## In my mind I am free

14 Mar 2018 by Liangzhao

ABC有一篇文章列举了他的很多Quotes，觉得很好，学习到很多他自己对世界的观察，列举如下。

We are just an advanced breed of monkeys on a minor planet of a very average star. But we can understand the universe. That makes us something very special.

Elon musk也说过类似的话，对于一只猴子来说，我们可以把火箭推上天，将人送到月球，对宇宙有如此的深刻认识，应该算不错了。

Life would be tragic if it weren’t funny.

The great enemy of knowledge is not ignorance, it is the illusion of knowledge.

For millions of years, mankind lived just like the animals. Then something happened which unleashed the power of our imagination. We learned to talk and we learned to listen. Speech has allowed the communication of ideas, enabling human beings to work together to build the impossible. Mankind’s greatest achievements have come about by talking, and it’s greatest failures by not talking. It doesn’t have to be like this. Our greatest hopes could become reality in the future. With the technology at our disposal, the possibilities are unbounded. All we need to do is make sure we keep talking.

My goal is simple. It is a complete understanding of the universe, why it is as it is and why it exists at all.

I believe the simplest explanation is, there is no God. No one created the universe and no one directs our fate. This leads me to a profound realization that there probably is no heaven and no afterlife either. We have this one life to appreciate the grand design of the universe and for that, I am extremely grateful.

If aliens ever visit us, I think the outcome would be much ad when Christopher Columbus first landed in America, which didn’t turn out very well for the Native Americans.

We are in danger of destroying ourselves by our greed and stupidity. We cannot remain looking inwards at ourselves on a small and increasingly polluted and overcrowded planet.

My disabilities have not been a significant handicap in my field, which is theorectical physics. Indeed, they have helped me in a way by shielding me from leturing and administrative work that i would otherwise have been involved in. I have managed, however, only because of the large amount of help I have received from my wife, children, colleagues and students. I find that people in general are very ready to help, but you should encourage them to feel that their efforts to aid you are worthwhile by doing as well as you possibly can.

Remember to look up at the stars and not down at your feet. Try to make sense of what you see and wonder about what makes the universe exist.Be curious. And however difficult life may seem, there is always something you can do and succeed at. It matters that you don’t just give up.

Intelligence is the ability to adapt to change.

We are all different, but we share the same human spirit.

My advice to other disabled people would be, concentrate on things your disability doesn’t prevent you doing well, and don’t regret the things it interferes with. Don’t be disabled in spirit, as well as physically.

So next time someone complains that you have made a mistake, tell him that may be a good thing. Because without imperfection, neither you nor I would exist.

BBC也列举了很多：

On Black holes:

Einstein was wrong when he said’God does not play dice’. Consideration of black holes suggests, not only that God does play dice, but that he somethimes confuses us by throwing them where they can’t be seen.

On life:

One, remember to look up at the stars and not down at your feet. Two, never give up work. Work gives you meaning and purpose and life is empty without it. Three, if you are lucky enough to find love, remember it is there and don’t throw it away.

On commercial success:

I want my books sold on airport bookstalls.

On God:

It is not necessary to invoke God to light the blue touch paper and set the universe going.

On euthanasia:

The victim should have the right to end his life, if he wants. But I think it would be a great mistake. However bad life may seem, there is always something you can do, and succeed at. While there’s life, there is hope.

On Artificial Intelligence:

The development of full artifical intelligence could spell the end of the human race. It would take off on its own, and redesign itself at an ever increasing rate. Humans, who are limited by slow biological evolution, couldn’t compete, and would be superseded.

On fame:

The downside of my celebrity is that I cannot go anywhere in the world without beiing recognised. It is not enough for me to wear dark sunglasses and a wig. The wheelchair gives me away.

On the possibility of contace between humans and aliens:

I think it would be a disaster. The extraterrestrials would probably be far in advance of us. The history of advanced races meeting more primitive people on this planet is not very happy, and they were the same species. I think we should keep our heads low.

On Space Colonies:

I don’t think the human race will survive the next 1000 years, unless we spread into space, There are too many accidents that can be befail life on a sigle planet. But I’m an optimist. We will reach out to the stars.

On being diagnosed with motor neurone disease:

My expectations were reduced to zero when I was 21. Everything since then has been a bonus.

On death:

I have lived with the prospect of an early death for the last 49 years. I’m not afraid of death, but I’m in no hurry to die. I have so much I want to do first.

##### Update:

Transcript:

There is nothing bigger or older than the universe. The questions I would like to talk about are: one, where did we come from? How did the universe come into being? Are we alone in the universe? Is there alien life out there? What is the future of the human race?

Up until the 1920s, everyone thought the universe was essentially static and unchanging in time. Then it was discoverd that the universe was expanding. Distant galaxies were moving away from us. This meant they must have been closer together in the past. If we extrapolate back, we find we must have all been on top of each other abouth 15 billion years ago. This was the Big Bang, the begining of the universe.

But was there anything before the Big Bang? If not, what created the universe? Why did the universe emerge from the Big Bang the way it did? We used to think that the theory of the universe could be divided into two parts. First, there were the laws like Maxwell’s equations and general relativity that determined the evolution of the universe, given its state over all of space at one time. And second, there was no question of the inital state of the universe.

We have made good progress on the first part, and now have the knowledge of the laws of evolution in all but the most extreme conditions. But until recently, we have had little idea about the initial conditions for the universe. However, this division into laws of evolution and initial conditions depends on time and space being separate and distinct. Under extreme conditions, general relativity and quantum theory allow time to behave like dimension of space. This removes the distinction between time and space, and means the laws of evolution can also determine the initial state. The universe can spontaneously create itself out of nothing.

Moreover, we can calculate a probability that the universe was created in different states. These predictions are in excellent agreement with observations by the WMAP satellite of the cosmic microwave background, which is an imprint of the very early universe. We think we have solved the mystery of creation. Maybe we should patent the universe and charge everyone royalties for their existence.

I now turn to the second big question: are we alone, or is there other life in the universe? We believe that life arose spontaneously on the Earth, so it must be possible for life to appear on other suitable planets, of which there seem to ba a large number in the galaxy.

But we don’t know how life first appeared. We have two pieces of observational evidence on the probability of life appearing. The first is that we have fossils of algae from 3.5 billion years ago. The Earth was formed 4.6 billion years ago and was probably too hot for about the first half billion years. So life appeared on Earth within half a billion years of it being possible, which is short comopared to the 10-billion-year lifetime of a planet of Earth type. This suggests that the probability of life appearing is reasonably high. If it was very low, one would have expected it to take most of the ten billion years available.

On the other hand, we don’t seem to have been visited by aliens. I am discounting the reports of UFOs. Why would they appear only to cranks and weirdos? If there is a government conspiracy to suppress the reports and keep for itself the scientific knowledge the aliens bring, it seems to have been a sigularly ineffective policy so far. Furthermore, despite an extensive search by SETI projects, we haven’t heard any alien civilizations at our stage of development within a radius of a few hundred light years. Issuing an insurance policy against abduction by aliens seems a pretty safe bet.

The brings me to the last of the big questions: the future of the human race. If we are the only intelligent beings in the galaxy, we should make sure we survive and continue. But we are entering an increasingly dangerous period of our history. Our population and our use of the finit resources of planet Earth are growing exponentially, along with our technical ability to change the environment for good or ill. But our genetic code still carries the selfish and aggressive instincts that were of survival advantage in the past. It will be difficult enough to avoid disaster in the next hundred years, let alone the next thousand or million.

Out only chance of long-term survival is not to remain inward-looking on planet Earth, but to spread out into space. The answers to these big questions show that we have made remarkable progress in the last hundred years. But if we want to continue beyond the next hundred years, our future is in space. That is why I am in favor of manned – or should I say, personned space flight.

All of my life I have sought to understand the universe and find answers to these questions. I have been very lucky that my disability has not been a serious handicap. Indeed, it has probably given me more time than most people to pursue the quest for knowledge. The ultimate goal is a complete theory of the universe, and we are making good progress. Thank you for listening.

## 罗伯特·M·波西格

12 May 2017 by Liangzhao

4月24日的时候，写那本《禅与摩托车维修艺术》的罗伯特·M·波西格（Robert M. Prisig）去世了。书翻看过很多次，这本书虽然讨论的是哲学，却不无太多抽象得让人眩晕，这是此书的一大特点，他在书中穿插讲述了自己和儿子克里斯（Chris）横跨半个美国，骑着摩托车旅行的故事，因此看起来不会累。

## 质子治疗基础（二）

07 Apr 2017 by Liangzhao

（内容摘录并改编自Harald Paganetti的《Proton Beam Therapy》。）

### 目前的技术挑战

#### 生物学因素

##### 相对生物效应

RBE值的不确定性使得一些TPS在优化时避免重要组织附近有高RBE值，下面一张图显示了即使是同样的剂量分布，从LET层面看来是多么不同。

#### 展望

1. 虽然多个治疗室只配置一台质子加速器，然而对于工作流程并不会带来多大限制，因为Beam-on 时间相对病人治疗摆位往往只占一小部分。

2. 对大多数治疗而言，不需要使用360度旋转的机架，可以利用六维床与病人体位的变化增加治疗的灵活性。

3. 例如，如果覆盖远端靶区需要10cm的水等效深度，那么加外扩后实际要在10.45cm左右，正常组织有近5mm进入到靶区中。

4. 可直接和间接地产生伽玛射线。直接：原子核退激以顺发伽玛辐射（Prompt Gammas）的方式释放能量；间接：原子核反应产生一些碳、氧、氮同位素，他们发出的正电子泯灭释放伽玛射线（类似于PET）。

5. 如可以探测高能伽玛射线探测板的研制；探测得到的信号有一定的不确定性，一是因为物理截面积计算是不精确，二是信号不是一对一的关系（剂量基于电磁反应，探测利用的是核反应）。所以不能直接对比原计划的剂量分布，需要使用蒙卡算法模拟出类似于PET一样的剂量分布，再和探测得到的分布比较。

6. 例如肝脏的一部分承受很高的剂量，其余部分仍然可以正常的工作。靶区中的不均匀性目前看来不仅没有坏处，而且对于放射不敏感的区域（如靶区中心）更有剂量学优势。

7. LET的变化导致了RBE的变化，估计在布拉格峰附近，RBE值的变化从1.0～1.5，所以RBE是一个非常复杂的概念，射线能量、剂量、剂量、细胞类型（生物效应）、氧合状态、放射敏感性等因素都会影响最终的结果，这些因素目前都不能定量地考虑进去，其中一些因素跟个体有关，必须借助血液或者基因标记才能确认。