RECENT ARTICLES

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.

The impossibility of building a perfect clock could help explain away microscale weirdness.

FQXI ARTICLE

June 25, 2019

Watching the Observers

Accounting for quantum fuzziness could help us measure space and time—and the cosmos—more accurately.

FQXi Awardees: Ivette Fuentes

June 13, 2017

Ivette Fuentes

University of Vienna

That, in a nutshell, is the question that quantum physicist Ivette Fuentes, of the University of Vienna, Austria, is seeking to answer.

Fuentes, like many other physicists, is intrigued about the nature of quantum gravity—the elusive theory that would unite the quantum physical rules of the microworld with general relativity, the laws of gravity on cosmic scales. Unlike many others striving toward the same goal, however, Fuentes and her colleagues are on this seemingly esoteric quest because they believe it could have tangible consequences in the lab today for our ability to measure time and space precisely and to make accurate astronomical observations. Fuentes notes that observers—the people making these experimental measurements—have profoundly different roles, and limitations, in these cornerstone theories of modern physics, and this could be the key to understanding how the theories interact.

In the usual way of thinking about general relativity, observers play a passive role. "When observers make measurements of the system, they don’t really affect it," Fuentes explains, "but their observations depend on their state of motion." In quantum mechanics, by contrast, an observer takes an active part in what happens. The mere act of choosing when and how to make a measurement can irrevocably change the properties of the underlying system being measured. "So you can’t separate the observer from the physical system that’s being observed," Fuentes says.

These two versions of an observer are not necessarily incompatible. But they are also not clearly the same thing. So, with the help of physicists David Bruschi of the University of York, UK, and Stefano Mancini of the University of Camerino, Italy, and an FQXi grant of almost $85,000, Fuentes is asking, is there a way to make these two ways of observing agree? And how does this affect the precision of measurements we take for granted?

"Quantum theory can tell us at the end what we can say and what we cannot about the universe," says Mancini.

The team’s approach may sound modest at first. Rather than trying to build a complete quantum gravity theory from scratch, they are looking at current theoretical and experimental methods and calculating their limitations—due to quantum, gravitational or other relativistic effects.

Radiation Bath

Thanks to quantum uncertainty, there’s a limit to how precisely physicists can measure the properties of tiny quantum objects. You famously cannot know both the position of a particle and its momentum simultaneously. This uncertainty is usually thought to be unimportant in large-scale astronomical observations, however. For instance, astronomers have learned huge amounts about the origins of the universe by precisely measuring the temperature of light particles in the cosmic microwave background—a radiation bath created roughly 400,000 years after the big bang that still pervades today’s universe.

But the team argues that astronomers must ultimately face the fact that the particles of light themselves are subject to quantum uncertainty, which will limit the precision of their measurements of the radiation. Bruschi blames this "blurriness" on the quantum nature of the spacetime fabric itself. The team wants to find out what this means for our attempts to pin down the basic properties of the universe.

Blurred Lines

Could quantum effects make us question data from the sky?

Credit: Planck/ESA

This could have profound implications. General relativity supposes that spacetime is smooth, but this quantum measurement limitation could define a grainy structure for spacetime’s fabric that might become a core feature of a new theory of quantum gravity, Fuentes explains: "Is that somehow the starting point of a quantized spacetime?” (See also "Wrinkles in Spacetime.")

Physicist Julian Barbour, an expert on time at Oxford University, UK, agrees that to truly understand time, we must consider the quantum laws that describe the motion of real clocks.

The project could also have an important impact in the field of quantum metrology, which aims to exploit quantum effects to improve measurement techniques. "Hopefully we’ll get interesting things that can be tested," says Tim Ralph, an expert on quantum optics at Queensland University in Australia. He also hopes that the project will yield "some useful techniques for improving metrology in useful situations."

The team hopes their work will connect quantum and gravity, theory and experiment, practical and fundamental—and finally start to bring questions that were once only intellectual musings, into the lab: "We are really at a tipping point," says Bruschi, "where these questions are becoming not just questions for a theoretician."

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.

TONY ROGERS wrote on June 15, 2019

The Chicago Cubs’ is an American professional baseball team and is loved by all the people. Such teams are rarely built. Many people love and support this team by wearing Chicago Cubs’ shirts and other apparels. These apparels are specifically designed for this particular sport and all the players who fall in this team. People get to choose from a variety of sportswear.

The Chicago Cubs’ is an American professional baseball team and is loved by all the people. Such teams are rarely built. Many people love and support this team by wearing Chicago Cubs’ shirts and other apparels. These apparels are specifically designed for this particular sport and all the players who fall in this team. People get to choose from a variety of sportswear.

GLORIA WILD wrote on June 17, 2018

Always if you wanna write more oF interesting articles you can visit original-writing.com.

Always if you wanna write more oF interesting articles you can visit original-writing.com.

GLORIA WILD wrote on June 13, 2018

Watching is always interested! Work is still working and enjoy the life you need to find the time. Each does it differently and surveillance one of the options. I wrote about it in my articles for writing-essays.net. Appreciate life and enjoy the observation! :)

Watching is always interested! Work is still working and enjoy the life you need to find the time. Each does it differently and surveillance one of the options. I wrote about it in my articles for writing-essays.net. Appreciate life and enjoy the observation! :)

read all article comments