The Time Traveller by Unknown

Author:Unknown
Language: eng
Format: epub
Published: 2016-06-20T04:00:00+00:00

Nine

My Expanding Universe

With the calendar showing the approach of fall, I could hardly wait for classes to resume. I was particularly enthused to be scheduled for a general relativity graduate course, which would cover tensor analysis, differential and Riemannian geometry, and, importantly, Einstein’s gravitational field equations, which show how a massive body like the sun causes empty space to curve. This curvature of space results in what we call gravity. In truth, the planets of our solar system are not influenced so much by gravity as they are pulled through this curved space created by the sun. It is basic, universe-building stuff that I knew could be taught entertainingly with experiments as well as with equations.

The class ended up with only twelve students, which I would learn was a decent number for a high-level graduate physics course. It was an older and rather sedate group, unlike the eager-beaver undergraduates I had taught the previous year. Nonetheless, I was excited to be leading these dedicated and focused students through this challenging course about some of the most vital elements of modern physics, with a sizable dose of Einstein stirred into the mix. It still felt unreal that I was actually a physics faculty member at a major university, with the opportunity to teach, of all things, general relativity.

During the term, I managed to slip in a lesson from Gödel’s study of cosmology, which I first read about in the air force. Although there was much I hadn’t understood the first time around, I had become instantly fascinated by Gödel’s work because it allowed for the possibility of time travel into the past.

Cosmologists frequently study theoretical model universes that may be similar or different from our actual universe. They study these model universes just to see what might be possible within the laws of physics. In his rotating-universe work, Gödel allowed for closed loops in time, or closed timelines. Normal time is represented as a straight line, the bottom of the line representing the past, the middle of the line the present, and the top of the line the future. Such a timeline shows the world as we normally experience it; that is, we move from yesterday, to today, to tomorrow. A closed timeline means that the ends of the line are connected. That meant, Gödel concluded, that travel into the future or the past is equally possible along a closed loop line.

Preparing for the general relativity course allowed me the opportunity to delve deeper into circular timelines. This came about in connection with the theory of black holes. Previously, I had only studied black holes that did not rotate. Real stars rotate just like the earth. Black holes are formed from the gravitational collapse of stars. If the rotation of the resulting black hole is slow enough, one can neglect the gravitational effect of the rotation. For a rapidly rotating black hole the situation becomes very complicated. In fact, it took nearly fifty years before a solution of Einstein’s field equations

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