Why is Bitcoin transaction not reversible

[pooya87]

Bitcoin was invented to solve problems that existed in the existing payment systems. One of the issues Bitcoin addresses is reversibility of transactions. Take the traditional payment systems: banks, credit cards, PayPal, ... one of the issues the "merchants" have faced for years (specially with things like PayPal) has been getting ripped off by their customers. Just search how many complaints have existed over the years by PayPal users (receivers/merchants) who got their transactions reversed.

Bitcoin was created to give merchants that reliable option to be able to receive a payment and be sure it won't be reversed.

However, once a transaction is broadcast and confirmed on the Bitcoin network, they cannot reverse it.

It's more accurate to say when the transaction is confirmed (is included in a block) then it becomes very difficult to reverse it since it requires a massive computing power to re-produce the same block and build on top of it to get the longest chain.
After that with each confirmation (as the chain grows and that tx goes deeper) it becomes exponentially more difficult to reverse it.

[bitbollo]

...
This is why most wait five or more confirmation
Because it gets more expensive as the confirmation increases for a reorg.

No way...You can easily trust bitcoin transaction after 1 confirmation!
I would never expect to wait 5 confirmations like early times for confirming a transaction with some one... no valid reason at all, once confirmed is confirmed.
This is not only me but also any kind of service has not this kind of request. Would you expect that some one would try to make a 51% attack for stealing a dozen of bucks and reverse a payment?
Definetely not possible... this was an issue of the past (like early times on 2013-2014) suggested for avoid forks - not use the longest chain...

[Ambatman]

...
This is why most wait five or more confirmation
Because it gets more expensive as the confirmation increases for a reorg.

No way...You can easily trust bitcoin transaction after 1 confirmation!

Rare but Natural reorganization occurs if a competing chain becomes the accepted chain.
The transaction In the old block would leave the blockchain.
Let's say
The latest Block is block 10
Miner A and Miner B both found Block 11A and Block 11B respectively at almost similar time
Different part of the network receives different version first
During that period some node would think Block 11A while others Block11B
Now if another or Block 12 is found on Block 11B
It becomes the longest chain or better still one with the most work.
While Block 11A becomes an orphan block

I would never expect to wait 5 confirmations like early times for confirming a transaction with some one... no valid reason at all, once confirmed is confirmed.
This is not only me but also any kind of service has not this kind of request.

Excahnges and some other platform wait for at least three confirmation.

Would you expect that some one would try to make a 51% attack for stealing a dozen of bucks and reverse a payment?

51% attack isn't the only way Reorg occurs

[SilverCryptoBullet]

Bitcoin was invented to solve problems that existed in the existing payment systems. One of the issues Bitcoin addresses is reversibility of transactions. Take the traditional payment systems: banks, credit cards, PayPal, ... one of the issues the "merchants" have faced for years (specially with things like PayPal) has been getting ripped off by their customers. Just search how many complaints have existed over the years by PayPal users (receivers/merchants) who got their transactions reversed.

Bitcoin was created to give merchants that reliable option to be able to receive a payment and be sure it won't be reversed.

They only need to wait for 1 confirmation to avoid double spend and if want more certainty they can wait for 2 confirmations for avoiding reorg. After that, transactions can be considered as laid solidly on Bitcoin blockchain and the trade between two people, customer and a merchant can be finalized for most transactions.

Except can be for transactions with big values, then 6 confirmations can be a higher standard.

https://jlopp.github.io/bitcoin-confirmation-risk-calculator/
The standard for high value payments is to wait for 6 confirmations, but it's not that simple!

Would you expect that some one would try to make a 51% attack for stealing a dozen of bucks and reverse a payment?

51% attack isn't the only way Reorg occurs

it seems 51% attacks and reorgs are different (likely in purposes). Years ago there was a reorg event on Bitcoin blockchain and Andreas Antonopoulos had a livestream about that.

Likely not this video, I remember it was a shorter one.
Cryptocurrency Explained: Understanding "Double-spend", Block Re-Organization, & Consensus [Bitcoin]

[Franklyn-wood]

...
This is why most wait five or more confirmation
Because it gets more expensive as the confirmation increases for a reorg.

No way...You can easily trust bitcoin transaction after 1 confirmation!
I would never expect to wait 5 confirmations like early times for confirming a transaction with some one... no valid reason at all, once confirmed is confirmed.
This is not only me but also any kind of service has not this kind of request. Would you expect that some one would try to make a 51% attack for stealing a dozen of bucks and reverse a payment?
Definetely not possible... this was an issue of the past (like early times on 2013-2014) suggested for avoid forks - not use the longest chain...

The higher the transaction the higher the security needed to mine new cryptocurrency transactions successfully just like our local currency. The processing time is always different due to the amount processed, it takes about 8 to 10 minutes per block, it's not only about the confirmation but also the time used in processing it matters.
There is no way Bitcoin can be reversed when you send it, because not middle man or agents to monitor it obeys commands giving to it.

[Hardyrobust]

What you said is correct OP. Anyone not been able to reverse transaction after they have being initiated is of great advantage to bitcoin. With this feature it is impossible to scam someone, the sender of the bitcoin and the receiver is being protected.
While initiating a transaction, we need to be careful by checking the network and wallet address if it is correct. Any form of mistake is not reversible once transaction has been initiated and this will result to lost of money, the funny part is there is no customer care that will be contacted if there is a mistake.
It is always advisable for newbies not to start with initiating a transaction that involves big amounts rather they can start with a smaller amount as a kind of learning. While doing this , the transaction fee may be high but it is far better than losing ones entire bitcoin to the wrong wallet address.

[Awaklara]

What you said is correct OP. Anyone not been able to reverse transaction after they have being initiated is of great advantage to bitcoin. With this feature it is impossible to scam someone, the sender of the bitcoin and the receiver is being protected.

I don't know how scammers use schemes like that if it can even be done. Simply put, if you're selling something, you won't hand over your item to the buyer before the money is in your hands. If the transaction is still waiting for confirmation, just wait. There's no reason to give away your item before the transaction is successful. 
It's important for anyone to double-check the recipient's address before deciding to send your Bitcoin, whether it's from scanning a code or copying and pasting the address that was sent to you.

[bitbollo]

Orphan blocks...
...
Excahnges and some other platform wait for at least three confirmation.

I have never seen a single service that require more than 1 confirmation since a couple of halving and maybe in 2014 this was a plausible request.
Now what service requires to wait so much time for deposit?
After 1 confirmation you have no doubts, avoid strange texts about "block reorganization" or "orphan blocks" there isn't a risk that after 1. Why I should wait 2 confirmations (or for 3!) did you really think an "hacker" could reverse a payment?
Bitcoin is the most secure form of the payment and after 1 confirmation you haven't any more doubt about proof of ownership of these coins/UTXO.

[Z-tight]

The higher the transaction the higher the security needed to mine new cryptocurrency transactions successfully just like our local currency.

I am having a hard time making sense of what you mean here, all BTC transactions are mined in the same way, irrespective of the amount that is involved. However, miners prioritize tx's paying more in tx fees, so if the network is congested, a tx that pays more would likely get into a block and be confirmed quicker than one that pays less.

The processing time is always different due to the amount processed, it takes about 8 to 10 minutes per block,

This isn't true in the BTC network, tx's only get priority from miners based on tx fees, not the amount involved in the tx.
It takes about 10 minutes on average to mine a BTC block.

[hd49728]

The higher the transaction the higher the security needed to mine new cryptocurrency transactions successfully just like our local currency. The processing time is always different due to the amount processed, it takes about 8 to 10 minutes per block, it's not only about the confirmation but also the time used in processing it matters.

When you write a post like this, it only shows you did not understand about Bitcoin blockchain, mining process as well as transaction confirmation process.

With Bitcoin blockchain, your transaction time (from broadcasting to having first one confirmation) depends on some main things: network hash rate (that gives computational power), blockchain difficulty, mempool status, and your transaction fee like whether fee rate is on tip of mempools and transaction fee is bigger than other transactions with same fee rate.

Bitcoin blocks are found in about 10 minutes, that is average block time, sometimes longer sometimes shorter time than 10 minutes but it does not depend on "amount processed" - that I guess you implied about either your transaction value or total pending transactions in Bitcoin mempools. I think you are talking about the first case (your transaction value) but both cases are not correct.

[Ambatman]

I have never seen a single service that require more than 1 confirmation since a couple of halving and maybe in 2014 this was a plausible request.
Now what service requires to wait so much time for deposit?

This was updated as at May this year was previously five confirmation if I'm not mistaken some years ago.


This is binance
If one confirmation is so safe they wouldn't place withdrawable after two confirmations.
I have personally used a mixer that required up-to two confirmation.

After 1 confirmation you have no doubts, avoid strange texts about "block reorganization" or "orphan blocks" there isn't a risk that after 1. Why I should wait 2 confirmations (or for 3!) did you really think an "hacker" could reverse a payment?

I never said Hacker and I stated it was a natural occurrence those occur rarely
Due to network propagation delay.

Bitcoin is the most secure form of the payment and after 1 confirmation you haven't any more doubt about proof of ownership of these coins/UTXO.

I never called it insecure.

[pooya87]

They only need to wait for 1 confirmation to avoid double spend and if want more certainty they can wait for 2 confirmations for avoiding reorg. After that, transactions can be considered as laid solidly on Bitcoin blockchain and the trade between two people, customer and a merchant can be finalized for most transactions.

Except can be for transactions with big values, then 6 confirmations can be a higher standard.

When considering how many confirmation one should require, there are a couple of things to consider.
Obviously the value of the transaction is an important factor. You should prefer higher number for higher values.

If there is some sort of network disruption (during forks for instance. We had some situation during 2017) where the chance of reorgs rise, then you should seek higher number of confirmation to be on the safe side.

The way you check the number of confirmation is important too. A full node is the most reliable way to figure out reorgs. If you are on a SPV client then depending on the implementation, you will be at a higher risk therefore a higher number of confirmation is required.

[Cookdata]

The higher the transaction the higher the security needed to mine new cryptocurrency transactions successfully just like our local currency. The processing time is always different due to the amount processed, it takes about 8 to 10 minutes per block, it's not only about the confirmation but also the time used in processing it matters.
There is no way Bitcoin can be reversed when you send it, because not middle man or agents to monitor it obeys commands giving to it.

At first, I thought you know what you wrote and after going through everything, I find out that you know how to write only jargons. What is the higher the transaction the higher the security to mine new transaction doing in your statement? If you are talking about mining difficulty, it has nothing to do with number of transactions but how the hashrate and the miners. If the hashrate increases, expect the difficulty to increase but not instantly, till it reach the next adjustment

Also it does not necessary that all blocks will be 10 minutes apart, there are some blocks that takes more than 10 minutes. This week, I sent a transaction that took almost 50 minutes despite paying best fee for consider but the average is 10 minutes at most blockwls.

Please do some research, so you don't get signature ban, it's for your own good.

[CryptopreneurBrainboss]

This gives consumers full confidence over their money, but it also means they must be careful to verify addresses and transactions payments before sending bitcoin.

Just imagine Bitcoin transaction being reversible like fiat currency, then will you trust the Bitcoin network, imagine how abusive scammers would have used such a feature and you should know that for any currency to have a reverse button it means there is a centralized panel  that operates the currency and which defeat the whole purpose of decentralization. Bitcoin being reversible means there is nothing we are standing on as what brought us together as an industry was because of Bitcoin decentralization and then the price benefits are a secondary reason. Bitcoin was built on trust and trust comes only when people believe that something can only go a certain way and as for Bitcoin that's it being different from other currencies that depend on the government for operation.