Gravitational Wave Signal

Gravitational waves from a double black hole merger about 1.3 billion light-years away from us were directly detected on September 14, 2015. This gigantic, distant, and ancient event caused our space-time to expand and contract by 1/100,000 of a nanometer due to the sub-atomic effects of passing gravitational waves. They were measured by the two Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors last year, while it recently made big headlines earlier this year celebrating 100 years of Albert Einstein's general relativity. This measurement provides a verification of the theory's correctness, more proof for the existence of black holes, and reveals a phenomenon which had never before been directly seen in nature, opening windows into new areas of astronomy and cosmology research.

""These amazing observations are the confirmation of a lot of theoretical work, including Einstein’s general theory of relativity, which predicts gravitational waves,” says physicist Stephen Hawking at the University of Cambridge, UK" (source).


A double black hole merger from long ago recently caused minute changes in our space-time (Image: LIGO).

General Relativity

Published in 1916, the general theory of relativity is often regarded as Albert Einstein's greatest achievement and one of the most remarkable scientific contributions of the 20th century. It is known for redefining gravity beyond the previous Newtonian interpretation and describing it as a geometric property of space-time. General relativity is viewed as an expansion of the special theory of relativity and it differs from the special case because it takes into account the motion due to gravitational fields and other accelerating reference frames, thought to be similar according to the equivalence principle. Along with quantum theory, general relativity is considered to be a central pillar of modern physics and is currently accepted as the leading theory for gravitation.


Earth's mass warps space-time and shapes the Moon's geodesic orbit (Image: NASA).

General relativity describes the attractive force of gravity as being the result of an acceleration produced when something interacts with curved space-time, usually there because of an object with a very large mass. The more mass an object has, the more it warps the space-time around it and the larger its gravitational field is. Any object with some mass or just energy is thought to have a gravitational influence as well but will always experience an attractive pull when it is close enough to another object with a sufficient amount of gravity. Even rays of light that approach a gravitational field will bend towards it in a phenomenon known as gravitational lensing. This effect was confirmed to exist when the light from stars behind the Sun was observed to travel around it during the total solar eclipse of 1919.

Other tests of general relativity include the observation of a gravitational redshift in visible light emerging from a gravitational field, which loses energy and increases its wavelength, shifting towards a redder color. When entering a gravitational field, it behaves in the opposite way by gaining a shorter wavelength and a bluer appearance. Gravitational redshift was first measured in the light emitted by white dwarf star Sirius B in 1925. When a very massive object rotates on its axis, it will also twist the space-time around it as it spins. This is known as frame-dragging and it too was confirmed to exist by observing the orbital shifts that emerged from satellites traveling around our planet. General relativity predicts the existence of gravitational waves, which are ripples in space-time that propagate at the speed of light and are caused by sudden changes in an object's gravitational field, but their direct detection is currently a subject of on-going research.

From the smallest interaction of an elementary particle to the behavior of the cosmos itself, Albert Einstein's ideas have altered the way we view our physical surroundings on many scales. While general relativity accurately describes the gravitational attraction between celestial objects, it is additionally useful for describing other processes such as the expansion or contraction of a universe. Exotic objects such as black holes, white holes, and wormholes are also predicted to exist according to the equations of general relativity. Einstein's dream was to find a theory of everything that could combine the fundamental interactions of nature, specifically gravity and electromagnetism, to show that they were all facets of the same unified force. The search for a theory of everything continues to this day with the goal of bringing together Einstein's laws of general relativity with those of the quantum world in order to develop a consistent theory for quantum gravity.

Universes and Black Holes

When I read articles about physics and astronomy, I can't help but get excited when a brand new theory catches my attention and completely changes the way I look at the world around me. A while ago, I stumbled upon such a theory developed by theoretical physicist Nikodem Poplawski, which instills in me great admiration towards modern cosmology research.


An artist's rendition of a universe containing a black hole (Image: Unattributed).

A black hole is a region of space from which light and matter cannot escape. It is twice as wide as its Schwarzschild radius and contains a singularity of infinite density and zero volume at its center. Here is an article from the National Geographic website that describes just how every black hole may contain another universe.

So, after reading this article, I was interested to know if anyone else was silently questioning their Earthly existence and what they thought about this. I wasn't about to get too excited before Discover Magazine was amusingly there to remind me just how our universe is not a black hole by clearing up the confusion.

"If anything, our universe bears a passing resemblance to a white hole" with a singularity in the past and no singularity in the future (source).

In this article, I learned that a solution to Albert Einstein's equation that describes the universe expanding from the Big Bang can be used to show how the time-reversal of a black hole is actually very similar. The author Sean Carroll is also careful to compare the extent of our observable universe (characterized as the Hubble length) with the Schwarzschild radius of a black hole in order to validate how the universe is spatially flat.