Like other kids, this was one of the first books I recall reading, and one that stoked my interest in science fiction and alternate history. I was pleased that I kept the original copy with me over the years and was able to read it with my daughter!
Overall, Earth Times Two didn't hold my interest all that well, and the author clearly doesn't understand basic science (Larry Niven could teach her a thing or two about visiting a planet made of antimatter), but I can't complain too much about any book in which a cat is a major character. The spiteful, competitive dynamic between the two teenagers got rather annoying during the first half; however, I never felt I wanted to disembowel them both with a rusty fork, so clearly I've read worse.
The story shares certain elements with A Wrinkle in Time, but the similarities don't stick out in the way one would expect if plagiarism were involved.
Earth Times Two may be unique in that its two protagonists are double first cousins. (If two brothers marry two sisters, the two couples' children are double first cousins; they share both sets of grandparents, and are as closely related as half siblings.)
I had been looking for this book, which I read when I was about 8 or 9, for almost 30 years, and it was thanks to a Google Book search on the phrase "twints" that I finally found it.
While I intended to get this for my almost 7-year-old, it's not a book for wee ones, and I think would be more appropriate for the 11-13 set. My son couldn't get interested in what appeared to be teleportation/science fiction aspects of the book (sigh) but did express an interest in reading it later.
This is a book straight out of the 70s, when ESP, psychic powers, and the menace of trans-dimensional humans was all the rage. I think despite the somewhat dated subject matter, it still holds up as an interesting science fiction YA novel, but it's a very abbreviated book, with an ending that comes almost too quickly to be satisfactory. Had this been written today, I would have expected a novel at least twice as long, with a much longer resolution to the story. But brief as the book is, I found the concept captivating and really quite forward-thinking, especially for the early 70s.
It's a dark book, flashing on Brave New World at times, but it resolves in a positive way. The children are definitely the heroes, so although there was no YA category in 1974, it would fit solidly on that shelf today. The science of the science fiction isn't all that hard to stomach (much easier than any of the "science" in Independence Day) and the writing is elegant and emotional. The author is famous for other novels, but I think this one is something of an overlooked gem, and I would love to see it brought back into print.
ETA: I'm somewhat surprised by the negative reviews complaining of the quality of the language. There is no clunky prose in this book and some of the imagery and descriptions are exceptionally vivid and evocative. My less than 5-star review came from the briefness of the resolution and the rushed feel of the ending. It's a bit of a "slow burn" as far as narratives go, and takes a bit to get into, but this is the kind of literature I was raised on, before everything became "slam bam flash action sequences," so I would put it in the category of books like Sounder and Walk Two Moons, as far as the speed of the plot unfolding. (Up until the end, that is.)
Not the most well-written book with annoying characters. But I read it at an age (grade 5) when I'd only experienced Baby-Sitter's Club and Sweet Valley. It sparked my interest in science fiction and the parallel universe/alternate reality sub-genre. Because it influenced my reading habits so heavily, I had to give it 3 stars... and for the age group it might even get 4.
Like another poster here, this book stuck with me for decades and I searched by keywords of remembered fragments (“cat,” “Terra,” “elevator,” “bread wrapper,” “in your eye, Herk”); in fact, I joined the Goodreads community for the express purpose of finding this book! I finally found it and, with great excitement, ordered a used copy. That I could not forget this book that I did not even own — checked it out at age 9 or so from elementary school library — is a testament that for its intended age reader it is a great story. I wish there had’ve been a sequel, or movie. Very happy to have rediscovered.
Read it when I was little and it set me on the path to the sci-fi reader I am today. I loved it then, haven't read it since then (70s), but I'd read it again if I had it here.