Space suspense nears end: All you need to know about gravity waves

The first direct detection of gravitational waves, ripples of radiating energy in space-time produced by collision between two black holes, is expected to be announced by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) on Thursday.

world Updated: Feb 11, 2016 22:09 IST
HT Correspondent
HT Correspondent
Hindustan Times
gravitional waves,Einstein,universe
A scientist working at the Laser Interferometer Gravitational Wave Observatory (LIGO) in Louisiana, US.(AFP )

A century ago, Albert Einstein had hypothesized the existence of gravitational waves, small ripples in space and time that dash across the universe at the speed of light.

On Thursday, at a news conference called by the US National Science Foundation, researchers are likely to announce, at long last, direct observations of the elusive waves.

Such a discovery would represent a scientific landmark, opening the door to an entirely new way to observe the cosmos and unlock secrets about the early universe and mysterious objects like black holes and neutron stars.

Scientists from the California Institute of Technology, the Massachusetts Institute of Technology and the LIGO Scientific Collaboration are set to make what they bill as a “status report” on the quest to detect gravitational waves. It is widely expected they will announce they have achieved their goal.

What are gravitational waves

Gravitational waves are ripples in space-time, the very fabric of the Universe.

The game-changing theory states that mass warps space and time, much like placing a bowling ball on a trampoline. Other objects on the surface will “fall” towards the centre -- a metaphor for gravity in which the trampoline is space-time.

Gravitational waves do not interact with matter and travel through the Universe completely unimpeded.

The strongest waves are caused by the most cataclysmic processes in the Universe -- two black holes colliding, massive stars exploding, or the very birth of the Universe some 13.8 billion years ago.

How are they created

The strongest waves are caused by the most cataclysmic processes in the Universe -- two black holes colliding, massive stars exploding, or the very birth of the Universe some 13.8 billion years ago.

The signal that LIGO is expected to announce on Thursday is believed to be produced by two merging black holes .

Why is their detection of interest

Finding proof of gravitational waves will end the search for a key prediction in Albert Einstein’s theory of relativity, which changed the way that humanity perceived key concepts like space and time.

If gravitational waves become detectable, this would open up exciting new avenues in astronomy -- allowing measurements of faraway stars, galaxies and black holes based on the waves they make.

So-called primordial gravitational waves, the hardest kind to detect, would boost another leading theory of cosmology, that of “inflation” or exponential expansion of the infant Universe.

Primordial waves are theorised to still be resonating throughout the Universe today, though feebly.

If they are found, they would tell us about the energy scale at which inflation ocurred, shedding light on the Big Bang itself.

Why are they so hard to find

Einstein himself doubted gravitational waves would ever be detected given how tiny they are.

Ripples emitted by a pair of orbiting black holes, for example, would stretch a one-million-kilometre (621,000-mile) ruler on Earth by less than the size of an atom.

Waves coming from tens of millions of lightyears away would stretch and squeeze a four-kilometre light beam such as the ones used at the Advanced Laser Interferometer Gravitational Wave Observatory (LIGO), by about the width of a proton.

How are they detected

Gravitational waves passing through an object distort its shape, stretching and squeezing it in the direction the wave is travelling, leaving a telltale, though miniscule, effect.

Detectors such as LIGO and its sister detector Virgo in Italy, are designed to pick up such distortions.

At LIGO, scientists split laser light into two perpendicular beams that travel over several kilometres to be reflected by mirrors back to the point where they started. Any difference in their length would point to the influence of gravitational waves.

(Sources: European Space Agency, Institute of Physics, LIGO, Nature and AFP)

First Published: Feb 11, 2016 16:29 IST