The correlation coefficient is in the range -1 to 1.

The Internet hasn't really made it much easier to invest in the types of illiquid assets that would interest large institutional investors. Those investments are still largely based on personal relationships and negotiations, often facilitated by brokers or bankers.

Yes but if they're negatively correlated and everything is tanking then they won't impact your returns as much than if they're positively correlatd.

The problem is that almost every asset class now becomes positively correlated during economic crises. It's very difficult to find negatively correlated or uncorrelated returns in those situations.