It simple. Before I continue , Gold and Oil are definited
as commodity and it is usually traded by Futures or contract
obligating the buyer to purchase an asset.Just remember that
to predict whether which is the best time to buy gold,
the idea is to take notice that some currencies from
some countries are heavily correlated with commodity
prices.(in this example Gold).In this case Australia's dollar
value is the same as gold value, so if Australian currencies raise,
this will indicate gold value is rising as well since Australian
has 85% positive correlation with Gold. A weaker, but
still important, correlation is that of gold prices and the Swiss
franc currencies since in case of "political uncertainty"
they have gold as their backing.
As for the reason why gold is still the best investment,
kindly visit this link so as not to bored your with lengthy
words , Link :
http://www.investopedia.com/articles/basics/08/reasons-to-own-gold.asp