String theory is intended to unify all four fundamental forces into one all encompassing theory (specifically by unifying gravity with the electronuclear force). It also unites matter with these forces “in a mathematically complete system.” Because of this, “string theory is the first candidate for the theory of everything.” One of the basic premises of string theory is that all matter and energy is made up of incredibly tiny, one-dimensional, vibrating “strings” of about 1*10^-35 meters. Thus, electrons and quarks are one-dimensional, not zero-dimensional. The way these strings vibrate determines its properties. In string theory, strings usually form closed loops. However, stings become one-dimensional lines upon encountering special surfaces called branes (which are also made of strings) that can be as large as a universe. The endpoints of the lines are able to slide around the brane but not able to break off of it. It is even possible that our universe is completely contained on a brane and that there are other universes in “the bulk.” This could explain why gravity is so much weaker than electromagnetism; it only appears to be weaker because it is not as confined. This also could explain the big bang as a collision of parallel universes.
Gravity is less confined than electromagnetism because gravitons are made of closed strings, not open ones that are bound to the brane of our universe (such as matter and light).
String theory was born in 1968 when Gabriele Veneziano of used Euler’s equations to describe the strong nuclear force. Eventually, Leonard Susskind discovered that Euler’s equations were also describing tiny, vibrating, one-dimensional strings. Early string theory required a massless particle and tachyons (“hypothetical subatomic particle[s] whose velocity is always greater than that of light”). John Schwarz discovered that the massless particle that string theory describes is a graviton.
String theory can be considered to be a theory of gravity and involves general relativity. In the 1980s, Michael Green and John Schwarz discovered that string theory contains no mathematical anomalies.
One important component of string theory is the holographic principle. The holographic principle “states that the description of the oscillations of the surface of a black hole must also describe the space-time around it.”
One of the main reasons for string theory’s conception was the un-ignorable conflicts between quantum physics and classical physics. NASA can send a rocket to the moon using little more than Newtonian physics to guide them but these laws hold almost no sway in the quantum world. On the other hand, the seemingly nonsensical rules of the quantum world have stood up to the criticism of many great scientists, even Albert Einstein. The laws of quantum physics are random and riddled with uncertainty while classical physics is ordered and predictable. String theory attempts to bridge the gap between the two conflicting theories.
One of the main “problems” with string theory is that it involves there being more dimensions of space-time than just four (anywhere from 10 to 26). These extra dimensions twist and “curl back on each other.” One way to account for these “extra” dimensions is that they are “hidden” or “rolled up” and are smaller than a plank length. A common analogy that is used that of an ant and a tight rope; to a human, there is only one dimension (forward/backward) but to an ant, there is an extra dimension (traveling around the wire). One of the reasons as to why these extra dimensions are necessary is to increase the number of ways that strings can vibrate and thus, increase the number of particles that strings can form.
Bosonic strings can vibrate in a “flat but unstable 26-dimensional space time” without fermions.
Strings interact by splitting and combining “in a smooth way.”
String theory is difficult to test. As of now, there are no microscopes that are capable of observing strings. Some even say that in order to properly test string theory, we would have to recreate the big bang.
5 string theories have emerged; Type I, Type IIA, Type IIB, SO(32), and E8 x E8. They each involve different mathematical details. In 1995, Edward Witten announced that the five string theories are really just one theory being looked at in multiple ways. The five string theories are now collectively referred to as M-theory.

As string theory is supposed to unite everything, it ties many of the topics we learned in class (such as gravity, electromagnetism, the standard model, modern physics, and relativity) together. It is also related to the equation E=mc² and the conservation of matter and energy. In addition, supersymmetry is a “central prediction of string theory.”

There are currently no applications for string theory. As theoretical physicist Michio Kaku states, string theory will not result in “better color TV … better sliced bread … [or] better microwave reception.” However, there are a large number of possible future applications. Kaku believes that a unified field theory could be used to make a “life boat” for intelligent life in order to travel to another universe when our universe dies. In addition, if string theory’s descriptions of gravity and parallel universes are correct, than, according to theoretical physicist and string theorists Brian Greene, it may be possible to use gravity waves to communicate with intelligent life forms (if such life forms exist) in parallel universes.

Currently, experiments are being done at Fermilab (and possibly at CERN) in an attempt to find gravitons and witness them vanish into another universe. The future of string theory involves solving the string theory equations and compare string theory “with the subatomic particles we see in nature.” Another possible path for the future of string theory is to find “fingerprints” of strings from beginning of universe that expanded with the rest of the universe after the big bang.



Works cited: - Main source of text - Source of graphics
The Elegant Universe by Brian Greene

Sonia Bansal - How big are the extra dimensions (ant picture)? The extra dimensions are smaller than a plank length. A plank length is about 16.163×10^−36 meters.

Robert Lopez - If string theory suggests other universes, and if gravitons would one day be discovered, how do you think one be able to travel between universes? The discovery of gravitons would not be enough to facilitate travel between universes. The possibility of travel between universes, as of now, is purely hypothetical (we have a much better chance of being able to communicate with other universes). All that is really "known" is that if travel between universes is even possible (are after all, the endpoints of strings of matter are bound to the brane that is our universe) it may involve the the use of a unified field theory to create another universe to use as a vehicle. Sorry if that doesn't answer your question.

Brandon Siegenfeld - If a two dimensional person went into a three dimensional world, what would happen, how would that work, and would the opposite work too going from a 3 to 2 dimensions? I do not understand what you mean by "a two dimensional person" and "a three dimensional world." All parts of our universe have the same number of dimensions. Hypothetically a two dimensional person in a three dimensional world would not realize that he/she/it was even in a three dimensional world and would not make use of the third dimension. Sorry if that doesn't answer your question.

Will Chan - How is the string theory significant to the average person? Currently, it isn't. Also, it is really too soon to tell how (and even if) string theory will be significant to the average person. However, is Michio Kaku is right about the end of the universe, his "life boat" will be very significant to the average person (as well as everybody else). In addition, the abillity to communicate with other universes may become significant to the average person.

Greg Sturm - How exactly does Michio Kaku think our own universe will theoretically end, or is he just referring to the "life boat" thing as a precaution for the unknown? Michio Kaku was a little vague but I believe he was referring to either a Big Freeze or a Heat death. A Big Freeze is "a scenario under which continued expansion results in a universe that is too cold." A Heat Death is "a related scenario ... which states that the universe goes to a state of maximum entropy in which everything is evenly distributed, and there are no gradients — which are needed to sustain information processing, one form of which is life."

James Song- How many dimensions does a normal person perceive on a normal day? On a normal day, a normal person perceives three dimensions of space and one of time.

Sohini Sheth - Isn't it true that scientists are beginning to doubt the effectiveness of the string theory as a theory for everything because it doesn't seem to encompass all the physical forces? No, I haven't read or heard anything about any of that. String theory does encompass all of the physical forces.

Douglas Chin - About the parallel M theory, what would happen if more than two membranes collided? No one really knows for sure what will happen; they're not even sure about what would happen if two branes collided.