From Wikipedia, the free encyclopedia
This article is intended as an accessible,
non-technical introduction to the subject. For the main
encyclopedia article, see
M-theory.
In non-technical terms, M-theory presents an idea about the
basic substance of the universe.
Background
In the early years of the 20th century, the atom - long believed to be the smallest
building-block of matter - was
proven to consist of even smaller components called protons, neutrons
and electrons, which are known as subatomic particles. Beginning in the
1960s, other subatomic particles were discovered. In the 1980s, it
was discovered that protons and neutrons (and other hadrons) are themselves made up
of smaller particles called quarks. Quantum theory is the set of rules that
describes the interactions of these particles.
In the 1980s, a new mathematical model of theoretical
physics called string theory emerged. It showed how all
the particles, and all of the forms of energy in the universe,
could be constructed by hypothetical one-dimensional "strings,"
infinitely small building-blocks that have only the dimension of
length, but not height or width. Further, string theory suggested
that the universe is made up of multiple dimensions. We are
familiar with height, width, and length as three dimensional space,
and time gives a total of four observable dimensions. However,
string theories supported the possibility of ten dimensions--the
remaining 6 of which we can't detect directly. These "strings"
vibrate in multiple dimensions, and depending on how they vibrate,
they might be seen in 3-dimensional space as matter, light, or
gravity. It is the vibration of the string which determines whether
it appears to be matter or energy, and every form of matter or
energy is the result of the vibration of strings.
String theory then ran into a problem: another version of the
equations was discovered; then another, and then another.
Eventually, there were five major string theories, the main
differences between each theory were principally the number of
dimensions in which they developed, and the strings´
characteristics (some were open loops, some were closed loops,
etc.) , and all of them appeared to be correct. Scientists were not
comfortable with five seemingly contradictory sets of equations to
describe the same thing.
In the mid 90s, a string theorist named Edward Witten of the Institute for Advanced
Study and other important researchers considered that the five
different versions of string theory might be describing the same
thing seen from different perspectives. They proposed a unifying
theory called "M-Theory", in which the "M" is not
specifically defined, but is generally understood to stand for
"membrane." M-Theory brought all of the string theories together.
It did this by asserting that strings are really 1-dimensional
slices of a 2-dimensional membrane vibrating in 11-dimensional
space.
Status
M-Theory is not yet complete, but the underlying structure of
the mathematics has been established, and is in agreement with not
only all the string theories but with all of our scientific
observations of the universe. Furthermore, it has passed many tests
of internal mathematical consistency, which many other attempts to
combine quantum mechanics and gravity failed. Unfortunately, until
we can find some way to observe higher dimensions (impossible with
our current level of technology) M-Theory has a very difficult time
making predictions which can be tested in a laboratory.
Technologically, it may never be possible for it to be "proven."
However, many cosmologists, including Stephen
Hawking, are drawn to M-Theory because of its mathematical
elegance and relative simplicity. Physicist and bestselling author
Michio Kaku has
remarked that M-Theory may present us with a "Theory of Everything" which is so concise
that its underlying formula would fit on a t-shirt.^{[1]}
See also
References
Books
- Brian Greene
has written books explaining string theory and M-theory for the
layperson in 1999, The Elegant Universe, ISBN
0-375-70811-1 and in 2004, The Fabric of the Cosmos, ISBN
0-375-41288-3.
- Musser, George (2008). The Complete
Idiot's Guide to String Theory. Indianapolis: Alpha.
pp. 368. ISBN
978-1-59-257702-6.
- Smolin, Lee. The Trouble With Physics: The Rise of String
Theory, the Fall of a Science, and What Comes Next (2006), Houghton
Mifflin. ISBN 978-0-618-55105-7.
- Woit, Peter. Not Even Wrong: The Failure of String Theory &
the Continuing Challenge to Unify the Laws of Physics, 2006. ISBN
0-224-07605-1 (Jonathan Cape), ISBN 0-465-09275-6 (Basic
Books)
External
links
- The Elegant Universe - A
Three-Hour miniseries with Brian Greene by NOVA (original PBS
Broadcast Dates: October 28, 8-10 p.m. and November 4, 8-9 p.m.,
2003). Various images, texts, videos and animations explaining
string theory and M-theory.
- Superstringtheory.com - The "Official String
Theory Web Site", created by Patricia Schwarz. Excellent references
on string theory and M-theory for the layperson and expert.
- Basics of M-Theory by A.
Miemiec and I. Schnakenburg is a lecture note on M-Theory published
in Fortsch.Phys.54:5-72,2006.