Time’s arrow may make U-turns in universe

The new millennium, or at least the new year, begins. Yet somewhere in our universe, the year 2000 may have just receded into the future, new research suggests.

Imagine a renegade world where in Reversed-Times Square, the ball moved up the tower last night instead of down and where calendars flipped back to Dec. 31, 1999, instead of ahead. Such time inconsistency from one world to another could occur even in our own galaxy, proposes Lawrence S. Schulman of Clarkson University in Potsdam, N.Y.

“The actual appearance of this [opposite-directed time] in our universe is something we would have to see by observation. The only thing I’m saying, theoretically, is it’s not ruled out,” Schulman explains.

“Time is an extremely important but very difficult field of research,” notes David T. Pegg of Griffith University in Brisbane, Australia. Although Schulman investigates concepts that may “seem like total science fiction,” Pegg says, he “makes some real progress.”

In his studies, Schulman assumes that the universe expands and then contracts: a Big Bang followed by a Big Crunch. He finds that celestial bodies with reversed time would have originated in our distant future and would already have experienced the cosmic turnaround. To us, these worlds would look like very old objects. Spectroscopic surveys looking for elemental composition typical of such old objects might reveal their presence.

Unlikely to be luminous anymore because of their enormous age, the bodies would still exert gravitational attraction. Detecting them might help clear up a profound mystery in cosmology: the identity of the invisible, or dark, matter that provides most of the gravitational glue of the universe, Schulman asserts. His exploration of time reversal appears in the Dec. 27, 1999 Physical Review Letters.

For the most part, equations describing the behavior of subatomic particles and the propagation of electromagnetic waves look the same if the flow of time is reversed. A year ago, however, scientists found experimental evidence that certain very rare interactions of particles called kaons imply a distinction between the forward and backward directions of time (SN: 10/31/98, p. 277).

In everyday experience, time appears to flow one way. Scientists have proposed that the second law of thermodynamics may orient time’s arrow. It holds that ordinary processes cause some irreversible loss of energy to randomness and disorder. If time reversed, improbable events would occur, such as broken eggs spontaneously reassembling.

Thomas Gold of Cornell University argued in the 1960s that the universe’s expansion dictates that time points in a particular direction. As time passes, the universe must grow bigger.

In Schulman’s bang-crunch universe, space expands until it reaches a maximum volume. Then, as it starts to contract, the arrow of time flips, á la Gold. Schulman contends that, by virtue of being isolated, a particular star or galaxy might survive through the universe’s rebound from expansion to contraction with time arrows intact and oppositely oriented to those of the rest of matter.

To explore the interactions of such a survivor, Schulman uses a computer model of two side-by-side boxes of gas molecules that exert a mild influence on each other as they compress or expand. He finds that the gases can communicate without destroying their direction of volume change, the time arrows.

The new theory could self-destruct, however, if opposed time streams interact in such a way that leads to unresolvable paradoxes, such as putting effects before causes, Schulman acknowledges. Also, recent evidence of accelerating expansion of the universe (SN: 10/31/98, p. 277) makes a Big Crunch seem less likely, he notes.

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