A Singular Place... Stretching the Fabric of Space

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Photo credit: WGBH Boston

"When Einstein developed relativity theory, it took him about ten years to work out the math using a daunting form of mathematics called tensor calculus. He was only able to approximate the solutions to his own equations and the math still perplexes even the best scientific brains. However, the challenge did nothing to deter one of Einstein's contemporary astronomers- a theoretical physicist named Karl Schwarzschild. Schwarzschild was a practical individual by nature. He pioneered new methods of studying spectra, for example. But he excelled in his abilities to deal with theoretical concepts and when Einstein's articles on general relativity were published in 1915, Schwarzschild was one of the first to recognize their importance.
Schwarzschild was also a German patriot, so he set aside his astronomical studies when World War 1 erupted and enlisted in the army. By the time he had read Einstein's papers, he had already seen action in Belgium, France and on the Russian front. Nonetheless, he was attracted to the essentialness of general relativity and began to seek exact answers for its equations. Two months after contracting a life threatening disease and being sent home to recuperate, Schwarzschild was finally able to concentrate on completing his calculations. Shortly before his death in 1916, Schwarzschild completed his work and it was published later the same year. Titled On the Field of Gravity of a Point Mass in the Theory of Einstein, it became one of the pillars of modern relativistic studies and in it Schwarzschild presented his solutions to Einstein's unfinished equations.
Significantly, it provided support for a, then, seemingly implausible situation about the effects of severely compressed matter on gravity and energy.
When Einstein wrote his general theory of relativity, he found a new way to describe gravity. It was not a force, as Sir Isaac Newton had proposed, but a consequence of a distortion in space and time, conceived together in his theory as 'space-time'. According to Einstein, matter and energy exist on a background of space and time. There are three spatial dimensions (backwards-forwards, left-right and up-down) and one time dimension (which flows at one second per second). Objects distort the fabric of space-time based on their mass- more massive objects have a greater effect.
Just as a bowling ball placed on a trampoline stretches the fabric and causes it to dimple or sag, so planets and stars warp space-time - a phenomenon known as the 'geodetic effect'. A marble rolling across the trampoline will be inexorably drawn towards the bowling ball. Thus the planets orbiting the Sun are not being pulled by the Sun; they are following the curved space-time deformation caused by the Sun. The reason the planets never fall into the Sun is due to the speed at which they are traveling. The astrophysicist, John Archibald Wheeler, who coined the name "Black Hole", said it succinctly: "matter tells Space-Time how to curve, and Space-Time tells matter how to move."
Schwarzschild realized the escape velocity from the surface of an object depends on both its mass and radius. For example, the escape velocity of the Earth is about 11.2 kilometers per second- this is the speed a rocket must attain before it can depart the Earth on a journey to the Moon or more distant planets. The Moon's escape velocity, however, is only 2.4 kilometers per second because the Moon is one fourth the size of our planet and possesses only slightly more than 1% of its mass. But, if nature can make the radius of a given mass small enough, the escape velocity will increase until it reaches the speed of light, or 300,000 kilometres (186,000 miles) per second. At that point, neither matter nor radiation can escape from the object's surface. Additionally, atomic or subatomic forces become incapable of holding the object up against its own weight. Therefore, the object collapses into an infinitesimal point- the original object disappears from view and only its gravity remains to mark its presence. As a result, it creates a bottomless pit in the fabric of space-time.
Scientists now refer to an object with zero-volume but all of its mass as a singularity. Schwarzschild also explained that a singularity was surrounded by a spherical gravitational boundary that forever trapped anything that ventured within. This boundary was called the event horizon. He presented a formula that enabled the size of an event horizon to be calculated. This is now known as the Schwarzschild radius and it marks the edge of a bottomless pit in space-time. Venture beyond the brink and you will never return.
The formula for the Schwarzschild radius is very straightforward: 3 times M (where "M" is the mass of the sun and the result is expressed in kilometers). For example, if the Sun were shrunk to a singularity, it's event horizon would occur at three kilometers above its surface. Interestingly, it would not disturb the orbit of our planet and we would not suddenly be sucked into oblivion! Similarly, the Schwarzschild radius of the Earth is a third of an inch: if the Earth were to be similarly compressed, the sphere of its event horizon would be about the size of a marble!
However, scientists did not grasp its significance in the role of stellar evolution for about fifty years and have only recently realized its dramatic impact on the development of the Universe itself!
Despite the radical predictions contained in Schwarzschild's papers, the scientific community regarded it as a curiosity rather than outrageous. The idea of a singularity troubled many scientists, including Einstein, because it flew in the face of their experience- after all, the world is finite and everything can be weighed and measured.
Leading thinkers of that period could not imagine conditions that would create a singularity but now we know they are common throughout the Universe. Where? In the fates of massive stars and at the center of most, if not all, galaxies!
Like discovering a neighborhood house assumed to be vacant is actually inhabited, over the past decade researchers realized that most galaxies have at least one black hole in residence in their central regions. But these black holes aren't the stellar variety with three to ten times the mass of our Sun. Their size swamps the imagination- they have millions, sometimes billions, of solar masses. Even our home galaxy, the Milky Way, has a four million solar mass black hole located at its center, about 27,000 light years from Earth. Galactically speaking, that places it in our own backyard! Well, there goes the neighborhood!
We also now know that supermassive black holes are inexorably linked to the galaxies that encircle them.
For example, the size of a supermassive black hole appears to have a direct correlation to the galaxy where it exists. Almost a decade ago, researchers calculated that the mass of a supermassive black hole appeared to have a constant relation to the mass of the central part of its galaxy, known as its bulge (think of the yolk in a fried egg). This 1 to 700 relationship supports the notion that the evolution and structure of a galaxy is closely tied to the scale of its black hole.
Other studies found another strong correlation. This one was between the mass of a supermassive black hole and the orbital speed of stars in the outer regions of their galaxy where the direct gravitational influence of the supermassive black hole should be weak: the larger the black hole, the faster the outer stars travel.
Thus it's now believed that black holes are not only common throughout the Cosmos but they play a fundamental role in the formation and evolution of the Universe we inhabit today.
In fact, we would not be here without them.
Although black holes started as a mathematical curiosity that was tolerated by the established scientific community of the early twentieth century, over the decades since Einstein suggested and Schwarzschild revealed their nature, science now sees them as indispensable forces of creation and the sculptors of mighty galaxies.
But, this new understanding compels some to indulge in a bit of speculation that's evocative, intriguing and somewhat disquieting. Could it be possible that the Big Bang was simply the consequence of some universal black hole that accreted all the matter of a previous Universe, imploded then exploded resulting in the Cosmos where humanmankind exists?
For some, it's not only possible but most likely probable.
For example, imagine crossing the event horizon of a black hole. Like plungling in a basket over Niagara, once it's crossed there's no hope of return- you will fall into the singularity and there is nothing that can prevent it. At the same time, you will never receive information from anything that may have preceded and is located closer to the singularity than your current position because no information can escape from within. You can only know about where you are and that which is behind you. Isn't this very similar to the way time functions in our Universe? While we move forward into tomorrow, there is no way for us to know anything about it beforehand. We only have knowledge about the present and all our yesterdays.
So, what's it like to journey past a black hole's event horizon? Some would respond, "Simply look around you."
These ponderings have the earmarks of metaphysical philosophy. Most likely, they can and never will be provisionally confirmed or completely dismissed. Yet, they stir our blood and awaken our yearning to pursue the most fundamental questions of all: where did the Universe, and therefore we ourselves, come from and what waits just over the waterfall's edge."