private void startCountdown()
	{
		start_time= new Date();
		is_running=true;
		thread = new Thread(){
			public void run()
			{				
				try {
					sleep(time_ms);
					gui.show_message();
					is_running=false;
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		};
		
		thread.start();
	}