Answers.Body: <p>Peruse <a href="https://wismuth.com/chess/longest-game.html" rel="nofollow noreferrer">this link</a>. Also see link for possible duplicate.</p>
  <p>Sum-up of first link:</p>
  <ul>
  <li>Longest game under FIDE rules: 8848.5 (Fabel)</li>
  <li>Maximum mobility number: 218 moves</li>
  <li>Shannon's number, assuming 40 (full) moves, 30 moves per ply, ignoring FIDE rules and duplicates: 10^120</li>
  <li>Upper bound: 10^34082</li>
  <li>Realistic lower bound (Monte Carlo): 10^29241</li>
  </ul>
  
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Answers.CreationDate: 2024-02-29T08:04:50.803Z
Answers.Text: Noted, with thanks. Your attached link is very helpful.
Answers.UserDisplayName: anti - Marshall
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Answers.CreationDate: 2024-02-29T08:21:46.020Z
Answers.Text: Also Shannon's number is an estimate of the number of positions possible after 40 ply or 40 moves?
Answers.UserDisplayName: anti - Marshall
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Answers.CreationDate: 2024-02-29T19:27:45.327Z
Answers.Text: I doubt that there are that many positions taking longer than either (although the retro genre knows many exceptions - but I bet they are rare).
Answers.UserDisplayName: Hauke Reddmann
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Answers.CreationDate: 2024-03-01T05:20:56.290Z
Answers.Text: The answer might be better if it at least summarized the link's estimate on the answer to the question. Links can disappear.
Answers.UserDisplayName: D M
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Answers.CreationDate: 2024-03-02T03:25:53.540Z
Answers.Text: The gap between the upper bound and lower bound is HUGE.
Answers.UserDisplayName: Zuriel
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Answers.CreationDate: 2024-03-02T18:22:27.820Z
Answers.Text: @Zuriel: Not for a professional mathematician - the gap between Ramseys upper bound and the actual value (whatever exact problem my remark references to - I am no professional mathematician) - THAT is huge :-)
Answers.UserDisplayName: Hauke Reddmann
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Body: <p>I have heard of Shannon's number (10^120) which is the supposed number of possible chess games computed in the 1950s. But Shannon's estimate is criticised for including illegal moves.
  What is a truer estimate under the given parameter</p>
  <ol>
  <li>no illegal positions</li>
  <li>FIDE rules of 3 fold rep and 50 moves are in force</li>
  <li>we start from the regular starting position</li>
  </ol>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2024-02-29T07:38:12.457Z
Comments.Text: Duplicate? https://chess.stackexchange.com/questions/8331/is-the-number-of-possible-chess-games-infinite?rq=1
Comments.UserDisplayName: Hauke Reddmann
Tags: <computer-chess><mathematics><game-complexity>
Title: More accurate estimate of chess games possible
ThreadText: # More accurate estimate of chess games possible
  
  (Asked by: username_0 on 2024-02-29)
  
  I have heard of Shannon's number (10^120) which is the supposed number of possible chess games computed in the 1950s. But Shannon's estimate is criticised for including illegal moves.
  What is a truer estimate under the given parameter
  
  1. no illegal positions
  2. FIDE rules of 3 fold rep and 50 moves are in force
  3. we start from the regular starting position
  
  **Tags:** computer-chess, mathematics, game-complexity
  
  > **Comments:**
  > **username_1**: Duplicate? https://chess.stackexchange.com/questions/8331/is-the-number-of-possible-chess-games-infinite?rq=1  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_1 on 2024-02-29. Score: 3 | Accepted answer
  
  Peruse [this link](https://wismuth.com/chess/longest-game.html). Also see link for possible duplicate.
  
  Sum-up of first link:
  
  * Longest game under FIDE rules: 8848.5 (Fabel)
  * Maximum mobility number: 218 moves
  * Shannon's number, assuming 40 (full) moves, 30 moves per ply, ignoring FIDE rules and duplicates: 10^120
  * Upper bound: 10^34082
  * Realistic lower bound (Monte Carlo): 10^29241
  
  > **Comments:**
  > **username_0**: Noted, with thanks. Your attached link is very helpful.  
  > **username_0**: Also Shannon's number is an estimate of the number of positions possible after 40 ply or 40 moves?  
  > **username_1**: I doubt that there are that many positions taking longer than either (although the retro genre knows many exceptions - but I bet they are rare).  
  > **username_2**: The answer might be better if it at least summarized the link's estimate on the answer to the question. Links can disappear.  
  > **username_3**: The gap between the upper bound and lower bound is HUGE.  
  > **username_1**: @username_3: Not for a professional mathematician - the gap between Ramseys upper bound and the actual value (whatever exact problem my remark references to - I am no professional mathematician) - THAT is huge :-)  
  
  ---
  
  