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Key Concepts

  • Time is an especially hot topic right now in physics. The search for a unified theory is forcing physicists to reexamine very basic assumptions, and few things are more basic than time.
  • Some physicists argue that there is no such thing as time. Others think time ought to be promoted rather than demoted. In between these two positions is the fascinating idea that time exists but is not fundamental. A static world somehow gives rise to the time we perceive.
  • Philosophers have debated such ideas since before the time of Socrates, but physicists are now making them concrete. According to one, time may arise from the way that the universe is partitioned; what we perceive as time reflects the relations among its pieces.

As you read this sentence, you probably think that this moment—right now—is what is happening. The present moment feels special. It is real. However much you may remember the past or anticipate the future, you live in the present. Of course, the moment during which you read that sentence is no longer happening. This one is. In other words, it feels as though time flows, in the sense that the present is constantly updating itself. We have a deep intuition that the future is open until it becomes present and that the past is fixed. As time flows, this structure of fixed past, immediate present and open future gets carried forward in time. This structure is built into our language, thought and behavior. How we live our lives hangs on it.

Yet as natural as this way of thinking is, you will not find it reflected in science. The equations of physics do not tell us which events are occurring right now—they are like a map without the “you are here” symbol. The present moment does not exist in them, and therefore neither does the flow of time. Additionally, Albert Einstein’s theories of relativity suggest not only that there is no single special present but also that all moments are equally real. Fundamentally, the future is no more open than the past.