by Brian Cox and Jeff Forshaw
A review by Jo Woolf
Everything moves in straight lines over the curved landscape of space-time. Not only is this a widely accepted theory in the study of astrophysics, it’s also a search term which someone recently used to find my site – yes, Jo’s Journal, my other blog.
How long have I been waiting for this? Too long, is the answer. Finally, I think I’m about to be recognised for my outstanding contributions to science.
How appropriate, then, that I have spent the last few weeks casting my expert eye over Brian Cox’s new book, ‘The Quantum Universe: Everything That Can Happen Does Happen’.
This nicely-presented little hardback book deals with quantum mechanics, which is “one of the three great pillars supporting the natural world… dazzling in its precision and explanatory power.”
I’m already fascinated, and ready to be dazzled.
After discussing Newton’s theories and those of more recent scientists, many of whom were dismissed by their contemporaries as ‘magician-physicists’ because of their reliance on intuition, the two authors go on to describe the double-slit electron experiment, which Professor Cox demonstrated in his lecture to the Royal Institution before Christmas.
A beam of electrons is fired through a barrier with two parallel slits, onto a single crystal of nickel. You would expect a pattern of electrons to build up on the nickel screen which mirrored the two vertical slits, like two piles of sand – but no. This is not the case at all. Instead, several parallel stripes of electrons appear, and continue to build up over time.
The reason for this, we are told, is that electrons behave as if they are waves. If you substituted the electrons for water, you would see the exact same ‘interference’ effect in the resulting water waves. But electrons are particles. How can a single particle behave like a wave?
Cox and Forshaw reassure us that “The details of how the electrons travel from source to slits to screen are not something we observe, and therefore need not be in accord with anything we experience in daily life. Indeed, the electron’s ‘journey’ need not even be something we can talk about at all.”
And this is where it starts to get interesting. Here’s the thing: a particle can be in more than one place at once. While my brain is still frozen in one spot (or maybe several), Professor Cox advises me that “we must keep an open mind and not be distressed by all the weirdness.”
He continues: “We need to describe a spread-out wave that is also a point-like electron, and one possible way to achieve this is to say that the electron sweeps from source to screen, following all possible paths at once.”
Having admitted that the electron’s ‘journey’ is something he can’t really talk about, I have to say that Professor Cox’s willpower is no match for the temptation. Not that I mind, because I really do want to know how these shape-shifting little specks manage to arrange themselves in neat, orderly rows. The answer probably lies in our pre-conceived idea about what a particle should look like, and how it should behave. As Professor Cox says, “Clearly the… electron is not an ordinary, everyday particle. This is what it means to be a quantum particle.”
That statement appeals to me, because it sounds like the trailer from a new blockbuster about super-heroes saving the world. All particles must surely aspire to be quantum particles, but sadly they don’t cut the mustard. They must lie helpless and inert, cowering in dark corners, dreading the sound of a Dyson… sorry, I’m going back to the book. Right now.
Feeling a bit like a blind person in the Minoan labyrinth, I’m now learning about waves. Using a clear diagram, Professor Cox describes the moon’s phases as perceived from Earth, and equates them with times on a clock face (midday for new moon, three for first quarter, six for full moon, nine for last quarter). I’m getting somewhere, because I understand that bit.
Then we move on to wave patterns. As a wave fluctuates above and below a set horizontal line, it is possible to illustrate its peaks and troughs by the use of clocks, with an hour hand pointing to 12 for the peak, three for the point at which it crosses the line, six for the lowest point of the trough, and nine as it crosses the horizontal line again in the upward motion.
Two different wave patterns can, in fact, cancel each other out if their peaks and troughs happen to coincide. With a sinking feeling, I read that you can actually add two clocks together and calculate a new ‘time’ at any point along the two combined wavelengths.
Cox explains that these clocks are “not real in any sense, and their hour hand has absolutely nothing to do with what time of day it is. This idea of using an array of little clocks to describe a real physical phenomenon is not so bizarre… as it may seem.”
So, back to the evasive little electrons that go through one or both of the slits before hitting the screen. The electron wave is largest where the electron is most likely to be.
But, for the love of Einstein’s hamster, how do we know where it’s most likely to be when we’ve just discovered that it can be in more than one place at once?
This is where I would say that we are perhaps becoming too possessive of these precious little electrons, when it is obvious that they want to do their own (very bizarre) thing. So, like a stroppy teenager or a newly-landed sea trout, we must let them go. We can’t stay up at night, waiting for them to come home, and we can’t keep tabs on them while they’re out.
A few more pages and a lot more clocks later, we reach this conclusion: “We can’t, even in principle, predict what the position of a particle will be. What we can predict, with absolute precision, is the probability that a particle will be found in a particular place if we look for it.”
So, does it boil down to this? I’m pretty sure I left my mobile phone in my handbag, but it’s not there. It’s unlikely to be on board an oil tanker in the Arabian Gulf, but it could very well be in my coat pocket. Ah, yes – there it is.
Passing blithely over the Schrödinger equation and Planck’s constant, I thought I’d surprise myself by opening the book at random. Sadly, this only proved that I can’t cheat by skipping pages. I came up with this: “Now we can go ahead and invoke the de Broglie equation from the last chapter to relate the wavelength of these sine waves to the momentum of the electron via p = h/λ.”
This is where I have to admit that my consumption of this amazing book is still a work in progress. I tend to get sidetracked by the wrong things. I do, however, love the way the authors express their genuine delight in the simplicity of theoretical physics. Their enthusiasm is contagious – to the extent that I find myself giving every last effort to mastering their outrageous propositions.
And I love this statement: “Saying that every atom in the Universe is connected to every other atom might seem like an orifice through which all sorts of holistic drivel can seep.” Brian Cox never disguises his contempt for anything even vaguely hippy or ‘woo-woo’, as he puts it. A shame, because the book’s cover incorporates all the colours of the chakras…
I’m less than half-way through, and I know that I must by-pass an invisible force that’s stopping me from appreciating the other chapters. This force is called my own ignorance.
What can I take from my gleanings so far? This comforting thought: in later life, when the questions of where I am and who I am might seem to be bothering me even more than they are now, it will be evident to those who know me that I’m pondering the values of Heisenberg’s Uncertainty Principle.
I’m not giving up yet, partly because I’m intrigued by Professor Cox’s frequent descriptions of equations and principles as ‘beautiful’. Undeniably, there is boundless beauty in the natural world and the Universe, which we can see with our own eyes. I’d just like to see it expressed in terms of atoms and their inner workings. So I shall persist, and if everything that can happen really does happen, then I’ll succeed. But it might take a few billion years.
‘The Quantum Universe: Everything That Can Happen Does Happen’ is written by Brian Cox & Jeff Forshaw and is published by Allen Lane, RRP £20.