Experiments are the only means of knowledge at our disposal. Everything else is poetry, imagination.
- Max Planck
I've never been able to find this quote in the original German (thus ensuring, I suppose, that by tomorrow morning I shall have a comment from someone who has managed to find it) but in English, I can endorse it unreservedly because of those three words 'at our disposal'. Doubtless there are more true statements than those that can be found by experiment, or that can ever be verified, but the means by which we apprehend them are definitely not 'at our disposal'.
I will now attempt to construct an elaborate metaphor.
The universe which we experience, let us call the Ocean.
Let us give ourselves an instrument for sampling the universe which is at our disposal, which will give reproducible results, with which we can experiment: this is the Cup of Reason.
Let us give ourselves another instrument for sampling the universe which is not at our disposal, which will give irreproducible results: this is the Net of Poetry and Imagination.
We can dip the cup in many times, and we can learn much about the wetness of the ocean, and the saltness of the ocean, and as we focus our energies more and more on understanding what we find in the cup we will uncover splendid chemical equilibria, and wondrous plankton, and all manner of marvels, and we will understand the ocean, this little cylinder of water circumscribed by reason.
We can dip the net in many times, and many times we will find nothing, but sometimes we might pull out a Crimson Gugfish, and we can show it to our friends and say: 'Look at this image of truth I have imagined' and they will say, if they are sensible and wise and know well the use of reason: 'That thing will not fit in a little cylinder of water'. And we will go away abashed.