读书笔记 --- A brief history of time by Stephen Hawking# LeisureTime - 读书听歌看电影
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This book summarized the history of development in modern physics.
Newton's gravity explained attraction between objects, and therefore why
apples fall down to the ground and why the earth orbits the sun.
Einstein's special theory of relativity explained that time and length are
not as absolute as everyday experience would suggest: Speed of light is
constant, moving clocks run slower leading to the twin paradox, and moving
objects are shorter. Another consequence of special relativity is the most
famous formula of all: E=mc², stating that two physical quantities
which physicists had defined separately, namely energy and mass, are in fact
equivalent.
To unite gravity and special theory of relativity, Einstein further
developed general theory of relativity, explaining that gravity leads to
curvature of space and time, and distorted space and time influence the way
that material objects or light move.
Quantum mechanics is one area I did not fully understand after reading the
book. Even though I can understand the wave and uncertainty property of
most particles, extending the concept to the anti-particles is a bit
illusive to me. Especially in one section it mentioned that even the empty
space is not empty, but rather exist virtual particles and antiparticles
that annihilate each other. And these particles will likely be separated
under the strong gravitational force, e.g. at the event horizon, causing one
particle to fall into the black hole while the other one escaping, leaving
to black hole being not fully black, but rather glowing. It also mentioned
the infinity problem occurs for these kind of theories, e.g. if there are
unlimited particles and antiparticles, therefore the universe will have
infinite mass. He did mention one way to resolve the problem but it is a
bit beyond my understanding.
The black hole is one of my favorite chapters. When the mass and therefore
density of an object becomes so great that light, once entered it's event
horizon, can no longer escape, then it becomes a black hole. It can happen
when massive stars explode in a supernova, the collapsing central region
will generically have so much mass that even neutron matter cannot halt the
collapse. The collapse continues, and when this happens, a black hole is
born. I think it is interesting talking about the astronaut unknowingly
enters the event horizon will not be able to come back. It also talks about
the gravitational force being so great that the head and feet will be
subjected to such a different force that the person will be tear apart
before falling into the center of the black hole.
The even newer theories that tries to unite the general theory of relativity
with quantum mechanics, such as the string theories are quite beyond me.
Remember the physics grad student mentioning that it would be an challenging
task to even explain it. But I think Stephen explained the dimension
question very well, that the string theory requires that space time is ten
or twenty six dimensions, however we only have four. And what could happen
to there other dimensions: they are likely folded up in a very microscopic
space. This is quite unbelievable although Stephen explained it well.
I like that the author is not just plainly stating the histories and
enumerating the year and events. He actually explained the thinking process
when each theories were being thought out, and even mentioned theories that
were eventually proved wrong. He spent a lot of time trying to correlate
the physics theories to human life, discussing why human being can only be
found on planet like earth, and why our space-time is four dimension. The
idea named "anthropic principle", or "we see the universe the way it is
because we exist" is interesting. Essentially the conditions necessary for
the development of intelligent life will be met only in certain regions of
the large universe that are limited in space and time.
In the last chapter, the author un-expectedly gave some personal accounts of
three major characters in modern Physics, Newton, although a great
scientist, was mean and blatantly suppressed his contender, another great
German philosopher Gottfried Leibniz. This reminded me that although famous
as great scientists, a lot of them are not really so admirable in "
personality" and "moral". Einstein, famous in Physics, however had been
against quantum mechanics and had been heavily involved in political
activities involving deployment of nuclear power. Galileo, his courageous
journey to expose the truth of science despite the threat from the Church.
Although he was forced to mute multiple times and he had been generally
following the church's command, I would not call him a coward. For if he
had acted like Nicolaus Copernicus, he would have died a long time ago and
there would not be another person who can help distribute the truth. The
courage to live and tell the truth is a lot more admirable than the courage
to die.
Newton's gravity explained attraction between objects, and therefore why
apples fall down to the ground and why the earth orbits the sun.
Einstein's special theory of relativity explained that time and length are
not as absolute as everyday experience would suggest: Speed of light is
constant, moving clocks run slower leading to the twin paradox, and moving
objects are shorter. Another consequence of special relativity is the most
famous formula of all: E=mc², stating that two physical quantities
which physicists had defined separately, namely energy and mass, are in fact
equivalent.
To unite gravity and special theory of relativity, Einstein further
developed general theory of relativity, explaining that gravity leads to
curvature of space and time, and distorted space and time influence the way
that material objects or light move.
Quantum mechanics is one area I did not fully understand after reading the
book. Even though I can understand the wave and uncertainty property of
most particles, extending the concept to the anti-particles is a bit
illusive to me. Especially in one section it mentioned that even the empty
space is not empty, but rather exist virtual particles and antiparticles
that annihilate each other. And these particles will likely be separated
under the strong gravitational force, e.g. at the event horizon, causing one
particle to fall into the black hole while the other one escaping, leaving
to black hole being not fully black, but rather glowing. It also mentioned
the infinity problem occurs for these kind of theories, e.g. if there are
unlimited particles and antiparticles, therefore the universe will have
infinite mass. He did mention one way to resolve the problem but it is a
bit beyond my understanding.
The black hole is one of my favorite chapters. When the mass and therefore
density of an object becomes so great that light, once entered it's event
horizon, can no longer escape, then it becomes a black hole. It can happen
when massive stars explode in a supernova, the collapsing central region
will generically have so much mass that even neutron matter cannot halt the
collapse. The collapse continues, and when this happens, a black hole is
born. I think it is interesting talking about the astronaut unknowingly
enters the event horizon will not be able to come back. It also talks about
the gravitational force being so great that the head and feet will be
subjected to such a different force that the person will be tear apart
before falling into the center of the black hole.
The even newer theories that tries to unite the general theory of relativity
with quantum mechanics, such as the string theories are quite beyond me.
Remember the physics grad student mentioning that it would be an challenging
task to even explain it. But I think Stephen explained the dimension
question very well, that the string theory requires that space time is ten
or twenty six dimensions, however we only have four. And what could happen
to there other dimensions: they are likely folded up in a very microscopic
space. This is quite unbelievable although Stephen explained it well.
I like that the author is not just plainly stating the histories and
enumerating the year and events. He actually explained the thinking process
when each theories were being thought out, and even mentioned theories that
were eventually proved wrong. He spent a lot of time trying to correlate
the physics theories to human life, discussing why human being can only be
found on planet like earth, and why our space-time is four dimension. The
idea named "anthropic principle", or "we see the universe the way it is
because we exist" is interesting. Essentially the conditions necessary for
the development of intelligent life will be met only in certain regions of
the large universe that are limited in space and time.
In the last chapter, the author un-expectedly gave some personal accounts of
three major characters in modern Physics, Newton, although a great
scientist, was mean and blatantly suppressed his contender, another great
German philosopher Gottfried Leibniz. This reminded me that although famous
as great scientists, a lot of them are not really so admirable in "
personality" and "moral". Einstein, famous in Physics, however had been
against quantum mechanics and had been heavily involved in political
activities involving deployment of nuclear power. Galileo, his courageous
journey to expose the truth of science despite the threat from the Church.
Although he was forced to mute multiple times and he had been generally
following the church's command, I would not call him a coward. For if he
had acted like Nicolaus Copernicus, he would have died a long time ago and
there would not be another person who can help distribute the truth. The
courage to live and tell the truth is a lot more admirable than the courage
to die.
