Love is a subjective experience of consciousness. We must first have some clue about what consciousness is, then perhaps we will be able to scientifically explain what love is.
If I create a device that predicts with 99% accuracy whether a test subject loves their mother (by looking at the subject's brain), without ever answering any of your questions about consciousness, would you retract the above statement?
No, because you would not be explaining what love is, any more than explain what pain is by showing me the brain patterns the light up when I twist your nipple.
Whether of not you can test for love is immaterial to explaining the experience.
> When did I say I want to be explaining what love is?
Well, you were asking me to retract this statement based on the theoretical existence of a test:
> Love is a subjective experience of consciousness. We must first have some clue about what consciousness is, then perhaps we will be able to scientifically explain what love is.
Anyhow, I was using it as an example of something that we can't currently test for, not asserting that it will never be testable. So no, I'm not arguing that it will never be testable.
If we do test, however, it will most likely be a test for the brain activity associated with love, not for the actual qualitative feeling of love. As I've said, we know nearly nothing about what subjective experience is despite all we know being subject to it.
As far as science is concerned, there's nothing beyond being able to objectively model a phenomenon and make useful predictions about it. If I can fully model the set of brain processes that humans typically call "love", and if I can make useful and accurate predictions based on my model, that's all that I care about as a scientist.
Now, it's entirely possible that reasoning about "love" scientifically requires several layers of new language / models on top of the currently established models in neuroscience, which is why I said it's _theoretically_ possible.
Subjective experience exists objectively, as in, the subjective experience in your consciousness is an objective reality of the universe. We do not yet know how to model such things, and making useful predictions based in brain activity is great, but it will not be a remotely satisfying model of consciousness.
In theory, yes. What happens inside your brain isn't untestable or sacred, we're just not there yet technologically (but we'll get there).