DS is 9 and likes reading, he also likes Maths and Sciences. He has read Murderous Maths and Horrible Science series.
Recently he is asking questions like: will a particle bounce back if crashed with another particle? Does light particle always travel at the same speed? What's the 4th dimension?
I could not answer such questions. I wonder if anyone can give me an advise on what sort of book that he can read so that he can find the answers himself?
Thanks in advance.