This book is an overview of modern particle physics (as of 2005) and a surprisingly deep look at how the universe works at the subatomic level. There are no equations or calculations, but you get far more technical detail here than a typical pop science book. While some parts are hard to follow, other parts are astonishingly well written, explaining incredibly complicated physical concepts through wonderful analogies. It’s not easy reading, but it’s worth the effort, as this book helps you realize that the real world is far weirder than anything you’ll find in fantasy books.
I found many of the concepts in this book to be delightfully mind-bending. The world is nothing like what we perceive. Humans used to believe the earth was flat or that the sun revolved around the earth; changing these notions changed everything about the world. I imagine discovering the true nature of matter will change the world profoundly yet again.
Some of the interesting ideas I got from this book:
Gravity is different
- One mystery in particle physics is that the force gravity is much, much weaker than all other known forces.
- There’s a great example of this in the book: a tiny magnet can lift a paper clip, showing that the magnetic forces from a few grams of metal can overcome the force of gravity generated by an entire planet.
- No one knows why this is.
Theory of everything
The fact that gravity is so different from other forces makes it tough to come up with a theory of everything (ToE).
- The goal of such a theory is to come up with a set of equations that could predict the outcome of any experiment.
- I had heard ToE before, but never in such terms—what an audacious goal!
- For some reason, I can only imagine the search for a ToE to end in failure due to a result similar to Gödel’s Incompleteness Theorem.
- Perhaps the universe, by its very nature, cannot be completely predictable.
Extra dimensions
One possibility for why gravity is different has to do with extra dimensions.
- No known law of physics limits us to the 3 dimensions we experience (or 4 dimensions if you count time). There may well be more.
- Gravity might be using most of its energy in those other dimensions, and we are only experiencing the weak amount of energy that exists in our dimensions.
The idea of extra dimensions is hard to think about and there are no easy ways to visualize it. This book does a great job of using analogies:
- Explaining concepts in 2d and 3d worlds we can reason about and explaining that the same reasoning would apply to higher dimensional worlds too.
- I loved the analogy of a bug crawling along a 2-dimensional plane curled up into a hose.
There’s also the interesting concept that the number of “dimensions” is really just the number of quantities you need to specify to uniquely locate something.
- In 3 dimensions, those are x, y, and z coordinates.
- In 4 dimensions, we might add a time coordinate.
- In higher dimensions, we’re just adding more coordinates.
- You might not be able to picture it, but you can still reason about it.
It’s possible for extra dimensions to exist without them being detectable.
- The extra dimensions could be exceptionally tiny (plank length).
- If the universe is warped in a certain way, the extra dimensions may be infinite in size, but still not detectable.
Heisenberg Uncertainty Principle
This principle states that there is a limit to the precision with which you can know certain pairs of physical properties. For example, you can never precisely know both the position and momentum of a given particle at any given moment. This book has a lovely analogy to explain why.
- Imagine you have a dripping sink in your kitchen, and you want to know how often it drips.
- You get out a stop watch, count for 10 seconds, and calculate 10 drops.
- So that’s 1 drop per second, right?
- Well, the issue is that your stop watch and your ability to use it isn’t perfect.
- The precision is probably only about ~1 second, so it’s possible you’re off by about 1 drip, and the rate is actually 11 drips per 10 seconds, which is an error of 10%!
- One solution is to measure for a longer time period, such as 100 seconds.
- If you do that and count 100 drops, now you know the answer is either 100 or 101 drops in 100 seconds, which is at most a 1% error.
- If you measure even longer, you can get the error lower, but you’d have to measure for an infinite amount of time to get the error to 0.
This same problem affects measuring small things too:
- Measuring ever smaller distances requires ever more energy, as you need higher frequency waves to investigate smaller distances (otherwise, the distance is smaller than the wave itself).
- Creating higher frequency waves requires more energy.
- If you wanted to measure something at the plank scale, you’d need a massive amount of energy.
- So much, in fact, that long before you got there, this energy would collapse into a black hole, and then the very information you were looking for would be trapped behind the black hole’s event horizon, preventing you from ever seeing it!
Side note on black holes:
- We actually expected the Large Hadron Collider to create tiny black holes!
- Apparently, this was no big deal, as all black holes evaporate over time (turning into Hawking radiation), and these tiny ones would evaporate almost instantly.
Branes
A brane is like a boundary for the universe or a dimension.
- It’s like the crust on bread.
- Branes are always lower dimensions than whatever they surround (e.g., 2d crust on 3d bread).
It is possible that we live on one of these branes.
- For example, a 3d brane in a universe that has 4 dimensions (or more).
- Any particles in a brane can never get out of the brane—all physical interactions remain within the brane.
- So even though our universe might be 4+ dimensions, all our interactions would behave as if there are only 3 dimensions.
The one exception to this rule is gravity, which must behave the same way in all dimensions.
What we’ve learned since this book was published
This book was published before the Large Hadron Collider (LHC) had come online. The LHC has now been running for a few years and scientists have been trying to use the data within it to verify many of the particle physics theories brought up in this book, including the ideas of branes and extra dimensions.
So far, there has apparently been zero evidence that any of these theories are right:
- No new particles have been found
- No missing or extra energy
- Nothing new other than the Higgs Boson, which is actually part of the standard model
Apparently, this is causing a bit of a crisis in the theoretical physics community.
