What is String Theory?

science engineering

String Theory, sometimes called the Theory of Everything, is thought by some to be the unifying field theory Einstein sought before his death. String theory is the first mathematically sound theory that reconciles the world of the infinitesimally small, with the world we know at large. It unites Einstein’s Theory of Relativity with quantum physics and offers a potential explanation for the Big Bang.

Prior to string theory, subatomic particles were envisioned as tiny balls or points of energy. String theory works on the premise that the tiniest subatomic bits that make up the elements of atoms actually behave like vibrating strings. The strings of string theory are so small that physicist Brian Greene has analogized that if a single atom were enlarged to occupy the footprint of our solar system, a string would still be no larger than a tree.

Because these tiny vibrating strings are responsible for the properties of all matter, the cosmos has been likened to a cosmic symphony of superstrings. While poetically appealing, the strength of string theory is that it accounts for all four known forces in one elegant theory. These fundamental forces are gravity; the strong and weak nuclear forces; and electromagnetism.

One of the surprising elements of string theory is that it requires extra dimensions to be free of mathematical anomalies. Scientists added an extra six dimensions, initially, for a total of ten. The six dimensions were predicted to be contained in tiny curled up formations at every point within our three-dimensional space.

But there was a problem: string theorists came up with several theories that all seemed to be correct. Ultimately scientists found that adding an eleventh dimension mathematically explained all of the seemingly different string theories as different aspects of the same theory. The one theory to rule them all is known as M-theory.

The eleventh dimension of string theory predicts a new kind of string, stretched infinitely long to create what is termed a floating membrane, or brane. According to string theory, infinite branes exist that each supports a separate but parallel universe. In this wildly exotic neighborhood the “problematic” force of gravity was also explained.

While the Standard Model of physics had already united three of the known forces, gravity remained elusive. Part of the problem was that gravity was such a weak force relative to the others. String theory mathematically predicts that gravity is weak because it is only leaking here from a parallel universe. How is this possible?

String theorists explain that strings can be open or closed. Open-ended strings have one endpoint attached to the brane on which they reside, keeping matter contained within that brane. Our bodies are believed to be made from open-ended strings. This explains why we can’t reach into or interact with other dimensions. Close-ended strings, however, are like tiny rings, unattached to their brane, able to “leak” away from it; which brings us to gravity.

Gravity is thought to be transferred via massless, hypothetical particles called gravitons. If gravitons were made from close-ended strings, scientists theorized, gravity might be leaking off our brane. It sounded good but it didn’t work mathematically. However, the opposite hypothetical did work. Gravity appears, according to string theory, to be leaking to our brane from a parallel universe. Fantastically, this notion is mathematically sound.

Finally, string theory offers a possible explanation for the Big Bang. It had long bothered scientists that although they could plot the stages of the Big Bang backwards to the singularity, the initial cause for the event was without explanation. Now string theorists believe that two branes colliding could have caused the Big Bang event.

String theory’s biggest challenge is that much of it is not provable. Scientists can’t test other dimensions, study migrating gravitons, or peek between the curtains of floating branes to witness a Big Bang event. For this reason string theory has many detractors and critics. Some scientists believe that without the ability to prove the theory, it is not true science at all. Nevertheless, proponents of string theory seem confident that proof of various sorts will come with technological progress and time. As many string theorists have quipped, "Something this elegant can’t be wrong!"

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3
Very well written article-one of the best summaries of string and M theory I have come across. Where does dark matter fit into this?
- anon43068
2
Actually, you see, your reservations towards the Big Bang Theory and its implications go not without explanation.

First of all, the microwave background radiation, regardless of stellar distribution, appears strikingly uniform-containing deviations in temperature no more than one part in a hundred thousand. Were you to be correct in asserting starlight be a determining factor, we would observe considerably more dramatic temperature differences distinguishing intergalactic voids from their matter-filled counterparts.

While not as exacting as my first description, this point too can be explained clearly. The Standard Model, arguably the most "correct" theory ever to be formulated, contains a staggering 19 adjustable parameters. Despite this rather embarrassing ambiguity, the theory remains so precise in its description of nature that scientists have had little qualms over accepting its predictions. So you see, requiring more than an arbitrary, aesthetically pleasing number of adjustable parameters is not necessarily a demerit for any theory.

The answer to your third assertion is actually in the form of an appendage concept to the original Big Bang Theory. Less than a fraction of a second after the initial singularity, there emerged an incredibly brief period of hyperinflation, during which the universe ballooned from the size of a single proton to a cosmic colossus one thousand times the size of our solar system.* This explains why the universe appears to be so much larger than a period of 10-20 billion years of constant expansion would allow.

As for the apparent brightness of various quasars as related to their respective redshifts, the incomprehensible distances at which we are viewing these objects would have an ultimately dampening effect on our observations, since their perceived variations in luminosity would be incalculably miniscule, causing them to appear at identical apparent brightnesses. Therefore, we need no longer necessitate that the actual luminosity of any quasar decrease with respect to time in order to compensate for the relatively slight variations in redshift relative to each other. Their huge distance from us (and comparatively negligible distances from each other) account for the perceived relationship.

The oldest globular cluster in the Milky Way Galaxy is measured to be approximately 10 billion years old (with a relatively narrow margin of error). The most accurate measurements yet, collected by NASAs WMAP satellite, of the current age of the universe stands at 13.7 billion years, well outside the possible deviation in age for our oldest globular clusters.

Your next point can actually be addressed from two angles. First, our universe is not necessarily finite in space, and, by all accounts, is only finite in our one temporal dimension, hence its age of 13.7 billion years. Secondly, in order to capture the uniformity of our universe, it must be observed on truly cosmological distances. The distances involved when observing the Local Group, spanning about 6 million light-years, are much too minute in order to appreciate the large-scale uniformities characteristic of the observable universe.**

This does not pose any inconsistency with the Big Bang Theory. It is able to describe the origin and evolution of our universe, meaning that it is consistent even with the presence of dark matter. Our own ignorance need not be invoked.

Quasars, contrary to popular belief, are not characteristic of the very earliest galaxies, since they had not yet accumulated sufficient gas and dust to sustain such an AGN (active galactic nucleus). Consequently, having existed prior to quasar formation, it is deducible that they would in fact retain higher redshifts.

Again, while not as exacting as my previous arguments, this too, can be explained. Put bluntly, you would be hard pressed to find a cosmologist susceptible to even a single flinch at this ratio. The cosmic microwave background radiation contains variations in temperature of one part in a hundred thousand-a significantly more impressive ratio, considering that it alone gave rise to the staggering density deviations we observe now! It seems to me that if a trifling amount such as this could have laid the foundation for such a magnificently diverse cosmos, then a difference of one part in a mere thousand or so would certainly be capable of having the even more consequential effect of creating an open universe.

*You would be correct, though, to pose the question of what in fact drove the phenomenon of inflation and what happened to shut it off. The Big Bang Theory does in fact say absolutely nothing about this.

**In cosmological jargon, this is referred to as The Horizon Problem.

- element92
1
hi, i was just wondering how does string theory prove the Compton effect and cosmic background radiation that is simultaneous with the Big Bang Theory...because there are many problems with the Big Bang theory as well

here are some:

he microwave "background" makes more sense as the limiting temperature of space heated by starlight than as the remnant of a fireball.

Element abundance predictions using the big bang require too many adjustable parameters to make them work.

The universe has too much large scale structure (interspersed "walls" and voids) to form in a time as short as 10-20 billion years.

The average luminosity of quasars must decrease with time in just the right way so that their mean apparent brightness is the same at all redshifts, which is exceedingly unlikely.

The ages of globular clusters appear older than the universe.

The local streaming motions of galaxies are too high for a finite universe that is supposed to be everywhere uniform.

Invisible dark matter of an unknown but non-baryonic nature must be the dominant ingredient of the entire universe.

The most distant galaxies in the Hubble Deep Field show insufficient evidence of evolution, with some of them apparently having higher redshifts (z = 6-7) than the faintest quasars.

If the open universe we see today is extrapolated back near the beginning, the ratio of the actual density of matter in the universe to the critical density must differ from unity by just a part in 1059. Any larger deviation would result in a universe already collapsed on itself or already dissipated.

- harvardgurl

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Last Modified: 12 October 2009

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