新年到了, 有点儿感叹时间的逝去, 又老了一岁, 离hike 到山上,到树下安乐死的距离又近了一步:-)。想着要好好利用还余下的时间。
问个吃饱饭才会想到的疑问:
什么是时间?时间不可能独立存在,时间只是人们的illusion吗?
点名哈, 浮生, gz 老圣,阿姗来谈谈纯物理的时间概念, 那小麦老圣来谈谈人文或者说哲学概念的时间。还有各位咖啡豆都来说说吧。
Zt 一本书的书评做引子吧:[The End of Time: The Next Revolution in Physics]
-----------------
The first is the Space+Time vision of Kant, Newton, etc., with two small modifications. One is that of Einstein Time + Space are fused into the idea of Space-time. In Relativity theory Space-time can be 'cut' by a 'now'-plane in different ways, under different angles, so that simultaneity is no longer absolute, but dependent on the state of motion. But this vision is just a further mathematical elaboration of Space + Time, and does not contain any essential new insight into time itself.
The second minor modification is implicit in Quantum Mechanics. One of the four famous Heisenberg relations dE * dt > h implies, that 'now' is not 'absolute, and 'infinitely small', as commonly is believed, but has an extension that depends on the energy content of any existing objects. The more mass the object has, the more energy it has, (through E = mc2) and therefore the smaller its 'now'-interval is. This implies, that the 'now' of different objects is different; dependent on how much energy they consist of. From it you can explain how come that electrons that spin around these atoms do not radiate electromagnetic radiation. For if the time they need to revolve around the atom is equal to the 'now' interval, they essentially do not have the 'time' to complete that movement, so that, in a sense, you can say that they do not move. For if they do not move, they do not accelerate, and therefore do not radiate.
The second vision on time is the Leibniz vision. According to Leibniz, time is 'not really existing', but it is the conceptual order that our minds puts on existence. It is an ordering imposed on existence in terms of 'sooner and later'. In a philosophical sense this implies, that past, present, and future all `really exist'.
- posted on 01/04/2011
the speed of time, a property of time?
1, uniform as Newton would like to agree, otherwise his motion formulas wouldn't be too accurate.
2, accelerated as Einstein's relativity theories imply. In Einstein's theories everything is ever-changing given different frame of references. The strangest thing about Einstein is that he thought that everything was changing except the concept of Logical Determinism.
I think the most interesting conjecture about time is that whether time has direction. By far, all the physics formulas involving time have no direction, which gives rise to the stories of time traveling.
As for possession of time, I don't think so either, but we do possess duration. I'm not 18 any more. It's truly a lamenting fact.
dE * dt > h implies that one of the pair, time and energy (or some other pairs), is certain, the other wouldn't be certain. - posted on 01/04/2011
fascinating!
Time has direction in my personal experience, just like you say, we are not 18 any more, we are not even 40 anymore in that case;-) so, time like 泼出去的水, 摔碎的玻璃,不能逆转。
Am I right? time traveling would not be the same like re living in 18 again?
If we don't possess the time, what do we possess?
I think the most interesting conjecture about time is that whether time has direction. By far, all the physics formulas involving time have no direction, which gives rise to the stories of time traveling.
- posted on 01/04/2011
我举手发言推荐一本书。也许时间是什么不重要,我们如何认识和用时间更重要。虽然关于时间的问题不是终极问题,但它跟终极问题关联密切。是世上每个人不可避免要遭遇的问题。正如频死经历很少人有过,经历过被告知生命所剩时间无几的人也很少。Time is far more delicate than most of us feel like.
The Time Paradox: The New Psychology of Time That Will Change Your Life [Paperback]
Philip Zimbardo (Author), John Boyd
Time is our most valuable possession: we are obsessed with schedules and multitasking to save time, say the authors of this insightful study of the importance of time in our lives. Yet people spend time less wisely than money. Zimbardo (The Lucifer Effect), professor emeritus of psychology at Stanford, and Boyd, research director for Yahoo!, draw on their two decades of research to explain why people devalue time. They blend scientific results into a straightforward narrative exploring various past-, present- and future-oriented ways of perceiving time and argue against becoming imprisoned or obsessed by any one of these. Zimbardo and Boyd have cogent insight into all of time's elements and show how they can be used for success, better health and greater fulfillment. For instance, understanding the role of time in investment can lead to wiser financial decisions, and a relationship will not work if one partner is focused on today's pleasure while the other wants to plan for the future. This is a compelling and practical primer (filled with quizzes and tests) on making every moment count - posted on 01/05/2011
谢谢rzp的介绍,我看了一下, 以下网站可以测一下自己的时间类型:
http://www.thetimeparadox.com/surveys/
People who have different time perspective behave differently and we can make general statements about their thoughts, feelings, and behavior:
Past-oriented people:
1- They are generally more concerned with their past and seem to be able to distance themselves from the realities of the present or the future.
2- They usually tend to be traditional, religious, and conservative.
3- They have a stable sense of self.
4- They usually tend to be family- and group-oriented and are distrustful of strangers; thus they may have a tendency to be prejudiced.
5- They usually focus on their obligations and commitments whether personal or collective (i.e. family, cultural, or tribal obligations).
6- Rituals and myths play important roles in their lives.
7- They may have guilt as a dominant feeling.
8- They usually try to maintain the status quo and thus may not be progressive.
9- They usually do not take risks and are not adventurous.
10- Within their group, they usually tend to be dependent and cooperative rather than competitive.
Present-oriented people:
1- They tend to focus on the present and their current sensations, feelings, and concerns while ignoring commitments made in the past or for the future; thus they are more concerned with "what is" than "what was" or "what may be".
2- Their thinking is more concrete rather than abstract (i.e. one hundred dollar right now is much better than two hundred dollars in the future).
3- It is difficult for them to give up temptations or delay gratification and thus they are easily distracted from the performance of necessary current tasks and tend to be procrastinators.
4- They tend to concentrate on activities that bring pleasure and avoid pain.
5- Their knowledge or insight may not deter them from performing actions that may not be beneficial to them.
6- They are usually more sensation and novelty seekers, more aggressive, more depressed, less conscientious, and less emotionally stable. They have less concern for future consequences, less ego and impulse control, and less preference for consistency. They also tend to lie.
7- Usually people who are poor or uneducated tend to be present-oriented since they usually tend to focus on emergent needs of the present.
8- Since they are not good in abstract thinking, are more concerned with immediate gratification, and less concerned about the future, they usually tend to get low grades in school.
9- Because they are immediate pleasure seekers, they usually don't pay good attention to their health and can additionally abuse substances.
10- They are usually considered to be fun people to be around.
Future-oriented people:
1- They are more focused on their future than the present or the past; their thoughts are concerned with the future consequences of their present actions; they logically analyze various outcomes that may result from their action.
2- They are goal-oriented and can delay gratification and endure an unpleasant situation in order to achieve long-term goals. They pay attention to responsibility, liability, efficiency, distant payoffs, and tend to optimize future outcomes. Thus they can work hard and avoid temptations, distractions, waste of time to accomplish a goal. They usually tend to rehearse various future plans.
3- Since they are concerned about the future, they tend to save their money and resources.
4- They could be either cooperative or competitive depending on which action results in the best outcome.
5- They tend to be health-conscious in order to prevent future negative health outcomes.
6- They may be unable to enjoy fun activities due to the fear of wasting time.
7- They may have difficulty in intimate relationships since they thrive on control, predictability, and consistency, factors that may interfere with the freedom and spontaneity of relationships.
8- Although they usually have low anxiety levels, concern for the future may increase their anxiety. They usually tend to be workaholic, and have midlife crises.
9- They tend to be more conscientious, less aggressive, less depressed, more reward-dependent, less sensation seeker, more studious, more creative, and use less addictive drugs and alcohol.
10- They tend to have more self-esteem, energy, openness, ego-control, and grade-point average.
- Re: 什么是时间?我们真正拥有吗? Is time a illusion?posted on 01/05/2011
我们并不拥有时间。跟一只五月蚊一样,我们拥有的只是一个过程。这个过程或是一百年,或是数小时。过程结束或中断,时间便完结。宇宙中每个过程都有自己的起始和终结,有自己的过程发展速度。时间只是对这个速度的度量方式。所以时间不是客观存在的事物,只是一个概念,一个参考系。 - RE: 什么是时间?我们真正拥有吗? Is time a illusion?posted on 01/05/2011
任何过程归根结底是一个物理或化学过程,有自己的发展速度。事物发展过程有一定方向,变化速度是个矢量,时间却不是矢量。事物发展过程有时可逆,时间却不可逆。时间既不顺流,也不倒流,只是过程发展的计量单位之一。生命过程是不可逆的,因此没有回到过去的可能性。 - Re: RE: 什么是时间?我们真正拥有吗? Is time a illusion?posted on 01/05/2011
How do you know? It's easy to say, but could you prove it? :-)
八十一子 wrote:
任何过程归根结底是一个物理或化学过程,有自己的发展速度。事物发展过程有一定方向,变化速度是个矢量,时间却不是矢量。事物发展过程有时可逆,时间却不可逆。时间既不顺流,也不倒流,只是过程发展的计量单位之一。生命过程是不可逆的,因此没有回到过去的可能性。 - posted on 01/05/2011
If we don't possess the time, what do we possess?
Just duration.
It's like we don't possess the sunlight, but we use it to shine on our sullen hearts. :-)
草叶 wrote:
fascinating!
Time has direction in my personal experience, just like you say, we are not 18 any more, we are not even 40 anymore in that case;-) so, time like 泼出去的水, 摔碎的玻璃,不能逆转。
Am I right? time traveling would not be the same like re living in 18 again?
If we don't possess the time, what do we possess? - Re: 什么是时间?我们真正拥有吗? Is time a illusion?posted on 01/05/2011
You don't own time, neither it owns you. you ARE time! you are a timed piece. Just like a time bomb. ;) - Re: RE: 什么是时间?我们真正拥有吗? Is time a illusion?posted on 01/05/2011
草叶学过生物化学。她明白。 :-)
pengyou wrote:
How do you know? It's easy to say, but could you prove it? :-)
八十一子 wrote:
任何过程归根结底是一个物理或化学过程,有自己的发展速度。事物发展过程有一定方向,变化速度是个矢量,时间却不是矢量。事物发展过程有时可逆,时间却不可逆。时间既不顺流,也不倒流,只是过程发展的计量单位之一。生命过程是不可逆的,因此没有回到过去的可能性。 - posted on 01/05/2011
Are time and process one concept?
八十一子 wrote:
草叶学过生物化学。她明白。 :-)
pengyou wrote:
How do you know? It's easy to say, but could you prove it? :-)
八十一子 wrote:
任何过程归根结底是一个物理或化学过程,有自己的发展速度。事物发展过程有一定方向,变化速度是个矢量,时间却不是矢量。事物发展过程有时可逆,时间却不可逆。时间既不顺流,也不倒流,只是过程发展的计量单位之一。生命过程是不可逆的,因此没有回到过去的可能性。 - Re: 什么是时间?我们真正拥有吗? Is time a illusion?posted on 01/05/2011
When will it explode?
touche wrote:
You don't own time, neither it owns you. you ARE time! you are a timed piece. Just like a time bomb. ;) - posted on 01/06/2011
草叶 wrote:
One of the four famous Heisenberg relations dE * dt > h implies, that 'now' is not 'absolute, and 'infinitely small', as commonly is believed, but has an extension that depends on the energy content of any existing objects. The more mass the object has, the more energy it has, (through E = mc2) and therefore the smaller its 'now'-interval is. This implies, that the 'now' of different objects is different; dependent on how much energy they consist of.
有人说人生一辈子的意义,不仅以存活的岁数来衡量,还要以掌握的权力、花费的金钱来计算。
引申到海森堡这个公式,mass = 权力, energy = 金钱,now = 寿命, 难怪越有权有钱的人,总觉得他们的"now interval"比人家来得短。 - Re: 什么是时间?我们真正拥有吗? Is time a illusion?posted on 01/06/2011
rzp wrote:
Time is our most valuable possession: we are obsessed with schedules and multitasking to save time, say the authors of this insightful study of the importance of time in our lives. Yet people spend time less wisely than money.
好像说漏了一项。
每个人都有三件宝,time, money, and love.
the one most wisely spent is always money, then time, and then love:) - posted on 01/07/2011
老瓦说,time, money, and love.是三件宝。
这三件宝,我认为最宝贵的是时间,对人来说,没时间了就没有了生命。
人类意识到这一点,对money就有超前的种种,寅吃卯粮,借贷, 赖债,死后欠一屁股债,呵呵。对love,就看运气了,遇到真正的love, 时间就无限!但情债不能欠,只能支出,也可能将耗尽time,和 money。甚至生命。
什麽是时间?时间能引出很多概念。
时间是量,是参照系很对,因为世界是运动着的状态存在。宇宙的一切,太阳,地球,一切行星,一切生命都是在运动,花落花开,周而复始,有我们人类肉眼看得到的,和看不到的,都在不知不觉地运动着。
人类用时钟来显示时间的连续性和非连续性,让我们能看着时间经过一小时,一分钟,一秒钟的运动过程。数字时钟的模式让我们提供当下时间的准确再现。其实体会一下自己心脏的跳动,那就是时间。
老瓦 wrote:
rzp wrote:好像说漏了一项。
Time is our most valuable possession: we are obsessed with schedules and multitasking to save time, say the authors of this insightful study of the importance of time in our lives. Yet people spend time less wisely than money.
每个人都有三件宝,time, money, and love.
the one most wisely spent is always money, then time, and then love:) - Re: 什么是时间?我们真正拥有吗? Is time a illusion?posted on 01/07/2011
谢谢各位的想法, 时间是illusion, 那我们就可以munipulate 时间了, 如秋子说的时间可以无限, 但我不sure 是只在in love 的时候, 我觉得是正相反。
我最喜欢图教授的比喻: we are walking time bomb. clock is always ticking:)Hey, anything with a bomb does not sound bad;-)
怎么没人来谈谈time traveling?
- posted on 01/07/2011
小时候一次滑冰被人撞到,失去知觉,醒来时发现自己在冰场边上的凳子上。没有什么严重后果,( 当然本来可能可以少傻些 :-) ) 有趣的是,当时完全不知道失去知觉有多长时间,一分钟或一小时。一直好奇时间在脑子里是怎样感知和纪录的。现在有了结果了:
http://www.sciencedaily.com/releases/2009/10/091019162921.htm
An MIT team led by Institute Professor Ann Graybiel has found groups of neurons in the primate brain that code time with extreme precision。
很崇敬这样 no-nonsense 的研究,没有丝毫 hand-waving, 全是 solid science. 只有这种对脑的研究是真正有价值有意义的。
不过话又说回来,这个结果大概还无法解释为什么和美女聊天觉得时间太快,而和话不投机的人却觉得时间太慢这种相对论。心理学家又有机会挥手了。 - posted on 01/07/2011
对不起,我领头跑题了,经常性地混淆物理学和社会学:) 应该留给在座的物理学家和社会学家们分别来解答。
秋子 wrote:
老瓦说,time, money, and love.是三件宝。
这三件宝,我认为最宝贵的是时间,对人来说,没时间了就没有了生命。
人类意识到这一点,对money就有超前的种种,寅吃卯粮,借贷, 赖债,死后欠一屁股债,呵呵。对love,就看运气了,遇到真正的love, 时间就无限!但情债不能欠,只能支出,也可能将耗尽time,和 money。甚至生命。
什麽是时间?时间能引出很多概念。
时间是量,是参照系很对,因为世界是运动着的状态存在。宇宙的一切,太阳,地球,一切行星,一切生命都是在运动,花落花开,周而复始,有我们人类肉眼看得到的,和看不到的,都在不知不觉地运动着。
人类用时钟来显示时间的连续性和非连续性,让我们能看着时间经过一小时,一分钟,一秒钟的运动过程。数字时钟的模式让我们提供当下时间的准确再现。其实体会一下自己心脏的跳动,那就是时间。
老瓦 wrote:
rzp wrote:好像说漏了一项。
Time is our most valuable possession: we are obsessed with schedules and multitasking to save time, say the authors of this insightful study of the importance of time in our lives. Yet people spend time less wisely than money.
每个人都有三件宝,time, money, and love.
the one most wisely spent is always money, then time, and then love:) - posted on 01/07/2011
谢谢关中这个林克,很有意思,现在日新月异的纯科学,可能就是脑科学了(心理学家要说,那也是心理学的分支)。
读初中的时候,电子表还是很时髦的东东,不是每个人都有。于是猜时间成了一时流行的游戏。我当年的感觉非常敏锐,误差基本在两三分钟之内,当然那也是根据学校每天的作息时间为基准。
大脑皮质的各个分区,分管各种人体基本功能。这么看来,如果能持续刺激这些监测时间的神经元,说不定人人都能达到活两百岁的体验了:))
gz wrote:
小时候一次滑冰被人撞到,失去知觉,醒来时发现自己在冰场边上的凳子上。没有什么严重后果,( 当然本来可能可以少傻些 :-) ) 有趣的是,当时完全不知道失去知觉有多长时间,一分钟或一小时。一直好奇时间在脑子里是怎样感知和纪录的。现在有了结果了:
http://www.sciencedaily.com/releases/2009/10/091019162921.htm An MIT team led by Institute Professor Ann Graybiel has found groups of neurons in the primate brain that code time with extreme precision。
很崇敬这样 no-nonsense 的研究,没有丝毫 hand-waving, 全是 solid science. 只有这种对脑的研究是真正有价值有意义的。
不过话又说回来,这个结果大概还无法解释为什么和美女聊天觉得时间太快,而和话不投机的人却觉得时间太慢这种相对论。心理学家又有机会挥手了。 - Re: 什么是时间?我们真正拥有吗? Is time a illusion?posted on 01/08/2011
Time traveling only exists in movies and TV. The notorious paradox is that what if a grandson killed his grandpa? If time traveling is made possible, this kind of things have to be prevented from happening. :-)
草叶 wrote:
怎么没人来谈谈time traveling? - posted on 01/08/2011
This paradox has long been recognized and people have come up with all kinds of hypothesis to resolve it, such as the claim that people don't really have free wills. In this context, those who do travel back in time will NOT kill their ancestors.
http://en.wikipedia.org/wiki/Grandfather_paradox
pengyou wrote:
Time traveling only exists in movies and TV. The notorious paradox is that what if a grandson killed his grandpa? If time traveling is made possible, this kind of things have to be prevented from happening. :-) - posted on 01/10/2011
谢。
en, 读了。一些是按determinism的观点,另一些是量子力学的观点。
其实我最喜欢的是concurent 观点, 就是:所有历史和现在同时在发生,不过不是在同一dimension上.
另外fatalism 也有意思,就是说 future is unavoidable, everything is predetermined. Perhaps, if the grandson lives, he has been decidedly not to kill his grandpa.
http://plato.stanford.edu/entries/time/
呵呵, 好玩。
gz wrote:
This paradox has long been recognized and people have come up with all kinds of hypothesis to resolve it, such as the claim that people don't really have free wills. In this context, those who do travel back in time will NOT kill their ancestors.
http://en.wikipedia.org/wiki/Grandfather_paradox - posted on 01/10/2011
我曾写过一篇关于时间的短文,只说明一个问题,时间是一笔糊涂帐。
我们只拥有过去,没有现在,至于有没有将来,谁也不知道。
什么是时间 (2)
2007年
回国期间,应南京大学软件学院一个草根学生社团之邀,我为他们开了一个讲座,非学术性,互动,题目叫“什么是时间?”
说老实话,这个题目我也讲不清楚。之所以出此题,无非是避个嫌疑,非学术可以,但不要和政治挂上钩。虽然我是个化外之人,可在国内讲话还是抖抖索索,生怕一个门没把好,抖落出几句人家不待见的话,弄得大家都没趣。不讲吧,看到孩子们一脸的渴望,一脸的盛情,实在不忍相拒,于是硬着头皮接下了这差事。
什么是时间?于我来说,似是而非,雾里看花。当年写《分布式系统》一书,为了搞清这个问题,着实翻了不少的书,却越读越糊涂。于是我告诉同学们:
时间是一条直线,
时间是一条曲线;
时间是凤凰涅磐,
时间是幼蚕破茧;
时间是花开花落,
时间是月缺月圆;
时间是思想跳跃,
时间是人生变迁;
时间是度日如年,
时间是光阴似箭。
我的时间 --
我说不清楚,
你们有时间 --
搞清你的时间!
韩愈老先生曾教导我辈:“师者,所以传道受业解惑也。”自己尚且搞不清楚,迷惑不解,又有何颜面开讲座呢?岂不是误人子弟吗?当然,我有我的道理。表面上看,什么是时间,这个问题太简单,似乎在询问一个人人都知道的普通常识。而仔细思考一下,却发现这个问题太复杂,直到今天科学家们都找不到一种令人满意的解释。正如公元四世纪思想家圣·奥古斯丁在他的《忏悔录》中所说的那样:“什么是时间?没人问我,我很清楚;一旦问起,我便茫然。”
抽象地说,时间应该是不依赖于任何其它事物而独立存在的、无休止地均匀流逝的客体。在中学数学、物理课本中,时间被表述成一条有起点、有单位、有方向、可以无限延伸的直线。这就是所谓的牛顿“绝对时间”,也是直到本世纪初被普遍接受的科学时间概念。从传统物理学的角度看,时间和空间都是绝对的。时间是在一定的参照系下,对宇宙中物质运动过程的一种“计量”,没有物质运动就没有所谓的“时间”。物质的运动过程具备持续性和不可逆性。所谓持续性,指的是过程的因果性和不间断性;而所谓不可逆性,指该运动过程可以重复但绝不能返回过去的那种性质。
人类进入二十世纪后,物理学、天文学的新科研成果、新科学发现向“绝对时间”的基本观念提出了挑战。爱因斯坦狭义相对论指出,时间不能脱离宇宙及其事件的观察者而独立存在,时间是宇宙与其观察者之间用来测度物质运动变化的定量方法。爱因斯坦将时间和空间看作是相对的。时间作为三度空间的另一维,构成所谓的四度空间。爱因斯坦的结论是,每一参照系都有自身的特殊的时间,除非我们对于时间的陈述定义是相对于那个参照系的,否则对时间的定义就没有意义。例如,由于引力场的原因处于地球表面不同高度的时钟走速不一样,海拔越高钟速越快,差值约为1.09×10-16秒/米(海拔),即每升高100米,时钟变快百万亿分之一秒。
然而,哲学家们并不满意物理学、天文学中对时间的表述。一个重要的哲学观点就是时间的存在并不依赖于某个参照系。黑格尔在《精神现象学》一书中说:“时间和空间或距离和速度在它们本身内并不能表示它们是从同一个根源派生出来,它们彼此之间是漠不相关的。”
史蒂芬·霍金(Stephen W. Hawking)在他的《时间简史》一书中写道:“时间箭头将过去和将来区别开来,使时间有了方向。至少有三种不同的时间箭头:第一个,是热力学时间箭头,即是在这个时间方向上无序度或熵增加;然后是心理学时间箭头,这就是我们感觉时间流逝的方向,在这个方向上我们可以记忆过去而不是未来;最后,是宇宙学时间箭头,在这个方向上宇宙在膨胀,而不是收缩。” 然而,无论物理上的时间定义还是史蒂芬·霍金所描述的时间都无法由数理模型或公式所表述及验证,而且在天文学、哲学、文学、生物学里,都存在对时间的不同理解、不同应用。
因此,时间到底是物理的还是心理的?是主观经验的还是客观存在的?对时间的感受是绝对的还是相对的?时间真的不可逆转吗?时间是无始无终吗?这些问题一直在困扰着古往今来的哲学家们。概言之,“什么是时间?”的问题实质上是探索时间的本质。这只是极少数科学家、哲学家潜心研究的课题,而且远没有得出一个令人满意的结果,看来还需要长期探索下去。
所幸的是,我们通用的时间概念,采用比较直观而且容易理解的定义。人类在历史上所用的方法是将地球围绕太阳的运动和月球围绕地球的运动作为时间定义的出发点。从认识和测量时间的发展历史看,人类在晨起暮归的生产劳作中,逐步产生了“日”的概念;从月亮圆缺中得到了 “月”的概念;从寒来暑往的四季变化总结出“年”的概念。古代中国人就已经知道,地球自转一周是一日;月亮绕地球一周是一月;地球绕太阳一周是一年。 时间是人们针对太阳、月亮的运动过程进行的量度。人类生活中的历史事件或日常事物所发生的种种变化,都笼罩在这个巨大的参照系之中。实际上,通过这样的定义,人们已经把天体运动的概念转化为一种抽象的概念,并以此作为时间定义的方法。这种时间定义及其相应的时间基准、时间度量被用来描述我们生活中的所有的事件的运动变化过程。换句话说,在某一事件运动过程中,人类生活中的其它事件也在(同时)发生。对所有的事件采用统一的运动变化过程的描述方法就是时间。而人类所使用的时间度量方法,从远古的日出日落,公元前的圭表日晷,千年前的沙漏水钟,六百年前的机械钟表,直到二十世纪的石英晶体震荡器乃至原子钟,时间越来越标准,也越来越精确。
自十七世纪以来,天文学家们以地球自转和世界时作为时间尺度:当地球绕轴自转一周,地球上任何地点的人连续两次看见太阳在天空中同一位置的时间间隔为一个平太阳日。由于一个平太阳日被分为24小时,每小时为3600秒,1820年法国科学院正式提出:一个平太阳日的1/86400为一个平太阳秒,称为世界时秒长。根据世界时秒长度量的时间被称为世界时(UT1:Universal Time 1)。 由于地球自转季节性变化、不规则变化和长期减慢,所以世界时每天只能精确到1×10-9秒。在原子钟问世前,秒长是基于自转时(平太阳时),但石英钟出现后,发现了地球自转的不均匀性,自转时不能作为时间基准。
1953年是时频科学的一个新的里程碑。世界上第一台原子钟在美国哥伦比亚大学由三位科学家研制成功。1963年13届国际计量大会决定:铯原子Cs133基态的两个超精细能级间跃迁辐射震荡9,192,631,770周所持续的时间为1秒,被称为国际原子时(TAI: International Atomic Time)。此定义一直延用至今。目前,有大约50多个分散于世界各地的实验室拥有铯原子Cs133时钟,这些实验室定期地向位于法国巴黎的国际时间局(BIH:Bureau International de l’Heure)提供测时信息。国际时间局为世界各国的授时中心提供准确的时间服务数据,并保持着国际原子时尺度。1979年开始,TAI已在全世界全面使用,历元时刻与时间间隔都用原子时。而原来的世界时仅在与地球自转有关的研究工作或应用领域中使用。
我们日常所用的北京时间既不是原子时(TAI),也不是世界时(UT1),而是协调世界时(UTC:Coordinated Universal Time)。世界时以地球自转为基础,而原子时以能级跃迁辐射震荡为基础。原子时是均匀的计量系统,这对于测量时间间隔非常重要。但世界时每时每刻都反映了地球在空间的位置,这也是需要的。为兼顾两者,便引入了协调世界时系统。UTC在本质上还是一种原子时,因为它的秒长规定要和原子时秒长相等,只是在时刻上,通过人工干预,尽量靠近世界时。
为了使协调世界时(UTC)尽量靠近世界时(UT1) ,我们就必须在必要时对UTC作一整秒的调整(增加1秒或去掉1秒),使得UTC和UT1的时刻之差保持在±0.9秒以内。这一技术措施就称为闰秒(或跳秒),增加1秒称为正闰秒(或正跳秒);去掉1秒称为负闰秒(或负跳秒)。是否需要闰秒,由国际地球自转服务(IERS:International Earth Rotation and Reference Systems Service)决定。闰秒的首选日期是每年的12月31日和6月30日,或者是3月31日和9月30日。如果是正闰秒,则在闰秒当天的23时59分60秒后插入1秒,插入后的时序是:…58秒,59秒,60秒,0秒,…,这表示地球自转慢了,这一天不是86400秒,而是86401秒;如果是负闰秒,则把闰秒当天23时59分中的第59秒去掉,去掉后的时序是:…57秒,58秒,0秒,…,这一天只有86399秒。
在许多国家,精密时间和频率是通过无线电播发出去的。1904年开始播发无线电时间信号(时号)用于海上导航,现在无线电时号用于科学和技术领域。高频发播时号的精度为1毫秒;而甚低频发播标频,校准频率的准确度达10-11。通过飞机搬运小型铯钟,可以将全球的时间同步到1微秒;人造卫星可同步到0.1微秒。
我想,这篇乱七八糟的东西,对想了解“什么是时间”的人们来说,也许会有所帮助。
- Re: 什么是时间?我们真正拥有吗? Is time a illusion?posted on 01/10/2011
感谢斋主科普。总结一下,时间和空间密不可分,是人为的抽象概念,但它不可能脱离空间这个概念单独存在,而且随着空间的变化而变化。时间的单位则是人为订立的。 - Re: 什么是时间?我们真正拥有吗? Is time a illusion?posted on 01/11/2011
“时间的单位则是人为订立的。”
Is there any other 单位 that is not 人为订立的? :-)
liaokang wrote:
感谢斋主科普。总结一下,时间和空间密不可分,是人为的抽象概念,但它不可能脱离空间这个概念单独存在,而且随着空间的变化而变化。时间的单位则是人为订立的。
- Re: 什么是时间?我们真正拥有吗? Is time a illusion?posted on 01/11/2011
什么都是人为的;什么都又是非人为的。
说什么是人为的,马上招来逻辑麻烦:为什么是这样人为,而非那样人为?那非人为的就从后门爬了回来。
刚看圣奥古斯丁《自白》中一段论时间。结尾短小精悍:今天就是永恒。
省省吧,体验今天即体验永恒。 - Re: 什么是时间?我们真正拥有吗? Is time a illusion?posted on 01/11/2011
"省省吧,体验今天即体验永恒。"
省省什么?体验什么?
说什么省省,马上招来逻辑麻烦:为什么是省省这样,而非省省那样?那非省省的就从后门爬了回来。 :-)
touche wrote:
什么都是人为的;什么都又是非人为的。
说什么是人为的,马上招来逻辑麻烦:为什么是这样人为,而非那样人为?那非人为的就从后门爬了回来。
刚看圣奥古斯丁《自白》中一段论时间。结尾短小精悍:今天就是永恒。
省省吧,体验今天即体验永恒。 - Re: 什么是时间?我们真正拥有吗? Is time a illusion?posted on 01/12/2011
当初学的辩证唯物论忘了?时间和空间是物质运动的形式。
我再补充:
物质运动的方式决定了时间和空间的主观感知。大城市的人总觉得时间不够,在农村晒老阳的人总觉得时间充裕。健康的人觉得时间不够,受病痛煎熬的人觉得度日如年。
有时候我们希望时间快点,其实这就是在希望自己早点死掉。不如从容等待。
- Re: 什么是时间?我们真正拥有吗? Is time a illusion?posted on 01/13/2011
我在里面,对时间也有很多思考,等我整理出来参加你们的讨论,谢草医开这条线。 - Re: 什么是时间?我们真正拥有吗? Is time a illusion?posted on 01/14/2011
今天早上在厨房接连犯两个严重错误,都与improper time tracking 有关,怎么修复那个烧焦的神经元?
想起一部电影《memento》, 因大脑受损的某保险经纪人,通过宝利莱速成照相的协助,成功复制出一条时间线索,并且复仇成功。
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