Nikola Tesla:

Today's scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality - Modern Mechanics and Inventions, July, 1934.

Eugene Wigner:

Physics is becoming so unbelievably complex that it is taking longer and longer to train a physicist. It is taking so long, in fact, to train a physicist to the place where he understands the nature of physical problems that he is already too old to solve them.

David Hilbert:

Physics is becoming too difficult for the physicists.

Daniel Bernoulli:

It would be better for the true physics if there were no mathematicians on earth.

Richard Feynman:

One does not, by knowing all the physical laws as we know them today, immediately obtain an understanding of anything much - The Character of Physical Law.

You can recognize truth by its beauty and simplicity. When you get it right, it is obvious that it is right.

Arthur Eddington:

We have found a strange footprint on the shores of the unknown. We have devised profound theories, one after another, to account for its origins. At least, we have succeeded in reconstructing the creature that made the footprint. And lo! It is our own - Space, Time, and Gravitation, 1920

Murray Gell-Mann:

Niels Bohr brainwashed a whole generation of physicists into believing that the problem [of the interpretation of quantum mechanics] had been solved fifty years ago - What are the Building Blocks of Matter? in Douglas Huff, Omer Prewett (eds.) The Nature of the Physical Universe. New York: John Wiley and Sons.

Albert Einstein:

Everything should be made as simple as possible, but not one bit simpler.

Insanity: doing the same thing over and over again and expecting different results.

We cannot solve our problems with the same thinking we used when we created them.

William Lawrence Bragg:

The electron is not as simple as it looks.