Ive been researching bonds quite a lot given I have a decision to make about whether to keep them in my portfolio or not.
Over the past 20 or so years, bonds have acted as a hedge to equity, they were inversely correlated so that if equities went down, bonds went up and vice versa. So its been seen as a way to diversify.
But, in the time before that, bonds and the stock market were more positively correlated so they went up and down together. This makes them not really a diversification to equities.
It seems that the negative correlation of bonds and stocks has been linked to the period of low interest rates, which were an anomaly over the past 100 years. If interest rates are returning to what is considered more historically normal, it may be that bonds return to their historical trend as well. Also the bond crash in 2022 has been linked to high inflation, which is now hopefully subsiding. I saw one article that said that during periods of high inflation, the best diversification would be commodities. They are no commodity funds I can invest in in my pension scheme though.
It seems that long term (100+ year) returns in stocks has been in the order of 10% and in bonds in the order of 6%. Actually that is not too bad, as an 80/20 mix would net you about 9% on average.
https://barbarafriedbergpersonalfinance.com/historical-stock-and-bond-returns/
So whilst stocks still outperform historically, it seems that if considering diversification it would still be sensible to hold bonds. As the past is no guarantee of future performance, who knows whether stocks will continue to outperform in future or whether the gap might close up. So on this basis I don't really understand why the recommendation is for 100% worldwide equities, because this would seem to be relying on the past performance of equities.