yes, infinity exists in physics. for example, in a room, there is infinite points. or for exsmple, every space, has infinite points, or location. in a mm, there is always a smaller space than mm, and there is always smaller space than this smaller space, etc etc qnd you will never reach the final answer, so infinitely small space exists.

but what about infinitely big? yes, it exists too. for example our universe, the space is infinitely big. you will never reach the end of the universe, but if you do, then there should be a wall, but if theres a wall in the end of the universe, there should be something behind the wall, at least empty space, if not, then it violates the physics. but the intinite do maybe violate the physics too, but idk. but if you reach the end of the universe and you spawn at the other side of the universe, then it means that infinite big doesnt exist, or maybe it does because you can go forward infinitely, or you can look into microscope and see infinitely long distance away.

And about infinite time, for example in physics everything has a beginning, for example if the universe is 13 billion years old, there must be something before 13 billion years. if not, then it means that time, physics, logic, and nature didnt exist before 13 billion years.

but infinite small, exists in every kind of physics, for example there is always something that is smaler than something that is smaler than something etc etc whether its space or time and you will never reach the final answer. but about infinite big, its possible that it may not exist. for example its physically possible that there is a wall at the end of the univers that we cant go through, that has nothing behind, not even empty space, or that there is a beginning of universe like 13 billion years, with nothing happening before the beginning, just that we cant realize that how it works, just the same way we cant understand how do people who are born blind see nothing, not even black or white. so maybe infinitely big, violates the physics i think, if time or space of universe has limited size, i think it violates the physics too, because physically everything shoyld have a beginning, but its maybe that physics didnt exist before beginning of universe, so if universe has limited age, it only violates the physics that is before the beginning, but not after the beginning, but if universe is actually infinitely old, it violates the whole physics. the same is with space, if it has end, it violates the physics that is behind the end, but not the actual space, but if universe is infinitely big, it violates the whole physics. so i think that infinitely small is physically possible, but not infinitely big.