Heisenberg? Basically he was famous for his uncertainty principle. In brief, it might be described as follows -
"the more precisely you know the position of a particle, the less precisely you know its momentum".
Doesn't sound very awesome, until you see it in the proper context. An important point to grasp here is that the uncertainty principle is not set out as a limitation of scientists or scientific equipment or current scientific knowledge, or as a description of an as-yet unsolved mathematical puzzele.
The uncertainty principle is stated as a feature of the universe itself.
So let's say, for example, that there is an object, and using the best methods available, you'd like to determine its "objective" reality better. For example, you'd like to describe, in the most precise terms, where the particle is, and where it is going.
Well, you can't.
The better you know where the particle is, the less you know where it is going. The better you know where it is going, the less you know where it is.
To put it another way, the "objective" reality of the particle changes, depending on what you are able to perceive about it. It
has no objective reality. (Uhh, sound familiar to you by now?).
Because Heisenberg was studying reality at a very fundamental level, the ramifications of his uncertainty principle are quite enormous. Essentially it indicates that reality is non-objective and endlessly changes and shifts, according to what you perceive about it.
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If you read "Power, Grace and Freedom", you'll find an explanation of what might happen if you take the uncertainty principle to its full ramifications. Essentially it leads to conclusions like:
(a) distance is an illusion
(b) time is an illusion
(c) solidity is an illusion
(d) you are everywhere and nowhere
(e) you are everything
But of course.
If position and momentum are not truly objective, then it follows that distance, time, solidity etc are all illusions.
Now, please don't ask me to elaborate and reproduce dozens of pages of text from PGF. Go read the book yourself, if you're interested.
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The uncertainty principle can sometimes be seen as a subset of the observer effect. Now, the observer effect is a bit of a loose term, and shows up in different contexts - not just in physics, but also in areas like psychology and IT and even theatre studies.
But in the realm of hard sciences, the observer effect means that the very act of observation changes something about what you're trying to observe. For example, if you measure the temperature of a container of water with a thermometer, the very act of measurement causes the thermometer to absorb or give some heat to the water (depending on the temperature differential), thereby altering its temperature to what it would not have been, if you had not measured it.
Therefore there is no "objective reality", or if there is, it is essentially unknowable and meaningless. Because your subjective observations are automatically altering reality.
In a more ultimate sense, there is no proof that reality is ever anything other than what you observe it to be. For you can never observe a reality that you did not observe. So that takes us right back to SR.