# Traversing Space in Time

To us, space is just emptiness, a backdrop to everything else. Time likewise, simply ticks on incessantly. When we walk along a straight line, it is a one dimensional experience. If we drive between two cities, it is a two dimensional experience and flying between two cities is a three dimensional experience.  When we add to the three dimensions of (length, breadth and height) or (X, Y and Z) the fourth dimension of TIME, the resulting mathematical model is called spacetime. The continuum of four dimensions (three in space and one in time) amounts to a universal way of labelling events from the point of view of a physicist. This was a profound idea of Einstein who however, hardly knew where to begin mathematically.  Later on, it was mathematician Hermann Minkowski in 1908 who had a way to reformulate this theory by describing its Mathematics.

This is the reason that the Four-dimensional manifold is now widely known as Minkowski space. Until 20th century, we were comfortable with the three dimensional geometry of the Universe which was thought to be independent of time. Classical physics treats time as a universal quantity of measurement which is uniform throughout space and has a constant rate of passage. It also assumes that space follows the geometry of common sense. However, in the context of relativity, the observed rate at which time passes for an object depends on its velocity relative to the observer.  An observer in most cases means a frame of reference from which an object or a set of objects or an event is being measured. This is significantly different from the ordinary English usage of the term. We can also find an explanation of how gravitational fields  slow the passage of time for an object as compared to an observer outside the field. Wherever matter exists, it bends the geometry of spacetime. This results in a curved shape of spacetime which can be understood as gravity. Imagine, a soft pillow as the fabric of spacetime and our head causing a dip in it. Einstein had postulated that gravity is not a force that propagates through space but a feature of spacetime itself. Although instruments can neither see nor measure space-time, several of the phenomena predicted by its warping have been confirmed.  As for instance, light around a massive object such as a black hole is bent causing it to act as a lens for the things that lie behind it.

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Astronomers routinely use this method to study stars and galaxies behind massive objects. Therefore time travels faster in space than on Earth because of the heavy mass of the Earth. According to Hawking, “If we want to travel into the future, we just need to go fast, really fast. And I think the only way we are ever likely to do that is by going into space. The fastest manned vehicle in history was Apollo 10. It reached 25,000 mph. But to travel in time, we will have to go more than 2,000 times faster. And to do that, we would need a much bigger ship, a truly enormous machine.”  In the backdrop of spacetime and time travel, Me’raj, an otherwise  controversial event in Islam, finds a reason to have been.  Some people believe it was only the spiritual ascension, and some say that it was a dream experienced by the Prophet. Yet some others call it a physical ascension to the heavens by the Holy Prophet Muhammad.  The steed brought to the Prophet was named Buraaq. It comes from the root Arabic word ‘Barq’ meaning current and current travels with the velocity of light.

Now once he got on the time scale of this spacetime, the time ran fast and he spent about 27 years worth of time on the absolute scale.  But once he got out of this scale, time again got slowed down for him and continued on the absolute scale. Only few seconds took out of this spacetime when he returned, so that the door-chain was still moving…! One more amazing learning outcome from the concept of spacetime is that present, past and future run parallel.

As for instance, the light from sun reaches us in 8 seconds.  Therefore the sun we observe now is a sun from 8 seconds in the past. Until the splash of light arrives, it is in the future, relative to those on Earth but in the past relative to the sun.  Similarly if we stand in front of a full length mirror, just 3 feet away, and since light travels at 1 foot per nanosecond, we see ourselves as we looked 6 nanoseconds ago. We are actually staring into the past. We are always younger in a mirror because we see ourselves from moments before. Mirrors are gateways to the past even though the past image we see is experienced in the “present.” So we only exist in the present.  It is incredible to learn that even Shams fakir has chosen to write entire Me’rajnama in present tense. He begins it as

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Karyo ronne rumalae waav

Tajdar soun Me’rajass draav

Although the present wouldn’t exist without the future, the future doesn’t itself, exist. Even Jesus, when asked at Pentecost, when the second coming was due, said: ‘The lord only knows’. He didn’t know and for good reason.

Dr. Qudsia Gani is Assistant Professor, Department of Physics, Cluster University Srinagar