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FQXI ARTICLE

October 22, 2014

Time Dilation Gets a Quantum Twist

Quantum vs general relativistic conceptions of time go head-to-head in a proposed table-top test.

FQXi Awardees: Caslav Brukner

October 1, 2012

Caslav Brukner

University of Vienna

Just talking about such an experiment has enticed experimentalists to Brukner’s door. It has long been assumed that the overlap between quantum theory, which governs the behavior of the very small, and general relativity, which deals with how planets and stars warp spacetime on cosmic scales, lies way beyond experimental reach—perhaps only within the center of black holes. But surprisingly, Brukner believes there may be a way to test these two theories much closer to home.

This would not be a test of quantum gravity—a theory uniting quantum mechanics and general relativity—itself, Brukner is quick to add. But he and his colleagues, Magdalena Zych, Fabio Costa and Igor Pikowski, are proposing a test in which the effects of both quantum mechanics and general relativity on a clock are important. Their idea, outlined in the journal

Particle Clocks

The team’s twist on this quantum classic hinges on an important aspect of the double-slit experiment: quantum particles do not like to be spied on. If you watch to see which path a particle takes—whether it passed through the right or left slit—you destroy this wave-like behavior and the interference pattern disappears. Instead, the particles appear to have shot through the slits like bullets. Brukner’s team has combined this effect, known as

This vanishing of interference

will really be a proof that

there was a general relativistic

notion of time involved.

will really be a proof that

there was a general relativistic

notion of time involved.

- Caslav Brukner

But here’s the kicker: quantum complementarity says that the clocks can only continue to behave as waves if there is no significant time dilation effect between the two paths. That’s because, if there is a discernible time dilation, you would be able to look at the clock and deduce which path it had taken, based on whether it seemed to have ticked faster or slower

The experiment pits two conceptions of time—the quantum mechanical and the general relativistic—head to head. On one side, the double-slit experiment puts the clock into a quantum superposition—a blurry confusion of multiple identities. We should not know which path it took during the experiment, and the time shown on the clock is undefined. This is in contrast with general relativity in which time has an objective status: it is well-defined at single points. "In this experiment the time shown by the clock becomes quantum mechanically indefinite, that is, before it is measured it has no predetermined value," says Brukner.

On the Fringe

The standard double-slit experiment creates a distinctive pattern of fringes.

Will the team’s proposed experiment destroy it?

Credit: Jordgette

It is a difficult practical undertaking because the separation so far achieved in experiments that can maintain the required superposition between the two paths is small, so it is tough to accumulate enough of a difference in gravitational potential between the two paths to discern a time dilation effect. The effect would be very tiny—to see a difference of the order of a quadrillionth of a second (10

There’s also the question of what to use as a clock: molecules that have different rotational and vibrational internal dynamics could be used. Arndt is frequently approached by colleagues about the relevance of such ‘internal clocks’ in macromolecules. In that sense, Brukner’s proposal did not come as a full surprise, he says. But their use for exploring time dilation gives it a conceptually important new twist.

Getting a molecule to move slow enough, so that it accumulates sufficient time dilation, is another issue to resolve. "One would first have to prepare a suitable rotational state that acts as the hand of the clock…in small molecules this might be done," says Arndt. In short, the experiment is far from trivial, "nothing for next year…" muses Arndt. "But the proposal addresses conceptual questions of quantum mechanics and should for that reason be experimentally realized."

What will the result of the experiment be? Only time will tell.

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AMRIT SRECKO SORLI wrote on September 1, 2014

rate of clocks is different bacause of diferent density of quantum vacuum. SR effect is 7 microsecond a day clocks on the satelite of GPS run slower than on the earth. 45 microseconds is GR effect, clocks run faster on the satelite bacause density of quantum vacuum there is denser than on the earth surface. And this corrections are VALID FOR ALL OBSERVERS.

rate of clocks is different bacause of diferent density of quantum vacuum. SR effect is 7 microsecond a day clocks on the satelite of GPS run slower than on the earth. 45 microseconds is GR effect, clocks run faster on the satelite bacause density of quantum vacuum there is denser than on the earth surface. And this corrections are VALID FOR ALL OBSERVERS.

AMRIT SRECKO SORLI wrote on September 1, 2014

there is no time dilatation at al, time cannot dilate as time is not phycical. Rate of clocks is "relative" regarding density of quantum vacuum. Less qv is dense less is speed of clocks and all other change, speed of light inclusding. Shapiro experiment shows light has a bit lower speed in lover density of quantum vacuum. But this change of C is so small that SR remains valid.

there is no time dilatation at al, time cannot dilate as time is not phycical. Rate of clocks is "relative" regarding density of quantum vacuum. Less qv is dense less is speed of clocks and all other change, speed of light inclusding. Shapiro experiment shows light has a bit lower speed in lover density of quantum vacuum. But this change of C is so small that SR remains valid.

PENTCHO VALEV wrote on August 31, 2014

Sabine Hossenfelder: "How is time-dilatation in a gravitational field less strange than entanglement?"

Gravitational time dilation is not just strange - it is absurd. Einstein fabricated it in 1911. According to him, the effect occurs even in a HOMOGENEOUS gravitational field, which means that the two clocks, although at different heights, are in EXACTLY THE SAME immediate environment (experience EXACTLY THE SAME gravitational field) and yet one of them runs faster than the other. In...

Sabine Hossenfelder: "How is time-dilatation in a gravitational field less strange than entanglement?"

Gravitational time dilation is not just strange - it is absurd. Einstein fabricated it in 1911. According to him, the effect occurs even in a HOMOGENEOUS gravitational field, which means that the two clocks, although at different heights, are in EXACTLY THE SAME immediate environment (experience EXACTLY THE SAME gravitational field) and yet one of them runs faster than the other. In...

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