John Cramer - Einstein's Bridge

“Okay, Iris,” George said, “we have about half an hour before we get to the other side, assuming the power stays on. You’d better explain your plan to us. What is it you want to do?

The beautiful child smiled. “We will try to deliberately create a time vortex, what your quantum field theorists call a ‘timelike loop’ or a ‘Cauchy horizon,’” she said. “The vortex will destroy your present universe, unravel it to a point in the past, and produce a new history in which the Hive does not create a Bridge and your world is safe.”

“Do you mean you want to build a time machine and change the past, to rewrite history?” said Roger. “I thought that was…”

“… impossible?” Iris finished. “In a way, it is. Creating a time vortex produces a catastrophic condition that is usually considered unacceptable. It destroys the part of the universe in which the loop is created.”

“How can that be?” asked Roger.

“You are a field theorist, Roger,” said Iris. “Surely you know about path integrals.”

Roger nodded. “Only too well,” he said.

“What happens when the space-time interval along the path goes to zero?” Iris asked.

“Oh, you mean the self-energy term,” said Roger. “That’s certainly a problem. It makes a singularity. The energy goes to infinity. We’ve learned to renormalize the theory by subtracting those infinities away. I should add that we always feel uncomfortable about doing that, but it works.”

“You subtract the singularity for a particle acting on itself, with zero interval between the particle and itself,” said Iris. “But suppose there was also another path that had a zero interval, a net zero space-time distance. What would you do then?”

“Another? There can’t be, because…” He stopped. “Oh, I see. With a wormhole back through time, you can make the negative timelike part cancel the positive spacelike part, so the net interval goes to zero. That would produce a very nasty singularity that probably couldn’t be disposed of by subtraction.” He smiled with the pleasure of a new idea, then frowned.

“You’re suggesting that the resulting singularity destroys the universe?”

Iris nodded. “It does indeed. We Makers have done it. Fluctuations in the vacuum are amplified and build up until all paths within the timelike loop acquire arbitrarily large energies. The part of the universe that is threaded by the loop is destroyed. History is nullified and must form again from the earliest point of the loop. That is what a time vortex is.”

“Hold it,” said George. “How can you destroy only part of a universe?”

“I suppose ‘destroys’ gives the wrong impression,” said Iris. “Perhaps ‘unraveled’ provides a better metaphor. Or consider it as the ‘rewind and restart’ of a recording. All events related to the existence of the time vortex are nullified, as if they never happened, and are replaced by new causal sequences that do not contain the loop.”

“You mean that we can go back to a time when Alice is still alive?” George asked. He looked a bit wild-eyed, Roger thought.

“Yes,” Iris replied, “of course.”

“Wait a moment,” said Roger. “Are you talking about moving back to some alternate-branch Everett-Wheeler universe?”

Iris laughed. “Since we established contact with your culture, many Individuals of our world, particularly our science meta-historian specialists, have derived great amusement from your quantum mythology, that area which you call the ‘interpretation of quantum mechanics.’ They were particularly amused by your Copenhagen interpretation, with its state vectors that are altered by the thoughts of intelligent observers, and by your EverettWheeler interpretation, with its splitting and resplitting into multiple universes. In this regard, your culture is unique among those that we have encountered. No other has provided such a remarkable demonstration of fertile creative desperation in seeking to understand physical behavior at the quantum level. We find these myths of yours quaint and charming.”

“In other words, ‘wrong’?” asked Roger.

Iris looked troubled. “No more wrong, say, than your Greek or Norse myths. Your excursions of scientific fantasy are an interesting manifestation of your culture, but they are not an accurate portrayal of the behavior of the universe. Human observers, for example, are not demigods with the ability to collapse a wave function with an act of measurement or of insight. It is better that they are not, believe me.”

“I’m not sure where this is leading,” said George, “or what it has to do with our present predicament. I gather that you were in the process of saying that there is a way of — how did you put it? — nullifying the Hive’s discovery of our universe.”

“Pardon me, George,” said Iris. “Yes, that’s what I was saying. This universe, all Bubbles individually and all of them together, moves forward in time at the quantum level by a chain of handshakes between past and future. The psi-star time-reversed wave functions of your formulation of quantum mechanics, though you have never realized it, represent the future reaching back to make an accommodation with the past that allows a quantum event to happen, to become reality. Each quantum event emerges into reality as the result of a feedback loop between past and future. These are allowed timelike loops that bring the universe into being.

“If we create an artificial timelike loop back to some point of space-time within the negative light cone of the present, we create a condition that nullifies all of those handshakes, those transactions between future and past. The events within the loop are in effect erased or unraveled and the universe starts over from the first instant where the forbidden loop would have begun to exist. The universe is wounded and heals itself with a new set of handshakes that do not bring a timelike loop into being. Nature, as your ancient Greek natural philosophers might have said, abhors a time machine.

“We will attempt to create a time-hole back to an era from which you can prevent the SSC from being built. If we can achieve that, then your world, your Bubble, will be safe from the Hive.”

“Why do we need to stop the SSC project?” George asked. “If the universe really reforms without the timelike loop, why do we need to do anything more? Won’t the universe heal itself to take care of the Hive problem?”

“Not necessarily,” said Iris. “There are many paths that could lead to the absence of a timelike loop. For example, your SSC is built and the Hive discovers your world, but we do not.”

“Does this time vortex thing really work?” asked Roger. “You’ve actually done it before?”

“We have been making contact with other Bubbles for a dozen gross of orbits, over seventeen of your centuries. For about the last half of that period, we have had to deal with the Hive civilization. In our last eight contacts, we were able to provide isolation from the Hive in five cases, and we had to create timelike loops in two cases. The other case was lost to the Hive altogether.”

“I don’t understand,” said George. “How could you know that you created the loop if it erases its own existence? Wouldn’t it erase its traces in your world, too?”

“Excellent question,” said Iris. “As a part of the process of creating the loop, we transmit a complete record to our past. In this way we know what has happened and also preserve all the new information we gained from the contact.”

They had come to a maintenance station, and their way was blocked by another vehicle on the rail. George brought their truck to a stop, and they got out.

“Well, if it ain’t George and Roger,” said a voice. “Howdy!”