Scientific Theory Flowchart
Flowchart that shows how an idea moves from hypothesis to accepted theory,
with room for revision.
67
String Theory: A Theory of Everything?
Present day physicists are currently dealing with one question: How does gravity fit in with the other three forces? Namely, the electromagnetic, strong and weak forces (which are thought to be mediated by force carrying particles called bosons). As discussed in this post, the question has guided scientists towards the Theory of Everything (TOE).
One proposed TOE is String Theory. It was originally based on the works of Gabriele Veneziano in 1968. Veneziano was dealing with something very strange, things called Tachyons. Tachyons are supposed to move faster than the speed of light! Venziano’s theory is no longer accepted. There have been some step-ups in the theory since then.
String Theory says that every single fundamental particle is actually made of a tiny, one-dimensional, vibrating ‘string’. They exist on extremely small scales, much smaller than atoms (If string theory is a theory of quantum gravity, then strings will be about a millionth of a billionth of a billionth of a billionth of a centimeter)! The different frequencies, or modes of vibration, of these strings gives each string it’s own respective properties.
It gets more diverse in the string theory world. Strings can exist as either open or closed models. Think of open models like pieces of spaghetti:
and closed models like flexible hoops:
Open string models are said to account for matter while closed string models are said to account for hypothetical particles of gravity, gravitons. Strings are thought to bend space and time while they vibrate, creating gravity just like Einstein predicts.
In both of these diagrams, you can see that each string has it’s own frequency. Of course you have to remember that strings are down-right-strange. These are just simply metaphors.
In fact, strings are said to vibrate in more dimensions than the ones we are familiar with. These dimensions are difficult to detect since they are said to be very, very small. Only the strings are said to contain them. A good comparison to explain these hidden dimensions is to think of a rope. Imagine you are standing 20 ft. away from the rope. To you, it seems just like a 2-dimensional rope. It is not until you come very close to it that you realize it exists as a 3-dimensional cylinder.
There have been multiple versions of string theory that include different number of dimensions and types of strings. There is a table of string theories here. Current progress is taking place in unifying all the versions of string theory into one “superstring” theory- M Theory.
String Theory has many profound implications. A single post cannot fully provide all of them. Some scientists think that we are stuck in a 3 space dimensions+1 time dimensional “brane” and that other branes exist, maybe just a fraction of a centimeter away.
Carl Sagan claims that “Remarkable claims require remarkable proof”. To be completely honest, there is no proof of string theory available today, and may not ever be. This article covers a variety of tests being conducted.
Gravitation
What is Gravity? The stuff that keeps our feet glued to the earth, the stuff that hit Isaac Newton’s head with an apple, the stuff that keeps our Earth revolving around the sun?
Isaac Newton’s Universal Law of Gravitation states that “Every particle in the universe attracts every other particle with a force along a line joining them. The force is directly proportional to the product of their masses and inversely proportional to the square of the distance between them”. ‘
Gravity seems to be very simple in definition, in that it “is always attractive, and it depends only on the masses involved and the distances between them”.
The Newtonian definition of gravity seemed to fit most-Earthly situations. But when you account for massive, stellar objects, Newton could not properly explain their properties! For instance, the Newtonian definition could not explain Mercury’s distorted orbit around the sun.
Albert Einstein’s Theory of General Relativity accounts for these situations with ease, though! General Relativity proposes that all of space and time is composed in a fabric-like structure. Stellar objects are suspended in this fabric. As any Earthly being knows— a dense object (such as a tennis ball) laid on a cotton sheet will cause the sheet to sink and form a dent.
If you place say, an M&M or a small candy in that sheet, the candy piece will be drawn to the dent and will sink! Say that cotton fabric was actually really long and wide. If you place the M&M on the edge of the sheet, away from the tennis ball, it could probably sustain itself.
Einstein applied this concept to the Universal fabric of space-time. Space-time is 4 dimensional, so it is not only space that is warped.
General Relativity has been experimentally accurate. It is the most current and up-to-date knowledge on the nature of space and time. The hunt has not ended, though. With the recent progress scientists have made, quantum mechanics proposes theory on forces at the subatomic level.
The electromagnetic, strong, and weak forces can be explained on the quantum level. Gravity, though, remains excluded. Modern physics aims to unify the four forces of nature. General Relativity must fit in the picture of Quantum Mechanics! This is a search for the “theory of everything”.
The quest for Quantum Gravity is a relatively new, unique field of research. One hope lies in String Theory.
It is exciting to notice how even an ordinary question, “Why does the apple fall on my head?” has far more depth behind it. The question has lead scientists to venture into new fields of study for more than decades.
