Rational thinking is thought based on logic supported by scientific facts and evidences.
But many rational thoughts depend on whether the science has expanded and investigated into the areas that are currently being debated.
And over a period of time rational thoughts become irrational and vice versa.
A millenium back it was rational in Europe to think that earth is flat! Today its irrational all over the world.
Before Einstein people used to think that time is an absolute phenomenon, that is the time taken for one second is the same all across the universe! Thanks to relativity , that is not the case any more. Time runs slower at Goa compared to the speed of the time on top of the Himalayas. Its called Time Dilation.
Many people who do not know about quantum mechanics still wrongly believe some thoughts to be irrational, while actually today they are rational thoughts verified and validated by science!
Let me give you some examples.
Is it irrational to think that walking through a wall is possible?
Is it irrational to think that somebody in India can instantaneously convey a message to somebody in USA without using any known external medium of communication just by using the thought process?
Is it irrational to think that something can pass through two adjacent holes at the same time?
Is it irrational to think that one thing could be converted into another thing by supplying required energy for the process?
Is it irrational to think that one can alter the outcome of a process by just observing it?
Is it irrational to think that if you know how fast something is moving in a given direction, then you CANNOT predict accurately where it will be after a given amount of time?
If your answer is yes, then you have to update your knowledge base supporting rationalism, because as per quantum mechanics the answers to all the above questions are valid, rational and possible.
The answers to the above questions are quantum tunneling, non-locality, wave-particle duality, particle decay, wave function collapse and uncertainty respectively.
Probably non-locality exists because at a quantum level the entire universe is a local phenomenon!