Scientific Paper

I wrote this paper about inflation theory for Astronomy 317: Our Universe, the Final Frontier (Galaxies and Cosmology). I researched a cosmological model and presented the evidence that makes it a viable school of thought in terms of the creation of our universe. With this paper, I show that I can write scientifically for the scientific community, which is stylistically much different than writing for the English fields.

Eternal Inflation Theory, the Multiverse, and Cosmology

Introduction

Inflation and inflationary cosmology have become a big part of the popular

creation belief since their inception almost 30 years ago (Gribben). When inflation

showed up in the late 70s to early 80s, it was to help explain missing parts of the

existing Big Bang Theory. This model was basic and told of an infinitesimally small

period of expansion, where the entire universe came into being in a fraction of a second.

This explained many observable aspects of the universe, which solidified it as a viable

theory (Shackelford), but it went on to become a separate theory of its own. Inflationary cosmology also has to do with what is commonly called a “multiverse” (Shackelford).

Around the mid-80s, eternal chaotic inflation emerged, which hypothesized that this

universe is just one of an infinite number of universes just like the known universe. Or

perhaps, these universes are so dissimilar to the known universe that life cannot exist or they operate under different laws of physics. Similar or dissimilar universes become a random roll of the dice; “chaotic” inflation means that universes can develop randomly

(Shackelford). The theory of inflation is backed by strong evidence that will be discussed later and has been integrated with the standard theory of cosmology. However, inflationary cosmology can also go further by including the idea of the multiverse and eternal inflation. By examining the evidence of inflation and comparing it to the Big

Bang theory, one can find that inflationary cosmology is a viable school of thought in the realm of cosmology.

History

Inflationary cosmology was first proposed in 1979 by Starobinsky (Shackelford) and again in 1981 by Alan Guth (Gribben) and underwent major revision in 1983 by 2

Andrei Linde to yield what is now known as “eternal chaotic inflation.” So far, the

eternal chaotic inflation theory has not been majorly revised since then, even though

there have been minor adjustments made.

Evidence

The evidence for inflation theory as a whole is about as strong as the evidence for

why inflation theory works. Alan Guth, creator of the original 1981 model proposes six main cosmological “problems” that inflation solves: the size of the universe, the Hubble

expansion, homogeneity and isotropy, the flatness of the universe, absence of magnetic

monopoles, and anisotropy of the cosmic background radiation. The universe is

incredibly big, containing about 1090 particles. “The exponential expansion of inflation reduces the problem of explaining 1090 particles to the problem of explaining 60 or 70 e-

foldings of inflation” (Guth). This exponential growth can account for how the universe

got so large but can also point to the fact that the known universe is a small fraction of

the entire universe, here meaning the entire scope of spacetime with its infinite pocket

universes.

The standard model uses the Hubble expansion as an initial condition, but inflation theory can postulate how this began (Guth). The Hubble expansion wants a

repulsive gravity that inflation can provide; the inflation theory puts the universe in

motion in a way where particles move with a velocity proportional to their separation.

Inflation theory can also account for the homogeneity and isotropy of the universe.

Moments after the big bang, the universe was uniform on microscopic scales; when it

expanded faster than the speed of light, that uniformity went with it (Guth).

Inflation theory solves the flatness problem of the universe by looking at the

density of the universe. Observations today have put the total mass density (Ωtot) very 3

close to 1. If Ωtot was equal to 1 exactly, it would remain that way forever, if it differed,

that discrepancy would just grow with time. Inflationary cosmology explains this current

flatness of the universe by having Ωtot grow towards 1 instead of away (Guth). In this

model, Ωtot can start at any number and get closer to 1 as time goes on no matter what.

Inflation also eliminates magnetic monopoles completely from the known universe,

even though they could still exist as particles in theory. If inflation takes place after

monopole production, the density of monopoles would be negligible (Guth). Monopoles could then still exist, but would not be able to be found in the universe because they would be so few and far between. Finally, the simplest inflationary model with a large cosmological constant fits observed data of the cosmic radiation background seen today

(Guth).

The above is all evidence for inflation as it is a part of the existing big bang theory. The solved cosmological problems are what caused inflation to find a home among astronomers’ deductions about the creation of the universe today. There is a second part to inflation, however, that goes far enough into the realm of the new and strange to make inflation a theory on its own. Eternal inflation raises a hundred new questions for every one it answers, but there is some evidence that makes eternal inflation a viable cosmological theory to this day. According to Andrei Linde, the universe spawned from a singularity that was a part of another universe or the false vacuum and it will collapse back to a singularity in the future (Shackelford). All it needed was to have the correct potential energy, measured in terms of a scalar field.

This is best thought of as a U-shaped structure, with a ball rolling up and down the ramp. When the ball is at the top of the U, it contains potential energy. As it falls down that U, it reaches equilibrium and releases energy in the form of elementary particles, to 4

create the universe as it is seen now (Shackelford). Guth elaborates, saying that the false

vacuum spawns universes as it decays and then expands back to its original size

immediately, creating a fractal universe in a process that could continue literally forever.

This multiverse system is described as “the universe as a whole is populated by pocket

universes” (Guth).

This inflation structure was validated by the “small variations in the intensity of

the cosmic background radiation,” (Shackelford) which it predicted. It was validated by

the COBE satellite in 1990 and WMAP in 2003. WMAP also verified that the universe

was not flat (Shackelford), something that inflation predicted/solved in its theory.

Inflation theory is the only solid theory standing so far that allows for a homogenous

universe with “ripples in background radiation” (Shackelford).

Comparison to Big Bang

Because inflation is now considered a part of the big bang (or more rightfully, the

big bang is a component of the inflation theory) the differences between the two can be described as inflation explaining what the big bang can’t. These were mentioned in the

previous section as the six main cosmological “problems” that inflation theory solves

and they are important because the standard big bang theory or the classical FRW

cosmological model cannot explain them without the help of inflation. For this very

reason, inflation was added as a part of the popular big bang theory that is surmised

today by many astronomers and laymen alike.

The classical FRW model postulated that the 1090 particles that make up the

universe today were there at the start, instead of growing at geometrical quantities of 2

or π (pi) (Guth), since that slow rate could not keep up with the large amount of

particles existing today. Inflation solves that by giving the rate exponential growth, 5 which accounts for the large universe today, but also claims that this universe is infinitesimally small in the grander scheme of things.

The standard cosmological model could also not explain the homogeneity of the universe. If the universe was growing at the same rate throughout all of history, how could both “ends” look identical (Gribben)? Even the intensity of the radiation is the same all over, after correcting for the Earth’s motion to the precision of 1 in 100,000

(Guth). The FRW model does not explain this, as its calculations would make this uniformity the result of signals being able to travel at 100 times the speed of light, which is not possible in the physics construct of this universe (Guth). Inflation theory, however, explains by having the entire universe expand faster than the speed of light, uniformity included.

The flatness problem is the last large question inflation theory answers for the big bang theory. The FRW model simply has no explanation for the flatness of the universe.

According to its calculations, Ωtot should grow like:

Ωtot 1 ∝ t (during the radiation-dominated era)

Ωtot 1 ∝∶ (during the matter-dominated era) (Guth)

In classical cosmology, this is an initial condition, even though modern calculations of

Ωtot show that it is very nearly 1, making its growth impossible. Comparatively, inflation theory suggests that:

Ωtot 1 ∝ (Guth)

This equation shows that Ωtot actually will approach 1 no matter what number it starts out at, making the calculation of Ωtot today accurate and lending more stability to inflation as a whole. 6

In comparison with the big bang theory, inflation explains more, especially with hypothesizing the origin or expiration of the universe. Eternal inflation and the idea of the multiverse means that there needs not be a beginning or an end to the universe (the universe in which Earth resides, however, will eventually collapse in a Big Crunch).

Conclusion

Inflationary cosmology still has a few holes in it, but it is a solid theory when it comes to explaining the universe. It gives an answer to what comes before the big bang and inflation itself solves many problems that the standard theory alone could not without help. As sky surveys and cosmic background radiation-mapping get more advanced, they could lead to new experiments that could validate the theory as a whole, create new versions of the theory, or expand on existing versions. According to Andrei

Linde, it may even become possible someday to create a universe in a laboratory, even if that possibility is far, far away. Inflationary cosmology holds many answers, but it is not closed to experimentation or revision. Astronomers may observe new evidence to strengthen or weaken the theory, but some aspects of it, such as the idea of the multiverse, may never be testable, and therefore never known.

Works Cited

Gribben, John. “Inflation for Beginners.” Cosmology for Beginners. N.d. Web. 21 April

2014.

Guth, Alan H. “Eternal inflation and its implications.” J. Phys. A. 2007. Web. 15 April

2014.

Shackelford, Scott. “Worlds Without End.” Standford Magazine. Stanford University

Alumni Website, 2007. Web. 15 April 2014.