RECENT ARTICLES

Why do we remember the past and not the future? Untangling the connections between cause and effect, choice, and entropy.

Philosophers, physicists and neuroscientists discuss how our sense of time’s flow might arise through our interactions with external stimuli—despite suggestions from Einstein's relativity that our perception of the passage of time is an illusion.

A devilish new framework of thermodynamics that focuses on how we observe information could help illuminate our understanding of probability and rewrite quantum theory.

An unusual approach to unifying the laws of physics could solve Hawking's black-hole information paradox—and its predicted gravitational "memory effect" could be picked up by LIGO.

Objective reality, and the laws of physics themselves, emerge from our observations, according to a new framework that turns what we think of as fundamental on its head.

FQXI ARTICLE

August 23, 2019

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.

Comment on this Article

Please read the important Introduction that governs your participation in this community. Inappropriate language will not be tolerated and posts containing such language will be deleted. Otherwise, this is a free speech Forum and all are welcome!

function ValidatePostText_main () {
form = document.addPostForm_main;
var recaptcha = $("#g-recaptcha-response").val();
if (recaptcha === "") {
event.preventDefault();
alert("The reCaptcha Box below must be checked before you submit the form");
}
else if (form.postText_main.value == '') {
alert ("The post contains no text");
return false;
}
else {
return true;
}
}

**Your name:**
(optional)

Recent Comments

read all article comments

Please read the important Introduction that governs your participation in this community. Inappropriate language will not be tolerated and posts containing such language will be deleted. Otherwise, this is a free speech Forum and all are welcome!

Please enter the text of your post, then click the "Submit New Post" button below. You may also optionally add file attachments below before submitting your edits.

HTML tags are not permitted in posts, and will automatically be stripped out. Links to other web sites are permitted. For instructions on how to add links, please read the link help page.

You may use superscript (10

^{100}) and subscript (A_{2}) using [sup]...[/sup] and [sub]...[/sub] tags.You may use bold (

**important**) and italics (*emphasize*) using [b]...[/b] and [i]...[/i] tags.You may also include LateX equations into your post.

Insert LaTeX Equation
[hide]

LaTeX equations may be displayed in FQXi Forum posts by including them within [equation]...[/equation] tags. You may type your equation directly into your post, or use the LaTeX Equation Preview feature below to see how your equation will render (this is recommended).

For more help on LaTeX, please see the LaTeX Project Home Page.

LaTeX Equation Preview

preview equation

clear equation

insert equation into post at cursor

LaTeX equations may be displayed in FQXi Forum posts by including them within [equation]...[/equation] tags. You may type your equation directly into your post, or use the LaTeX Equation Preview feature below to see how your equation will render (this is recommended).

For more help on LaTeX, please see the LaTeX Project Home Page.

LaTeX Equation Preview

preview equation

clear equation

insert equation into post at cursor

Attachments
[hide]

You may optionally attach up to two documents to your post. To add an attachment, use the following feature to browse your computer and select the file to attach. The maximum file size for attachments is 1MB.

Once you're done adding file attachments, click the "Submit New Post" button to add your post.

You may optionally attach up to two documents to your post. To add an attachment, use the following feature to browse your computer and select the file to attach. The maximum file size for attachments is 1MB.

Once you're done adding file attachments, click the "Submit New Post" button to add your post.

THOMAS HOWARD RAY wrote on January 9, 2016

"If the speed of light were independent of the motion of the observer, then there would be no reasonable explanation for the fact that the frequency measured by the observer shifts from f=c/λ to f'=(c+v)/λ when the observer starts moving with speed v towards the light source. "

Simply, there is no c + v. You can invent terms all day long, and they still won't change the fact of the measured speed of light in all reference frames.

"If the speed of light were independent of the motion of the observer, then there would be no reasonable explanation for the fact that the frequency measured by the observer shifts from f=c/λ to f'=(c+v)/λ when the observer starts moving with speed v towards the light source. "

Simply, there is no c + v. You can invent terms all day long, and they still won't change the fact of the measured speed of light in all reference frames.

PENTCHO VALEV wrote on January 9, 2016

If the speed of light were independent of the motion of the observer, then there would be no reasonable explanation for the fact that the frequency measured by the observer shifts from f=c/λ to f'=(c+v)/λ when the observer starts moving with speed v towards the light source. The only reasonable explanation is this:

The frequency measured by the observer shifts from f=c/λ to f'=(c+v)/λ because the speed of the light relative to the observer shifts from c to c'=c+v, in violation of...

If the speed of light were independent of the motion of the observer, then there would be no reasonable explanation for the fact that the frequency measured by the observer shifts from f=c/λ to f'=(c+v)/λ when the observer starts moving with speed v towards the light source. The only reasonable explanation is this:

The frequency measured by the observer shifts from f=c/λ to f'=(c+v)/λ because the speed of the light relative to the observer shifts from c to c'=c+v, in violation of...

THOMAS HOWARD RAY wrote on January 9, 2016

" ... it is the speed of the light relative to the observer ..."

Since the speed of light is constant in all frames of reference, the lie is yours, not John Norton's. We know why you waste your time here. Any other forum blocked you long ago.

" ... it is the speed of the light relative to the observer ..."

Since the speed of light is constant in all frames of reference, the lie is yours, not John Norton's. We know why you waste your time here. Any other forum blocked you long ago.

read all article comments