Well there are the Messengers who give themselves as the greatest proof. They also say they are why it all started. That they came and looked like you and I was most likely why the Wow moment is hidden from us all.
This is that passage, which is from God to answer this OP question about proof;
"....Know thou of a certainty that the Unseen can in no wise incarnate His Essence and reveal it unto men. He is, and hath ever been, immensely exalted beyond all that can either be recounted or perceived. From His retreat of glory His voice is ever proclaiming: “Verily, I am God; there is none other God besides Me, the All-Knowing, the All-Wise. I have manifested Myself unto men, and have sent down Him Who is the Day Spring of the signs of My Revelation. Through Him I have caused all creation to testify that there is none other God except Him, the Incomparable, the All-Informed, the All-Wise.” He Who is everlastingly hidden from the eyes of men can never be known except through His Manifestation, and His Manifestation can adduce no greater proof of the truth of His Mission than the proof of His own Person..."
By the way, we know that there is no way the mind can fathom the extent of creation. All we can know is but one lamp of another 100,000,000 other lamps.
All planets have creatures. Some have beings like us that can also know and love God. Baha'u'llah is a universal Manifestation, not restricted to earth.
The future will be mind blowing for us that live in this age with such dull minds. Wish I had the vision of the whole in this matrix, but most likely will leave this matrix before those eyes develop.
Great hey
Regards Tony