Time Travel and Warp Drives: A Scientific Guide to Shortcuts through Time and Space

by Allen Everett, Thomas Roman

To see video demonstrations of key concepts from the book, please visit this
press.uchicago.edu/sites/timewarp/ind... . 

Sci-fi makes it look so easy. Receive a distress call from Alpha Centauri? No punch the warp drive and you're there in minutes. Facing a catastrophe that can't be averted? Just pop back in the timestream and stop it before it starts. But for those of us not lucky enough to live in a science-fictional universe, are these ideas merely flights of fancy--or could it really be possible to travel through time or take shortcuts between stars?

Cutting-edge physics may not be able to answer those questions yet, but it does offer up some tantalizing possibilities. In Time Travel and Warp Drives , Allen Everett and Thomas A. Roman take readers on a clear, concise tour of our current understanding of the nature of time and space--and whether or not we might be able to bend them to our will. Using no math beyond high school algebra, the authors lay out an approachable explanation of Einstein's special relativity, then move through the fundamental differences between traveling forward and backward in time and the surprising theoretical connection between going back in time and traveling faster than the speed of light. They survey a variety of possible time machines and warp drives, including wormholes and warp bubbles, and, in a dizzyingly creative chapter, imagine the paradoxes that could plague a world where time travel was possible--killing your own grandfather is only one of them!

Written with a light touch and an irrepressible love of the fun of sci-fi scenarios--but firmly rooted in the most up-to-date science, Time Travel and Warp Drives will be a delightful discovery for any science buff or armchair chrononaut.

Genres: Science, Nonfiction, Physics, Time Travel, Space, Research, Popular Science

278 pages, Paperback

First published November 7, 2011

Reviews

[Riku Sayuj]

I actually received my copy as part of this giveaway! It is the best feeling in the world to get a free book. Gratitude to University of Chicago Press. Will read and post a review soon!

[Grace Morris · Rating 3 out of 5]

Okay so this is my second time trying to write this review. I don't normally read these kinds of books, I mean sometimes I do, because I kind of *umm like* this kind of stuff. But I actually pick this up for my WIP (Work In Progress) I am writing.

This book says I should understand it with only high school algebra. It also says I should be able to understand some of it without math. Truth? I am *cough, cough* not very good at math. Plus in the beginning of the book I had no idea what they were talking about. (After awhile I started scanning through the pages instead of reading them). So I was thinking to mark this book as DNF (Did Not Finish).

Obviously though that didn't happen. Why? Well, I have this idea to read through the book, get as much as I could out of it, then mark it as 2 stars and leave a funny review. (Actually it *was* a funny review. It had what the book promised me and my response to the book. It was filled with superheroes and super villains. And at the end it had me hitting my face with the book. Then it had me recommending it to college professors trying to understand what it means.)

Obviously though I *must* have gotten something out of this book, because I gave it 3 stars and I *didn't* post that funny review.

SO WHAT DID I THINK ABOUT THIS BOOK???

*It was interesting*. Seriously, I mean it, I wouldn't lie. After I got past the beginning part of the book and more towards the middle, *I stopped scanning and did more reading*. But why? Because it suddenly grabbed my attention. I think I was on the chapter on Einstein's theory of General Relativity. Okay, I will confess. I have read stuff about General Relativity before, but never really understood it. This is probably my third/fourth time reading about General Relativity, and it finally is beginning to make sense. You probably still can't come up to me and go: "Hey, can you explain Einstein's theory of General Relativity to me?" and have me explain it (because I just don't know enough about it yet to do that). But I am beginning to understand.

And I love, love the chapter called "Banana Peels and Parallel Words". It was so interesting, and I understood a good 90% of what they were talking about. And all the information about paradoxes helped me so much with my research.

By the way, this book is about time travel and warp drives. =D

Who I Would Recommend the Book To:

People who are writing a sci-fi book and need to research things (you might find things are looking for like I did). People who like to just read books about science (like me =D). People who have a little bit of math behind them. People who just want to try the math problems in this book (Hey, go for it!). Scientists who already studied these things (but then again if you already studied this stuff then you probably already know what's in here). People who are planning to make a time machine (just make sure you read through the paradoxes =O).

And finally college professors, because why not? Just make sure you let me know how to understand the math and other places. =)

[John Park · Rating 4 out of 5]

Three and a half stars.

An engaging, readable and non-mathematical, but quite technical account of the scientific background to time travel. Seven appendices present some of the mathematics, including the basic algebra of special relativity and an outline of Hawking's exotic matter theorem.

The first chapters set the scene, invoking H. G. Wells and other SF writers, plus some basics like the question of arrows of time, and aspects of relativity including the equivalence principle, the speed of light as a fundamental limit and the twins paradox, plus a brief discussion of trivial time travel—viz, at various rates into the future.

The connection between faster-than light communication and time machines is quite direct. According to relativity theory, if you have two superluminal devices you can use them to travel into the past or communicate with the past—they act as a nontrivial time machine. (Even one superluminal device—a wormhole—can be used as a time machine if its mouths are separated at high speed and then brought back together like the two individuals in the classic "twins paradox".) This of course unleashes all the dilemmas and contradictions—encapsulated in the homicidal/suicidal "grandfather paradox"—that Wells sidestepped and many of his science-fictional descendants have explored and exploited.

In some of these situations conservation of energy seems to be violated: when the traveller from the future visits their earlier self about to enter the time machine where did the mass of the second body come from? The authors consider this with a wormhole as the time machine and conclude that the extra mass must come from the wormhole itself, to be returned there once the traveller enters it. (Heinlein's "All You Zombies" is not one the stories cited by the authors but presumably its narrator's closing question would have to find an answer in a similar mechanism.)

Such a meeting of two copies of an individual needn't entail any paradoxes—but of course it might, and the very possibility that one could alter the past causes problems for the whole idea of time travel. Outright paradoxes seem incompatible with our reality: you will kill your grandfather only if your grandfather was killed before he had any children; the way this shutter works means that this billiard ball will exit the wormhole in the past only if it did not enter the wormhole in the future. . . .

There seem to be two main ways of avoiding such paradoxes, which the authors refer to as the "banana-peel" and the "many worlds" scenarios. In the first, something always intervenes to stop the paradox-creating act from being completed—someone slips on a banana-peel, a gun jams or whatever. The authors suggest persuasively that this seems to require an arbitrary inventiveness on the part of the universe that we don't normally observe.

In the second escape route, the paradoxical event is shifted into another universe; the "grandfather" you kill never did have children in this world, although the one in the world you left did; but that is no longer the world you live in, and apart from some questions about how you got here, as long you are content to accept an infinite set of parallel worlds, there are no major problems.

Then again perhaps things aren't quite that simple: the question of exactly when the split or shift between worlds happens perhaps deserves more thought. Everett and Roman consider a billiard ball emerging from a wormhole into its own past and triggering a shutter that will prevent its future self from entering the wormhole—thus setting up a paradox that could be resolved in the many-worlds scenario.

But what happens if the shutter is triggered the moment part of the billiard ball emerges from the wormhole? Presumably the worlds would split at that instant, while part of the ball is still in the wormhole and thus in the future. For billiard balls and other large, possibly living, bodies, Everett and Roman explore the consequences in a section they call "Slicing and Dicing".

They go on to consider suggestions for actual time-machines based on the theory of relativity. Here they make extensive use of Hawking's exotic-matter theorem. Exotic matter is matter that has a negative energy density; it exerts a gravitational repulsion rather than attraction and is needed, for instance, to hold the throat of a wormhole open. Hawking's theorem says (roughly) that a time machine must either include exotic matter or be infinite in size. (The sketch of the proof given in Appendix 6 seems to imply that the "infinite in size" requirement comes from the assumption that the universe itself is infinite; if this impression is right but the universe is not infinite, perhaps the size criterion would be merely "significantly larger than the observable universe".) The authors accept the validity of Hawking's theorem and indicate that the majority of workers in the field do too, but they also report some objections.

We glimpse negative energy densities in the Casimir effect, but no one knows how to make or find any structural material with negative energy (neither antimatter nor dark matter qualify). Unfortunately all useful-sized time machines appear to require large—perhaps astronomically large—quantities of it.

One example is the Alcubierre warp bubble, in which a shell of exotic matter is arranged to distort spacetime in such a way that the inside of the bubble has normal gravity but the bubble itself can travel at several times the speed of light. The original model needed an amount of exotic matter equivalent to at least 10∧20 times the mass of the galaxy. . . . A later analysis suggested this might be reduced to few solar masses, at the cost of some exotic geometry, but still with the original very thin walls—approaching the Planck length in scale. Other objections also emerged. (My own intuitive objection may not carry much weight: viewed from a great distance, the trajectory of an interstellar warp bubble would look like a point particle travelling though flat spacetime faster than a light signal—a situation that could be described by, and would clearly violate, special relativity.)

Claims out of NASA that the amount of exotic matter needed for a ship-sized warp-bubble might be "only" 700 kg (perhaps small enough to make the underlying principle testable) probably appeared too late to be discussed in the book, but the underlying calculations do not seem to have been published in the peer-reviewed literature.

Mallet's briefly celebrated rotating-cylinder time-machine also seems to fall foul of Hawking's theorem, which was not acknowledged in its derivation, and of the fact that it contains an originally unrecognised singularity along its axis; it turns out too that the physical size of the paths one would need to take to return to one's own past are beyond cosmologically huge: 10∧N times the radius of the cylinder, where N is 10∧46.

All the model time machines considered have similar problems. And it seems to be a common feature of them that they will not permit one to travel back to times before the machine was created—so whatever the practicalities, unless something has been achieved in incredible obscurity, it looks as though we will not be going back to hunt big game in the Cretaceous or intervene in the birth of any major religions or prevent the start of recent world wars. Unless quantum gravity somehow changes everything.

[Hannah K · Rating 3 out of 5]

The authors claimed this book would be less focused on the equations and hard science and cater more to a novice audience but I feel like some serious previous understanding of the laws of physics is required to understand what’s going on. Personally, I understood what was going on about 70% of the time. It’s kind of a bummer that the secret conclusion is that time travel isn’t likely. Also, I’m curious why there wasn’t any discussion of interactions in higher dimensions, but it might be that such topics are too theoretical and impossible to model using current science.

[Leanne · Rating 5 out of 5]

It turns out that physicists like to think about time travel just as much as the rest of us. Unlike the rest of us, however, they don’t do it to out-run debt collectors, exploit information to make their riches, or to go back in time to kill Hitler like we all would do. Instead, they do it to engage in what can best be described as formal thought experiments. This book is one of my favorites. Having been written by two very clever and witty physicists, it is a tour de force. It is definitely weak in providing skills one can use to build a time machine or survive in different time periods, but it does a great job in describing what is theoretically allowed by the current standard model of physics. Yawn... I know. It’s almost possible to ignore the equations in this book, which I strongly suggest ignoring. Just pretend like they aren't really there and focus on the concepts so to come to an understanding. And not to spoil the fun with spoilers, but it turns out that general relativity allows for faster-than-light shortcuts and backward time travel. But that even there, there remain severe restrictions on any actual realization of travel using wormholes or warp drives. Interestingly, it’s quantum mechanics that poses the biggest problem.

Following this logic, it becomes obvious that the standard model should be completely overturned for a better model which allows for time travel to the past. The problem is not time travel but the standard model and physicists simply must up their game.

The chapter on banana peels and paradoxes was my favorite. The arrow of time chapter should be skipped because Sean Carroll wrote a book on it. The light cone chapter was also fantastic, even though I had to read it 10 times to understand what it was saying and what it had to do with banana peels. To go boldly.... Authors seemed to like the movie Twelve Monkeys... putting it on my list!

[Wing · Rating 3 out of 5]

After explaining the nature of spacetime and the equivalence principle, the authors then show backward time travel is the conversion of spacelike curves to timelike curves through supraluminal motions that are allowed by the theory of relativity. So far, so good, and the mathematics up to this point is easy to follow. The authors then discuss quite comprehensively the issue of consistent causal loops. This bit also is easy to follow. However, when they start describing the way to physically construct a time travelling machine, they need to introduce rather difficult topics such as negative energy. They do so in relative detail but essentially without any mathematics. Their conclusion is that the chronology protection conjecture whilst not proven remains probable unless future theories in physics supersede current ones drastically. The level of difficulty of this book is perhaps inconsistent with the intended readership – so, three stars from me.

[Michael · Rating 3 out of 5]

Yikes, this one will give your non-Physics centric brain a workout. And you'll likely understand less than half of it. Unless of course this is your field. I gave it a three because for some reason I was led to believe that this was a physics book for the non-physics trained individual. I will admit this may have been my own fault and the misunderstanding may be all mine. It's not written like a text book, and the authors make it as easy as possible to follow it's just not that easy - unless it is for you.
So, I do recommend it but only if you really love math and getting into the weeds. Otherwise, read the introduction and the conclusion as the book is very nicely summarised in those two sections. Physics is hard and the concepts literally span the universe and what we don't know is still vast. This book does a good job of explaining why.

[Harry Harman]

the “grandfather paradox.” According to this scenario, were it possible to travel into the past, a time traveler could in principle murder his own grandfather before the birth of his mother. In this case he would never be born, in which case he would never travel back in time

there is an intellectually re- spectable idea in physics called the “many worlds interpretation of quantum mechanics,” first introduced in an article in Reviews of Modern Physics way back in 1957 by Hugh Everett (no relation to Allen as far as we know). According to (the other) Everett there are not just two parallel worlds but infinitely many of them, which, moreover, multiply continuously like rabbits.

[Kelly Massey · Rating 4 out of 5]

This is a book to pick up when you really want to consider the possibilities and think them through. The authors do use mathematics that a high school graduate would understand when explaining their theories on space travel, so it is accessible by most. Overall, a good read for the material that it conveys.

[Michael Gelli · Rating 4 out of 5]

interessante e spiegazioni chiare, vengono usati strumenti matematici alla portata di tutti (non scontato visti gli argomenti trattati). Consigliato per chi è appassionato di fisica e film di fantascienza.

[David Agranoff · Rating 2 out of 5]

DNF at 43% Look this is a subject I love but I found this hard to digest. I found it to be not accessible for laymen.

[Ray boycott Reading Challenges until they fix app]

Look I'm sorry but I just wanted a yes/no answer not pages covered in nothing but the square root symbol bruh

[Greg Heaney · Rating 3 out of 5]

Everett and Roman's book on time travel is a drastically different take on the subject than any I'd read before. What sets it apart, both to its detriment and triumph, is that the authors are primarily covering the material through mathematics, rather than physics. In my extremely limited experience, I've found that physicists are particularly good at explaining the rather odd phenomena related to relativity. What I've learned here is that you might not be able to say the same about mathematicians. Each equation and inequality is given some context, sure, but the focus is invariably on the math.

Now, this might sound obvious to someone who read the introduction. The authors claim to have attempted primarily to make the book accessible to anyone with a background in high school algebra. This is technically true... None of the operations are all that complicated. However, high school algebra never covered equations with 4 or more variables, or compared multiple reference points, or used constants that are important only to cosmology. So, none of the math actually performed in the book is terribly difficult, but the equations and inequalities used are very dense and not clear to the armchair reader.

Because of the difficulty in really "getting" the math, I'd say I understood around two thirds of what the authors told me. I'm fine with that amount. Still, I wish that it would have been a little higher. Unfortunately, some of the material that I didn't understand was some of the more interesting ideas. In particular, Krasnikov Tubes are poorly explained, and how two of them form a time machine went right over my head, despite reading the section three or four times. Some other questions that the authors don't explicitly ask still should have been answered, because they reader is clearly drawn to ask them. For example, it is adequately explained that the Alcubierre drive doesn't work because even if you had enough energy to power it, you can't steer it. The audience has to ask the question "What happens if you just turn it on? Where would it go?" But the authors themselves don't ask it, and don't answer. What a shame!

Further, it seems that an inordinate amount of time is spent disproving time machines that just clearly don't work, such as the Mallett machine. From the introduction of the idea, we are told that it doesn't work because it breaks one of Hawking's proofs, but we're still led on a 20 page journey further explicating the failures of the machine. Combined with some pretty passive aggressive comments and footnotes (actually, more aggressive than passive,) in the conclusion, and it seems to me like the authors are harboring some not so secret ill will toward a number of colleagues, and they are using this book as a bit of a soap box. I don't care if they're right - toward the end of a book about science, I spent more time wondering about personal/academic vendettas than the content of the book. That's the fault of the authors.

Still, I appreciated the book for its refusal to talk down to the audience. The authors are confident that with careful reading the audience will be able to manage just fine. It definitely leads to some over extension on the part of the authors, as I've said, but it also means that when you do finally grasp the material, it is much more clear and full. Had the book been written by a physicist, we might have gotten much more general statements, and been told to just trust that the math works out, or doesn't. Instead, we get to see the mess the whole way through. It's dirty, but I appreciate that.

All in all, this was a fun challenge, but I don't know that I'd say it's worth it. I don't feel like I understood the book well enough to explain it, which is a good way to judge your comprehension, I think. I feel like I read a collection of interesting problems in math and physics, but I don't feel like I'm much more knowledgeable concerning time travel. I'd recommend this to people with a good background in math and solid knowledge of relativity. Without those things, this might not be a great use of your time.

[Bonnie · Rating 3 out of 5]

This is not exactly a layman's science book. It is a lot of detailed explanations and equations and while it is probably a good read for people who, say, have a subscription to Scientific American, it is not easy to get into for someone who thought physics was the hardest thing her brain had ever gone through and found proofs in geometry class absolutely pointless (because I am more than happy to accept that the math works on blind faith). I do better with books like The Clockwork Universe: Isaac Newton, the Royal Society, and the Birth of the Modern World.

That being said, skimming through the equations and concentrating on the explanations it held my attention well enough. The chapter on time travel, "Banana Peels and Parallel Worlds,” was easily the most accessible and interesting. Although I'm not going to double-check the authors' equations (I mentioned that I hated proofs, right?), according to them and their math, and science as it now stands, time travel and warp drives are not scientifically possible. Too bad. That being said, the authors admit that perhaps a yet-to-be-discovered theory of science will allow for the possibilities of these things. I can only hope.

In a nutshell: despite the pretty cover, publisher's description and catchy title, this is a book more for science geeks than the Average Joe, but if you're willing to wade through some equations, it's worth a look.

[Terra · Rating 4 out of 5]

iniziamo dallo spoiler. è possibile oggi viaggiare nel tempo? no. sarà possibile in futuro? chi lo sa. detto questo, confesso che negli ultimi due capitoli - quelli speculativi - i due autori mi hanno persa per strada. prima invece mi sono divertita e ho scoperto che il tempo passato a spaccarmi la testa sulla relatività semplificata, studiata a scuola, non è stato tempo perso. ho letto che gli strumenti per evitare i paradossi dei viaggi nel tempo sono due: le bucce di banana e i mondi paralleli. mi sono resa conto che stephen king, nel libro sull'assassinio di kennedy, dissemina il passato di bucce di banana (e in conclusione se la cava con un mondo parallelo). mi sono segnata due o tre libri da leggere. ho ripassato per bene il paradosso dei gemelli. ho scoperto che esiste la materia esotica. ho imparato varie cose di dubbia utilità nella vita quotidiana, ma per farlo il mio cervello ha lavorato come i bicipiti di un sollevatore di pesi, provocando in modo analogo il rilascio di endorfine (ma niente acido lattico).

[Julia · Rating 3 out of 5]

I'm sure it's very informative and very accurate, and I know it is moderately entertaining and sometimes downright funny. Unfortunately, the authors presuppose both facility and interest in somewhat advanced physics (although the math is fairly easy if you've gone through high school algebra even though the equations themselves look scary) and having neither, I got lost somewhere mid-2nd-chapter. Still, I read what I could and now have some understanding about what is and is not possible re space/time travel based on what we know at this moment. Time travel to the future: possibly possible. Time travel to the past: mostly impossible. Wormholes through space: theoretically possible on a molecular level. Time paradoxes: cannot exist.

[Folkert Wierda · Rating 5 out of 5]

A great read, much more on Special and General Relativity than on actual time travel. Time travel is used as a theme to discuss physics.

Several reviewers complain about the math in the book. Actually the math is very minimal and easy. The difficulty of the book, as any work on topics concerning Relativity and Quantum Theory, is that the concepts are so much counter-intuitive that the reader must revert to a level of abstract thinking that many of us are not used to. I must admit that several of the discussions in the book I do not fully grasp. But overall a great read, explaining that Warp Drive, for now, is still a long way away.

Folkert

Www.ExcitingTechnology.net

[Duff · Rating 3 out of 5]

Everett and Roman do a fine job of synthesizing theoretical physics for the non-scientist in this work. I liked their approach and writing style...that said, at times I had to make an effort to sustain interest in longer explorations of theory. I did not ever lack appreciation for the author's knowledge or love of the subject, however.

[Sim Kern · Rating 2 out of 5]

This is a really challenging read for me. Makes me wish I hadn't dropped AP physics in my senior year. Sometimes I just don't have the math/science background to follow what the author is saying, but I'm hanging in there.

...Got halfway through and hit a wall in my scientific knowledge. The first half was cool, in a brain-hurting way.

[Cara · Rating 4 out of 5]

The authors are Star Trek fans so I felt they understood where a reader like me was coming from. I hate to say that even though I looked at all the math and thought, I used to know that, now I couldn't follow it and had to rely on their word alone. Alas, there is no antimatter/matter to make a warp drive and those pesky wormholes have yet to appear.

[Sarah Macgregor · Rating 4 out of 5]

Quite interesting.

I came across this in the science section of my local library around the same time as I was completing a physics assignment on special relativity and the scientific developments leading up to Einstein's theory. It explained key concepts really well, especially the Michelson- Morley experiment, as well as simply being an entertaining read.

[Bryan Kornele · Rating 5 out of 5]

This was a very slow read because of the details the book goes into discussing the different theories. Very interesting if one wants a brief discussion of the science, formulas, and road blocks that pertain to the possibility of time travel and speeds that approach light.

[Amy · Rating 3 out of 5]

I thought the book was interesting, but is definitely not an easy read for an "arm-chair" science follower. I skimmed most of the math sections and just enjoyed the explanations the authors wrote.

[Noah Richardson · Rating 2 out of 5]

Concept-heavy but fascinating so far...

[Mari Biella · Rating 4 out of 5]

Intriguing, but a challenging read (at least for those of us with little or no scientific background).

[Francesca Fernandes]

skimmed entire thing but super mathy & dry

[Ch J Loveall · Rating 1 out of 5]

Nothing new here for me

[Rebecca · Rating 4 out of 5]

A mostly accessible overview of the theories of general and special relativity and the developing field of quantum gravity that canvasses the possibility of forward and backward time travel via devices such as warp drives, 'warp bubbles', exotic matter and 'Krasnikov tubes' while delving into many worlds theory and/or 'the banana peel mechanism' versus the 'grandfather' and other time travel paradoxes. Some of the mathematical proofs were pretty challenging, but still fascinating reading.