Why There Is An Absolute Constancy In The Speed Of Light?


Why there is An Absolute Constancy in the Speed of Light?

Two theories that completely changed the Newtonian view of space and time, two most influential theories are:

1.   Einstein General Theory of Relativity

2.   Quantum mechanics

These theories were formulated about 100 years ago but still we are still trying to fuse these two theories with some other ingredients in order to form a unified theory which was the dream of the Albert Einstein – The Theory of Everything. Theory of everything describes all the observations of physical universe and on the other hand General Theory of Relativity predicts that physical time has physical shape and the four dimensional space and time is not flat, the distribution of energy and matter wraps the four dimensional space-time. 


In the universe celestial bodies tries to follow straight line path but as the space-time is not flat, as predicted by general theory of relativity, they don’t follow this path. The General Theory of Relativity also predicts that the gravity is distortion of space-time due to uneven distribution of matter and energy; precisely you can say that curvature of space-time gives birth to gravity, even light doesn’t follow straight line path due to this curvature of space-time. It is already calculated that speed of light is 300000000 m/s which is independent of frame of reference i.e. it doesn’t matter whether source or observer are moving or not with respect to each other and this makes the speed of light absolute constant in vacuum. Now the question arises how this can be an absolute truth or what are causes or reasons that make the speed of light constant?

Recent developments in field of modern physics declines the traditional view of light and shows that the light doesn’t travel instantaneously from source to observer, it is rather has an absolute constant speed  - 186000 miles/sec which is independent of reference frame. We know that all the bodies in our present universe has positive mass that restricts the light to travel in a straight line path due gravitational force which exists due to mass of that body.

Light always follows a curved path from source to observer due to which it takes a little bit longer time to reach observer, so with reference to the observer physical time runs slower. As observer cannot recognize this curved path it seems to him that light travels in straight path. If both the sources and observers would have zero mass then would have zero gravity too (according to Newton’s law), light would be in a straight line path which is straight line between them.


Spacetime Curvature




Let the straight line distance between observer and source is D and the time taken to travel light to observer in straight line is T then the speed of light is “c“ which is equal to D/T. i.e

C= D/T

If both the observer and source have masses the path will be curved by the distance D’ > D and the time taken will be more say by ‘t’. In this case speed of light will be D’/(T+t). Here observer and source both are at rest but it can be concluded with little mathematics that whatever be the motion between them, the speed of light will be constant.


The speed of light is always a constant at 186,000 miles per second or 300,000 kilometer per second. The change in masses due to the motion of objects makes the distortion of the light path to be positively curved. The curvature is directly proportional of the increase of effective masses. Thus, the speed of light is independent of the motion of the source and the observer. The light path will always be bent when bodies are in motion due to increased masses of both the source and the observer. The light path would be negatively bent for anti-particles and for anti-universe as well. The light path is positively bent for us because the bodies are all made of positive matter of our Universe, thus, gravity is always attractive due to all positive masses. The reason why all light-bents are positive and they occupy the upper half of the X axis in an X-Y plane. Thus, we can conclude that the speed of light always has an absolute constancy value: 300,000 kilometers per second or 186,000 miles per second and it is completely independent of the speed of source and the observer- it has an absolute constancy in terms of speed of light is concern.


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a)    Stephen Hawking, “A Brief History of Time”, Bantam Books, London 2011, pp. 156-157. ISBN-978-0-553- 10953-5 


b)    Stephen Hawking, “Black holes and Baby Universes and otheressays”, Bantam Press, London 2013, pp. 42- 61. ISBN 978-0-553-40663-4 


c)    Stephen Hawking, “The Universe in a Nutshell”, Bantam Press,London 2013, pp. 58-61, 63, 82-85, 90- 94, 99, 196. ISBN 0-553-80202-


d)    Stephen Hawking, “The Grand Design”, Bantam Books, London2011 


e)    Stephen Hawking, “The Beginning of Time”, A Lecture


f)     Stephen Hawking, “Stephen Hawking’s Universe: Strange Stuff Explained”, PBS site on imaginary time. 


g)    Gerald D. Mahan, “Many-Particle Physics”, Third Edition, Springer, 2000 


h)    Uno Ingard, K “Fundamental of Waves & oscillations”, Cambridge University Press. P. 38, ISBN-0-521-33957- X Oxford: The British Academy, 1999 


i)     A. Zee, “Quantum Field Theory in a Nutshell”,     Princeton University Press, 2003 


j)     Storrs McCall, “A Model of the Universe”, Oxford:     Clarendon Press, 1994

k)    Craig Callender, “Time, Reality and Experience”,    Cambridge, UK: Cambridge University Press 


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