by Prasad Ganti

One of my favorite all time great scientists postulated that time and space are relative, which means that they do not seem to be as straight forward as they appear to us Earthlings. Under normal circumstances, they are very straight forward, but once conditions change, they show different colors. In essence, this is Albert Einstein’s theory of relativity. The recent movie “Interstellar” is based on these “out of this world” concepts proposed by the genius who lived and taught in our neighborhood of Princeton.

Special theory came first, which said that time can slow down depending on how fast a clock is moving. Clocks slow down in a fast-moving train. Next came the General Theory which said that space curves in the presence of mass. More massive a body is, more is the space curvature. The curvature is implied by bending of light in gravitational fields. Gravity also impacts time. Clocks slow down in the presence of gravity.

There are several implications of these seemingly unearthly concepts. Nothing in the Universe can move faster than the speed of light. Seems like the sculptor of the Universe ordained such a speed limit that can impose severe limitations on space travel. Probes takes nearly 6 months to reach Mars, which is in the vicinity of the Earth, and much longer for interstellar travel; a human lifespan being trivial in comparison.

Fortunately Einstein’s same theories come to our rescue during interstellar journeys. The faster our spaceship travels, the slower our clocks will run, which means that human beings on interstellar journeys will age less than their counterparts on the Earth. The movie portrays this concept well when a father who left his young daughter back home, comes back to see her as an old woman while he is still young. The father is young not only because he traveled in space at high speeds, but also because he spent time near a black hole.

Black hole is an idea that rose from Einstein’s theories. It is a gravitationally intense place presumably caused by compacting mass to incredible densities. Just imagine a garbage compactor working ceaselessly to compress further and further until a black hole is formed! Since a gravitational field bends light, and the field is so intense in a black hole, the light just keeps bending in and in until it is totally trapped within the black hole. It cannot come out, so no one can really “see” a black hole but one can feel the presence as one approaches it. Astronomers use the movement of other bodies in the vicinity to deduce the presence of a black hole. In the movie, it is depicted by a halo of light surrounding a very dark region.

The next implication of Einstein’s fabulous theories rises from the curvature of space, which means that our Universe is not a flat region of space stretching on and on for trillions of light years. It curves itself into oddball shapes. It is speculated that the space curvature can result in a journey back to the starting point after traveling for billions of light years; going round and round in circles!

The concept of a “wormhole” comes up as a result. It is a tunnel or a shortcut between seemingly distant points in space. One of the astronauts in the movie illustrates this idea by folding a paper and poking a hole using a pencil from one side of the paper to the other side indicating the short cut, while the paper itself is curling around to the same point.

Another implication is that gravity can be created. Artificial gravity is used in the spacecraft to reduce the effect of weightlessness. As a result, the astronauts feel like they are sitting in their living room, rather than floating in space. The movie shows the spacecraft rotating as it moves ahead in its journey. This rotation causes the artificial gravity.

All these pieces come together in making the complete movie: an Earth in danger of getting destroyed, a small mission of astronauts to find a new home, a spinning spacecraft on an arduous journey accelerated by entering a wormhole right to emerge somewhere else to find alternatives to our home, including the vicinity of a black hole! An excellently woven tapestry of Mr. Einstein’s ideas, colored by human frailties and ulterior motives!