void Start()
    {
        //Create a World
        Debug.Log("Initialize physics");
        List<CollisionShape> CollisionShapes = new List<CollisionShape>();

        DefaultCollisionConfiguration CollisionConf = new DefaultCollisionConfiguration();
        CollisionDispatcher Dispatcher = new CollisionDispatcher(CollisionConf);

        DbvtBroadphase Broadphase = new DbvtBroadphase();

        DiscreteDynamicsWorld World = new DiscreteDynamicsWorld(Dispatcher, Broadphase, null, CollisionConf);
        World.Gravity = new BulletSharp.Math.Vector3(0, -10, 0);

        // create a few dynamic rigidbodies
        const float mass = 1.0f;
        //Add a single cube
        RigidBody fallRigidBody;
        BoxShape shape = new BoxShape(1f, 1f, 1f);
        BulletSharp.Math.Vector3 localInertia = BulletSharp.Math.Vector3.Zero;
        shape.CalculateLocalInertia(mass, out localInertia);
        RigidBodyConstructionInfo rbInfo = new RigidBodyConstructionInfo(mass, null, shape, localInertia);
        fallRigidBody = new RigidBody(rbInfo);
        rbInfo.Dispose();
        Matrix st = Matrix.Translation(new BulletSharp.Math.Vector3(0f, 10f, 0f));
        fallRigidBody.WorldTransform = st;
        World.AddRigidBody(fallRigidBody);

        //Step the simulation 300 steps
        for (int i = 0; i < 300; i++)
        {
            World.StepSimulation(1f / 60f, 10);

            Matrix trans;
            fallRigidBody.GetWorldTransform(out trans);

            Debug.Log("box height: " + trans.Origin);
        }

        //Clean up.
        World.RemoveRigidBody(fallRigidBody);
        fallRigidBody.Dispose();

        UnityEngine.Debug.Log("ExitPhysics");
        if (World != null)
        {
            //remove/dispose constraints
            int i;
            for (i = World.NumConstraints - 1; i >= 0; i--)
            {
                TypedConstraint constraint = World.GetConstraint(i);
                World.RemoveConstraint(constraint);
                constraint.Dispose();
            }

            //remove the rigidbodies from the dynamics world and delete them
            for (i = World.NumCollisionObjects - 1; i >= 0; i--)
            {
                CollisionObject obj = World.CollisionObjectArray[i];
                RigidBody body = obj as RigidBody;
                if (body != null && body.MotionState != null)
                {
                    body.MotionState.Dispose();
                }
                World.RemoveCollisionObject(obj);
                obj.Dispose();
            }

            //delete collision shapes
            foreach (CollisionShape ss in CollisionShapes)
                ss.Dispose();
            CollisionShapes.Clear();

            World.Dispose();
            Broadphase.Dispose();
            Dispatcher.Dispose();
            CollisionConf.Dispose();
        }

        if (Broadphase != null)
        {
            Broadphase.Dispose();
        }
        if (Dispatcher != null)
        {
            Dispatcher.Dispose();
        }
        if (CollisionConf != null)
        {
            CollisionConf.Dispose();
        }
    }
    //IMPORTANT Time.fixedTime must match the timestep being used here.
    public static List<UnityEngine.Vector3> SimulateBall(BRigidBody ballRb, UnityEngine.Vector3 ballThrowForce, int numberOfSimulationSteps, bool reverseOrder)
    {
        var ballPositions = new List<UnityEngine.Vector3>(numberOfSimulationSteps);

        //Create a World
        Debug.Log("Initialize physics");

        CollisionConfiguration CollisionConf;
        CollisionDispatcher Dispatcher;
        BroadphaseInterface Broadphase;
        CollisionWorld cw;
        SequentialImpulseConstraintSolver Solver;
        BulletSharp.SoftBody.SoftBodyWorldInfo softBodyWorldInfo;

        //This should create a copy of the BPhysicsWorld with the same settings
        BPhysicsWorld bw = BPhysicsWorld.Get();
        bw.CreatePhysicsWorld(out cw, out CollisionConf, out Dispatcher, out Broadphase, out Solver, out softBodyWorldInfo);
        World = (DiscreteDynamicsWorld) cw;

        //Copy all existing rigidbodies in scene
        // IMPORTANT rigidbodies must be added to the offline world in the same order that they are in the source world
        // this is because collisions must be resolved in the same order for the sim to be deterministic
        DiscreteDynamicsWorld sourceWorld = (DiscreteDynamicsWorld) bw.world;
        BulletSharp.RigidBody bulletBallRb = null;
        BulletSharp.Math.Matrix mm = BulletSharp.Math.Matrix.Identity;
        for(int i = 0; i < sourceWorld.NumCollisionObjects; i++)
        {
            CollisionObject co = sourceWorld.CollisionObjectArray[i];
            if (co != null && co.UserObject is BRigidBody)
            {
                BRigidBody rb = (BRigidBody) co.UserObject;
                float mass = rb.isDynamic() ? rb.mass : 0f;
                BCollisionShape existingShape = rb.GetComponent<BCollisionShape>();
                CollisionShape shape = null;
                if (existingShape is BSphereShape)
                {
                    shape = ((BSphereShape)existingShape).CopyCollisionShape();
                }
                else if (existingShape is BBoxShape)
                {
                    shape = ((BBoxShape)existingShape).CopyCollisionShape();
                }

                RigidBody bulletRB = null;
                BulletSharp.Math.Vector3 localInertia = new BulletSharp.Math.Vector3();
                rb.CreateOrConfigureRigidBody(ref bulletRB, ref localInertia, shape, null);
                BulletSharp.Math.Vector3 pos = rb.GetCollisionObject().WorldTransform.Origin;
                BulletSharp.Math.Quaternion rot = rb.GetCollisionObject().WorldTransform.GetOrientation();
                BulletSharp.Math.Matrix.AffineTransformation(1f, ref rot, ref pos, out mm);
                bulletRB.WorldTransform = mm;
                World.AddRigidBody(bulletRB, rb.groupsIBelongTo, rb.collisionMask);
                if (rb == ballRb)
                {
                    bulletBallRb = bulletRB;
                    bulletRB.ApplyCentralImpulse(ballThrowForce.ToBullet());
                }
            }
        }

        //Step the simulation numberOfSimulationSteps times
        for (int i = 0; i < numberOfSimulationSteps; i++)
        {
            int numSteps = World.StepSimulation(1f / 60f, 10, 1f / 60f);
            ballPositions.Add(bulletBallRb.WorldTransform.Origin.ToUnity());
        }

        UnityEngine.Debug.Log("ExitPhysics");
        if (World != null)
        {
            //remove/dispose constraints
            int i;
            for (i = World.NumConstraints - 1; i >= 0; i--)
            {
                TypedConstraint constraint = World.GetConstraint(i);
                World.RemoveConstraint(constraint);
                constraint.Dispose();
            }

            //remove the rigidbodies from the dynamics world and delete them
            for (i = World.NumCollisionObjects - 1; i >= 0; i--)
            {
                CollisionObject obj = World.CollisionObjectArray[i];
                RigidBody body = obj as RigidBody;
                if (body != null && body.MotionState != null)
                {
                    body.MotionState.Dispose();
                }
                World.RemoveCollisionObject(obj);
                obj.Dispose();
            }

            World.Dispose();
            Broadphase.Dispose();
            Dispatcher.Dispose();
            CollisionConf.Dispose();
        }

        if (Broadphase != null)
        {
            Broadphase.Dispose();
        }
        if (Dispatcher != null)
        {
            Dispatcher.Dispose();
        }
        if (CollisionConf != null)
        {
            CollisionConf.Dispose();
        }

        return ballPositions;
    }