0.0000001%

Years ago, there was a billboard you could see while driving along the Mass Pike outside Boston. It read "We don't know one-millionth of one percent about anything. - Albert Einstein"

That's not true.

It was originally said by Thomas Edison (ref ).

The part about how little we know IS true and this can be proven. I recently viewed this video showing the large scale structure of just a small chunk our little universe:

Entire galaxies are mere points of light in this depiction and we see them forming into even larger universe-spanning alignments.Yet, despite the vast amount of matter and structure we see in this video, it still represents only what we can see and measure in the universe. We know there is also what we call dark matter and dark energy (Just because we name them does not mean we know what they are. We don’t.) which comprise 95% of the universe (ref). All we are seeing in that video is our universe like foam on the waves of an ocean we can’t see. Even if we knew everything about the visible universe, we’re at 5% tops.

Lastly, a current model of the universe posits that everything we know as existence is likely only a multidimensional “skin” or membrane/m-brane formed between two “bubbles” (of something) intersecting outside in the wider multiverse, well beyond anything we know. (http://brane-space.blogspot.com/2010/09/how-could-universe-originate-from.html ). That easily brings us in under 0.0000001%.

In my first class in physics in my freshman year at college, Professor Milton Stecher taught that we would not begin to learn physics until we learned how much we did not know. I immediately put down my pen and started not knowing. I almost failed that course. But, thirty years later, I think I am finally beginning to learn.