Our senses are pretty limited. We cannot see radio waves, ultraviolet light, or infrared light. We cannot hear ultrasound. We cannot sense radioactivity.
But our senses are NOT the only means of detecting things. As with the things above, we can use *other* things to detect them and convert that detection into something we can detect. So, we have built radios to radio waves. We have devices to detect ultraviolet and infrared. We have ways to detect ultrasound and radioactivity.
So, it is quite common to know something exists that we cannot directly detect with our senses. We can extend those senses using various devices and use those devices to detect things.
But, does it even make sense to say that something exists if there is literally NO WAY to detect it, even when our senses are extended. even in theory?
To *that* question, I would say that the existence, at that point, has no meaning at all.