In this episode, Velma goes through a long explanation about how ghosts are scientifically proven to be a "sheer myth". Did science really declare ghosts to be false in the '70s? The only thing I can think of happened recently and it had to do with the Large Hadron Collider.
Well what do you mean by science? Science has many domains some considered 'harder' than the other e.g. molecular biology vs social psychology for example. With ghosts what are you testing, what are you measuring? If you can't do both then you are not doing science, hell you aren't even doing engineering.
She might just have said that as it sounded good in the dialogue. If anything I would guess physics as most of what happen would be precluded, forbidden even, by the laws of physics as we know then. As the man says...
One thing you have to check with ghosts etc is if it breaks the Second Law of Thermodynamics
If someone points out to you that your pet theory of the universe is in disagreement with Maxwell’s equations—then so much the worse for Maxwell’s equations. If it is found to be contradicted by observation—well these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation. — Sir Arthur Stanley Eddington