Adding gravity to my gameobject causes lagg

I got a problem. When i add gravity to my prefab and click on play, everything gets slowed down.

The gameobjects won't fall in a normal way. ( it seems like they got some kind of delay, they drop down for a second and stops for a second, this repeat itself over and over again. )

The strange part is that this problem will only appear when my map of blocks is 30x30x1 (x,z,y) or higher.

 var block : GameObject;
 
 //Change to adjust the lenght = x and z
 var worldWidth : uint  = 30; 
 var worldHeight : uint  = 30;
 
 function Start () {
  
 CreateWorld();
   
 }
   
 function Update () {
 }
  
 function CreateWorld() {
    
     //Space between each block (x)
         for(var x : uint =0; x<worldWidth; x+=1) {
        
        
      //Space between each block (z)
          for(var z : uint =0; z<worldHeight; z+=1) {
          
  
          
           var block = Instantiate(block);
           block.transform.position = new Vector3(this.transform.position.x + x, this.transform.position.y, this.transform.position.z + z);
    
          
          
           }       
           }    
           }

This is the script i use, its Javascript.

Can someone please explain why it laggs so badly. Is it my script? has it to be in C#? I want to use it to make a floor out of cubes, those cubes will fall down when triggered by the player.

I hope you can help me

• Kind regards, Hexer