until the next random event

(To be clear, this is an academical / theoretical proposal, I don't actually want to say that any real coins should use this.)


ETFbitcoin

1. That sounds like another FOMO3D 
2. Not sure I understand this idea?

The simplest Proof-of-Stake protocol is one where the participants lock down their stakes, after which the system randomly assigns the block reward to one of them. However, this random selection of the next awardee must be done in a way that is independently verifiable by someone who does not trust the system. The obvious way is to use a pseudorandom number generator in a known state. If I'm not wrong, this is how some of the initial PoS coins actually did things. However, this approach makes the random selection not only verifiable, but also predictable, which in turn incentivizes the participants to game the system.

There are of course counters to such gaming, and there are far more complex PoS and dPoS protocols. However, if I'm not mistaken, none of them at the moment are generally accepted as superior to bitcoin's PoW.

So, I was wondering if instead of building more complicated protocols we could just find a natural source of random numbers that would be suitable for cryptocurrency mining? What I mean by that is: something that would not be predictable, but could serve as a source of consensus between multiple participants that do not trust each another.

The random events suitable for task should have the following properties:

• be observable by multiple independent observers, not restricted to a single location;
• be impossible to predict in practice;
• be convertible to a discrete value.

Ideally, they also should:

• either happen with a reasonably high frequency, or be measurable with a reasonably high frequency (on the order of seconds or minutes, not months or years);
• be measurable with today's technology.

Such as source could be simple a binary event, as long as everyone can agree on the outcome with a high degree of certainty. In contrast, a categorical value that depends on vague definitions is a bad choice.

The best I could come up with is some kind of astronomical measurement. In particular, I was thinking of the number of supernovae in the Milky Way (or in multiple nearby galaxies). It seems to be a discrete number, something that almost everyone could agree on, and unpredictable for all practical purposes. The drawbacks are that the frequency of new supernovae is low, and that we cannot reliably determine this number with the current technology. What do you think?