The Universe’s Weird Rapid Expansion

** Synopsis: Without cosmic inflation, models explaining the early universe require “exotic physics,” like a speed of sound faster than the speed of light, UB researchers say. **

The widely-accepted theory of cosmic inflation states that our universe expanded rapidly in the moments after its birth, resulting in the immense expanse we see today.

Cosmic inflation explains why the universe is billions of years old, as well as why the universe is nearly flat. The theory’s conclusions about how the universe should look match observations by NASA’s Wilkinson Microwave Anisotropy Probe (WMAP).

But is inflation the only model that can explain the beginnings of the universe? That’s the question that University at Buffalo physicists Ghazal Geshnizjani, Will Kinney and Azadeh Moradinezhad Dizgah set out to answer with their study, “General Conditions for Scale-Invariant Perturbations in an Expanding Universe.”

The research, which appeared November in the online Journal of Cosmology and Astroparticle Physics, found that while inflation isn’t the only viable model of the early universe, other possibilities would require strange physics — such as a speed of sound faster than the speed of light.

The UB team found that only three kinds of early universe theories can explain the distribution of matter in today’s universe, assuming that the standard theory of gravity is correct and that the universe was expanding in early times (both widely accepted suppositions).

According to the physicists’ calculations, viable early universe theories must incorporate either an accelerated cosmic expansion (inflation); a speed of sound faster than the speed of light; or energies so high that scientists would need to invoke a theory of quantum gravity such as string theory, which predicts the existence of extra dimensions of space-time.

“The takeaway result here is that this idea of inflation turns out to be the only way to do it within the context of standard physics,” said Kinney, an associate professor of physics who credits UB research scientist Geshnizjani with formulating the idea for the study. “I think in many ways it puts the idea of inflation on a much stronger footing, because the available alternatives have problems, or weirdnesses, with them.

“It may well be that you can come up with a speed of sound faster than the speed of light, but I think people, as a general rule, would be more comfortable with something that doesn’t involve super-luminal propagation,” Kinney continued. “Inflation doesn’t require any exotic physics. It’s just standard particle physics.”

Cosmic inflation accounts for the distribution of the matter in the universe by incorporating quantum field theory, which states that under “normal” circumstances, particles of matter and something called antimatter can pop into existence suddenly — before meeting and annihilating each other almost instantly.

According to cosmic inflation, materializing pairs of matter and antimatter particles flew apart so quickly in the rapidly expanding early universe that they did not have time to recombine. The same principle applied to gravitons and antigravitons, which form gravity waves.

These particles became the basis of all structure in the universe today, with tiny fluctuations in the matter in the universe collapsing to form stars, planets and galaxies. The concept relies on widely studied ideas to explain how the universe began and evolved.

Still, however bizarre alternatives to inflation might seem, Kinney acknowledges that other models are possible. His own work has included exploring other theories, including ones that rely on superluminal sound speeds.

One colleague in UB’s physics department, Assistant Professor Dejan Stojkovic, recently published a paper examining the possibility that the very early universe may have had just one spatial dimension before expanding to include two, and then three and possibly four (this model would fall under the category of theories invoking quantum gravity). Source: The University at Buffalo.

 

 

Alexander Friedman, The Inventor of the Big Bang

Physicists today are able to tell us that the universe started with a big bang. But for centuries, the origin of the universe was a mystery. It took the work of a young mathematician named Alexander Friedman to show us how it all started.

Alexander Friedman was born in St. Petersburg Russia in 1888, when the country was under the rule of Tsar Alexander III. Both of his parents were performers, his father a ballet dancerand his mother a pianist.

At the age of 8, young Alexander began going to school at the St. Petersburg Gymnasium, graduating second in his class behind his friend and future colleague Yakov Tamarkin. The two would remain close friends and pursue their mathematical education together at the University of St. Petersburg.

In 1913 Alexander completed his examinations for a Master’s Degree and was appointed to a position in the Aerological Observatory in Pavlovsk, a suburb of St Petersburg. The next year Europe exploded into the First World War, and Alexander suspended his work to volunteer for the Russian Airforce.

Alexander Friedman
Russia pulled out of the war a few years later only to be plunged into its own Civil War, with the Communist Bolshevik Party fighting for supremacy of the country. In the confusion and violence of the war, Friedman’s work at the Central Aeronautical Station was stopped.

He was lucky enough to survive the war without getting conscripted or killed, and once the Communists won Alexander was about ready to submit his Master’s Thesis on the hydromechanics of a compressible fluid.

With a degree firmly under his belt, Friedman moved to the city of Petrograd in 1922 where he took an interest in the works of Einstein. The theory of general relativity had been published in 1915, but had not reached Russia because of the First World War and the Civil War.

Discovery of the Big Bang

General relativity is a modern theory on the inner workings of gravity. Before Einstein, Isaac Newton discovered that a force of  attraction exists between two objects based on their masses and the distance between them. His universal law of gravitation was a short equation that could describe the movement of everything from the planets orbiting the Sun to an apple falling from a tree. Einstein’s theory in 1915 explained the how to Newton’s what.

An object with mass actually bends the fabric of space time causing trajectories to curve towards it. The Moon orbiting the Earth is actually following a straight path in an area of curved space. The exact relationship between mass and space and time is explained in a series of 10 differential equations that we call the Einstein field equations.

Friedman started with the assumption that the universe is homogenous and isotropic; meaning that it is more or less made of the same stuff and spread out evenly in every direction. With this view the universe can be thought of as one giant fluid, which Friedman just happened to have a master’s degree in.

He manipulated Einstein’s field equations to show how the universe as a whole would act under this new theory of general relativity, but realized that he was missing some very important information. He had no idea what the density of matter or the force of pressure was throughout the universe.

Possible space curvatures

Without this vital information, Friedman was forced to admit that there were three possible ways for the universe to pan out. The curvature of the universe could be flat, it could be a sphere with a positive curvature, or it could be a hyperbolic space with a negative curvature. With respect to time this curvature could either be an increasing or a periodic function, meaning that the possibility of an expanding universe fit in with Einstein’s theories. He was the first person to create a mathematical model for an expanding universe, which would go on to be the basis for the Big Bang theory.

Friedman’s Legacy

When Friedman made this amazing discovery he published an article called On the Curvature of Space in the journal Zeitschrift fur Physik in June 1922. Three months later Einstein wrote in to the journal to say that Friedman’s work seemed “suspicious” and that his solution did not fit in with his own field equations, but he neglected to explain why. While Einstein was without doubt one of the most important scientists of all time, he was still wrong about a lot of things.

A hurt Friedman responded to Einstein to beg for some kind of explanation of an error in his equation, but the letter never got to Einstein because of a trip to Japan. It would take a year before a friend of Friedman’s named Krutkov let Einstein know about Alexander’s letter, and upon further study Einstein was able to admit his error. He immediately wrote once again to Zeitschrift fur Physik saying that Friedman’s results were in fact “correct and shed new light”.

A vindicated Friedman set out on a triumphant tour of Europe. He left Petrograd to visit Germany, Norway and the Netherlands to give lectures and attent the First International Congress for Applied Mathematics. In August 1925 after a record-breaking balloon ascent to 7,400 meters for a meteorological study Alexander started feeling sick.

He was diagnosed with typhoid and brought to a hospital where he died two weeks later at the age of 37. Cut down at the very beginning of his career, the death of Alexander Friedman dealt a huge blow to the field of cosmology. The contributions that he did make before his death remain a cornerstone for our understanding of the universe. Source: Bright Hub

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