Network latency briefly desynchronizes how participants see the same object's state

What it is

You see the lid already closed; the other person is still feeding a part into the open mouth. Nobody’s eyes failed — the state update is still on the wire. Consistency delay leaves participants holding different versions of the same object for a few hundred milliseconds. The window closes, but actions taken inside it (keep feeding, already released, start the next step) commit against the wrong version.

This is a brief fork of object state, not a misalignment of “where is he standing.” People’s positions travel on another link.

Why it happens

Authoritative state lives on a host or in a replication protocol. Locally, for feel, your own action is simulated immediately (optimistic update); theirs waits on a packet. Two pictures result: lid shut on your side, mouth still open on theirs. In physical collaboration, light and sound reach every eye at once; the network splits “the same moment.” People decide on the version in front of them; once the decision is out, reconciliation arrives as a conflict or a baffling jump.

Dead reckoning, interpolation, and state merging can make the fork look smooth. Smooth is not consistent: they may still put something into the mouth you have already closed. If the interface treats a smoothing animation as “both sides already agreed,” people will start the next step before reconciliation finishes.

Studying it

Joint operation under injected delay: 50–300 ms one-way delay and jitter in the lab, two people taking turns or acting together on the same object’s open/close, colour, or pose. Record whether both reports of “current state” agree, and wrong actions issued on a stale state.

Network factors: mean delay, jitter, loss, optimistic update on or off. Behavioural scores: how long the inconsistency lasts, stale-action count, undos after a jump, ratings of “did they not see that.”

“The WLAN feels fast” is not a manipulation. Delay has to be an independent variable, turned up until the fork is overt.

Where it stops holding

Same-room, short-range sync, delay below the action time-constant: the fork is too short to decide inside, and an explicit cue can be skipped. Rarely changing, delay-insensitive state (a room light, a label) is cheap to leave briefly inconsistent. Authority in the cloud, across cities: the fork is the normal case and will not vanish if “the net gets faster.” Object-state agreement does not fix pointing error: if the two coordinates are unaligned, “that mouth” still points at the wrong hole even when both agree the lid is open. Arbitration handles how a conflict ends; it does not erase the fork. Stack them.

Applying it

• For state that triggers the next step (open/close, lock, insert), do not draw it as final until the other side is confirmed. Use an in-syncing look, or an appearance neither side has confirmed.
• Keep optimistic update for the in-between frames of a continuous drag. Wait for the authoritative ack at the commit (drop, tighten, delete).
• If reconciliation will jump, give a perceptible transition and allow undo of the action taken on the stale picture.
• How to check: inject about 200 ms, have A close the lid and B feed a part into the mouth in the same second. B’s part should not vanish or clip through with no cue; they should see that state is not aligned yet. Both think they succeeded and the object is nonsense after reconcile: the fork was treated as truth.

Related

• Same group：N5.10.1 Avatar pose is the main cue to others' intent; without it, collaboration drops · N5.10.2 Simultaneous operation of a shared object needs an explicit control-arbitration rule · N5.10.4 When devices of different capability share a room, the experience must align to the weakest · N5.10.5 Accuracy of pointing in a joint task depends on precise sync of participant positions
• Nearby：N5.05 Shared Space · N5.09 Spatial Anchors and Persistence
• Search terms：consistency delay · optimistic update · state divergence