This probably just furthers the hijack, but there’s a common misconception to this kind of discussion that’s also been brought up here – saying ‘maybe it’s some kind of unknown energy’ isn’t any more scientific that saying it’s the souls of dead people, and saying ‘scientists were wrong before’ does not lend any more credence to that assertion.
See, when scientists were wrong before (in the sense of disbelieving phenomena that turned out to be real), it’s generally been about things small compared to the precision of measurement during their time, like plate tectonics – today, we can use precision satellite measurements to determine the rate at which South America and Africa drift apart, back when the theory of continental drift was formulated, not so much.
However, to find something large compared to contemporary measurement precision is very rare and surprising (I can’t actually think of a single time that’s happened), and a new form of ‘energy’ capable of manifesting ghost-like phenomena certainly would be such a discovery; I won’t say it’s impossible, but only because, strictly speaking, everything is possible.
Consider an analogy: Mankind started out in a dark room, filled with stuff. At first, we just kinda shambled around and bumped our heads, but then, we started actively feeling around, getting a good overview of our surroundings, sort of a mental map of all the furniture and some basic ideas of what it was that’s around us, and at some point, we found a flash light to brighten up the dark a bit, and then somebody stumbled upon the light switch, and we didn’t have to feel around any more, we could just observe, and over time, we discovered ever more sophisticated means to examine our surroundings, perhaps microscopes and what have you, and right now, we’re basically busy examining every square inch of every object in our little room – and there’s certainly still a lot of stuff to be discovered, and maybe there’s even a drawer or two nobody’s looked into yet, but certainly, we don’t expect to one day just stumble over a new armchair everybody’s just missed all the time. It’s not, strictly speaking, impossible; but it’s highly unlikely and thus, nobody seriously considers that possibility, it wouldn’t be a reasonable assumption.
(At each point in the process, to look at this from a different angle, there’s been people who have been grossly wrong – a supposed cupboard might have turned out to be a hanging bookshelf, and certainly philosophizing over the pattern decorating the tablecloth was a thoroughly academic exercise before the discovery of the flash light, and once the switch got flipped, that discussion became moot real quick – and, in hindsight, obviously so, and this pattern is likely to continue into the foreseeable future; however, the size and impact of the things one could be wrong about has, similarly steadily, continuously declined the more was discovered about the room and its furnishing.)
Of course, now I fully expect someone to lift a carpet next week and find a trapdoor beneath it, but even then I’d still be justified in reasonably assuming now that this won’t happen. 
