Being and Becoming · Episode 6 of 10 · 5:38
What changes when you act?
What changed, and what did we learn about before and after?
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Why this question matters · 0:00
To help a system, we may need to change it, rather than only observe it. After an action, knowing where it is now may leave open where it began. Watch what an action changes, what a later reading teaches us, and why these are different steps.
Origin and current state · 0:17
Earlier question trees held the unknown state fixed. Now allow a button press between readings. Ask two separate questions: where did the device begin, and where is it now? Call the beginning its origin. Use the same known rules: RESET sends every configuration to u. PULSE sends u to w and leaves v, w and z unchanged. READ gives the exact current lamp output without changing the state. This nondisturbing reader is an assumption of our example. Start a fresh run with either u or w as the origin.
Run A: observation · 0:50
No reading has arrived yet, and no button has been pressed. The origin and current state are the same in each possible history. Take READ and suppose it returns zero. Only the u history fits that report, because w would give one. No action occurred, so origin and current state are both u. The observer has ruled out a possible history; the model still contains w.
Run B: RESET · 1:23
Begin a separate comparison run from u or w, with no prior reading. Do not carry over the conclusion of Run A. This time, press RESET before taking a reading. RESET is now the executed action in this run. Starting in u, RESET gives current u. Starting in w, RESET also gives current u. Preserve both origin labels. We know the current state from the supplied rule and the executed action, without knowing which origin was present. Now READ returns zero.
Run B: what remains unknown · 1:58
The record, RESET followed by zero, is the same for both origins. The possible histories are origin u to current u, and origin w to current u. Exactly one happened, but the record does not choose which. After this RESET and reading, must the device have started in u? Keep the origin column separate from the current-state column while you decide. No. The current state is u; the origin could have been u or w. RESET made the current states converge. It did not supply a measurement distinguishing their origins.
Run C: PULSE and a new report · 2:42
Start another run, this time from u or v. Execute PULSE. The u origin leads to current w; the v origin leads to current v. These are the possible histories of this run, not two actions on one device. With this declared u-or-v starting set, suppose the exact READ after PULSE reports one. What is the current state, and what was the origin? The current state is w and the origin was u. The other possible history, v to v, would have reported zero. This origin inference depends on starting with only u or v. If the new report were zero instead, the current state would be v and the origin v. A complete plan includes both possible answers, although an actual run receives one of them.
Move then filter · 3:39
For a time-stamped replay, first let READ give zero before PULSE. That earlier zero describes the lamp before the action. After PULSE, current possibilities are w or v. Do not reuse the old zero as if a new reading had just arrived. For a known action, move each current possibility through its transition rule. For a new report, keep the resulting possibilities that match it. Keep an origin tag when the question concerns the past. The current set of possibilities is sometimes called the support.
Target and schedule · 4:17
Compare asking READ before RESET with asking it afterward. Before RESET, the lamp distinguishes the u and w origins. After RESET, both give zero. A plan that identifies the origin must therefore check the permitted timing of observations and actions. If the goal is only to know the current state after RESET, that same plan succeeds. If the goal is to reconstruct the origin, it fails. More constrained research models add other rules; this example establishes the timing distinction under its stated assumptions.
Current known, origin unknown · 4:55
After RESET from u or w, the current state is known to be u. The origin remains u or w. Saying only that we know the state would hide this difference. Some actions bring different current states to the same state. In our RESET run, later readings cannot distinguish the two origins. Our PULSE example showed how an action followed by a reading can instead distinguish the declared u-or-v origins. Every reading here was exact and every transition rule known. Next, keep the transitions fixed but declare a noisy reader. We will ask how a report changes an estimate when it cannot simply eliminate every disagreeing state.