Tag Archives: interferometer

A Gravitational Wave Comes Ashore


On February 11, 2016, a historic day for astronomers the world over, scientists announced a monumental discovery, which was made on September 14, 2015! Thank you LIGO, the era of gravitational wave (G-Wave) astronomy has begun.

One hundred years after a prediction from Einstein’s theory of general relativity scientists have their first direct evidence of gravitational waves. These waves are ripples in the fabric of spacetime itself rather than the movement of fields and particles, such as from electromagnetic radiation. These ripples show up when gravitationally immense bodies warp the structure of space in which they sit, such as through collisions or acceleration.


As you might imagine for such disturbances to be observed here on Earth over distances in the tens to hundreds of millions, of light-years requires not only vastly powerful forces at one end but immensely sensitive instruments at the other. In fact the detector credited with discovery in this case is the Laser Interferometer Gravitational-Wave Observatory, or LIGO. It is so sensitive it can detect a change in length of its measurement apparatus — infra-red laser beams — 10,000 times smaller than the width of a proton. LIGO is operated by Caltech and MIT and supported through the U.S. National Science Foundation.

Prof Kip Thorne, one of the founders of LIGO, said that until now, astronomers had looked at the universe as if on a calm sea. This is now changed. He adds:

“The colliding black holes that produced these gravitational waves created a violent storm in the fabric of space and time, a storm in which time speeded up and slowed down, and speeded up again, a storm in which the shape of space was bent in this way and that way.”

And, as Prof Stephen Hawking remarked:

“Gravitational waves provide a completely new way of looking at the universe. The ability to detect them has the potential to revolutionise astronomy. This discovery is the first detection of a black hole binary system and the first observation of black holes merging.”

Congratulations to the many hundreds of engineers, technicians, researchers and theoreticians who have collaborated on this ground-breaking experiment. Particular congratulations go to LIGO’s three principal instigators: Rainier Weiss, Kip Thorne, and Ronald Drever.

This discovery paves the way for deeper understanding of our cosmos and lays the foundation for a new and rich form of astronomy through gravitational observations.

Galileo’s first telescopes opened our eyes to the visual splendor of our solar system and its immediate neighborhood. More recently, radio-wave, x-ray and gamma-ray astronomy have allowed us to discover wonders further afield: star-forming nebulae, neutron stars, black holes, active galactic nuclei, the Cosmic Microwave Background (CMB). Now, through LIGO and its increasingly sensitive descendants we are likely to make even more breathtaking discoveries, some of which, courtesy of gravitational waves, may let us peer at the very origin of the universe itself — the Big Bang.

How brilliant is that!

Image 1: The historic detection of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (LIGO) is shown in this plot during a press conference in Washington, D.C. on Feb. 11, 2016.Courtesy: National Science Foundation.

Image 2: LIGO Laboratory operates two detector sites 1,800 miles apart: one near Hanford in eastern Washington, and another near Livingston, Louisiana. This photo shows the Hanford detector. Courtesy of LIGO Caltech.


Measuring the Quantum Jitter

Some physicists are determined to find out if we are mere holograms. Perhaps not quite like the dystopian but romanticized version fictionalized in The Matrix, but still a fascinating idea nonetheless. Armed with a very precise measuring tool, known as a Holometer or more precisely twin correlated Michelson holographic interferometers, researchers aim to find the scale at which the universe becomes jittery. In turn this will give a better picture of the fundamental units of space-time, well beyond the the elementary particles themselves, and somewhat closer to the Planck Length.

From the New Scientist:

The search for the fundamental units of space and time has officially begun. Physicists at the Fermi National Accelerator Laboratory near Chicago, Illinois, announced this week that the Holometer, a device designed to test whether we live in a giant hologram, has started taking data.

The experiment is testing the idea that the universe is actually made up of tiny “bits”, in a similar way to how a newspaper photo is actually made up of dots. These fundamental units of space and time would be unbelievably tiny: a hundred billion billion times smaller than a proton. And like the well-knownquantum behaviour of matter and energy, these bits of space-time would behave more like waves than particles.

“The theory is that space is made of waves instead of points, that everything is a little jittery, and never sits still,” says Craig Hogan at the University of Chicago, who dreamed up the experiment.

The Holometer is designed to measure this “jitter”. The surprisingly simple device is operated from a shed in a field near Chicago, and consists of two powerful laser beams that are directed through tubes 40 metres long. The lasers precisely measure the positions of mirrors along their paths at two points in time.

If space-time is smooth and shows no quantum behaviour, then the mirrors should remain perfectly still. But if both lasers measure an identical, small difference in the mirrors’ position over time, that could mean the mirrors are being jiggled about by fluctuations in the fabric of space itself.

 So what of the idea that the universe is a hologram? This stems from the notion that information cannot be destroyed, so for example the 2D event horizon of a black hole “records” everything that falls into it. If this is the case, then the boundary of the universe could also form a 2D representation of everything contained within the universe, like a hologram storing a 3D image in 2D .

Hogan cautions that the idea that the universe is a hologram is somewhat misleading because it suggests that our experience is some kind of illusion, a projection like a television screen. If the Holometer finds a fundamental unit of space, it won’t mean that our 3D world doesn’t exist. Rather it will change the way we understand its basic makeup. And so far, the machine appears to be working.

In a presentation given in Chicago on Monday at the International Conference on Particle Physics and Cosmology, Hogan said that the initial results show the Holometer is capable of measuring quantum fluctuations in space-time, if they are there.

“This was kind of an amazing moment,” says Hogan. “It’s just noise right now – we don’t know whether it’s space-time noise – but the machine is operating at that specification.”

Hogan expects that the Holometer will have gathered enough data to put together an answer to the quantum question within a year. If the space-time jitter is there, Hogan says it could underpin entirely new explanations for why the expansion of our universe is accelerating, something traditionally attributed to the little understood phenomenon of dark energy.

Read the entire article here.