A Song by Kumar Vishwas

मैं भाव सूचि उन भावों की,

जो बिके सदा ही बिन तोले | 

तनहाही हूँ हर उस ख़त की,

जो पढ़ा गया है बिन खोले |

हर आसूं को हर पत्थर तक,

पहुँचाने की लाचार हूक  |

मैं सहज अर्थ उन शब्दों का,

जो सुने गए हैं बिन बोले |

जो कभी नहीं बरसा खुल कर,

हर उस बादल का पानी हूँ |

लव कुश की पीर बिना गयी,

सीता की राम कहानी हूँ |

जिनके सपनों के ताज महल,

बनने से पहले टूट गए |

जिन हाथों मैं दो हाथ कभी,

आने से पहले झूट गए |

धरती पर जिनके खोने,

और पाने की अजब कहानी है |

किस्मत की देवी मान गयी,

पर प्रणय देवता रूठ गए |

मैं मैली चादर वाले उस,

कबीरा की अमृत वाणी हूँ |

लव कुश की पीर बिना गयी,

सीता की राम कहानी हूँ |

कुछ कहते हैं मैं सीखा हूँ,

अपने झक्मो को खुद सी कर |

कुछ जान गए मैं हसंता हूँ,

भीतर भीतर आसूं पी कर |

कुछ कहते हैं मैं हूँ,

विरोध से उपजी एक खुदार विजय |

कुछ कहते हैं मैं रचता हूँ,

खुद मैं मर कर खुद मैं जी कर |

लेकिन मैं हर चतुराई की,

सोची समझी नादानी हूँ |

लव कुश की पीर बिना गयी,

सीता की राम कहानी हूँ |

Time Travel - Arrow of Time

The term "Arrow of Time" was first coined by Arthur Eddington in 1927. It is used to describe the "one way direction" in which we perceive the passage of time. Time is a rather curious dimension in that we only see it increasing in one direction. The laws of physics at the microscopic level stay the same under something called the "T-Symmetry". T-Symmetry states that the laws of physics stay invariant under the time reversal transformation. A notable exception to this is the second law of thermodynamics. Entropy of the universe increases with passage of time. Or in other words we perceive time in the direction of increase of entropy. Since the beginning of universe started at big bang the entropy of universe has been increasing. The early universe had a low level of entropy as all the mass was concentrated at one point. With the expansion of universe this mass gets distributed across the space. The following figure shows a graph plot of Entropy v/s Time. 

Thus we see that the arrow of time points to a state of increasing entropy (or expanding space). The direction of the arrow in a way gives a default form of Time Travel. We are all traveling in the future at all times. Even though the universe had a single big bang singularity in the past, we have several black hole singularities in our observable universe. We know now that information loss can occur when a black hole evaporates. As such the entropy at the edge of a black hole may actually increase. What does it mean for the direction of Time ? We will explore some of these ideas in the next post on possibilities for Time Travel.

For now we update our previous picture of the pear shape of time with a direction as follows. 

Not only does Time have a space but also it has a direction. Possibilities of Time Travel should take into account our physical understanding of Time. The shape and arrow of Time limit the forms of Time Travel we may imagine.

Poem - Itni Rang Birangi Duniya - Dr Kumar Vishwas (Video and Lyrics)

इतनी रंग बिरंगी दुनिया, 

दो आखों में कैसे आये | 

हमसे पूछो इतने अनुभव, 

एक कंठ से कैसे गाये |

ऐसे  उजले लोग मिले जो,

अन्दर से बेहद काले थे | 

ऐसे चतुर लोग मिले जो, 

मन से भोले भाले थे |

ऐसे धनी लोग मिले जो, 

कंगलो से भी जयादा रीते थे | 

ऐसे मिले फकीर जो, 

सोने के घट में पानी पीते थे |

मिले परायेपन से अपने, 

अपनेपन से मिले पराये |

हमसे पूछो इतने अनुभव, 

एक कंठ से कैसे गाये |

जिनको जगत विजेता समझा,   

मन के हारे धारे निकले |

जो हारे हारे लगते थे, 

अन्दर से ध्रुव तारे निकले |

जिनको पतवारें सौपी थी, 

वे भवरों के सूदखोर थे |

जिनको भावर समझ डरता था, 

आखिर वही किनारे निकले |

वे मंजिल तक क्या पहुंचेंगे, 

जिनको खुद रास्ता भटकाए |

हमसे पूछो इतने अनुभव, 

एक कंठ से कैसे गाये | 

Time Travel - Nature and Shape of Time

In order to understand the possibilities of time travel it is important to understand time itself. What is time ? How is it caused ? Which physical phenomenon are responsible for the passage of time.Writer and physicist Paul Davies has called "time" Einstein’s unfinished revolution. Aristotle had speculated that time may be motion. He however added that motion could be slower or faster but not time. Aristotle did not have the privilege of knowing about Einstein’s relativity in which time also becomes amenable to change. Similarly when Einstein was working to develop theory of general relativity and proposed the revolutionary idea that mass curves space he did not know that the universe was expanding. 

This discovery by astronomer Edwin Hubble came 13 years after Einstein had published his theory of General Relativity. Had Einstein known of this great discovery he may have incorporated these ideas into his theories. Conceptually it is easier to derive space curvature in an expanding universe as an area of slower expansion under the influence of gravitons. One of the most dramatic aspects of the universe is that it is expanding and the presence of motion, forces and curved space-time happens in the expanding space.

The nature of time is such that it increases in the direction of the expanding universe. Our current understanding of time is based on general relativity. The general relativity when applied to the whole cosmos gives a peculiar shape to time. In order to understand that first consider the notion of a light cone and how it relates to time. To simplify things consider a 2 dimensional space with the observer at  a particular point on this plane. Let the time be represented in the 3rd dimension coming out of the plane as shown in the figure below.

Light Cones

The surface of the observer represents the present time. The light rays from the observe propagate in all directions but light has a limited speed so they cannot go beyond the surface of the cone. This conical structure forms a boundary of observable region emanating from the point of the observer. In the future time dimension it represents a cone called the future light cone. Similarly we can also build a past light cone which captures the history of the observer in the past. Now if we extrapolate the past light cone of the observer all the way back to the big bang it will represent the shape of time until the current epoch. 

Pear Shape

This actually gives a pear shape to the past light cone. The point of the big bang singularity represents a region of space which had huge matter density. As we know from Einstein's theory of general relativity matter causes light to bend in. Hence at the big bang singularity all the light rays were actually bent inwards.

Thus based on the current understanding of the universe and physics we can conclude that time is pear shaped.

The following video illustrates the concept of shape of time.

Ray Cummings, an early writer of science fiction, wrote in 1922, "Time... is what keeps everything from happening at once"

End Notes

1. On the Nature of Time - http://www.wfu.edu/~brehme/time.htm
2. Essay on The Nature of Time - http://www.fqxi.org/data/essay-contest-files/Barbour_The_Nature_of_Time.pdf
3. What Is Time? One Physicist Hunts for the Ultimate Theory - http://www.wired.com/wiredscience/2010/02/what-is-time/
4. What causes Time? - http://www.timephysics.com/index.html
5. Time Illusion and Reality - https://sites.google.com/site/smithjcn/time
6. The Nature of Time - http://www.integralscience.org/abouttime.html
7. Spatial Curvature - http://www.astro.ucla.edu/~wright/cosmo_03.htm