Sensitive measuring instrument rules out ‘pixelated universe’ space-time theory
The Holometer is not much to look at but actually is a small array of lasers and mirrors with a trailer for a control room. The low-tech appearance of the device
belies the fact that it is an unprecedentedly sensitive instrument, able to measure movements that last only a millionth of a second and distances that are a billionth
of a billionth of a meter – a thousand times smaller than a single proton.
Our common sense, and the laws of physics, assumes that space and time are continuous. The Holometer challenges this assumption. We know that energy on the atomic level, for instance, is not continuous and comes in small, indivisible amounts. The Holometer was built to test if space and time behave the same way.
If they do, this would mean that everything is pixelated, like a digital image. When you zoom in far enough, you see that a digital image is not smooth, but made up of
individual pixels. An image can only store as much data as the number of pixels allows. If the universe is similarly segmented, and hence more blurry than we think, then there would be a limit to the amount of information space-time can contain.
The main theory the Holometer was built to test was posited by Craig Hogan, a professor of astronomy and physics at the University of Chicago and the head of
Fermilab’s Center for Particle Astrophysics. In a new result released this month after a year of data-taking, the Holometer collaboration has announced that it has
ruled out Hogan’s theory of a pixelated universe to a high level of statistical significance. This means the Holometer did not detect the amount of correlated
holographic noise – quantum jitter – that this particular model of space-time predicts.
But as Hogan emphasizes, that’s just one theory, and with the Holometer, this team of scientists has proven that space-time can be probed at an unprecedented level.
“This is just the beginning of the story,” said Hogan. “We’ve developed a new way of studying space and time that we didn’t have before. We weren’t even sure we could attain the sensitivity we did.”
The Holometer is a deceptively simple device. It uses a pair of laser interferometers placed close to one another, each sending a one-kilowatt beam of light through a beam splitter and down two perpendicular arms, 40 meters each. The light is then reflected back into the beam splitter where the two beams recombine. If no motion has occurred, then the recombined beam will be the same as the original beam. But if fluctuations in brightness are observed, researchers will then analyze these fluctuations to see if the splitter is moving in a certain way, being carried along on a jitter of space itself.
According to Fermilab’s Aaron Chou, project manager of the Holometer experiment, the collaboration looked to the work done to design other, similar instruments, such as the one used in the Laser Interferometer Gravitational-Wave Observatory (LIGO) experiment. Chou said that once the Holometer team realized that this technology could be used to study the quantum fluctuation they were after, the work of other collaborations using laser interferometers (including LIGO) was invaluable.
“No one has ever applied this technology in this way before,” said Chou. “A small team, mostly students, built an instrument nearly as sensitive as LIGO’s to look for
something completely different.”
The challenge for researchers using the Holometer is to eliminate all other sources of movement until they are left with a fluctuation they cannot explain. According
to Fermilab’s Chris Stoughton, scientist on the Holometer experiment, the process of taking data was one of constantly adjusting the machine to remove more noise.
“You would run the machine for a while, take data, and then try to get rid of all the fluctuation you could see before running it again,” said Stoughton. “The origin
of the phenomenon we’re looking for is a billion billion times smaller than a proton, and the Holometer is extremely sensitive, so it picks up a lot of outside
sources, such as wind and traffic.”
If the Holometer were to see holographic noise that researchers could not eliminate, it might be detecting noise that is intrinsic to space-time, which may mean that information in our universe could actually be encoded in tiny packets in two dimensions.
The fact that the Holometer ruled out his theory to a high level of significance proves that it can probe time and space at previously unimagined scales, Hogan said.
It also proves that if this quantum jitter exists, it is either much smaller than the Holometer can detect, or is moving in directions the current instrument is not
configured to observe.
So what’s next? Hogan said the Holometer team will continue to take and analyze data, and will publish more general and more sensitive studies of holographic noise.
The collaboration already released a result related to the study of gravitational waves.
Hogan is already putting forth a new model of holographic structure that would require similar instruments of the same sensitivity, but different configurations
sensitive to the rotation of space. The Holometer, Hogan said, will serve as a template for an entirely new field of experimental science.
“It’s new technology, and the Holometer is just the first example of a new way of studying exotic correlations,” said Hogan. “It is just the first glimpse through a
newly invented microscope.”
Related articles and links:
www.fnla.gov
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