diff --git a/simulator/src/main.rs b/simulator/src/main.rs
index eefe249..daaec28 100644
--- a/simulator/src/main.rs
+++ b/simulator/src/main.rs
@@ -1,5 +1,7 @@
 use std::cmp::max;
-use std::sync::Arc;
+use std::sync::{Arc, RwLock};
+use std::thread;
+use std::time::Duration;
 use cgmath::num_traits::ToPrimitive;
 use cgmath::Rotation3;
 use pollster::FutureExt;
@@ -10,6 +12,7 @@ use winit::dpi::PhysicalSize;
 use winit::event::WindowEvent;
 use winit::event_loop::{ActiveEventLoop, EventLoop};
 use winit::window::{Window, WindowId};
+use solar_engine::{Body, Simulator};
 
 pub async fn run() {
     let event_loop = EventLoop::new().unwrap();
@@ -154,6 +157,8 @@ struct State<'a> {
 
     num_vertices: u32,
     num_indices: u32,
+
+    simulator: Arc<RwLock<Simulator>>,
 }
 
 impl<'a> State<'a> {
@@ -175,21 +180,50 @@ impl<'a> State<'a> {
         let num_vertices = VERTICES.len() as u32;
         let num_indices = INDICES.len() as u32;
 
-        let instances = vec![
-            RenderInstance {
-                position: cgmath::Vector3::new(0.0, 0.0, 0.0),
+        let mut sim = Simulator::new(60.0 * 60.0 * 24.0);
+        sim.add_body(Body {
+            name: "Sun".to_string(),
+            position: [0.0, 0.0],
+            velocity: [0.0, 0.0],
+            mass: 1.989e30,
+        });
+        sim.add_body(Body {
+            name: "Earth".to_string(),
+            position: [1.496e11, 0.0],
+            velocity: [0.0, 29780.0],
+            mass: 5.972e24,
+        });
+        
+        let simulator = Arc::new(RwLock::new(sim));
+
+        let sim_clone = simulator.clone();
+        thread::spawn(move || {
+            loop {
+                {
+                    let mut sim = sim_clone.write().unwrap();
+                    sim.step();
+                }
+                thread::sleep(Duration::from_millis(16));
+            }
+        });
+
+        let instances = {
+            let sim = simulator.read().unwrap();
+            sim.bodies.iter().map(|b| RenderInstance {
+                position: cgmath::Vector3::new(
+                    (b.position[0] / 1.496e11) as f32,
+                    (b.position[1] / 1.496e11) as f32,
+                    0.0,
+                ),
                 rotation: cgmath::Quaternion::from_angle_z(cgmath::Deg(0.0)),
-            },
-            RenderInstance {
-                position: cgmath::Vector3::new(1.0, 1.0, 0.0),
-                rotation: cgmath::Quaternion::from_angle_z(cgmath::Deg(45.0)),
-            },
-        ];
+            }).collect::<Vec<_>>()
+        };
+
         let instance_data: Vec<InstanceRaw> = instances.iter().map(RenderInstance::to_raw).collect();
         let instance_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
             label: Some("Instance Buffer"),
             contents: bytemuck::cast_slice(&instance_data),
-            usage: wgpu::BufferUsages::VERTEX,
+            usage: wgpu::BufferUsages::VERTEX | wgpu::BufferUsages::COPY_DST,
         });
 
         Self {
@@ -209,6 +243,8 @@ impl<'a> State<'a> {
             
             num_vertices,
             num_indices,
+
+            simulator,
         }
     }
 
@@ -217,7 +253,17 @@ impl<'a> State<'a> {
     }
 
     fn update(&mut self) {
-        // TODO: Update logic here
+        let updated_instances: Vec<RenderInstance> = {
+            let sim = self.simulator.read().unwrap();
+            sim.bodies.iter().map(|b| RenderInstance {
+                position: cgmath::Vector3::new((b.position[0] / 1.496e11) as f32, (b.position[1] / 1.496e11) as f32, 0.0),
+                rotation: cgmath::Quaternion::from_angle_z(cgmath::Deg(0.0)),
+            }).collect()
+        };
+
+        let instance_data: Vec<InstanceRaw> = updated_instances.iter().map(RenderInstance::to_raw).collect();
+        self.queue.write_buffer(&self.instance_buffer, 0, bytemuck::cast_slice(&instance_data));
+        self.instances = updated_instances;
     }
     
     fn create_index_buffer(device: &Device) -> wgpu::Buffer {
@@ -380,12 +426,14 @@ impl<'a> State<'a> {
                 occlusion_query_set: None,
                 timestamp_writes: None,
             });
-            
+
             render_pass.set_pipeline(&self.render_pipeline);
             render_pass.set_vertex_buffer(0, self.vertex_buffer.slice(..));
-            render_pass.set_vertex_buffer(1, self.instance_buffer.slice(..));
             render_pass.set_index_buffer(self.index_buffer.slice(..), wgpu::IndexFormat::Uint16);
-            render_pass.draw_indexed(0..self.num_indices, 0, 0..self.instances.len() as u32);
+            if !self.instances.is_empty() {
+                render_pass.set_vertex_buffer(1, self.instance_buffer.slice(..));
+                render_pass.draw_indexed(0..self.num_indices, 0, 0..self.instances.len() as u32);
+            }
         }
 
         self.queue.submit(std::iter::once(encoder.finish()));