Can a yogi attain to a state of consciousness in which he scan know all things, answer all question, relating even to abstruse scientific problems, such as, for example, the theory of relativity?

Theoretically and in principal it is not impossible for a yogi to know everything: all depends upon the yogi.

But there is knowledge and knowledge.

The yogi does not know in the way of the mind.

He does not everything in the sense that he has access to all possible information or because he contains all the facts of the universe in his mind or because his consciousness is a sort of miraculous encyclopedia.

He knows by his capacity for a containing or dynamic identity with things and persons and force.

Or he knows because he lives in a place of consciousness in which there the truth and the knowledge.

If you are in the true consciousness.

The knowledge you have will also be of the truth.

Then, too, you can know directly, by being one with what you know.

If a problem is put before you, if you are asked what is to be done in a particular matter, you can them, by looking with enough attention and concentration, receive spontaneously the required knowledge and the true answer.

It is not by any careful application of theory that you reach the knowledge or by working it out through a mental process. The scientific mind needs these methods to come to touts conclusions. But the yogic knowledge is direct and immediate: it is not deductive. If an engineer has to find out the exact position for the building of an arch the line of its curve and the size of its opening, he does it by calculation, collating and deducting from his information and data. But a yogi needs none of these things: sees that it is to be done in this way and not in another, and this seeing is his knowledge.