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Quantum Reality : Nick Herbert


  11:31:25 am, by Nimble   , 1520 words  
Categories: Reviews, Attractions, Science

Quantum Reality : Nick Herbert

Link: http://www.amazon.ca/exec/obidos/ASIN/0385235690/thecerealkill-20

Full title: Quantum Reality | Beyond the New Physics

This is a pretty appealing book about the mysteries of quantum physics. If you know a little math (no calculus required) and perhaps the way sound waves work, this is a great introduction to what quantum theory is all about, and some really good insights into attempts to figure out what it all might mean.

Make no mistakes about it, quantum effects are weird. In the days of just plain old classical physics, we were pretty sure of the reality behind everything. Electrons were little balls that had charge, definite position, definite momentum, and existed independent of anything watching them.

Quantum physics changed all that.

Ever since quantum physics equations were described, every experiment we've thrown at them shows them to be true. They don't make sense in our common, everyday experience, but quantum physics works.

If you aim a beam of electrons through two slits, and record all the flashes the electrons make when they hit a phosphor screen (much like the fast-disappearing traditional TV screen), they add up to make a picture of dark and light bands, just like light does, known as an interference pattern. You can do experiments like that with ripples in your bathtub. Okay, you've maybe heard that electrons can be waves and particles in some science magazine. It's not quite so simple, though...

Let's start turning down the speed that the electrons are emitted at. We can slow this down a lot. Let's slow it down to one electron every fifteen seconds, or more. If you add up the flashes on the screen, you still get the interference pattern. What are these single electrons "interfering with".

You get a tour of this and more with the book.

You may also have heard of 'Heisenberg's Uncertainty Principle', that you can't measure both the position and momentum of a particle to more than a certain combined accuracy.

This book does a marvellous job of explaining how this works. It is not, as has been repeated in some popular literature, because we modify/poke/alter the particle when we measure it.

They make an analogy to the two different ways of making sounds with synthesizers. This bit will appeal to some music makers. Analog synthesizers combine waves together to create sounds. Digital synthesizers combine short spikes together to create sounds. It turns out that these two are polar opposites when it comes to reproducing sounds. Representing a pure sine wave with spikes completely accurately would require an infinite number of infinitely short spikes.

Conversely, there are some spikes sequences that are very hard to represent as a collection of sine waves, and indeed to represent some spike sequences perfectly would require an infinite number of them. There is a mathemetical approach to getting sine waves out of spikes called Fourier Analysis which is used in things like showing sound levels on your equalizers, searching for extraterrestrial life and even mechanically in your ears.

That's not to say that you can't get pretty close. It's just to say that you can't analyse every wave to infinite accuracy as both spikes and sine waves.

So this is just the nature of waves.

It's weird. Quantum theory is a theory all about probability.

These waves of which it speaks are not waves of water or even waves of energy. They are waves of probability, i.e. how likely your particles you shot through your experiment will end up at the given point. Shooting one particle through won't tell you whether the equations are correct, but throw 1,000 through, 100,000 through, and you get closer and closer to what the equation tells you. If the equation says 50% chance at this point, then 50,000 plus or minus a couple will actually show up. It's so strong a correlation, you would have to figure that this is related to what's "really going on" in nature. After all, what does an equation of probability tell you about what nature's really doing?

A large part of the book is dedicated to figuring out what these things might mean and what limits are imposed on any theory of what's really going on behind the scenes.

The disappointing part is that there are eight main ways to interpret what's 'really going on' in the universe, and:

  • They all have problems
  • They all produce exactly the same results

This book is a little on the older side... from 1985. From keeping up with the literature, there are some engineering advances, but the questions remain unanswered, and as far as I've been able to tell, all eight camps are alive and well.

The majority mindshare is still held by the decades-old Copenhagen Interpretation. This holds that the theory is all that there is, that it actually represents reality. Special classical physics status is accorded to the measurement device.

I find this position untenable not just because it removes the measurement device from being part of the quantum system, but because it casts a pall over asking any more questions about reality.

On the extreme end are those who believe that consciousness is what causes measurement. They base this on von Neumann's work showing that if you have the measurement device inside the quantum realm when you treat it in your equations, you can get a measurement when you 'collapse the wave function'... but you can in theory do this anywhere and still get the same results. It could happen halfway to the computer, or halfway to your eye, what have you, and still give the same results. So where do you pick? What's going on?

I have an unabashed hate-on for this position, in large part because it seems to seek to put humans back at the centre of the universe again, and that every time I see or hear quotes related to this view, consciousness is treated extremely "magically", and seems to show some serious ignorance of the relative 'ordinariness' of brains and the findings in the field of neurology.

There are other positions, varying from a different kind of logic framework, to the "universe splits into bazillions of other universes at every moment" (I'm not keen on that view - it does not seem particularly 'useful', and I grate when people start talking about trying to contact those other universes, because that goes contrary to the way it would have to work, although Robert Sawyer made a pretty fun novel out of the concept), to the "neorealists" trying to insist that something is really there.

One thing that throws a very strange seeming limit on reality is Bell's Theorem. This basically says that no matter what you do with a theory of reality, it cannot be local. What does that mean? It essentially means that you cannot explain it with ordinary pieces that go slower than the speed of light, period.

Particles behave as though they are communicating instantaneously... despite distance. That puts some odd-seeming limits on what's really going on behind the scenes. For the neorealists, it means that there are faster-than-light components to it.

So far, according to everything theorized and tried so far, there's no way to take advantage of that seeming faster-than-light connection. You get experiments with light where a photon polarized one way affects the way a photon a long long way away is polarized, but since this effect happens only when you have randomized results (e.g. you're polarizing at 45 degrees, so half go one way, half the other) and you can't actually control the polarization, it makes it utterly useless as a communication device.

This last piece is actually explained in some detail in the book, but it seems slightly more hastily written than the rest, so it can be a bit hard to follow.

This book certainly helped me figure out what our options are in describing reality a whole lot more than any of the more math-oriented books, and it bent my mind and threw questions into my head. For example, it seems that electrons really, really behave like points; you can throw electrons at one another faster and faster and they never deviate from what you expect from just a plain electrical field (if they struck one another's "surface", you'd see a change). So how can they "spin"?

Besides the usual mind-benders, there are some real doozies in there. I didn't know how stellar interferometry, one of the techniques they're using in the search for planets, actually is based on quantum effects. Throw two mirrors on a railcar (as an example), and point them towards the same spot on a screen. They will reflect light from a distant star, but add up all the flashes, and you get an interference pattern, regardless of how few photons come through. If you move the mirrors apart, you get to a point where all of a sudden the pattern goes fuzzy. This means you're outside of the 'probability wave' coming from that star. Move back in, and it reappears. It can be the size of a parking lot, or even larger. What... the... hell? What are these waves, really??

A thought-provoking book. I thoroughly enjoyed it :)

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