Was Crocodile stronger at Marineford? Or was he holding back in Alabasta?

 During the Alabasta arc, Crocodile displayed a level of power that was initially considered overwhelming by the Straw Hat Pirates. He possessed the Logia-type Devil Fruit called the Suna Suna no Mi (Sand-Sand Fruit), which granted him the ability to control and transform into sand. He had a reputation as a Shichibukai and controlled the desert kingdom of Alabasta from the shadows. His strength was showcased through his battles with Luffy and others. At Marineford, Crocodile was present as part of the war that took place at Marine Headquarters. While he did participate in the battle, he didn't display the same level of dominance as some other powerful characters present. This has led fans to speculate that he might not have been as strong as initially portrayed in Alabasta. It's important to note that power scaling and character abilities can be subject to interpretation and development by the author. Oda often keeps details deliberately open-ended to keep the story intriguing.

scientists who predicted time travel possibility

 Many scientists and philosophers have speculated about the possibility of time travel throughout history. Some of the more well-known scientists who have proposed ideas about time travel include:

Albert Einstein: Einstein's theory of general relativity, which describes the way that gravity works, suggests the possibility of time dilation, or the idea that time can appear to pass at different rates for different observers. This has led some to speculate about the possibility of time travel, although Einstein himself did not believe that it was possible.

Kip Thorne: Thorne is a physicist who has studied the possibility of time travel through the use of hypothetical objects called wormholes. A wormhole is a theoretical passage through space-time that could potentially be used to travel through time. Thorne has proposed the idea that it might be possible to manipulate a wormhole in such a way as to allow for time travel, although this remains purely theoretical.

Michio Kaku: Kaku is a theoretical physicist who has written extensively about the possibility of time travel. He has proposed the idea that it might be possible to travel through time using advanced technologies or by manipulating black holes. However, these ideas are purely theoretical and have not been proven to be feasible.

Overall, while many scientists have proposed ideas about the possibility of time travel, there is currently no scientific evidence to suggest that it is possible. The concept of time travel remains purely theoretical at this time.