I think I get that, but to my simple head.
1. the FTSE closes at 4:30 7000
2. overnight stuff happens but the FTSE is closed so cannot move.
3. at 7:59 the FTSE is still at 7000
4. why can't I place an order at the price of 7000? why do we accept a fictional position of e.g. 7040 made by providers?
Is there no way to buy at the close/open price. accepting that I will be in a que and won't get the exact price but a lot closer than something calculated by a company?
Thanks
I think you have a few things mixed up in your understanding, which is easily done because it's a very complicated matter. I cannot claim to be an expert but I found it very interesting when I started out and this is my current understanding...
Firstly the close and the open price are in no way related or connected - once the market is closed that price is gone. Even with a single stock they are not related - each morning there is a pre market auction which matches buyers and sellers and sets the new opening price.
Now with index trading the picture gets a bit more complicated. Obviously the FTSE 100 index value is calculated by some formula using the top 100 companies on the LSE. The price for each individual company will be reset each morning at 8am (cash open) after they have all had their pre market auction and then you will have a new index value. You cannot actually trade this value unless you were to buy/sell all constituents simultaneously, which is not possible for small fish like us. What you can do however is place a trade with your broker on their version of the FTSE (it's usually called UK100 because it's their own creation and not the actual FTSE). This is an OTC - over the counter - trade because you are trading directly with the broker and not over an exchange, as you would with a stock.
The picture is further complicated by the existence of index futures contracts, which are a relatively recent invention, largely made possible by modern technology. Futures are contracts traded on exchanges (seller to buyer directly) and they have a set value (eg the ICE FTSE contract is £10 per index point). They are traded for much longer hours than stocks - the market opens at 11pm Sunday UK time and closes again for the weekend on Friday evening. In theory people from all over the world can trade FTSE futures 24 hours a day.
So professional traders and institutions will be buying and selling futures contracts (for hedging or speculation or whatever) independently of the stock index. The value for the cash/spot FTSE is then kept in line with the FTSE futures by arbitrage traders who will make a profit by selling one and buying the other if they start to diverge. Obviously that requires a lot of capital so it's the preserve of instituions. What it means is that price discovery comes from the futures market and the cumulative value of the index stocks, with one running 24 hours and the other running 8-16:30 (cash hours).
What's very interesting is that in the US most index traders trade futures directly on exchanges (eg 'ES' on CME) whereas in the UK the CFD and spread bet firms have managed to insert themselves as middle men (or not) between market participants. There are advantages and disadvantages to both systems, but if you are serious about index trading then it is usually better to trade futures directly on an exchange. What's also interesting is that trading FTSE futures ('Z' on ICE) is actually quite difficult for retail to do, some brokers don't even list it. It's generally much easier to trade ES, FESX or even other wierd and wonderful things like bund/gold/oil. So if you just want to trade the FTSE/stocks you would be better of with a CFD firm.