They do, the heater 1 and heater 2 increase the temperature, and reducing the volume increases the pressure. Both of these mean that less argon is necessary to create the singularity. It tells you P = nRT/V, P is pressure, n is moles of gas (that you are increasing), R is a constant, T is the temperature which increases with heater upgrades, and V is volume which you decrease. All of this increases P, a minimum amount of which is required to complete the game.