Probably everybody ran and they halt trading immediately. The exchanges dont warn people so they can dump their portfolio before pulling the plug. But they had to open the next day for at least a shortened session per federal regulations because they can only be closed 3 days in a row.
The NYSE was closed for 4 business days from 09/11/01 to 09/14/01 and opened for trading on 09/17/01. Please specify which federal regulations regulate exchange closings.
I remember having some orders in to buy QQQ at the open on 9/11. Before 9am I saw a breaking bulletin on CNN.com about the first plane hitting the WTC and cancelled the orders. The markets never opened that day so no advance notice.
I thought that question was clear enough, but here is another way of asking it- do you think the exchanges are going to close down from an event, and what is that event?
The SPU's were down 20 handles all of a sudden (watching premarket - huge move back then). Didn't know why. A minute or two later looked up and saw what looked like a "smokestack" on CNBC. The markets never opened that day - they were closed when the 2nd plane hit. I believe Cantor Fitzgerald got hit with the first plane. News spread almost immediately to the pits from there I would guess. I doubt they knew exactly what happened, just something bad had happened. And BTW, I think the 3 day maximum closure law refers to banks.