Do computers play like top humans? Or different stylistically?
ie - if you were a top player and looking at the moves of an opponent, could you discern if the style was more similar to a top rated human or a top rated computer?
They can also show up when for instance there are multiple checkmates in a position. The computer will choose the one requiring the least number of moves even if it requires deep calculation and perfect play. Humans will just trade off material and go for an easy win.
Now that chess engines have started to use neural networks in move selection the amount of "computer moves" has decreased noticeably.
> if you were a top player and looking at the moves of an opponent, could you discern if the style was more similar to a top rated human or a top rated computer?
With a large enough sample size I believe that top players would be able to tell the difference. But that sample size is much larger than a single game or likely even the ~10 games being played in a tournament.
Edit:
Oh I should also mention that in the context of cheating with computers there are more signals to look at than the moves themselves. Time management is normally a huge giveaway for cheating. In online chess this normally manifests itself as players using the exact same amount of time for each move in spite of the positions being very different in terms of complexity.
In the match being talked about above Hans, the challenger, used a suspicious amount of time during the opening sequence. He played the opening moves in around 10 minutes which is weird because if he had memorized the lines he would have played them much faster. If he didn't memorize the lines then it would have taken him much more than 10 minutes to calculate it all.
To elaborate on this, humans use pattern recognition to identify themes within a position. This is a shortcut that prevents needing to mentally brute-force your way down an enormous tree of possible positions. Elite chess-playing humans are very good at this, but are still very good at spotting potentially non-thematic (perhaps "surprising") moves that offer some quantifiable advantage.
Computers operate very differently from humans. They rigorously evaluate positions to absurd depths. They can examine lines further than 30 moves deep without too much time. Often the moves they come up align with the thematic ideas that humans have (after all, there's a reason why humans have identified these patterns). But at the end of the day, the computer isn't playing thematically. It only cares that the position at the end of best-play by both sides has the score most in its favor.
This leads to computers playing moves that humans would only come up with exceedingly rarely. And if a human came up with that move, there would generally be some clearly-identifiable reward that humans can pick up on several moves later. When a human player plays computer moves, those noticeable rewards are often missing. The cheating human makes a puzzling move, play continues, and many moves later their opponent is worse off. But even after serious analysis it's not entirely clear how that original move brought about this advantageous position.
Of course maybe the human in question really wasn't cheating and stumbled into a brilliancy. Perhaps it's even one they didn't even truly understand the ramifications of when they played it! But when a human makes several of those types of moves in a single game, or even across a single tournament, it brings about extreme suspicion.
[0]: https://en.wikipedia.org/wiki/Unified_Sports_Classification_...
The situation would be more like, there is a forced checkmate in 12 but it involves navigating a sharp position that is complex and any miscalculation could equalize the position.
On the other hand, you can simply exchange queens and rooks and have a clear winning endgame, but it will only result in a checkmate in 20 moves.
Almost any human would opt for the latter to avoid the risk. From the computer's perspective, there is no risk.
So no, I stand by my point that a specific choice of one of multiple possible checkmates is quite a poor indicator of using a computer to calculate moves.
> other than in end-game
This is frequently where such scenarios occur. Many end games are difficult for humans to play with absolute precision, even seemingly simple ones like knight and bishop vs. king. But when there are fewer pieces on the board is exactly when computers are able to perform incredibly deep calculations.
A good example is the notorious 30 move forced mate that Caruana "missed" in game 6 of his world championship match with Magnus, which occurred with only 3 pieces and 3 pawns left on the board.
However, I do look up a post-game analysis, and if there are some mid-game deep checkmates, they show up in it, and it is extremely rare. The example you cite about Caruana/Carlsen game actually quite falls into the category of what I referred to as 'endgame mates' - and looking at it with a potentially cheating player in mind, such cases are rather irrelevant: a cheater will win a game or arrive to an overwhelmingly better position in the endgame so such extreme measures with 30+ precise move checkmates will not be necessary.
That Kf8 really is the move of somebody living in another universe.
Generally, the biggest heuristic for identifying cheating is identifying somebodies moves share statistical similarity to the top moves of common engines (Especially stockfish). This doesn't really work after a single game, but anybody playing the top move of stockfish 90% of the time over 100 games is a cheater. Nobody that isn't cheating can do that. Cheaters are savvy though, they will notice in a position there are maybe 5 decent moves they can choose from, so for just that position they will choose stockfish's 5th choice. Or maybe they'll only check the engine at the most critical moments of the game and turn the engine off and play normally afterwards. Notice that the person being debated in this article is somebody with a history of cheating, the evidence they cheated in this specific game is likely not as good as the evidence they are just generally a cheater.
On top of this more empirical analysis, there's more subjective analysis. Humans tend to try to simplify games when they're ahead to reduce computational complexity, but computers don't do this as it's not a good strategy for a computer. Humans will tend to follow a narrative and follow a general idea throughout a game with ideas they calculated earlier in the game or in their preparation, whereas computers don't care about narratives and will completely switch plans on a dime. In the endgame the computer starts having a LOT of winning moves that it hasn't calculated to the end and can start making very offbeat choices, whereas humans tend to use a set of rote memorised strategies that are known wins. Again though, a skilled cheater realises all this and will choose weaker more human-like moves that are probably the engines 2nd or 3rd choice.
There's also metadata. Cheaters usually take a few seconds to think about a move that a human would make instantly (this came up in the article where it took the cheater 20 seconds to make their first move), they probably exhibit different browser/app interaction habits. Humans have all sorts of particularities about UI interaction and time management. A lot of people play blitz and bullet chess because cheaters struggle to cheat convincingly under time pressure.
At this level, players know all opening lines to some depth. The first move? I don't see how 20 seconds indicate anything other than a passage of time.
Maybe I overemphasized the first move because it was emphasized in the article, in general cheaters use their clock in weird ways throughout the game since for them pretty much any move is similarly complex. In this case the shoe operating cheating device raised the minimum time to make a move, which is a characteristic common to many forms of cheating.
Which would still require a considerable skill. If you can't figure out why a single move is brilliant, you won't be able to find the entire line.
If stockfish tells you the entire line, and the opponent plays something that wasn't included in stockfish's line (because it's worse), you're also going to be at a loss.
The clearest example in modern play is a4 and h4 as white (eg early h4 vs the King's Indian Defense) or a5/h5 as black. These are now frequently played in various positions because since they were discovered a few years back by alphazero, they have been extensively examined and found to be good, but prior to that, no strong human would play them.
It would be very hard to detect a sophisticated cheater solely by examining their moves in a vacuum. They could pick moves that appear to be "human" e.g. moves that appear to be chosen based on the common heuristics that strong human players tend to rely upon, rather than moves based on very deep brute force calculations, where we could never match the strongest chess engines.
The giveaway is usually in the time required for each move. Humans will tend to spend varying amounts of time on each move, with significantly more time spent at critical moments in a game. A computer will pretty much spend the same amount of time for each move. But even here, a sophisticated cheater could disguise this side effect by only using computer assistance at critical moments.
[1] https://wismuth.com/elo/calculator.html#rating1=3546&rating2...
In a nutshell, computers do some things that are very unlikely for humans to do. A lot of the play is similar, but some things are outliers and high level chess players will notice the unusual style and high accuracy moves of a person assisted by a computer.
After the fact, it'd probably be more obvious. Human players will typically avoid unnatural moves that require long sequences of perfect play before they pay off.
But top players are also the best qualified at cheating in a way that wouldn't raise suspicion. Many games are lost or drawn because of small mistakes or inaccuracies during the endgame. And playing a perfect endgame is not implausible at this level.