Why Does E=mc²? (And Why Should We Care?)

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Why Does E=mc²? (And Why Should We Care?)

3.93 of 5 stars 3.93 · rating details · 1,735 ratings · 183 reviews

The most accessible, entertaining, and enlightening explanation of the best-known physics equation in the world, as rendered by two of today’s leading scientists.

Professor Brian Cox and Professor Jeff Forshaw go on a journey to the frontier of 21st century science to consider the real meaning behind the iconic sequence of symbols that make up Einstein’s most famous equatio...more

Hardcover, 264 pages

Published July 14th 2009 by Da Capo Press (first published 2009)

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Jan 06, 2011 Courtney Johnston rated it 4 of 5 stars

Shelves: big-ideas-made-accessible, borrowed, science

I loved this book, and it wasn't just that cheeky Brian Cox going on all the time about being covered in tweed and chalkdust (somebody please hand me a fan).

'Why does E=mc2' is my fifth book from the Royal Society science book shortlist. If Marcus Chown is magical cellulite cream, this is physics bootcamp - no corners cut, no let's-take-it-easy-today-shall-we. Cox and Forshaw don't just want to explain this equation - they want you to understand it, to understand its power (predictive and descri...more I loved this book, and it wasn't just that cheeky Brian Cox going on all the time about being covered in tweed and chalkdust (somebody please hand me a fan).

'Why does E=mc2' is my fifth book from the Royal Society science book shortlist. If Marcus Chown is magical cellulite cream, this is physics bootcamp - no corners cut, no let's-take-it-easy-today-shall-we. Cox and Forshaw don't just want to explain this equation - they want you to understand it, to understand its power (predictive and descriptive) and understand how, despite being just a diminutive collection of letters and symbols, it underpins nearly a century of contemporary science, and captures some of the most fundamental characteristics of the universe.

I feel like the target market for this book - a person who gave up on maths in fourth form, and stumbled through sixth form physics before escaping the next year to classics class, my natural home. Cox and Forshaw are punctilious in their care for the mathematically challenged, to the point where even I wished they'd quit apologising for bringing the maths in to it - because for once, I was following it.

I'll need to read the book at least one more time to really get to grips with the subject. But I started to feel the magic tingle of understanding when I read sentences like 'temperature is essentially nothing more than a measure of the average speed of things', or when I looked up from the book and listened to the waves breaking and thought of them as energy, drawn from the moon's gravitational force, dispersing itself through friction and sound (yep - an unusual beach read, I'll concede, but perhaps that suggests the book's measured pace and gentle writing).

I felt my usual moment of cosmic connectedness when I read in here about the Super-Kamiokande experiment in Hida, Japan, where neutrinos are 'seen' passing through a cylinder filled with 50,000 tonnes of pure water at the bottom of a mine shaft. Knowing that every second every part of my body, everthing I can see - everything I can't see - is being lanced through by innumerable particles spat out from the sun fills me with a sense of wonder that is the nearest I come to a religious sensation.

In addition to their explication of the equation, Cox and Forshaw do a good job of describing the sense of wonder physicists themselves feel, not just at the deep movements of the world, but at the almost magical way that mathematics can be used to describe them. Writing about the master equation that lies at the heart of the Standard Model of Particle Physics and sums up - well, basically everything - they note:

It is certainly impressive that we can shoehorn so much physics into one equation. It speaks volumes for Wigner's "unreasonable effectiveness of mathematics". Why should the natural world not be far more complex? Why do we have the right to condense so much physics into one equation like that. Why should we not need to catalog everything in huge databases and encyclopedias? Nobody really knows why nature allows itself to be summarized in this way, and it is certainly true that this apparent underlying elegance and simplicity is one of the reasons why many physicists do what they do. While reminding ourselves that nature may not continue to submit itself to this wonderful simplification, we can at least for the moment marvel at the underlying beauty we have discovered.

Highly recommended if you have the itch to scratch, but a word of warning - if you're not interested in understanding why the theory of special relativity is so important, then this is not the book for you. The authors are intentionally avoided adding to the (understandable) hero worship that surrounds Einstein, and this is not biography-as-science: this is a maths and physics primer, kindly and interestingly written. (less)

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Mar 16, 2010 Kristin rated it 4 of 5 stars

On a good day, high school physics class used to leave me feeling kind of (for lack of a better word) high. This book brought back that old, familiar feeling, but in an even better way. In the end, I walked away with a much clearer understanding of Einstein's theories of special and general relativity than I ever achieved slogging through high school physics. (I think our teacher must have been unable to articulate and synthesize the underlying questions that the equations sought to answer.) The...more

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Apr 16, 2012 David Gillanders rated it 4 of 5 stars

Shelves: popular-science

This was an excellent walk through of an introduction to particle physics, which I was able to follow, mostly! I got lost on the maths so just had to accept that part, but its written in an engaging manner and explains things well. It helps having watched Brian Cox on T.V. a bit, because then you have his voice in your head narrating the book! As well as having a basic overview of particle physics the book also gives some good examples of how science progresses, which I think is interesting from...more

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Mar 31, 2012 Katie Welch rated it 3 of 5 stars

I decided to give this book a try because I've seen Brian Cox's show, Wonders of the Universe, before and really enjoyed it. I thought it would be interesting to read a book expounding the relevancy of Einstein's equations in our world. However, science is definitely not my best or favorite subject, and I was a bit worried it might not keep my attention. I was pleasantly surprised. The authors seemed to direct the book at newcomers to physics, and their explanations were clear and easy to unders...more

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Feb 29, 2012 Bob Nichols rated it 2 of 5 stars

For those trying to nudge themselves into Einstein's world a little more, this book's title has great appeal. At some very general level, the equivalence of energy and mass can be understood, but the role of light ("c") and light squared remains a challenge.

The authors do a good job of describing how mass converts to energy (heat/photons/light carry away mass; when wood burns, energy is released and mass is reduced). In the reverse, energy adds to mass. When energy (heat) is added to mass, mass...more For those trying to nudge themselves into Einstein's world a little more, this book's title has great appeal. At some very general level, the equivalence of energy and mass can be understood, but the role of light ("c") and light squared remains a challenge.

The authors do a good job of describing how mass converts to energy (heat/photons/light carry away mass; when wood burns, energy is released and mass is reduced). In the reverse, energy adds to mass. When energy (heat) is added to mass, mass increases because energy itself has mass. At the heart of the understanding of reality, the authors make it clear that mass and energy are the same thing. They are not "disconnected entitites." Matter is, in short, "capable of popping into and out of existence" but (presumably) continues to exist as energy.

This all prompts one to wonder what underlies and connects these two disconnected entities and why does conversion from one to the other occur. Is the "pull - push" phenomena related in the sense that mass pulls energy into itself and energy seeks to escape mass? Is concentrated energy in mass gravity? Is energy escaping mass "liberation"? [The authors make a few references to "liberated energy"]). If, as the authors note, the sun loses 4 million tons of mass every second in the form of radiated energy, does this mean that the earth is gaining some mass from that energy?

While the authors are quite lucid here and there, their discussion of the role of light in Einstein's equation was frustratingly opaque. Intriguingly, they seem to suggest that the speed of light is not the central factor. It is, rather, a way to measure distance in a time direction, but it is not clear how time (spacetime) relates to the discussion that energy and matter are equivalent. The authors are clear that time and space is one thing, and that light years (a unit of time) can be used to measure distance. The authors seem to say that "c" is relevant because particles of light are massless. It's almost as if they are saying that at the speed of light there's no mass but only pure energy (but if this is so, how do photons/energy add to mass; if mass is shedded by radiated light, doesn't mass go with that light in some way? Elsewhere, the authors say that spacetime is like "cosmic maple syrup" with some mass (Higgs field?). When that happens, does light pick up mass?

The authors say other things about light that are also unlcear: that there's a cosmic speed limit and that there is such a thing as "allocated speed" and a cosmic "speed quota," and that everything hurtles through spacetime at the same speed. All of this is somehow related to the "c" in the Einstein equation. At this point, it's an achievement for the lay reader to simply identify what he or she does not understand. This is all challenging stuff. Perhaps the real problem is the inability to transfer our earth-bound perspective as that has evolved to be into these cosmic realms that operate on such vastly different scales. (less)

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Aug 03, 2011 Dan Cohen rated it 3 of 5 stars

A good and thought-provoking book, and it certainly gave me some things to ponder. I am still mulling over the not entirely convincing explanation of the definition of distance in Minkowski spacetime and on the rather sleight-of-hand way that the famous equation emerges from conservation of momentum. I felt that deriving it this way was a bit of a con for a book whose title suggests the reader will acquire a better understanding of why it's true, not just how to prove it.

I wasn't so sure about t...more

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Jul 29, 2011 Steve Mitchell rated it 5 of 5 stars · review of another edition

Although I have always had a love of science at school and college I concentrated on chemistry, biology and geology. Physics was literally a closed book to me until fairly recently after rediscovering Carl Sagan's excellent series ""Cosmos"" and the book that accompanied it. The real problem for me with physics has always been the maths and formulae that make it hard to follow unless you have a teacher willing to slow down and lead you through the numbers very slowly. Step forward professors Bri...more

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Nov 30, 2009 Danielle rated it 3 of 5 stars

Shelves: biography, history, nonfiction, science-technology

I was expecting, from the first few paragraphs of the book, that I was going to breeze right through this. It didn't really happen that way. I had to take college physics, which included the basics of relativity and quantum theories, so I probably have a bit more knowledge than the average non-physicist. All the same, there were areas of this book that just did not seem to click at all, even after reading paragraphs over and over again. Usually the parts that didn't click were the "easy" example...more

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Aug 12, 2009 Thermalsatsuma rated it 5 of 5 stars

Shelves: book-a-week-2009

This is probably the best known equation in science but knowing how it is derived and what it actually means is a whole different story.

In this book Professors Brian Cox and Jeff Forshaw start with Galileo's profound insight into the nature of relative motion which led him to the inescapable conclusion that the Earth was not the centre of the Universe. They then progress to the observations of Faraday and Maxwell on the curious link between electricity and magnetism describing simple experiment...more This is probably the best known equation in science but knowing how it is derived and what it actually means is a whole different story.

In this book Professors Brian Cox and Jeff Forshaw start with Galileo's profound insight into the nature of relative motion which led him to the inescapable conclusion that the Earth was not the centre of the Universe. They then progress to the observations of Faraday and Maxwell on the curious link between electricity and magnetism describing simple experiments that everybody has probably tried at some point in their life. They show how Maxwell was able to accurately predict the speed of electromagnetic waves with his equations establishing the importance of experimental evidence as well as elegant theories.

Using maths no more complex than Pythagoras' Theorem and a little bit of algebra they lead the reader along the same paths of reasoning that Einstein followed to develop his theory of special relativity, examining the strange consequences of the speed of light having a fixed value. Almost without realising it, you are in a strange world where space and time become a single entity dependent on the observer. Again, the effects that are predicted by the theory have been demonstrated in practical ways, and indeed how things like GPS satellites have to account for the warping of spacetime and the time dilation effect to correct their internal clocks compared to Earthbound timekeeping.

The final chapters take the boldest leap of all, talking about the standard model - an equation for describing how all subatomic particles and forces interact with each other with just a handful of symbols. Most importantly they stress how any theory, no matter how elegant, is absolutely dependant on experimental proof which is why the LHC experiment at CERN is so important and interesting - it will either find the elusive Higgs Boson to complete the standard model or it will open the way to a new and more complete description of the nature of matter.

This is certainly not a dry book - there are plenty of wry observations and humour along the way, including an description of the link between mass and energy by comparing the mass of a hot meat pie purchased at half time at Oldham Athletic on a wet Saturday afternoon with the same cold pie at the end of the match. This book should be accessible to just about everybody - the areas where the maths gets a little tricky are clearly sign posted and the reader is encouraged to follow the working so that they can appreciate the lightbulb moments as the conclusions fall into place.

Read it and wonder at the sheer strangeness and charm of our universe.

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Mar 01, 2012 Dave rated it 4 of 5 stars

Shelves: physics

Awesome book but I don't get why they didn't explain the math better. It was frustrating as hell trying to figure out how they came up with some of the different equations, since I haven't taken math in years. However maybe it was a good thing because it inspired me relearn algebra. Here's some explanations on some of the math for those who are struggling with it. page 47-
c^2t^2=1+v^2t^2
subtract v^2t^2 from both sides.
You're left with c^2t^2-v^2t^2=1
Factor out t^2 and you get t^2(c^2-v^2)=1
Divid...more

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Feb 20, 2012 Si rated it 5 of 5 stars Recommends it for: did wong

I've been a fan of Brian Cox for years. His infectious enthusiasm, his ability to boil down complex concepts for an average dude without a physics degree, and his clear passion for what he does, make him compelling viewing.
So after seeing him and Jeff Forshaw lecture on the subject of this book, I decided to get a bit more in depth and check out the book.
It’s excellent. The guys are able to help me to understand and visualise relativity. This is easier said than done with such a counter-intuitiv...more

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Dec 27, 2012 Andy rated it 4 of 5 stars

Shelves: science-and-math

Cox and Forshaw do an excellent job guiding the reader through the scientific journey that led to Einstein's famous equation. Those lacking a strong background in physics (such as myself) should be cautioned that many passages will require a second, third, or even fourth reading before the concepts start to sink in. That said, after finishing this book I am confident that I can explain the following concepts in simple, easy-to-understand language:

(1) All motion is relative
(2) Space and time cann...more

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Jul 12, 2012 Alazzar rated it 4 of 5 stars

My previous experiences with physics were limited to watching How the Universe Works (which, by the way, is an excellent program that you should check out if you've got Netflix streaming), so I went into this book armed only with the knowledge that E equaled MC Hammer and STOP!

Hammertime!

[Dance mode INITIATED.]

Anyway, authors Cox and Forshaw did a good job of dumbing things down and using interesting examples that helped me understand a lot of the concepts they outlined. Granted, there were part...more

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Nov 19, 2012 Georgina rated it 4 of 5 stars · review of another edition

Many moons ago when I was younger my dad gave me a copy of 'A Brief History of Time' I remember it took me absolutely ages to get through, and I'll admit, not everything made sense to me or sunk in but I finished it.

Why Does E=mc2? is a great book. Both Cox and Forshaw have a brilliant way of simplifying what could potentially be a headache for the reader, or anyone who doesn't hold mathematics as a strong point. I was able to explain otherwise complex theories in a simplistic way to friends, w...more

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Apr 15, 2011 Simon Logan rated it 3 of 5 stars

Shelves: audiobook

This review is specific to the audio edition

Whilst far from being an expert physicist I have read a fair bit about relativity and quantum mechanics etc so I was coming to this book looking to get a clearer understanding of the subject matter it deals with. The only problem is that I don't think I'm any clearer now than when I started.

I have no doubt that this is in large part due to the fact I was listening to it as an audiobook rather than reading it so don't want to put the book down too much....more

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May 28, 2011 Steve rated it 2 of 5 stars

Shelves: science

From the man that bought us the 1997 New Labour election theme tune, comes a book about the origins and meaning of Einstien's E-Mc2.

The main problem with the book is there is far too much going on about 'deeper understanding' and time spent telling us how things are being explained to us poor intellectually subnormal non physicists in v e r y s i m p l e t e r m s so we can keep up.

If you can get over the condescending tone, and the jumbled narrative (too many tangents), the information is easy...more

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Dec 12, 2011 Martin Sidgreaves rated it 4 of 5 stars

Shelves: science, non-fiction

After reading several books that centre around the complex, at at times, mind-boggling world of Quantum Mechanics I was looking forward to tackling this offering co-authored by the ever popular Prof. Brian Cox.

From the start I realised this wasn't like any of the other books I'd read and Cox makes no apology for the fact that to get the the solution, the reader has to wade through some pretty heavy-duty maths. In previous books one has been asked to perform thought experiments in regards to conc...more

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Jul 27, 2012 Jay rated it 4 of 5 stars

Shelves: factual

I didn't expect much from this book at first and presumed it would be quite basic and over-simplified. While I did feel that in places some of the explanations went on a bit too long and the analogies were quite long-winded, I think the scope of this book and the wealth of information it gave was great - covering a lot of different areas from Physics related to relativity. Explaining relativity in terms most people can understand is no easy feat, but Why Does E=mc2 manages to do it reasonably we...more

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Aug 22, 2009 Shinynickel marked it as to-read

Off this review: Why Does E=MC2? (And Why Should We Care?)
By Brian Cox and Jeff Forshaw (Da Capo Press)
To move beyond a cursory understanding of Einstein’s iconic equation, put yourself in the adept hands of physicists and science educators Brian Cox and Jeff Forshaw. Using clear language and a few clearly explained equations, they demystify physics’ most counterintuitive claims, connecting the dots between space-time, electromagnetic fields, invariance, and Galileo’s earlier theory of relativit...more

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Nov 24, 2009 Robb rated it 3 of 5 stars

I felt like this book went back and forth between being written in real simple terms to being hard to follow mathematics written in narrative form. It went back and forth between being exciting to being boring in its presentation of equations, and that's coming from a math major who enjoyed every math class I had in school. Some of the concepts in the book, which are considered by some to be basic and foundational to modern physics, are truly fascinating to ponder. I love stretching my brain thi...more

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Aug 16, 2011 Lucas Wiman rated it 5 of 5 stars

Excellent and intuitive explanation of relativity. The first several chapters provide an amazingly clear explanation of how to derive special relativity from a small set of intuitive premises (using very few equations, which you can skip). I highly recommend it to anyone interested in understanding Einstein's theory. My only objection would be that his caveat about Einstein's brilliance in the final pages does not emphasize the extent to which Einstein's ideas were in the air of the time among P...more

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Mar 19, 2013 Mike rated it 5 of 5 stars · review of another edition

The first book on Relativity/Quantum theory I've read that explains spacetime in a sensible way, in that it doesn't hide the (not particularly complex) mathematics. It makes it so much easier to understand if you have a passing knowledge of Pythagoras.

Loved the explanations of how the counter-intuitive properties of the universe were derived from simple rules. Lots of 'ah-ha!' moments for me, especially when talking about "everything travels at the speed of light", and "distances are smaller at...more

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Dec 23, 2011 Jim Lawrence rated it 5 of 5 stars · review of another edition

I had never been able to grasp fully the 'basic' explanations of relativity before I read this excellent book. Ok,I was fine with the concept of space not being absolute, but that was about it. I certainly had no real idea why time should pass at different speeds according to one's frame of reference or why spacetime makes sense of things. And as for why energy should be equivalent to mass x the speed of light and why this matters for causality, well forget it.

But thanks to 'Why Does E=mc2 and W...more

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Apr 17, 2012 Joanna rated it 5 of 5 stars

Shelves: favorites

I loved this book - it actually takes you through the processes of deriving e=mc2 and provides the necessary context on people and theory to understand the meaning behind what this equation means. Good detail. Good big picture. Also sheds some light on the experiments the lovely people at CERN are doing. I had to re-read several sections (some many times) to really get it but it was well worth it. The math gets pretty deep towards the middle (you can skip it, but it's there if you're inclined to...more

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Apr 14, 2013 Rachael rated it 3 of 5 stars

There is a lot of good insight in here, and the concepts are explained carefully and clearly. The reason I had to give this 3 instead of 4 stars though is because I was offended by the constant need to apologize about the smallest amount of math. I don't know if I should blame the authors for this per se, but I only found it distracting and sad that the simplest algebra had to be explicated. Nevertheless if you can skim over the 'I'm sorry but math is important and here's why and if you don't li...more

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May 24, 2011 Matt rated it 5 of 5 stars

An outstanding book and must read.

They managed to explain such complex concepts as the distortion of space and time with just the Pythagorean theorem (you know, the length of the hypotenuse of a triangle). And then reaches the famous equation by adding momentum into the discussion. The concepts may be mind bending, but the maths is very basic and explanations clear and concise.

The enthusiasm of the authors is infectious, and I came out of this book desperate to know more about relativity, partic...more

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Nov 17, 2009 Dan rated it 3 of 5 stars

I have a slightly better grasp of relativity, and if I were to read the book again I think I would get even more. However, there seemed to be a lot of basic stuff.

My main problem is that it doesn't answer the question in the subtitle. I was hoping for more everyday application stuff. One of the more interesting parts was about the global positioning satellites and it didn't come until the end.

Part of my problem is that I would read before I went to bed and there were a lot of easy places to stop...more

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Sep 26, 2012 Wayne Lincourt rated it 5 of 5 stars · review of another edition

An exceptional work by Brian Cox and Jeff Forshaw. Formerly you had to be a physicist or brilliant mathematician to "get" the science of Einstein. They've made it understandable to the lay person and have opened the door for all of us to a greater understanding of our universe. To be perfectly honest, I didn't absorb it all in my first time through, although I did learn more than I knew going in. The second time, investing a little more concentration and taking notes, will get you there. If you...more

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Jul 01, 2012 John rated it 2 of 5 stars

Why is E=mc^2? It was an enormous ask, and Cox and Forshaw were never going to deliver.
It is easy reading, but unless you understand maths you won't get it at all.
When I read on page 77 "although we did not prove (the maths)" I began to feel cheated, and then they tried to explain in several thousand words space-time vectors, which could have been done in two lines of maths, then I thought to myself it would have been much easier if they had used the maths throughout, and dispensed with all thos...more

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Aug 17, 2011 David Boyce rated it 1 of 5 stars · review of another edition

This book isn't concise in any way. Cox Rambles on, goes off on pointless tangents and generally makes something really simple into something really complicated. Seeing as the whole book is just about deriving E=mc^2 and that takes the average physicist about 8 minutes to do you would think it would be simple. You would expect that for a wider readership Cox would expand, slow down and generally make easier the intermediate stages of the derivation. However, Cox doesn't make it easier. He mainta...more

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About Brian Cox

Brian Edward Cox, OBE (born 3 March 1968) is a British particle physicist, a Royal Society University Research Fellow, PPARC Advanced Fellow and Professor at the University of Manchester. He is a member of the High Energy Physics group at the University of Manchester, and works on the ATLAS experiment at the Large Hadron Collider (LHC) at CERN, near Geneva, Switzerland. He is working on the R&D...more

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