# Relativity of simultaneity in observing the best confirmed double-spend in a COO-less Tangle

How is the 'Relativity of simultaneity' in observing the best confirmed double-spend in a COO-less Tangle resolved?

For example, in answering this question, it was answered that the double-spend "which is directly and indirectly referenced by more transactions (i.e. has a larger cumulative weight) will most probably get confirmed."

However, the problem remains that in a COO-less Tangle, the position of the observer also plays a role in determining which spend has a larger cumulative weight.

In one node the transaction T1 might be decided to take precedence. In another node, at the same time, T2 might be decided to take precedence. On top of that, a few moments later, each node might still come to a different conclusion.

So for the understanding of participants, where a dispute could occur as to what the state of the network is, how is the problem introduced by 'Relativity of simultaneity' solved?

• Basically, you are asking how a double spend is resolved ? no ? Dec 20, 2018 at 22:13
• Suggestion: reformulate your question to make it easier to understand. The term "relativity of simultaneity" is unclear. Also the term "selected" is paragraph 2 is unclear. Dec 21, 2018 at 8:02
• The Coordinator's "relativity of simultaneity" = double-spend DoS Attacks Jan 10, 2019 at 10:21

The time to propagate a transaction through gossip is orders of magnitude smaller that the time required to accumulate a significant cumulative weight (so that it start to be relevant to look at the confirmation confidence).

Therefore the information-delta (i.e. the difference between the Tangle from node A and Tangle from B) is negligible when computing confirmation confidence.

To convince yourself, just send a transaction, measure the time it takes to be visible on thetangle.org, and measure the time it take to have a significant amount approvers.

In other word, your following assumption:

In one node the transaction T1 might be decided to take precedence. In another node, at the same time, T2 might be decided to take precedence. On top of that, a few moments later, each node might still come to a different conclusion.

can be truth for very young transactions, but as soon as a transaction start to accumulate significant weight (i.e. confirmation confidence >> 50%) : the confirmation confidence on node A and node B will converge.

To answer your question: "the 'Relativity of simultaneity' in observing the best confirmed double-spend" don't need to be resolved, because it is not a problem.