It is usually specified at exactly what block height the update will become the rule and is expected that most nodes must update the software by them.
On bitcoin not that often since we don’t want to. If there is an updated needed that it will be arranged.
Other chains have hard forks all the time like for example Monero that has a hard fork every few months.
Protocol update.
When we talk about the blocks getting bigger say from 1 mB to 2 mB, are the transactions within the blocks getting bigger or just more transactions within the block?
Hi Filip
Has it ever happened/is it possible that 3 blocks join the block chain at the same time fro 3 different miners?
What other reasons or example are forks done beside block size or is it just block size? It was used in the lesson and I saw an article using the same thing.
Theoretically it is possible, not sure if that ever happened though. But the process of solving this would be the same 
There are many reasons why it might happen, the block size change is the most simple one to understand so it is mostly used as an example. Some other protocol update like increasing the mining reward or script update with new OP codes could happen as well
Filip, you state towards the end of this lesson that on must wait for 5 - 6 confirmations to occur otherwise you can lose your money - i thought that the transaction contained within the stale blocks were returned to the mempool to be picked up by another miner. How then can one lose their money??
One could then double spend the unconfirmed transaction by using the same UTXO and set a higher fee to make the transaction get into the block quicker
ooooh very sneaky!!
thanks
Happy to learn 
In the final homework; my answer "Segwit removerd the signature was marked wrong, not that it matters a great deal, but…
@Philip I have a question about the stale blocks.
You said that if my transaction would be put in a stale block the money is gone. But what I understood from Ivan is that the transactions go back in the mempool. (which would not lose your money I guess. I am a little bit confused. Can you explain to me in more detail?
This is not true. The money would be fine, it might also already be confirmed on the other block (in these cases there is no way of knowing really, your tx can be part of both blocks). In either case your funds would be safe, they just might take a bit longer to confirm
Oke thank you for the input 
Hello,
I have a few questions:
What happens to the block reward and tx fee that was given to the miner that has a stale block? Does he give it back or something?
For a soft fork, will the nodes that did not update will do it eventually or they can never update?
Will the blockchain that has a hard fork return to only one chain when all the network updates?
Everytime when is a harfork does a new coin appear? I did not understand very well the connection between harfork and cryptocurrencies.
Thank you!
The reward is just a special transaction called a coinbase and will get dropped just like any other transaction that is part of a stale block.
It kind of depends on the softfork itself and the role of the node. If for example the block size is lowered and the node is a miner it can mine blocks that are larger than the consensus allows. This can be a problem for the miner since his blocks will not get accepted if the majority of nodes updated to the newer version. In a segwit fork this is not the case since the block size remained the same and both miners wold be able to continue mining valid blocks.
Well if a miner continued to mine on the old chain and eventually updated their nodes, all their blocks would become invalid. He would loose all the work he has done, so better update fast 
Not neccessarily, Monero for example has hard forks all the time. It is its method of staying ASIC resistant.
Thank you very much! Can you please explain me the connection between hard forks and new coins that gets formed in one?
Well, two coins get formed when a community gets split in two and keep their common history. Hardforks are placed at a specific block height in the future and at that time the miners that have updated the node run the new version and the old ones stay on the old one thus splitting the chain in two and creating two currencies
