Sean Carroll is an American theoretical physicist and philosopher who specializes in quantum mechanics, cosmology, and the philosophy of science. Among other things, Carroll writes about cosmology, the arrow of time, and the Higgs boson.
Sean Carroll
This book addresses a variety of topics, but concentrates largely on 'time.' There are many ways to define time, but in essence, "Time is the agent of change. We move through it, or - equivalently - time flows past us, from the past, through the present, towards the future." In other words, time goes one way - from past to future.
In the first Superman movie, Superman flies around the Earth so fast that he reverses time....time runs backwards instead of forwards so that Superman can rescue Lois Lane.
Can we really go back in time? No! Sean Carroll writes, "In the actual, non-imaginary world, it never happens. Time has a direction, and it has the same direction for everybody."
A corollary is that "Paradoxes do not happen." For instance, you can't go back in time and kill your grandfather, so that you will not be born....and then you wouldn't be around to go back in time. Several whimsical examples are included in the narrative as Carroll makes this point.
Don't get me wrong. For the lay person, this book is VERY HEAVY on physics. But Carroll has a good sense of humor and his levity helps the medicine go down (so to speak). 🙂
In this review I'm going to include a few things I found especially interesting in the book, just to provide a tiny feel for the topics.
🌌 Entropy
Most people who've taken a basic science class have heard of the Second Law of Thermodynamics, which (in simple terms) states that, "something called entropy, which measures the 'disorderliness' of a system, has a tendency to increase as time passes. And the reason is deceptively simple: There are more ways to be disorderly than to be orderly." It's not that hard to break an egg and scramble the egg molecules, but putting them back into the shape of a whole egg is impossible.
The Second Law of Thermodynamics has profound implications for the universe, where the entropy is increasing every second. It means that at the time of The Big Bang, the universe had VERY LOW ENTROPY....in other words was very orderly (in some fashion). So is OUR universe part of some larger multiverse? Carroll speculates about this from several angles, and he seems to come down on the side of yes.
The Big Bang
🌌 Quantum Mechanics
Classical mechanics is the study of the motion of bodies acted upon by physical forces, and refers to Newton's Laws of Motion. For instance:
First Law of Motion: an object in motion will continue to move in the same direction and speed unless forces act on it.
Second Law of Motion: the greater the mass of an object, the more force it will take to accelerate the object.
Third Law of Motion: for every action, there is an equal and opposite reaction. An example is throwing a ball on the ground and having it bounce back up.
In the macroworld we observe around us, all this makes complete sense.
In the world of quantum mechanics (the world of the teeniest 'particles'), things work differently. Quantum mechanics doesn't jive with our intuition, and it's fascinating. Carroll uses 'the quantum cat' as an example.
Imagine your cat, Miss Kitty, has two favorite places in your house: on the sofa and under the dining room table.
In quantum mechanics, however, there is NO SUCH THING as 'the location of the cat.' The whereabouts of the cat is specified by something called a 'wave function' which says things like "if we were to look, there would be a 75% chance that we would find the cat under the table, and a 25% chance that we would find the cat on the sofa."
So far so good. That makes sense. However, according to Carroll, this does not mean there is a 75% chance the cat IS under the table and a 25% chance the cat IS on the sofa. There is no such thing as 'where the cat is.' Her quantum state is described by the superposition of the two distinct possibilities.
It gets even weirder.
Imagine that Miss Kitty has two routes to her favorite spots. She will either stop by her food dish or her scratching post, and then settle on the sofa or under the table. If we sneakily watch Miss Kitty, we observe that it doesn't matter whether she stopped at the scratching post or the food bowl....Miss Kitty ends up on the sofa half the time, and under the dining room table half the time.
However, if we don't watch Miss Kitty, and don't keep track of whether she stops at the food bowl or the scratching post, Miss Kitty ends up on the sofa 100% of the time. WOW!
Carroll observes that this experiment has been done, not with cats but with photons, and that this happens because the wave function collapses. Carroll explains this in physics terms, and it makes sense in the quantum world.
🌌 Black Holes
The classical description of a black hole is a region where gravity is so strong that nothing, including light and other electromagnetic waves, can escape. According to physicist Stephen Hawking, however, black holes do give off radiation. Thus, unless a black hole continues to take in matter, it will - over a long long long time - dissipate into nothingness.
The book, which is over 400 pages long, contains a lot more stuff and is very interesting (if a bit dense for the non-physicist). I'd urge folks who want to know more to browse through the book themselves.
Rating: 4 stars
No comments:
Post a Comment