diff --git a/sources/reactphysics3d/engine/DynamicEngine.cpp b/sources/reactphysics3d/engine/DynamicEngine.cpp
index 20a13313..ff2238d5 100644
--- a/sources/reactphysics3d/engine/DynamicEngine.cpp
+++ b/sources/reactphysics3d/engine/DynamicEngine.cpp
@@ -24,9 +24,13 @@
 using namespace reactphysics3d;
 
 // Constructor
-DynamicEngine::DynamicEngine(DynamicWorld& world, const Time& timeStep)
+DynamicEngine::DynamicEngine(DynamicWorld* world, const Time& timeStep)
               :PhysicsEngine(world, timeStep) {
-
+    // Check if the pointer to the world is not NULL
+    if (world == 0) {
+        // Throw an exception
+        throw std::invalid_argument("Exception in PhysicsEngine constructor : World pointer cannot be NULL");
+    }
 }
 
 // Copy-constructor
@@ -52,30 +56,33 @@ void DynamicEngine::updateBodyState(RigidBody* const rigidBody) {
 // Update the physics simulation
 void DynamicEngine::update() {
 
-    // While the time accumulator is not empty
-    while(timer.getAccumulator() >= timer.getTimeStep().getValue()) {
+    // Check if the physics simulation is running
+    if (timer.getIsRunning()) {
+        // While the time accumulator is not empty
+        while(timer.getAccumulator() >= timer.getTimeStep().getValue()) {
+            // For each body in the dynamic world
+            for(std::vector<Body*>::const_iterator it = world->getBodyListStartIterator(); it != world->getBodyListEndIterator(); ++it) {
+                // If the body is a RigidBody and if the rigid body motion is enabled
+                RigidBody* rigidBody = dynamic_cast<RigidBody*>(*it);
+                if (rigidBody && rigidBody->getIsMotionEnabled()) {
+                    // Update the state of the rigid body
+                    updateBodyState(rigidBody);
+                }
+            }
+
+            // Update the timer
+            timer.update();
+        }
+
         // For each body in the dynamic world
-        for(std::vector<Body*>::const_iterator it = world.getBodyListStartIterator(); it != world.getBodyListEndIterator(); ++it) {
+        for(std::vector<Body*>::const_iterator it = world->getBodyListStartIterator(); it != world->getBodyListEndIterator(); ++it) {
             // If the body is a RigidBody and if the rigid body motion is enabled
             RigidBody* rigidBody = dynamic_cast<RigidBody*>(*it);
             if (rigidBody && rigidBody->getIsMotionEnabled()) {
-                // Update the state of the rigid body
-                updateBodyState(rigidBody);
+                // Update the interpolation factor of the rigid body
+                // This one will be used to compute the interpolated state
+                rigidBody->setInterpolationFactor(timer.getInterpolationFactor());
             }
         }
-
-        // Update the timer
-        timer.update();
-    }
-
-    // For each body in the dynamic world
-    for(std::vector<Body*>::const_iterator it = world.getBodyListStartIterator(); it != world.getBodyListEndIterator(); ++it) {
-        // If the body is a RigidBody and if the rigid body motion is enabled
-        RigidBody* rigidBody = dynamic_cast<RigidBody*>(*it);
-        if (rigidBody && rigidBody->getIsMotionEnabled()) {
-            // Update the interpolation factor of the rigid body
-            // This one will be used to compute the interpolated state
-            rigidBody->setInterpolationFactor(timer.getInterpolationFactor());
-        }
     }
 }
diff --git a/sources/reactphysics3d/engine/DynamicEngine.h b/sources/reactphysics3d/engine/DynamicEngine.h
index 4fda081d..8c6f5bb1 100644
--- a/sources/reactphysics3d/engine/DynamicEngine.h
+++ b/sources/reactphysics3d/engine/DynamicEngine.h
@@ -46,7 +46,7 @@ class DynamicEngine : public PhysicsEngine {
         void updateBodyState(RigidBody* const rigidBody);                                                           // Update the state of a rigid body
 
     public :
-        DynamicEngine(DynamicWorld& world, const Time& timeStep);       // Constructor
+        DynamicEngine(DynamicWorld* world, const Time& timeStep);       // Constructor
         DynamicEngine(const DynamicEngine& engine);                     // Copy-constructor
         virtual ~DynamicEngine();                                       // Destructor
 
diff --git a/sources/reactphysics3d/engine/PhysicsEngine.cpp b/sources/reactphysics3d/engine/PhysicsEngine.cpp
index b5293d34..361ce365 100644
--- a/sources/reactphysics3d/engine/PhysicsEngine.cpp
+++ b/sources/reactphysics3d/engine/PhysicsEngine.cpp
@@ -24,9 +24,13 @@
 using namespace reactphysics3d;
 
 // Constructor
-PhysicsEngine::PhysicsEngine(PhysicsWorld& world, const Time& timeStep)
+PhysicsEngine::PhysicsEngine(PhysicsWorld* world, const Time& timeStep) throw (std::invalid_argument)
               : world(world), timer(Time(0.0), timeStep) {
-
+    // Check if the pointer to the world is not NULL
+    if (world == 0) {
+        // Throw an exception
+        throw std::invalid_argument("Exception in PhysicsEngine constructor : World pointer cannot be NULL");
+    }
 }
 
 // Copy-constructor
diff --git a/sources/reactphysics3d/engine/PhysicsEngine.h b/sources/reactphysics3d/engine/PhysicsEngine.h
index c1d36172..2759ddad 100644
--- a/sources/reactphysics3d/engine/PhysicsEngine.h
+++ b/sources/reactphysics3d/engine/PhysicsEngine.h
@@ -35,17 +35,42 @@ namespace reactphysics3d {
 */
 class PhysicsEngine {
     protected :
-        PhysicsWorld world;                     // Physics world of the physics engine
+        PhysicsWorld* world;                    // Pointer to the physics world of the physics engine
         Timer timer;                            // Timer of the physics engine
 
     public :
-        PhysicsEngine(PhysicsWorld& world, const Time& timeStep);       // Constructor
-        PhysicsEngine(const PhysicsEngine& engine);                     // Copy-constructor
-        virtual ~PhysicsEngine();                                       // Destructor
+        PhysicsEngine(PhysicsWorld* world, const Time& timeStep) throw (std::invalid_argument);     // Constructor
+        PhysicsEngine(const PhysicsEngine& engine);                                                 // Copy-constructor
+        virtual ~PhysicsEngine();                                                                   // Destructor
 
-        virtual void update()=0;                // Update the physics simulation
+        virtual void start();                                   // Start the physics simulation
+        virtual void stop();                                    // Stop the physics simulation
+        virtual void update()=0;                                // Update the physics simulation
+        void initializeDisplayTime(const Time& displayTime);    // Initialize the display time
+        void updateDisplayTime(const Time& newDisplayTime);     // Update the display time
 };
 
+// --- Inline functions --- //
+
+// Start the physics simulation
+inline void PhysicsEngine::start() {
+    timer.setIsRunning(true);
+}
+
+inline void PhysicsEngine::stop() {
+    // TODO : Implement this method
+}
+
+// Initialize the display time
+inline void PhysicsEngine::initializeDisplayTime(const Time& displayTime) {
+    timer.setCurrentDisplayTime(displayTime);
+}
+
+// Update the display time
+inline void PhysicsEngine::updateDisplayTime(const Time& newDisplayTime) {
+    timer.updateDisplayTime(newDisplayTime);
+}
+
 }
 
 #endif
diff --git a/sources/reactphysics3d/engine/Timer.cpp b/sources/reactphysics3d/engine/Timer.cpp
index ae9199b4..fde22eff 100644
--- a/sources/reactphysics3d/engine/Timer.cpp
+++ b/sources/reactphysics3d/engine/Timer.cpp
@@ -30,7 +30,6 @@ Timer::Timer(const Time& initialTime, const Time& timeStep) throw(std::invalid_a
     if (timeStep.getValue() != 0.0) {
         accumulator = 0.0;
         isRunning = false;
-
     }
     else {
         // We throw an exception
diff --git a/sources/reactphysics3d/engine/Timer.h b/sources/reactphysics3d/engine/Timer.h
index fc9882a7..5d8f0437 100644
--- a/sources/reactphysics3d/engine/Timer.h
+++ b/sources/reactphysics3d/engine/Timer.h
@@ -23,6 +23,7 @@
  // Libraries
  #include "../physics/physics.h"
  #include <stdexcept>
+ #include <iostream>
 
  // Namespace ReactPhysics3D
  namespace reactphysics3d {
@@ -52,7 +53,8 @@ class Timer {
         void setTime(const Time& time);                                         // Set the current time
         bool getIsRunning() const;                                              // Return if the timer is running
         void setIsRunning(bool isRunning);                                      // Set if the timer is running
-        double getAccumulator() const;                                           // Return the accumulator value
+        double getAccumulator() const;                                          // Return the accumulator value
+        void setCurrentDisplayTime(const Time& displayTime);                    // Set the current display time
 
         void update();                                          // Update the timer
         double getInterpolationFactor() const;                  // Compute and return the interpolation factor between two body states
@@ -103,6 +105,11 @@ inline double Timer::getAccumulator() const {
     return accumulator;
 }
 
+// Set the current display time
+inline void Timer::setCurrentDisplayTime(const Time& currentDisplayTime) {
+    this->currentDisplayTime = currentDisplayTime;
+}
+
 // Update the timer
 inline void Timer::update() {
     // Update the current time of the physics engine