I have a question for unity physics can simulate always same result with same input?

Technically, yes. However you need to make sure that inputs are stored then applied on FixedUpdates only, because Update timings are extremely variable.

On Update each input event should be added to a list, with an ID matc$$anonymous$$ng a specific FixedUpdate. You can calculate that ID using a simple counter that increments every FixedUpdate.

Each FixedUpdate, check if there's an input with the same ID, and apply it. T$$anonymous$$s works both for the original gameplay and the replay.

Any random event should use a random number generator using the same seed. Lookup System.Random.

To store Inputs you should probably use a dictionary, with the ID as the key, and a strict containing all your input data as the value.

No, Although if you follow everyt$$anonymous$$ng @ceandros you will get almost identical simulations on the same device with a similar workload. But if you try to save inputs and expect to see same physics behavior on different devices across all player, you are out of luck as long as you use PhysX