I found this:

"Ten minutes was specifically chosen by Satoshi as a tradeoff between first confirmation time and the amount of work wasted due to chain splits. After a block is mined, it takes time for other miners to find out about it, and until then they are actually competing against the new block instead of adding to it. If someone mines another new block based on the old block chain, the network can only accept one of the two, and all the work that went into the other block gets wasted. For example, if it takes miners 1 minute on average to learn about new blocks, and new blocks come every 10 minutes, then the overall network is wasting about 10% of its work. Lengthening the time between blocks reduces this waste." -- https://en.bitcoin.it/wiki/FAQ#Why_do_I_have_to_wait_10_minutes_before_I_can_spend_money_I_received.3F

If the broadcast of a newly discovered block could be made very fast to all the miners, couldn't the transaction time be significantly reduced?

In practice miners have fast Internet connections. I don't know the technical details of how newly discovered blocks are broadcast to all the miners. Maybe it's a cumbersome process. My assumption that the broadcast can be done in milliseconds is perhaps unrealistic.

That's not a guarantee, as infrastructure could be destroyed or damaged by some bad happenings (not going to go into conspiracy theories here) or the political situation may change restricting miner connectivity.

actually bitcoin transfers need a change
10 minutes it is too long and almost everything requires a minimum of two confirmations,that is at least 20 minutes to take a bitcoin to another address
too long nowadays

I think that's the point. Since transactions propagate so fast the confirmation time could probably be reduced safely.

I suggest reading this wiki page:
https://en.bitcoin.it/wiki/Scalability

The 7 txps limit is arbitrary, not a design choice, and can be increased quickly if necessary.
Miners won't suffer from this - they only have to confirm each transaction once per pool.

In reality what may happen is that payment channels will be used as a layer on top of Bitcoin. Here is Jeff Garzik talking about payment channels:

CoinSummit London 2014 - Will Bitcoin Last the Distance Beyond the 51% Challenge? -- https://www.youtube.com/watch?v=m2q9pItnO0U&t=17m52s

That sounds like a good solution. It will prevent the block chain from becoming bloated and it will allow very fast (I guess) transaction times and a huge number of transactions per second. Would be excellent even for micropayments.

Oh noes! Unless Jeff Garzik meant some new kind of payment channel in the video I posted earlier, I found a big problem with it:

"Example 7: Rapidly-adjusted (micro)payments to a pre-determined party ... This protocol has been implemented in bitcoinj" -- https://en.bitcoin.it/wiki/Contracts#Example_7:_Rapidly-adjusted_.28micro.29payments_to_a_pre-determined_party

"This article describes how to use payment channels, a way to set up a pending transfer of value from one wallet to another such that the amount that will be transferred is incrementable at high speed and by very small amounts. Whilst this does not allow you to send micropayments at high speed to different recipients each time, many applications can fit within this framework - typically anything that involves micro-billing for a metered service." -- https://bitcoinj.github.io/working-with-micropayments

That's a serious limitation. The customer can only send microtransactions to ONE recipient. So, as I understand it, if you prepay say 0.1 bitcoins to do microtransactions with one company, you will have to make another prepayment in order to be able to do microtransactions with another company, and a third prepayment for a third company/service and so on. That actually sucks.

I heard that shorter transaction times leads to more orphaned blocks. And someone said that Bitcoin will probably be used for large transactions. I think that may happen; that the block chain will still have 10 minutes transaction times and relatively few large transactions. And then a layer on top of Bitcoin will handle the fast and smaller transactions with payment channel servers or something similar.

So what we may have in the future are million dollar transactions on the block chain. And the large number of ordinary transactions handled on a layer above Bitcoin.

A distributed system of payment channel servers could have the servers compete with each other in terms of prepayment fees. If there are too few servers and they have large fees in a cartel-like setup, new servers would quickly be added by other people around the world with lower fees. That will make the distributed system self-stabilizing and optimizing in terms of fees (costs for users). And the fees incentive would make sure that there will be enough servers to run the network. If the fees become too low, then many servers will be shut down, but many big merchants will make sure there are enough servers because their business depends on the system.

The fast off-chain transactions can then be done with zero transaction fees, since the fees have already been prepayed. This means minimal friction for the fast transactions all the way down to micropayments. Spam transactions would cost money due to the prepayment fees and will therefore be limited. If the fees go down to zero, then spam transactions would still be unproblematic since the system can handle a massive number of transactions per second. The fees also have a lower limit dependent on ordinary bitcoin transactions since the payment channel servers need to make bitcoin transactions to the block chain, and those ordinary transactions will likely have fees even in the future.

The distributed payment channel system allows both senders and recipients to interact in a full many-to-many way without the need for special payment channel servers for specific services. A customer paying at Starbucks, McDonald's and on an online gambling site can use the same single system.

To use the system the user only needs to prepay an amount of bitcoins to the system as a whole. An algorithm can automatically pick the server with the lowest fee. And the server will receive the fee gradually by performing transactions for the system as a whole and not only for that particular user.

The system needs to be trustless to prevent fraud servers to be able to steal bitcoins from people.