RECENT ARTICLES

Why physics and astronomy communities must take diversity issues seriously in order to do good science.

Einstein’s relativity pushes physicists towards a picture of the universe as a block, in which the past, present, and future all exist on the same footing; but maybe that shift in thinking has gone too far.

Resolving the black hole firewall paradox—by calculating what a real astronaut would compute at the black hole's edge.

Defining a ‘quantum clock’ and a 'quantum ruler' could help those attempting to unify physics—and solve the mystery of vanishing time.

Calculating the odds that intelligent observers arise in parallel universes—and working out what they might see.

FQXI ARTICLE

April 21, 2018

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.

RESMI GIRL MALIK wrote on March 5, 2018

There are many places where you can take your Escorts in Delhi. You should meet to learn what fun is real. Delhi Escorts are several young, gorgeous Escorts via around the world so whatever your flavor is, it will fully be satisfied.

Call girls in Delhi

There are many places where you can take your Escorts in Delhi. You should meet to learn what fun is real. Delhi Escorts are several young, gorgeous Escorts via around the world so whatever your flavor is, it will fully be satisfied.

Call girls in Delhi

SHAWN wrote on February 2, 2018

This is quite interesting. But the topic in this area is really a vast one. For a person like me who is a normal one, would take days to get to the idea that you are working on. It needs much of a study to understand the depth of it alone.

louvre museum tour

This is quite interesting. But the topic in this area is really a vast one. For a person like me who is a normal one, would take days to get to the idea that you are working on. It needs much of a study to understand the depth of it alone.

louvre museum tour

SHERAPOVA SMITH wrote on December 10, 2017

The printing company must offer multiple materials for use in printing. Of course, the company details should be present as well. www.55printing.com

The printing company must offer multiple materials for use in printing. Of course, the company details should be present as well. www.55printing.com

read all article comments