particles/Main.cs

using Godot;
using System;

public class Main : Node
{

    public void StartSimulation(int nParticles)
    {
        var particleSimulationPackedScene = GD.Load<PackedScene>("res://ParticleSimulationScene.tscn");
        var particleSimulationScene = particleSimulationPackedScene.Instance<ParticleSimulationScene>();
        AddChild(particleSimulationScene);
        particleSimulationScene.Initialize(nParticles);
        GetNode<Control>("MainMenu").Hide();
        //OS.WindowResizable = false;
    }
    
}