The Bible? Ok, I jest. You observe nature. For instance, that apple that just fell. Then you make predictions about why it fell down and not up or sideways. You

The Bible? Ok, I jest. You observe nature. For instance, that apple that just fell. Then you make predictions about why it fell down and not up or sideways. You hypothesize that this apple and all apples fall at the same rate, call it 5m/s. You then observe that if it fell from higher up, it is traveling faster than if it fell from a lower branch. Your first model was wrong. Time to revise your model. Then you invent new mathematics to explain what was wrong about your model and call it the Calculus. With calculus, you hypothesize that it can predict how fast it would be falling if it fell from a completely different height fit constants that match your first and second observations. You then observe that an apple at another completely different height matches your prediction. Now go and observe other things and hypothesize about them too. With regards to the Solar System, you observe that the Earth has an atmosphere and observe that it has a magnetic field that affects particles coming towards it from space. You hypothesize that the Sun has significant influence on particles further away from Earth. In your planetary travels, you observe that there seems to be data that supports your model. You hypothesize that eventually, the Sun will lose its influence and interstellar space will be radically different, that at some point the solar winds generated by the Sun will fall off. This is more or less where we are now, but we observe that the edge isn't quite as we predicted it would be. This could be because we haven't left the heliosphere yet, or it could be that our model was wrong. We are currently collecting those observations that will allow us to refine our models, and with any luck, the revised model will be tested by the next Voyager. Observe, Predict, Observe. Even with the next Voyager, we won't know for sure that our model is correct, but it gives you a starting point.