I suppose that it's not too much of an exaggeration to say that this book has become something of a "classic" ... it's still available in hardcover a dozen years down the road from publication, and goes for $40 on Amazon (the paperback can be had for a lot less). In Hyperspace: A Scientific Odyssey through Parallel Universes, Time Warps, and the Tenth Dimension Michio Kaku looks at the cutting edge of cosmology, sketches out the history of how we got here, and does some projecting into the future.
One of the key elements here is, obviously, the concept of multi-dimensionality, which is often a hard thing to wrap one's brain around. Relying on the classic "flatland" examples (of how beings in a 2-D world would perceive 3-D objects), Kaku shows how, as odd as they seem, higher-dimension models go a long way towards explaining "issues" with many of the other theories. Most of this has to do with mathematics, and I'm not going to try to explain any of that here, but suffice it to say, stuff that "looks wrong" in the Standard Model suddenly "fits" if one posits a 10-dimensional (or 26-dimensional) universe. In fact, many of the "problems" with the vast proliferation of subatomic particles could also be explained as being expressions of a few specific things in differing harmonics (or something like that).
Oddly enough, a version of the multi-dimension theory had been popular in the 1800's, and was embraced by various Theosophists and the "spiritual research" folks of the day (many of whom also held prestigious university science chairs). This is part of the reason why it took such a long time to come back to it (as it had become the province of seances, rather than the laboratory). Indeed, Kaku holds that we wouldn't have this theory now if not for the brief, and almost lost, mathematical career of the prodigy Srinivasa Ramanujan (who died in his 30's), which he describes as "injecting 21st-century physics" into our current models.
Kaku also looks to the future (and helps explain why we've not had confirmable contacts with alien civilizations) by using Nikolai Kardashev's "Type I, Type II, Type III" civilization model. Kaku points out that we're currently in a "Type 0" civilization, and suggests that the stresses involved in this phase (conflicting nation-states with nuclear weapons and limited natural resources) are quite likely to result in a collapse of the civilization before it can reach beyond its home world. Frankly, in this model it appears that one cannot move from a "Type 0" to a "Type I" without having a "winner" that imposes its culture over the whole civilization ... a thing to consider when one thinks of current global politics! Even more concerning is his observation that whatever beings do end up successfully reaching a "Type I" civilization, they will almost certainly be evolved from high-functioning predators in their environment, and are not likely to be cute and cuddly ETs ... leading to the supposition that the interactions with them would likely more resemble the Spanish in Tenochtitlan than any newage vision of "enlightened beings".
Anyway, if you have an interest in these sorts of things, you should definitely pick up a copy of Hyperspace. As noted above, it's still in print, so should be available at your local bookstore, as well as on-line. You can get a "like new" version of the hardcover edition for under six bucks (and a "very good" copy for under $2), and Amazon has the paperback on-sale for just under $11.00 ... so it shouldn't break the bank to check this out if it piques your curiosity.