3. Can a user add someones wallet address to the network without his knowledge? What I meant is that must the sender and receiver be authenticated before transaction? It would be better if there is a scenario that an organisation can pay her thousands of staff through LN without involving the staff in the network(since there might not be a time that the staff will send money to the organisation)Like, campaign managers paying users here through Lightening Network opened and closed from their end. I don't know if someone understands me.
Aside from the payment invoices, there are also keysend payments. You can receive such a payment only if you are running your own node. A keysend payment requires only the amount and the destination node id. Payment invoices include more information like: hash of the payment preimage, description, routing hints etc.. So, keysend payments are basically spontaneous payments.
4. Since the blockchain only records transaction at opening and closing a channel, will it be nice to have a mechanism that mirrors the transaction in the LN to the blockchain for on blockchain record keeping and security even when they are not charged transactions fees?
That's what commitment transactions are for. They can enforce the current state of the channel on the first layer. They are actually quite complicated, so I am not going to explain them here in detail, but there is one important thing that you need to know. See the answer below.
2. Can the LN be used as a store of value? Which means that I can transfer some amount of btc there and leave it for a long time for saving purposes? If yes, any security risk?
There is a risk that the other party might attempt to close the channel with an outdated commitment transaction while you are offline. Once such transaction is confirmed, you have a certain amount of time (usually 144 blocks/~1 day) to broadcast a penalty transaction which sends all of the coins from the channel to your address. If you don't come back online in time, you can lose all or most of your coins.
To mitigate this attack, you could
set up a watchtower. If you were using a mobile wallet, you would very likely have 2016 blocks/~2 weeks to broadcast the penalty transaction.
5. Can someone explain to me that LN is not centralization in decentralization?
Some people complain that users are more likely to open channels with large HUBs rather than small nodes to avoid routing problems. The thing is that there might be thousands of large nodes in the future.
6. The increase in the adoption of LN will invariably reduce the reward of the miners, Will this not amount to further increase in the on blockchain transaction fees?
I don't think so. You still have to pay a transaction fee to open and close a channel. Also, keep in mind that the Lightning Network was designed for micro-payments which would not be economically viable on the first layer, especially when the transaction fees spike for some reason. Still, you can send fairly large payment over the Lightning Network. Payments can be split into smaller chunks and routed through different channels. My node routed quite a few 900k satoshi payments through a single channel.
7. In the off chain transaction, is it that there is a very low transaction fee or there isn't a transaction fee at all. If the former holds true, are there node operators in LN, if yes, how sufficient is their reward.
Most LN node operators, including me, operate at a loss. I am running my own node to support the network and I am not really looking for profit. Earnings from payment routing are a nice bonus since I would keep my channels open for my own use anyway.
9. Is there a demo version to try out the LN without using real btc in other to get acquainted with the process.
If you have an Android phone then you can download
Eclair Mobile Testnet. You can get some testnet coins from a random faucet. Alternatively, download
BlueWallet, create a Lightning Wallet and post here a payment invoice for 500 satoshi. I will pay it and show you some services where you could spend those coins.
