Just how did Thanos recognize Tony Stark in Avengers: Infinity War, and does it actually set up a plot for the as-yet-untitled Avengers 4? There's a sense in which this was the strangest scene in Infinity War. Thanos, the Mad Titan, caught a glimpse of Tony Stark's face, and recognized him at once. "Stark," he snarled. When Stark expressed surprise at being recognized, Thanos responded that he isn't "the only one cursed with knowledge."

Tony Stark has lived in fear of Thanos for the last six years. In The Avengers, Stark caught a glimpse of an alien armada when he flew through a wormhole, and although that fleet was destroyed, he's always been convinced another alien invasion is inevitable. Thanos seems to know this, recognizing that Stark is "cursed with knowledge" of the Mad Titan's eventual return. But Thanos' words imply a strong parallel between the two of them, as though each carries specific knowledge related to the other - knowledge that is a curse.

Related: One Thing Infinity War's Writers Wish They Could Change

Infinity War goes to great lengths to create some subtle parallels between Thanos and Tony Stark, but this is where they get explicit. No doubt the purpose of this scene was really to emphasize the personal conflict between Thanos and Stark. As Joe Russo explained, Thanos has "the most specific connection to Tony because Tony is a futurist, and he has predicted a threat like Thanos." In exactly the same way, Thanos fancies himself a futurist, and he has predicted a catastrophe that would destroy all life in the universe. Stark created Ultron out of his fear, and Thanos launched his insane quest to erase half the life in the universe in order to save the rest.

But this scene goes beyond that, and suggests a very personal enmity between the two. Just what is really going on?

Does Thanos Recognize Tony Stark From The Battle of New York?

The first possibility is simply that Thanos is a master of the Art of War. As Sun Tzu noted on Earth, "Know your enemy and know yourself, find naught in fear for 100 battles." Thanos has no doubt triumphed in far more than a hundred battles, and that's probably not just because he believes in overwhelming force. Rather, as a master tactician, he's likely a firm believer in researching his enemies in order to defeat them.

Humanity proved itself unexpected resilient back in 2012, when the Avengers successfully defeated the invading legions of the Chitauri. And Tony Stark delivered the critical nuclear warhead personally, destroying the Chitauri mothership before returning to Earth through the wormhole. If Thanos has researched anybody on Earth, it's Tony Stark, the man who caused so much damage to his armies.

On the face of it, this seems like a satisfying explanation. But there are two major problems with the theory. The first is the fact that Thanos only recognizes Stark when the distinctive Iron Man helmet is damaged, and he sees Stark's face. Had this simply been an example of Thanos's research, he would no doubt have recognized an Iron Man armor. What's more, this doesn't explain why Thanos would view this kind of knowledge as a "curse." The scene really does feel as though something else is going on.

Related: Infinity War’s Thanos Isn't Really Marvel’s Thanos

Does This Knowledge Come From The Soul Stone?

A second possibility is that Thanos knows Stark because of the Soul Stone. In theory, the Soul Stone could give the Mad Titan the ability to examine the soul of anyone he encounter - to peer into their hearts and minds and examine their motives. This would explain why he seems aware of the depth of Stark's "cursed knowledge." Some fans have suggested an extension of this theory, in order to explain why Thanos believes the Soul Stone to be, in part, a curse. They suggest that the Soul Stone actually grants Thanos the ability to see into the hearts of people he kills, granting him an empathy that - up until acquiring the Soul Stone - he lacked. That would be a neat explanation of why Thanos seemed more hesitant to kill during his battle with the Avengers on Earth; he actually experiences their thoughts and emotions, their desperation and pain.

This is a fascinating concept, but it's not actually alluded to in the film itself. The rest of the Infinity Stones shine at the moment Thanos uses them, but there's no telltale glow around the Soul Stone at the moment Thanos says this. So, if Thanos' knowledge of Tony Stark doesn't come from the Soul Stone, where else could it come from?

Page 2: Are We Seeing the Ripples of Time-Travel?

Are We Seeing the Ripples of Time-Travel?

Neither of these theories really feels satisfactory. The first doesn't explain Thanos's specific dialogue, in which he suggests he is "cursed with knowledge." The second, while more complex, doesn't really have any supporting evidence - not even a glow around the Soul Stone. So neither of these explanations quite fits the facts.

There is another possibility, though. What if Thanos has actually met Tony Stark before? There's strong evidence that Avengers 4 explores the idea of time-travel, with the surviving Avengers traveling back to the past. As such, it's entirely possible that Thanos could have met a future Tony Stark. That would fit with the snarl of fury in Thanos's voice when he recognizes Stark's face. Meanwhile, it would also explain why Thanos didn't recognize Tony in his armor; none of the set photos suggesting time-travel have actually featured Tony in the Iron Man suit. Going one step further, this may well explain why Thanos snarls, "I hope they remember you." Perhaps he already knows when Stark will finally die - because he's seen it happen?

Related: A Complete History Of The Marvel Cinematic Universe

The fundamental problem with this theory, though, is it doesn't quite match up with the MCU's model of temporal physics. So far, all evidence seems to suggest that traveling to the past creates a new timeline. So, for example, let's say that Ant-Man travels to the Battle of New York, and takes the Mind Stone - that would create a new timeline, one in which the Mind Stone disappears, Wanda and Pietro Maximoff are never granted their powers, and neither Ultron nor Vision is ever created. If the MCU stays true to the comics, though, there's strong evidence the time-traveler could still return to their own timeline; that was proven in the classic X-Men story Days of Future Past. Assuming Marvel aims to use a consistent model of temporal physics, any encounter between Stark and Thanos should create another branch in the timeline.

But it's important to remember that the MCU - like the comics - doesn't exactly handle its pseudo-science in a consistent manner. Just look at the Pym Particles: does a person retain their mass when they shrink, or not? Some scenes suggest they do, with Ant-Man cracking a paving stone when he drops to the ground. Others suggest they don't, with Hank Pym carrying a tank on his key-chain or wheeling a shrunken building away. The MCU is scientifically consistent, right up until the moment it isn't. There's no reason to assume Marvel would take a different approach with time-travel.

Ultimately, we still don't know how Thanos knew Tony Stark. Avengers: Infinity War doesn't explain that single line of dialogue, and frankly every single theory has major issues. The time-travel theory at least fits with the little we know of Avengers 4, but it still raises some disturbing paradoxes. Whatever the truth may be, hopefully it will be revealed in next year's sequel.

More: The MCU Made Up For Its Poor CGI With Thanos

Key Release Dates