How big will the blockchain core wallet be to download in 2025? To have the full chain on my computer?
First of all, there's no such thing as "blockchain core". There is the Bitcoin blockchain. Bitcoin Core is the most commonly used node software for Bitcoin.
Over the last 30 days, the average block size has been 1.188 MB, let's call it 1.2 MB to make calculations easier. There are about 3.468 million minutes between now and the end of 2025. Assuming blocks every 10 minutes (this is not necessarily a safe assumption because blocks are actually produced faster than that, though I don't know the exact number off the top of my head), there will be ~346800 blocks found between now and then. At 1.2 MB per block, that's an additional 416160 MB of block data, which is 416 GB. According to my node, the blockchain is currently 207 GB (this ignores the indexes, databases, and other data necessary to make a node work with just the raw blocks), so 207 + 416 = 623 GB. Thus by the end of 2025, the Bitcoin blockchain will be around 623 GB in size, assuming no block size increase or decrease.
Why not, since every block is a save point, the way I see it. If people want to become full nodes they only have to start from the last block? the last check point,
What you are proposing is not safe. By starting from the last block (or even just a recent block), new nodes will be unable to verify the entire blockchain and thus they cannot be sure that they are not using some chain produced by an attacker. They now have to trust that the person who gave them their starting point is honest. This is additional trust and reduces the security of such nodes. Furthermore, too recent of a block can result in issues when blocks are reorged, i.e. orphan blocks.
or is there a way to compress this data and if the compress data matches they can download the entire chain in like 1gb.
Because the blockchain contains a large amount of random data, it is not very compressible. Lossless compression algorithms do not perform very will with random data.
What stops someone from making a trillion addresses before they update their chain? won`t there be collisions in the future? How does the bitcoin wallet know if it is not connected that I created trillion^256 addresses before it rolls out? I can make wallets offline right?
No, there won't be. Firstly, addresses aren't registered with the blockchain or anything like that. When you generate an address, you typically don't check whether it has been used before by someone else because the probability of that is so so tiny that it is basically 0. It's practically impossible to accidentally produce two of the same addresses (barring things like bad RNGs).
The number of possible addresses is so large that if you generated a trillion addresses per second it would take you over 38000 years just to have a 50% probability that you have found a collision. Furthermore, you would have generated so many addresses that whatever collided is almost definitely going to be an address that you had generated, not someone elses. The number of addresses is just so unfathomably large that the human mind cannot comprehend such numbers. There are so many possible addresses that a collision is basically impossible.
Additionally, by 2025, everyone will probably be using some other address scheme at that point which allows for even more possible addresses.
edit: I fat-fingered 2022 and not 2025
